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Credits
The International WELL Building Institute also acknowledges the important work of Melcher Media in bringing this document to market in its current state.
President, CEO: Charles Melcher
VP, COO: Bonnie Eldon
Creative Producer: Katy Yudin
Senior Digital Producer: Shannon Fanuko
Associate Editor: Luisa Lizoain
Assistant Editor: Karl Daum
Design & Development by Crush + Lovely
Illustrations by Kaarina Mackenzie
Animations by Vita Newstetter
Melcher Media would like to thank Callie Barlow, Jess Bass, David Brown, Dylan Butman, Tova Carlin, Maria Gagliano, Barbara Gogan, Luke Jarvis, Weronika Jurkiewicz, David Kahn, Susan Lynch, Sami Melcher, John Morgan, Lauren Nathan, Julia Sourikoff, Tori Spencer, Saif Tase, Zoe Valella, and Megan Worman.
Acknowledgments
The International WELL Building Institute (IWBI) and Delos Living LLC (Delos) acknowledge the work of the following IWBI and Delos technical staff that developed and created the WELLographies: Oriah Abera; Niklas Garrn; Trevor Granger; Soyoung Hwang; Michelle Martin; Vienna McLeod; Anja Mikic; Renu Nadkarni; Brendan O’Grady; Chris Ramos; Eric Saunders; Sara Scheineson; Nathan Stodola; Regina Vaicekonyte; Sarah Welton; Kylie Wheelock; Emily Winer.
IWBI also is grateful for the input and insight provided by the following Subject Matter Experts:
Air: Terry Gordon, PhD; Eric Liberda, PhD; Tim McAuley, PhD; Ellen Tohn, MCP
Water: Eric Liberda, PhD; Tim McAuley, PhD; Margret Whittaker, PhD, MPH, CBiol, FSB, ERB, DABT, ToxServices LLC
Nourishment: Sharon Akabas, PhD; Alice H. Lichtenstein, DSc; Barbara Moore, PhD
Light: Chad Groshart, LEED AP BD+C; Samer Hattar, PhD; Steven Lockley, PhD, Consultant, Delos Living LLC and Member, Well Living Lab Scientific Advisory Board, Neuroscientist, Brigham and Women’s Hospital and Associate Professor of Medicine, Harvard Medical School
Fitness: Dr. Karen Lee, MD, MHSc, FRCPC, President & CEO, Dr. Karen Lee Health + Built Environment + Social Determinants Consulting; Jordan Metzl, MD
Thermal Comfort: Alan Hedge, PhD, CPE, CErgHF; David Lehrer, MArch; Caroline Karmann, PhD, MArch
Acoustics: Arline L. Bronzaft, PhD, Professor Emerita of The City University of New York; Charles Salter, PE
Mind: Anjali Bhagra, MBBS; Lisa Cohen, PhD; Keith Roach, MD; John Salamone, PhD; Nelida Quintero, PhD
Disclaimer
None of the parties involved in the funding or creation of the WELL Building Standard™ and the WELLographies™, including Delos Living LLC, its affiliates, subsidiaries, members, employees, or contractors, assume any liability or responsibility to the user or any third parties for the accuracy, completeness, or use of or reliance on any information contained in the WELL Building Standard and the WELLographies, or for any injuries, losses, or damages (including, without limitation, equitable relief) arising from such use or reliance.
Although the information contained in the WELL Building Standard and the WELLographies is believed to be reliable and accurate, all materials set forth within are provided without warranties of any kind, either express or implied, including but not limited to warranties of the accuracy or completeness of information or the suitability of the information for any particular purpose.
The WELL Building Standard and the WELLographies are intended to educate and assist building and real estate professionals in their efforts to create healthier work and living spaces, and nothing in the WELL Building Standard and the WELLographies should be considered, or used as a substitute for, medical advice, diagnosis or treatment.
As a condition of use, the user covenants not to sue and agrees to waive and release Delos Living LLC, its affiliates, subsidiaries, members, employees, or contractors from any and all claims, demands, and causes of action for any injuries, losses, or damages (including, without limitation, equitable relief) that the user may now or hereafter have a right to assert against such parties as a result of the use of, or reliance on, the WELL Building Standard and the WELLographies.
Welcome to WELL
The buildings where we live, work, learn and relax have a profound effect on our well-being: how we feel, what we eat and how we sleep at night. By examining our surroundings and our habits, and making key optimizations and changes, we have the power to cultivate spaces that promote wellness, and support efforts to live healthier, active, mindful lives – a right for every human.
The WELL Building Standard™ (WELL) envisions this reality and opens this critical dialogue. It provides a roadmap and a comprehensive set of strategies for achieving building and communities that advance human health.
WELL consists of a comprehensive set of features across seven concepts (Air, Water, Light, Nourishment, Fitness, Comfort and Mind). Together, these components address the various individual needs of the people inside buildings, while also setting forth a common foundation for measuring wellness in buildings as a whole. The standard was developed by integrating scientific research and literature on environmental health, behavioral factors, health outcomes and demographic risk factors that affect health; with leading practices in building design and management. WELL also references existing standards and best practice guidelines set by governmental and professional organizations, where available, in order to clarify and harmonize existing thresholds and requirements.
The result is the premier building standard for advancing human health and wellness – and a blueprint for creating better buildings that can enhance productivity, health and happiness for people everywhere.
How to Use This WELLography™
WELLographies™ present research relevant to health and well-being in buildings and communities. The sources included span health, wellness, and scientific and professional literature specific to the seven concepts within WELL, and other core focus areas. WELLographies are meant to complement the WELL Building Standard™ (available at standard.wellcertified.com) and provide architects, building managers, engineers, and interior designers, among others, with health- and science-focused background to support and guide their efforts to advance the healthy buildings movement.
WELLographies have three primary goals:
Provide background information for key topics relevant to understanding human health as it relates to the built environment.
Synthesize and present the science that underpins the WELL Building Standard.
Outline specific, evidence-based strategies that building professionals can apply to create spaces that promote health and well-being in buildings and communities.
There are nine WELLographies:
Air
Water
Nourishment
Light
Fitness
Thermal
Acoustics
Materials
Mind
The Acoustics WELLography™ has the following sections:
Sound and the Built Environment, which broadly describes how sound relates to the human experience in buildings.
Properties of Sound, describes important technical components, including any terms that will be discussed throughout the WELLography.
Sound and the Human Body, which provides an explanation of the biological mechanisms relating to sound, describing how the body functions under normal, healthy conditions.
Elements of Sound, which describes environmental conditions or behaviors that are linked to health, focus, or occupant comfort, and that are subject to interventions in building design or policy. Each element includes coverage of associated health effects as well as solutions, interventions that can be implemented to impact the element. Some solutions may address several different elements.
Explanations of Solutions, which provides a definition and/or more detail for each solution.
Appendices include technical resources such as acoustic performance recommendations for indoor environments.
Introduction
Hearing, one of the five traditional senses, can enrich our lives by helping us gather, process, and interpret sound in our environment. Understanding the sounds around us lets us learn, work, relax, and socialize.
Acoustic comfort is defined as a person’s satisfaction with the sound environment of the spaces where they live, work, and play. Optimal acoustic comfort does not imply an absence of sound; rather, it requires that sound be of the appropriate type and level.
Acoustic comfort is determined in part by the physical qualities of the environment through which sound travels. It is also affected by an environment’s contents: materials, building systems, people, and other sound sources. Additionally, acoustic comfort is influenced by an individual’s subjective experience–what one person may consider a desired sound might be noise and distraction to another. When designing for acoustic comfort, we should aim to create buildings that will be acoustically pleasing to the majority of people who use those spaces.
Acoustic discomfort is often discussed with respect to noise. Noise is generally defined as unwanted sound that affects our well-being and comfort. We are actively and passively exposed to noise in both acute and chronic durations in our buildings and natural environments, including in our neighborhoods, schools, homes, hospitals, and workplaces. We experience noise that is generated internally (inside of buildings) by people, building systems, and electronics, as well as externally (outside of buildings) by our neighbors, transportation traffic, and industry.
Just like sound exposure itself, health effects from sound exposure are experienced across a spectrum. Health effects from sound exposure can be both auditory and non-auditory.
Hearing loss, a potential effect of acute or chronic noise exposure, is growing significantly in the United States (U.S.).
According to the American Speech-Language-Hearing Association (ASHA), the number of Americans with some form of hearing loss has doubled during the past 30 years.1
The Centers for Disease Control and Prevention (CDC) estimates that one in eight children and adolescents between the ages of six and 19 years already have permanent hearing damage from excessive exposure to noise.2 Prevalence of hearing loss among people aged 12-19 years has increased over the last two decades, and individuals within that age group living below the federal poverty threshold have significantly higher odds of experiencing hearing loss.3
Hearing loss is prevalent across the lifespan. The National Institute on Deafness and Other Communication Disorders (NIDCD) reports that, within the U.S., approximately 15% of people between the ages of 20 to 69 years old (26 million Americans) suffer from high frequency hearing loss that may have been caused by occupational or recreational exposure to loud sounds.4 Nearly 25% of adults ages 65 to 74 and 50% of adults age 75 and older have disabling hearing loss, according to the NIDCD.5
While acute exposure to a loud noise can cause temporary or even permanent hearing loss, a person may also experience a non-auditory reaction to sound exposure. Continuous exposure to noise leads to sustained stress and activation of the sympathetic nervous system. This can lead to physiological and psychological wear and tear that can have serious short- or long-term health effects, including annoyance, sleep disturbance, impaired cognitive performance, and cardiovascular disease.678
As populations continue to grow and global urbanization intensifies, the prevalence of noise and the number of people negatively impacted by noise increases. Data from six European countries points to traffic noise as the third most important stressor related to environmental disease burden, after particulate matter pollution and second-hand smoke.9 The World Health Organization (WHO) estimates that “at least 1 million healthy life years are lost every year from traffic-related noise” in western European countries alone.10
Addressing environmental noise has great potential to improve health worldwide.
While noise is ubiquitous, we can adopt technologies, practices, and policies that create quieter environments and minimize our exposure to harmful and unnecessary noise. We can use objective measures to determine what sound levels are healthy and most comfortable for individuals in similar environments, and we can leverage established techniques to control sound and promote acoustic comfort.
Sound insulation, absorption, and blocking are common solutions to addressing noise issues. These and other solutions discussed in this document represent a small sample of approaches and are best used in tandem with the prioritization of acoustic comfort in a space.
It is essential to continue to study the ways in which sound affects our bodies and behaves in buildings. This research helps us develop effective interventions and strategies to mitigate exposure and improve individual and population health, well-being, and satisfaction.
Sound and the Built Environment
Sound moves through space very much like light or water. It can leak through holes and cracks in floors and ceilings and spill into spaces unexpectedly. The indoor and outdoor environment can harbor sounds that are not only harmful to human hearing but also distracting and disruptive to work and relaxation.
Understanding how sound moves through structures and how that movement affects people in those environments helps us better design and build spaces that prioritize acoustic comfort.
Properties of Sound
In order to understand how sound impacts health, communication, well-being, and satisfaction, and to develop solutions for the challenges it presents, we must first understand its fundamental properties. The following section explores the physics of sound movement and measurement.
Components of Sound
Sound is the result of pressure fluctuations between particles that make up media such as gases, solids, or liquids.11 When these pressure fluctuations reach the ear, they travel to the cochlea where they are converted into electrical impulses before traveling to the brain to be interpreted as sound.12
Sound Waves
Sound waves are made up of a pattern of air pressure disturbances that move through a medium in mechanical waves. In mechanical waves, energy is transferred via vibration from one particle to another within a medium.11 Sound typically travels in two different types of configurations: longitudinal and transverse, both of which displace particles in systematic patterns. The motion of sound waves depends on the properties of the medium through which they travel.13
Longitudinal Sound Waves
Sound waves travel longitudinally in any fluid medium (e.g., liquids and gases). As a sound wave moves through a medium, particles exposed to the wave’s energy move back and forth, creating fluctuations in pressure in the same direction that the wave is moving or opposite to the direction that the wave is moving.13 This transfer of energy between particles creates areas of high and low particle density. Areas of high particle density within the medium correspond to high pressure areas (compared to atmospheric pressure) and are known as compressions. Areas of low particle density within the medium correspond to low pressure areas (compared to atmospheric pressure) and are known as rarefactions.13
A good illustration of a longitudinal wave’s movement is the way in which a slinky moves; the distance between the coils increases and decreases with each oscillation.14 Figure 1 illustrates the particle displacement that occurs in a longitudinal wave.
While sound waves that travel longitudinally cause particles to vibrate in the same direction (parallel) or opposite direction (anti-parallel) that the wave is traveling, sound waves that move through solids in a transverse configuration displace particles perpendicular to the direction that the sound wave is moving.14 The particles move up and down as the wave moves horizontally, creating crests and troughs. Whereas a longitudinal wave acts in one dimension, a transverse wave acts in two dimensions.14 Figure 2 demonstrates the movement of transverse waves.
Pressure variations in a sound wave are repeated in space over a specific distance. The distance that it takes the pressure variations of a disturbance to complete one cycle (return to the same phase of compression or rarefaction) is termed the wavelength.13 The time that it takes a full wavelength to complete one cycle is termed the period. For each unit of time, the number of periods that repeat themselves (the number of complete back and forth vibrations of a particle) determines the frequency.13
Frequency
Frequency is commonly measured in Hertz (Hz), where one Hz is equivalent to one cycle per second. Frequency is often synonymized with “pitch”; pitch and frequency are related in that pitch is a relative term that refers to the human ear’s perception of a sound’s frequency. High and low frequencies are interpreted as higher- and lower-pitched sounds respectively. The unimpaired human ear can detect pressure waves of varying frequencies, ranging from approximately 20 to 20,000 Hz, with the most acute hearing being from 1,000 to 6,000 Hz.15 The upper frequency limit tends to lower with age. Frequencies above and below the human hearing thresholds are referred to as ultrasound and infrasound.15 Figure 3 illustrates a range of sound frequencies from 1 millihertz to 30,000 gigahertz.
