800watt, 12' Long 16" Diameter Bass Cannon.

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Intro: 800watt, 12' Long 16" Diameter Bass Cannon.

I built this Bass cannon, based on the Bose WaveCanon. Its a resonating tube driven by an internal sub woofer.
Basically a Giant Sub Woofer.

I built this as part of an audio visual project for Burning Man 2007. Using a tube with the driver mounted inside it resonates much like a church pipe organ within a specific frequency range. Hopefully the bass frequency range.

Called "Rare Angles" it comprises 12' of cardboard Sonotube as used by concreters to form columns. Its cheap, easy to work with and rigid enough to use for this application. You can get it at a concrete supplier.

As soon as I laid eyes on what Holly and team over at positron.org did, I knew it was just a matter of time, and any flimsy excuse to build my own.

This Bass Cannon is designed very basically. I was able to buy a 12' length of 16" sonotube. The driver has to be placed exactly 1/4 the distance down the full length of the tube or 3 feet.

From what I can gather from research, the longer the tube length will raise your resonant frequency. I figured my resonant frequency was about 30Hz. I am probably wrong. I did the calc a while ago so can't be sure how I arrived there.. It wasn't too loud on the "test fire" audio sweep, but a neighbour from 2 doors down, certainly heard it and came running down the street.. "Are you making that noise?!"
Maybe me sitting on my deck with a giant carboard tube and earmuffs on gave me away.


Step 1: Ingredients

Materials;
1 x sub woofer 12 or 15" depending on the sise of tube you want 15" in this case
1 x length of sonotube slightly larger than your sub woofer diameter 16" in this case
1 x sheet of 3/4" ply
wood screws
glue / sealant (sikaflex works well)

Tools;
Router
Circle cutting jig for router
3/4" spade bit
Drill
circular saw or jig saw.

Step 2: Cut the Sonotube Into Two Pieces

Work begins by cutting the sonotube. The sub woofer mounting flanges need to meet 1/4 of the way down the length of the tube. For me and my 12' long piece thats 3' along.
Do do this accurately I measured with a large sqaure 3' from one of the ends at about 6 points around the circumference of the tube. I then wrapped a piece of masking tape around, making sure one edge of the tape passed through the points I'd just marked. I used this as a guide for the jigsaw. I drilled a starter hole to get the jig saw blade in then went at it! Afterwards I removed the tape. The cut will be kinda fury but that ok, this will be concealed inside the flanges.
I didnt take a photo of this step so I drew it. See the diagram with the light grey lines being my 3'
long marks then the dark band being the tape which i used as a guide to cut the tube squarely.


Step 3: Cut the Sub Woofer Mounting Flanges

The flanges are used to mount the driver and also to couple the two tube sections. The following description is kinda general as if you make one of these, your dimensions will be different to match your tube and your driver.

I used a circle cutting jig, consisting of a strip of ply with the router mounted on one end. This was nailed to the centre of a board of 1/2" ply which would become the first flange. I began to cut out a the diskusing a 1/4" bit at 10" radius to give a 20" flange disk.
Starting from the outside of the flange in, I cut out the perimeter.
Then cut a 1/4" wide groove 1/4" deep at 8" radius for the top half of the sonotube to sit in. This is where the cut is concealed, and also provides a little extra surface for the adhesive to bond and create an airtight seal.
Then I flipped the disk over and cut a 10mm deep groove at 7.5" (I love changing between metric and imperial) then another 2 at the same depth inside that, which makes a shoulder for the driver to sit in.
The next cut is just inside the last to go all the way through to remove the centre section.

The second flange was identical.

Again I have drawn a cross section of the flange piece.

I then clamped the two flanges together and drilled 4 x 3/4" holes with a spade bit for the bolts to hold the two flanges together. When drilling through ply (or any timer) with a spade bit, keep an eye on the underside and when the point of the bit starts to emerge flip the piece over and finish the hole from the other side. This will prevent tear outs and give a nice clean hole..

Step 4: Install the Sub Woofer.

As seen in the photo, the sub woofer faces downward. It can go either way around without too much issue..
I screwed the sub woofer securley onto the lower flange, added the second flange ontop then added the second length of sonotube.

