Scary Sub-Audio Generator

Mainly as a laxative or emetic depending on which internal organs the low frequency resonance is targeted at.

ISTR there was some giant pea whistle design intended as a non lethal weapon for crowd control ~1970's? but it proved to be pretty hopeless.

On a sunny day (Tue, 25 Mar 2014 21:48:44 +1100) it happened snipped-for-privacy@frontier.com wrote in :

It says: 0bama 0bama 0bama

It shouldn't take that long. Looks like a big tube.. then driving and finding the low frequency resonance(s). I don't know what frequencies are most "scary".

George H.

Seventeen hurts!

Cheers

OK .. the seven meters of sewer pipe will be a bit ungainly. (I'm not sure if the lowest resonance will be at wavlength/2 or one fourth... Wavlength = speed / frequency ~ 300m/s / 17 Hz = 17 meters.)

George H.

Doesn't have to be straight...

Cheers

rubs the visceral tissues together, makes for severe nausea and pain. [not sure, but believe the mechanism is heating]

Recently, San Jose, CA PD proudly announced the purchase of a high energy low frequency generating crowd control device. Which is very surprising having lived there for over 30 years, SJ being the sleeping community for Silicon Valley, NEVER saw any need for 'crowd control' in all those years. Makes one wonder what EXACTLY is coming down the tubes that will require that much crowd control.

Closed end lowest frequency is 1/4 wavelength. Open end lowest frequency is 1/2 wavelength.

From only thinking about it, I'd say 3 to 4 Hz would be the most scarey, by producing a noticeable wuh, wuh, wuh sound. If you add some variable/random high frequency sizzle, with 1/f rolloff [dampening the really high frequencies] like muffled steam escaping, the mind will try to make a pattern out of the bruhaha and the listener may perceive 'talking' and/or moving about.

Yes, you can 'fold' the tube back and forth and you can get much length in a 2 meter wide stack. Envision a trumpet, or tuba.

Hmmm 1100ft/sec is around 335m/s, 1/4 wavelength of 3Hz would then be 28 m long, in 2 meter sections, need 14 sections

Take a closed tube that is 20mm in diameter, Approx 14 sections of 2m long would yield 3-4Hz. Stacked four across and 4up [the turns add length] would be only .4m by 2+m long by .4m tall, big, but not too big, or stand on end 1/2m m by 1/2m and 2+m tall. Plus, the wall of the tubes can be THIN! no need to make them 8mm thick, cost a fortune, and weigh a lot. If you got clever, you could make the outside of one tube be the 'inside' of another tube and so on, [clever use of baffles] saving half the material.

An air hose at a 'proper' angle across the tube's opening would be sufficient to excite the resonance. like blowing across a soda bottle.

Interesting project.

Uh, don't forget that low frequency is not well attenuated in the earth's atmosphere. Waves lapping on a shore create low frequency sound. Those sound pressure waves have been measured to go by an observer [around the earth] something like 7 times before dissipating.

On a sunny day (Tue, 25 Mar 2014 11:44:55 -0700) it happened RobertMacy wrote in :

I dunno if it was here, but some years ago there was a thread about electromagnetic low frequency activation. I have seen a demo once of a train rail segment with an electromagnet under it to drive it into resonance (was that at Philips Evoluon? cannot remember where. Anyways if you can 'activate' the steel in the concrete in a building, then you can make it swing IIRC, Now that would be _really_ scaring. Not much power needed, ...

In the Wikipedia example, they used a 7 meter tube with the speaker 2/3 of the way along. That would give 17Hz if the 2/3 section (4.7m) were closed at the end to be 1/4 wavelength - I guess the 1/3 section was the sound port and was for impedance matching.

Cheers

ISTR there's a way to project sound to appear as if it's coming from right beside the observer. You take 2 different ultrasonic signals the difference of which is inside the audio spectrum, amplify this difference signal and beam it towards your subject (say an unwanted cat pissing over your begonias) and bingo!

Yes, two separate ultrasonic beams - where they cross the combined energy is enough to heat the air to 'mix' the signals. I don't know how well it works, if at all, but I seem to recall it was something to do with Patriot Scientific, the one-time producers of the PSC1000 processor.

Cheers

This fan powered 8Hz sub-woofer is interesting. How does it work? Just a fan blowing into a box??

Does it have to do with the fan speed an/or the dimensions of the box?

This must relate to the effect that occurs in air conditioning ducts in offices, etc.

How would I get the specs to build one?

Richard Clarke

OK. Here is a bit more. it uses _variable pitch blades_.

That's a bit complex.

However, I think there should be a similar way to get a fixed single frequency with fixed blades.

Maybe bend two blades directly opposite each other to create turbulence and then adjust the rpm accordingly.

I like this approach because it eliminates the need for a resonant enclosure.

Would it be that simple, or does there need to be a constant change (ie. 8Hz cyclic) in the blade geometry itself?

Richard Clarke

I recall a long, long time ago I read a report about an old aero engine suspended from a hot air balloon that had two barn doors attached either side of it as resonators. Its output peaked at 17hz and gave onlookers a *seriously* bad time. I think several were killed in fact. Never been able to find anything about it on the net since, though.

I heard the effect from hvac. A simple speaker will be ineffective outdoors. Positioning in a room is critical. The movie earthquake used 16 hz.

Greg

On a sunny day (Tue, 25 Mar 2014 23:05:09 +0100) it happened Cursitor Doom wrote in :

Yes I am aware of that, and have experimented with high power ultrasound some years ago. AFAIK that effect you describe is based on the non-linearity of sound travelling in the skull, so 2 frequencies mix and you hear the difference frequency. But even a single carrier single source will scare away most small animals, they can hear it, dogs too.

police forces all over USA are militarising. be afaraid.

it sounds like you are describing a siren,

Replacing it with the need for large hardware.

a fan with symmetry 2 would need to turn at 60*17/2 = 510 rpm to produce 17 hz, that's pretty slow.