Bending a little a Bass Trapp...

Feni, Portable is fine, but it's best to stay near the walls - most especially near the corners - since this is where the absorbers will be most effective. Eric, I just "hand" drew it in Paint Shop Pro. Thomas

Thanx barefoot ! it is a chellanging DIY ! must call for help ! Best regard ! Feni

i tend to agree with zikaj about this designs lack of effectiveness as a membrane absorber... coming from the background of one who used to build wooden acoustic instruments for a living (violins, violas, cellos, guitars, mandolins, etc..) a bent peice of wood (ie, one that is under stress) will not excite as freely as a flat peice of wood, and also will not excite evenly, as the resistance is not even... in other words, certain areas of the board would excite at certain pressure levels, but others would not. this is why on instruments that have a curved soundboard (like a violin) you carve a solid peice of wood down into a dished shape starting with a peice of wood that is the entire depth of the dish... it is also vital to make sure the thickness of the curve is the same across the entire dish.... instruments made from plywood are much more difficult to excite, and instruments made from BENT plywood are even worse!.. as a diffusor however, bending the plywood would increase it's functionality... although, now that i've said that, i think i understand your reasoning for suspending the panel in a flexible membrane... this way, any force moves the whole panel, rather than flexing it, as in the traditional panel absorber design. so the shape of that panel becomes irrelevant to it's function in the absorber.... would this reduce or increase the absorbers effectiveness? does a flexing panel or a suspended moving panel have a better result? hope i'm not making a fool of myself. (: _illium

illium, Yes, this design uses a flexible suspension around the perimeter of the panel. It's more like a loudspeaker cone, rather than a violin soundboard. It should be more efficient than a flexible membrane because almost the entire panel can move with equal amplitude. A flexible membrane has maximum amplitude in the center falling off to zero amplitude at the edges. Thomas

this design would also give a wider frequency range for the absorber (Q)... since the flexible meduim is actually the cloth around the panel, it is far more flexible than wood, and would react to higher frequencies and lower volumes. btw: i would suggest titebond alphalytic resin glue (off-white bottle, red cap, not blue!!) for combining the panel layers. also, soaking the panels in water (warm to hot preferablly, though that would be hard with something this size...) will help them to bend more freely... i would soak the panels over night... just leave an outdoor hose/sprinkler running over them all night... that's how we used to make our skateboard ramps. (: wetting the boards will make them have a smoother contour than just bending them dry, and will allow a deeper dish.. _illium

illium wrote:

this design would also give a wider frequency range for the absorber (Q)... since the flexible meduim is actually the cloth around the panel, it is far more flexible than wood, and would react to higher frequencies and lower volumes.

No, not really. The resonance frequency, and Q are primarily determined by the mass per unit area of the panel, the air volume behind the panel, and the internal damping. The only high frequency "advantage" of this design that I can imagine is that it would probably have a more linear set of harmonics. In other words, the higher panel resonances would be closer to 2*fo, 3*fo, 4*fo, etc,... rather than something like 2.1432*f0, 3.2105*fo, 4.763*fo,.... Thomas