Speaker Related Projects

   2-Way Ribbon Tweeter Speakers
(Vifa and Pioneer. May-2020)

   Transmission Line Speakers
(Aborted attempt at a TL. September-2012)

   Acoustic Research AR-4x Rehab
(Rehab of a garage sale find. January-2016)

   Infinity RS-4000 Rehab
(Rehab of a garage sale find. June-2015)

(A tall, thin, upwards firing omnidirectional speaker. May-2010)

(A powered subwoofer using a 12" driver and 15" passive radiator. Jan-2010)

(A computer speaker; redux. December-2005)

(A computer speaker in a light canister. Jan-2005)

(10" vented subwoofer in a cardboard tube, powered by a Parapix amp. May-1999)

   MTM Center Channel Speaker
(A Madisound design. Nov-1997)

   2-way Surround Speakers
(5" woofer and 1" tweeter. July 1997)

   3-piece mini system
(6" DVC bass module mated to 4" car speaker. June 1997)

   3-way Vented Floorstanding Speaker
(vented 10" woofer, 5" mid and 1" tweeter in a 4 ft tower. Summer 1995)

   NHT1259 Subwoofer
(A 12" woofer in a sealed architectural pedestal. Winter 1994-95)

   Inexpensive Speaker Stands
(Particle board, sand and spray paint. Fall 1994)

   2-way satellite
(6.5" woofer and 1" tweeter. Summer/Fall 1994)

Audio Electronics Related Projects

  900 MHz Audio Receiver
(Better use for bad headphones. Jan-2008)

  Buster - A Simple Guitar Amp
(Perfect for the beginner. Jan-2010)

  A PC-based Audio Console
(Use a PC to play tunes. Jan-2010)

  LM-12 Amp
(Bridged LM-12 opamps. Aug-2003)

(A CD player and FM tuner from spare computer parts. Oct-2002)

   Quad 2000 4-Channel Amp
(Premade modules by Marantz. May-1998)

   Zen Amp and Bride of Zen Preamp
(by Nelson Pass. Apr-1997)


  Using Wood in Speakers FAQ
(Work in progress)

   MDF FAQ for speaker builders

   Woodworking Tools for the DYIer
(HomeTheaterHiFi.com Oct-1998)

  Some Thoughts on Cabinet Finished for DIY Speakers

   Large Grills Made Easy

   Some Parts Suppliers

Other Useful Stuff

   DIY Audio Related URLs

  Veneering Primer
(by Keith Lahteine)

   How to get a Black Piano Finish
(by DYI Loudspeaker List members)

   Sonotube FAQ
(by Gordon McGill)

   Excerpts from the Bass List
(Oldies but Goodies)

DIY Loudspeaker List

  DIY Loudspeaker List Archives

Sonotube FAQ

By Gordon McGill

Updated 22-June-2002


Q: What is Sonotube ?

Sonotube is the commercial name for a paper tube used for forming concrete. It is used when builders want to make a concrete pillar. They set up this paper tube (comes in diameters from 8 inches to 56 inches and in lengths to about 18 feet or so) and pour concrete into it and let it dry. When the concrete is dry, they strip the paper tube off, and voila, instant pillar.

Q: Why is Sonotube good for Speaker enclosures ?

Strong. A tube is a very strong shape for resisting internal pressures. Coincidentally, this makes it ideal for use as a speaker enclosure. When building speakers, wall strength is an important consideration, especially in subwoofer cabinets where internal pressures are relatively high.

Cheap. A Sonotube is very inexpensive when compared to the cost of the wood required for a conventional speaker cabinet. A sonotube enclosure will probably be at least 1/4 the cost of a conventional wood speaker cabinet.

Easy to Build. A cabinet using Sonotube needs a top plate and a bottom plate (to seal either end of the tube) and that's it. A conventional cabinet requires much more exacting woodwork and much more time, wood, and effort (not to mention weight!) to get a cabinet as strong as a Sonotube enclosure.

