LOUD 11-13hz generator?

[Scodiddly]

Damn, I'm stuck trying to remember the name...

There was a company making subwoofers with a big horn cabinet and a clever sort of driver - it used an AC motor type of thing, and was able to convert rotary motion into push/pull speaker motion.

[Scodiddly]

Hey, why not just build something like a pulse jet that you run at 11 Hz? Just have a horn, and at the throat have an explosion every eleventh of a second. It would be plenty loud.

[Professor]

OK, let's cover some basics first.
The human range of hearing is roughly 20Hz to 20kHz.
The practical range of most large PA speakers is about 20Hz up to about 18kHz. It's very rare to get a sub that will go infrasonic.
There are amplifiers that can drive infrasonic signals, but they will draw LOTS of power and if the speaker can't handle it, all the power will simply be turned to heat, frying the driver. But many amps, expecially for live PA systems are fitted with roll-off equalizers to drop infrasonic and ultrasonic frequencies to protect the speakers.
Because of the limitations of human hearing, the limitations on the output electronics and the limitations of the speakers, most computers and synths cannot generate frequencies below 20Hz.
Oh, and frequencies below about 100Hz are non-directional, so if you are closer to the driver than your "target" you will be shitting first - even if you are 'behind' the speakers.

With all that said, let's look at what you really can do.
- Clean, high-end, solid-state amps, especially those designed for home hi-fi will usually be able to hit frequencies below 20Hz. I'm talking higher-end Adcoms, Bryston, Krell, Ayre, that sort of stuff. Best thing to do is to check the specs on the amp and to make sure they don't have a low roll-off.
- The easiest way to generate these low frequencies is with what are called 'difference tones'. Difference tones relate to the way multiple frequencies interact and 'comb filter' each other. The general idea is that if you create two tones, a third will be derived that is equal to the difference between the two frequencies. So, let's say you generate an A-220 Hz and an A-440 Hz. When the two combine they form a difference tone of 220 Hz, which reinforces the lower note in the octave. And if you generate an A-110 and an A-440, you will generate a 330 Hz combination tone which is actually the E a fourth below A-440. And it works for any two numbers, so if you generate a 200Hz tone and a 250Hz tone, you get a 50Hz combi-tone. If you generate a 100Hz tone and a 111Hz tone, you will get an 11Hz combi-tone.
- Now, that said, it is easy to hear a 100 hz tone, so you won't be very discreet. Also it is helpful if your tones are harmonics of the frequency you're tryinng to hit. So, generating a 22Hz tone and a 33Hz tone will not only give you an 11Hz tone, but it will reinforce the tone with it's first and second overtones, the octave and 5th.
But combination tones aren't going to function properly inside your computer or synth because of the limitations on the outputs. Your best solution is to generate two signals, route one to the left and one to the right and feed them to two speakers that will then deliver the 22 & 33Hz tones so they combine acoustically in the air to form the 11Hz combi-tone.
As a benefit to this approach, you also don't push the amps as hard, and have an easy time finding speakers that can cover the task.

- As for the directionality, that's a really tough one. The closest thing you might find is the Clark Synthesis 'Tactile Sound Transducers'. These move mass instead of air and so will only vibrate an object, not the air around it. You can mount them under a floor, under a deck, under a couch, hell you could bolt it onto a steel bridge and turn whatever object it is into a speaker. The beauty is that if you step off the deck or get up from the couch, the sound goes away - it is more felt than heard. I personally own two of these discs and have one mounted to the bottom of my couch running as the sub for my 5.1 system so I can get the bass for the movies, without disturbing the apartments next door or downstairs.

And now that you have lots of information to potentially harm yourself and others, I should add that you do so at your own risk. Keep in mind that while there is some truth to the myth of low, 'infrasonic' sounds effecting the human body, the frequencies are not so specific or well rounded as "11Hz = shit" and "13Hz = vibrating eye-balls". All bodies are slightly different and won't vibrate sympathetically at the same frequencies. There are also lot's of other organs that could be adversely affected by your attempts. While the bowels may well resonate at 11Hz, it's also possible that the heart does, or the pancreas, or the spleen, and you do risk 'missing the target' and causing more serious damage. Plus, as mentioned these devices are not acurate because bass gets everywhere, and while you might torment some enemy, you might also kill his neighbor's dog. So be safe.

And as a parting thought, consider using your new-found knowledge to make LOVE, not WAR. I've said for a while that I wanted to find the resonant frequency of the clitoris and install a generator and tactile sound tranducer in the passenger seat of my car so I could flip a switch and give any female passenger an instant orgasm - because after an experience like that, are they going to want anyone else driving them home from the bar? Maybe you could aim your creative energies in that direction.

