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/sci/ - Science & Math

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5243865 No.5243865 [Reply] [Original]

I need to build a Long Range Acoustic Device. Does anyone have links to resources they can share?

>> No.5243870
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5243870

There you go...

>> No.5243905
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5243905

>>5243870
>Wall of Sound

>> No.5243906
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5243906

Umm... not yet, but I'll help you hunt, as this is relevant to my interests.

I've been reading up on radar a bunch recently, and while it's not EXACTLY the same, there are a lot of the same principles. For instance, the gain/directionality of an antenna is proportional to the ratio of aperture area to wavelength squared. Your emitter will likewise follow a similar law, and thus it will be desirable to use high frequencies (if possible) and a large emitter in order to form a coherent, flat wavefront.

How hardcore do you want this thing to be? Do you just want a ghetto-rigged sonic beam or something crazy like an electronically-steered phased array?

>> No.5243931

>>5243906
>>5243865
And the digging begins....
http://dsearch.dtic.mil/search?site=default_collection&q=LRAD&btnG.x=0&btnG.y=0&btnG
=Google+Search&client=dticol_frontend&proxystylesheet=dticol_frontend&proxyreload=1&
filter=0&tlen=200&getfields=*

>> No.5243976

>>5243931
Yep... okay, all of these seem pretty general, but sure enough, the first result is the most specific one I can find:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA435642&Location=U2&doc=GetTRDoc.pdf
>The Long Range Acoustic Device (LRAD TM) developed by American
Technologies Corporation (ATC) is a flat panel, multi-transducer, phase coherent emitter. It transmits highly directional voice and warning tones with clarity and authority in excess of 500 yards over water and 300 yards over land. The LRAD transmits a focused beam of less than 30 degrees.
30 degrees? That must be for lower-frequency emissions. It ought to be able to do better than that.
>Power requirements are less than 500 watts
Interesting.
>Directionality: -20 dB @ +/- 15 degrees @ 2.5 kHz
Erm...
Having trouble interpreting that one. It's not exactly a standard measure of performance.

Anyways, you want me to start pitching design ideas?

>> No.5243987

Did anyone else read "How LARD works"?

>> No.5244027

>>5243987
no.

>> No.5244033

>>5243865
Its called constructive interference, and you can do it with any form of wave, its how lasers work too.
Also called resonance, its what most of tesla's work was based on.
Idea is pretty simple, get some speakers, and tune a microphone next to the speakers. Shoot some high pitched tones out for a milisecond or less, have the microphone time the delay. Synch up the speaker so that it emits another sound pulse right as the reflection comes back. It will take some tinkering to get the timing right, but thats about all it takes.

>> No.5244059

>>5244033
That'd be a phased array. And there are better ways of making one besides trial-and-error. Not to mention, there are also simpler, cheaper options for a directional sound emitter.

For instance, you could use a large horn to crudely (but still somewhat effectively) direct the noise from a single, loud, high-frequency speaker. You could also use a large parabolic reflector to catch radial sound from a single speaker and reflect it in a directional wavefront.