A good test of an enclosure’s air seal (for sealed enclosures) is to mount a fairly large, soft-to-medium-suspension stiffness, long excursion  woofer in a relatively small enclosure.  (A good example would be our PR12G30BPR1 12″ Rubber Roll Woofer, in a 1 cu. ft. enclosure.)  If one pushes down on the cone with moderate pressure, it should feel like you are pushing a much stiffer spring than the driver’s own springiness, and the cone will bounce back at you instantly when you let go, with very little of a “slow return.”*  Of course, no seal is perfect, so if you keep the pressure on, for, say, 60 seconds, you will push displaced air out of the cabinet as the pressure inside equalizes with the air pressure outside.  Now, quickly release the cone, and it will STAY pushed in, taking a long time to fully return to it’s rest position.  This is a great indicator of a very good air seal.

If, on the other hand, the cone seems to take just a few seconds or less to gradually “ooze” inward when you push on it, that means there is an air leak(s) somewhere.   And then when you release it, if it returns to it’s rest position in several seconds or less, again, this is an indication of air leakage somewhere.

Most people do not realize that particle board (especially the coarser / looser grades), and MDF, are fairly porous.  Taking the same situation as above, one can put a little soapy water on the exterior of an enclosure panel, and push down on the woofer cone vigorously.  (Be sure to do this only with a woofer with a very stout cone, and take care not to damage the dust cap!)  If the material is leaky, and not sealed from the inside, you will probably see tiny soap bubbles form in the soapy water!  This test is something like the “soapy water” test to find an air leak in a tire, but, in this case, the enclosure panel materials themselves are a bit leaky. 

Then coat all interior surfaces of the enclosure with a good sealer, including the interior surfaces of the driver cutouts.  Caulk all joints with silicone cement or a good silicone enhanced latex caulk (try to find one rated for 35 years or more).  Treat / coat all the interior surfaces first, let dry, and then caulk the corners carefully, leaving no gaps.  Other likely sources of air leaks are terminal cups (and their cutouts, much as with driver cutouts) terminal boards, carpet used as a gasket under a driver flange, etc.

Once the caulk has fully cured, try the above test(s) again.

Incidentally, when doing the “soapy water test”, be sure to do the test quickly, then wipe the water off the MDF or particle board immediately, so it does not damage the material.)

A good way to find individual air leaks, such as at a woofer screw hole, etc., is to run a 5-10 Hz sine wave into the woofer, at a moderately high level, and then go around the enclosure listening for and / or feeling for (as with a cheek — a facial cheek, that is!) air leaks.

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More info. to be added soon…