Q: What are its disadvantages ?

They are ugly. If you put up something resembling a missile silo in your livingroom, your spouse or significant other may object. You can cover them with paint or with a big black cloth sock slid over the top. On the other hand, you could veneer them, or just paint them red with a big "radioactive" sign on the front and let friends draw their own conclusions. So, this is the drawback, they are hard to hide or make decent looking. Some builders have disguised Sonotube enclosures as plant stands or as Greek columns. If you can overcome the nasty look, you are all set.

Q: How thick does the tube have to be ? It looks too thin to be effective !

The tube walls don't have to be very thick at all. Sonotube walls are usually no more 1/4 inch thick. Their shape provide amazing shape - more than enough to hold the weight of concrete without deforming.

Doug Purl posted the following on the DIY Loudspeaker list on 12-January-2001 :

"Once again a thread on tubes as speaker enclosures has appeared. And once again all the posters have been laboring under a misapprehension of how the thing works. Folks, the walls don't flex. You don't have to lard them up with damping. It is precisely the reason that pipes conducting fluids and gasses under pressure are round and not square.

If you stood inside a garbage can and pushed your arms outwards the walls would flex. But if you had an infinite number of arms and pushed outwards equally at every point, the can would not flex. The net effect would be to try to stretch the walls rather than bend them.

Boxes flex because their panels have different resistance to flexure at different points. Tubes have the same resistance to flexure at every point, and receive identical pressure at every point."

Q: How is a Sonotube used as a speaker enclosure ?

In constructing a Sonotube enclosure, the first decision you have to make, is the location of the drivers in the tube. Will the driver(s) be mounted in the ends firing up or down? Or will they be mounted in the side of the tube firing out (perpendicular to axis of tube) ?

Mounting in End of Tube. This method is the most common for subwoofer cabinets. Building a driver into the side is much more difficult, and the frequencies below 80 Hz are omnidirectional, (mounting a subwoofer driver facing down or up, does not have much effect on the sound) so most people building with Sonotube just mount them in the end caps.

To mount a driver in the ends of Sonotube, it is first necessary to fabricate the end plugs. The plugs each generally consist of two circular layers of MDF. One of the circles is cut to the inside diameter of the tube so that it will just barely fit and the top layer is cut to the outside diameter of the tube so that it sits on top and is flush all the way around the tube. The layers are glued together and glued into the tube, perhaps with epoxy. Make sure to fill any cracks or gaps with epoxy or silicone caulk. Now that you have one endcap, repeat and make another one.

Next, measure out the hole(s) for the driver in one of the end caps. Try to leave space between the drivers so that the endcap does not become too weak. Now that you have fabricated the endcaps and cut out the driver holes, you are just about done. The next part of construction is the addition of threaded rod(s) to the enclosure to maintain tension between the endcaps. Here, you want to use some reasonably stiff rod, perhaps 1/2" or so and run 1 (for aSonotube to 12" dia.), 2 (to 16-18" dia.) 3-4 (to 24-30" dia.) or more if your Sonotube is even larger. The idea here is to put holes in the endcaps in roughly the same place and then drop the rod in and tighten at each end with nuts and washers. Some people have used 3-4 rods in their enclosures, and cut the threaded rod long enough to act as feet on the bottom!

Well, other than adding some stuffing (pillow stuffing (Dacron) or fibreglass insulation) to damp out standing waves, you are pretty much done. You can drill the holes for wiring the driver, bolt it into the endcaps and fire it up! Of course, your Sonotube looks terrible, it still has its waxy coating and is still that nasty brown colour with the construction company's lettering on it. Ah well, we'll take care of the finishing a little bit later.

Q: What about Standing Waves ?

Stuffing to Get rid of Standing Waves. We will use either the fluffy pillow stuffing (sold around here, (Toronto, Ont.) as Polyester Fiberfill) or the standard pink fiberglass insulation.

