Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
References: <firstname.lastname@example.org> <3E0B018F.F2FB4CC3@t-online.de>
Subject: Re: Sound cancellation technology?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Thu, 26 Dec 2002 22:10:17 -0000
NNTP-Posting-Date: Thu, 26 Dec 2002 22:10:21 GMT
Reinhard Zwirner wrote:
> Kevin Aylward schrieb:
> [Noise cancelling system for a bedroom]
>> Sure, in practice this is a very difficult thing to do, but in
>> principle or theoretically, it is possible. Its called feedback.
>> Sound measurements are continually made, and if any signal is non
>> zero, the loop forces a correcting sound to cancel the disturbance.
>> In effect, the room impedance is made to approach zero so that it
>> S/C any sound coming into the room. It does not matter what the the
>> input source spectrum is, as long as it is within the correction BW
>> of the loop.
> Today's (active) noise cancellation is done by acoustical addition of
> the 180 degrees phase shifted noise signal to the original noise.
> Therefore, you need to know the noise signal for every place where you
> want to cancel it.
Yes, in such a method as you describe here, you would "need" to know the
signal. However the principle I described doesn't, although I have not
examined the details to see how practical such a system could be. There
are some obvious technical issues.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.