At the lowest end of the sound spectrum, infrasound comprises frequencies lower than 20 Hz and is usually observed in natural currents (ocean storms and waves), low vibrations (construction and traffic), and animal communication (elephants) and navigation (homing pigeons).14 Ultrasound, at the upper end of the sound spectrum, has a frequency above the range of human hearing. One typical application of ultrasound is medical imaging, which uses energy from sound waves to measure the distance from the surface of the body to various internal structures and to measure the speed at which those structures are moving. For example, an echocardiogram produces an image of the heart’s contractile patterns and allows technicians to see the direction and speed of blood flow.14
Amplitude
Amplitude refers to the degree of change in atmospheric pressure that is created as energy travels from one particle to another in a sound wave.13 Amplitude is measured as the force that is applied over an area. The greater the amplitude of a wave, the greater the change in atmospheric pressure. Our subjective experience of “loudness” is directly related to the amplitude of a sound wave as it travels through a medium; the larger the amplitude, the louder we perceive the sound.13
Sound Pressure
Sound pressure, also called acoustic pressure, is the difference between the pressure produced by emanating sounds and the average atmospheric pressure (ambient pressure). Sound pressure is one of the most frequently used metrics in acoustics and is expressed on the decibel (dB) scale as the Sound Pressure Level (SPL).11 SPL is explained further in the Metrics of Sound section.
Behaviors of Sound
Sound Propagation
Understanding how sound moves through a space and interacts with the environment can help us understand how building acoustics can promote or hinder health and comfort. These fundamentals will help us employ effective strategies to manage noise pollution and intrusion to maximize a space’s acoustical performance and the acoustical comfort of the people who use the space.
Propagation describes the movement of a wave through a medium and is influenced by the medium’s conditions, such as temperature, and properties, such as its physical state, as well as the sound wave properties.
When sound encounters barriers, furnishings, people, or other objects in the environment, the wave can be reflected off the obstacle (reverberated), transmitted across the obstacle (refracted), bent around the obstacle (diffracted), or reduced in strength (attenuated).13
Reverberation is the persistence of sound created when a sound wave continues to reflect off surfaces and objects in an enclosed space even after a source stops producing a sound wave. Sound waves change direction as they bounce off barriers within a space. Reflection is affected by the size and shape of the room, the type of building materials and the construction techniques used to install them, as well as the presence of furnishings and people within a room.11
Refraction is the change of a sound wave's direction as it passes into a medium where its speed is different (e.g., air to water). This can occur when a sound wave passes from one medium to another of differing fundamental properties, but this can also occur within the same medium (e.g., due to temperature differences).11
Diffraction of a sound wave is a change in the direction of wave propagation as it passes through an opening in an obstacle or around an obstacle. The magnitude of diffraction is influenced by the properties of both the obstacle (e.g., width of openings in a slated barrier) and the sound waves (wavelength).13
Sound Propagation Loss
Above, we discussed three behavior changes that could happen to a sound wave as it moves (propagates) through space. As a sound wave propagates through space and comes in contact with various obstacles, the wave not only changes its behavior but also loses energy.15
Sound propagation loss (attenuation) is expressed as dB per doubling of distance from a source, and is explained by the inverse square law, where the sound pressure level varies inversely by the squared distance from the source. In a free field, spherical propagation of sound, equal in all directions from a point source, results in reduction or attenuation of sound level by six dB for each doubling of distance from the source. Sound propagation from freely flowing traffic or an electric power line represents a line source and a type of cylindrical propagation where there is equal sound pressure output per unit length of the line. The sound level attenuation for a line source is three dB per doubling of distance from the source. Figure 4 illustrates sound wave propagation with point and line sources. These attenuation estimations will vary in real world environments due to many factors, including environmental geography, weather, obstacles, and the properties of a medium.16
Figure 4: Wave Propagation With Point Source And Line Source.16
Understanding the different paths of sound transmission in our indoor and outdoor environments help us to plan for sound control and acoustic comfort.
Sound Transmission
Sound transmission describes how sound travels from a source along a transmission path to a receiver.
Figure 5 illustrates several ways that sound can be transmitted through the environment. Notice that while internally generated sound can travel both within and between rooms in a structure, externally generated sound can also intrude on the indoor sound environment.
Figure 5: Sound Transmission In The Built Environment.17
The ASHRAE Handbook—Fundamentals identifies different types of sound transmission, a sampling of which is discussed below.17 The sound control and mitigation solutions discussed later in this document (sound insulation, absorption, masking, source control, etc.) work to address these different forms of transmission. As a note, ultimately, all types of sound transmission (airborne, structure-borne, room-to-room, duct-borne, etc.) are best addressed through source control.
Airborne Transmission
Sound that radiates directly from a source into the air travels to a receiver via airborne transmission.17 Airborne sound transmits easily in both indoor and outdoor environments. Indoor airborne sound may travel directly to a receiver or it may reflect off hard surfaces, such as walls, structural elements, ceilings, and floors, to reach a receiver.17 Common indoor airborne sound sources include conversations, appliances, and mechanical, electrical and plumbing systems.18
Reflection of airborne sound in the outdoor environment may occur if a sound source is near large reflective surfaces, such as adjacent buildings or glass facades.17 Common outdoor airborne sound transmission sources include traffic and industry.
Airborne sound can impact hearing, communication, concentration, and relaxation.
The best way to address airborne sound is to control it at its source.17
For example, building engineers can adjust the air velocity of an HVAC system (within acceptable human health limits) to help lessen the airborne sound it generates. Turning off unnecessary alarms on appliances and electronics helps to reduce the generation of airborne sound.
If sound cannot be controlled at its source, then different sound control approaches must be adopted. To reduce the propagation of airborne sound, designers can also employ sound absorption and insulation techniques. Adding mass through the application of sound-absorbing materials (e.g., materials with a high Noise Reduction Coefficient (NRC)) helps to reduce airborne sound that is reflected within a space. In addition, ensuring that there are no gaps or holes between adjacent spaces through air sealing helps to prevent airborne sound leakage.19 This strategy is often overlooked, especially around door and window openings. Remember, anywhere that light or water can leak through an opening, so too can sound. Insulation techniques include the use of special triple glazed windows or glazing that incorporates an acoustic interlayer to help block the transmission of noise from the outside.
Additionally, because airborne sound radiates directly from a sound source, installing sound enclosures can help to limit airborne sound transmission by reducing airborne sound’s ability to propagate into a space. Separating receivers from the source producing a sound also helps to reduce their exposure to airborne sound, as sound intensity decreases as the distance between the receiver and the source increases (see discussion of Sound Propagation and The Inverse Square Law).1417
Structure-borne Transmission
Structure-borne sound (or impact noise) passes through solid building materials.19 Frequently in structure-borne sound transmission, sound initially travels through a solid structural element, such as a wall system, window, floor, piping, or ductwork, before a smaller proportion of the structure-borne sound is radiated as airborne sound.18 Typical sources of structure-borne sound include footfalls or mechanical, electrical, and plumbing systems. Exterior noise that intrudes into interior spaces can also be experienced as structure-borne sound.19 Figure 5 illustrates structure-borne sound transmission within a space.
Structure-borne sound affects acoustic comfort in that we can both feel (through vibrations) and hear (once airborne). Like airborne sound, it can impact hearing, communication, concentration, and relaxation.
Structure-borne sound is best controlled at its source. For example, vibrating mechanical units can be treated with vibration isolation techniques, including the installation of mounts, springs, or pads to separate the source from the structure receiving the vibration.20
Source separation is also helpful for controlling structure-borne sound. Situating equipment rooms away from regularly occupied spaces helps to reduce the structure-borne sound experienced by people in buildings.20
Structure-borne sound is often controlled with the addition of both mass and space. Designers should aim to minimize sound transmission that occurs through building components (e.g., isolate noisy machinery with barriers or enclosures) and improve the transmission loss (TL) of materials used in building components that affect structure-borne sound transmission (e.g., increase the insulating properties of walls).21 The addition of mass serves to insulate against structure-borne sound. Space acts as an additional attenuator for sound. Structure-borne sound is greatly reduced when it is forced to travel between a well-insulated wall, air space, and then another insulated wall instead of through a single poorly insulated wall.
Room-to-room Transmission
Room-to-room transmission is a combination of airborne and structure-borne transmission and is used to describe the movement of sound between spaces (Figure 5). In room-to-room transmission, a source produces a sound in a room where it travels in the form of a vibration through a barrier such as a wall system, door, or window, into an adjacent room, where it radiates from the barrier as airborne sound energy.17
Room-to-room transmission affects acoustic comfort in the same ways that airborne and structure-borne sound transmission do, and it is controlled using the same sound mitigation techniques. Particularly, the addition of sound-insulating materials between adjacent rooms (e.g., materials with high Sound Transmission Class (STC)) helps to reduce the transmission of airborne sound from one room to another.20
It is important to note sound that is moving from room to room cannot be mitigated using sound-absorption techniques; sound absorption techniques reduce reverberant noise within a room but not between rooms.
Duct-borne Transmission
Sound between rooms can also transmit via ventilation ductwork in a building. Sound travels through ducts both upstream and downstream from the source, regardless of airflow directionality. Sources of duct-borne sound vary, from HVAC equipment to conversations between coworkers.17
Duct-borne transmission is of special concern to acoustic comfort because it facilitates sound travel between rooms in an effect known as crosstalk.17 Sound in one room can be carried into another via shared ductwork. Whether that sound emerges on the other end of the duct as intelligible or unintelligible noise, it can be distracting and disruptive to receivers.17
Duct-borne transmission can be reduced through design by separately routing HVAC ducts into individual rooms from a common duct.18 Lining ductwork with absorbent materials also helps to reduce the amount of sound transmitted via ducts.17
Metrics of Sound
The following section describes how sound is measured and quantified in the environment.
Sound Pressure Level
Sound pressure level (SPL) is introduced briefly earlier in this chapter; however, its application as a metric used in sound measurements is explained in greater detail below.
Sound pressure level tells us the relative power or intensity of a sound.15 An increase of 10 dB means that the sound is 10 times more powerful or intense, and is perceived by the human ear as being twice as loud.22
Absolute decibel measurements within an environment can fail to capture an accurate picture of the greater soundscape. For instance, impulse sounds that occur sporadically over a period of time can cause disruption and distraction but may not be captured with absolute decibel measurements taken at a single point in time. In order to more accurately capture environmental exposure, researchers have developed a variety of sound pressure level metrics.
Equivalent Continuous Sound Pressure Level
The Equivalent Continuous Sound Level (Leq) (or energy-average sound level) is often used to report an “average” of the sound energy in an area over a period of time.11 Leq is not, however, simply the arithmetic average of the sound pressure level in decibels over a specified time in a given place. Leq is the sound pressure level that, if produced continuously over a given period of time and in a given place, would have the same total sound energy as the non-steady-state noise in the measurement conditions. Since sound pressure level is logarithmically derived from sound intensity, brief loud sounds “count” much more in Leq than in a simple average of all the decibel levels observed.23 Figure 6 demonstrates how Leq is derived from measured SPL.
Since environmental noise exposure is often neither continuous nor steady state, variations of Leq can be useful in determining more accurate environmental exposure to noise over a period of time. For example, in an urban environment, noise levels usually differ throughout the day, evening, and night. Using a variation of Leq such as the Ldn (day, night), which adds a 10-dB penalty for sounds measured during nighttime hours (10 p.m.–7 a.m), allows researchers to more accurately capture the total sound energy that individuals are exposed to over a 24-hour period.15 Lden (day, evening, night), similarly, is an average equivalent continuous sound level measurement that includes a 10-dB penalty for sounds measured during nighttime hours (like Ldn) and an additional five-dB penalty for sounds that are measured during the evening hours (7 p.m.–10 p.m.).
A-Weighting
The human ear is less sensitive to sound at low frequencies than sound at high frequencies, and weighting sound pressure level measurements to approximate this differing sensitivity gives us a better estimate of a sound’s relative loudness than an absolute decibel measurement. A-weighting accounts for human hearing’s frequency limitations by deemphasizing low frequency sound; however, the weighting does not reflect the full range of auditory perception. The A-weighted decibel is written as dB(A) or dBA.15
Noise Criteria
Noise criteria (or noise criterion) (NC) is a common metric used by engineers to describe the ambient sound level within a space due to HVAC background noise.17 NC is a closer approximation to perceived loudness than the A-weighting technique, which combines all frequencies within a range into a single number.
NC is a single-number rating based on criterion curves that relate sound pressure level (dB) and octave band frequencies to describe the relative loudness of a space. To calculate NC, the measured background sound spectrum measurements are plotted along a series of criterion curves that are set across a specified range of frequencies (16 Hz to 8,000 Hz).17 The lowest criterion curve that contains the entirety of the measured values determines the NC.17
Figure 7 depicts a measured sound spectrum plotted with the criterion curves. The dotted red line is the lowest criterion curve that captures the entire measured spectrum. Therefore, the sound spectrum depicted in the chart below has an NC rating of 43. NC values are formally reported in increments of five dB, with intermediate values being determined by discretionary interpolation.17
Figure 7: Noise Criteria Curves and Tangent Method.17
Reverberation Time
Reverberation time is the length of time required (in seconds) for the average sound pressure level in a space to decay 60 dB from its initial level once its source has stopped producing sound.25 Reverberation is frequency-dependent and can either be measured in frequency bands or as an averaged value. Reverberation time can be approximated based on the room volume and known properties of the room’s contents (absorptive and reflective surfaces) or measured in the field.25
Optimum reverberation time values vary depending on room volume, intended use of the space, and the frequency of the transmitted sound.14 Recommended reverberation times for different space types can be found in the Explanations of Solutions section.
