🚀 go-pugleaf

In article <595@mercury.iotek.UUCP>, garyb@iotek.UUCP (Gary Burrell) writes:
> 
> Apparently Lotus (Sportscars not Speadsheets :)) was working on a noise
> cancillation system for a car, it was something like based on the data
> from a whole bunch of sensors out put a waveform which cancels all the
regular
> (repeating) noise ie regular engine noise, road noise etc.
> 
> Does any one have any information on this.  I could see all sorts of

I believe Bose makes such a system, and it was used by Dick Rutan
and the woman co-pilot who flew around the world on a single tank
of gas.  I don't have any further information on this, I just
remember it being discussed in this newsgroup about 2 years ago.

Greg Sandell

****************************************************************
* Greg Sandell (sandell@ils.nwu.edu)              Evanston, IL *
* Institute for the Learning Sciences, Northwestern University *
****************************************************************

> Does any one have any information on this.

Sounds like you'd be interested in the following article:

  "Adaptive Noise Control"

The title page description is:

  'Malcom MacDonald and David Quinn from Lotus Engineering
  describe a new development in "anti-noise."'

This article appears in the Feb '90 issue of "Noise & Vibration
Worldwide."  This magazine is published in the U.K. so it may be
a little difficult to find a copy...

James Vasil

In article <595@mercury.iotek.UUCP> garyb@iotek.UUCP (Gary Burrell) writes:
>I was just reminded by a previous article which mentioned to sine waves
>cancelling each other out of an item I heard of a few months ago.  
>
>Apparently Lotus (Sportscars not Speadsheets :)) was working on a noise
>cancillation system for a car, it was something like based on the data
>from a whole bunch of sensors out put a waveform which cancels all the regular
>(repeating) noise ie regular engine noise, road noise etc.
>
>Does any one have any information on this.  I could see all sorts of
>places were a system like this could be used, factories, aircraft etc. 

I remember hearing something about active noise suppression being used at
some power plants in Britain, but this was about 4-5 years ago and
my brain is old and tired now.

Brad Garton
Columbia University Music Department
brad@woof.columbia.edu

I suppose this question belongs in sci.energy, but since "noise
cancellation" started here:

In an audio noise canceller (sp?), one injects energy into the air.
Like a truly soundless room, no sound is heard, but now there is
energy.  What does this energy get converted into, heating the
air maybe?  In a soundful room, would the energy heat other objects
(walls)? 
-- 
Ralph Finch			916-445-0088
rfinch@water.ca.gov		...ucbvax!ucdavis!caldwr!rfinch
Any opinions expressed are my own; they do not represent the DWR

A pilot friend of mine tells me that active noise-suppressing headsets are
quite common in small-plane cockpits now.  As you can imagine, this is a
*much* easier device to build, since there aren't any position or phasing
problems to cope with.  They are just a set of headphones, with microphones
just outside.  This way, cockpit noise can be actively cancelled, while
pilot radio audio is fed in with wires.  Note that the active cancellation
in this case doesn't depend on complicated analysis -- the inverted
microphone input at each ear is just added directly back into the headphone
speaker.

My apologies if any of the above is incorrect, as it's all 2nd or 3rd hand...

					Bart Massey
					..tektronix!videovax.tv.tek.com!bart
					..tektronix!reed.bitnet!bart

Most of the work I've seen on noise cancellation stems from the work of
Widrow and Hoff - the most widely quoted reference being

Widrow, B. et al. 1975 Adaptive noise cancelling: Principles and
Applications: Proc IEEE v63 1692-1716.

Widrow's method employs an adaptive filter within a control loop, such that
the filter parameters are modified to maximise the correlation between
the error signal 'removed' from noisy signal and some approximation to
the interfering noise (e.g. a microphone in the cockpit near the
driver's or pilot's head).  There have been some very neat variants on
this technique; some of them in areas far removed from this application,
and no doubt some of them the subject of patents or commercial secrecy. 
Is anyone out there aware of alternative approaches to the problem?

Russ

In article <5845@videovax.tv.tek.com>, bart@videovax.tv.tek.com (Bart Massey) writes:
> A pilot friend of mine tells me that active noise-suppressing headsets are
> quite common in small-plane cockpits now.  As you can imagine, this is a

    I had the privilege of listening to a demonstration of an active noise
cancellation system at Wright-Patterson AFB a couple of years ago.  You 
could select helicopter, transport, or fighter jet noise.  The cancelling
could be activated independently so that you could hear the underlying
intended message.  It was fairly impressive.

    Cancellation of low frequencies is pretty straightforward where the
wavelengths are long.  It's when wavelengths get under two feet or so that
stability problems crop up.  At that lambda 180 degree phase shift is only
one foot.  The corresponding frequency is 1100 fps divided by 2 feet or
about 550 Hz.  Most cancellers will be effective only below 500 Hz or 
especially below 1 kHz.

