jwm@stdc.jhuapl.edu (Jim Meritt) (03/10/89)
have heard of this, but applied to a pair of earphones for jet pilots. They would receive the external sound, and generate the counter wave for inside the headset. The radio communications would come in the same line, but now could be easily heard. In demo's (public) quite a few db's were effectively cancelled - I understand marketting is also getting them lined up for expensive sterio sets to shut down the background noise so the music would be clearer... The above was test data, and not the responsibility of any organization.
pfarrell@anselm.UUCP (Gladiator) (03/10/89)
In article <4225@watvlsi.waterloo.edu>, kmheal@watvlsi.waterloo.edu (K. Michael Heal) writes: > In article <723@wucs1.wustl.edu> kumar@wucs1.wustl.edu (Arun Kumar) writes: > >For the last few days I have been sharing my room with a very noisy pair > >of machines -- a Pixar and a Sun -- and I have been thinking about > >generating some anti-noise.... > >Arun Kumar (kumar@wucs1.wustl.edu) > > Off hand, I doubt that even a theoretical noise reduction is > possible with your "anti-noise" sources, unless you also fix the > location of your ears. > > Anyway, vast reductions could be achieved practically by surrounding > the machine with surfaces covered with 4 or 6 inch accoustic foam > (with the wedged surface), especially at or above 1000 Hz. > -- > Michael. > ( kmheal@watvlsi.waterloo.edu ) Well if I understand the theory correctly, which I don't. IN order to cancel outa sound. A sound travels in waves. If you have a sound equal in magnitude to equal in magnitude to the one you are trying to supress that hits it's peak, at the same moment that the other hits it's low, the waves will cancel each other out. It is possible in nature, because the waves work like ocean waves. At rock concerts, they have to spend hours to set up speakers, because there are places if set up incorrectly that there will be hardly any sound from the music at all where as in others where the peaks line up, will be considerably louder than normal so it is possible to last a stereo and through creative positioning not hear a thing. Unfortunately, I fail to see how one could plan this without a little super computer help. Something like a raytracing prog perhaps? That is just to line up the speakers transmitting the anti noise. Now problem of keeping them in sync. How are you going to make sure that one is constantly it it's high when the other is at it's low. If you don't do it right, often it will be quieter than normal, but often louder as well. Any thoughts on this? I don't touch this newsgroup for lack of knowledge normaly, but I have a strong notion of theories. If Someone has a better one, or wishes to correct any errors I have made (There might be for all I know) please post em. -- Patrick Farrell @ St. Anselm's college, Goffstown N.H. 1-603-472-2378 dartvax!anselm!pfarrell "Laugh and the world ignores you. Crying doesn't help either."
inc@tc.fluke.COM (Gary Benson) (03/11/89)
The theory says that the *best* you can hope for is total cancellation of the offending noise. The idea behind "anti-noise" as you call it is that you generate an exact replica of the offending noise, except opposite in polarity. It must be the same frequency and the same amplitude, just reversed. As the tops of the wave fronts collide, they dissipate each other's energy, and the same thing happens all down the trough and up the next wave. The dynamic case would monitor the signal and generate it's equal-but-opposite counterpart in real-time. It sounds like you are looking for a "static" anti-noise generator, so you'll monitor the signal first, and replicate it via some kind of noise generator-amplifier arrangement. I have never heard either of these in action, so I have no idea what the result might sound like, or how successful you are likely to be in blocking it out. However, I am really interested in that whole topic, and would appreciate it if you post a summary of your responses, and also a description of your final setup and the results. Off the topic, but while you are researching and building the anti-noise gizmo, you might consider adding more absorptive material in the room. Curtains, drapes, and rugs will help absorb some of that sound energy. Also, in the past I have successfully blocked noise (traffic noise in my case) with a little "surf synthesizer". It was just a little 15 transistor circuit -- a white noise generator modulated by three asynchronous multivibrators. You might consider something like that, too. Gary Benson John Fluke Mfg. Co. Inc.
phil@mips.COM (Phil Arellano) (03/11/89)
A recent "NASA Tech Brief" contained an article on work done on noise
cancellation techniques applied to engine exhuast muffling. A speaker
enclosure was built around some protion of the exhuast pipe while microphones
were placed around the enclosure. A feedback/amplifier circuit was used to
drive the speaker such that only a slight exhuast noise was produced.
