Just for the record, I am skeptical of the notion that cone material makes an audibly significant difference in the low bass region, as long as the cone is stiff enough to behave as a piston. I don’t doubt that a person could hear a difference between different subs and that difference could seem to correlate with cone material, but cone material would not be the actual cause of the difference.
As for "speed", the ear has incredibly poor time-domain resolution in the bass region. We cannot even detect the presence of bass energy from less than one wavelength, and we must hear several wavelengths before we can hear pitch. So whatever it is we are perceiving as "speed", it is actually something other than the leading edge of a low frequency signal. We will come to exactly what it is in a minute.
What the ear is extremely good at, in the bass region, is hearing differences in SPL. Look at a set of equal-loudness curves:
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/imgsou/eqlou.gif
See how the curves are close together below 100 Hz? What that means is, a small change in SPL is perceived as a much larger change in loudness. So a 3 dB change at 30 Hz can SOUND LIKE as much of a difference as a 10 dB change at 2 kHz!
(Incidentally the ear’s exaggerated sensitivity to small changes in SPL at low frequencies is one of the reasons why it takes a long time to get the gain dialed in properly on a subwoofer system.)
Low frequency speakers in rooms have a minimum-phase characteristic, which means that the time-domain response tracks the frequency response. So when we have a peak in the frequency response, we also have ringing at that frequency (conversely if we fix the peak, we fix the ringing). At low frequencies it is this MODAL RINGING ASSOCIATED WITH FREQUENCY RESPONSE PEAKS that sounds "slow"! This happens on the TRAILING EDGE of a low-frequency waveform, where our perception is well-equipped to detect what we interpret as "speed" (because we are good at hearing loudness), NOT on the LEADING EDGE!!
Recall how it takes us several cycles to hear the pitch of bass energy. By the time we hear bass, the energy has reflected off of room surfaces numerous times. So PERCEPTUALLY, we cannot hear the leading edge of a bass waveform, nor can we separate the subwoofer from the room. They are a SYSTEM, as far as human hearing perception goes. So imo it makes sense to design subwoofers that work with the room instead of against it. If the in-room frequency response is smooth, then we don’t have some frequencies decaying significantly more slowly than others, which contributes to the perception of "speed".
Now it is common knowledge that sealed boxes sound "faster" than vented boxes. This is explained by their in-room frequency response trends. A vented box tends to be flat down to a much lower frequency, and then roll off rapidly below the tuning frequency. A sealed box starts rolling off higher up, but more gently. Once we factor in "room gain" from boundary reinforcement, the vented box typically has a net rising in-room response as we go down in frequency. Couple this with room-induced peaks plus the ear’s significantly increased sensitivity to small SPL changes in the bass region, and vented boxes do indeed tend to sound boomy. The more gentle rolloff of a low-Q sealed box has a much better synergy with room gain from boundary reinforcement in most cases.
"Typical" room gain from boundary reinforcement is ballpark +3 dB per octave below 100 Hz. A low-Q sealed box has a rolloff rate that approximates -6 dB per octave, so the synergy there is good. Imo it still leaves room for improvement, but that would be another topic for another day.
Controlled blind listening tests have shown that group delay on the order of what we might expect from a well-designed high-quality vented box is inaudible on program material, and just barely detectable on test tones. But the difference in frequency response is highly audible. In the real world the time and frequency domains are linked in the bass region, but it is our perception of loudness in the frequency domain that dominates our perception of "speed". When a kickdrum goes from full-on to very quiet very quickly because there is no modal ringing (because the in-room response is smooth), that sounds very FAST and TIGHT. (The frequencies that give the kickdrum impact are largely above the subwoofer range, so we use the gain, frequency, and phase controls to optimize that blend.)
I’m not saying there would be no audible difference between a sealed box and a vented box equalized to have the same in-room frequency response, but I am saying that any difference would have nothing to do with the leading edge of the waveform.
Anyway my point is, the differences in the perceived "speed" of subwoofers are due to factors other than cone material or the leading edge of a bass waveform. Perceived "speed" in the bass region is more closely related to the in-room frequency response than to anything else (which is in turn linked to modal ringing or lack thereof), so that is the thing we should focus on first. I’m not saying that’s the only thing that matters, but I am saying it matters far more than the subwoofer cone material or the leading edge of a low-frequency waveform, neither of which human hearing is well-equipped to hear.
Duke
