h a l f b a k e r yMake mine a double.
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Although an idea similar to this has been posted [link], that idea's author didn't say how it might work.
The apparatus comes as two parts: a transmitter (placed near the noise source) and a reciever (a pair of headphones).
The transmitter has a microphone and a radio transmitter.
The reciever
has a radio receiver, an outwards facing microphone near each ear, and an inwards facing speaker near each ear.
The reciever calculates, for the left and right sides seperately, the time delay and reduction in volume between the audio signal from the transmitter and the audio signal from the microphones.
Then (well, simultaneously), it plays the signal from the transmitter, with high pressures and low pressures reversed, at the appropriate delay and appropriate volume, through the speaker facing each ear.
Original Idea
Audio-Cancelling_20Headphones
[goldbb, Mar 29 2009]
Like this, but half-baked?
http://en.wikipedia...ncelling_headphones
Noise cancellation with microphone near ear works better [loonquawl, Mar 30 2009]
Noise-cancelling Speaker
http://www.longcom....ssories/nes10-2.asp
Looks like what you're after. OMNOMNOMNOM becomes omnomnomnom... [Defiler, Mar 30 2009]
[link]
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actually if I read it right, the other idea was to use headphone output on a TV to cancel speaker output or something like that. |
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So really, noice-cancelling headphones, but in the shape of a speaker? The problem with antiphase noise-cancellation is that you need to know *exactly* where the listener is for them to work. *Or*, you need to have the speaker *exactly* where the sound is coming from. |
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Schwardo's idea is closest, but... |
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He doesn't describe how to get the data signal from the TV's jack's to the headset (a wire, a radio signal, bluetooth?), or how to the gadget determines how much delay is needed for each ear. More importantly, it would only work with sound sources which have audio jacks, or the like. |
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With my idea, the transmitter could be clipped onto a vacuum cleaner, for example, and the headphones would then cancel out the noise of the vacuum, and only that noise, whilst leaving all other noises in the room perfectly audible (including sounds from the TV, the doorbell, the telephone ringer, etc.). |
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The noise cancelling headphones loonquawl linked to are designed to reduce *all* noises... which isn't what my idea's about. If I were wearing them so as to not be bothered by the vacuum cleaner, I wouldn't be able to hear the TV, someone at the door, or my phone ringing, or someone in the next room calling for me, etc.. |
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And as for that noise-cancelling speaker -- it only eliminates "noise" from what it's playing, it doesn't eliminate noise from the room it's playing in. |
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I'm thinking a little remote control that you can use to selectively tune out sounds based on direction... a couple mic/speaker buds that plug into a little mp3-player-sized box with a dial and a few buttons on front; twist the dial until the noise that's annoying you is the one that disappears then punch the 'include' button; rinse and repeat until all you can hear is the television. |
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FT, The problem with tuning out sounds based on direction is that if you turn your head, you're facing the wrong direction to cancel out the sounds. Also, what happens when the sound source moves? |
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89tortoise, the transmitter helps because it is nearer to the unpleasant noise than you are, and hears it louder and more clearly than you do -- in fact, the transmitter hears the unpleant noise louder and more clearly than it hears anything else. |
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Thus, by having the receiving unit cancel out the sound sent by the transmitter, and only that, it *avoids* canceling out other (more pleasant or more important) sounds. |
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As for the sound not really being a point source... well, so what? If I hear *only* the reflected sounds coming from the vacuum cleaner, but not the vacuum cleaner itself, that's still a huge improvement. |
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As for noise cancellation having been baked... as I said, I don't want to cancel out everything... I only want to cancel out unpleasant sounds, whilst leaving all other sounds audible. |
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As for using a bullet-tracking-like system... that would be too big, bulky and expensive... Plus, due to the time delays needed for data processing, it would probably hear the sounds *after* the user, so it wouldn't have them in time to cancel them out. |
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My idea is simple enough to do parallel processing... one circuit repeatedly measures delay between radio and mic, and stores the measurement in a buffer, the other circuit (and parallel with the first) repeatedly reads that buffer, delays the radio signal by that amount, and plays it (inverted) through the speaker. |
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I can do this with *prerecorded* audio in audacity, it should be a simple matter of engineering to do this for real using highly directional (i.e. laser) microphones and speakers. But its more trouble than its worth, except perhaps for military purposes (The Ultimate Silencer). |
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