Engine efficiency was improved, as well as noise reduced.
The point is that cyclical sounds can be easily cancelled out if the
cancellation signal was generated at or around the sound generator, or if the
cancellation signal was generated at the ear. Noise cancelling headsets are in
use now by pilots.
phil
--
UUCP: {ames,decwrl}!mips!phil -OR- phil@mips.com
USPS: MIPS Computer Systems, 930 Arques, Sunnyvale, CA 94086, (408) 991-0358lfoard@wpi.wpi.edu (Lawrence C Foard) (03/12/89)
In article <7260@fluke.COM> inc@tc.fluke.COM (Gary Benson) writes: >... >The idea behind "anti-noise" as you call it is that you generate an exact >replica of the offending noise, except opposite in polarity. It must be the >same frequency and the same amplitude, just reversed. As the tops of the >wave fronts collide, they dissipate each other's energy, and the same thing >... I think that inorder to make this work over a large area you would need to completely surround the area with speakers and have a massive computer system to figure out how to get the correct cancellation. But headphones would probably work very well. Interesting things could be done like taking out an annoying range of frequencys while allowing voice through (this would be nice with the old VT52's). If you really wanted to get sick you could rearange the sound to make voices come from different places. It would be pretty neat to have a walkman type thing with an EQ on it and have the ability to knock out or boost certain frequencys. I wonder if there is any market for this?? There where several messages that I have tried to reply to recently that our system barfed on, one was a request for the full Guassian Quadrature routine, is there another address I can try sending it to? -- Disclaimer: My school does not share my views about FORTRAN. FORTRAN does not share my views about my school.
kumar@wucs1.wustl.edu (Arun Kumar) (03/14/89)
In article <7260@fluke.COM> inc@tc.fluke.COM (Gary Benson) writes: >it out. However, I am really interested in that whole topic, and would >appreciate it if you post a summary of your responses, and also a I will. Arun Kumar (kumar@wucs1.wustl.edu)
sparks@corpane.UUCP (John Sparks) (03/15/89)
In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes:
] The theory says that the *best* you can hope for is total cancellation of
] the offending noise.
]
] The idea behind "anti-noise" as you call it is that you generate an exact
] replica of the offending noise, except opposite in polarity. It must be the
] same frequency and the same amplitude, just reversed. As the tops of the
] wave fronts collide, they dissipate each other's energy, and the same thing
] happens all down the trough and up the next wave. The dynamic case would
] monitor the signal and generate it's equal-but-opposite counterpart in
] real-time. It sounds like you are looking for a "static" anti-noise
] generator, so you'll monitor the signal first, and replicate it via some
] kind of noise generator-amplifier arrangement.
]
] I have never heard either of these in action, so I have no idea what the
] result might sound like, or how successful you are likely to be in blocking
] it out. However, I am really interested in that whole topic, and would
] appreciate it if you post a summary of your responses, and also a
] description of your final setup and the results.
Hmm, In theory you can try taking two speakers from a stereo system and
wire one of them opposite polarity from the other. Then when one cone
is extending the other is retracting. The two sound sources will be
180 degrees out of phase with one another. Make sure you feed the same sound
into both speakers.
But in reality this won't work. Since each sound source is the center of
a 3 dimensional spheroid of sound waves, They would have to both be located
in the exact same space in order to cancel out each other.
But it might be fun to experiment with.