Acoustic Properties of Building Elements
The following section explains how to rate the acoustic properties of a structure’s components, including walls, floors, ceilings, windows, and partitions. It’s important to understand the principles of these measurements to properly plan for acoustic comfort. Measurement of sound transmission requires consideration of how sound moves within a room or space as well as how sound moves between rooms or spaces.
Generally, the following metrics describe one of two properties of a structural component: sound absorption or sound insulation. Sound absorption describes an object’s ability to absorb sound energy. Sound insulation describes an object’s ability to block sound transmission.
Absorption and insulation measurements are discussed below and divided into two categories: laboratory and field measurements. Laboratory ratings refer to determinations made in a lab by manufacturers or regulators. Laboratory testing is conducted in a controlled environment, where building components are carefully assembled and installed.
While a material may perform exceptionally well in the laboratory, the same performance cannot always be guaranteed in the field. The quality of construction, in accordance with acoustic design guidelines, may have a greater impact on sound transmission than will the acoustical rating of the materials used in the construction. For this reason, field measurement rating methods have been devised to determine a closer approximation to a material’s sound control capabilities in real world applications.
Measurements of Absorption
Laboratory
Sound Absorption Coefficient: a single-number laboratory rating of a material’s sound absorption, which indicates the proportion of sound that a surface absorbs compared to the proportion of sound that it reflects. Coefficients range from zero to one. A coefficient of one means that the material absorbs 100% of the sound and that no sound is reflected into the space, while a coefficient of zero means that the material provides no absorption and that all of the sound is reflected. The sound absorption coefficient of a material is frequency-specific. Denser materials typically work better at absorbing low-frequency sounds, while less dense materials tend to be better at absorbing high-frequency sounds.1120
Since sound absorption coefficients cover a broad range of frequencies, they are suitable for assessing how well a material absorbs sounds of frequencies outside of the speech frequency range, for example, music or mechanical noise.
Noise Reduction Coefficient (NRC): a single-number laboratory rating of the sound-absorption properties of a material.26 NRC is calculated by taking the arithmetic average of a material’s sound absorption coefficients at four different mid-frequencies (the frequency bands most critical to speech), rounded to the nearest 0.05. The higher the NRC, the better the absorption.11
NRC helps us understand how effective a material is at reducing reverberation and echo. Knowledge of NRC is useful for addressing sounds that fall within the speech frequency, but not for sounds of lower frequency.
Field
There are no field measurements for sound-absorbing materials, but there is a field measurement for approximating the “absorbency” of a room. See discussion of Reverberation Time
Measurements of Insulation
Laboratory
Transmission Loss (TL): a laboratory measurement of the difference in sound pressure level at a given frequency on each side of a barrier to determine how much sound it blocks (measured in decibels). TL values describe the sound insulation (or isolation) provided by a barrier between spaces (exclusive of flanking). TL ratings, like measurements of a material’s absorptiveness, vary depending on the frequency of the sound.11
Sound Transmission Class (STC): a single-number laboratory rating that describes the sound-insulating performance of materials used in constructing walls or floor/ceiling assemblies. STC assesses how well a wall reduces airborne sounds between two adjoining spaces.27 In laboratory conditions, a sound of 100 dB will be reduced to 50 dB when it crosses a wall with an STC rating of 50.
Generally, the higher the STC value, the greater the sound attenuation.27 STC is limited as a measure of sound attenuation, because it only tests the partition’s ability to insulate against sound at frequencies from 125 to 4,000 Hz (i.e., the range of speech frequencies), meaning that it fails to assess a partition’s ability to block lower frequency sounds.26
Ceiling Attenuation Class (CAC): a single-number laboratory rating that measures how well a suspended ceiling construction blocks airborne sound at frequencies from 125 to 4,000 Hz between adjacent rooms that share a common ceiling plenum.11 The higher the CAC value, the greater the sound attenuation.
Impact Insulation Class (or Impact Isolation Class) (IIC): a single-number laboratory rating that describes a partition’s ability to block or reduce structure-borne sound. IIC is typically measured between vertically adjacent spaces (floor/ceiling assemblies).26 It is calculated by “measuring the resistance to transmission of impact noise or structure-borne noise (simulated footfalls, objects dropped on the floor, etc.).”28 Decibel measurements across specific frequencies (100 to 3,150 Hz) are entered into a mathematical formula to calculate a whole-number IIC rating.29 Higher IIC values indicate greater noise reduction of that assembly.
Field
Field Sound Transmission Class: a single-number field measurement of Sound Transmission Class (STC).
Noise Isolation Class (NIC): a single-number field rating that describes the level of sound attenuation provided by a partition, or the partition’s ability to block airborne sound transmission. NIC measures TL from 125 to 4,000 Hz, but, unlike STC, NIC does not modify for “reverberation time, size of room, or size of test partition,” making it “highly dependent on field conditions.”26 The higher the NIC rating, the greater the sound isolation between two spaces.
Field Impact Insulation Class: a single-number field measurement of Impact Isolation Class.
Sound and the Human Body
The following section outlines the biological components of the auditory system in humans and explains how sound waves are captured and converted into sensory signals and interpreted via neural pathways.
The Structure and Function of the Auditory System
The process of hearing requires the capture of acoustic waves and conversion of those waves into neural signals that the brain can process. Acoustic waves reaching the outer ear are reflected, conducted and filtered to control the sound levels and frequencies that reach the neural system responsible for hearing. Sound waves travel through three parts of the ear—outer, middle, and inner—before being translated to nerve impulses that reach the brain.30 Figure 8 illustrates the parts of the human ear.
The auditory system can be divided into two subsystems: the peripheral auditory system and the central auditory system. The peripheral auditory system is comprised of the outer, middle, and inner ear, while the central auditory system includes the neural pathways that help our brains interpret neuroelectrical signals into what we know as sounds.
Peripheral Auditory System
The Outer Ear. The outer ear consists of the pinna (or auricle) and the ear canal. The pinna collects sound waves and channels them into the ear canal. Sound waves travel through the ear canal and strike the tympanic membrane (eardrum), reaching the middle ear.32 The frequency content of the sound determines how quickly the eardrum vibrates and is interpreted by our brain as pitch.13
The Middle Ear. Vibrations from the tympanic membrane transmit the pressure changes to the bones in the middle ear (ossicles). The ossicles—the malleus, the incus, and the stapes—are commonly referred to by their shapes: hammer, anvil, and stirrup, respectively. Attached to the eardrum is the first of the ossicles: the malleus. As the malleus vibrates, it hits the incus, which in turn connects to the stapes. The foot of the stapes is located on a membrane opening in the bony wall of the cochlea called the oval window, which separates the middle ear from the inner ear.33 See Figure 8 for an illustration of the middle ear.
The middle ear system not only transfers vibrations from the outer ear to the inner ear; it’s also responsible for attenuating or amplifying sound vibrations as they travel along the middle ear before entering the inner ear. The arrangement of the bony ossicles helps to amplify sound by reducing energy lost to friction, while the small muscles of the middle ear help to decrease movement that may be damaging.12 This is in part due to the size difference between the tympanic membrane and oval window. Because the tympanic membrane is much larger, it concentrates the force of its initial movement as it transfers the energy along the ossicles to the inner ear.32
The stapes vibrates against the oval window, and the oval window creates pressure waves in the fluid of the inner ear (perilymph), transferring the vibrations of the middle ear to the inner ear. The round window, another opening located just beneath the oval window, helps to facilitate the movement of the perilymph in the cochlea.12
The Inner Ear. The fluid of the inner ear is contained in the cochlear and vestibular systems (the vestibular system is what gives us our sense of balance). Sound waves are converted to action potentials (the brain’s neural signals) in the cochlea.33 The cochlea, a bony snail shell-like structure, contains three fluid-filled, coiled chambers. The two outer chambers of the cochlea allow plasma fluids to move in pressure waves that travel the length of the cochlea. The innermost chamber, the cochlear duct, contains endolymph, a type of intracellular fluid that vibrates as pressure waves move through the cochlea.12
The organ of Corti is also located on the floor of the cochlear duct and contains the hair cells that serve as the ear’s sensory receptors. This tiny sensory structure is supported by a basilar membrane and partially covered by a tissue called the tectoral membrane. Fluid movement in the two outer chambers of the cochlea vibrates the two membranes that meet the organ of Corti and causes displacement of the hair cells within the structure, which is the source of sensory signaling.30 There are two kinds of hair cells housed by the organ of Corti: inner and outer hair cells. The inner hair cells are responsible for transmitting information to the brain, while the outer hair cells act to amplify and refine auditory stimuli received by the cochlea.33 See Figure 8 for a cross-section of the cochlear duct.
The “bottom” of each hair cell, the end opposite the tectorial membrane, is held in a cellular junction that allows for electro-chemical communication via neurotransmitters. Both outer and inner hair cells are attached to two types of synaptic nerves: afferent and efferent.33 Within the inner ear, afferent nerves transmit sensory information away from the hair cell toward the central nervous system, while the efferent nerves transmit sensory information from the central nervous system back to the hair cells.33
The “top” of each hair cell, the part embedded in the tectorial membrane, contains stereocilia: tiny, hair-like structures. Stereocilia are organized in rows that increase in length. The size, shape, and organization of stereocilia vary depending on their precise location along the cochlea. Stereocilia are responsible for converting mechanical energy from pressure waves into electrical impulse signals.33
The movement of fluid within the cochlea causes the basilar membrane and tectorial membrane to shift along with the organ of Corti, mechanically stimulating the stereocilia. The movement of the hair cells creates a biochemical change within the cell body of each cell that ultimately changes their internal electrical potential and results in the release of neurotransmitters that carry information in the form of bioelectrical signals along the auditory nerve (cochlear nerve) to the central auditory system.33
Central Auditory System
The cochlear nerve carries signals from the cochlea to the cochlear nuclei on each side of the lower brain stem. From there, projections transmit the signal farther up the brainstem both ipsilaterally (same side) and contralaterally (opposite side), meaning that sounds from both ears are transmitted to each side of the brain.33 Next, these electrical signals synapse on sensory nuclei of the midbrain, the inferior colliculus and again in the medial geniculate body of the thalamus before being projected to the auditory cortex of the brain.35 Figure 9 illustrates the movement of an electrical impulse from the cochlea to the auditory cortex.
Frequency of sound is interpreted as “pitch.” Despite possessing an incredible range of sensitivity in frequency and volume, the human ear does not respond equally well to all frequencies. The ear responds best to frequencies most similar to the human voice and is most sensitive between 1,000 and 6,000 Hz, with perception ranging from approximately 20 to 20,000 Hz.15
Sound Pressure Level
Perceptible sound levels are quite broad, with human hearing ranging from approximately zero dB to 130 dB. The lower end of the range, 10 dB, is the average threshold for hearing, and is near perceived total silence. The upper end of the range, 130 dB, is the threshold of pain.36 However, the lower and upper threshold for perceptible and painful sound is dependent on an individual’s sensitivity.14
Since the decibel scale is logarithmic and its calculations are based on powers of 10, increasing sound level to a level twice as loud requires a 10-dB increase. Changes of one dB are imperceptible, while changes of three dB are just barely noticeable. Figure 10 demonstrates the sensitivity of the human ear across different frequencies and sound levels.
Figure 10: Sensitivity Of The Human Ear Across Sound Pressure Level And Frequency.37
Even when our bodies are in a non-conscious sleep state, our auditory systems are still functioning and responding to external stimuli.
Noise
Noise can be described as unwanted sound in a given environment. This includes loud noise that disrupts communication and physiological processes like sleep, or noise that competes with sound that is considered wanted. Unwanted sound can also be noise that is relatively quiet but is perceived to be distracting or annoying by people within a space.15
Noise can be characterized as “impulse”, a short, sharp spike in sound pressure level, or it can be sustained and last over a long period of time. Low-frequency noise can be especially annoying and can be experienced as vibrations from structure-borne sound.38 Sources of noise are diverse and can include industry, traffic (air, road or train), people, animals, electronics, appliances, or building systems. Common environmental sound levels in both indoor and outdoor environments are shown in Figure 11.
Figure 11: Common Environmental Sound Levels.36373940
Our built and natural environments can contain noise that interferes with our health and comfort. The list below discusses a sampling of those environments, identifying sources of noise and touching on potential issues associated with exposure.
Home
Noise in the home can impact health and well-being in a number of ways, one of the most researched being its potential to interfere with one of the body’s most critical activities: sleep.4142 Research states that “maximum sound pressure levels as low as LAmax 33 dB can induce physiological reactions during sleep including autonomic, motor, and cortical arousals.”8
Sleep disturbance has been noted as “the most deleterious non-auditory effect of environmental noise exposure.”8 Wherever people get the majority of their sleep, it is important that a quiet environment, conducive to healthy and restorative rest, be maintained.
