Looking for a discussion of this technology. It would be a neat homebrew project!
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What frequency is the ultrasound? Do some systems mix two ultrasound sources? There is correction for nonlinearity of air is that correction performed at ultrasound frequency or audio frequency?
Here's a couple of youtube videos about the subject. I'd like to hear your input. :-) Note the bnc connector to the speaker! Mike
"amdx" wrote in news:d8c1a$48109d20$450139ad$8021 @KNOLOGY.NET:
Because of air attenuation, as low as possible while still safely outside the audible frequency range. Call the manufacturer and ask. Given that it's easily measured, it can't be a secret.
That depends on your definition of a source. Two ultrasonic signals, yes. Two ultrasonic transducers, only if they are stupid.
At the ultrasound frequency.
Here's a semi-technical review article published by another company on the subject.
Am I the only one who worries about sitting in a 140dB ultrasonic field? This can't be good for biology???? My brain is already sufficiently scrambled, thank you...
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No. Hearing damage does not in principle depend on anything but on the amount of energy delivered to the sensory organ, ie. audio does not have to be audible to do damage.
Wouldnt a honking great phased array of ultrasound transducers, in conjunction with IR cameras and some clever software make a great burglar "alarm" - 140dB that tracks their head. Betcha that'd make you leave a room, fast.
Good Point. Expseriens and measureemnts around 1950 at Penn State showed that heat deposition occurs at an above this level. A ball of cotton will smoulder and catch fire at and above 160 dB. Bare skin reflects the energy, but who wants to take that chance.
What do you base your statement on? I can see where the energy
*would* need to be in the audible range. The detectors in the human ear are thousands of tiny cilia that are each tuned to a unique frequency of sound. They literally resonate at a particular frequency. The damage happens when the cilia are over stimulated and mechanically damaged. So if the energy is not in the audible range, they don't resonate and it is much harder to damage them. Of course if you use a high enough level of sound, even outside the hearing range, it can do damage. Like someone posted, at some point a ball of cotton will burst into flame! I don't like the idea of spontaneous human combustion.
Reality. Notice that it is by design a very general statement.
"Be audible" implies that it is heard by the actual person and "in the audible range" implies that it could be heard by a ""normal"" person. It is an important distinction to be aware of, because people with pre-existing hearing damage often neglect obvious aural risks or plain fail to detect them as being at "risk loudness level", whatever that may be.
At what Q? - my level of information is that this is still kinda softish tissue with a "frequency range preference" rather than metallic high Q precision resonators a lá tuning forks. But the image you project is more like the tuning fork model ....
Seem to be the agreed facts on this.
Just how much harder?
Just what part of my statement: "Hearing damage does not in principle depend on anything but on the amount of energy delivered to the sensory organ" is it that you disagree on, you seem to me to have written exactly the same as a correction to what I posted.
You guys are making the obvious (mis)assumption that hearing loss is the ONLY danger here. This technology has been proposed for use in an automobile to give each passenger a different audio program.
"Hey mommy, what's inside this little hole I've got my eye plastered against?" "Makes my eye feel warm..."
Wonder the resonant frequency of the tails on your swimmers?
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As I do agree with Rick on the damage of the specific sensory organ, nobody says that damages could occur elsewhere i.e. in the ear due to temperature raises when source is directly pointed at the membrane of the drum or other kinds of effects. Ultrasounds can interfere with blood circulation... fetuses do react when the beam is pointed at them in normal scanning, thus while a listening commodity for the gravid it could be a torture for the fetus. On the other hand many physiotherapy centers use ultrasounds to give relief to subjects with particular pains or conditions, so such sound systems could also make us feel better! hehehe (I know there hasn't been any official research on that).
I believe that a company before placing in the market such technology must do and must have done some homework to avoid any lawsuit against them. If smart they might even seek some medical safety board approval...I see that on the original question nobody has answered and personally I would take the risk :) and have a listen... I'm very curious about that. If anybody in south east Asia has any, please post.
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