Speakers from the sewer

By Esben Beck
02 Mar 1997

Assembly

First, I mounted the internal rings for the woofers. The rings were fastened with standard Araldit (epoxy-based glue to be mixed with hardener) that hardens within 24 hours. I also glued on a few plywood supporting wedges in order to obtain the best possible hold without bolts. The mounting holes for the Scan-Speak 8545 and the holes for the internal wiring had to be drilled before the ring was mounted, because it is difficult to reach them inside the narrow pipe.

Then the 22 mm MDF partition wall between the bass/midrange enclosure and the CC-subwoofers' sealed enclosure was mounted. The partition wall was tilted in order to complete the cabinets' asymmetrical structures. The partition wall was also fastened with Araldit. In the centre of the partition wall, I mounted a oak rod to be connected to the top plate, in order to increase the rigidity.

Even though the pipes were quite rigid at this point, they were making a ringing sound when I beat them with a hammer. The ringing was quite pure, indicating a dominant resonance peak that would be fatal. In order to reduce the resonance peak, I covered all internal surfaces (except the subwoofer's reflex chamber) with a thick floor carpet that had a viscous rubber base. The carpet was fastened with contact glue, and I spent a lot of effort insuring that every square millimetre of the carpet stuck well to the contact glue undercoating. The carpet successfully reduced the ringing to a insignificant level. I'll recommend you to use something else than contact glue, because it will introduce a quite intoxicating amount of vapourized formaldehyde in your living room while playing bass-heavy music for the first three weeks after gluing.

At this point, I considered the moulded junctions hard enough to be glued back on. (I don't think they were quite ready yet, but the successfull resonance killing made me so excited that my power of judgement disappeared). I used huge amounts of Araldit for this purpose as well. In order to test the Araldit joints after 24 hrs. of hardening, I unsuccessfully tried to pull off the junctions with my hands. Then I used Plastic Padding to stop up the small gaps between the junctions and the pipes. This picture Fig. 11. Filling the junctions shows you the situation at that time. As you can see, it now for the first time felt like I was getting somewhere.

The remaining works were routine. First, I primed the whole cabinets followed by two layers of black varnish Fig. 12. Primed cabinets.

Then I mounted the Scan-Speak 8545 woofers, the bass ports and the terminals Fig. 13. Scan-Speak 8545 woofers. Due to the narrowness of the pipes, I decided to avoid floor carpets in these sections, making it possible to replace the 8545's. Besides, these parts of the cabinets is only producing low frequency sound way below the resonance frequency of the concrete. The bass ports were squeezed into their holes, and the gaps around them were stopped up with non-sticky putty in order to make them removable. The terminals were fastened with wood screws and plastic expansion plugs, and so were the bottom plates with the crossover networks Fig. 14. Crossovers installed.

Due to the high content of oil in mahogany, I could not use Araldit for mounting the mahogany baffles and tops. Instead, I used Sica-Flex, a seaming compound for naval purposes that sticks well to oil-containing types of wood like teak and mahogany. The black Sica-Flex also matched the varnish perfectly.

The Seas G17RE-P bass/midrange unit and the H519 tweeter was finally mounted, and there they were -- the worlds' most aristocratic sewage pipes Fig. 15. Before and after.

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