Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!ames!ptsfa!ihnp4!mhuxu!davec
From: davec@mhuxu.UUCP (Dave Caswell)
Newsgroups: rec.aviation,sci.electronics,rec.audio
Subject: Re: Noise-cancelling microphone
Message-ID: <6506@mhuxu.UUCP>
Date: Fri, 22-May-87 09:11:21 EDT
Article-I.D.: mhuxu.6506
Posted: Fri May 22 09:11:21 1987
Date-Received: Sat, 23-May-87 18:23:39 EDT
References: <1027@mips.UUCP>
Organization: Bell Laboratories, Reading, PA
Lines: 41
Xref: mnetor rec.aviation:1659 sci.electronics:729 rec.audio:1705

In article <1027@mips.UUCP>, mark@mips.UUCP writes:
> I recently read (in Aviation Week & Space Technology) an article about
> a noise-cancellation system for military pilots' helmets.  Seems that
> military cockpits are _very_ noisy, with helicopter blades whooshing,
> fighter engines roaring, etc, so the pilot can barely hear his/her radio.
> 
> The new system puts a microphone in each earcup, and uses the resulting
> signal to measure the "error" at the pilot's ear [error == signal at ear
> minus signal from radio] and thus cancel much of the ambient noise
> (about 30 dB as I recall).  So the pilot hears the radio but not the
> loud powerplant.  Pretty cool.
>
> Now, a few questions:
>  1.  Has anybody out there experimented with this sort of thing?  How
>      well did it work?

	I got a demonstration of these things in an early prototype
version a couple of years ago.  The difference between ordinary tight
fitting headphones and these things was really dramatic.  Apparantly
sounds below a certian frequency  just aren't stopped by the passive
systems.  Turning on the active electronics eliminated the rumble noises
as well as the hisses and pop's.

	Bose donated a set of these things to the Voyager flight.  Rutan
was really skeptical until he tried them out once.

	If anyone is interested e-mail me and I'll try and get the
current spec's for them.  

    --->Dave Caswell
	{allegra|ihnp4|...}!mhuxu!davec
		-or-
  	davec@borax.lcs.mit.edu



-- 
    --->Dave Caswell
	{allegra|ihnp4|...}!mhuxu!davec
		-or-
  	davec@borax.lcs.mit.edu