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Noise Induced Hearing Disturbances

Timothy C. Hain, MD Page last modified: October 26, 2016

Noise induced hearing loss (NIHL) defined

Noise is a common cause of hearing loss in the US. Twenty-five percent of the US work force is regularly exposed to potentially damaging noise (Suter and von Gierke, 1987). Because of occupational risk of noise induced hearing loss, there are government standards regulating allowable noise exposure. People working before the mid 1960's may have been exposed to higher levels of noise where there were no laws in the USA mandating use of devices to protect hearing.  An example of an audiogram showing noise induced hearing loss is shown below.  There is a clear "notch" at 3000 hz, with better hearing at both lower and higher frequencies. NIHL is usually slightly worse on the left side, possibly due to less efficient protective reflexes (Nageris et al, 2007).

The situation with noise is that it is clear that noise is bad for hearing, but it is also clear that many people like loud music and also that certain jobs can't get done without loud noise. The current regulatory enviroment seems to be an attempt to balance the good and bad aspects of noise. There are many intrinisically dangerous activities where one has to balance benefit and risk.

wpe1.gif (111838 bytes) Noise notch
Example audiogram showing noise induced notch. Another example of a noise notch (between 2K and 6K).

There are at least 4 different algorithms to detect noise notches (Nondahl et al, 2016). The sensitivity of these algorithms varied remarkably, and at least 11% of patients scored as having noise notches, had no noise exposure at all. They concluded " in light of the degree of discordance in women between noise history and notches by each of these algorithms, researchers should be cautious about classifying noise-induced hearing loss by notched audiograms." McBride and Williams (2001) found that 3 raters (an ENT, audiologist and occupational physician) rating audiograms for noise notches had considerable disagreement, suggesting that opinions of various specialists is not a reliable method for identifying noise notches.

To make matters even worse, a "noise notch" does not necessarily imply exposure noise. Lie et al (2016) reported that "The prevalence of notches in the 3 to 6 kHz range (Wilson, Hoffman, and Coles) ranged from 50% to 60% in subjects without occupational noise exposure, and 60% to 70% in the most occupationally noise-exposed men. The differences were statistically significant only for bilateral notches. For 4 kHz notches, the prevalence varied from 25% in occupationally nonexposed to 35% in the most occupationally exposed men, and the differences were statistically significant for both bilateral and unilateral notches. For women, the prevalence of notches was lower than in men, especially for 4 kHz notches, and the differences between occupationally noise exposed and nonexposed were smaller. Recreational exposure to high music was not associated with notched audiograms."

This very large study "puts the lie" to the general idea that all notches are noise induced.

Algorithms to calculate the effect of noise on hearing:

Three published algorithms available to identify notched audiograms are as follows:

Coles, Lutman & Buffin (2000) defined a high-frequency notch as "the hearing threshold level (HTL) at 3 and/or 4 and/or 6 kHz, after any due correction for earphone type, is at least 10 dB greater than at 1 or 2 kHz and at 6 or 8 kHz." Thus they required 10 dB (which is not much). The Coles algorithm was designed for medicolegal cases.

The McBride and Williams (2001) algorithm was based on narrow notches and wide notches in the audiograms. A narrow or V-shaped notch is one with only one frequency in the depth of the notch and a wide or U-shaped notch has more than one frequency in the depth the notch. They suggested "…the narrow notches should be at least 15 dB in depth and that broad notches should have a depth of 20 dB, with a recovery of at least 10 dB at the high end." Thus they required a 15-20 dB difference from the lower frequency, and 10 from the higher. This is a little more specific than the Coles algorithm.

Dobie and Rabinowitz (2002) defined a Notch Index (NI). This is calculated by deducting the mean of the thresholds of 1 and 8 kHz from the mean of the thresholds at 2, 3 and 4 kHz in the same ear. When there are increased thresholds at 234, compared to 1-8, the NI is positive. 6Khz was not included (unlike the Coles algorithm). Rabinowitz, Dobie and others reported again on this noise metric in 2006, using a NI > 2 as being positive, and suggested that it had "excellent agreement with expert notch consensus". This seems to us to be a reasonable position right now, with the caveat that this algorithm presumes that the subject being tested is cooperative (often not the case in medicolegal situations), and also that the statistical noise -- i.e. test-retest variability intrinsic to measurements made by humans, is low.