--
John Sparks // Amiga | {rutgers|uunet}!ukma!corpane!sparks
\X/ UUCP | >> call D.I.S.K. @ 502/968-5401 thru 5406 <<
If at first you don't succeed, you're doing about average.gmark@ihlpf.ATT.COM (Stewart) (03/15/89)
In article <1290@wpi.wpi.edu>, lfoard@wpi.wpi.edu (Lawrence C Foard) writes: > In article <7260@fluke.COM> inc@tc.fluke.COM (Gary Benson) writes: > >... > >The idea behind "anti-noise" as you call it is that you generate an exact > or boost certain frequencys. I wonder if there is any market for this?? As a matter of fact, I got the idea in junior high school, so I imagine a lot of people had it. As for marketability, there is a British firm, I believe, that make both huge speakers and headphones using the cancelation technique for repetitive, easily predictable, and therefore needing very little computational power to cancel, for the noise created by road construction equipment. Reportedly makes work much less destructive to workers' ears. An interesting use for this I was considering was to do this (assuming computational power was available) for cars. Sound takes a while to transmit through the vehicle. Place microphone(s) outside at different points, such as near the muffler and suspension components and just generate anti-noise for them. Would make a Pinto sound like a Caddy, maybe? Or a Mercedes sound like your front room? In any case, it would have to have some effect on the noise. And a car already has the sound equipment. Essentially, this is just a computerized version of "tailoring" a sound system for a particular make of car. The ultimate version of this might take into account wind noise at different points in the car, as well as probably have a lessening effect on non-vehicle related sounds, like nearby cars & trucks, etc., since all the noise outside the vehicle would probably be picked up the bye microphones and hence, compensated for. This could also be hooked to transducers on the frame itself, compensating, possibly, for conducted noise. Wow, hook this with the computerized shock absorption system in the next generation Vette, and you could have quite a comfortable quiet rocket. - Mark G. Mark Stewart ATT_BTL, Naperville, Ill. ix1g266 ihlpq!gms (312)979-0914
casley@polya.Stanford.EDU (Ross T. Casley) (03/15/89)
I heard a report on the CBC science show about anti-noise just a few weeks ago. Most of the report involved a Canadian or US company whose name I don't remember. It seems that they already have an anti-noise device which uses headsets and is intended for pilots. They have a research contract for developing a replacement for mufflers (silencers, if you will) for cars. This prototype system is not very successful, but they are still working on it.
jack@cwi.nl (Jack Jansen) (03/16/89)
In article <1989Mar10.173840.732@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >My understanding is that practical "anti-noise" systems essentially have >to be on the path between the noise source and your ears -- either very >close to a distant source, or in headphones through which the noise has >to pass. Wouldn't it be good enough if only the microphone were on your head? I would prefer a little mike plus IR transmitter on my head with the bulky equipment in the corner over having to wear headphones all day... -- -- Een volk dat voor tirannen zwicht | Oral: Jack Jansen zal meer dan lijf en goed verliezen | Internet: jack@cwi.nl dan dooft het licht | Uucp: mcvax!jack
MJB@cup.portal.com (Martin J Brown-Jr) (03/16/89)
I believe that one of the major U.S. auto manufacturers is using noise
cancellation by having the stereo equipment in the car put out white noise
out of phase. This was written about a couple (or more) times in various
mags available to the public. It might even been used is some print
advertising. Sorry, but I don't recall which and when.
- MJB -B.Witts@ucl-cs.UUCP (03/17/89)
From: Bill Witts <B.Witts@uk.ac.ucl.cs>
The idea of putting anti-noise systems into cars is being
looked at by some UK car company, maybe Lotus - I will see
if I can find out some more about it before sending lies
to the net.
