Resonance of the Human Ear Canal Hz). The exact amount of amplification, the acoustic resonance, is particular to the individual and depends on the length, volume and curvature of the canal.
H
ave you ever wondered why the sound of nails against a chalkboard is so irritating? It has to do with the acoustic resonance of the human ear canal. The auricle (the outer part of your ear) and the ear canal (the passage down to the eardrum) serve not only to collect and funnel sounds, they also serve to amplify sounds. The ear canal, specifically, amplifies sound in the high frequencies (for an adult, typically in the region between 2000-4000
Ear canal resonance plays an important role when it comes to protecting our ears from loud sound. Anything placed inside the canal (a foam earplug for example) interferes with ear canal resonance. A foam ear plug does an adequate job of protecting our hearing; however, if one wishes to protect the ear and preserve the quality of the sound, ear canal resonance must be maintained.
There are a couple types of earplugs which can help maintain ear canal resonance: an off-the-shelf version (ETY plugs) and a custom version (e.g., ER 15s). The ETY plugs make sounds quieter while replicating the frequency response of the average ear canal. The custom ER 15 earplugs require ear impressions and use a specialized filter to maintain the exact resonance of an individual’s ear canal. The acoustic buttons are available in different levels of attenuation (e.g. ER 9s, 15s or 25s). The custom plugs have the additional advantages of retention, comfort and reusability. I use my pair of ER15s during long road trips as the road noise requires me to turn my music up to levels
that would otherwise damage my hearing. I also wear them while mowing the lawn, on an airplane and anytime I listen to music and do not have control over the volume. Back to the chalkboard‌..it turns out that the frequency of the sound of nails against the chalkboard is very similar to average ear canal resonance. So, a loud annoying high frequency sound is made even louder and more annoying by our own ears!
Terence Miranda is a Doctor of Audiology and the owner of Resonance Hearing Clinic
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