-Jeremy

[extremenoiseterror]

Hey, why not just build something like a pulse jet that you run at 11 Hz? Just have a horn, and at the throat have an explosion every eleventh of a second. It would be plenty loud.

again, do you have a schematic?

if anyone knows the rough resonant frequencies of naughty bits, then that would indeed be an awesome thing to aim for

thanks a lot everyone! that last post was really helpful.

anyone else?

[housepig]

a few thoughts to add...

if you have any ham radio organizations near you, check with them and see if they do any swap meets (there's one coming up in Buffalo, MN, in the next month or so).

I got 2 solid-state oscillators and a tube oscillator for about $40 all together.

when I was first investigating the brown notes, a friend who used to build concert speaker rigs told me the best way to do it was to build a phased-array of tweeters - his explanation was if you built it right, you could use phase-cancellation to eliminate everything above 20hz. don't know if it works, as we never got that far in the design.

lastly, if you want to play around with some frequencies you can reproduce easily, try this - pick a frequency, generate a sine wave. add 13 or 16 or whatever <20 you want, generate that frequency as well. (ie. 300 & 313, 6000 and 6016, etc.)

play back both frequencies, loud. we did this in our practice space, using about 1,000 watts driving 600 & 615. didn't make us shit, but definitely made us uneasy - the actual tones were okay, but the beat-frequency of the difference was quite bothersome.

*edit - yep, professor beat me to it - the "difference tones" he was talking about.*

[extremenoiseterror]

jeezus i just cranked my monitors with 100hz and 115-112 hz... definately feel a bit naseous after that...

[Professor]

jeezus i just cranked my monitors with 100hz and 115-112 hz... definately feel a bit naseous after that...

Like I said, experiment at your own risk.
And of course, for best results you should use harmonics, even if they are higher up the chain. Using 88Hz and 99Hz to generate an 11Hz tone will be slightly more effective and should be less rough since they are not dissonant at the upper harmonics.

-J

[extremenoiseterror]

i wasnt expecting anythign less to be honest thankyou!

[joel hamilton]

My grandfather was at MIT during WWII and worked on LFO cannons. He also helped develop EMP cannons like the one "goldeneye" is based on. He saw a man vaporized (by accident) when he accidentaly grounded himself to some scaffolding and made contact with the tip of something set to discharge to ground. They had a FIELD full of oil caps connected to that thing the size of 50 gallon drums...He was 6 feet off the ground, and almost nothing but ash hit... Anyway...

The LFO cannon things were described to me as long waveguides made of very thick steel and concrete sandwiches basically, and they had a servo driven "cone" made of metal, that could produce some insane (a zillion Db i dunno... ) amount of energy. essentialy a tidal wave of air, and the rarefaction behind the compression cycle of the wave. They were blowing the windows out of specific target houses at a range of somethiing like half a mile. The amazing part is that it was SPECIFIC houses and targets. A bomb will blow windows out, but also kill anyone standing near it (duh). But this thing had such an elaborate waveguide system that it could be aimed! So amazing. I am pretty sure this technology lead to the belt/servo woofers of the early 50's that were referenced above, where it was acually a motor responding to the LF energy and "driving" the cone in and out.

Amazing stuff. LF technology is really interesting. Nikola Tesla was an amazing man all around, but the early studies of resonance points (including for the earth!) were really amazing. Me and Dave Sardy had a really long rant together about tesla one night. Really funny. Read about him. "man out of time" is one of my favorite books about the man, and I have almost all of them ever printed....

[psychicoctopus]

Hey, why not just build something like a pulse jet that you run at 11 Hz? Just have a horn, and at the throat have an explosion every eleventh of a second. It would be plenty loud.

Awesome idea. It would be dangerous, though. I wonder what the V-1 Flying Bomb sounded like?

here's some info on pulse jets, and a quote from the page.
http://home.earthlink.net/~famcaine/pul ... lseJet.htm

The pipe forms a simple acoustic resonator. The frequency is based then largely upon the speed of combustion and the local speed of sound in the pipe. The local speed of sound is dependant on the temperature of the gas column. As this is largely unknown and so is the combustion speed of the fuel-air charge it is very difficult to calculate the resonant frequency. Hence the pipe length of these model engines is usually found by trial and error. It is possible to calculate both the approximate valve frequency and pipe frequency but it?s too much for my simple web page!!

[cvanwinkle]

Acoustic Weapons - A Prospective Assessment


This one takes some time, but is very authoritative.

-C