... BillB.Witts@ucl-cs.UUCP (03/17/89)
From: Bill Witts <B.Witts@uk.ac.ucl.cs> >Wouldn't it be good enough if only the microphone were on your head? >I would prefer a little mike plus IR transmitter on my head with the >bulky equipment in the corner over having to wear headphones all day... No, I think not - the inverse phase sound waves have to hit your ears in phase synch with the source of the noise. The speakers would have to know not only the sound waveform, but your head position in order to get the phasing right. Also, you would have all sorts of weird problems if the mike were within the anti-noise zone - as soon as the anti-noise cancelled the real noise, it would lose the sound info it needed, and would turn itself off, and then oscillate ... ... Bill
phupp@warwick.ac.uk (S Millington) (03/17/89)
This is now being introduced for gun users. The headphones cut out noise above a certain level, by anti-noise, while still letting lower level noise through to the users ears. This allows converstions to carry on without removing the headphones. Cancelling external noise in stereo headphones appears only to need a mic on the outside of the headphones to pickup the external noise which is then fed to the appropriately phased anti-noise circuits. Stuart Millington. University Of Warwick.(Don't let my ideas ALTER their reputation) __JANET phupp@UK.ac.warwick.cu __OTHERS phupp@UK.ac.warwick.cu
gmark@ihlpf.ATT.COM (Stewart) (03/17/89)
In article <453@corpane.UUCP>, sparks@corpane.UUCP (John Sparks) writes: > In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > ] The theory says that the *best* you can hope for is total cancellation of I'll settle for that. > 180 degrees out of phase with one another. Make sure you feed the same sound > into both speakers. > > But in reality this won't work. Since each sound source is the center of > a 3 dimensional spheroid of sound waves, They would have to both be located > in the exact same space in order to cancel out each other. Which leads me to believe that one might design headphones (as is currently used by the British system, and, I guess, Bose), but with the amp. inside (or in a pocket/walkman-type unit), with the microphone(s) on the set (ideally, in locations near and approximating the quality of the human ears. Coupling to the output of the earcup speakers would be a problem. But, it should minimize noise quite a bit. Now, the processing comes in when you decide what you do want to hear. You might have several switches on the control to allow you to select music (using a circuit similar to the ones that remove vocals from music), voice, or to remove these (for who knows what reason). This would be nice to wear in a noisy bus, for instance, and could be sold with a walkman attached to allow music in a noisy environment to sound like sitting in a quiet room. 'Course, safety for joggers would be quite a spectre of doom. - Mark G. Mark Stewart ATT_BTL, Naperville, Ill. ix1g266 ihlpq!gms (312)979-0914
bjornl@octopus.tds.kth.se (Bj|rn Lisper) (03/18/89)
In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: %In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: %] The idea behind "anti-noise" as you call it is that you generate an exact %] replica of the offending noise, except opposite in polarity. %Hmm, In theory you can try taking two speakers from a stereo system and %wire one of them opposite polarity from the other. Then when one cone %is extending the other is retracting. The two sound sources will be %180 degrees out of phase with one another. Make sure you feed the same sound %into both speakers. %But in reality this won't work. Since each sound source is the center of %a 3 dimensional spheroid of sound waves, They would have to both be located %in the exact same space in order to cancel out each other. It depends on how close together you can place the speakers. Far away (as compared with the distance between the speakers) one would expect the amplitude field to decrease with the distance r as 1/r^3, whereas one "undisturbed" speaker alone would have an amplitude field decreasing as 1/r^2. It is assumed that the waves are propagating in all three dimensions. Cf. electromagnetic theory for dipole (sp?) fields, with two close charges of opposite polarity, as compared with the field around a single point charge. Bjorn Lisper
todd@ivucsb.UUCP (Todd Day) (03/19/89)
In article <15890@cup.portal.com> MJB@cup.portal.com (Martin J Brown-Jr) writes:
~I believe that one of the major U.S. auto manufacturers is using noise
~cancellation by having the stereo equipment in the car put out white noise
~out of phase. ^^^^^^^^^^^
^^^^^^^^^^^^
Out of phase with respect to what?