The WHO recommends a maximum year-round outside nighttime noise average of 40 dBA to avoid sleep disturbance and its related adverse health effects. The WHO estimates that more than 30% of the population in the European Region is exposed to noise levels exceeding 55 dBA at night.43 Of those affected, children are among the most vulnerable to nighttime noise.44 Those whose sleep structure is already under stress (e.g., shift workers, the elderly, and those who are chronically ill) also tend to be more sensitive to disturbance.43 Furthermore, those who are less affluent are also at adverse risk as they may not be able to afford homes in more quiet residential areas or to effectively insulate their homes against noise.43
Noise that does not interfere with sleep but instead disrupts relaxation or leisure activities can also provoke a sympathetic stress response, instigating health effects independent of sleep disturbance. Traffic noise (from roadways, airports, and railways) is most often cited as the dominant source of annoyance due to environmental noise in living environments.45 The WHO estimates that 20% of the population in EU countries is exposed to road traffic noise levels exceeding 65 dBA during the daytime.43
Workplace
Noise in the office impacts employee performance and satisfaction.4647 Common problems associated with open-plan offices include complaints of loss of privacy, aural distractions, and frequent interruptions from other employees.4849
Despite the opportunity for open offices to be more aesthetically pleasing, sociable, adaptable, and environmentally sustainable, open-plan offices can introduce sound-related challenges.
Common aural distractions for workers in these settings are telephones, conversations, and office equipment.50
Noise in the industrial workplace can also affect worker well-being. Reduced noise in factory settings is better for workers’ hearing health, but it has also been shown to benefit worker job and environmental satisfaction.51
Hospitals are also acoustic environments with great risk of adverse health effects from noise. Acoustic comfort is an important aspect to creating a healing space in hospitals and other healthcare settings. Post-occupancy survey results from the Hospital Consumer Assessment of Healthcare Providers and Systems show that noise routinely receives “the poorest response of all the questions asked of patients.”52
The U.S. Environmental Protection Agency (EPA) sets regulatory sound level standards for hospitals at a maximum of 40 dBA by day and 35 dBA by night, while the WHO recommends that day, evening, and nighttime noise levels not exceed 30 dB Equivalent Continuous Level (LAeq) in wards and 35 dB LAeq in patient rooms.53 More often than not, average noise levels in hospitals exceed those recommendations. A 2005 study at Johns Hopkins Hospital found that no location in the facility was compliant with the guidelines set forth by the WHO, with average equivalent sound levels (Leq) of 50 to 60 dBA.54 A 2007 literature review found that peak hospital noise levels often exceed 85 to 90 dBA.55 A meta-analysis of 11 research papers found that staff conversations and alarms were cited as being the most disturbing for ICU patients’ sleep.56 A 2012 prospective laboratory study that subjected sleeping volunteers to more than a dozen common hospital sounds found that electronic sounds were the most sleep-arousing.57
Equally important is the impact of noise on speech intelligibility. Broad-band noise from sources including ventilators and ventilation systems, as well as loud impulse sounds, such as equipment alarms, can mask speech. Given the risk of “sound-alike” medical errors, it is critical that acoustic solutions for healthcare environments minimize sound maskers and create spaces for communication and concentration that are undisturbed by noise.
School
Noise in schools can impact learning through several pathways, including disrupted speech intelligibility, impaired attention, and annoyance.58 In 1975, seminal research found that noise near classrooms significantly impacted students’ reading ability.59 Despite years of subsequent research on the physiological, motivational, and cognitive effects of noise on children, it still remains an issue in learning environments.606162 The American National Standards Institute recommends that sound levels in unoccupied classrooms not exceed 35 dBA.63 The WHO’s Guidelines on Community Noise state that sound levels in classrooms should not exceed LAeq of 35 dbA while class is in session.64
Elements of Sound
For the purposes of this WELLography™, we have selected five elements of sound exposure that can affect health outcomes. The elements are classified into two categories of sound exposure: indirect or direct.
The first element, distracting sound, involves sound that interferes with activities like sleep, work, and recreation. This element includes comprehensible (intelligible) sounds, which tend to be more distracting than incoherent sounds. The second element, interfering sound, describes sound that impedes communication. The third element, speech privacy, underscores how guaranteeing the confidentiality of spoken words (largely through the reduction of intelligible sound) improves comfort and focus. The fourth element, intentional sound, explores how sound can be applied in a therapeutic setting to benefit well-being and comfort. The fifth and final element, damaging sound, describes sound that harms the auditory system, through both intentional and unintentional exposures.
Indirect Pathway Sound Exposure
Indirect pathways involve sound exposure that affects the human body through cognitive interpretation of sounds (as opposed to effects that are linked to the hearing organs). These interpretations can have varying health effects, including physiological and psychological outcomes. Noise that disrupts concentration may cause stress (which corresponds to its own series of physiological reactions), while noise that interferes with communication can affect human comfort and safety.65
While sound exposure can cause harm, it can also be beneficial. Sound that is appropriately introduced into the indoor environment can help guarantee speech privacy. It can also be used in therapeutic applications to improve human health and wellness.
1. Distracting Sound
Distracting sounds are sounds that interfere with sleep, concentration, and recreation. The section on Sound and the Human Body: Noise presents different settings where noise exposure can be particularly problematic for human health and well-being.
Acute noise exposures can startle or surprise us. Noise can act as a biological stressor, causing both acute and chronic reactions affecting mental and physical health and well-being.66 As an evolutionary adaption, humans are wired to react to noise by engaging both the autonomic and hormonal stress response systems in a combined effect known as fight-or-flight response. The activation of the neuroendocrine system in response to acute exposure to noise triggers bodily responses including increased blood pressure, heart rate, and stress hormone levels.67 Although this is an evolutionarily well-developed biological alarm, it is not adaptive when activated on a regular basis.6869 Chronic exposure to noise can cause long-term activation of these responses.
Chronic exposure to noise can lead to stress, which can lead to stress-related health effects.70
A growing body of evidence associates noise pollution with stress-related health effects by way of overstimulation of the autonomic nervous system and dysregulation of stress hormones.70 While we may feel like we “get used to” noise, researchers are unsure of whether or not our bodies completely habituate to chronic exposure without detriment to our physiological health.7 Noise can trigger endocrine and sympathetic autonomic responses that may be associated with a variety of adverse health conditions of the endocrine, neurologic, and cardiovascular systems.66 Figure 12 illustrates acute and chronic health outcomes related to noise exposure.
Figure 12: Summary Of Possible Clinical Manifestations Of Noise Exposure.71
Aside from sound’s ability to impact physical health, certain sounds may be particularly annoying or affect mental health. Unwanted intelligible speech—speech where the information content is clearly understood—has shown to be particularly distracting, and is more attended to than unintelligible speech or nonsense speech.477273
In a study of 31 office workers relocated from private office rooms to open-plan offices, researchers found that the most commonly reported sound that disturbed concentration on work was “voices and laughter from general areas” in open-plan offices.49
While “annoyance” has traditionally been the term used to describe the behavioral response of people exposed to intelligible and unintelligible noise as described above, the body of research linking noise to adverse physiological health effects is growing.
Intelligible conversations between coworkers are often identified as the most annoying source of office noise.74
Health Effects
Endocrine System
Catecholamine excretion. Exposure to both internally and externally generated noise at levels as low as 55 dBA is associated with an increase in urinary stress hormone excretion.75
In a study of 234 women aged 30 to 45 years old, researchers found that those whose bedrooms and/or living rooms were oriented toward streets with high nighttime outside noise levels (mean levels L m > 57 dBA) showed significantly increased nocturnal excretion of catecholamines (stress hormones) in urine compared to women who lived in quieter areas with outside nighttime mean noise levels L m < 52 dBA.70
In a daytime study investigating the effect of low intensity noise exposure in an office setting, 40 female clerical workers were randomly assigned to a quiet-office control condition (average ambient sound intensity of 40 dBA) or to low-intensity noise exposure designed to simulate noise levels commonly found in open-office settings (average sound level of 55 dBA, with peaks of up to 65 dBA).75 Over two, three-hour experimental sessions, researchers observed that the workers exposed to the simulated open-office noise experienced elevated urinary epinephrine levels (but not elevated norepinephrine or cortisol levels).75
Diabetes. Residential exposure to road traffic noise has been linked to an increased risk for diabetes.
In a Danish population-based cohort study of 57,053 adults that from 1993-2006, researchers examined the association between long-term road traffic noise exposure and the risk of diabetes.79 Researchers identified 3,869 cases of incident diabetes and found that each 10 dB increase in average traffic noise exposure at a current residence or during the previous five years was associated with an increased risk of incident diabetes (incidence rate ratio (IRR) 1.08 and IRR 1.11 respectively) after adjusting their estimate to include confounders such as age, body mass index, and air pollution, among others.79
Cardiovascular disease. Cardiovascular health effects have been observed with long-term daily exposure to noise levels above 65 dB or with acute exposure to noise levels above 80 dB.66
In one US study examining the association between exposure to aircraft noise and hospital admission rates for cardiovascular disease among those 65 years or older, researchers found that “long-term exposure to aircraft noise is positively associated with hospitalization for cardiovascular disease.”82
Myocardial infarction. Epidemiological research shows that long-term exposure to daytime road traffic noise (>70 dBA) is associated with increased risk for heart attack among men.83
More recent research has found that long-term, residential exposure to road traffic noise is associated with elevated risk for heart attack among both men and women at an even lower exposure threshold (>60 dB).84 A study conducted in Europe found that exposure to long-term road traffic noise was associated with a 12% higher incidence rate of heart attack per 10 dB increase in noise exposure.84
Stroke. Studies on residential exposure to road and air traffic noise show an association between noise exposure and stroke, though the evidence is not as strong as that for other cardiovascular health effects. The effect is generally stronger in elderly populations.678586
A prospective-cohort study of 57,053 people found 1,881 cases of first-ever stroke.85 Researchers found an incidence rate ratio of 1.14 for stroke per 10 dB higher level of road traffic noise (Lden). They observed a statistically significant interaction with age, noting a strong association between exposure to road traffic noise, and stroke among people older than 64.5 years of age (IRR 1.27) and no association for those under 64.5 years of age (IRR 1.02).85
In a 2015 in a study of 8.6 million people living in London, exposure to daytime road traffic noise increased the risk of hospital admission for stroke in both adults (age ≥25 years) (RR 1.05) and the elderly (age ≥75 years) (RR 1.09) in areas with noise levels >60 dB compared to areas with noise <55 dB.86
Hypertension. Exposure to road and air traffic noise has been associated with an increased risk for hypertension in adults in a dose-dependent manner.8788
The HYENA (Hypertension and Exposure to Noise near Airports) study assessed the relationship between noise generated by aircraft and road traffic near airports and the risk of hypertension.87 Researchers interviewed 4,861 adults (aged 45 to 70 years) who had been living near one of six major European airports for at least five years. Researchers found that a 10 dB increase in exposure to nighttime aircraft noise was associated with an OR of 1.14 for hypertension. The exposure-response relationship remained similar when assessing average daily road traffic noise exposure, and was stronger for men (OR 1.54) in the highest exposure category (>65 dB).87
Some research shows that women may be particularly sensitive to this exposure risk, though the significance of the difference in strength of association requires further investigation.8990
A 2007 study of 667 subjects between the ages of 19 to 80 years old found that the odds ratio for hypertension was 1.38 per each five dBA increase in residential exposure to outdoor road traffic noise within the range of Leq 24-hour <45 dBA to >65 dBA.89 Researchers observed a stronger association between exposure and hypertension among women (OR 1.71), though they note that the difference between male and female subjects was not significant. Notably, the results of the study showed the strongest association between road traffic noise exposure and hypertension among “those with the least expected misclassification of true individual exposure, as indicated by not having triple-glazed windows, living in an old house and having the bedroom window facing a street” (OR 2.47), factors that the researchers posited to contribute to measurement error of the exposure.89
Elevated blood pressure. Research shows that noise exposure can cause elevated blood pressure independent of hypertension.91
A hospital-based study of 40 (mostly male) adults in ICU recovery post–cardiac surgery found that noise generated by ICU medical devices was positively and significantly associated with increased heart rate and blood pressure.91 Mean sound level in the ICU in the study was between 59.0 to 60.8 dBA. Researchers found that a “one-dBA increase in noise level in the ICU was associated with an increase in heart rate” (0.07 beats/minute) and systolic arterial blood pressure (0.58 mmHg), diastolic blood pressure (0.15 mmHg) and mean arterial blood pressure (0.53 mmHg).91
Though an early review on the effects of noise exposure on cardiovascular health in children concluded that noise exposure was associated with slightly elevated blood pressure, it did not find that children were experiencing hypertension.62 However, previous studies included in the review noted that elevations in blood pressure among youth appear to track into their adult years, which is cause for concern, as elevated blood pressure among adults increases their risk of adverse cardiovascular conditions.62 A second review noted that elevated blood pressure was found in a study conducted during the relocation of the Munich airport where researchers observed that children highly exposed to aircraft noise at school “showed a marginally significant higher systolic blood pressure” compared to those not highly exposed to aircraft noise at school.92
Despite some evidence from early studies, more recent research states that “no unequivocal conclusions can be drawn about the relationship between community noise and blood pressure” in children.93 Researchers in a 2006 study (the RANCH project) found statistically non-significant increases in blood pressure in children exposed to aircraft noise at school but statistically significant increases in blood pressure in children exposed to aircraft noise both at home and during the night.93 These conflicting findings regarding blood pressure changes in children in the home and school discussed in the paragraphs above warrant further research in order to draw more concrete conclusions.
