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Hearing aids

Todd Schneider todd.schneider at sympatico.ca
Thu Aug 29 08:42:42 EST 1996

mikey wrote:
> Gary Holland <gary at gholland.demon.co.uk> wrote in article
> <+g9mHHAALrIyEwkp at gholland.demon.co.uk>...
> > In article <4vnag5$qq4 at sjx-ixn5.ix.netcom.com>, "David G. Delage"
> > <dgdelge at ix.netcom.com> writes
> > >
> > >While we're posing questions <grin>, why would you NOT want to use
> > >real ear measurement to fit hearing aids?
> > >
> > >It seems to me that not using REM is like measuring the length of a
> > >building by saying the average human foot is 12 inches long and
> > >walking along the edge of the building.  -You'll be close, but not
> > >exact.
> > >
> > >-Dave
> > Interestingly both Widex with the senso and Oticon with the Digifocus
> > are advising that REM  is not used when fitting the instruments due to
> > the 'complexity of the algorithms operating the DSP chips. Both these
> > instruments have a 'test mode' which is used for QC checking.  It does
> > seem a little unfortunate that we spend such a lot of time and money
> > investing in state of the art measurement equipment to the benefit of
> > both ourselves and our clients only to find that using the latest high
> > technology hearing instruments makes it obsolete.

I think this is partially true ... and partially marketing. Some algorithms 
(eg., noise reduction) will give unusable results when standard test methods 
are applied. Test equipment will need to change and incorporate new tests 
that can measure the effectiveness of new processing strategies. However, 
I don't think that this makes the current test equipment useless. All new DSP 
aids do frequency shaping and compression. It is still a good idea to have some 
independent verification of how an aid is performing. Hearing aids have been
known to malfunction (and I'm sure their algorithms are not bullet-proof).

Also, from what I have heard (somewhat limited because I work for a competitor), 
the Widex aid measures the audiogram at three frequencies (the center frequencies 
of each of three channels). Many audiologists I have spoke with feel that this 
is too coarse a sampling of the audiogram. If you buy into their fitting strategy 
... great! If you don't, then you may have some problems with this approach.

> > Gary Holland
> > The Hearing Care Centre
> > Ponteland
> > UK
> >
> IMHO, using real ear measures as if they have anything to do with hearing
> aid success is like saying that you have to know the cubic volume of a room
> before you can wallpaper it. Its a nice thing to do and all, and probably
> impresses the patient no end, but there is no real validity to the
> measures, in ensuring a better fit. The hearing aid companies have probably
> just stopped humoring unthinking audiologists brainwashed by ditzy
> professors (who receive free trips and "consultation" cash from RE
> manufacturers).

If all of you patients have ears that have the same acoustic characteristics
as 2cc couplers, then you are correct :-) Granted, REM equipment is expensive 
and the measurements take longer, but it seems obvious that you should measure 
the audio characteristics of a hearing aid at the point where the sound energy 
is transduced in mechanical energy. If you don't do this, you are introducing 
all sorts of systematic measurement errors.

(I'm probably considered a heretic ... but I also think that real-ear audiometry is 
a good idea because you are measuring the SPL at the point where it is transduced.)

> Michael Ridenhour


  Todd Schneider -- todd.schneider at sympatico.ca
  Unitron Industries Ltd.
  Tel  : +1-519-895-0100
  Fax  : +1-519-895-0108
  Email: todd.schneider at sympatico.ca
  Web  : http://www.unitron.com/~unitron/

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