I worried that the wind would possibly snap the tube out of the 1/4" grooves so re enforced the tubes with ply triangles made from scraps.

I used marine Sikaflex to glue the tube into the grooves, then screwed the ply rib triangles from inside the sonotube. I used more sikaflex to bead between all the support ribs. It ended extremely strong.

I did have to drill a hole through the lower flange to let the sub woofer cable pass through. This was an oversight. In future I'd run the cable to the sonotube wall and pass through to lugs on the outside.

Step 5: Wire Up and Test.

Thats the majority of the work done!

I made a stand for the whole thing to stand on, but this was an error. The resistance of the bass cannon standing close to the ground created back pressures that introduced some unwanted characteristics.. nasty resonances that caused humming and nasty distortions.

This should always be mounted with plenty of room beyond either end of the tube.

Finally is a pic of the bass cannon in situ on the playa with the remainder of the paraphenalia attached..

See a full description here;
http://fle33.com/public/content/view/5/2/

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120 Discussions

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thelandlord

9 years ago on Introduction

There's an easy way to make people very ill without needing tubes big enough to resonate right down there... make two tubes, one tuned for about 20HZ, another for about 27HZ. Feed your stereo amplifier with the matching tones on each channel.

Aim them toe-in to make the 'beams' cross a safe distance away, and turn up the steam... where the two soundfronts meet, they'll beat against each other and that'll make two tones other than the ones you've put in... 20+27=47Hz, and 27-20=7Hz.

47Hz you will hear as a very loud hum, slightly flat of a mains hum.
7Hz, you will not hear at all (unless you're an elephant) however anybody unfortunate enough to encounter the 'sweet spot' will soon feel very poorly indeed as their internals begin to resonate - think extremely seasick, only so much worse - they'll pray for death to come quickly. :-)

If you have a bad neighbour, this could completely ruin their night. ;-)

15 replies
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sinbad13thelandlord

Reply 1 year ago

How do you determine the sweet spot? Lets say my feed room at the end of a two hundred foot barn.

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thelandlordgrungehead

Reply 9 years ago on Introduction

Originally, by spending too much time with 'musical theatre' types - there was a musical called 'Time' written by Dave Clark that was quite popular in the UK a while ago, and it used something similar as a special effect. They needed the audience to feel 'space-sick' during a rocket-launch, and clearly couldn't physically pick the auditorium up and shake it... so somebody had the idea of beating a 20Hz tone against a 17Hz one through the PA system... not loud enough to risk an 'accidental brown' if somebody was a little weak in that department (google 'Ben Folds' and 'Improv Everywhere' for one of the best pranks ever...) but enough to shake the room a bit and make everybody feel 'nervous' without quite understanding why. Of course, then you have to 'experiment', don't you? ;-)

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ilpugthelandlord

Reply 6 years ago on Introduction

I suppose you are talking about infrasonics... Look that up on this site, someone made a woofer that does it.

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fwaterthelandlord

Reply 9 years ago on Introduction

WAY more complicated than that. One minus the other and one plus the other is not what you end up with. You constructive and destructive interference, and a great deal of cancellation and diminished output. You'll get one modulated tone, not two seperate ones.

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frollardthelandlord

Reply 9 years ago on Introduction

I was always curious about the brown note...they said it was busted on mythbusters, but I dont 100% trust those guys. It's crazy neat either way.

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jhuddleston

7 years ago on Introduction

i started reading about this last night, i was so amazed about it. So this morning i took a small surround speaker to see what i could make on a small scale. I used four foot of 2 1/2 in. pvc pipe, and i was blown away cause it hits and sounds just as good as my surround system sub woofer. I will defiantly have to go bigger and see what i can accomplish, i would like to thank you guys for all the info you have said here.

1 reply

it's called a transmission line speaker, it's made to reduce the low end roll off that a lot of speaker cabinets will give to a loudspeaker, try quarter-wave dot com to learn more about them if you'd like.

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Hogbroom

5 years ago on Step 5

So...can I play dubstep at the Talent Show this year with this thing, or is the frequency off?