Jtinn, how do you measure "preferences" of electronic devices ? What are you basing your criteria on to say what it likes best ?
If it is simply measurable power output, you will find an impedance where an amp will peak at and then fall off both below and above that. As mentioned above though, distortion and heat dissipation ( loss of efficiency ) will climb as impedance is lowered. Obviously, most any device will have a "sweet spot" where it will perform best i.e. reasonable distortion and heat generation with good power ouput. All things being equal, a SS amp will "prefer" or work optimally into a lower impedance than a tube amp would.
This is not to say that all SS amps work optimally at low impedances though. This is evidenced by their lack of ability to "double down" as impedance is halved. While a true "voltage source" would do this, there are very few amps built anywhere close to that. Some obviously do better than others in this respect.
If an amp was a true voltage source though, it would not matter what impedance was presented to it. The power output would increase or decrease at a linear rate as impedance was halved or doubled. As such, the amp might do more power at lower impedances, but that doesn't mean that it was running optimally there. The point of optimal operation ( or what it "liked best" ) would be that of highest efficiency with the lowest distortion. Depending on the design, that could be at any specific impedance, not necessarily the lowest possible.
Besides all of the above, damping factor is lowered as the speaker impedance is dropped. This results in less control over the drivers with greater susceptability for the reflected EMF to "modulate" the power supply of the amp. This is the reason why some amps sound good at low impedances and others don't. Their "linearity" goes out the window even though power output might increase. Sean
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