hearing aids

Gary Holland gary at gholland.demon.co.uk
Tue Mar 21 03:25:29 EST 1995

In article: <3kheh4$l0q at news.primenet.com>  eric at Primenet.Com (Eric Smith) writes:
> Xref: demon bionet.audiology:72
> Path: 
> From: eric at Primenet.Com (Eric Smith)
> Newsgroups: bionet.audiology
> Subject: Re: hearing aids
> Date: 19 Mar 1995 14:19:15 GMT
> Organization: Primenet
> Lines: 20
> Message-ID: <3kheh4$l0q at news.primenet.com>
> References: <3kctfp$d17 at necco.harvard.edu>
> NNTP-Posting-Host: usr1.primenet.com
> In article <3kctfp$d17 at necco.harvard.edu>,
> Anthony Hartman <hartman at das.harvard.edu> wrote:
> >I am not sure that this is the proper place to ask, but rec.audio
> >seemed even more unlikely. Is there a source for information regarding
> >the manufacturers and brands of hearing aids? Are there any advantages
> >in getting the larger in-the-ear or the external type. Perhaps they
> >can do some more sophisticated sound processing or filtering. 
> >Finally, are there any devices that deal with the problem of background
> >noise well enough to understand a conversation in a crowded room?
> >--
> >Tony Hartman
> >hartman at harvard.harvard.edu
> I have a more specific request for information.  I want to get
> information about the Danavox DFS 145 hearing aid.  I want to know
> how long it's been available, how good it is or isn't, what features
> it has, how much it costs, etc.  Does anyone reading this know
> anything about it?
>A lot of questions to answer but here is a short summary based on my own experience:

Each hearing instrument manufacturer has mounds of information , both technical and user 
orientated on their own products, I only have UK addresses available, althogh I am sure someone 
would be able to supply US addresses. 

As for advantages for larger ITE or BTE hearing instruments as with most other things the 
electronics have miniaturised to the stage where it is indeed possble to have sophisticated 
processing circuitry in a completely -in - the canal (CIC) instrument. The K amp circuit 
produced by etymotic research in the USA is one such example, this chip uses an advanced form of 
compression which effectively amplifies only quiet sounds whilst allowing louder sounds to pass 
through with little or no amplification. However complex multichannel circuits such as the 
Multifocus from Oticon do need more space and are currently only available in BTE and largish 
ITE models. BTE instruments may also be indicated where very high outputs and gains are required 
to minimise the risks of acoustic feedback - a common problem with high power ITE's. Both of 
these circuits go some way to improving signal to noise ratio in background noise situations and 
can certainly improve a listeners speech discrimination capabilities in difficult circumstances. 
It is also generally accepted that the use of binaural instruments and , where possible, 
directional microphones can also offer improvements.

The Danavox DFS Genius 145 is a very interesting instrument. It was introduced, I think around 
1990- 1991. The DFS stands for Digital Feedback Supression and the instrument was designed to 
help individuals with limited residual hearing who needed very high power and gain but were 
experiencing difficulties with acoustic feedback due, in the main, to earmould leakage.The DFS 
works by introducing a white noise test signal into the amplifier circuit, (this is usually 
inaudible to the user). When feedback occurs the instrument sets up the DFS filter to produce a 
correction signal which has the same amplitude as the returning feedback signal , but with exact 
opposite phase. When the two signals are mixed together phase cancellation occurs and the 
feedback signal is eliminated. The DFS allows approximately 10dB greater real ear gain without 
feedback - this can have real significance to someone with severe/ profound loss.

I have a number of customers using the instruments, all previous high power users, and each one 
is delighted with the diffrence. Danavox supply a range of Audiological and Technical manuals on 
the DFS 145 and I am sure they would be happy to supply anyone interested.

By the way anyone going to AAA in Dallas next week who would like to have a chat about Hearing 
Aid fitting in the UK versus USA please mail.


Gary Holland 

| Gary Holland    Holland Audiological Services UK                                            |

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