--
-Todd Day-
Internet: todd%ivucsb.UUCP@anise.acc.com
UUCP: {pyramid, ucbvax}!ucsbcsl!nessus!ivucsb!todd
Other: todd@ivucsb.UUCP may not work yet.kumar@wucs1.wustl.edu (Arun Kumar) (03/20/89)
In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: >Hmm, In theory you can try taking two speakers from a stereo system and >wire one of them opposite polarity from the other. Then when one cone >is extending the other is retracting. The two sound sources will be >180 degrees out of phase with one another. Make sure you feed the same sound >into both speakers. > >But in reality this won't work. Since each sound source is the center of >a 3 dimensional spheroid of sound waves, They would have to both be located >in the exact same space in order to cancel out each other. There is a troublesome "near-field effect" just as in optics. If the speakers are reasonably close together, and if you listen to the arrangement from a little distance ("little" = function of frequency) certainly the sound would be attenuated. I think it is possible to determine the characteristics (position and frequencies) of all sound sources (including secondary sources: walls and other reflectors) using some space-frequency transform implemented in hardware. If we (roughly) collocate the primary sorces of noise and the sources of anti-noise, the far-field approximations should hold beyond a distance of about 3ft from the noise-antinoise pairs (approx (2 or 3) * diameter of the hi-fi woofers). It is possible, I think, to solve the wave-equations for multiple primary- noise and antinoise sources in hardware, using finite-element analysis (whether or not the noise-antinoise sources are collocated). There should be enough time to do all this since we are not dealing with frequencies above 20K. One problem is how do we treat secondary sources when solving the wave-equations? Another problem that I see at this stage is a model that would allow us to determine what antinoise to produce. It should all reduce to a simple approximation problem I think. Something like: given a vector x in some vector (or Hilbert) space V, find a vector y in some subspace W such that ||x-y|| is a minimum. Is there someone who has some ideas about such a formulation? Danny Cameron of Intergraph Corp called me to say that a NY company manufactures an active noise cancellation system. I have written to the company asking for a brochure, and for info about any installations in the St Louis area, at the adress provided by Danny. I will post soon as I have a response. Arun Kumar (wucs1.wustl.edu) Box 1045, Computer Science Dept, Washington University, St Louis MO 63130 314-726-4464
verma@mahimahi.cs.ucla.edu (Rodent of Darkness) (03/21/89)
In article <7996@ihlpf.ATT.COM> gmark@ihlpf.ATT.COM (Stewart) writes: >Which leads me to believe that one might design headphones >[...] approximating the quality of the human ears [...] But, >it should minimize noise quite a bit. Disclaimer: I hacked up the quote quite a bit, so it may not reflect Stewart's opinion. I have one question about this noise cancellation. If you only cancel the noise that somone can hear, then wont his `ears relax' (analogous to pupil dialation) allowing the unhearable noise to cause lots of damage? Also to cancel very loud noises you need to generate very loud counter noise. What happens when your hardware fails resulting in additive noise? Last of all what does this have to do with sci.math? ---TS
sparks@corpane.UUCP (John Sparks) (03/21/89)
<BJORNL.89Mar17175300@octopus.tds.kth.se> > In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: > %In article <7260@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > %] The idea behind "anti-noise" as you call it is that you generate an exact > %] replica of the offending noise, except opposite in polarity. > > %Hmm, In theory you can try taking two speakers from a stereo system and > %wire one of them opposite polarity from the other. Then when one cone > %is extending the other is retracting. The two sound sources will be > %180 degrees out of phase with one another. Make sure you feed the same sound > %into both speakers. I just thought of something else. If you took headphones, an amplifier, and a mike and: 1> mounted the mike close to your ears so that it heard what you would hear. 2> then made the output of the amplifier 180 degrees out of phase with the input. Reversing the wires on the headphone speakers would be easiest. 3> wear the headphones and adjust the volume till the anti-sound was just as loud as the sound and it should cancel out. I have an old pair of headphones at home. I might try this on the upcoming weekend. somehow it sounds too simple to work. but what the hey! -- John Sparks | {rutgers|uunet}!ukma!corpane!sparks | D.I.S.K. 24hrs 1200bps ______________| sparks@corpane.UUCP | 502/968-5401 thru -5406 If we weren't supposed to juggle, tennis balls wouldn't come three to a can.
