Build an Infrasonic Subwoofer

Intro: Build an Infrasonic Subwoofer

Infrasound is sound that is below your hearing threshold which general drops off at 20-30hz, i.e. lower than big booty bass. It can have a profound effect on your body, and should be experimented with carefully! Infrasound is used by the military as a weapon, or science to monitor earthquakes, whales ect.. In this instructable we will walk you through the process of building your own Infrasonic Subwoofer.

from wikipedia:

Infrasound is sound that is lower in frequency than 20 Hz (Hertz) or cycles per second, the "normal" limit of human hearing. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. The ear is the primary organ for sensing infrasound, but at higher levels it is possible to feel infrasound vibrations in various parts of the body.
The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz. This frequency range is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth, and also in ballistocardiography and seismocardiography to study the mechanics of the heart. Infrasound is characterized by an ability to cover long distances and get around obstacles with little dissipation.

STEP 1: Speaker Cones

First, You must find an appropriate speaker cones. We decide to build a double speaker system with a cone on each end of the enclosure. You could also build it with only one cone. When choosing a cone it should one that is 21" or 24" in diameter. We chose to use a Pyle 21" speaker. For good sound quality you should use a driver that has a QES of .38 + - 20%. We found Pyle speakers at J&R for only $250.00 which for such a low speaker is cheap!!

What is Qes?
http://www.bcae1.com/spboxad2.htm
http://en.wikipedia.org/wiki/Q_factor

STEP 2: Step Two

Select a wood type. We chose 18mm plywood. This is probably the best material. Avoid Chinese plywood if possible because it is not as consistant. Plywood is very sturdy and holds up well the air pressure produced by the large speaker cones. You need enough wood to make both the box and the bracing structure. Each wall should be braced to handle all the bass. You should try to make the box as big as you can. We built ours to be 30" x 30" x 70" It should NOT be square. This will greatly reduce its ability to produce infrasonic frequencies low enough.

STEP 3: Bigger the Case

Now build the main box. As mentioned, the bigger the better. Cut all the sides to the proper dimension, and plan out how you will create support system within the box using braces. THere is a lot of pressure exerted on the walls and the stronger the walls are the more efficiently the subwoofer will be able to create such low frequencies.
We used a combination of wood glue, and as few screws as possible. The box should be airtight so each screw increases the possibility of air leaks and rattling. Then we used Kwik Seal to seal all of the corners and potential air leaks.

STEP 4: Installation

Install the speakers into the enclosure. Make sure the mounting is solid. Next install the bracing. The bracing should be on all sides of the enclosure and should be glued in using would glue. We created to braces from speaker to speaker, from side wall to side wall, and from bottom to top, and then used clamps to hold everything in place while the wood glue set overnight.

STEP 5: Electronics + Test, Test, Test

Test the cone to make sure it works. We connected the cone up to a 1000 watt amplifier and ran sine tones through it in order to confirm that it was working properly. Sometimes when speakers are shipped they are DOA ( dead on arrival), as was our case with one of our speakers. In order to break the cone in we ran a sine tone through ours  for 24 hours. 
You will want to find powerful amplifiers. We chose two livesound amplifiers. Each channel was 500watt amplifier and switch to serial mode to which collectively made one amplifier a mono 1000 watt amplifier.
Once the cone works, then solder together the thick gauge audio cable, connect it from the speaker to a 2 channel Speakon wall-mount connector which we will insert into the wall of the speaker. This will enable you to unplug your speaker but also insert it into a larger live sound system. Then solder on male speakon connecters to thick audio cable and then connect this to your amplifier and add the compatible connector for your amplifier. For us, we used balanced 1/4" connectors.
Test all the wiring by running sine tones through the input to make sure all of your connections wokr.

STEP 6: Cabling

Now once you have tested and solder together your cabling install l all the cabling, solder the speakers, cut holes to the exact size of the speakon jacks + corresponding panel. Then test all the wiring by running sine tones through the input again. At this point you may want to add wooden or metal handles to the side of the Subwoofer because its heavy and awkward to lift!! Ours was close to 70lbs. 

