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Discussion Starter · #1 · (Edited)
Hey yall! I am attempting to create a speaker system for my engineering teacher's haunted yard that he holds every year. Essentially, I'll program an Arduino board to play a consistent sound at 19hz, have that hooked up to an amp and have the amp hooked up to 1 or 2 subwoofers placed throughout the yard. If you don't know, 19hz is just below human hearing so while you cant hear anything, you can still feel the vibrations and it makes you feel anxious / on edge.
I've got the programming down I'm just wondering if anyone here has tried something like this before? and if so, how did you do it/ what gear did you use?
Budget isn't really an issue as it's not my money so I don't care. I just need a good speaker and amp that can go down that low.

TL;DR need amp/speaker to play 19hz sound, any recommendations?


Edit: thanks for the gold, kind stranger!
 

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I have heard of this 'fear frequency' and seems like I might have tried it a dozen years ago, or more. A couple of point that seemed to occur to me which might be useful.

First, 19Hz isn't really sound that you can hear, and isn't really sound that subwoofers can create in any normal sense. It is more of air rushing back and forth at a fairly fast pace. In fact, the best way to produce it is typically a 'rotary subwoofer' which is almost literally a fan with pulsing blades. Your arduino can do a 19Hz frequency no problem, but without some modest programming/filtering, it's going to be a square wave. All of the resonance / sideband of a square wave will kill the effect of a 'pure' 19Hz frequency...sort of like having a bunch of unfiltered light with a UV blacklight. You might google rotary subwoofer, infrasound, infrasound subwoofer, etc to get a better idea of what you're up against, and some ideas to build big resonance boxes to help boost the ultra low end frequencies. But given that subwoofers have a hard time making the sound, amps have a hard time boosting it, and it is going to attenuate quite rapidly in open air, definitely an up hill battle!

Secondly is the effect. Don't expect to play this note and suddenly everyone freaks out and goes running for their lives. It's not really like that at all. If anything (and I do mean if anything) it is sort of like a subtle 'suggestion' to already existing circumstances. Like if someone was already in a dark room with odd sounds / mice, rats, etc, then maybe this might add to that uneasy feeling. But if you're walking around the house or setting around watching TV and suddenly "hummmmmm"...19Hz... you probably won't even notice.

Anyway, hope this helps. Let us know how the progress goes!
 

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For all the reasons stated above, generating low frequency effects can be problematic. For outdoor use, if you can't muster something in the 18" / 1.5k - 2k watt (or larger) range it might not be worth it.

Although a smaller sub might not be able to physically generate a 19Hz wave, what you do wind up doing is creating some vibrations in the local environment which can be quite unnerving. Low frequency waves are very long so you need to place the sub quite a ways away from the scene for the best effect. A 19Hz wave is close to 60ft long. I have an 18" sub that I use with a lightning simulator and the best low end is usually one block over and quite a few houses away. When you are closer you experience more environmental vibration than the <30Hz sound, but it's still effective.

What can often be an easy effect to pull off, and quite often creepier, is creating a variably out of phase sound field that people walk through. Find a creepy low end drone that you like the sound of, mix in a low sine wave with Audacity or REAPER if it needs so more low end, and make it a mono file. Make a copy of that mono file and flip the phase in your DAW of choice and save it. Now either play each mono file to seperate amp/speaker runs, or create a stereo file with one track panned hard left and one track hard right. When you play this file(s) with a very wide stereo image, say either edge of the yard, you will get some very weird out of phase effects. Out of phase low end is very unnerving and will give you what you're looking for without needing to generate an actual very low frequency sound.

EIther way it's still fun.
 

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Good points. I was doing a bit more searching and came across this:


Seems this researcher linked his fear (of working alone at night in a lab [well, yeah!!]) and ultimately tracked it to a vent fan which was putting out "19Hz standing waves".

That got me thinking a bit and doing some quick math ...19Hz (cycles per second) x 60 seconds = 1140 cycles per minute. ...and it just so happens that 1140 rpm is a pretty popular motor speed.


It probably happened that this researcher had an 1140 rpm vent fan in the lab. Possibly you could do something similar... maybe an 1140 rpm motor with an offset weight to create 19Hz vibration or even a crank arm to drive some sort of diaphragm. The benefit is that you don't need to reproduce a range of frequencies, just this monotone vibration, but all the standard 'hard to produce' admonishment still applies.
 

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Is this the best use of your time and energy? Was it an assignment? There are lots of things you can do with sounds that can be heard. I remember an old movie called Them…about ants. That sound was the most memorable thing about the giant ants. In Jaws, the shark is rarely seen…but that beating music scared the bajesus outta us.
 

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It probably happened that this researcher had an 1140 rpm vent fan in the lab. Possibly you could do something similar... maybe an 1140 rpm motor with an offset weight to create 19Hz vibration or even a crank arm to drive some sort of diaphragm. The benefit is that you don't need to reproduce a range of frequencies, just this monotone vibration, but all the standard 'hard to produce' admonishment still applies.
You're inspired me to make a single frequncy rotary subwoof to try. This guy made his own —


If you don't try to make this a 'real' subwoofer, a simple shaft collar in place of the voice coil makes this an almost trivial project. Just move the sahft collar to angle the blades to produce the freqeuncy you're going for and power it up. You could also skip the variable frequncy drive and three phase motor. Definitely going to try.
 

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Interesting start. I think he should use stiff metal for the blades - if they are flopping around, then that is just wasted movement. Interesting use of the 'swash plate' and RC helicopter parts, though! Obviously anything which could make that system 'tighter' would reduce the rattling and increase fidelity. Also note that he basically uses two rooms as 'resonance cavities' That probably boosts the effect quite a bit and obviously something that is lost outside.
 

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Discussion Starter · #9 ·
Definitely gonna look into the rotary subwoofer. Looks like a pretty easy physical adaptation of the much more complicated project I have in my head... I didn't even think about the length of the wave. I'll have to talk with the teach to figure out the best placement for this. Thanks!
 
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