tom@neptune.AMD.COM (Tom Lynch) (03/21/89)
Yes, I read a sci-fi story about the noise eater also. It was in "Tales of the Whitehorn" I believe (read it in high school). The story was about the Fulton Silencer. If you like this idea you'll love the book. It blew up at a concert after eating too much music energy. You know all that energy has got to go somewhere! Harvey come back we need you! (isn't that how the book ended?) tom
MJB@cup.portal.com (Martin J Brown-Jr) (03/21/89)
In my initial posting on this subject, I mentioned that a U.S. car company
used the stereo in some of its cars to cancel out road noise, using white
noise out of phase. Todd (Day?) wondered "out of phase to what"? I as
remember(?), analysis of the road noise rumbling was done, and this noise
was cancelled by having the stereo generate noise(?) of the same frequency,
as far as the stereo could generate, but out of phase with the noise. If I am
somewhat hazy on this, sorry. This isn't my field, and the first posting was
done in order to provide another source of info for those who wished to
explore more fully?
- MJB -sukenick@ccnysci.UUCP (SYG) (03/22/89)
Quick ref: High Technology magazine had an article a few months ago on this subject.
cjh@petsd.UUCP (Chris Henrich) (03/22/89)
In article <805@neptune.AMD.COM> tom@neptune.AMD.COM (Tom Lynch) writes: > >Yes, I read a sci-fi story about the noise eater also. It was in >"Tales of the Whitehorn" I believe (read it in high school). The >story was about the Fulton Silencer. If you like this idea you'll >love the book. It blew up at a concert after eating too much music >energy. You know all that energy has got to go somewhere! > Probably Tales of the White Hart, by Arthur C. Clarke. The tales are very tall, and amusing in a dry British way. Regards, Chris UUCP: ...!rutgers!petsd!cjh (201)758-7288 106 Apple Street, Tinton Falls,N.J. 07724
greg@bilbo (Greg Wageman) (03/22/89)
In article <453@corpane.UUCP> sparks@corpane.UUCP (John Sparks) writes: > >Hmm, In theory you can try taking two speakers from a stereo system and >wire one of them opposite polarity from the other. Then when one cone >is extending the other is retracting. The two sound sources will be >180 degrees out of phase with one another. Make sure you feed the same sound >into both speakers. > >But in reality this won't work. Since each sound source is the center of >a 3 dimensional spheroid of sound waves, They would have to both be located >in the exact same space in order to cancel out each other. This isn't quite true. There will be places (nodes) in space where the waves will cancel each other. The real trick would be to guarantee that one of these nodes is where you want it to be. Longish .signature follows. Skip now, or don't complain! Greg Wageman DOMAIN: greg@sj.ate.slb.com Schlumberger Technologies UUCP: ...!uunet!sjsca4!greg 1601 Technology Drive BIX: gwage San Jose, CA 95110-1397 CIS: 74016,352 (408) 437-5198 GEnie: G.WAGEMAN ------------------ Opinions expressed herein are solely the responsibility of the author. (And the author wouldn't have it any other way.)
jbn@glacier.STANFORD.EDU (John B. Nagle) (03/22/89)
1. It's "Tales from the White Hart", by Clarke.
2. Noise-cancelling headphones were used on the Voyager round-the-world
flight, but the units quit working partway through the flight. The
book on the Voyager project gives the maker, but I do not have the
reference handy.
3. Noise cancelling only works for small volumes of space, smaller than
a wavelength. Attempts to produce cancellation over a large space
with a cancellation source located at a different point than the
noise source will result in nulls at some points in space and
twice the sound level at other points. So headphones work, but
large-area cancellation doesn't.
