hearing aids

Jochen Wolters jochenw at tschil.informatik.rwth-aachen.de
Wed Mar 29 06:42:35 EST 1995

sirianni at uts.cc.utexas.edu (Jeffrey Sirianni) writes:

>>>The MultiFocus has two microphones that

Sorry, I made a mistake here: the device in question is _not_ the MultiFocus
(built by Danavox), but rather Phonak's Audiozoom. Sorry for that...

>I'm not sure what the Multifocus does with the 2 microphone signals, but
>I wonder if they are using the info to cross-correlate and remove redundant
>info (i.e. noise).

It is possible to remove noise that way, but the mics in the Audiozoom are
much to close for that. The idea is rather to be able to switch between
directional and not-so-directional :-) operation of the hearing aid. This
is most likely achieved by using the two microphones as an array, which --
depending on the relative position of the two mics -- has a considerable
influence on the direcational sensitivity of the device as a whole. The
same can be used, BTW, to build directional loudspeakers. The directional
characteristics depend on the phase of each loudspeakers signal and the
arrangement of the speakers. 

Just recently, I read about another approach with a differential microphone.
This mic's membrane is build into a housing with openings on both sides of
that membrane so that by using a small tube on one end to induce a certain
run time delay of the signal, this device can be fine tuned. According to
the article, with this approach, some kind of automatic directional function
of a heaering aid using this microphone can be achieved. I just hope I can
still find that mag so I can give you more info on this project.


Jochen Wolters - jochenw at POOL.informatik.rwth-aachen.de - cand.ing. EE 
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