Take a resonanting cavity with flexible, diaphragm-like ends, filled with gas at some suitable density. Rapidly heat the gas with microwaves (or other EM radiation as appropriate) to generate pressure waves and so sound. It'd probably have really bad sound quality, but it might be a neat toy. Problem: how to cool the gas rapidly when necessary?
-- cosma, Apr 28 2000

Pyrophones http://www.windworld.com/emi/pyronw.html
A similar idea, but with a gas flame. [krevis, Apr 28 2000, last modified Oct 04 2004]

Plasma Tweeters http://members.aol....ann2/plasma/ion.htm
Believe it or not, some of them dang fool audiophile-types already done it. Ionize gas with a high-voltage discharge; the resulting plasma is electrically conductive. Pressure waves, hence sound, are generated by changing the electric field near the plasma. The ultimate high-end gear: expensive, vastly inefficient, and dangerous (the discharge that produces the plasma also produces ozone). But if you need frequency response into the range of dogs, bats, and radio, plasma's your answer. Course anything that expensive probably Sounds Real Nice. [rmutt, Apr 28 2000, last modified Oct 04 2004]

Don't use microwaves; use IR lasers in some frequency absorbed by air. That way you can just heat up a thin slice of air, which should cool quickly.

Sound quality could actually be quite good, especially since you could steer the laser with an AOM for true sonic imaging.

(It would double as a bug zapper!)
-- egnor, Apr 29 2000, last modified Nov 30 2000


May as well let on the other idea that came immediately thereafter, cosma:

Set of headphones which use intense but tuned EM to produce the perception of sounds in the wearer's sensorium by (a) inducing physical vibrations detected by the normal hearing mechanism, or (b) inducing the sensation of sound directly in the portion of the brain responsible for processing auditory (and maybe visual, too) inputs.

Avoid standing near a computer while wearing these, though.
-- vaguery, Apr 29 2000


Eek! With all the problems that just talking on cellphones is supposed to cause, do you really want 'intense EM' emitters on both sides of your head?
-- StarChaser, Apr 29 2000


i think a detail we're overlooking here is the fact that the speaker functions via heat. as in, it's gonna get really hot. normal speakers can be picked up, or you can put piles of paper near them and they won't burst into flame.
-- urbanmatador, Apr 29 2000


Someone built a motion simulator that stimulates the inner ear directly, and of course hearing-aid researchers have cochlear implants and such.

(I'm too lazy to look up URLs for you this time, sorry.)
-- egnor, Apr 29 2000


OK, so we slap a big "Caution: Speaker Is Hot" warning label on it. I imagine that would only _increase_ sales, and could be put to good use in rock concerts and other sorts of performance art. Support the actual sounding body by metal struts which in turn rest on a dense, high heat-capacity base, done up in a nifty dead black.
-- cosma, Apr 30 2000


Would look -really- cool in a concert, a bunch of clear Pyrex tubes with flashing flames inside them...
-- StarChaser, Apr 30 2000


As resident know-it-all, a few technical corrections: neither microwaves nor IR lasers will heat air, which is transparent to both. (Otherwise microwave ovens and CD players would only work in a vacuum). Also, electrostatic speakers don't make the air expand, they make a charged membrane vibrate, which moves the air.
-- rmutt, May 01 2000


Air does absorb many frequencies of IR (depending on the amount of water vapor and CO2 present, among other things). It's transparent to the frequency used for CD lasers (though that laser really doesn't have to go through very much air in any case).
-- egnor, Nov 30 2000


rmutt: Plasma speakers != electrostatic speakers. Plus, plasma speakers are GREAT for reproducing high frequencies, but don't expect them to put out ghetto-fab bass.
-- TerranFury, Aug 02 2004



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