How Noise-Induced Hearing Loss Happens


The human sense of hearing is downright amazing. A person with healthy hearing can hear sounds as quiet as 0db and withstand short-term exposure to sound as loud as 85db without sustaining permanent hearing damage. The frequency range at which we can detect sound is also wide, ranging from about 20Hz to 20kHz. Most of us take our hearing for granted, that is until it’s gone or damaged.

Understanding the Risk of Hearing Loss

Most of us know that we risk hearing loss from being exposed to extremely loud noises, but many do not understand how it happens and when they are at risk. Everyone in the performance, stage, sports, music, and A/V industries, from stagehands to sound engineers, are at an extreme risk of noise-induced hearing loss or NIHL.

Of the roughly 40 million Americans suffering from hearing loss, 10 million cases can be attributed to NIHL, according to hearing protection agency Dangerous Decibels (bit.ly/SD_PSA_DangerousDecibels). What many fail to consider is that seemingly comfortable sound levels in the 80-100db range — like heavy city traffic or a sporting event — can cause permanent hearing loss depending on the duration of exposure. Our “pain threshold” for sound is about 140db, but once you feel pain from this level of sound, permanent hearing loss likely already occurred.

Without the immediate pain, there is often little aversion to exposure to noise, and that’s how most of us end up with NIHL. This chart shows the sound levels and durations that will cause hearing damage: 
PSA Hearing Table
One of the most surprising data points is how loud an orchestra can be — the sound of a symphony orchestra playing a big classical piece at treble forte has been measured at 98dB! Music festival staff can be exposed to sound levels exceeding 100db3. It goes to show, that no matter what kind of event you are working, you might be at risk of hearing loss.

How Hearing Loss Happens

Hearing loss can be the result of physical injury, age, genetics, disease, and exposure to loud noises. Here we will focus on the latter, specifically how occupational noise exposure damages the inner workings of the ear. Here’s how the National Institute on Deafness (bit.ly/SD_PSA_NIDCD) explains it:

To understand how loud noises can damage our hearing, we have to understand how we hear. Hearing depends on a series of events that change sound waves in the air into electrical signals. Our auditory nerve then carries these signals to the brain through a complex series of steps.

Sound waves enter the ear canal, which leads to the eardrum. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.

As the hair cells move up and down, microscopic hair-like stereocilia that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cell, creating an electrical signal. The auditory nerve carries this electrical signal to the brain, which translates it into a sound that we recognize and understand.

Most NIHL is caused by the damage and eventual death of these hair cells. Unlike bird and amphibian hair cells, human hair cells don’t grow back. They are gone for good.

Preventing Hearing Loss

The best way to prevent hearing loss is knowing what sounds are damaging and avoiding exposure to them. Of course, those of us in the entertainment and performance business can’t avoid being exposed to damaging sound levels. While you’re working, protecting your hearing can be as easy as using approved earplugs or earmuffs. But it’s often trickier than that—as you may need to use a headset or other comms gear, too.

In that case, you can protect your hearing by using a noise-rejecting in-ear headset (bit.ly/PSA_intercom_headset)). These intercom headsets with in-earphones can protect your hearing and allow you to remove one or both earphones to exit the listening mode or monitor a mix of feed audio and surrounding acoustics. Check out this video to see how the Carolina Panthers’ Panther Vision team is using them.  

Here is a link to a video hearing test: bit.ly/SD_PSA_HearingTest  

Whatever you do, listen to this: protecting your hearing can’t wait. Because once it’s gone, it’s gone forever. 

1 NIOSH, 2013  bit.ly/SD_PSA_MayoClinic

2 OSHA, 2008  bit.ly/SD_PSA_MayoClinic

3 NCBI, Noise Health. 2003  bit.ly/SD_PSA_NCBINoiseHealth

 The Sounding Board monthly column is presented in partnership by Point Source Audio and Stage Directions magazine. To read the PSA Sounding Board Blog, go to www.point-sourceaudio.com/sounding-board