You may end up with a bass response that sounds boomy if the enclosure is too small......You probably will not have a very musically sounding lower end, again, if the enclosure is too small.......For example: the kick drum could possibly sound muddy...........Conrad Hoffman is describing a .707 Q, which is considered a flat response for a woofer, which, in many circles, is a preferred Q response to achieve........By taking it up to .9 to 1, he is extending his upper bass sound levels by decreasing his box size, and .9 to 1 is still a Q factor which has a fair degree of damping, so he is not losing control of his woofer response, while he is extending and gaining a bit more SPL for his given woofer.........My guess is that he has an understanding of his woofers parameters, and can design his box accordingly. If you are doing a 3 way design, you may want to gain an understansing of how box size affects woofer performance......Extending your upper bass with too small of an enclosure for a particular woofer could have a negative effect on the midrange, in addition to the fact that we are not sure if you are using a sealed enclosure or vented......If you have ever heard a car drive by that is sporting a loud subwoofer, you may be able to relate to what I am describing here, and alot of car subwoofers are notorious for being mounted in enclosures that are way too small for good, musically sounding performance........Continue to do some research..........Vance Dickasons' Loudspeaker Design Cookbooks does a very nice job of discussing your topic..........I might recommend you start there...........Respectfully........Omni