NEED HELP FOR AIDs Spec

Glen R. Meier gtniowa at netins.net
Mon Mar 3 11:23:36 EST 1997


DonPhan at world838.com wrote:
> 
> I am trying to understand the spec from my 3yrs old daughter's aids,
> 
> manufacture from Phonak ( Super-Front PP-C-4)

PP means push pull. This is a means of amplifiying sound to higher
intensity with less distortion.
C=compression.  This is a limiter for how loud the hearing aid can go. 
The dispenser can adjust the hearing aid's maximum amount of sound that
it can produce.

> SSPL 90:  <140dB SPL
This is the most amount of sound that the hearing aid will make.  It
means that if we put a 90 dB (decibel, or unit of loudness) sound into
the hearing aid, 140 dB will come out of the aid. 90dB is a very loud
sound and will test the limits of the aid.  SPL=Sound Pressure Level. 
SPL is just a unit of reference for the decibel.

> HF Average SSPL 90:  132dB SPL
This is the average level of just the high frequencies (avg of 3) with
the same 90 dB of input.

> HF Average Full-on Gain/Input 50dB SPL:  70 dB
This is the High Frequency average of the amount of gain (increase in
volume) when a 50 dB input sound and the volume control set to maximum. 
In other words, if I set the volume to maximum and put in 50 dB of
sound, then 70 dB of increased sound will be added in the high
frequencies.

> Reference Test Gain:  55dB

This is the average of the amount of gain (increase in volume) when a 50
dB input sound and the volume control set to approximate the users
level.  In other words, if I set the volume to the level that your
daughter will probably wear it and put in 50 dB of sound, then 55 dB of
increased sound will be added (avg).

> Frequency Response Range with setting
> LC-O/HC-O:  300-4900Hz
> LC-8/HC-0:  650-6200Hz
> LC-0/HC-B:  250-4600Hz

These tell you over what pitches the hearing aid will amplify sound.  LC
is low cut and HC is high cut.  The nembers 0 through 8 are different
settings from no reduction of gain to maximum reduction of gain.  The
dispenser will set the LC and HC so that the aid matches the slope or
configuration of your daughters hearing loss.

> THD at 500Hz:  <6.5%
> THD at 800Hz:  <2.5%
> THD at 1600Hz:  <1.5%

These are tests of Total Harmonic Distortion.  It tells you how well the
aid is able to reproduce sound cleary.  The higher the level of THD the
more distorted the sound will be.

> Equivalent input noise level:  <23dB SPL

This is more technical and I would have trouble explaining this in basic
terms, sorry.

> Battery Current Drain:  <3.3 mA

This is telling you how fast the battery will go dead.  We know how much
storage a battery has and so if we find out how fast the hearing aid
will drain that storage, we know how long a battery should last.

> Induction Coil Sensitivity:  126 dB SPL

This tells you how well the induction coil (telephone or t-coil) works.
The induction coil allows a person to use a telephone via
electro-magnetic fields instead of the regular microphone.  This
prevents whisteling (feedback) and stops outside sounds from the room
interfering with the sound from the telephone.  Since your daughter is 3
years old, the telephone is not the only thing that she can use this
coil for however.  Many schools, churches and other places have a
special setup that allows a hearing aid wearer to choose the t-coil
setting and thereby eliminate the room noise and hear a person wearing a
microphone instead.

I am thrilled to see a parent educating themself about the childs
hearing loss.  More power to you!!!

I hope that I was able to provide some help for you.  I tried to talk in
generalities without going into technical specifics.  If you have
anymore questions, I would be happy to offer whatever help I can.

Good Luck to you,
Glen R. Meier, M.S., CCC-A
gtniowa at netins.net



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