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Question of the Week / Re: QotW - 07.11.18 - Hearing Damage - Hammer vs Chainsaw
« on: 15/11/2007 23:20:38 »I've heard that tools like hammers that make short, loud noises are supposed to be more damaging to hearing than something that makes a more continuous noise. I'd just like to get some confirmation on that.Well, it's going to depend also on the relative loudness of the sounds, and I'm not exactly sure how you define the loudness of very short sounds.
Hearing damage is also reckoned to be a function of both sound level and duration of exposure (for the same loud sound, days worse than hours worse than minutes, for example).
However... the ear has an interesting little muscle on one of the little bones (the malleus, I think) connecting to the eardrum which can act to reduce the amount of sound-energy transferred to the cochlea when the sound gets too loud. This muscle operates when the sound gets too loud... but takes a few (tens of?) milliseconds to respond. Consequently short-sharp sounds can do more damage than you might otherwise expect compared to more continuous sounds.
I've no idea how long it takes for the muscle to release and restore the normal sensitivity again after the loud sound has passed.
Take care of your ears folks; in mammals the little hair cells in the ear don't repair themselves when damaged, and living with a hearing problem is a misery. []
When the inner hair cells get damaged you can lose all sensitivity to certain frequencies (cochlea dead regions), and no amount of amplification can bring them back.
I'm 32 and have a Dead Region in my left ear (no idea why, I've evidently had it since I was very young), and I cannot perceive pure tones with frequencies between about 2.8kHz and 5-6kHz with that ear. When a tone of that frequency is really turned up loud enough I perceive an "ethereal" sound which has a vague lower-frequency component and a much higher screechy-squeaky component (presumably detected by the nearest functioning hair-cells which are centred on very different frequencies). It doesn't have a proper pitch, and doesn't sound anything like a "proper" tone of that frequency as heard in my right ear.
Nice animation of the cochlea at http://147.162.36.50/cochlea/cochleapages/overview/history.htm
Various other illustrations and microscope images at http://147.162.36.50/cochlea/ (but the site isn't easy to navigate)
The Anatomy section has some of the clearest drawings of the cochlea I've found yet.
There's a cool video of a dancing hair-cell at http://ccrma.stanford.edu/courses/220a-fall-2001/lectureNov2.html
The ear is fascinating - especially all the signal-processing that happens in the cochlea.