Suggestions for minimizing acoustic resonances in large sealed box ?

BlueWizard

Member
2007-06-29 8:49 pm
Well, the most obvious is to line the inside of the cabinet (sides and back) with fiberglass, polyester, or acoustical foam insulation. Some prefer to line the walls, other prefer to loosely fill the cabinet.

The other is to not have flat parallel surfaces. The cabinets could be built with curved sides or in a shape similar to a pentagon (more like pentagon-ish).

You can get some construction ideas for both curved sides and multi-sided geometic shapes from this discussion-

Bendable plywood-mdf combination-
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116653&perpage=25&pagenumber=1

Of course to keep the cabinet itself from vibrating or resonating, you need adequate bracing.

Just a thought.

Steve/bluewizard
 

Hezz

Member
2002-12-22 6:52 am
Utah
My understanding of the old methods for the best sounding closed boxed systems were to use a combination of acoustic foam on the sides of the walls and a near complete filling of polyester batting and fiberglass cut in 1-2 inch size squares. The stuffing density is important and need experimentation for best sound.

Some also drilled a couple of small holes 2-3 mm in diameter to make the enclosure slightly lossy and aperiodic. This can improve the sound a lot.

Of course, adding the matrix bracing and baffling inside will also help and it's best to use a combination of all methods and balance as necessary. As has been stated the wall lining is probably less important than the inner volume stuffing. For midrange you will want more stuffing. For bass driver you want somewhat less so you don't over damp the bass response.
 
Theorize, select the best concepts and then experiment. Connect your measurement microphone to the internal volume of the box and you will see the effect of cavity resonances. You will have to measure a number of points inside the box. This may help you to select the bst concept and to optimize it.