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From: "Phil Allison"
Subject: Re: Sound cancellation technology?
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Thu, 26 Dec 2002 16:09:58 +1100
NNTP-Posting-Date: Thu, 26 Dec 2002 16:00:23 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Bill Shymanski" wrote in message
> OK, maybe I've got a bug in my bonnet this month. Anyway, while waiting
> for an impulse test to be set up on a large power transformer, I was
reading a draft IEEE guide covering noise suppression techniques to be used
with large power transformers. One of the methods proposed is active noise
cancellation, which apparently gives 10 to 15 dB of suppression of the
"tonal" hum associated with power transformers. The draft guide seems to
indicate that this technique is commercially available today.
** This is a case where the noise source is known, constant, low level
and *can* be dealt with - you are dealing with the sound at source not a
bedroom affected by god knows how many unrelated noises.
> Other places I've read of sound cancellation being used is aboard
> aircraft; some of the commuter jets
> has speakers throgh the cabin to hold down the noise.
** Can you give details ?
Mr. Rutan used a
> noise-cancelling headset during
> his round-the-world flight a few years ago.
** Again a steady and known noise source was involved.
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