It is the shape of the in-room bass frequency response curve, rather than the "speed" of the woofer, that is primarily responsible for how "fast" the bass sounds.
Lumpy bass = "slow" bass, as over-emphasis somewhere in the bass region gives the subjective impression that we tend to describe as "slow" or "fat" or "boomy".
And,
Smooth bass = "fast" bass, it's actually not any faster, but it sounds that way when the fundamentals and their overtones are in proper proportion.
Group delay is of far less subjective significance than we'd tend to think, because the ear's time-domain resolution is quite poor in the bass region. Controlled listening tests that used digital signal processing to isolate group delay from frequency response have shown that group delay on the order of what we'd get from a vented speaker system is barely audible on test tones and statistically inaudible on program material. The reason sealed subs generally sound faster is the shape of their frequency response curve (which is generally more room-gain-friendly), rather than their actual "speed".
Anyway, imo the key to smooth, and therefore "fast", in-room bass is how the subwoofer(s) and room interact. What the room does to the sub's output dominates. Yes we can hear the difference between one sub and another in a given room, but still the room's generally detrimental signature is imposed on whatever the sub is doing.
The solution I advocate is, multiple small subs distributed around the room. Each will inevitably have a different room-induced peak-and-dip pattern, and the sum of these multiple dissimilar peak-and-dip patterns is much smoother than any single sub's output would be. And to address the issue of room gain (more precisely boundary reinforcement) boosting the low end a bit, I prefer subs whose native frequency response starts out as approximately the inverse of typical room gain.
Let me go off on a psychoacoustic tangent here. The ear/brain system tends to average out peaks and dips that are fairly close together, but if they are too far apart, the ear/brain system can't average them and they stick out like sore thumbs (especially the peaks - dips are harder to hear). The room-induced peak-and-dip pattern of a typical home listening room with a single sub has the peaks and dips spread way too far apart for the ear/brain system to average them. But with a distributed multisub system, not only are the peak-to-dip ratios significantly reduced, but we also have more peaks and dips bunched up closer together, so that the ear/brain system's averaging-out characteristic can work to our advantage.
Imo this approach has advantages over a single equalized sub, in that the bass response is much more uniform throughout the room. And if you do want to equalize a multisub system, you get better results because you don't have as much response variation from one location to another.
For deepest-loudest-bang-for-buckest bass, go with a single mighty ubersub. For smoothest (and therefore subjectively fastest) bass, I think the acoustics and psychoacoustics both favor a good distributed multisub system.
Duke
dealer/manufacturer (yes, of multisub systems... grains of salt all around)
