possible to make directional infrasound from a small device?

OK, thanks!

On a sunny day (Wed, 19 Jan 2011 12:37:57 +0100) it happened Bob Fnord wrote in :

I think that is wrong. Some time ago there was this pop toy that could blow peoples eardrums at short distance. It produces what is called a 'soliton' wave. Do not remember the name of that toy, but is was for sure small and directinal. Think it was some tube with a rubber membrane and a trigger. Look up 'soliton' on wikipedia. Creating solitons at 7 Hz should be possible. But try it on your own ears first :-)

short distance.

tinal.

Hello Jan,

I can't imagine that the non-linearity in air is sufficient to get significant increase of directivity with respect to a linear approximation, given a structure with size < lambda. I assume that the original poster wants to limit the frequency content to below 20 Hz.

If you could provide me a link that shows significant higher directivity (w.r.t. to regular wave interference theory), it would be grateful.

Best regards,

Wim PA3DJS

On a sunny day (Wed, 19 Jan 2011 09:09:07 -0800 (PST)) it happened Wimpie wrote in :

I dunno, but you could look for that toy I described.

On a sunny day (Wed, 19 Jan 2011 09:09:07 -0800 (PST)) it happened Wimpie wrote in :

PS you are probably right if talking about pure sinewaves. But here we can use an impulse with as flat a front (short risetime) as you like and a repetition rate of 7 to 20 Hz.

An EM impulse with a risetime of 1 ps and repetition rate of 7 Hz behaves and propagates very different from a 7 Hz sinewave. The OP never mentioned 'sinewave'.

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propagates

Hello Jan,

He wants to make infrasound, and that excludes pulses containing harmonics in my honest opinion. Maybe he can clarify himself.

When he accepts the harmonics, the "HF" components will travel more or less directed, but the fundamental components will spread out quickly.

Best regards,

Wim PA3DJS

On a sunny day (Wed, 19 Jan 2011 11:47:19 -0800 (PST)) it happened Wimpie wrote in :

like

propagates

pie

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ves and propagates

Hello Jan,

If you need more power, use a vortex ring gun (fast expansion of gas into a conical shaped barrel). I have done some experiments with fast gas discharges. You can blast objects into pieces at distance much larger then the valve's bore, but this is more due to the shock wave and the supersonic jet I think.

When you mentioned the soliton wave, I started to think of the vortex ring gun and the hail cannons. The only problem with these devices is that they make lots of noise, especially the low frequency components travel to all directions (some fruit growers want to use hail cannons over here, but the people around don't like it).

I have doubts whether you can make this work at frequencies of 7.. 20 Hz without creating lots of other frequencies. I see such vortices more like energy transport via kinetic energy (like you launch a real ring) instead of waves.

Best regards and thanks for the link,

Wim PA3DJS

pie

s you like

ves and propagates

hello Jan,

I tried to send you PM, but it bounced,

When you remove abc from my address, it will reach me.

Wim

short distance.

directinal.

This toy was basically a membrane across a tube, that then went into a smaller diameter tube. It was just a gust of air that did the deed, and it quickly attenuated. Very little directivity beyond the near field! 8-)

Charlie

Nah. Shock waves are acoustic solitons ~1cm wavelength, and pack enough of a pressure excursion to alter the speed of sound as well as significantly heating the air. After a certain distance they become normal sound again, and change from a perceived "crack" noise into the familiar "thump" of a sonic boom. If your ~30KHz transducers can output a single pulse with enough joules, the speaker cones will go nearly transonic, and a genuine shockwave will be formed. Maybe cap discharge through a spark gap with a parabolic reflector would work better.

On the other hand, the "Woody Norris" technique might produce some significant subsonic energy. Those propagating ultrasonic beats really do cause the air itself to become a low-freq emitter, and I suspect it's analogous to a yagi antenna: a long row of small sources which, because each interacts with neighbors, dumps out significant low-freq wattage. A small array of 30KHz tweeters should produce a fairly narrow ultrasound beam. Or pay a couple hundred bucks to experiment with those HSS H450 "sonic spotlight" devices commonly seen on eBay sold as "used."

Give it a square wave 30KHz drive, but invert the phase at 7HZ to produce a crude DSB SC spectrum.

Could this alter the "non-lethal area-denial weapon" into a lethal one? An ultrasonic Brown Note death ray, the TMTE or "Tesla-Mark- Twain-Effect device."

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer beaty, chem washington edu UW Chem Dept, Bagley Hall RM74 billb, eskimocom Box 351700, Seattle, WA 98195-1700 ph 206-543-6195

Why the scare quotes around "used"? You think they fell off the truck?

BF > Is it possible to produce infrasounds BF > (in the 7 to 20 Hz range) with a small BF > (coat pocket size) electronic device? BF > For example, can a small speaker NF > produce such low sounds?

BF > And if so, is it possible to use a reasonably BF > small parabolic reflector to aim them?

G > Is this what the tin foil hat brigade is on about?

Archie > Ask your friends in the KOOK group, you KOOK bastard.

G > Why are you so cranky about this, Archie?

Archie > Go away, you retarded KOOK bastard.

I just want you to know that I'm a member of your fan club, Archie!

Um... same as the reason for quotes around "sonic spotlight," "Woody Norris?"

Hey, I found a manual. Looks like these things are terrible at long wavelengths. No Brown Notes then. I guess if your beam is half a kilohertz wide, then only half a kilohertz sound will propagate along it.