Hearing Aid Theory

Jeffrey G. Sirianni sirianni at UTS.CC.UTEXAS.EDU
Sat Jun 15 14:10:29 EST 1996

>X-POP3-Rcpt: sirianni at curly.cc.utexas.edu
>Date: 11 Apr 96 22:52:35 EDT
>From: "Richard D. Ciervo" <76202.1213 at CompuServe.COM>
>To: "Jeffrey G. Sirianni" <sirianni at uts.cc.utexas.edu>
>Subject: Hearing Aid Theory

B.A. Participants...

A friend of mine recently wrote to me with an interesting question.  I am
opening it up for general discussion.  He is an electrical engineer in
amplifier design (too bad, huh?) and doesn't know about dB HL, and so he
uses dB SPL instead.  Comments would be appreciated.

>I have a theory pertaining to the inabilities of hearing aids to really TREAT
>HOH patients.
>1. Picture a hearing aid (HA) inserted in a persons ear.  If the unit is on
>and functioning, a sound that generates a 30 dB SPL signal outside the ear
>(or at the pinna) is amplified and results in a 60 dB SPL signal inside the
>auditory canal.  Not knowing much about HA I assume that this is a pretty
>fair picture of what happens.

{Send verses on canal resonance theory, recruitment, and half-gain theory}

>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?

Oh, I see, if one "expects" the feel of a sound based on loudness, doesn't
this fool the listener?  Well my feeling is that sound is the primary aspect
in audition, while tactile sensations are secondary.  If you are "expecting"
the tactile "thump" and it doesn't happen, then you are fooled.  Isn't this
like the sensation one gets from listening to electrostat speakers (no "cone")?

* Jeff Sirianni, M.A., CCC-A           *
* Sound Advice / R.G. Delaney, M.D.    *
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* sirianni at uts.cc.utexas.edu           *
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