thnking wrote:If someone is going to have an encompassing conversation on woofer speed, all aspects need to be looked at]
I agree - but I think "attack" is where people get confused.
Attack - the rise time of the speaker - and in it's most extreme form (and only in that extreme form), that would be the sudden presence of a waveform, requiring the speaker to rise to response at a given amplitude.
Ideally, the cone motion would follow the waveform exactly - and as such, the waveform will NEVER make the speaker move any faster than the highest frequency component of that waveform - and the highest frequency the speaker is capable of playing well is essentially dependent on the inductance of the speaker.
(phew)
So, even in an idealistic sense, inductance DOES determine the "attack" (speed) of the speaker in this way.
However, there is an amplitude component to consider:
If you suddenly hit the speaker with a 100hz waveform, would the speaker actually reach full excursion right from cycle #1 [of those 100 cycles-per-second]? Or are there a few cycles worth of "rise time" before the cone excursion matches the amplitude of the waveform? There are some dynamics related to standard physics, such as momentum and inertia. But realistically, such a rise time is going to be inaudible, because of how many cycles really are happening "per second", and how few it takes to 'rise' - if there is any rise time.
The impulse response test of a speaker is interesting, both in the context of "attack" an "sustain". The speaker is simply hit with a DC pulse which is then sustained, and the cone motion is monitored. The speaker will rise at something less than "perfectly vertical" (the waveform does rise exactly vertical), and then does tend to overshoot that maximum peak and oscillate a bit. The 'rise' response is credited to the inductance of the speaker. The overhang/oscillation is both motor and suspension, and IMO doesn't really represent a scenario encountered with the speaker playing music - if the speaker is playing music, those are AC signals, and the speaker naturally will be oscillating - across the entire excursion range of the speaker. But it's a good segue into...
Sustain - I really don't think this is much of an issue. A Boss coaxial will "sustain" just as well as a Focal Utopia, once it's risen and is playing a sustained tone (That's NOT to say the Focal won't sound better
).
Decay - measured as per the waterfall plot, and here's where I believe oscillation matters. The speaker is played, and signal removed, to learn where the speaker fails to control its natural oscillations well enough. It's a very interesting plot, and one measurement where the speaker's natural resonance is it's own worst enemy.
Release - ...wouldn't really seem to be a function of the speaker, but rather the electronics.
...from the speaker's standpoint, when signal is removed, if the cone isn't moving already, it's not going to start moving on it's own.
"Static impedance" - ie. inertia (more recognizable physics term)
"Motional impedance" - ie. momentum (ditto)
"External impedance (ie. air loading)" - by "external" you mean to the speaker, not "the outside of the box". The greatest pressure forces affecting what really translates into the speaker's efficiency (not speed - in fact, rather the opposite... low frequencies become mechanically impeded) are actually the pressure forces INSIDE the enclosure (both static air and port pressure forces).
In terms of perceived fast vs slow woofers, I believe most people confuse the “speed” with the mid/sub pass band.