Comfort and Focus
Proofreading. Few studies have investigated the effects of noise exposure on proofreading tasks. Preparatory research for a small laboratory study indicated that on average, proofreading performance decreases by about 7-10% in noise conditions.72 In one study of 36 subjects, performance of proofreading tasks (correctly finding spelling and contextual mistakes) deteriorated in those exposed to the “speech” sound exposure condition compared to those exposed to continuous noise.72 However, some studies show that neither intensity nor spatial location of noise exposure were associated with a detriment to proofreading.94
Reading comprehension. In 1975, seminal research on noise in schools found that children exposed to train noise suffered decreases in their reading ability development. Reading scores of children in noisy classrooms lagged three to four months behind those in quiet classrooms.59
Decades later, the evidence for this effect is still strong. More recent research investigates the effect of aircraft noise exposure on children’s reading ability and finds that exposure to aviation noise is associated with delays in development of reading skills.9596
Impaired reading comprehension from exposure to noise is not limited to noise exposure from industry and traffic. Speech noise can also be particularly distracting. Laboratory research has shown that continuous speech conditions can impair reading comprehension.97 In a study of 36 university students, subjects demonstrated a 13.2% reduced reading comprehension performance in continuous speech conditions than in silence.97
Memory. Noise exposure, particularly aviation and road traffic noise, has also been shown to impact memory task performance.9899100
A prospective study of 326 children near the flight path of an old Munich airport and children near the flight path of the new Munich airport found that children exposed to aircraft noise near the new airport suffered from impaired long-term memory, while children in the formerly exposed group near the old airport (no longer in use) experienced an improvement in long-term memory.98 Researchers noted that short-term memory also improved in the group of children living near the old airport once the airport closed.98
Mental arithmetic. In a study of 36 university students, performance of mental arithmetic was significantly better (P < 0.05) in quiet conditions (p<.05) compared to two conditions of office noise (with and without speech).101 Authors noted no significant differences in performance between the two sound conditions (office noise with speech and office noise without speech).101
Reaction time. In a laboratory study of 112 participants and a field study of 64 participants, researchers observed that after nocturnal aircraft noise exposure, participants worked significantly less accurately.102 Researchers found a dose-response relationship between nocturnal noise exposure and reaction time both in the laboratory and in the field. Reaction time increased with rising equivalent noise level (LAeq); 0.13 ms/dB LAeq in the laboratory and 0.3 ms/dB LAeq in the field.102
Additionally, a nighttime laboratory study of 40 people who had been living either near a railway track or in a quiet environment for more than 10 years found that reaction time was chronically elevated in the subjects who lived near the railway tracks.103
Motivational deficits. In a study investigating the effect of low-intensity noise exposure in an office setting, 40 adult female clerical workers were randomly assigned to a quiet-office control condition (average, ambient sound intensity of 40 dBA) or to low-intensity noise exposure designed to simulate noise levels commonly found in open-office settings (average level of 55 dBA, with peaks up to 65 dBA).75 Over two, three-hour experimental sessions, researchers observed that the workers exposed to the simulated open-office noise had behavioral aftereffects indicative of motivational deficits (fewer attempts at unsolvable puzzles).75
A 2003 review also presents evidence for an association between chronic noise exposures and diminished motivation.7 In the review, two studies taking place in the U.S. and Germany about motivation in children found that children exposed to aircraft noise were more likely to give up solving a challenging puzzle than non noise-exposed children.7
Annoyance. A cross-sectional study of 3,097 adults aimed to determine the principle factors for high noise annoyance in an adult urban population.104 Out of the factors surveyed, researchers found that residents who had their living room/bedroom oriented toward a noisy street had the highest increased risk for high level of annoyance (OR 2.60).104
Researchers in the West London Schools Study, a study of 451 children aged 8-11 years old, compared children who attended schools in high aircraft noise areas (16-hour outdoor Leq > 63 dBA) and children who attended schools in lower aircraft noise areas (16-hour outdoor Leq < 57 dBA).105 Results showed that the children who attended schools in high aircraft noise areas experienced elevated annoyance when compared to those children who did not experience the noise condition.105
In a 1998 study of people living within the flight pattern of a major New York City airport and people living in a non-flight area, researchers found that nearly 70% of subjects living within the flight pattern of a major airport reported annoyance from aircraft noise.106
More recently, a 2008 study conducted in New York City surveyed residents living near La Guardia Airport found that “more than 55% of the people living within the flight path were bothered by aircraft noise, and 63% by highway noise.”107 Researchers noted that the percentages of people living near the airport who reported to be bothered by aircraft noise and highway noise were “significantly higher percentages than for residents in the non-flight area.”107
Distraction and dissatisfaction. In a field study of 2,391 employees at 58 sites, 54% of employees reported being “bothered often by noise, especially by people talking and telephones ringing.” Intelligible speech was a leading factor.47
A field survey of 88 office employees assessed subjective reports of distraction and the amount of exposure workers had to noise in two different office spaces (55 dBA or 60 dBA).108 Researchers found no difference between the two office spaces, so the data was collapsed to one sample including both exposure conditions. Of the eight total categories of noise sources, surveys found that almost all (99%) workers felt that their concentration was impaired by at least one office noise; 82% reported impairment from three or more sources; and 57% of respondents reported that at least one source lead to a “major deterioration in their concentration.”108
Similar noise effects are found in children where 52% of the teachers surveyed in areas of high aviation noise exposure (55 dB and above) reported that “children were ‘often’ or ‘very often’ distracted from their lessons due to aviation noise.”96
Solutions
1. Acoustic Barriers
For homes and buildings near busy roadways, the U.S. Department of Transportation recommends erecting acoustic barriers to decrease traffic noise that reaches a structure.109
2. Low Noise Appliances and Building Systems
The International Institute of Noise Control Engineering (I-INCE), National Institute for Occupational Safety and Health (NIOSH), National Aeronautics and Space Administration (NASA) and the New York City Department of Environmental Protection recommend purchasing and installing low-noise equipment, appliances and building systems in order to limit environmental and occupational noise exposure.110
3. Separation From Noise Source
Separating the receiver from the noise source through acoustic planning can reduce the receiver’s exposure to noise.
4. Sound-absorbing Materials
Sound-absorbing materials applied to ceilings, walls, and floors can absorb sound before it can be reflected into a space and therefore reduce noise. Absorptive materials can also absorb sound that has already been reflected to further reduce internally generated noise.
5. Sound-insulating Materials
Sound-insulating materials can isolate sound and reduce its transmission to other spaces.
6. Sound Masking
The Center for the Built Environment states that sound masking can reduce the intelligibility of noise.111
In spaces with intruding sounds, the U.S. General Services Administration recommends covering noise by utilizing sound-masking systems to create a minimum level of non-disruptive background sound.112
2. Interfering Sound
Interfering sounds are sounds that impede communication. Through auditory masking, interfering sounds inhibit intended communication, making speech difficult to understand.
Interfering sounds can decrease speech intelligibility and inappropriately mask speech. This disruption can result in the loss of important information that may be critical to health and safety in all types of environments. In industrial settings, disruptive sounds may interfere with verbal warnings of caution or danger. Disruptive sounds can also affect communication between staff in hospital settings. Miscommunication is cited as a leading contributor to error in the medical field as high levels of background noise can hinder effective communication and cues among medical care teams.113
Designers are faced with the challenge of balancing speech intelligibility with audibility. They should aim to improve the intelligibility of wanted speech and sounds (including non-speech, such as alarms or other warning signals) and reduce the transmission of noise.
Health Effects
Comfort and Focus
Communication. Speech comprehension can be impaired by the presence of background noise. A study of surgeons in simulated operated room environments found that comprehension performance declined as background noise increased.113
Students experience similar issues with understanding speech in noisy classrooms. Data from the NORAH study indicates that teachers teaching in areas with relatively high aviation noise exposure (55 dB and above) “reported unanimously that the noise causes considerable disturbances to lessons.”114 In schools in these areas, research shows that more than one third of children are “sometimes unable to hear the teacher properly due to aviation noise.”114
Solutions
1. Sound-absorptive Materials
Sound-absorbing materials applied to sound-reflective floors, walls, and ceiling surfaces can limit echo and reverberation of unavoidable noises.
The Center for Health Design recommends using sound-absorbing materials (specifically ceiling tiles) to improve speech intelligibility by reducing sound propagation and reverberation.55
2. Source Control Through Policy
Adopting administrative policies that reduce noise production by limiting unnecessary communication and activity can reduce the overall level of disruptive noise.
3. Separation From Noise Source
Separating the noise source from the receiver through acoustic planning reduces the receiver’s exposure to noise.
4. Low-noise Appliances and Building Systems
The International Institute of Noise Control Engineering (I-INCE), National Institute for Occupational Safety and Health (NIOSH), National Aeronautics and Space Administration (NASA) and the New York City Department of Environmental Protection recommend purchasing and installing low-noise equipment, appliances and building systems in order to limit environmental and occupational noise exposure.110
3. Speech Privacy
Speech privacy refers to the degree of confidentiality for spoken words within a space.
Speech privacy is especially important in office and healthcare settings and in any space where confidentiality of speech content is a priority. Adequate speech privacy in offices prevents workers from being disturbed by background sounds and guarantees them a degree of confidentiality in their communications. Speech privacy in hospital settings allows doctors and patients to maintain healthcare information confidentiality.
Low speech intelligibility translates to better speech privacy.73 Speech privacy is addressed largely through the reduction of intelligible sounds, including the adequate insulation of airborne sound and masking of intelligible speech.
Health Effects
Comfort and Focus
Dissatisfaction. The Center for the Built Environment database shows that dissatisfaction with speech privacy is responsible for low average acoustic ratings.115 In a survey of nearly 24,000 office workers, about 80% of respondents working in cubical spaces reported that it is dissatisfying when others can overhear private conversations.115 The survey showed that acoustic dissatisfaction in the workplace is more often associated with speech privacy conditions than noise levels.115
Post occupancy surveys administered by the Center for the Built Environment show that shared or open office spaces performed much lower on sound privacy questionnaires compared to more private office spaces.116
Solutions
1. Sound-absorptive Materials
Sound-absorbing materials can reduce speech intelligibility and therefore increase speech privacy. Sound-absorptive materials applied to ceilings, walls, and floors can absorb sound before it can be reflected into a space and therefore reduce the potential for private conversations to be overhead. Sound-absorbing materials can also absorb sound that has already been reflected, further reducing the intelligibility of speech.
The Center for Health design recommends using sound-absorbing materials (specifically ceiling tiles) to increase speech privacy by reducing sound reverberation and propagation into adjoining areas.55
2. Sound Masking
The Center for Built Environment states that sound masking can be used to provide sufficient background noise needed to improve speech privacy.111
Of note is research from the Center for Health Design that highlights the “lack of research demonstrating the effect and appropriateness” of utilizing sound masking in healthcare settings.55 Sound masking may be inappropriate in a setting where it has the potential to interfere with communication between staff or staff and patients.55
3. Sound-insulating Materials
Utilizing sound-insulating materials can isolate sound (including intelligible speech) and reduce its transmission to other spaces.
4. Source Separation
Separating the receiver from the noise source through acoustic planning can reduce the receiver’s exposure to noise.
Providing a separate, enclosed space where individuals can go to have private conversations or make telephone calls can increase speech privacy in open spaces.
In hospital settings, source separation may take the form of acoustic planning that includes enclosed spaces (including patient rooms) that allow for confidential conversations between healthcare providers and patients.55
When deciding whether to add sound to a space, one must take into account the impact of unintended masking, the impact on communication and the potential of competition with existing sounds in a space.
4. Intentional Sound
Achieving acoustic comfort does not always require the elimination of all sound or noise. For some individuals, adding certain types of sounds creates a more comfortable acoustic environment. Music, white noise and other soothing sounds may have an analgesic and stress-reducing effect (in addition to any sound-masking effects), though preferences for these are highly subjective.68
It is important to note that the effectiveness of interventions involving music’s effectiveness as a sound intervention may be influenced by a person’s subjective music preferences. There is also potential for confounding with locus of control when subjects are allowed to select the music used in the intervention.117
Health Effects
Comfort and Focus
Stress and anxiety. In a hospital study on the therapeutic effects of live harp sounds on patient symptoms and quality of life, researchers found that among 92 patients approximately 30 to 50% showed a significant increase in quality of life measures after receiving harp treatment along with standard care.118
Researchers found a similar association in a different hospital-based study investigating the effect of music on patient anxiety. Patients who listened to music showed greater relaxation compared to those in a control group.119
Music has also been shown to reduce anxiety among mothers and may have beneficial effects for infants as well.120 A randomized control study investigating the effect of listening to music during kangaroo care on maternal anxiety and preterm infants’ responses found that maternal anxiety was significantly lower among mothers who listened to music during kangaroo care than mothers who did not listen to music.120 Note, mothers in the treatment group were allowed to listen to a lullaby of their choice during the experiment, so there may be some confounding due to locus of control effects. While researchers observed no significant differences in the infants’ physiologic responses between the treatment and control group, they did note that infants in the music treatment group experienced “more occurrence of quiet sleep states and less crying.”120
In a 2013 review, researchers sought to evaluate how “music improves health and well-being through the engagement of neurochemical systems” for stress and arousal, among other behaviors.117 The researchers found that there is growing support that relaxing music improves the body’s immune system function and reduces stress and anxiety.117
Agitation. In an experimental study of 104 elderly participants, music therapy alleviated agitated behavior in participants with dementia.121 Those who received 30-minute group intervention sessions twice a week for six weeks showed better performance at the midway and final study checkpoints. Participants who received the treatment also performed better one month after cessation of the program. “Performance” was based on “reductions in agitated behavior in general, physically non-aggressive behavior, verbally non-aggressive behavior, and physically aggressive behavior.”121
Cognitive performance. In a non-clinical study of 51 students, researchers found that inattentive children performed better on verbal episodic recall tests in a background noise condition created by white noise (78 dB) than in a low noise condition without added background noise.122 Researchers believe that a moderate amount of task-irrelevant noise improves performance on a target task through the effect of stochastic resonance.122 Their theory is that stochastic resonance enhances attention and performance by adding noise to sensory signals that are otherwise below the detection threshold. Attentive children in this study experienced a performance decrement in the high background noise condition.122 Note that the sound level of white noise in this study borders close to the OSHA eight-hour time-weighted average limit for occupational exposure and far exceeds ANSI-recommended classroom sound levels (ANSI/ASA S12.60-2010).
