Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Sound cancellation technology?
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Thu, 26 Dec 2002 12:08:42 -0000
NNTP-Posting-Date: Thu, 26 Dec 2002 12:08:45 GMT
Phil Allison wrote:
> "John Woodgate" wrote in message
>> I read in sci.electronics.design that Lady Liberty
>> wrote (in
>> ) about 'Sound
>> cancellation technology?', on Wed, 25 Dec 2002:
>>> Fine but not my question. Could someone please answer the actual
>> OK, it is almost certainly possible, but would be very costly, not
>> necessarily in terms of equipment but in the custom DSP software
> ** Really ?
> How do you cancell by a factor of 60 dB *any* noise that
> intrudes into a bedroom ? This may include barking dogs next to the
> window, road traffic noise of all sorts at close range, aircraft
> noise, neighbours activity impacting the floor/ceiling interface
> with deep, powerfull sub sonics etc, etc.
> These create sudden and disturbing noise in the room at almost
> any frequency 60 dB or more above ambient with attendant internal
> reverberation and varying phase at any point and arriving from any of
> dozens of sources and directions ??
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.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.