The safe noise level to prevent hearing loss is probably lower than you think

Daniel Fink – djfink01@aol.com
Twitter: @QuietCoalition

Board Chair, The Quiet Coalition, 60 Thoreau Street Suite 261, Concord, MA, 01742, United States

The Quiet Coalition is a program of Quiet Communities, Inc.

Popular version of 3pNS1-What is the safe noise level to prevent noise-induced hearing loss?, presented at the 183rd ASA Meeting.

Ear structures including outer, middle, and inner ear. Image courtesy of CDC

If something sounds loud, it’s too loud, and your auditory health is at risk. Why? The safe noise exposure level to protect your hearing- to prevent noise-induced hearing loss (NIHL) and other auditory disorders like tinnitus, also known as ringing in the ears, might be lower than you think. Noise damages delicate structures in the inner ear (cochlea). These include minuscule hair cells that actually perceive sound waves, transmitted from the air to the ear drum, then from bones to the fluid in the cochlea.

Figure 1. Normal hair cells (left) and hair cells damaged by noise (right). Image courtesy of CDC

[A little detail about sound and its measurement. Sound is defined as vibrations that travel through the air and can be heard when they reach the ear. The terms sound and noise are used interchangeably, although noise usually has a connation of being unpleasant or unwanted. Sound is measured in decibels. The decibel scale is logarithmic, meaning that an increase in sound or noise levels from 50 to 60 decibels (dB) indicates a 10-times increase in sound energy, not just a 20% increase as might be thought. A-weighting (dBA) is often used to adjust unweighted sound measurement to reflect the frequencies heard in human speech. This is used in occupational safety because the inability to understand speech after workplace noise exposure is the compensable industrial injury.]

Many audiologists still use the industrial-strength 85 dB noise level as the level at which auditory damage begins. This is incorrect. The 85 dBA noise level is the National Institute for Occupational Safety and Health (NIOSH) recommended occupational noise exposure level (REL). This does not protect all exposed workers from hearing loss. It is certainly not a safe noise level for the public. Because of the logarithmic decibel scale, 85 decibel sound has approximately 30 times more sound energy than the Environmental Protection Agency’s 70 decibel safe sound level, not about 20% as might be thought.

The EPA adjusted the NIOSH REL for additional exposure time- 24 hours a day instead of only 8 hours at work, 365 days a year instead of 240 days- to calculate that 70 dB average noise exposure for a day would prevent noise-induced hearing loss. This is the only evidence-based safe noise level I have been able to find.

But the real safe noise level to prevent NIHL must be lower than 70 dB. Why? EPA used the 40-year occupational exposure in its calculations. It didn’t adjust for lifetime exposure (approaching 80 years in the United States before the COVID pandemic). NIHL comes from cumulative noise exposure. This probably explains why so many older people have trouble hearing, the same way additional years of sun exposure explains the pigmentation changes and wrinkles in older people.

My paper explains that the NIOSH REL, from which EPA calculated the safe noise level, was based on studies of workers using limited frequency audiometry (hearing tests), only up to 4000 or 6000 Hertz (cycles per second). More sensitive tests of hearing, such as extended-range audiometry up to 20,000 Hertz, shows auditory damage in people with normal hearing on standard audiometry. Tests of speech in noise- how well someone can hear when background noise is added to the hearing test- also show problems understanding speech, even if standard audiometry is normal.

The actual noise level to prevent hearing loss may be as low as 55 dBA. This is the noise level needed for the human ear to recover from noise-induced temporary threshold shift, the muffling of sound one has after exposure to loud noise. If you’ve ever attended a rock concert or NASCAR race and found your hearing muffled the next morning, that’s what I’m talking about. (By the way, there is no such thing as temporary hearing loss. The muffling of sound, or temporary ringing in the ears after loud noise exposure, indicates that permanent auditory damage has occurred.)

55 dB is pretty quiet and would be difficult to achieve in everyday life in a modern industrialized society, where average daily noise exposures are near 75 dB. But I hope that if people know the real safe noise level to prevent hearing loss, they will avoid loud noise or use hearing protection if they can’t.

The FAA allows Americans to be exposed to unsafe levels of aircraft noise

Daniel Fink – djfink01@aol.com
Twitter: @QuietCoalition

Board Chair, The Quiet Coalition, 60 Thoreau Street, Concord, MA, 01742, United States

The Quiet Coalition is a program of Quiet Communities, Inc., Lincoln, MA, USA

Popular version of 4aNS8-The Federal Aviation Administration (FAA) allows Americans to be exposed to unsafe levels of aviation noise

Presented at the 183rd ASA Meeting

Photo credit: Pixabay 

The American Public Health Association states, “Noise is unwanted and/or harmful sound.” Noise not loud enough to damage hearing causes high blood pressure, heart attacks, and strokes. The Federal Aviation Administration (FAA) considers noise an annoyance but does not acknowledge the adverse health effects of aircraft noise. Based on the Schultz curve, the FAA adopted 65 dBA Day-Night Level (DNL) as “the threshold for significant aviation noise, below which residential land use is compatible.”  The FAA’s recent Neighborhood Environmental Survey found that many more Americans are annoyed by noise than previously known.

