In my opinion the central problem of low bass reproduction is room interaction. Low-frequency gain from boundary reinforcement has a significant impact on subwoofer in-room performance, so let's look at that.
But first a bit of background: The ear has relativly poor resolution in the time domain at low frequencies, but has good resolution in the frequency domain. What this means is, the in-room frequency response is the most significant factor. Subjective impressions of bass reproduction (slow, fast, tight, flabby, boomy, whatever) correlate well with the in-room frequency response.
Twelve dB per octave boost from room gain at low frequencies is theoretically possible in a perfectly rigid room, but in practice that never happens. Three or 4 dB per octave is more likely. But if we start out with a sub that is -3 dB at 25 Hz anechoic, by the time room gain is factored in, it may well be +3 to + 5 dB at 25 Hz, and thus will sound slow and sluggish (we are ignoring room modal effects here for the sake of simplicity).
A sealed box with at Qtc = .50 rolls off at 6 dB per octave, which comes pretty close to being the inverse of room gain. Therefore, subwoofers with low-Q sealed boxes often sound pretty darn good in-room, and are subjectively characterized as "tight" and "fast".
In order to generate a rolloff that even more closely approximates the inverse of typical room gain, i.e. about 3 dB per octave, we have to go to a specialized vented box. Now I realize this is counter-intuitive because vented boxes tend to be "boomy", but what we do is choose a woofer, box size, and tuning frequency that give us a 3 dB per octave rolloff from about 100 Hz on down. Such a system can be scaled to give very good in-room response to 20 Hz or below.
So I believe that both sealed and vented enclosures offer excellent opportunities for high quality in-room bass, provided the basic design takes the anticipated environment into account. Just for the record, there is much more to subwoofer design and room interaction than what I've described here.
Now if we are looking at subwoofers in general, and if we are merely speaking in generalities, sealed subs tend to give more natural-sounding in-room response. But that is because most vented subs are designed for loudest-deepest-possible-bass, because most subwoofer buyers buy based on specs. The types of subs I described above do not have impressive specs, as the -3 dB point may well be in the 50 to 60 Hz range... before room gain.
Duke
dealer/manufacturer (of both sealed and vented subs)
