Half a croissant, on a plate, with a sign in front of it saying '50c'
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Spy microphone

Secret spy flame microphone
  (+7, -2)
(+7, -2)
  [vote for,
against]

Speakers can act microphones and microphones can act as speaker. Flames are well proven to act as speakers so they should be able to act as microphones as well. A Reubens tube is the closest example of a flame microphone that I am aware of. A decorative dinner or holiday candle, Tiki Torchs, gas grills and lamps would be good microphone candidates. James Bond's Q could whip one up fast I bet. The only problem is the the dancing of the flame, accompanying the surrounding music or voices, would have to to be advertised to the guest as a form of art that reacts to the sounds it hears, if anyone should notice.
Sunstone, Jun 22 2007

Speaker/microphones http://www.zyra.org.uk/sp-mic.htm
All speakers are microphones [Sunstone, Jun 22 2007]

Flame speaker http://www.swtpc.co...e_Amplification.htm
Flame speaker [Sunstone, Jun 22 2007]

Reubens tube http://www.youtube....?v=RyIphO4Ypoo&NR=1
Reubens tube [Sunstone, Jun 22 2007]

Flame Microphone citation http://users.pandor...rophone_history.htm
Search for "Blondell and Chambers" [csea, Jun 22 2007]

[link]






       A very cool "something new" today.   

       Thanks.   

       Speakers and microphones are similar and conceptually one is the inverse of the other, but they are not the same. In loudspeakers you can achieve a decent signal-to-noise ratio by cranking up the volume so inherent noise is not a problem. In microphones you are trying to separate very small vibrations in the air from any background noise, so low inherent noise is crucial.   

       Given that flames have an inherantly high noise floor as they are constantly moving, this would make them more suited for use as a loudspeaker than a microphone. I doubt this would work, but it would probably be fun to try.
wagster, Jun 22 2007
  

       I trust [wags]'s knowledge, but you have done some research and it sounds really cool, so here's a flaming croissant..............+
xandram, Jun 22 2007
  

       Cool links, good idea. Any unwanted noise inherant to the flames could be filtered out by a computer?
zeno, Jun 22 2007
  

       The problem here is that the flames are not the speaker but rather are (in the Reubens tube) deformed by the audio pressure wave and therefore only a visual indication of varying pressure waves. The assumption seems to be that a reversal of this process, somehow measuring the pressure of the flame(?) would allow one to recreate any acoustic vibrations that effected it. Without going into exhaustive analysis, which I will leave for the more eggheaded among us, I see some clear difficulties in measuring fluctuations in gas backpressure from an uncontined freely burning flame, not the least of which has to do with original gas pressure behind it. A bun nonetheless for the idea and a cool physics demonstration, though I would have preferred something by Pink Floyd. [+]
nuclear hobo, Jun 22 2007
  

       IIRC, some early experimenters with wireless telegraphy thought they had discovered something new when they saw the flame in their gas jet jumping in time with their signal. It turned out that the flame was not responding to the radio energy, but to the sound of the clicking telegraph key, which pushed a little more oxygen into the flame with each pressure wave.   

       I'd say you could get sound signals out of a flame in two ways. Overall brightness might increase with each sound pulse, and the flame itself might flicker side to side. Either way, a damn good camera with a telephoto lens could feed an image to a computer for analysis. Brightness or position or both could be used. A filter for flame noise could be developed, maybe, but that's a' whole 'nother challenge.   

       I'm fishboning this for two reasons. It's really a WIBNI, as it just says that something might be possible, but doesn't give any clue at all as to how it could be done. The title is only the category that this should be in, instead of "Flame Microphone" or something informative. [-]
baconbrain, Jun 22 2007
  

       Apparently, in the early 1900s, a couple of researchers developed a "flame controller" for use as a microphone. [link] (about 2 pages down)
csea, Jun 22 2007
  

       [-] removed in the light of [csea]'s link. It's still a long way short of a concealed microphone but a cool idea nonetheless.
wagster, Jun 22 2007
  
      
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