Schultz Curve and Neighborhood Environmental Survey results, showing that many more Americans are annoyed by noise than the Schultz Curve showed. Source: FAA

Schultz Curve and Neighborhood Environmental Survey results, showing that many more Americans are annoyed by noise than the Schultz Curve showed. Source: FAA

[I have to tell you a little about the science of sound or noise measurement. The words sound and noise are used interchangeably. Sound is measured in decibels (dB). The decibel scale is logarithmic. This means that a 10 dB increase from 50 to 60 dB indicates 10 times more sound energy, not merely 20% more. Because noise disrupts sleep, DNL measures noise for 24 hours but adds a 10 dB penalty for noise between 10 p.m. and 7 a.m.  A-weighting (dBA) adjusts sound measurements for the frequencies heard in human speech. A-weighting is not the right measure for aircraft noise because aircraft noise has lower frequencies than speech. A-weighting also reduces unweighted sound measurements by about 20-30 dB.]

According to the Environmental Protection Agency (EPA), though, safe noise levels are only 45 dB DNL for indoor noise and 55 dB DNL for outdoor noise. The World Health Organization (WHO) recommends lower aircraft noise levels: 45 dB Day-Evening-Night Level (adding a 5 dB penalty for noise between 7-10 p.m.) and 40 dB at night.  Both EPA safe noise levels and WHO recommended aircraft noise levels are obviously much lower than the FAA’s 65 dBA DNL, especially because they use unweighted dB.

Being annoyed or disturbed by aircraft noise is stressful.  Stress increases heart rate and blood pressure. Stress increases blood levels of stress hormones.  Stress causes inflammation of the blood vessel lining. in turn causing cardiovascular disease, including hypertension and heart attacks, and other adverse health effects. Scientific experts think that the evidence is strong enough to establish causality, not merely a statistical association. Epidemiological studies demonstrating these effects have been confirmed by human and animal research. The biological mechanisms are now understood at the cellular, subcellular, molecular, and genetic levels.  Aircraft noise also affects poor and minority communities more than others. Children are also more sensitive to damage from noise, which also interferes with learning.

The FAA insists that more research is needed, but no more research is needed to know that aviation noise is hazardous to health.  The FAA must establish lower noise standards to protect Americans exposed to aircraft noise.

4pNS2 – Use of virtual reality in designing and developing sonic environment for dementia care facilities

Arezoo Talebzadeh – arezoo.talebzadeh@UGent.be
Ph.D. Student
Ghent University
Tech Lane Ghent Science Park, 126, B-9052 Gent, Belgium

Popular version of 4pNS2 – Use of virtual reality in designing and developing soundscape for dementia care facilities
Presented in the afternoon of May 26, 2022
182nd ASA Meeting in Denver, Colorado
Click here to read the abstract

Sound is essential in making people aware of their environment; sound also helps in recognizing the time of the day. People with dementia have difficulties understanding and identifying their senses. The sonic environment can help them navigate through the space and realize the time; it can also reduce their agitation and anxiety. Care facilities and nursing homes, and long-term cares (LTC) usually have an unfamiliar acoustic environment for anyone new in the place. A well-designed soundscape can enhance the feeling of safety, elevate the mood and enrich the atmosphere. Designing the soundscape that fosters well-being for a person with dementia is challenging as mental disorders change one’s perception of space. Soundscape is the sonic environment as perceived by a person in context.

This research aims to enhance the soundscape experience during the design and development of care facilities by using Virtual Reality and defining the context during the process.

Walking through the space while hearing the soundscape demonstrates how sound helps spatial orientation and understanding of time. Specific rooms can have a unique sound dedicated to them to help residents find the location. Natural soundscape in the lounge or sounds of coffee brewing in the dining room during breakfast. Birds sound inside residents’ rooms during the morning to elevate their mood and help them start their day.

Sound is not visual (tangible); therefore, it is hard to examine and experience the design before implementation. Virtual Reality is a suitable tool for demonstrating sound augmentation and the outcome. By walking through the space and listening to the augmented sonic environment, caregivers and family members can participate during the design process as they are most familiar with the person with dementia and their interests. This method helps in evaluating the soundscape. People with dementia have a different mental model. Virtual Reality can help feature diverse mental models and sympathize with people with dementia.

