garyb@iotek.UUCP (Gary Burrell) (06/08/90)
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 know noise cancelation is theoretically possible but how does one
deal with it in reality. ie ensuring the output signals are in the opposit
phase from the input, delay due to distance traveled (does this make it
feasable only for very small areas.)
Inquiring minds want to know
Gary R. Burrell
<<<<<<******>>>>>>
Gary R. Burrell, Iotek Inc, |*| E-Mail: garyb@iotek.uucp |*|
1127 Barrington St., Suite 100, |*| Fax: (902)420-0674 |*|
Halifax, N.S., B3H 2P8, Canada |*| Phone: (902)420-1890 |*|
Damm it Jim
I'm a Doctor not a Computer Scientist!
*************************************sandell@ils.nwu.edu (Greg Sandell) (06/09/90)
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 * ****************************************************************
jamesv@hplsla.HP.COM (James Vasil) (06/09/90)
> 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 Vasilgarton@cunixa.cc.columbia.edu (Bradford Garton) (06/09/90)
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
rfinch@caldwr.water.ca.gov (Ralph Finch) (06/10/90)
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
bart@videovax.tv.tek.com (Bart Massey) (06/10/90)
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
ngse18@castle.ed.ac.uk (J R Evans) (06/11/90)
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
cdc@uafhcx.uucp (C. D. Covington) (06/11/90)
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
bart@videovax.tv.tek.com (Bart Massey) (06/12/90)
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
ghfeil@white.toronto.edu (Georg Feil) (06/12/90)
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)
jgk@demo.COM (Joe Keane) (06/12/90)
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.
black@beno.CSS.GOV (Mike Black) (06/13/90)
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!: -------------------------------------------------------------------------------