You're welcome!
Actually 4 types, there's also damping the rear of the driver with a loosely attached felt 'blanket' or similar to act as a diaphragmatic absorber. Not aware of any available speaker design program that can sim this unless AkAbak can.
You can mod the spider to lower Fs, raise Vas and add viscous damping by injecting silicone in the VC gap to some drivers [not sure about Altec/GPA] and of course add weight to lower Fs, increase Qts.
Correct, though an impulse response is the best way to measure it. Note that at the extreme, ~aperiodic loading [~completely flattens the impedance peak] occurs at high damping densities, so to optimize it requires measuring impedance.
GM
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