Speakers and Tube Amps

IMHO, I would look at a speaker's "impedance curve" in determing where or not it's "tube-friendly". If the impedance is relatively flat throughout the speaker's frequency range, with whatever deviations represented by smooth curves, than those speakers are likely to work well with tube amplifiers. If the "impedance curve" shows some sharp peaks and dips where the impedance is changing quickly, then a tube amplifier will probably have some problems dealing with those changes. I know Duke said the same thing I just said, but hopefully I said it in a way that some of us who are less "technically oriented" than others can understand.

My understanding is consistent with what Duke and CUH said.

Cleaneduphippy, you can also have the case where the impedance goes high and the tube amp will put out constant power. This is OK if the designer expects that. Impedance dips are usually not a problem too, as you have to sometimes shut down the output of the amp right at the area of the dip, as in the case of the older Wilson Watts.

Electrostatics can have low impedance at high frequencies and very high impedance in the bass- tube amps will often play that with constant power at all frequencies and actually get the speaker to play bass, where a transistor amp will make way too much power in the highs (so it will be bright), and not be able to make any power at all in the lows.

Really, the best way to find out is to look at the designer's intent- what he uses for reference, what manufacturers are using his product, who he shows with at shows.