Building an Infrasound Emitter

90 dB at 5 meters is a lot of energy.

Sound level decays 6dB with every doubling of distance from the sound source.

@ Anon Hero:

the rotary woofer will not serve my purpose as it is primarily designed for indoor use.

my purpose is outdoor. basically mob dispersal. a non lethal weapon, if you please.

@lyn:

the effective range of this device would be around 300 feet. so i think (a very uneducated guess) that about 0.75 KW (about 1HP worth of power) should work.

i have come across some maths regarding Pipe Construction:

http://www.rwgiangiulio.com/math/

but it seems that it is a bit beyond my math skills.

i think i have to study a bit more!

Arkantos!

Yes, you can see the length of the pipe is going to be very, very long, even at 1/2 wavelength.

A 10 Hz signal needs a 17 meter pipe (55 feet). 5 Hz will be twice that length.

You could reduce those lengths by 2 if you used a pipe closed at one end, but the lengths are going to still be very long.

"the effective range of this device would be around 300 feet. so i think (a very uneducated guess) that about 0.75 KW (about 1HP worth of power) should work."

750 watts? Not even close I ran far more than that in my car sound system when I was in high school and that was enclosed in a small four door sedan.

If you want to disperse people at 300 feet with infrasonic waves you will need to be up in the megawatts range unless you can make it extremely directional and even then it's likely going to be needing a few KW's or more base power.

Humor him.

If he thinks it can be done with 1HP, he'll be harmless enough.

I humor everyone and let them think I am harmless!

As far as crowd control goes I have found giant robots and large construction machinery to be very effective.

It's sort of like when my one cat found a group of mice once. They all think they are real tuf and winning the fight until she bit the head off one. After that the rest gave up and run!

an aggravated/angry mob cannot be disbursed by classical music. difference - passive mob (loiters, squatters, and sitters) and an aggressive mob (armed and dangerous, politically motivated, etc, etc.)

Then you have to bring out the hard stuff - elevator music.

Actually, this has proven to be 100% effective...

I can't believe you would dis Slim Whitman (LOL).

WALOOB. The helicopter gunships used in the Vietnam war used Wagner's "Flight of the Valkyries" played at high volume.

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Infliction of pain is not my field.

Use a water hose.

Found some info here....

https://sites.google.com/site/appliedbiophysicsresearch/sound/infrasound/infrasound-design

The police use water cannon.

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http://www.spiegel.de/international/spiegel/the-weapon-of-sound-sonic-canon-gives-pirates-an-earful-a-385048.html

canon ≠ cannon

[Fault in the original article, even though Pachelbel's Canon might chase away some.]

--Editor Crankshaft

Maybe pirates don't like classical music

https://en.wikipedia.org/wiki/Canon_(music)

Ever think of building a pulse-jet? That would be very entertaining as well!

Self powered stimulation!!!

Find a place where these frequencies are generated. Record the sounds. Amplify. Play back the recordings to your mob. Note that the people dispersing the mob are going to be closest to the sound and thus most likely to be affected. Water cannon are used because they are directional and can be aimed at specific areas of the crowd to damp down trouble spots. (Sorry couldn't resist the pun). Sound is non-directional so would be a very blunt instrument. Sound is also not a non-destructive weapon. Burst ears drums are not repairable. Bursting the ear drums of innocent bystanders will get you vilified in the press - sued - fined - imprisoned of assault, in many places. Find out who would be willing to use it before your spend time and effort developing it.

The U.S. Army has such a device already perfected. It uses a high-technology flat panel transducer (speaker) to emit high energy infrasound. I am pretty sure the design is classified. Good luck making your own. Have your considered an odorant similar to vomitus (butyric, caproic acids, etc.) that when sprayed into a crowd would make them nauseated? OR you could just play a really scratchy record of Willie Nelson. (just kidding Willie).

If you insist on the infrasound approach do a patent search, then engineer your own distinctly different device and patent it as an upgrade/more efficient device. Try using a group of solenoids to move a membrace back and forth or something.

elevator music.... i have to research more on that...

infliction of pain is not the objective. the objective is non-violent dispersal.

if pain was the objective, i could have used guns, tear-gas, home made anti personnel mines, IEDs, ad infitum.

SolarEagle:
That site is quite informative, i have to read more.

Water Cannons cannot be used by me. requires costly equipments, and highly visible.

@RonClarke:
that is one beautiful device!
but USD30K is too much :)

@James Stewart:
I think your advice is the best one!

i will do some research in the patent angle, and get back to all of you in some time.

thanks to all of you!
Arkantos.

You wrote, "Water Cannons cannot be used by me. requires costly equipments, and highly visible."

Well, sub-sonic acoustics will be no different.

The physics are pretty simple. In order to get the high sound pressure levels (SPL) required for the job you will need some big @ss transducers to move all that air.

The formula for transducer element displacement is as follows:

p=Sd*Xmax*f^2*pi*rho0/(r*sqrt(2))

Where:

p = SPL in Pascals
Sd = transducer piston area in square meters
Xmax = the excursion of the piston in meters
f = frequency in Hz
rho0 = 1.2kg/m^3
r = Distance from the transducer to the measuring microphone

It is clear as frequency goes up the displacement and transducer piston area will go down for the same SPL.

This is why tweeters are so tiny with no visible movement of the cone, but sub woofers are large in diameter with deep cone excursion.

Going sub-sonic only increases the required piston area and its displacement to match the same sound pressure levels.

Bottom line, the lower in frequency you go, the more volume of air you must displace.

Next time you are at a large outdoor concert have a look at all the speakers the bands use and just multiply that by 5 to 10 times to get the low frequencies you need at the SPL required.

You will see why Slim Whitman with a megaphone might be a better choice.

I don't know if anyone has tried this, but one could record the sounds of various insects in the forest, and amplifly with low frequency shift, this would certainly unnerve if not make them head for the hills.

Have you considered the effect on Indian elephant population. You might have an adverse environmental concern, or might even cause whales to beach themselves if you are not careful.

Heck why not record elephant infrasound and amplify that? The stampeding elephants would make good riot control, if not for the problems with having to purchase scrapers to remove slow protestors from the street.

my good sir!

i am looking for practical and implementable ideas and solutions.

i am situated far from elephant reserves, and quite a distance from the open ocean. so i think i will not be hampering elephant and whale patterns any much.

Have you changed identities?

Infrasonic Horns / Whistle Can Be Manufactured?

Now I'm gone again.

Lyn:
i stumbled into your CR4 forums through rajagopal's thread, but i can assure you that i am not him. my command of the English language should be evident enough.

Well,

You intend to cause pain to people that you want to disperse. For reasons unknown to the forum.

Your intentions are suspect, not your language skills.

Build yourself a big 4 X 20 pushups per second modulated bellow. Depending on the design of the spout 90 db from 5 meters guaranteed.

Well, if you don't like my pulse jet idea, I think this answers your question pretty much to a T:

http://fiziks.net/Music%20Sample%20Chapter%20Seven/musicsamplechapter7.htm

I still think the pulse jet would be highly entertaining.