While I'm generally in agreement with the authors, I'd offer a slightly different take on "bass speed" than the article Al so kindly linked (based on my own experience with subwoofers over the last 5 or 6 years).
The issues of acceleration/deceleration of the woofer cone is real, but a small (i.e. lightweight) cone is not the only answer. As in a car, there are 3 primary factors at work: weight, motor power, and brakes.
High quality subwoofers have oversized motor assemblies and accelerate more than quickly enough to make that issue moot regardless of driver size (per the article). However, the "brakes" are to me, the more interesting part of the equation.
The suspension system is the effective "brake" in a subwoofer, and different subs are tuned quite differently. Sealed boxes inherently provide a pretty stiff suspension, while ported subs can vary widely. The trick is to properly "damp" the cone so that it stops moving when the input signal stops. The result is "fast" bass. One measurement of this is "group delay" and, IME, it seems to correlate pretty well with the phenomenon that I'm describing.
Even though instantaneous start/stop cone response (zero group delay, if that were possible) might seem ideal, I've concluded that faster is not always better.. IME, subs can even be "overdamped" (too fast?), because you're really trying the match the sub's damping to the low frequency behavior of the the bass driver in your main speaker, rather than to some abstract ideal of "high speed". And, depending on the design of the main speaker in question, that behavior will vary considerably.
I use a pair of 12" Rythmik subs with adjustable damping and, at various times, I've mated them to Ohm 100s, Maggie MMGs, SF Minuettos, Monitor Audio Radius 270s, and a few others. I optimize the interface for flat, smooth response with a sub controller (most often Velodyne SMS-1), and then tweak the damping by ear, then re-optimize the frequency response (if necessary). I have ended up with different damping settings, depending on the speaker with which I've tried to mate the sub.
As a general rule, maximum displacement capability will dictate how low and loud a subwoofer can cleanly go. In this regard, large drivers are a much more efficient solution than small drivers. This is why the measured distortion of various subs at high(ish) SPL and low frequency almost always favor the large driver, and almost always by a very large margin.
My bottom line:Speed matters, but faster isn't always better. And, while speed matters, smaller (drivers) does not mean higher speed. As a general rule for high quality subwoofers, bigger is better.
In some ways I'm just re-stating what the authors of the linked article are saying, but doing so thru the lens of my own experience, FWIW.
Marty
