Greetings; I'm building a rhumba box not exactly like anything I've been able to google up on the net. But I saw one a week ago that I thought worked very well as an acoustic standup bass substitute when it was close miked. My boxes panels are 5.2mm birch plywood, with double rabbeted cherry glue strips, and except for the sound port holes in the front panel, will be air sealed for best resonance. Total capacity then is 3.535 cu feet. My question is, given that the port holes will be a larger one in the dead center of the front panel, and two smaller ones flanking it, splitting the space so the smaller ones will be centered on 1/2 the distance from the center point of the center hole, sort of a | o 0 o | where the vertical lines are the ends of the box by its longest measure. Is there a formula for lowest frequency vs cubic feet that is commonly used to determine the sizes of these 'sound' portholes? Thanks all. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Yes, but every time I try to see things your way, I get a headache.