Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 18 Mar 2003 00:59:16 -0500
Message-ID: <redirect-2070798@logan.com>
From: Newlan2dl@aol.com
Subject: Re: [LML] Re: Decibels
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Hi Wendell

You bring up a valid point. Active noise reduction might be a good way to go 
but it would cost a lot.  And you also bring up another good point.  Air 
coming in will be an acoustic leak.  The probelm with active noise 
cancallation is that it is very expensive to set up in your plane and it 
doesn't deaden all frequencies.  If it did, you wouldn't hear anything from 
them except those frerquencies which were not matched by the amplitude of the 
ANR or conversely, by being of a higher amplitude.  They also need to be 
tuned for each installation.

The problem with trying to eliminate the noise only from around the head 
level is that the noise comes from all over.  And it is also often coming 
from the skins of the fuselage acting like a drum head. So vibration from the 
engine or boundary layer can excite the skin and act like a speaker, turning 
vibration into noise and transmitting it elsewhere.

Hopefully, the acoustic tests I'm hoping to start on soon can give some real 
numbers to it and also help us make informed decisions as to weight 
/noise/dollar trade-offs.

Dan Newland