STEP 7: Seal the Connections

Now you need to seal all possible air leaks in your subwoofer. Seal all joints and corners with silicon or Qwik Seal. Also put apoxy on all connections on the subwoofer prevent connections from loosing. You don't want to have to open up the Subwoofer again because of a loose connections!

STEP 8: Step 8

Put the lid on the finished unit and test one last time. Seal all of the seems with silicon as you screw the lid on. If you plan on staining or painting it you will want to cover the cones with plastic to protect them.

STEP 9: Step 9

Next, stain the wood and repeat again to get a rich color. If you would like to take the project one step further you can add 100 grams of bondo to the cone you can lower the frequency. To half the resonance double the cones mass. The Pyle's resonant frequency is 22 hz. We decided not to do this but it is certainly worth a try.

STEP 10: Rock

Next crank it up but be slow about it to see how you react to the low frequency. A 15hz sine tone is a good start or even better a sliding tone from 60hz down to 10hz and then back up. From this you will be able to tell when your body feels it intensely and also how low the speaker will be able to reproduce a frequency. Enjoy but be careful!!

Comments

[atpmarcus]

i have no background in any of this i have 3 questions:

1. can anybody suggest a generator that can produce 1.05hz for the purpose of producing HGH in the pituitary gland while i sleep

2.can anybody give me some advice via private communication on how to go about making sub audible frequencys

3.is a frequency the same as a sound i.e if i was to use a online tone generator is it the same and if so is simply turing up the volume while it is running make a difference.

I AM NOT A SOUND TECHNICIAN I AM A HEALTH FREAK so dont go judging guys! lol

thanks

[JoesphanL]

Just don't. 1.05hz (seems like you need accuracy) will be very hard to generate, not to mention accurately. You would need a speaker the size of your house. The lower the frequency the lower the energy, therefore the more power you would need. The most effective way to generate 1.05hz is to set up a robot punching you every 1 second (I'm not joking - 1 hz = 1 wave cycle per second).

[MardyMcFly]

Ha! I was wondering the same thing about producing 3Hz. Speaker would be very big I'm guessing.

[guzziebrad]

I noticed that you added two driver's to the enclosure at both ends. This is a compounded Isobaric box, so the other woofer must be wired out if phase in order for this to work. The Isobaric enclosure should use half of the Vas(volume) for the box or use the same volume or bigger to get deeper bass. I was also wondering why you didn't choose a EBS(Extended Bass Shelf) type ported enclosure tuned to 15-20hz, as it is much louder than a sealed box with less cone motion due to porting the box. Overall I loved the design of this box.

[rfoster4]

Were you able to discover the elusive "brown note"? :)

[rallen71366]

When I was in the service (many moons ago) one of my Commo buddies commented that he had done some research like that, but they didn't use normal speakers with a diaphragm. They were spraying propane into the air and detonating it at a rapid speed. They were using a fuel/air explosion as a speaker!

He also said that they had to wear depends. That assignment was the sh*t. :-)

[ttitus]

The Mythbusters did a whole episode on "The Brown Note", with the conclusion being that it didn't exist. Although some tones will make you feel a bit dizzy. I get that way when I listen to bi-naural beats too long. Air explosions though...I don't remember them testing that. I cant imagine that a short blast of frequency, whatever it may be, could make someone shat themselves.

[Hiwatt Dr504]

Im probably wrong but didnt mythbusters use a pulsed wave versus a continuous way. I too have experimented bunaural beats. Did you uae audio or audio synced to visual stimului? (I used cheap goggles, mounted my leds). Im a fat old man now but the software i using at the time was i believe was calked wavelab s (?). Even included presents and DETAILED INSTRUCTIONS on how to craft and encode your very own binural beats....im going to hunt around for the software. Im sure i saved it.
Man sorry I just realied I have may hijacked this thread. Im a idiot. Sorry again.

