In Reply to: 2 pi tower posted by Colin on November 26, 2002 at 07:36:31:
In most cases, there is no difference between front-facing and rear-facing ports. Bass-reflex speakers are simply Helmholtz resonators with low frequency of resonance. The exception to this is if the speaker is large enough to develop internal standing waves in the passsband. In this case, it is not an issue of whether the port is on back or in front but whether or not the port location is near a standing wave node. This is the case in the two π tower, and for this reason, the locations of the port and the midwoofer are important.About acoustic insulation, there are lots of materials that could work but I always find myself coming back to R11/R13. It works very well. This is also germane to the discussion about standing wave modes. The reason we want insulation spanning the cross-section is it tends to damp the standing wave modes better than just having it on the sides of the cabinet. This is important in the two π tower.
As for panel thickness, one school of thought is the thicker the better. I wouldn't object to that but it does get heavy. I would prefer a well braced cabinet to one having thicker panels but no bracing. If a cabinet is small enough, braces become less important but larger cabinets really need them. In the case of the two π tower, the braces 1/3 up from the bottom and 1/3 the way down from the top also serve as attachment points for sheets of insulaton that span the cross-section. So in this case, the braces serve a double purpose.
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