In last month’s Allegro, audiologist Ellen Kelly outlined some of the factors that put music professionals at particular risk of hearing loss. This tutorial provides more specifics about various forms of hearing protection.

How does overexposure to sound affect your hearing?

High levels of sound pressure cause changes in the microscopic fibers called hair cells that are located in your inner ear, or cochlea. Researchers believe that too much sound acts like a stressor to hair cells, causing the blood vessels that supply them to constrict, and creating metabolic changes that lead to their eventual breakdown. Initially, the response of the hair cells to high sound is one of fatigue, characterized by symptoms such as fullness and ringing (tinnitus). With repetitive exposures, however, the hair cells are less able to recover and will start to show permanent changes. Because the changes occur so insidiously, most people may not be aware of a problem until the damage is fairly substantial.

How much sound is too much?

For the most part, noise-induced hearing loss results from high levels of sound over an extended period of time. Occasional episodes of high-level sound are unlikely to cause permanent damage unless you are exposed to an extreme event, such as a blast.

Since World War II researchers have tried to determine what level puts individuals at risk for hearing loss. The question is posed as “what level, over an eight-hour day, will lead to more hearing loss than would have naturally occurred from the aging process?” The answer is complex and depends on many factors, such as the type of noise, measurement techniques, definitions of hearing loss, design of the experiment and population sampled. As a result, not everyone is in full agreement. In the United States, most industries refer to criteria established by the Occupational Safety and Health Administration. OSHA stipulates a maximum level of 90dB each eight-hour day. Other agencies in the U.S. and in other countries use an 85dB maximum exposure level for each eight-hour period.

How does hearing damage affect your perception?

The most obvious change, as measured on an audiogram (hearing test), is a decrease in the ability to hear sounds in the frequency range around 3000-6000 Hz. As the exposure continues over time, other frequencies become affected as well.

Perceptual problems relating to pitch and loudness start to emerge from damage to the cochlea. One such problem is referred to as recruitment – an abnormal perception of loud sound. Individuals with hearing loss accompanied by recruitment have trouble hearing soft sounds (they need it to be louder) but at the same time have difficulty tolerating loud sounds. Thus, their dynamic range is reduced. If you’ve ever noticed someone turning his or her hearing aid volume up and down, it is because this phenomenon is occurring. Fortunately, new hearing aid technologies are now available to regulate this automatically. But who wants a hearing aid? The bottom line is that it can become frustrating to listen to certain music applications when sound levels modulate between soft and loud and you have recruitment.

A second consequence of hearing loss is altered pitch perception. One pitch can begin to sound like another because the acoustic cues necessary to separate them are lost. Your perception of pitch may become distorted. Not only will music be harder to monitor, but speech discrimination is affected.

Some people also suffer from tinnitus (head noises). While this is often temporary, resulting from single exposures to loud sound, it can become permanent and bothersome once hearing loss occurs.

What does hearing protection do?

It lowers the sound pressure delivered to the ear by acting as a barrier.

What do many store-bought plugs make everything sound unnatural?

This is because your open ear canal has a natural resonance around 2700 Hz. When you put a plug into your ear, it changes the naturally occurring resonance properties because the canal length becomes shorter and blocked at both ends. This results in a drop in the high frequencies, making sound more muffled. Also, because the plug does not sit deeply in your ear, when you verbalize it vibrates the cartilage in the outer-most portion of your ear. The additional vibration travels to your ear and changes your perception of how your voice sounds when you are speaking.

What are Musicians Plugsä ?

Musicians Plugsä were designed by Etymotic Research. These are custom-made plugs which use some of the natural acoustic properties of the ear in conjunction with a special filter to offset the loss of high frequencies and provide more balanced isolation responses. If the plugs are made deep enough to extend past the cartilaginous portion of the ear canal, the additional low frequency vocalization component can be reduced as well. The plugs depend on a good fit, a deep impression, and an adequately sized ear canal in order to achieve the desired results. The isolation qualities and frequency response of the plug can be measured objectively, using a special probe microphone to verify a proper response.

What are in-ear monitors?

In-ear monitors are monitor speakers built into an ear piece. They have a number of applications: to improve stage levels, problems associated with competitive monitoring, and feedback. They reduce vocal strain because singers can hear themselves better and are not singing over loud levels. Finally, they have been gaining popularity as a means of lowering exposures. To achieve this requires a custom shell that isolates well enough so that the user can monitor at lower levels. If the user cranks the volume up on the device, however, in-ear monitors can be dangerous to the ear. If you are considering in-ears, you should carefully assess all these issues with an audio professional or audiologist who fits them.

How can you protect your hearing?

Reduce recreational and vocational exposures whenever possible. And even if you cannot tolerate hearing protection all the time, wear it when you can. Have your hearing tested annually in order to monitor for changes. Stay aware of symptoms of overexposure – such as tinnitus and fullness – after performing.

More information about hearing loss is available at www.neatnoise.com . You may also contact Ellen Kelly, M.S. CCC-A at (732) 238-1664 or through the Musicians’ Injury Prevention Program at the Mount Sinai/Irving J. Selikoff Center for Occupational Medicine at (212) 241-4833.