2aNS7 – Directional Processing in Assessment of Wind Turbine Noise

Alexander Sutin -asutin@stevens.edu
Hady Salloum – hsalloum@stevens.edu
Alexander  Sedunov- asedunov@steves.edu
Nikolay Sedunov – nsednov@stevens.edu

Stevens Institute of Technology
Sensor Technologies & Applied Research (STAR) Center
Hoboken, NJ  07030

Popular version of 2aNS7 – Directional Processing in Assessment of Wind Turbine Noise
Presented Tuesday morning,  May25, 2022, 10:50-11:05 AM, Mountain
182nd ASA Meeting, Denver
Read the article in Proceedings of Meetings on Acoustics

Assessments of Wind Turbine Generator (WTG) noise are required to comply with the US Environmental Agency and local governments and avoid legal action that may result of non-compliant operation. Current methods for WTG noise measurements require the comparison of long-term sound data recorded before and after a WTG installation. These measurements must be conducted during several months for various wind speeds and environmental conditions.

The acoustic measurements conducted for a working WTG are not reliable due to the contamination of the measurements by sources other than the noise from the wind turbines[1]. Such sources of noise include traffic (highway, rail and air), construction, industrial facilities, wind in the trees, social activities, animals, birds , etc.

The goal of our paper is to provide suggestions on how the use of a microphone array could improve the WTG noise assessment by two ways: (1) identifying and attributing noise contribution to specific sources  (2) by emphasizing of acoustic signal from the WTG.

As an example of the microphone array, we consider the sensors developed at Stevens Institute of Technology [2], [3] for low-flying aircraft and drone detection (see Figures 1a and b), these  arrays have between 5 and 10 microphones.

These sensors use a signal processing algorithm based on the correlation between the signals received by the elements of the array to find direction towards sound sources and beamforming to emphasize the acoustic signal coming from specific directions.

As a result, it is possible to identify sounds not originating from the wind turbine and remove the affected time frames from the averaged measurement of noise levels. The Stevens array directivity (see Figure 1c) shows enhancing of the signal using beamforining.

wind turbine noise

LFADSystem

wind turbine noise

DARAPicture

wind turbine noise

ARADirectivityPattern

 

Figure 1: Examples of acoustic arrays capable of direction-finding: a – acoustic system for low flying aircraft detection [2], b –array for unmanned aerial vehicle detection,c – the beam pattern for the latter array shown as relative gain depending on steered direction and frequency.

Previous prolonged deployments have provided examples of noise observation and angular localization from various sources. Figure 3 displays the spectrogram and signal angular output showing a complex situation with passing trains and vehicles.

wind turbine noise

Figure 2. An example of SRP-PHAT processing shows a complex situation with noise from a cargo train (T) and vehicles (V).

The configuration of the current Stevens system was optimized for low flying aircraft and unmanned aerial vehicle detection and localization. Since the low-frequency noise components from wind turbines are a concern for the WTG assessment, the placement of the micropnes in the arry arrays can be  modified to operate in the appropriate frequency band.

References

[1]       S. Cooper and C. Chan, “Determination of Acoustic Compliance of Wind Farms,” Acoustics, vol. 2, no. 2, pp. 416–450, 2020.

[2]       A. Sedunov, A. Sutin, N. Sedunov, H. Salloum, A. Yakubovskiy, and D. Masters, “Passive acoustic system for tracking low-flying aircraft,” IET Radar, Sonar Navig., vol. 10, no. 9, pp. 1561–1568, 2016.

[3]       A. Sedunov, D. Haddad, H. Salloum, A. Sutin, N. Sedunov. and A. Yakubovskiy, A., “Stevens drone detection acoustic system and experiments in acoustics UAV tracking.”  In 2019 IEEE International Symposium on Technologies for Homeland Security (HST) (pp. 1-7). IEEE.

1pNS1 – Innovative Solutions for Acoustic Disturbances Occurring in Slender Buildings

Bonnie Schnitta – bonnie@soundsense.com
Sean Harkin – sean@soundsense.com
Patrick Murray – patrick@soundsense.com
Collin Champagne – collin@soundsense.com
jeremy Newman – jeremy@soundsense.com

SoundSense, LLC
39 Industrial Rd, Unit 6
PO Box 1360
Wainscott, NY 11975

Popular version of paper ‘1pNS1 – Innovative solutions for acoustic disturbances occurring in slender buildings
Presented Monday Afternoon, 1:20PM, November 29, 2021
181st ASA Meeting, Seattle, Washington
Click to read the abstract

