Speakers from the sewer

By Esben Beck
02 Mar 1997

Preparing the pipes

Building these sewer pipe cabinets turned out to be a lot more complicated than building ordinary MDF cabinets. Due to this fact, I will try to describe the building process in detail, step by step. Hopefully, you will pick up a few tips and tricks if you decide to accomplish mine or a similar project. I recommend you to take a look at the cabinet drawing Fig. 2. Cabinet drawing, which will make the article easier to understand.

The manufacturer had the necessary equipment for drilling big holes in the pipes. And I was in bad need for big holes at this point, because the area needed for mounting the bass/midrange drivers were just a few centimetres smaller than the inner diameter of the pipe itself. In fact, the bass/midrange holes had to be as big as possible without any risk for cracks in the thin edges that would appear around them. They recommended a 178 mm (7") hole located with its periphery about 70 mm (2 3/4") from the edge of the pipe. Since the edges of the 178 mm drill had to be entered almost tangentially onto the inner diameter of the pipes, I had to ask the drill operator to be a little bit more accurate that he was used to, by telling him about how silly the speakers would look if he practised his normal sewage pipe tolerances. He did a very good job, and I was now the proud owner of the world's cheapest speaker cabinets ($10 each), but with the Milky Way's most expensive driver holes ($50 each). I decided to take out the bass port holes myself.

The pipes were transported to my closet-sized workshop. Then I placed them on the floor, and for the next 14 days, I just sat there staring at the pipes, worrying about where to begin, while my circle of acquaintances worried about my mental condition. This is what I stared at for 14 days without getting anywhere Fig. 3. The pipes before start.

After the two weeks of brainwork, I decided to start working with the junction between the pipe and the baffle. In order to carry out a all-concrete concept, the junction had to be made from concrete too. A mould had to be made, and I decided to make it from a piece of vinyl floor covering. After making a supporting frame for the vinyl, I made a cupboard template for the outer vinyl sheet. I transferred the template pattern to the vinyl, and started to cut with a razor-sharp blade cutter. After only half a minute of work, the knife accidentally slipped. Luckily, I never achieve sexual excitement during speaker building, so the injury was limited to a small cut in my right groin. After returning from the casualty department, I completed the mould by cutting the vinyl sideways. Check out the result here Fig. 4. The completed mould.

It is not possible to mould the junction directly to the pipe, because it will not stick adequately. Therefore, the junctions had to be removed from the pipes after hardening, and then be glued back on. However, the junction concrete will stick quite good to the pipe, and in order to ease the loosening of the junctions, the pipes were covered with a thin plastic sheet Fig. 5. Pipes covered with a plastic sheet before the moulds were filled Fig. 6. The moulds filled. After 24 hours, the junction was hard enough to be removed from the mould, and the second junction was made the same way. Each junction was moulded on its respective pipe, in order to insure perfect matches.

Concrete is supposed to harden under constant humid conditions over a period of at least 24 days. (I didn't have the patience required, so I glued them back on the tubes after keeping them in my drying closet for one week. More about this later).

During the period waiting for the concrete junctions to harden, I continued working on the cabinets. First, I made the bass reflex holes. I used a Hilti hammer drill to perforate the circumference of the bass port hole Fig. 7. Drilling port holes, followed by some excellent craftsmanship using a hammer and a chisel Fig. 8. Port holes finished. You might use a ordinary hammer drill, but I strongly recommend that you use a Hilti with its unique cushion hammer system due to the extreme hardness of non-reinforced concrete. The Hilti system also reduces the risk of cracks and shatterings. Ear protection during work like this is essential. I'm a true audiophile, and I intend to keep it that way for a while.

The baffles, tops and terminal bases was cut out from a large 2 x 8" mahogany board, using a powerful jigsaw. The partition walls, subwoofer mounting ring and bottom plates were made from 22 mm MDF. Take a look at the baffles here Fig. 9. The baffles, and the rest of the wood parts here Fig. 10. Wood parts.

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