C. David Covington (WA5TGF)  cdc@uafhcx.uark.edu     (501) 575-6583
Asst Prof, Elec Eng          Univ of Arkansas        Fayetteville, AR 72701

In article <170@locke.water.ca.gov> rfinch@caldwr.water.ca.gov (Ralph Finch) writes:
> In an audio noise canceller (sp?), one injects energy into the air.
> Like a truly soundless room, no sound is heard, but now there is
> energy.  What does this energy get converted into, heating the
> air maybe?  In a soundful room, would the energy heat other objects
> (walls)? 

My physics background makes me suspect it works something like this:

In a room where sound is being generated, the generator is an engine which
converts some "higher" form of energy into some "lower" form, while emitting
sound energy.  The sound is eventually absorbed (damped) by the people, walls,
etc., and thus turned into mechanical energy and eventually heat.

Similarly, an active noise canceller is also an engine which converts some
"higher" form of energy into some "lower" form, while emitting sound energy.
Since this sound energy just cancels existing sound energy, there's no net
dissipation of energy into the surroundings.  Effectively, you've set the
two engines working with each other, coupled by the air.  Thus, any heat
emitted comes from the audio source and the noise canceller in this case.

					Bart Massey
					..tektronix!videovax.tv.tek.com!bart
					..tektronix!reed.bitnet!bart

In article <170@locke.water.ca.gov> rfinch@caldwr.water.ca.gov (Ralph Finch) writes:
>What does this energy get converted into, heating the
>air maybe?  In a soundful room, would the energy heat other objects
>(walls)? 

I think you just pay the price that the noise is twice as loud in other
locations. No?

Georg.

--
Georg Feil                                 Internet: ghfeil@white.toronto.edu
                                             -or-  : georg@sgl.ists.ca
..if all else fails, try:
{uunet,pyramid,watmath,utzoo}!utcsri!white!ghfeil      (UUCP)
ghfeil%white.toronto.edu@relay.cs.net                  (ARPA)

In article <170@locke.water.ca.gov> rfinch@caldwr.water.ca.gov (Ralph Finch)
writes:
>In an audio noise canceller (sp?), one injects energy into the air.
>Like a truly soundless room, no sound is heard, but now there is
>energy.  What does this energy get converted into, heating the
>air maybe?  In a soundful room, would the energy heat other objects
>(walls)? 

If the sound is really cancelled, there can be no power transmitted through
the air.  Therefore, if one sound source is putting power in, the other has to
be taking it out.  After you add up various losses, it may or may not be
generating electrical power.  It's really more of a sound sink than a source.

Note that to completely cancel the sound everywhere, the sound sources have to
occupy the same point in space.  The previous comment still applies to partial
cancellation, one is probably taking power out.

In article <2923@demo.COM> jgk@osc.COM (Joe Keane) writes:
>In article <170@locke.water.ca.gov> rfinch@caldwr.water.ca.gov (Ralph Finch)
>writes:
>>In an audio noise canceller (sp?), one injects energy into the air.
>>Like a truly soundless room, no sound is heard, but now there is
>>energy.  What does this energy get converted into, heating the
>>air maybe?  In a soundful room, would the energy heat other objects
>>(walls)? 
>
>If the sound is really cancelled, there can be no power transmitted through
>the air.  Therefore, if one sound source is putting power in, the other has to
>be taking it out.  After you add up various losses, it may or may not be
>generating electrical power.  It's really more of a sound sink than a source.
>
>Note that to completely cancel the sound everywhere, the sound sources have to
>occupy the same point in space.  The previous comment still applies to partial
>cancellation, one is probably taking power out.

I beg to differ, but just because the sound is 'cancelled' doesn't mean that
there is no power being transmitted.  A sound wave in a gas has accociated 
with it an excess pressure, an excess density, a particle displacement, and
a particle velocity.  It is the oscillation of these that produce the effect
we know as sound.  If you provide an opposite phase oscillator (typically
by simply inverting the signal close to the ear of the listener), you will
make these items constant instead of oscillating.  In effect, you will
create a constant increase in pressure, density, displacement, and velocity.
You still have the energy deposited by both transmitters, but without the
oscillations a human won't hear it.  An atmospheric pressure gauge might
(if it could detect the one-millionth atmospheric pressure change).  
You could also take this to the extreme and eventually cause quite a bit
of pain to someone (probably from heat before pressure) and they'd never
hear a thing.

--
-------------------------------------------------------------------------------
: usenet: black@beno.CSS.GOV   :  land line: 407-494-5853  : I want a computer:
: real home: Melbourne, FL     :  home line: 407-242-8619  : that does it all!:
-------------------------------------------------------------------------------