Solutions
1. Addition of Sound
When added to the environment (where the need for masking is not a concern), music, white noise, or other soothing sounds can be beneficial. This solution leverages sound not for the purpose of masking distracting noises, but as an intervention with its own beneficial function.
Direct Pathway Sound Exposure
Direct pathway elements of sound are those that directly affect hearing by causing damage to the auditory system. Exposure to sounds that harm hearing can lead to temporary or permanent hearing loss in the form of acoustic trauma, tinnitus, noise-induced temporary threshold shift, and noise-induced permanent threshold shift.123 Direct pathway sound exposure can happen at work (occupational) or at play (recreational).
The National Institute on Deafness and other Communication Disorders (NIDC) reports that, within the U.S., 15% of people between the age of 20 and 69 (26 million Americans) suffer from noise-induced hearing loss (NIHL) that may be the result of occupational and/or recreational noise exposure.4 Researchers expect incidence of hearing loss to increase as younger people experiencing hearing damage grow older.124
Hearing impairment cannot be reversed, but it may be prevented or minimized through protection from exposure.125 There are also options available to help individuals adapt to permanent hearing damage. Hearing aids may offer some relief; however, they are not corrective devices and the extent to which they can improve hearing is limited. Additionally, many who would benefit from hearing aids do not wear them. NIDC statistics indicate that fewer than 16% of adults aged 20 to 69 and 30% of adults aged 70 and older who would experience hearing improvements with hearing aids have ever used them.5
1. Destructive Sound
Destructive sound is sound that damages hearing by affecting one or more anatomical features of the ear. This type of sound may be encountered in all types of environments and is important in consideration of human health and wellness.
The NIH states that prolonged exposure to sound pressure levels above 85 dB can cause hearing loss and regular exposure to sounds at 110 dB for more than one minute puts an individual at risk for permanent hearing loss.22 Additionally, exposure to impulsive sounds at harmful decibel levels, like the noise of an explosion, can cause damage to the eardrum, ossicles in the middle ear, or inner ear, resulting in hearing loss.22
I. Occupational Exposure
The Occupational Safety and Health Administration (OSHA) cites noise-induced hearing loss as “one of the most prevalent occupational health concerns in the United States for more than 25 years,” estimating that 30 million people a year are occupationally exposed to hazardous noise.126
Nearly 125,000 workers have suffered significant, permanent hearing loss since 2004, according to the Bureau of Labor Statistics.126 Worldwide, it is estimated that 16% of disabling hearing loss in adults is caused by occupational noise exposure.127 The National Institutes of Health (NIH) identifies occupations that carry a high risk for hearing loss including “airline ground maintenance, construction, farming, and jobs involving loud music or machinery.”128
Despite making up only 13% of the US workforce, workers in the manufacturing industry comprise more than 72% of all reported cases of occupational hearing loss.129 The CDC estimates that up to 50% of construction workers may have some job-related hearing loss.130 A 2014 study published in the American Journal of Industrial Medicine estimated that construction workers have a 73.8% lifetime risk of developing hearing damage.131
OSHA states daily limits for occupational noise exposure. Exposure above the legal limits requires protective measures to be taken by both the employee and the employer.126 OSHA requires that employers provide a safe workspace through either personal protective devices or through alteration of the work environment. CDC notes that occupational hearing loss is 100% preventable, but managers and workers must commit to preventing it.132 Figure 13 illustrates the maximum daily noise exposure allowable to avoid hearing damage.
Recreational noise exposure also poses a risk for hearing loss. Recreational activities, such as listening to loud music, riding motorcycles, and shooting firearms, put an individual at risk for hearing loss.4134 Many personal use devices may exceed 85 dB (personal music players, for example, can range between 105 and 120 dB).135 Concerts and live shows also pose a risk, as typical sound intensity in nightclubs can reach as high as 112 dB.136
Researchers believe that the recreational risk factors for noise-induced hearing loss may be more dangerous than those posed by occupational exposures, as there exists an attitude of indifference among the general public (especially youth) of the risks associated with recreational noise exposure.137
Health Effects
Nervous System
Hearing Loss. The NIH National Institute on Deafness and Other Communication Disorders (NIDCD) reports that noise-induced hearing loss can be caused “by a one-time exposure to an intense ‘impulse’ sound or by continuous exposure to loud sounds over an extended period of time.”4
In a case-control study of 42 nonprofessional pop/rock musicians and 20 young adults with no history of long-term noise exposure, researchers observed a mean hearing threshold of six dB in the musicians compared with 1.5 dB in the control group.138 Musicians who reported never using hearing protection experienced hearing loss at 6.7 dB higher than the control group.138
Temporary Threshold Shift. OSHA states that temporary threshold shifts (TTS) may be the result of “short-term exposure to noise.”123 Hearing sensitivity typically returns to the level it was before the noise exposure in a relatively short amount of time (from a period of a few hours to a few days).123
In a study of 33 college-aged subjects, changes in temporary threshold shifts were “reliably detected after higher levels of sound exposure” from a personal music player.139 Subjects were tested in three groups (about 94 dBA, about 98dBA and about 100dBA) of incremental levels of sound exposure.139 Results showed that the most robust change in TTS was observed between the 2nd and 3rd exposure levels; recovery from exposure was largely complete at four hours post-exposure for all groups.139
Tinnitus. The CDC cautions that tinnitus (ringing in the ears) can occur after exposure to loud noise from sources such as industrial equipment or loud concerts.140
In a cross-sectional study of 2,015 people aged 55 and older, researchers found that self-reported work-related noise exposure was related with tinnitus.141 Subjects who reported working in environments where they were “unable to hear speech” were 1.6 times more likely to have tinnitus when compared to subjects who reported working in a “relatively quiet environment.”141 Additionally, subjects who reported working in environments where the noise was “tolerable” were 1.35 times more likely to have tinnitus than subjects who reported working in a “relatively quiet environment.”141
Solutions
1. Low-noise Construction Equipment and Tools
The CDC recommends reducing exposure to noise generated by equipment by utilizing the quietest machinery and tools available.130
2. Acoustic Enclosures
To protect individuals from exposure to dangerous noise levels, OSHA recommends airtight enclosures that serve as a barrier and often incorporate additional absorptive materials.142
3. Sound-absorptive Materials
OSHA recommends using absorptive materials to both absorb sound before it can be reflected and to reduce sound that has already been reflected.142
4. Acoustic Barriers
When noise cannot be reduced to a safe or comfortable exposure level in an indoor setting, separate receivers in the direct sound field from the noise source by inserting acoustic barriers between the noise and the receiver.
5. Separation From Noise Source
Separating the receiver from the noise source through acoustic protocols can reduce the receiver’s exposure to noise.
6. Personal Hearing Protection Devices
OSHA requires that employers provide hearing protection devices to all workers whose daily average noise exposures is over 85 dBA.126
7. Hearing Conservation Programs
OSHA also requires that employers implement hearing conservation programs in industries where “workers are exposed to a time-weighted average noise level of 85 dBA or higher over an eight-hour work shift.”126
Explanations of Solutions
Three factors must be considered when attempting to decrease sound transmission and intrusion: the source of sound, the transmission path, and the receiver. The solutions and strategies for addressing issues associated with acoustic comfort are designed with these three components in mind.
Acoustically, every environment is different. Even with current technologies, it can be difficult to obtain an accurate assessment of sound disturbances. Periodic testing or averaged reading from a dosimeter (an instrument used to measure sound pressure levels) may fail to detect extremely loud but infrequent noise events. This makes it especially challenging to detect and suppress noise in areas where there are many different sources of sound. Further, satisfaction is a subjective experience that varies from person to person, adding yet another dimension to the challenges of achieving acoustic comfort.
Figure 14: Sound transmission from a source along a path to a receiver.143
Understanding the hierarchy of noise control helps us to conceptualize solutions for acoustic comfort. At the top of the solution hierarchy is reducing or containing the noise at its source.142 This is often accomplished through engineering controls that require a physical change either to or at the location of the noise source. Examples include: eliminating the noise source through design; replacing noisy equipment; utilizing sound barriers and acoustic enclosures to limit the noise that enters a space; and incorporating sound-absorbing materials to attenuate sound that has already entered a space.
One can also reduce or contain the noise source through acoustic planning. This includes creating designs with geometries, layouts, and dimensions that minimize sound propagation, resonance or reverberation.
Moving down the hierarchy, administrative controls provide a degree of protection through scheduling or policies that prevents noise exposure. At the very bottom of the hierarchy lies exposure control by modifying the receiver, such as moving an individual away from a noise or requiring them to wear a personal hearing protection device.
Outside of this hierarchical approach to noise control, a final solution may involve adding sound. The following section describes solutions that architects, designers, and builders can utilize in improving acoustic comfort.
Sound Insulation
Sound-insulating materials can isolate sound and reduce its transmission to adjacent spaces, helping to control sound transmission from room-to-room.
STC, NIC, and IIC are the metrics most often used to describe building materials’ sound-insulating abilities. While this section is divided into separate building components, keep in mind that all parts of a room are connected and the construction and assembly of each piece affects the performance of each and every section.
Floors. The Canadian National Research Council’s Institute for Research in Construction (NRC-CNRC) explains that impact insulation class (IIC) is affected by the floor structure and the finished floor surface (topping).144 Concrete-slab floors finished with hard surface materials like marble or tile do not attenuate sound well. IIC can be improved by adding a “resilient (flexible) layer” that cushions the impact between the floor structure and the topping. These flexible layers are most commonly made from rubber, cork, or plastic mats. As a general recommendation, “the softer and thicker the floor cover, the better the IIC.144 In joist floors, impact sound attenuation is most influenced by the “total mass of the subfloor and the ceiling layers.”144 Each doubling of the total mass of the subfloor and ceiling layers increases the IIC by approximately seven points.144
The NRC-CNRC provides reference charts for typical IIC values for a combination of different floor types (slab and joist) and floor coverings. See Figure 15 below.
An IIC rating of 50 allows for footfall noise to remain pronounced and audible in the space below while a rating of 75 renders footfall noise inaudible.
Common guidelines for selection of materials across various spaces is as follows:145
IIC 50: lower range of transmission reduction considered effective
IIC 60: considered to be the medium level of transmission reduction
IIC 65: considered to be a high level of transmission reduction and would satisfy most occupants
Ceilings. The Ceilings and Interior Systems Construction Association (CISCA) states that a CAC of 35 or greater is generally considered “very good” at reducing sound intrusion.146
Walls. Designers should choose wall assemblies and partitions with high STC values. According to the American Institute of Architects, as a general rule, increasing STC by 10 points decreases the noise perceived by half.147
GSA provides some basic rules of thumb for understanding STC values of materials:147
STC 35: Loud speech audible but not intelligible
STC 40: Onset of “privacy”
STC 45: Loud speech barely audible
STC 50: Loud speech not audible; shouting barely audible
STC 55: Very loud sounds such as musical instruments or a stereo can be faintly heard
STC 60: Superior soundproofing; most sounds inaudible
The efficacy of walls and partitions in reducing sound transmission can be greatly compromised by “leaks.” Builders should properly seal all acoustically rated partitions at the top and bottom tracks to create an air seal and reduce sound transmission.147 Staggering electrical connections and gypsum board seams also helps to reduce sound transmission between rooms. When possible, builders should avoid back-to-back installation of fixtures that require wall penetration, such as cabinets. Back-to-back placement of these fixtures allows for a direct sound path between rooms. The International Building Code advises builders to pack, seal, line, insulate, or otherwise treat all wall penetrations (with the exception of entrance doors) to reduce airborne sound transmission.148
When installing doors, designers and builders should choose doors with solid or insulated cores, as hollow core doors are not very effective at insulating sound. Sliding glass doors do not typically have high STC ratings and sound can leak through the parallel top and bottom tracks.112 Doors should have gaskets to prevent sound transmission.
In offices, GSA recommends partitions at least 1.2 m [4 ft] high (maximum 1.7 m [5.5 ft] high) in quiet, open workspaces as a way to insulate against sound intrusion and reduce intelligible noise.112
Figure 16: LEED STC Recommendations According To Adjacent Room Type.150
The U.S. Department of Housing and Urban Development’s Office of Community Planning and Development also provides STC ratings for various wall, floor, window, and door assemblies.27
Additionally, GSA PBS-100 provides examples of wall assembly constructions that typically satisfy the minimum recommended NIC by room type.147
Sound Absorption
Sound-absorbing materials applied to floors, walls, and ceiling surfaces can absorb sound before it can be reflected or can reduce sound that has already been reflected.20 Absorptive materials can be used to decrease reverberation time, which in turn can decrease sound level within a space.
Reverberation Time (RT60) and NRC are the metrics most often used to describe the sound-absorbing abilities of rooms or building materials.
When reverberant noise is a major contributor to noise exposure, builders and designers should use absorptive materials to treat the sound-transmission path.
Sound-absorbing materials are best used in smaller spaces (<10,000 ft²) and are best used to address middle- to high-frequency sounds.20
Hard surfaces provide poor absorption and create a good amount of reflection. Softer surfaces are more effective in absorbing sound waves and shortening sound reverberation time. Sound-absorptive materials are usually porous or fibrous and are often made of fiberglass, mineral wool, felt, or polyurethane foam.142 Textured surfaces, such as thick grass, can “result in sound levels being reduced by up to 10 dB per 100 meters at 2,000 Hz.”149
LEED-recommended reverberation times (that can be achieved with the help of absorptive materials) by space type are found in Table 4 below.150 NRC of common surface materials and finishes calculated from sound absorption coefficients provided by OSHA are found in Appendix A.142 Additionally, GSA recommendations for reverberation time by space type can be found in Appendix B.147
Floors. Absorptive materials on floors can help control sound produced by people (especially footfalls) and equipment. GSA recommends using carpet, cork, linoleum, or other absorptive materials as floor coverings.112
Walls. Acoustic panels or artwork can also be applied to walls to absorb sound, serving both a functional and an aesthetic purpose. Designers and builders can increase wall and ceiling absorption by using materials with high NRC values, such as heavy curtains or window shades.
