Matt's Pillar of Power

Pilar of Power This is from my archived web pages. The Adire Audio 15" subwoofer was a great sub, but Adire audio is no longer in business. If you are interested in a sealed sub, be sure to use a speaker that has a long throw (Xmax) and give it plenty of power. I still use this sub in my home theater. It does a great job

The pillar of power is one of the many "Sono-tube" subs on the web. There are many great how-to web pages (linked below) so I will just show general info and a few specific things that I found helpful when making a sonosub.
The specs: I chose to put an Adire Audio Tempest 15" subwoofer in a sealed enclosure. The enclosure is approximately 4.6 cubic feet (130L). The long sides of the enclosure are made out of 20" diameter sonotube. The top and bottom of the sonotube is capped with 1.5" MDF (two 3/4" pieces glued together). Two 24" "beauty caps" add a little style and match my Audio/Video center. The woofer down fires the air in/out of the 4" gap between the bottom of the cylinder and the bottom beauty cap.
Background: My friend Will originally built a ported sonosub with a 12" Radio Shack woofer which later became an isobaric sub with two Radio Shack speakers. He had already built a very nice traditional box for his 15" Tempest and the sonosub was an experiment. The sub sounded good, but perhaps a bit on the boomy side. The Radio Shack woofers do well for inexpensive speakers, but the THX Moooo! trailer (on Toy Story 2) made the woofers bottom out and produce a truly horrible sound. I was very impressed with the sound of his Tempest and decided to get my own Tempest, but put it in a sonotube. His Sonotube was sitting in a closet not being used so he volunteered it. I had to cut off some length to get the volume I wanted for my sealed design. Since the bottom was already cut for a 12" woofer plus port, it got the axe. The top section of the sub was altered only slightly.

Here is the original sub just after it was finished. It looks like one of those stand up tables you find in bars. Will and Trey bask in the glory of a freshly finished sub. You can see some fresh "Liquid Nails" oozing top and bottom.

Here the original sonotube is being cut down to give 4.6 cubic feet. I used a "L" type tool to mark the desired cut in pencil. The L tool was slid around the cylinder (with one part of the L sliding along the top) with a pencil at the desired height. I used a jigsaw to cut the sonotube.

The decapitated sonotube. The bottom was cut off. You can see the old hole for a 12" driver and a short port. I was glad to see those funky legs go. The yellow stuffing is fiberglass.

This is the bottom cap that the Tempest bolts to. It started off as 3/4" + 3/4" MDF glued together. I used a router to gradually dig through the 1.5" MDF to form the round circumference and the inner hole. The four legs are 1.25" diameter avocado dowels (how appropriate for a California sub). They go into the countersunk holes on the bottom beauty cap( more on that later). I drilled the four holes for the binding posts (I brought both coils to the outside world in case I decide to do something different later). I have one binding post in to check for fit. The posts are from Parts Express (# 091-1245). They become wider near the top of the post and have a ribbed pattern to help grip into the wood to keep them from spinning while tightening down the speaker wire. I drilled the holes just slightly smaller than the rib and used a rubber mallet to pound them in once I painted the bottom cap.

Here are the two beauty caps. I got the idea of using the lower beauty cap and legs from the company SV subwoofers. Half way through the build I decided to put an identical beauty cap on the top also. Sonosubs aren't the prettiest things plain, but some wood make them presentable. The bottom piece is the one with the four countersunk holes in it. This is where the four legs will slide into. The 24" circles were bought from Home Depot already cut with the edges rounded. All I had to do was stain them. The staining process started with a pre-stain treatment that is suppose to help the stain go on evenly. Next was one coat of stain. Finally, two coats of polyurethane. I bought the semi-gloss polyurethane to give it a shine, but not so much of a shine that it made every imperfection stand out. My wife's car makes a nice alternate workbench....shhhhh.

This is the inside of the bottom piece. You can see the four heads of the screws that hold the legs on. The four consecutive countersunk holes are for the speaker binding posts. The posts I got from Parts Express are good for up to 1" wood. Since I used 1.5" MDF, I had to countersink a bit so the end of the bolt came through enough to get the two bolts (as well as the metal tab that you solder your wire to) on. One of the binding posts is visible if you look through the speaker cutout (laying on the table).

Here the bottom cap being drilled for the four binding posts. I mostly put this picture up to show off my $39 drill press. Can you believe that? For someone that has uses a drill press five times a year, you can't beat it. I can't understand how they can make something like that, ship it from China (it is heavy), mark it up in price for the retailer, and still sell it for less than $40.

The bottom is now painted black and has the speaker binding posts mounted. The bottom sits lightly in the sonotube. This made it convenient to mount the speaker to it before it was glued in. I added some Acousta-Stuf insulation (Parts Express # 260-317). It is the white insulation. I left the previous fiberglass in there. Speaker sealing caulk (Parts Express # 269-300) can be seen on the circumference of the speaker hole

I forget how truly monstrous a 15" woofer is. It was a little unwieldy pulling that thing in and out of the box. Next to it sets a 6.5" woofer used in the Dayton III speaker. Will was building a pair while I was working on the Tempest. He has fancy router bits and it sure is nice to be able to leave all that MDF dust behind.

