From: Fredmoreno@aol.com
Message-ID: <ad66238f.249a8bd1@aol.com>
Date: Thu, 17 Jun 1999 13:35:13 EDT
Subject: cockpit ANR
To: lancair.list@olsusa.com
Mime-Version: 1.0

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I have had similar thoughts.  One has been to put speakers facing up on the 
top of the panel, reflecting off the windshield, and canceling the propeller 
beat coming in through the windshield.  I subsequently learned that the most 
successful ANR in a cabin was in a helicopter where the frequencies are low 
and the wavelengths long.  As wavelengths shorten and bounce around, 
cancellation becomes more difficult.  ANR headsets work because they cancel 
right at the ear.  I spoke to a few headset guys at OH, and they said it is 
much more complicated that it first appears.  So I am not hopeful, but would 
like someone smarter than me to fire some neurons at the problem and see if 
there is a way.  At least we should be able to get rid of the low frequency 
stuff in our small cabins.  Would some acousto-techno type care to comment?  

	Related: those little foam ear plugs provide 28 dB of isolation.  For 
years I have used a boom mike clipped to a custom ear piece in one ear, and 
foam in the other when flying in hot weather.  Works fine.  Or for the 
ultimate, put foam plugs in your ears, then don your head set and turn up the 
volume.  It gets nice and quiet inside the cranium.  Except for the low 
frequency stuff which jiggles the bone a bit.

Fred
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