Posted by Wayne Parham on September 24, 2001 at 04:24:24

In Reply to: box dimensions posted by Observator on September 24, 2001 at 02:47:16:

You're right to be concerned about standing waves inside the box. They can become a problem if a cabinet dimension becomes acoustically large. Fortunately, this doesn't usually happen at bass frequencies except for the largest boxes.

Some cabinets use staggered dimensions and some use non-parallel walls. Both are good ideas, but neither removes standing waves, they just space them out so they are not harmonically related. I think the most important thing is to damp the standing wave modes if they fall in the passband of the loudspeaker.

Standing waves usually tend to fall in the midrange, which is attenuated with acoustic insulation inside the box. It is important that the insulation be set away from the panels, so that waves are forced to pass through it. Otherwise, it is just part of the boundary. So use a thick sheet of insulation to line the walls, and if the cabinet is large, span the cross section in one or two places. An easy way to do this is to set a sheet of R13 on braces, spanning the cross section of the cabinet. Bass will pass right through, but midrange will be attenuated.