It is ready for travel back home now that I smeared Liquid Nails inside the bottom of the sonotube and pounded in the bottom cap (using a rubber mallet). It is only missing the top and bottom beauty rings to be complete. When I got home I took out the eight bolts holding the speaker down and pulled the speaker out a few inches to let the Liquid Nails dry. I am glad I did because there were some nasty fumes coming out of there for several hours. You can see one of the advantages of using a sealed enclosure.... the woofer can almost be the same size of the Sonotube diameter. For ported designs, you have to use a much larger diameter of tube or put the port on the opposite end.

Back home now for the finishing touches. I bolted on the bottom beauty cap and I am trying to center the top beauty cap so I can mark it before I apply the Liquid Nails. I rotated the top cap after I put on The Liquid Nails to line the grain of the wood in the top and bottom caps. After applying the "nails", I put three boxes of leftover kitchen tiles on top to keep pressure on until the glue dried. I was sure to not put too much Liquid Nails near the outer edge so it wouldn't ooze out and get on the painted Sonotube or the bottom side of the beauty cap. It would be hard to retouch either since they are soon to be inseparable.

These were my two favorite items that made construction easy. The Allen head bolt allowed me to use a 1/4" bolt, but not have the huge head associated with a 1/4" bolt. I started out with standard nuts, but it was going to be a very tight fit using the standard. Even though the outer rim of the Tempest is wide, I was going to have to push over the gasket material to get it to fit. Also, you don't have much room for error with the big heads. If you drill just off center of the bolt hole, a standard bolt head won't fit down in the outer lip of the woofer. It will catch on the out edge or be smash the rubber gasket. The Hurricane nut (Parts Express # 081-1084) made things much more easy. The standard 1/4" T-nut has teeth that stick out very wide. For a big speaker, you probably have enough room for it, but then you have to worry about getting the teeth to dig into the MDF. The teeth don't sink into the MDF very well and tend to take chunks out. You can put a piece of particle board underneath for the T-nuts to go into, but that requires more work. From the picture you should be able to make out a slight raised edge near the top of the hurricane nut. This "bump" travels down the side of the bolt and has a twist to it. There are several of those edges along the side. They dig in and prevent the nut from turning when you are tightening down your speaker. They don't look like they could do much, but I didn't have any of them twist on me. I drilled a hole big enough for the smooth shaft to fit into, but smaller than the raised edge. The raised edges then grip into the wood when you pound the nut in with a hammer or rubber mallet.

The Speaker:
Adire has been making well reviewed speakers for several years. The Shiva 12" was a big hit in DIY circles. The Tempest and the Shiva are popular for the most basic reasons. They produce tremendous amounts of bass and are a good value. The Tempest sells for $150 and has over 16mm of one way linear travel (>32mm peak to peak travel). Sound is all about moving air and the Tempest can move a lot of it because of its large diameter/radius (area) and its long excursion (length) = a bunch of air movement.

Sealed VS. Ported:
I have always like sealed speakers... especially subs. Ported speakers got a bad name from companies that used a small woofer and had to tune the port frequency high. They can have poor bass extension and be boomy. However, with a large driver, you can tune your port way down there and have a nice sounding sub. Many of the ported Sono-sub designs out there are tuned in the 16-30 HZ range. That means there is not much music below the tuning frequency of the port which is good since music well below the tuning frequency can cause the cone to become uncontrolled. That being said, I still prefer a sealed sub to even a properly built ported sub. Maybe it is a psychology thing. I chose sealed for a couple of other reasons. Sealed designs are the simplest for the DIYer. You don't have to worry about getting your port the right length or fitting all of your port in the enclosure by using L or U fittings. There is no high air velocity port noise to worry about. You have to use a very large port if you don't want port noise and distortion during large cone movements. I think some people worry about not getting enough bass from a sealed design.... that shake your foundation crowd pleasing bass that most people desire, but don't want to talk about with there hi-fi friends. I was concerned a bit myself until I went over to Will's and told him I wanted to see what his sealed Tempest could do. With my sleeves frayed from vibrating at 30Hz and a slight feeling of motion sickness, I left knowing that I would be quite happy with a sealed design. Sealed subs do require more power than ported designs to achieve equivalent levels of low bass, but power amps are very inexpensive these days. I am using a Carvin DCM1000 which will put out 1000W of power bridged into a 4 ohm load (the Tempest dual voice coils in parallel). I recommend Carvin's amplifiers. I tested and repaired amplifiers and mixers for Carvin for a short time in the 90s. Their amplifiers were very solid and an incredible value.


Sonosub:
This project was all made possible by Sonosub tubing. You just can't beat the strength of a cylinder shape for equal pressure (darn close) applications. The woofer can be breathing deeply, but the Sonosub walls don't flex. It sure does make the woodworking part of the project much easier. This picture was taken off the Hub web page (a concrete accessory store). You can see the intended application for Sonotube. Aren't speakers a much better use?


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Matt Tucker Escondido CA.