One problem with most vented subs is that they are approximately "flat" under anechoic conditions, often down to a very low frequency. So when room gain is factored in (typically +3 dB per octave below 100 Hz), the result is a slow and bass-heavy presentation. Yuck.
A sealed box typically avoids the problem of excess deep bass energy, which is definitely an improvement. Its rolloff slope is closer to the inverse of room gain. That being said, I think it's possible to do even better.
"Even better" is a low-tuned vented sytem designed such that its anechoic response rolls off at about 3 dB per octave from about 100 Hz down to the tuning frequency, below which it of course rolls off rapidly. Even this doesn't solve all the problems - there's still the inevitable peaks and dips imposed by room interaction, and these can ruin an otherwise good sub's presentation. Rather than equalization, I suggest using multiple small subs distributed asymmetrically around the room, so that the sum of their individual peak-and-dip patterns is smoother than any one of them would have been.
In other words, work with the room instead of fighting it - sort of an acoustic application of the "sometimes it's easier to plow around the stumps" concept.
Duke
dealer/manufacturer