John Naglejwm@stdb.jhuapl.edu (Jim Meritt) (03/25/89)
In article <5341@lynx.UUCP> neal@lynx.UUCP (Neal Woodall) writes: }In article <805@neptune.AMD.COM> tom@neptune.AMD.COM (Tom Lynch) writes: } }>Yes, I read a sci-fi story about the noise eater also. It was in }>"Tales of the Whitehorn" I believe (read it in high school). The }>story was about the Fulton Silencer. } }Pretty good memory (if you went to high school in the 50's or 60's anyway). HA! Look up "Tom Swift and his Silentenna" - it "does" exactly this! And entire BOOK based on it.... Disclaimer: "It's mine! All mine!!!" - D. Duck
taylord@cs.glasgow.ac.uk (Donald Taylor) (03/28/89)
In previous postings, the idea of a headphone/microphone combination to cancel out unwanted noise has been discussed. I started thinking, "why all the electrical stuff?" You have this (mechanical) wave, right, travelling along towards the ear.. by the time it gets there, it will have a flat wavefront (in the majority of cases)... a very small part of this flat wavefront will hit the ear and pummels the ear drum, while the rest of the mechanical energy bouces about uselessly.. you could use that waste energy to cancel the sound at the ear. a 'diagram'... ||||||| ||||||||||| | ||||||||||| | |_|| ||_| Large circular disk |( O O )| __ diaphragm |_@ @_| mounted on headphone structure. /| | ___ | | / | \ / | ear cup \_____/ Sound incident on the above diaphragm, will cause it to oscilate in a standing wave, with the centre moving in anti-phase to the sound... getting the proportions of surface area inside, and outside of the ring of the ear-cup correct will result in the diaphragm adjacent to the ear being entirely stationery i.e. NO SOUND Anyone got any further ideas along these lines?? The resulting headphones would be quite bulky.. could they be reduced by having more surface area in less volume? And what about directionality?? All these questions, and less, next week same bat time, same bat channel. Disclaimer: I don't know what a disclaimer is, but this one is going to be squiggly ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.
rogers@falcon.SRC.Honeywell.COM (Brynn Rogers) (04/06/89)
I realize I am a bit late on this thread, but..
Was the active muffler for cars ever discussed?
basicly trys to cancel loud exhast using anti-noise, with a mike some
where in the system (near the tailpipe?) and a speaker (heat resistant) inside
a muffler chamber. Has been built and tested, but I don't know where it
is going.
Brynn Rogers Honeywell S&RC rogers@src.honeywell.com
nic.MR.net!srcsip!rogersusenet@cps3xx.UUCP (Usenet file owner) (04/06/89)
I heard that Mazda was at some point attempting to incorporate anti-noise into their audio system in forthcoming RX-7's. Yet another tidbit from the Rumor Mill...
paszkows@prlhp1.prl.philips.co.uk (paszkows) (04/17/89)
In article <20031@srcsip.UUCP> rogers@falcon.UUCP (Brynn Rogers) writes: >I realize I am a bit late on this thread, but.. > >Was the active muffler for cars ever discussed? >basicly trys to cancel loud exhast using anti-noise, with a mike some >where in the system (near the tailpipe?) and a speaker (heat resistant) inside >a muffler chamber. Has been built and tested, but I don't know where it >is going. I wish to express my scepticism over the oversimplified solution to the problem. The fact that sound is being radiated from the exhaust ( muffler in US ) which is not a point source and then the wavefronts etc are distorted relflected by the interior of the car means that the system to cancel the noise will need to be fairly complex. I can imagine you will need a microphone and a tiny speaker sited within the ear to be a close to what the individual is hearing. ( I may of course be wrong ) There was a final year project at my university which was an investigation into just such a problem, and the conclusion drawn was that an array of speakers totally enclosing the person was necessary to achieve the noise cancellation. As you can imagine this is not very practical in a motor vehicle. -- ######################################### # "If this is heaven ahm bailin' out" # # - THE BIRTHDAY PARTY # #########################################
