Hearing Protectors

[Jory A. Olson]

Arguing with basic physics hasn't proved to be very successful in my experience.  In-other-words you can insist all you want, but that doesn't change the facts.  When I asked you to explain your thinking, I thought you were going to go into a detailed description of the limitations of noise canceling headphones (there are several).  Yes, they do, in fact, keep soundwaves from reaching your eardrum.  They will not stop conduction of the sound through the bones in your head, nor will they stop the incredible damage that can occur when very high amplitude (greater than 120 dBA) low frequency (2-5 Hz) sets up a resonance inside your chest, ripping the organs from your chest wall.  This is a real concern when doing vibration testing on spacecraft (I've done it), but not when listening to acoustic instruments with no mechanical connection to your head.

One must realize that wearing noise cancellation headphones doesn't give you "super powers", but it does stop (cancel out, negate, eliminate) the majority of sound from getting to your ears.  It can even cancel out some of the bone conduction originating in the region of your ear.

Think of a simple problem:  a hockey puck is sitting on the ice.  One player is pushing the puck with a force of 10 lbs to the left.  Another player is pushing with exactly the same force in exactly the opposite direction.  The puck doesn't move.  Now, if your eardrum is the puck and one soundwave from a jet engine is pushing it one direction and the soundwave from the headphone is pushing it the other; it doesn't move.  This is highly simplified, but the principle is the same.

BTW, there is a mass market for these headphones.  Consumer's Report rated them in the past two or three years.  There were a dozen companies in the listing.  In my industry, we use them all the time because they're more effective than passive (non-electronic) means.  What's the hitch?  They require a battery and they cost more than passive hearing protectors.

There's no magic here.  What you hear is what you hear.  Noise cancellation headphones do not change your perception of reality.

Jory




Date:	Fri, 16 Oct 1998 22:27:12 EDT
From:	JIMRPT@AOL.COM
Subject:	Re:  Re: Hearing Protectors

In a message dated 10/16/98 6:16:07 PM, nhunt@jagat.com wrote:
<<". . A harmful noise level without use of a noise canceling device is just as harmful with the use of one."
Jim, this is not true.">>
Newton;
As calmly as I can I must insist that it is.  The devices we are speaking of are noise 'canceling' devices and not a form of hearing 'protection'. What these jewels do is remove a perceptible noise and  keep the noise, i.e. sound waves, from 'perceptibly' reaching the eardrum. They work by creating a reverse, or mirror image, of the sound frequency (ies) you want to attenuate as perceived or audible sound. They do nothing about keeping these sound waves, both of them, from reaching your eardrum.  If these dillys worked for 'protection' as well as they work for 'cancellation' they would be mass marketed with a zeal and perspicacity the likes of which have yet to be seen.
Jim Bryant (FL)