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.

4pNSa4 – Inciting our children to turn their music down: the “Age of Your Ear” concept

Jeremie Voix
Romain Dumoulin
École de technologie supérieure, Université du Québec, Montréal, Quebec, Canada

Popular version of paper 4pNSa4, “Inciting our children to turn their music down: the AYE concept.”
Presented Thu, Nov 08   1:45pm – 2:00pm in SALON C (VCC)
176th Meeting Acoustical Society of America and 2018 Acoustics Week in Canada (Canadian Acoustical Association) at the Victoria Conference Centre, Victoria, BC, Canada

Problem
According to the World Health Organization (WHO), more than 1.1 billion people are currently at risk of losing their hearing due to excessive exposure to noise. Of this, a significant proportion consists of children, youth and young adults who are exposing themselves to excessive levels of sound through various leisure activities (music players, concerts, movies at the theatre, dance clubs, etc.).

Existing solutions
To address this issue, many approaches have been developed, ranging from general awareness messages to volume limiters on personal music players. For instance, the recent “Make listening safe” [1] initiative from WHO aims at gathering all stakeholders, public health authorities, and manufacturers to define and develop a consolidated approach to limit these non-occupational sound exposures, based on dosimetry. Indeed, significant efforts have been put into the idea of assessing directly on a PMP (personal music player) the individual noise dose, i.e. the product of the sound pressure level  and the duration, induced during music listening.

Need to find a better way to sensitize the users
While many technical issues are still actively discussed in some related standards, a major concern arose with regards to the message communicated to the end-users. End-users need to be educated on the risk of noise induced hearing loss (NIHL) and its irreversibility, but at the same time they also need to be made aware that NIHL is 100% preventable pending safe listening practices are followed.

More importantly, end users have to be left with an appealing noise dose measurement. In that regard, expressing equivalent sound pressure level in decibels (dB) or the noise dose in percentage (%) is of little value given the complexity of one and the abstraction of the other. But communicating about the dangers of music playback is definitely something very new for most of the hearing conservation specialists and communicating with this particular group of youth is only adding to the difficulty.

Our approach
In the quest for a meaningful message to pass to these young end users, this article introduces a new metric, the “Age of Your Ears” (AYE), that is an indication of the predicted extra aging caused by the excessive noise dose each user is exposed to. To perform such prediction, a multi-regression statistical model was developed based on normative data found in ISO 1999 [2] standard. This way, an AYE value can be computed for each subject, using only his age, sex and sound exposure, to represent the possible acceleration of aging caused by excessive music listening, as illustrated in Fig. 1.

Age of Your Ear

Fig. 1: While hearing will normally worsen because of the natural aging process (dotted black line), this ageing can be dramatically accelerated because of over-exposure to noise (solid color lines).

Conclusions
In a world where personal musical players are ubiquitous, and have also been putting hearing at risk, it is interesting to see them as potential tool, not only to address the issues they created, but also for raising awareness on the dangers of Noise-Induced Hearing Loss at large.

The proposed AYE metric will be first implemented in a measurement manikin setup that is currently under development at the Centre for Interdisciplinary Research in Music Media and Technology, housed at the Schulich School of Music at McGill University (CIRMMT). This setup, further described in [3], is inspired by the “Jolene” manikin developed though the “Dangerous Decibels” program [4]. The resulting measurement kiosk will be complemented by a smartphone-based measurement app that will enable musicians to assess their entire noise exposure. It is hoped that the proposed AYE metric will be relevant and simple enough to have a beneficial impact on everyone’s safe hearing practices.

[1] WHO – Make Listening Safe- http://www.who.int/deafness/activities/mls/en/.

[2] ISO 1999:2013 – Acoustics – Estimation of noise-induced hearing loss, 2013.

[3] Jérémie Voix, Romain Dumoulin, Julia Levesque, and Guilhem Viallet. Inciting our children to turn their music down : the AYE proposal and implementation. In Proceedings of Meetings on Acoustics , volume Paper 3007868, Victoria, BC, Canada, 2018. Acoustical Society of America.

[4] Dangerous Decibels – JOLENE – http://dangerousdecibels.org/jolene

 

 

 

1aPP44 – What’s That Noise? The Effect of Hearing Loss and Tinnitus on Soldiers Using Military Headsets

Candice Manning, AuD, PhD – Candice.Manning@va.gov
Timothy Mermagen, BS – timothy.j.mermagen.civ@mail.mil
Angelique Scharine, PhD – angelique.s.scharine.civ@mail.mil

Human and Intelligent Agent Integration Branch (HIAI)
Human Research and Engineering Directorate
U.S. Army Research Laboratory
Building 520
Aberdeen Proving Ground, MD

Lay language paper 1aPP44, “Speech recognition performance of listeners with normal hearing, sensorineural hearing loss, and sensorineural hearing loss and bothersome tinnitus when using air and bone conduction communication headsets”
Presented Monday Morning, May 23, 2016, 8:00 – 12:00, Salon E/F
171st ASA Meeting, Salt Lake City

