Hearing Aid Theory

Mary S. Grandin occam at nrv.net
Sun Jun 16 20:28:37 EST 1996


I
>>2. Very loud sound is usually accompanied by some sort of a physical 
sense of
>>the sound pressure wave - think about loud bass at a concert; you can 
feel
>>the bass energy.  If a person was wearing headphones and listening to 
music
>>at the same level as the live sound, he (or she) would not be fooled 
into
>>thinking it was a recreation of the event, because the physical air
>pressure >cues are missing.  No smack in the chest thump from the sound
>pressure waves. >The same would hold true for a recording of wind - 
you'll
>always know it is a >recording because the physical cues are missing.
>
>The sounds that a hearing aid picks up originate externally, unlike under
>headphones... right ??
>
>>3. SO:  My question:  Is it possible that the brain is not fooled by a
>>hearing aid in the same way that the headphone listener is not fooled 
into
>>thinking he is at a live show?  The ear canal walls are experiencing SPL
>>levels in the 60's, the pinna and face are registering SPL levels in the
>30s, >and the brain still can't decipher what the sound really is. To the 
HA
>>wearer, the sound is fake, or at least not quite right, because the air
>>pressure sensations don't fit the sound he is perceiving.  Has anyone 
ever
>>done research into the tactile effects of sound?  Do the air pressure
>levels >on the face and external ear play a part in the location of a 
sound
>source?  >I kknow that the air presure changes due to normal sound would 
be
>minute, but >would they still be important?
>
>
Interestingly enough, I have done some research on these phenomena 
reported in the August 1988 issue of Hearing Instruments. 
In order to explain to physicians how a person can feel "dizzy" from a 
sudden onset HL w/o a true vertiginous or "inner ear" condition, I ask the 
physician to stand with his ear very close to the wall of the soundbooth 
door, but not touching. The reduced reverberant sound gives one a feeling 
of falling or of "dizziness". One expects to hear the energy of the sound 
pressure and to feel it. We are supported by the sound pressure in a way 
described by the writer. While it is seldom a conscious sensation, it is 
demonstrable. The analogy to hearing aids, however, is where the 
similarity breaks down. A hearing aid does not reduce in any way the 
physical effects of hearing, and in fact can produce such a maelstrom of 
sound that it is distracting and annoying. In the industry we call this 
the occlusion effect. Too much of the man's own voice is amplified. This 
throws off the normal balance and is irritating. Also, the sounds the 
writer describes are not "felt" anyway, that is, the frequencies above 
about 1.5kHz are too small to induce a reaction from the pascinian 
corpuscles in the skin which cause the feeling of sound to be interpreted 
as pressure.
I love it when engineers confront audiologists. I had a man tell me he 
could build a hearing aid for his profoundly deaf son that was 10X better 
than the commercially available ones, and it would cost him less than 
$100. I told him I would buy all he could produce and would even pay 
double.
Needless to say, he declined.




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