by EWBrown » Sun Nov 15, 2009 3:14 pm
THis is an exponential hon, or at least as "exponential" as it can be made, with the use of all right-angle cuts.
The purpose of filling the two bottom cavities with bags of sand or aquarium gravel is to create a smoother, angled "plane" for the bottom of the horn's mouth. A sheet of 18 mm or 3/4 inch plywood would also work very well, but that would require some pretty fancy angled (mitered) cuts in order to get it to fit perfectly and leave no unwanted gaps.
Otherwise, the two unfilled cavities on the bottom would create all sorts of nasty resonances, and the bass response would be impacted.
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The Madisound BK-16 kits had several angle-cut pieces (and the side panels were routed in order to create a "perfect" seal, and because of this feature, the order of installation of the various pieces was VERY critical, one "goof" and some of the smaller cut pieces could not be installed.
This required a dry-fit tryout before any glue was applied, and then only one side was was to be glued, until everything was in place, This was a reiterative process, which meant that the dry-fit side had to be removed and re-installed after each step of installing the interior pieces.The other side had to be used "dry", in order to make sure that all of the interior pieces didn't shift around, and all of these steps thusly ensured a perfect fit, when the other side was finally glued in place.
The provided instructions did this one piece at a time, but after some dry fit experimentation, I determined that sometimes 2 or 3 pieces could be installed (and glued) in one "step" of the assembly.
The BK-16 did end up having a couple of empty hollow cavities, and for sheer "perfection" these could have been filled with dry sand, though I didn't bother with that step, the cabs were already more than heavy enough.
Even as a precisely ready-cut and routed kit, it was still a pretty daunting project to get it all together.
From the Cyrillic alphabet inspection stamps on some of the wood pieces, I believe that the BK-16s were from Russia. At teh time, the cab kits were $98 each, and only required some light sanding before the assembly process began. If the 11-layer (baltic birch) plywood and the woodworking had been done in the USA, I'm sure the unit cost would have been a LOT higher.
/ed B
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