In homes, the U.S. Department of Housing and Urban Development (HUD) Office of Community Planning and Development recommends solid partitions designed to absorb sound to separate living areas intended for quiet use from noisy public areas.27
In offices, GSA recommends partitions at least 48 inches high in quiet, open workspaces to reduce speech intelligibility and thus overall levels of intelligible noise.112
Ceilings. Absorptive acoustic panels can be placed above noisy spaces to limit the amount of sound that propagates into different areas. In one hospital study, the replacement of sound-reflecting tiles with sound-absorbing tiles reduced noise by five to six dB in patient rooms.151 OSHA cautions that noise “will not be significantly reduced for workers at ground level” if sound-absorbing panels are installed at ceiling heights greater than 4.6 m [15 ft].142
Laboratory studies at the Institute for Research in Construction show that ceiling sound-absorption values below 0.9 do not guarantee acceptable speech privacy (speech intelligibility index begins to measure above 0.2 at that value).152
The Center for Health Design notes that acoustical ceiling tiles enhance speech intelligibility as their absorptive properties reduce reverberated sound within a space and help to promote speech privacy by limiting sound transmission into adjoining spaces.55
Recommendations
GSA recommendations for NRC values of absorptive materials on walls are provided in Figure 18.153 Additionally, GSA NRC recommendations by space type for materials used on walls by can be found in Appendix B.147
Figure 18: GSA-Recommended NRC Values For Materials Used On Walls.153 Spin the wheel to explore NRC values for different space types.
GSA recommendations by space type for minimum NRC for absorptive materials used on ceilings are listed in Figure 19.153 Additionally, GSA NRC recommendations by space type for materials used on ceilings by can be found in Appendix B.147
Figure 19: GSA-Recommended NRC Values For Materials Used On Ceilings.153 Spin the wheel to explore NRC values for different space types.
Sound Masking
Sound masking systems reduce distraction resulting from surrounding speech by providing a continuous, even background sound level to make other sounds more difficult to perceive.154
Masking systems have become common in recent years as a solution to the persistent levels of background noise in open offices. Electronic sound-masking systems can be localized (a single sound source at a workstation) or centralized (a single source distributed throughout a space via a net of loudspeakers in a three- to four-meter dense grid).155
In order to mask most effectively, the frequency characteristics of the sound-masking sound must be similar to the frequencies of the sounds being masked.156
For example, research conducted at the Institute for Research in Construction (IRC) found that masking spectrums similar to the human speech spectrum are effective at masking conversations.156 The introduction of noise similar to the human speech spectrum masks the perception of both intended and distracting speech sounds, and the positioning of masking noise should therefore be carefully considered.
Office. GSA recommends using electronic speech masking, matched to work zones, at 45 to 48 dBA for normal speech privacy in an open plan workspace.112 For normal speech privacy in private offices, GSA recommends electronic sound masking at 40 to 42 dBA.112
Hospital. In hospitals, sound masking has been found to have a positive effect on patient sleep. In a review of 11 studies on noise and its effect on ICU patients’ sleep, researchers found that sound masking had the “most significant effect in promoting ICU patients’ sleep,” producing an overall improvement of 42.7%.56
Addition of Sound
Applying additional sound should be considered carefully within specific contexts, as studies about its benefits are variable according to characteristics of the population sample, the relevancy of the noise to the task, the complexity of the task, and the content and intensity of the added noise.
White and pink noise machines can be used to provide continuous background noise with a non-masking effect. They offer external auditory noise stimulation that has been suggested to help activate cognitive processes and phenomena that can improve performance.122
School. In classrooms, educators should consider utilizing white noise machines to provide background noise for inattentive children; according to the parameters laid out in the included study (see Intentional Sound), this intervention would best be suited for small group work environments that involve only inattentive children.122
Home. In residential and group-living facilities that house individuals suffering from dementia, research shows that individuals may benefit from group music therapy.121 Evidence from a study of 104 elderly subjects suggested that music therapy sessions lasting 30 minutes, conducted twice weekly over six weeks lead to a decrease in physical and verbal agitated behaviors among elders.121
The same study found that music therapy was associated with enhanced emotional relaxation, development of interpersonal interactions, and reduced episodes of future agitation among the subjects.121 The benefits of music interventions have been observed in programs conducted by both healthcare providers and certified music therapy professionals. Music interventions typically consist of four to 16 separate sessions of passive music engagement (listening) or active music engagement (participating in musical activities, including singing) completed either individually or in groups.121
Hospital. In hospitals and other healthcare settings, therapeutic sounds can improve the patient experience. A study of 92 patients found that harp therapy lasting 30 to 40 minutes was associated with reduced fatigue, anxiety, sadness and pain, and improved relaxation.118 Additionally, 30 to 50% of the patients in the study showed significant improvements in QOL following music therapy.118
Separation From Source (Through Acoustic Planning)
Separating the noise source from the receiver through acoustic planning reduces the receiver’s exposure to noise. Acoustic planning in design requires architects and builders to carefully consider how people will use the spaces of a building.
A good general rule is to consider project and building siting early in the planning process. Minimum setback distances from noise sources like highways can help decrease the amount of noise experienced by people in buildings.
Home. In homes, acoustic planning requires considering centers of activity, room types, and proximity to interior and exterior noise sources. One way to separate residents from a common exterior noise source–traffic noise–in homes is to orient quiet areas and spaces for sleeping away from busy streets.
Appliances within homes can be sources of interior noise. The New York City Department of Environmental Protection recommends that designers and builders install interior appliances that produce mechanical noise (such as HVAC units) away from noise-sensitive places.157
Office. In offices, GSA recommends optimizing office layout by grouping workstations into work type zones depending on type of task.112 For example, sales workers typically spend a large portion of time on phones, which may be distracting to editors, researchers, or individuals who spend significant time in activities that demand quiet environments. Separating workers based on job type can significantly increase individual acoustic satisfaction by decreasing distractions in the immediate vicinity of workspaces. GSA recommends providing small rooms, or “phone booths” for making private calls and using speakerphones.112 Additionally, designers should situate loud office machines like printers and copiers away from workspaces.158
Hospital. In hospitals, designers should situate healthcare team consultation stations away from patient rooms, where providers can speak to one another, keeping voice transmission low in open hallways and helping to guarantee privacy.159 In operating rooms, when possible, hospital staff can lower background noise by separating noisy machinery from areas that require high speech intelligibility, such as anesthetizing locations or surgical fields.160
Separation From Source (Through Acoustic Protocols)
Separating the noise source from the receiver through acoustic protocols reduces the receiver’s exposure to noise.
Industry. In industrial settings, OSHA recommends controlling exposure to potentially hazardous noise through distance.126 Individuals should be separated from a noise source until safer sound exposure levels are met.126 Additionally, OSHA recommends that employers provide designated quiet areas where workers are able to rest and gain relief from exposure to hazardous noise sources.126 The protective effect of quiet areas and recovery time comes from the reduced duration of exposure to continuous noise.
Hospital. In hospitals, the Center for Health Design recommends limiting patient exposure to the most arousing sound sources: phone and biometric alarms, voice paging, and staff conversations.159 Hospital staff should reduce the volume of such alarms to the extent possible without compromising patient care. Moreover, daily patient alarms and reminders could be located at central locations, such as nurses’ stations, rather than in patient rooms to the extent possible without compromising patient care.159
Acoustic Barriers
Acoustic barriers attenuate noise by providing an obstacle that blocks the path of sound between the sound source and the receiver.
According to the New York City Department of Environmental Protection, acoustical barriers must “break the line-of-sight, have no gaps, and be sufficiently massive (>four lbs/SF).”161 Additionally, the New York City Department of Environmental Protection recommends that absorptive materials used on the source side of acoustical barriers have NRC values greater than 0.7.161
Sound barriers should be constructed from solid, dense material with high TL of at least 10 dB greater than the expected insertion loss are preferable.142. Specifically, OSHA states that noise barriers with TL of at least 10 dB greater than the expected insertion loss are preferable.142 When possible, barriers should be composed of multiple layers, and materials of a different density than the layers (such as air) should be sandwiched between the layers.
OSHA states that “two, five-inch masonry walls spaced a few inches apart will have a greater transmission loss from one side to the other than a solid masonry wall that is 10 inches thick.”142
Acoustic barriers can also be used in residential areas to reduce traffic noise that reaches homes and buildings near roadways. Barrier walls should “block the line of sight from the noise source to the receiver.”162 At a height that blocks the line of sight from the source, a noise barrier can provide five dBA of noise level reduction. Every additional meter in height provides approximately 1.5 dBA of additional sound blockage.162 Figure 20 illustrates how noise barriers work.
The U.S. Department of Transportation states that environmental barriers, such as those that separate a residence from a busy highway, should be at least eight times as long (in total length) as the distance from the receiver to the barrier.163 This requirement effectively reduces the noise that can spill around the sides of the barrier and reach the receiver.163 Single barriers typically have an upper attenuation limit of 20 dB, while double barriers have an upper limit of 25 dB.164
In industrial settings, when noise cannot be reduced to a safe exposure level in an indoor setting, OSHA recommends separating workers in the direct sound field from the noise source by inserting acoustic barriers between the noise and the receiver.165 Acoustic barriers work to reduce noise by blocking sound transmission. OHSA specifies that indoor barriers are most effective when workers are in the direct sound field of a noise source.165
Acoustic Enclosures
Acoustical enclosures work similarly to acoustic barriers in that they attenuate noise by blocking the sound transmission path to the receiver.
Acoustical enclosures work to reduce noise in the direct sound field by covering the sound source. OSHA identifies acoustical enclosures as the most common path of noise treatment.142 Acoustical enclosures can be temporary or permanent and can be built from materials on-site (such as plywood) or purchased prefabricated. Researchers at the WHO recommend a minimum TL of 20 dB for acoustical enclosure materials,166 however the overall sound level determines the effectiveness of the TL. For example, a 20 dB reduction of a 120 dB sound would be insufficient.
To protect individuals from exposure to dangerous noise levels, OSHA recommends covering noisy machinery like generators with temporary sound barriers constructed from materials on-site.142 OSHA also recommends adding acoustic-absorbing material (such as foam) to at least 25% of the interior surfaces of the temporary enclosure. The New York City Department of Environmental Protection recommends that absorptive materials on the source side of acoustical enclosures have NRC values greater than 0.7.161 According to OSHA, acoustical enclosures are able to provide 20 to 40 dB of noise reduction.142
Source Control
Source control methods are typically the most effective form of noise control, as they prevent or reduce noise generation and thus the transmission of noise within a space.
Tools and Equipment. The International Institute of Noise Control Engineering (I-INCE), National Institute for Occupational Safety and Health (NIOSH), National Aeronautics and Space Administration (NASA), and the New York City Department of Environmental Protection recommend purchasing and installing low-noise equipment, appliances, and building systems in order to limit environmental and occupational noise exposure.167
The CDC recommends reducing exposure to noise generated by equipment by utilizing the quietest machinery and tools available. Using equipment rated three dB lower than the current tool cuts the noise energy reaching a worker’s ears in half.130
Purchasing low-noise construction equipment and tools is a component of the NIOSH-recommended Buy Quiet Program.130 NIOSH suggests four elements that comprise a Buy Quiet program: an inventory of existing machinery and tools and their corresponding noise levels; a Buy Quiet policy of commitment, educational, and promotional materials to inform employees, customers, and the community about the program; a cost-benefit analysis; and educational materials for employees.130 This is a NIOSH initiative mainly focusing on occupational noise exposure and construction workers (but it does also aim to reduce community noise).130
Appliances and Building Systems. The New York City Department of Environmental Protection recommends purchasing equipment, such as HVAC units, with low-noise ratings.161 Designers and builders should refer to sound level and noise criteria specifications provided by manufacturers when purchasing and installing appliances and building systems.
The New York City Noise Code requires that HVAC equipment noise level, when “measured within a receiving property at a distance of three feet from the open portion of a window,” does not exceed 42 dBA Lmax for a single air-circulating device and 45 dBA Lmax for the “cumulative noise level of multiple air circulating devices.”161
To decrease the amount of noise produced by an existing building system, such as HVAC units, consider vibration-isolation methods and noise attenuation through the use of springs, pads, silencers, or duct liners.161
Furthermore, all equipment and machinery should be properly maintained to support its proper functioning and sound-controlling capabilities, including replacing worn or overused parts as necessary.
Recommendations
Noise Criteria recommendations by room type are found in Figure 21.
Figure 21: GSA And ASHRAE Maximum NC Recommendations.21112147
Administrative Policy. In hospital operating rooms, minimize staff-produced noise by adopting a “sterile cockpit environment” rule. The “sterile cockpit environment” is an adaptation of the Federal Aviation Administration’s sterile cockpit rule developed in the 1980s.168 The analogous sterile cockpit environment rule in the operating room requires that staff cease nonessential communication and activity during the most critical phases of surgery; specifically, during anesthesia induction and emergence.160168 This policy reduces disruption of important communication between hospital staff by lowering unnecessary noise in the operating room.
Building owners and managers can post signs requesting that employees and other building users lower their voices or limit or refrain from cell phone use in spaces where minimal noise is desired.
Public Noise Abatement Policies. In addition to providing individual acoustic comfort, many municipalities and governments have introduced noise restrictions to create quieter communities.