[whoiswhere]

Should've kept up the research & published it, may need your help & insight in the near future, never be sorry for living.

[MarkK23]

University of Wisconsin in Madison built a 6 foot subwoofer that hits it.
http://soundworkscollection.com/news/the-biggest-subwoofer-in-the-world

[rallen71366]

Ever been on the firing line when they cut loose with the heavy weapons? A .50 BMG firing shakes you to your bones. Standing too close to REAL heavy weapons (like a Patriot Missile, or Naval cannon) can kill you just from the shock wave (a Patriot is going Mach 6 when it clears the launch tube). Loosening your bowels without killing you is more a matter of control, than power.

[katesisco]

I would also like to know if you can build an infrasound detector to monitor hobby drones?

[whoiswhere]

I would also like like to know this.
One day I'll have them manufactured.

[bradhouser]

You don't say if the speakers should be in phase with each other or out of phase. I would think at these low frequencies, with a sealed box, you would want them out of phase, so that one is going in, while the other is going out and vice versa. That would keep the air pressure in the box constant. Or am I missing something?

[mgann1]

Wow what are these people saying..

They need to be in phase, and it doesn't matter what side the speakers are mounted. Pressure inside the box is a good thing and when he says "no longer compresses air" he isn't just talking about inside the box, this is true for outside the box too. Sound is compressed air, no longer compressing the air is no longer making sound. You want to pressurize the room. That's probably why it effects your body too.

If you wanted to put them out of phase you would have to separate the two chambers so that each speaker can pressurize when it needs. Phase does change with distance, but the frequencies are so low that they will not be out of phase being on opposite sides of the box, this would only be true for higher frequencies. I'll bet that the designer of this box put the drivers on each side of the box to limit any movement that might occur from these large diaphragms moving, if you put the drivers on the same face the box might get pushed around or vibrate distorting the "silence" of the subsonic frequencies. Honestly I would look into designing this as a ported box instead of sealed to get more decibels out of the low frequencies, that's a post for another day. If you keep it sealed though, larger the box the better the low frequency response but you put the drivers at risk, they're only made to reach 22hz or so. Also would recommend applying resin to the cone as they suggested to lower the resonant frequency.

Unless maybe you guys were thinking of reversing the polarity and playing each driver at a different frequency? You can use the frequency cancellation to your advantage, but you must separate each driver into its own chamber. Build this box with a wall in the middle and reverse the polarity as you thought. Then play each driver at different, but at their rated and loud, frequencies they will cancel out some of the waves but not all leaving you with the difference. Hopefully high decibel low frequency waves will be left. If your resonant frequency with the sealed box is 54hz that means the box will play those frequencies the loudest. So with reversed polarity try playing one speaker at 50hz while the other at 60hz hopefully giving you a 10hz overall sound. Actual results might vary, try different tones.

[whoiswhere]

They'll knock on your door soon, you know too much lol.
What would happen if you attached that 10Hz to a carrier frequency...

[Offroadie]

If they were out of phase they would cancel out and you would have no bass.

[keriksen1]

No they won't, since they are facing opposite directions.

[Offroadie]

You guys need a lesson in acoustics...

[bradhouser]

Offroadie: Your reply is not very informative. Which part of your acoustics training can you share with the rest of us to better explain your position?

Not being a sound engineer, my understanding is limited. So I welcome clarification based on sound (pun intended) principles.

This is what I think is happening.

In a normal stereo setting, when the woofers are out of phase they tend to cancel each other, an effect that is increased with lower frequencies.

However, this scenario is different. For one, they are not in separate boxes, and they are pointing in opposite directions. Add the fact that the box is sealed, keeping them in phase causes both cones to move in and out together. This increases and decreases the pressure of the air in the box. Being sealed with no port to the outside, this would tend to dampen the sound, making it quieter.

If the two speakers are anti-phase, one moves in while the other moves out, keeping the pressure on the internal air the same. Wouldn't that tend to boost the volume instead of reducing it?