Build an Infrasonic Subwoofer





Introduction: Build an Infrasonic Subwoofer

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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?

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!!



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    94 Discussions

    how can i measure the frequency of the subwoofer because i need a specific frequency in my work

    1 reply

    Dayton audio DATS (dayton audio testing system).


    1 year ago

    has absolutely nothing todo with ulf. ulf ranges from .01 to to 19.5 hertz

    the numbers that currently matter are .8 to 19.2 hertz if your actualyl using ulf. if you want good sounds the lowest sound humans enjoy is 40 hrtz.

    1 reply

    Its the feeling of an earthquake that counts man. Less of the sound, more of the feel.

    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 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


    1 reply

    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).

    End product looks awesome! What amplifiers did you buy for driving those speakers? It seems like most amplifiers only go down to 20Hz... :/

    1 reply

    Most amplifiers only say they go down to 20hz, but in reality they go much lower. The chips just don't provide the low graphs in the datasheet, because in "practical" terms its not very useful. Your safest bet is to go on Aliexpress (or ebay) and build off a prebuilt typical board. Those have less filtering on them. They are also super cheap.

    Yea I don't know why people try to put on a show like that.. There are many many many car audio systems that easily produce sub 20hz frequencies up into the 140+db region and as long as proper hearing protection is worn, nothing bad happens lol. It is a nice subwoofer don't get me wrong, I love bigger than 18" subs, just because of the sheer beast-ness of them lol.

    2 replies

    Also car audio has cabin gain to help it, the smaller space makes it easier to pressurize the cabin. You put those car audio systems in a large room and they won't play as loud or as low.

    it's not lower than 20 and sine at the same time with the most of car speaker systems...all they do is frying the sound and what comes out is triangular waves

    Is it necessary to play the sound through amplifiers and if so why? I'm asking this because i dont know anything about producing infrasound sound.

    1 reply

    You need power to drive the speakers. They're rated for 1000w. You can drive them at lower power but they will only be quieter. In this sense you're not suppose to hear the sound, but if you're looking for that feeling that they talk about it giving you I assume it comes from the higher air pressure

    Im a noob and just interested, Is infrasound only playable by special speakers? or could basic earphones, or phone speakers already play infrasound?


    1 reply

    Even the speakers in this instructable isnt made to play below 22hz but they get them to. The key to this is that size matters, that's why they started with two 21" cones and to make the largest box for them that you can. Bigger the better. You want large displacement to pressurize the room for low frequencies. While shopping for drivers look for cone size but also for a lower FS parameter. Usually one comes with the other but I've seen some 12" speakers have the same fs as 15" or 18".

    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?

    4 replies

    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.