The Noise Control Act was passed by the U.S. Congress in 1972, and it was the first federal law that regulated noise pollution in the U.S. Major goals included (1) establish means for coordination of research and activities in noise control; (2) establish the Federal noise emission standards for goods; and (3) provide education to the public about these standards.169 The Act established the Office of Noise Abatement and Control (ONAC) as an office within the U.S. EPA. While ONAC has since been de-funded, the Noise Control Act is still in effect, though unenforced.
The U.S. Department of Housing and Urban Development (HUD) requires a 24-hour average sound level of less than 65 dB. If the noise levels in a particular area exceed 65 dB, additional approvals and permits are required.170
Limiting environmental noise may also be accomplished through the passage of zoning acts and ordinances on local and federal levels. Communities and municipalities may promote walking, bicycling, and using electric vehicles (including golf carts) as means of transportation through communities because they contribute less to overall background noise. Incorporating noise restrictions into a community’s general plan, along with instituting ordinances against noise, is a good way to include noise control in local policy.
For example, New York City’s Noise Code establishes restrictions on noise from construction, animals, vehicles, air conditioners, restaurants, and bars, among other sources.171 On the federal level, the U.S. Department of Transportation Federal Railroad Administration allows communities to establish quiet zones that require trains to cease use of their horns at public highway–rail grade crossings within the designated zones.172
Hearing Conservation Programs (Including the use of HPDs)
OSHA requires that employers implement hearing conservation programs in industries where worker noise exposure is “equal to or greater than 85 dBA for an eight-hour exposure.”126
Hearing conservation programs are made up of numerous elements, two of which include annual audiometric testing and proper selection and distribution of hearing protection devices (HPDs). Audiometric testing should be conducted yearly to detect threshold shifts.173
HPDs are a form of receiver treatment that can help protect individuals from potentially damaging noise. Earplugs and earmuffs are popular forms of HPDs. Hearing protectors should reduce noise exposure at the ear to below 85 dB. When properly fitted and worn, earplugs or earmuffs reduce noise 15 to 30 dB. When worn simultaneously, earplugs and earmuffs can add up to 10 to 15 dB more protection than when either is used alone.174
The American Hearing Research Foundation notes that earplugs offer better protection from low frequency noise while earmuffs offer better protection from high frequency noise.174
OSHA requires that employers provide free hearing-protection devices, such as earmuffs and earplugs, to all employees whose average daily noise exposures are 85 dBA or above.126 NIOSH suggests an even more protective measure, recommending hearing protection use if noise exposure reaches or exceeds 85 dBA, regardless of exposure duration.175 The selected HPD needs to keep noise exposure at the ear below 85 dBA. Estimates for the amount of sound attenuation hearing protectors provide (Noise Reduction Ratings) are required on all hearing protection devices sold in the U.S.132
The American Speech-Language-Hearing Association recommends using personal hearing protection devices when engaging in recreational activities that may expose individuals to harmful levels of sound.176
Appendices
Appendix A: Noise Reduction Coefficients
Noise reduction coefficients of popular surface materials and finishes calculated from sound absorption coefficients provided by OSHA are found in the table below:142
Brick, unglazed: 0.05 Brick, unglazed, painted: 0.00 Carpet, heavy, on concrete: 0.30 Carpet, heavy, on 40 oz hairfelt or foam rubber pad: 0.55 Carpet, 40 oz per square yard, with latex backing, over felt or foam rubber pad of same density (on concrete): 0.35 Concrete block, coarse: 0.35 Concrete block, painted: 0.05 Fabric, light velour, 10 oz/square yard, hung straight in contact with wall: 0.15 Fabric, medium velour, 14 oz/square yard, draped in half: 0.55 Fabric, heavy velour, 18 oz per square yard, draped in half: 0.60 Plywood paneling, 3/8 inch thick (1 cm): 0.15 Floors, concrete or terrazzo: 0.00 Floors, linoleum, asphalt (vinyl), rubber, or cork tile on concrete: 0.05 Floors, wood: 0.10 Floors, wood parquet in asphalt on concrete: 0.05 Glass, large panes of heavy plate glass: 0.05 Glass, ordinary window glass: 0.15 Gypsum board, ½ inch, nailed to 2x4 wood frame 16 inches on center: 0.05 Marble or glazed tile: 0.00 Opening, covered by grill (e.g., ventilating): 0.25-0.75 Plaster, gypsum or lime, smooth finish on tile or brick: 0.05 Plaster, gypsum or lime, rough finish on lath: 0.05 Plywood paneling, 3/8 inch thick: 0.15 Water surface (pond or swimming pool): 0.00 Fiberglass boards and blankets, 2 inches thick, 1.5 to 3 pounds per square foot: 0.80
Appendix B: GSA Recommendations
Figure 22: NC Recommendations for Mechanical Noise by Space Type.147
Figure 23: NRC - Minimum absorption and coverage for ceilings.147
Figure 24: NRC - Minimum absorption and coverage for Walls.147
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A cross-sectional analysis of data collected by the CDC from 4,699 individuals found that the prevalence of hearing loss has increased significantly among young persons aged 12 to 19 years from 14.9% in the period between 1988-1994 to 19.5% in the period between 2005-2006, with individuals from families below the federal poverty threshold having significantly higher odds of hearing loss (prevalence, 23.6%) than those living above the threshold (prevalence, 18.4%).3
In a 2002 study conducted in two factories, one with high noise levels and one with strongly reduced noise levels, workers who moved to the factory with reduced noise levels experienced “greater environmental satisfaction, greater job satisfaction, reduced stress symptoms, reduced difficulty of communication, and a more positive company image, and greater attachment to the company.”51
In a two-day study, mean change in urinary catecholamines (norepinephrine and epinephrine) were measured over two consecutive eight-hour work periods in a group of 20 industrial workers exposed to workplace noise (mean for one hour, 98.2 dBA).76 This change was also compared to a control group of 20 workers from the same factory who were not exposed to workplace noise. On day one, a urine sample was collected at the end of the shift in both the exposed and unexposed groups; on day two, the exposed group of workers were asked to wear ear plugs during their shift and a second urine sample was collected at the end of day two for all participants. Results showed a significant reduction in urinary norepinephrine across the study days (p=.017) for the exposed group while the drop in epinephrine was considered “nearly” significant (p=.055). In addition, significant differences between the exposed and unexposed group across both days were noted despite a reduction in catecholamine levels observed in the exposed group.76
In a study of 217 third- and fourth-grade children, conducted during the relocation of the Munich airport, researchers found that children exposed to aircraft noise experienced elevated catecholamines levels.77 Children from the neighborhood that housed the new airport (dBA Leq = 62 following the airport inauguration compared to a dBA Leq = 53 prior) were compared to children whose neighborhoods remained “quiet” (dBA Leq = 55) over the study period of two years. Exposure was assessed by 24-hour dBA Leq measurements, and catecholamines were measured in the urine overnight. Children who were exposed to the relocation of the Munich airport over the study period showed a sharp rise in epinephrine and norephinephrine (p<.001) compared to children whose neighborhood remained quiet over the study period.77
A systematic review and meta-analysis on the risk for type 2 diabetes due to long-term noise exposure conducted in 2015 found that “people exposed at their homes to roughly Lden >60 dB had a 22% higher risk for type 2 diabetes in comparison to those exposed to Lden <64 dB.”80 However, there were mixed results from a few studies included in their review. Included in the analysis was a prospective cohort study conducted with 5,156 Swedish residents that found no clear association between long-term exposure to aircraft noise and type 2 diabetes.78 Also included in the analysis was a study utilizing data from the German National Health Interview and Examination Survey that examined the association between residential road traffic intensity and incidence of type 2 diabetes. Researchers in the study observed a “twofold higher risk of type 2 diabetes” for people exposed to intense traffic compared to people living in traffic-calmed areas.81
In a hospital-based case-control study, researchers observed that chronic exposure to high levels of road traffic noise was associated with increased risk for myocardial infarction (MI) (i.e., heart attack) among men.83 The study included 4,115 adults (1,881 patients with confirmed diagnosis of MI and 2,234 controls), with a total of 3,054 men and 1,061 women. Researchers determined outdoor traffic noise level exposure for each subject using city noise maps. For men exposed to daytime sound levels >70 dBA, the adjusted odds ratio (OR) for MI due to noise exposure was 1.3 compared with men whose daytime sound exposure did not exceed 60 dBA. The OR was even higher when researchers separated out a subsample of men who had lived at their current address for at least 10 years (OR 1.8). In this study, women who were exposed were not at higher risk.83
In a population-based prospective cohort study of 57,053 adults aged 50 to 64 years, researchers identified 1,600 cases of first-ever myocardial infarction (MI).84 Residential exposure to road traffic noise (defined as noise below Lden 60 dB, median exposure Lden 56.4 dB) was determined based on address history. Researchers found a dose-response relationship between exposure to long-term traffic noise and risk for myocardial infarction. Exposure to long-term road traffic noise was significantly associated with a 12% higher risk for myocardial infarction per 10 dB higher exposure to noise.84
In a small area study conducted on the 3.6 million residents living near London’s Heathrow Airport from 2001 to 2005, researchers assessed hospital admission rates between those living in areas with high daytime aircraft noise levels (greater than 63 dB) and those living in areas with low daytime aircraft noise levels (less than or equal to 51 dB).67 Researchers found that people living in areas with high daytime aircraft noise had a higher risk for hospital admission for stroke (relative risk (RR) 1.24).67
A 2012 meta-analysis of 24 observational studies from 1970 to 2010 found that road traffic noise was positively and significantly associated with hypertension.88 Researchers observed a dose-response relationship between road traffic noise exposure and hypertension, with an OR of 1.034 per five dBA increase in 16-hour average road traffic noise level within the range of 45 to 75 dBA.88
A 2009 panel study of 60 subjects (30 male, 30 female, aged 18 to 32 years), investigating the effects of environmental noise exposure on 24-hour ambulatory blood pressure found that young females were more susceptible to noise exposure than their male counterparts.90 Researchers reported: “Per 5 dBA increase in 24-h average noise exposure was significantly associated with sustained increments of 1.15 (CI = 0.76-1.54) mmHg SBP and 1.27 (CI = 0.96-1.58) mmHg DBP in males (57.4+/-16.0dBA), as well as the higher levels of 1.65 (CI = 1.36-1.94) mmHg SBP and 1.51 (CI = 1.27-1.75) mmHg DBP in females (55.9+/-17.0dBA).”90
In the study of 161 school-aged subjects, researchers found that noise from elevated trains near classrooms significantly impacted students’ reading ability.59 The average noise level in the classrooms included in the study was 59 dB, with sounds levels up to 89 dB when trains passed. The researcher compared reading test scores of children from classes on the loud and quiet sides of the school building. Of the 10 classes on the noisy side of the building, nine of the classes’ reading scores measured three to four months behind those students on the quiet side of the building.59
In a cross-national, cross-sectional study (the RANCH project) of 2,844 children aged 9-10 years who attended school around three major European airports, researchers found that a five dBA increase in aircraft noise was associated with a one- to two-month reading delay.95
The Noise-Related Annoyance, Cognition, and Health Study (NORAH), conducted in Germany from 2011 to 2014, examined residents’ exposure to road and rail noise near three major airports and included a specific section on the study of the chronic effects of aviation noise on primary school children.96 At 29 schools, 1,243 second-graders were surveyed and tested. Researchers found a linear connection between exposure to aviation noise and reading development; “an increase of the continuous sound level by ten decibels delayed acquisition of reading skills by one month.”96
A laboratory study of 123 fourth-grade schoolchildren exposed to chronic railroad or road traffic noise found that children exposed to ambient noise at 60 dB or above (based on 24-hour Ldn measurements) performed worse on memory tasks, including intentional, incidental, and recognition tasks compared to their peers who were exposed to ambient noise levels of 50 dB or below.99
Researchers in the RANCH project found aircraft noise exposure to be associated with impairment of recognition memory in children.100 Noise measurements of 16-hour LAeq for aircraft noise ranged from 32 to 77 dB. Results showed that “as aircraft noise increased by five dB, performance on the recognition task decreased by 0.09 marks.” The same effect was not found when assessing exposure to road traffic noise (with levels ranging from 31 to 71 dB.100
In a prospective investigation, 15 surgeons were tested for their ability to understand and repeat words in four different simulated operating room sound environments (quiet, filtered noise through a surgical mask, background noise with and without music).113 Surgeons were randomized to two different types of situations: engaged in a surgical task and un-tasked (task free), and asked to perform word recall under each of the four sound conditions. Overall, recall was worse among surgeons randomized to the tasked condition compared to the un-tasked condition (P <.003) and there was a decline in performance from quiet to background noise to background noise plus music observed in both treatment arms.113
In a hospital study on the therapeutic effects of live harp sounds on patient symptoms and quality of life, treatment consisted of 30 to 40 minutes of live harp music performed by a conservatory-trained musician.118 Researchers hypothesized that the sound vibrations produced by the harp influence the vibrational patterns of a patient’s body through entrainment and alter how symptoms are experienced. Specifically, researchers believe that entrainment decreases “the arousal of the sympathetic nervous system, thus contributing to relaxation and anxiety reduction.”118 Auditory and neural systems respond to the properties of sound waves by altering the release of stress hormones to produce positive changes in heart rate, anxiety, and blood pressure.118
In a randomized control trial of 64 subjects on the effects of music on the anxiety of patients on mechanical ventilation in a hospital setting, patients in the study’s experimental group underwent 30 minutes of music intervention, while patients in the control group were assigned to a rest period.119 Patients that listened to music “appeared to show greater relaxation as manifested by a decrease in physiological indices and an increase in comfortable resting behaviours.”119 Note that participants in the study were permitted to select the type of music used in the intervention from a collection presented by the researcher.