Military personnel are at high risk for noise-induced hearing loss due to the unprecedented proportion of blast-related acoustic trauma experienced during deployment from high-level impulsive and continuous noise (i.e., transportation vehicles, weaponry, blast-exposure).  In fact, noise-induced hearing loss is the primary injury of United States Soldiers returning from Afghanistan and Iraq.  Ear injuries, including tympanic membrane perforation, hearing loss, and tinnitus, greatly affect a Soldier’s hearing acuity and, as a result, reduce situational awareness and readiness.  Hearing protection devices are accessible to military personnel; however, it has been noted that many troops forego the use of protection believing it may decrease circumstantial responsiveness during combat.

Noise-induced hearing loss is highly associated with tinnitus, the experience of perceiving sound that is not produced by a source outside of the body.  Chronic tinnitus causes functional impairment that may result in a tinnitus sufferer to seek help from an audiologist or other healthcare professional.  Intervention and management are the only options for those individuals suffering from chronic tinnitus as there is no cure for this condition.  Tinnitus affects every aspect of an individual’s life including sleep, daily tasks, relaxation, and conversation to name only a few.  In 2011, the United States Government Accountability Office report on noise indicated that tinnitus was the most prevalent service-connected disability.  The combination of noise-induced hearing loss and the perception of tinnitus could greatly impact a Soldier’s ability to rapidly and accurately process speech information under high-stress situations.

The prevalence of hearing loss and tinnitus within the military population suggests that Soldier use of hearing protection is extremely important. The addition of hearing protection into reliable communication devices will increase the probability of use among Soldiers.  Military communication devices using air and bone-conduction provide clear two-way audio communications through a headset and a microphone.

Air conduction headsets offer passive hearing protection from high ambient noise, and talk-through microphones allow the user to engage in face-to-face conversation and hear ambient environmental sounds, preserving situation awareness.  Bone-conduction technology utilizes the bone-conduction pathway and presents auditory information differently than air-conduction devices (see Figure 1).  Because headsets with bone conduction transducers do not cover the ears, they allow the user to hear the surrounding environment and the option to communicate over a radio network.  Worn with or without hearing protection, bone conduction devices are inconspicuous and fit easily under the helmet.   Bone conduction communication devices have been used in the past; however, as newer devices have been designed, they have not been widely adopted for military applications.

Manning1a - headsetsA. Manning1b - headsetsB.

Figure 1. Air and Bone conduction headsets used during study: a) Invisio X5 dual in-ear headset and X50 control unit and b) Aftershockz Sports 2 headset.

Since many military personnel operate in high noise environments and with some degree of noise induced hearing damage and/or tinnitus, it is important to understand how speech recognition performance might be altered as a function of headset use.  This is an important subject to evaluate as there are two auditory pathways (i.e., air-conduction pathway and bone-conduction pathway) that are responsible for hearing perception.  Comparing the differences between the air and bone-conduction devices on different hearing populations will help to describe the overall effects of not only hearing loss, an extremely common disability within the military population, but the effect of tinnitus on situational awareness as well.  Additionally, if there are differences between the two types of headsets, this information will help to guide future communication device selection for each type of population (NH vs. SNHL vs. SNHL/Tinnitus).

Based on findings from speech understanding in noise literature, communication devices do have a negative effect on speech intelligibility within the military population when noise is present.  However, it is uncertain as to how hearing loss and/or tinnitus effects speech intelligibility and situational awareness under high-level noise environments.  This study looked at speech recognition of words presented over AC and BC headsets and measured three groups of listeners: Normal Hearing, sensorineural hearing impaired, and/or tinnitus sufferers. Three levels of speech-to-noise (SNR=0,-6,-12) were created by embedding speech items in pink noise.  Overall, performance was marginally, but significantly better for the Aftershockz bone conduction headset (Figure 2).  As would be expected, performance increases as the speech to noise ratio increases (Figure 3).

Manning2

Figure 2. Mean rationalized arcsine units measured for each of the TCAPS under test.

Manning3

Figure 3. Mean rationalized arcsine units measured as a function of speech to noise ratio.

One of the most fascinating things about the data is that although the effect of hearing profile was significant, it was not practically so, the means for the Normal Hearing, Hearing Loss and Tinnitus groups were 65, 61, and 63, respectively (Figure 4).  Nor was there any interaction with any of the other variables under test.  One might conclude from the data that if the listener can control the level of presentation, the speech to noise ratio has about the same effect, regardless of hearing loss. There was no difference in performance with the TCAPS due to one’s hearing profile; however, the Aftershockz headset provided better speech intelligibility for all listeners.

Manning4

Figure 4. Mean rationalized arcsine units observed as a function of the hearing profile of the listener.