How to calculate Freq of Standing waves. Any enclosure will have standing waves associated with it's shape and size. These standing waves will exist between to parallel surfaces. For instance, a sphere will have one standing wave, because all points are perpendicular to a line drawn through the centre. A tube enclosure will have two, one between the walls of the tube and one between the endwalls. A rectangular enclosure will have three, top to bottom, right to left, and back to front. To caculate the frequency of the standing wave that will exist between two points use this equation:

Wavelength = speed of sound/ frequency of sound

W = v / f

v = 340 meters/second

How to Reduce the effect of These Standing Waves. These standing waves are harmful to the sound because they influence the cone making it vibrate in the absence of a signal. That's the short explanation. The long explanation involves resonant frequencies.

Resonant Frequencies. A standing wave is actually a type of resonant frequency. A resonant frequency will exist for any panel you may build. Each material has it's own resonant frequency as well. So, if a signal of all frequencies is put into the space or panel or material, and we measure the loudest frequencies coming out of it, those will be the resonant frequencies.

The general strategy used when dealing with resonances is:

break the resonant frequencies into many resonant frequencies that are much smaller. You see, when two resonant frequencies are the same, they add to each other, doubling the power at that frequency. When the freq. are different, the power cannot sum and influences the response we hear less. In a speaker box, this can be done by using non-parallel interior walls and bracing the panels so that no two unbraced areas of the panels have the same area 2) Reduce the energy of the standing wave. This is usually done with stuffing. The stuffing may line the walls, but is more effective if suspended few inches off the walls. This is the primary method to be used in our Sonotube enclosures. 3) Make the enclosure walls lossy.

How to nullify Standing waves.

<Not written yet>

Q: Can I use them for other speaker enclosures? (not just subs?)

<Not written yet>

Q: How do I contact the author of this FAQ ?

Send all questions, comments, and corrections to this site - see the About page.

Reports from Builders

(permission to post this granted by original author)

From: Szewczyk, Robert
Date: Thu, 3 Dec 1998 13:53:46 -0600

I read your instructions on building a subwoofer using SonoTube. I have been building subs with this medium for a bit over a year. But my method to assembly is a bit stronger and perhaps simpler.

I have only used the 12" and 20" tubes. I prefer the 20" tubes because their sides are a bit over 1/4" thick. I use 3/4" MDF throughout.

For the bottom (this is where I mount the 12" driver, the 4" flared port, and the 5-way binding post cup):

  1. I cut two 20" diameter disks (I use 2 because this is the drivers mounting flange and should be strong). I glue them together and cut out the required holes when the glue has dried.
  2. I use whatever color fabric I want (usually black, but I have done a Hunter green, and white) and sew a seem on the inside. I usually use polyester because when stretched over the sonotube, you still can not see the lettering behind it. I fold about an inch of the fabric over the bottom, then insert the bottom plate until it sits about 1/8th" to 1/16th" below the bottom lip. Once the disk is in place, I use drywall screws in a criss-cross pattern (,',',',',',',',',',) to secure it in place. But using several screws, (and taking into account that I took my time to make the outside edge of the disk as round as I could) I can seal up the bottom without going back with silicon or caulk. (I paint the bottom and top the same color as the fabric)

For the Top:

  1. I cut a 20" ring that is about 4" to 6" thick (or you could say the ring has an 8" to 12" hole in the center). I place this in the top and mount it flush. I secure it again with drywall screws. I make the ring fairly thick to give the sub some weight.
  2. Next I pull the fabric up and fold it over the ring. I staple the fabric to the inside of the ring.
  3. I cut a 20 1/2" disk and router the upper edge. I then prep it for a glassy smooth finish. I place this over the flush mounted ring and, entering from the bottom through the 12" driver cutout, I use drywall screws going through the ring and into the top plate. I usually apply a bit of caulk from the inside.

As for legs, I use 1" dowels with little rubber pads on the bottom. This process works very well. I found that when using the messy epoxy, it mad my skin break out! So I stopped using it and figured out an alternate method.



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