Noise index calculator -- positive NI is > 2 (this calculator requires javascript)
1K 2K 3K 4K 8K NI

Noise index

Other tests for noise

Noise notches often have a corresponding notch in the sweep OAE.

OAE noise notch
Notch in OAE corresponding to notch in hearing (on figure above, R). On this figure, the "strength" of the OAE response is proportional to the vertical distance between the red and black lines above. There is no distance at all between about 3000 and 4500 Hz -- the same place as the hearing notch. There is also no OAE at high frequencies. This is a common pattern in persons who have experienced noise induced hearing loss.

Temporary Threshold Shifts

Noise can also cause a reversible hearing loss, called a temporary threshold shift (TTS). This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event (tinnitus). TTS can be caused by listening to ordinary digital music devices at volumes that are not especially high -- e.g. 100 dB (Le Prell et al, 2012). Sound pressure levels can routinely reach levels of 126 db (Breinbauer et al, 2012). Non-occupational noise are also regularly encountered during recreational activities and are a source of premature hearing reduction. Peak noise levels, in dB, are provided in the following table taken from Smith et al, 1999).

Firecracker 180
Gunshot 167
Car Stereo


Children's toys 150
Sporting events 127
Rock Concert 120
Health Club 120
Motorboats 115
Video Arcade 110
Snowmobile 99
Movie 94

A more dramatic illustration of loudness can be found on the AAO site, by clicking here.

Motorcycle riding is an example of an activity that is associated with hearing loss. Temporary threshold shifts occur after a run of 1 hour at 80 mph. The greatest TTS was reported to occur at 1KHz, with a mean loss of 10.3 dB (McCombe et al, 1995). Hearing in motorcyclists has been reported to be worse than age-matched controls, with the most marked changes at 0.5 to 1 Khz (i.e. lower frequencies). One might think that the noise index developed above, might not work as well for this type of hearing loss.

Cycling exercise classes, and presumably other similar health club classes have high noise levels. Sinha et al (2016) found that in cycling classes, "Average noise exposure for one 45-minute class was 8.95 ± 1.2 times the recommended noise exposure dose for an 8-hour workday."

Airbag deployment and blast injury.

Airbag deployment in auto accidents is a potential source for noise induced hearing loss or tinnitus.  (McFeely, Bojrab et al. 1999; Price and Kalb 1999; Yaremchuk and Dobie 2001). This is a type of "impulse noise", similar to a fire-cracker or explosion. The intensity of an airbag noise is high -- about 160-180 dB. There can be a 10dB difference between ears due to the head shadow effect. Presumably there is a bigger difference when the airbag deployment is very close to one ear. We have not yet encountered a patient with a PLF post airbag deployment, but as airbags can cause TM perforations, this seems possible.

There is an obvious similarity between airbag and blast injuries (Shah et al, 2014). The main difference is that the impulse in blast injuries can be louder, and perforations are more common. Damage to the hair cells, and possibly also spiral ganglion neurons is the main source of hearing disturbance in experimental models (Cho et al, 2013).


Noise induced hearing loss from hearing aids:

It has long been realized that hearing aids and hearing assistive devices are potential sources of noise induced hearing injury. At this writing, while the possibility is there, evidence suggests that this is not a significant problem for hearing aids. See the hearing aid page for more on this topic.

That being said, we find the argument that hearing aids do not cause hearing loss extremely dubious, as we do not see why hearing loss should be a consequence of recreational listening (as documented above), but not a consequence of hearing aids which are designed to produce loud sounds. It is our impression that there is a trade-off between hearing deterioration and the utility of communication. This is the reason why we generally do not recommend hearing aids in persons with minimal hearing loss - -they have a lot to lose, but only a little to gain.

