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Natural Science Forum / Physics / Acoustics / December 2003The Power of Sound
had once seen an old late 50's sci-fi program where the announcer did experiments with light, sound, radiation that would e consider insane these days. But one in particular intrigued me: the guy set up an oscillator connected to a transducer that was at the focus of a three or four foot metal dish. This arrangement was pointed at a wall, and when the guy turned on the ultrasonic generator, the wall paper burst into flames as the man moved the dish around. I never thought ultrasound could be used like a laser before. Does anyone know how much acoustic power needed to create that kind of heat? Is there some particular frequency that's needed or can any ultrasonic frequency be used? Any ideas on this would be deeply appreciated. Thanks. Ron > had once seen an old late 50's sci-fi program where the announcer did > experiments with light, sound, radiation that would e consider insane these I think the opposite (if those experiments were indeed real). Thus stuff gets re-invented every 20 years or so, as you example below. > But one in particular intrigued me: the guy set up an oscillator connected > to a transducer that was at the focus of a three or four foot metal dish. > This arrangement was pointed at a wall, and when the guy turned on the > ultrasonic generator, the wall paper burst into flames as the man moved the > dish around. I never thought ultrasound could be used like a laser before. We did that sort of thing (make cotton burn) routinely at Penn State around 1950-55: The sound source was an utrasonic siren, and the ignition place was just at the sound outlet. In your example, the transucer was either piezoeletric or magnetostrictive, and the diverging field was captured by the dish and refocussed, to create much the same effect. > Does anyone know how much acoustic power needed to create that kind of heat? About a kilowatt. > Is there some particular frequency that's needed or can any ultrasonic > frequency be used? Focussing needs to be sharp. The dish must be perhaps 10 wavelengths in diameter, and the focus spot (typically no smaller than a wavelength in diameter) must be small (you do the math to get many watts per square cm). Angelo Campanella Thanks for the information, Angelo. I've always been fascinated by what sound could do I think ever since I was a kid and first saw some old Star Trek episode where some guy knocked out the crew of the Enterprise using sound waves. I was really surprised when the Sci-Fi Channel a few years ago started airing this old program (whose name I can't remember) where during the first few minutes the narrator would do something cool to illustrate what the following story was about. But this guy on occasion was doing things with high voltages, sound, liquid helium, and even some radioactive substances that were potentially hazardous; the kind of thing Mr. Wizard would sure think twice about handling these days. :-) The "sonic cannon" was the most spectacular of the experiments and I would love to replicate that someday. What kind of transducer do you think would work best is such an application? Ron > > had once seen an old late 50's sci-fi program where the announcer did > > experiments with light, sound, radiation that would e consider insane these [quoted text clipped - 26 lines] > diameter) must be small (you do the math to get many watts per square cm). > Angelo Campanella [snip] >I was really surprised when the Sci-Fi Channel a few years ago started >airing this old program (whose name I can't remember) where during the first >few minutes the narrator would do something cool to illustrate what the >following story was about. But this guy on occasion was doing things with [snip] Any chance the show is "Science Fiction Theater" and the narrator/host is a grey-haired guy named Truman Bradley? Looks somewhat like the head of the Metalunan contingent in "This Island Earth?" If so, I've been asleep at the switch - gotta check the Sci-Fi channel listings. That show was one of my favorites. Ken Plotkin I was over at my friends house when I posted yesterday, but when I got home it took me a little while to go through my video collection, but eventually I found it. You were right, Ken, the show was indeed called Science Fiction Theater w/ Truman Bradley. > [snip] > >I was really surprised when the Sci-Fi Channel a few years ago started [quoted text clipped - 11 lines] > > Ken Plotkin > Thanks for the information, Angelo. I've always been fascinated by what > sound could do... So has the military. See: http://www.arcanemethods.com/KillerHorn.jpg Bob  Signature"Things should be described as simply as possible, but no simpler." A. Einstein Yeah,the military has been interested in sonic weaponry for years; there have been articles on it in News Week and many other publications for a long time. I think the US is trying to outdo the pioneering research the Germans had done during WWII. But what I would like to see is a working sonic screwdriver like that seen on Doctor Who. The principles are sound (er, no pun intended), but making a pocket-sized, self-contained device is one heck of a technological challenge. Ron >> Thanks for the information, Angelo. I've always been fascinated by what >> sound could do... [quoted text clipped - 10 lines] > > A. Einstein >> Thanks for the information, Angelo. I've always been fascinated by what >> sound could do... > > So has the military. See: > > http://www.arcanemethods.com/KillerHorn.jpg geez. what the hell is that, Bob? r b-j >>http://www.arcanemethods.com/KillerHorn.jpg > geez. what the hell is that, Bob? Jerico II > >> Thanks for the information, Angelo. I've always been fascinated by what > >> sound could do... [quoted text clipped - 4 lines] > > geez. what the hell is that, Bob? Dunno for sure. I can't remember exactly where I found it but the context of the discussion which yielded it was using sound in military offense. From the signage on the side of it I assume it's to assist some "directorate" in creating a certain "battlefield environment". :-) I'd love to see closeups of what's on the business end. Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >geez. what the hell is that, Bob? It's called MOAS - Mother Of All Speakers. It's not a weapon. It's a high amplitude sound source, used mostly for propagation experiments. It's also been used as an active source in successful demonstrations of active control of low frequency jet engine noise. It's a Wyle WAS3000 sound source driving a rather large speaker. Ken Plotkin |
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