Can an amp overdamp a speaker?

Duke, I am confused. Can you please explain how one can tell by looking at a speaker response curve if it has a solid state or tube amp in mind? I always thought that those curves were amplifier-independent and any off-bass responses were the result of an amplifier's inability to keep up current at low impedances or room effects.

My understanding of speaker design tells me that the amplifier's output impedance affects the electrical Qe, which in turn, affects the speaker's Qt. If the damping factor is infinite (zero output source impedance) then the electrical Qe is just the voice coil and crossover resistances. Would this not be the ideal, the smallest possible value of Qe?

My view is that damping factor is way misunderstood. I think some envision the amplifier physically starting and stopping the speaker cones. It's the magnet that does that. The motion of the cone is the same no matter what the damping factor. What a high DF does is minimize the effect of any back emf, reducing distortion. Its measure also indicates the amplifier's ability to put out higher current at lower speaker impedances.

I would not even consider damping factor in choosing an amplifier, period. If an amp/speaker combo is not meant to be, you will hear it.

Duke, I agree that using speaker equations can show that the lower cutoff frequency is a function of Qe. For example, if you assume a speaker design with a Qt of 0.707 with a driver that has a voice coil resistance of 5 ohms, a Qm of 3, 8 ohm impedance, and a Fs of 40 hz, then Qe at a DF of 1000 or greater will be 0.925 and give a lower cutoff of 40 hz. If you go down to a DF of 10, Qe is 15% higher and the lower cutoff drops 3 dB to 36 hz. But that's not a free lunch...

What you have to take into account is that the SPL ultimately depends on pressure generated by the driver. The factors affecting pressure are the driver magnet force factor, piston area, voice coil resistance and mechanical compliance. The SPL using these factors is inversely proportional to voice coil resistance. So decreasing the DF has the same effect as increasing the coil resistance so any -dB frequency drop by increasing Qt is offset by the reduction in SPL which is a wash. Otherwise, you could simply place a variable resistor in line with the driver which you can then adjust Qt to play with the frequency response in your room, independent of amplifier power.