test the effectiveness of foam and/or stuffing in your box.

[Borat]

take your box and mount your woofer on standoffs about 1/2 inch to 2 inch high depending on the size of the woofer.

this way woofer's direct output will be reduced through back wave cancellation but enclosure's contribution ( standing waves etc ) will be increased because more will be able to escape through the gap.

yes the actual nature of the standing waves will also be affected but not very strongly. on the other hand you should be able to hear if your stuffing is doing the job. any box honkyness should not be able to escape your ears this way.

make sure to use the same driver and crossover when testing as would actually be used in the final speaker.