metcalf@marc.ircam.fr (Chris Metcalf) (04/21/89)
In article <859@prlhp1.prl.philips.co.uk> paszkows@prlhp1.UUCP () writes: >just such a problem, and the conclusion drawn was that an array of speakers >totally enclosing the person was necessary to achieve the noise cancellation. As >you can imagine this is not very practical in a motor vehicle. Isn't there an ambiguity as to what 'enclosing' means, i.e., doesn't an array of speakers surrounding the car enclose the outside world as much as it encloses the car? (Cf. _So Long, And Thanks For All The Fish_). More practically, doesn't surrounding the muffler with speakers work just fine? Chris Metcalf -- l'Institut de Recherche et de Coordination Acoustique-Musique metcalf%ircam@uunet.uu.net / ...!inria!ircam!metcalf / metcalf@ucbingre.bitnet
ISW@cup.portal.com (Isaac S Wingfield) (04/21/89)
Well, there's been a lot of talk about automobile engine noise cancellation, using some kind of "active muffler". The first thing that occurs to me (and I don't know, even approximately) is HOW MUCH ACOUSTIC POWER ARE WE TALKING ABOUT? Because it'll take pretty much exactly the same amount of "negative power" to make it go away. I bet it's lots of watts, and if you think even *one* acoustic watt isn,t that much, then you've never heard that much coming from a Hi-Fi (especially at low frequency). Isaac isw@cup.portal.com
du4@mace.cc.purdue.edu (Ted Goldstein) (04/25/89)
In article <17419@cup.portal.com> ISW@cup.portal.com (Isaac S Wingfield) writes: >Well, there's been a lot of talk about automobile engine noise >cancellation, using some kind of "active muffler". All this talk about cancelling the muffler noise of a car has reminded me of a study of highway noise I once read (sorry I don't remember where). The conclusion they arrived at was that most noise coming from a highway is from car TIRES on the road surafce, and not engine noise.
nelsonaf@thor.acc.stolaf.edu (Andrew F. Nelson) (04/27/89)
In article <17419@cup.portal.com> ISW@cup.portal.com (Isaac S Wingfield) writes: >Well, there's been a lot of talk about automobile engine noise >cancellation, using some kind of "active muffler". > >The first thing that occurs to me (and I don't know, even >approximately) is HOW MUCH ACOUSTIC POWER ARE WE TALKING ABOUT? >Because it'll take pretty much exactly the same amount of "negative >power" to make it go away. > >I bet it's lots of watts, and if you think even *one* acoustic >watt isn,t that much, then you've never heard that much coming >from a Hi-Fi (especially at low frequency). > >Isaac isw@cup.portal.com This sounds vaguely like what in radio controlled aircraft is called a 'Tuned Pipe'. According to the catalogs I've seen (now around 8-10 years ago since I haven't been involved in RC since then), these things are actually mufflers which _increase_ the power output of your engine somehow. I don't have any idea how although I'd hazard a guess that it facilites the removal of the exhaust gases from the cylinder. I wonder if this is a similar thing to what you're talking about with an active car muffler? This 'Tuned Pipe' thing isn't electronic in nature though. As I look back though old articles in this thread I get the sense that most of the things that have been mentioned are active electronic speakers and such. -- Andy Nelson |Disclaimer: I didn't do it!! Did I do it?? nelsonaf@thor.acc.stolaf.edu |Well if I did it it was for a good cause. nelsonaf@stolaf.UUCP |Are there any good causes out there? I haven't |found one yet....Help!!!!
tfb@unf7.UUCP (t blakely) (05/04/89)
In article <2283@mace.cc.purdue.edu> du4@mace.cc.purdue.edu (Ted Goldstein) writes: >All this talk about cancelling the muffler noise of a car has reminded me >of a study of highway noise I once read (sorry I don't remember where). >The conclusion they arrived at was that most noise coming from >a highway is from car TIRES on the road surafce, and not engine noise. That's mostly the case. However for a small (but not tiny) percentage of vehicles, most of the noise is the "thump...thump...thump" of the bass from the overpowered stereo. I guess that as exposure to loud music (loud to drown out tire noise?) goes on, you just have to keep turning it up.