The construction of tall, slender buildings is trending globally. Structural engineering has made it possible for architects to achieve soaring heights with a smaller building footprint, leaving yesterday’s skyscrapers a thing of the past. The typical height to base ratio of a slender building is 10:1, although an 18:1 ratio is more common today. Tall buildings must flex and bend to absorb wind loads. As the ratio of height is increased, the impact caused by the wind on the slabs of each floor is also increased. This impact causes added movement of the walls, floors and ceilings which generate audible sounds of snap, creak, and pop. Regular exposure to this phenomenon may negatively impact the health and quality of life for the occupants. These disturbances can cause someone of normal hearing to wake from sleep or have their concentration disrupted, which is a growing concern for those individuals working from home. Medical experts have stated that exposure to this type of noise at home may cause stress, depression, high blood pressure, tension, tiredness, fatigue, or sleeplessness.
The presentation by SoundSense’s Founder and CEO, Dr. Bonnie Schnitta, at the upcoming Acoustic Society of America conference will show how to measure the sound and vibration in slender buildings during high wind conditions and what solutions exist for the findings. Case studies will be used to show how novel techniques have been used by SoundSense successfully in various projects.

In addition to showing how to engineer rooms that will acoustically withstand high wind conditions without excessive building sounds, interior architecture will be discussed to highlight how some designs may actually contribute to secondary noises. The presentation will cover the following:
• Use of insulation, density and resiliency to upgrade the acoustic properties of walls, preventing room to room noise transmission;
• Attachment of pipes and ductwork to walls or slabs using flexible connections, springs or rubber pads;
• How to appropriately use resilient seals in windows.

A device recently patented will be introduced to show how to assess acoustic leakage points, as even the smallest gap in the construction of a wall may compromise the efficacy of an acoustic treatment.

The importance of including materials that function as acoustic absorbers in any project’s design will also be discussed. Slender buildings typically utilize hard, reflective materials in large rooms, such as glass or drywall. When sound waves bounce off such surfaces it will create an echoey space that often amplifies noise.
The solutions developed by SoundSense to be presented at the upcoming ASA conference, will inform the attendees on the benefits of thoughtful, acoustic design to ensure the reduction or elimination of interior noise in Slender Buildings.

 

Bonnie Schnitta of Soundsense

4pNS2 – Sound of the City: Creating a Balanced Sound Composition in Urban Green Spaces

Lauren Gray – lreedgray@gmail.com
Jack Sullivan – jack@umd.edu
Christopher Ellis – cdellis@umd.edu
Ian Hoffman – ihoffman@jhu.edu

University of Maryland
4291 Fieldhouse Dr
College Park, MD 20742-5235

Popular version of paper ‘4pNS2 – Sound of the city: Creating a balanced sound composition in urban green spaces’
Presented Thursday afternoon, December 2nd, 2021
181st ASA Meeting, Seattle Washington

Sound in the landscape is an important and often-ignored aspect of the human experience. In different landscapes seemingly cacophonous sounds can create a symphony, combining the beloved sounds of nature and humans with the often less desirable, but no less important, sounds of traffic and sirens. This symphony of sounds forms a soundscape, a “sonic environment” (Schafer, 1977) that humans experience. Much like landscapes, soundscapes can vary greatly depending on the sound sources adding their voices. This thesis puts the urban soundscape, and its relationship to the landscape and design, under a microscope.

The work of this thesis began with an investigation into the theories of composers John Cage and R. Murray Schafer, along with key research of outdoor soundscape design and application. By establishing ways in which sound had previously been explored from a musical perspective and practical application, the creation of a new design theory and methodology for surveying sound was formed. The design theory demands that the existing soundscape of a landscape be documented and analyzed to ensure that it best suits the wants and needs of its users. Once the soundscape has been documented and the needs established, any necessary changes can be made by altering the landscape. The method of sound documentation was formed in using both auditory and visual components. The auditory portion for this sound documentation methodology has the surveyor take auditory recordings using a portable recording device. The visual portion was created in this thesis and inspired by styles of notation in Western Classical Music, John Cage, R. Murray Schafer, and Landscape Architect, Lawrence Halprin. This combined method allows for sounds in the landscape to be recorded for both the eyes and ears, showing the many attributes of a soundscape over the course of 10-minute intervals.

To test the theory and method, they were then applied to the re-making of an urban soundscape and landscape. Located in Washington D.C., the site was chosen based on a variety of factors including but not limited to, sound sources, size of space, and geographic location. To begin the design process, the site was then analyzed both sonically and visually. The resulting soundscape and landscape design created a more varied and engaging sonic experience, further exploring the impacts of sound on the perception of place and a close examination of the conscious, subconscious, beautiful, and necessary in the design of landscape.

Urban Green Spaces

Schafer, R. Murray. (1977). The tuning of the world. Knopf. https://catalog.hathitrust.org/Record/000086818