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this is really ot but here in sf,cali there is that wacky place called 'the exploratorium' where there all these exhibits of weird and wonderful manmade and natural phenomenon and one of them is these two chairs that sit across from each other aprox.50ft. or so(maybe not that far!) and you are to sit in them and talk to each other in a normal voice and thru all the cacaphony of the place which is more like a warehouse and echoey as hell w/ alotta kid and people,the person at the other chair can hear you perfectly and you can have a conversation as if there was no one else around-how is it done?no idea-but there is a kinda acoustic cone that is actually the chair and i guess that sends the voices i dont know,kinda sorry i brought it up...but it would be great for restaraunts of which you speak! stanner ---------- >From: Tom Ritchford <tom@swirly.com> >To: Loopers-Delight@loopers-delight.com >Subject: Re: OT: Personal Audio Space? >Date: Mon, Jun 18, 2001, 6:21 PM > >From: "Allan Hoeltje" <ahoeltje@best.com> > >>Have you ever been in a loud restaurant and couldn't make out what the >>person sitting across from you was saying because the background noise >was >>so loud? >> >>What I want is a "perception aid". It seems to me that DSP's are good >>enough that if combined with a couple good microphones you could cancel >out >>the noise and enhance the nearby sound. Fit the electronics and mics >into a >>battery powered, walkperson sized box, plug into it with head phones (the >>ear plug kind, like what some performers use on stage) and have yourself >a >>"personal audio space". >> >>Anyone know if this is possible, or available? >> >>For looping or recording, it could be used as a pre-amp (a de-amp?) in >noisy >>places. > >This is a great idea and it's certainly not implausible at first glance. > >You all know about the sound cancellation earphones (that were invented >for the first round-the-world plane flight when they worked out that >the pilots would be deaf before the halfway point because of the >noise!) > >But a similar idea is used in professional sound reinforcement in large >spaces, >where speakers with signals out of phase with the original are placed >in order to reduce the effect of reflections and improve intelligibility. > >The trouble is setting the correct phase and thus delay for each >frequency and direction. The pros do it with a complex series of >measurements and experiments in the space itself... > > >Now suppose you just had a speaker and a mic and a little microprocessor >(uP). > >the mic faces outward. >the speaker faces inward. >the uP is logically "in between". > > > blah \ / -blah > THEM blah - -> mic -- uP -- speaker - -> - -blah YOU > blah / \ -blah > > >then >1. the mic gets a signal and send it to the uP. >2. the uP inverts the signal, > (then adds a negative feedback/delay term in order to damp out > the feedback through the mic -- this is where the tricky > part comes in) >3. and sends it to the speaker, thus cancelling out the noise, at > least in the direction of that speaker and YOU! > >have five of these things and you are set! (you'd want one >overhead because a lot of the sound would be coming from >ceiling reflections, particularly in a restaurant where >the ceiling is usually the only good reflector!) > >even two might work pretty well. > > >now, with a bigger uP you could do stuff like this: > >... have a lot of small mics > >... compute the actual 3-d "sonograph" of the sound > >... reduce it similarly to holography to a three channel version > >... send the inverse to three speakers and "completely" cancel the > sound in a small area. > >the amount of computation involved is large but not inconceivable >and the mathematics is "well-known" (to people other than myself, >mind you...) > ><http://herodes.feld.cvut.cz/akustika/akhol.htm> is a really >nice short though slightly technical summary of this technique. > > /t > > > that was fast > >.......all legal games of chess ><http://solveChess.com/chess?refresh=0>...... >.....programmer's documentation ><http://solveChess.com/doc>.................. >