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Natural Science Forum / Physics / Acoustics / December 2003*Intentional* phase-cancellation necessity/problem
I am working on an audiovisual installation and I need to obtain *acoustically* the same result one obtains by electrically summing two 180 deg. out-of-phase signals - i.e. silence. Somehow the results of my first experiments are somewhat frustrating, as all I obtaing is a diffuse soundfield without any clear directional component - but that's not what I need. I believe this has primarily to do with room reflections bouncing around and messing up the cancellation effect. For your info, I am feeding a monophonic spoken-voice recording in two speakers set exactly opposite, one of the speaker being wired (of course) out-of-phase and I'm looking to find that null-spot where both signals cancel each other out. The final installation would (in theory) feature 2 sets of opposite placed speakers, each pair running a different signal, of course, but at the end of the day I'm starting to believe that this may not be possible unless I create a perfect anechoic chamber (extremely expensive and out of the scope of the artist), but I'm still willing to give other solutions a try... Does anybody have any ideas in this respect? Thank you! Paul Weber JingleJungle Music [Please note this message has been intentionally cross-posted to other goups such as rec.audio.pro, alt.scy.physics.acoustics, da7.com, musicplayer.com, etc] > I am working on an audiovisual installation and I need to obtain > *acoustically* the same result one obtains by electrically summing two [quoted text clipped - 15 lines] > to give other solutions a try... > Does anybody have any ideas in this respect? Hallo Paul, Don't forget that your two ears are not at on point in ambience, some 20 cm (8 inch) apart. You receive binaural sound. Close one ear and you get a little more success. Eberhard Sengpiel > Hallo Paul, > Don't forget that your two ears are not at on point in ambience, > some 20 cm (8 inch) apart. You receive binaural sound. > Close one ear and you get a little more success. > Eberhard Sengpiel Thank you, Eberhard... I've already received some answers along these lines from the fellows at rec.audio.pro. Guess I was looking for the Holy Grail, or the acoustic equivalent of the philosopher's stone! ;) Anyway, do have a Very Happy New Year, wherever that may be... Paul Weber San Pietro Ticino, Switzerland > I am working on an audiovisual installation and I need to obtain > *acoustically* the same result one obtains by electrically summing two [quoted text clipped - 4 lines] > course) out-of-phase and I'm looking to find that null-spot where both > signals cancel each other out. With stereo now on TV, I sense that their audio guys are playing with it to the extent that when they put a dubbed sound in, with opposite phases on right vs left, the sound I hear seems (to my ear/brain system) to be coming from somewhere to the right or left of the screen; e.g., a doorbell or phone ring. My comment leap-frogs ahead of your discussion of sound cancellation, but it serves to demonstrate the much bigger picture of 3-dimensional properties of sound propagation. In my example, you can see that the sound was cancelled as expected in the direction where the two speakers were equidistant from my ears. But in the direction 90 degrees away right and left, sound was not cancelled, but went on to enter the reverberant field of my living room. This reverberat sound then was perceived by me as coming from "somewere else" (than theTV in front of me). > The final installation would (in theory) feature 2 sets of opposite > placed speakers, each pair running a different signal, of course, but > at the end of the day I'm starting to believe that this may not be > possible unless I create a perfect anechoic chamber (extremely > expensive and out of the scope of the artist), but I'm still willing > to give other solutions a try... Try projecting mono-speech trough the stereo pair, oppositely phased as I mentioned. Could make a nice demo for the spatial properties of rooms and stereo..... Also implies the difficulty/futility of 3D noise cancellation. Angelo Campanella Have you thought about pulling out the mains plug.? ;-) > I am working on an audiovisual installation and I need to obtain > *acoustically* the same result one obtains by electrically summing two [quoted text clipped - 28 lines] > goups such as rec.audio.pro, alt.scy.physics.acoustics, da7.com, > musicplayer.com, etc] |
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