We believe that any loud device can cause hearing loss, whether it is sold by an audiologist or bought to use as a musical reproduction device.

We also don't buy the argument that sound up to a certain threshold is safe, and beyond that is unsafe. We think that there is a continuum. Of course, this topic is a "hot button" one for those who sell devices that make loud noises.

Ototoxic drugs and noise

Hearing loss and tinnitus (usually temporary), can also be associated with high doses of aspirin or other ototoxic drugs such as the nonsteroidal anti-inflammatory drugs.

Ear surgery.

Drilling on the bone around the ear, or using instrumentation in the ear canal can generate extremely high sound intensity, in some cases resembling blast injury (i.e. as high as 157 dB). (Wang et al, 2014). Thus individuals who have undergone surgery using high-speed drills on their ears may lose some hearing from the surgery itself.

Surgery that involves drilling on the skull is associated with hearing loss, even on the opposite side (Shenoy et al, 2015)

Groups with high susceptibility to noise.

Race -- according to Jerger et al (1986), who tested 28 firefighters exposed to high levels of ambulance siren noise. They found that whites are more susceptible to noise than blacks.

Axelsson et al (1981) studied the effect of listening to loud music in 538 teenagers at vocational schools. Hearing loss correlated with family history of hearing loss.

Musicians and the prevention of hearing loss:

Musical instruments can generate considerable sound and thus can also cause hearing loss. The most damaging type of sounds is in the high-frequencies. Violins and violas can be sufficiently loud to cause permanent hearing loss. This is typically worse in the left ear which is nearer the instrument. Unlike other instruments, the ability to hear the high-frequency harmonics is crucial to these musicians. Mutes can be used while practicing to reduce long term exposure.

Schmidt et al (2014) tested 182 professional musicians. Most symphony orchestra musicians had better hearing than expected for their age, but they had a work-related risk of noise induced hearing loss. Trumpet players and the left ear of first violinists had significantly worse hearing than other musicians. Of course, symphony orchestras do not have the same volumes as do rock musicians.

There are a number of strategies that can be used to reduce the change of noise injury from other instrumentalists. Musicians ear plugs are generally "flat" so that bass and treble notes are not relatively favored, thus distorting perception. Nevertheless, a"vented" ear plug can be used to tune the ear cavity to low frequencies, which are less damaging. Drummers should use musicians ear plugs, such as the ER-25. Guitarists and vocalists can use the less attenuating ER-15. Too much ear protection can result in overplaying and not enough protection can result in hearing loss.

Plexiglass baffles can be used to reduce the noise from other instruments.These are particularly relevent for drummer's high-hat cymbals. Drums and brass can be particularly a problem. Ear monitors are small in-the-ear devices that look like hearing aids, that can be used to electronically protect hearing, while allowing the musicians to hear themselves. Acoustic monitors are stethescope like devices that block sound from other in the group, but allow the instrumentalist to hear their own instrument.

Loudspeakers produce both high and low frequency sounds. High frequencies tend to emanate in almost a straight line, while low frequencies are present in nearly all directions. Thus, standing besides a high-frequency source may provide some protection. Humming just prior to, and through a loud noise such as a cymbal crash or rim shot may provide some protection. Small protective muscles in the ear contract naturally when we sing or hum, and thus humming may protect from other noises.

Strategies that reduce the loudness of sound to the ear reduce the chance of damage. As people routinely increase the volume of what they are hearing when there is outside noise, one strategy that can help is simply to use devices that reduce outside noise such as "ear bud" earphones or supra-aural earphones (Breinbauer et al, 2012).

(Most of this material comes from two articles by Chasin M, 2000. According to his articles, Mr. Chasin has published a book entitled "musicians and the prevention of hearing loss", which is available from Singular Publishing group, San Diego).


Excessively loud noise can also induce perilymph fistulae and cause Meniere's disease to worsen.


Musicians and hearing loss

Airbag, surgery, and blast references:

Copyright October 26, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on October 26, 2016