Impedance or sensitivity?

In my opinion the impedance curve is more important. We had an opportunity to exhibit at THE SHOW in Las Vegas with FritzSpeakers. The Carbon 7's are 87dB sensitive. One would think this would not be a good match for a 300B zero feedback SET amp rated at 10 watts. However, the Carbon 7's are 6 ohm minimum and a very smooth impedance curve that matched up with the 6 ohm output transformers very nicely. We were getting very loud levels with no distortion from the amp. Several people were amazed at the fact that the combo could actually work let alone sound as good as it did.

Typical, but another excellent post by Al(Almarg).

So often, the published literature of a loudspeaker does not offer much useful insight, but the plot that comes with JA's Stereophile measurements more than justifies a subscription to the magazine.

I agree with Clio09 as a moderate to high impedance level 'with' a smmoth/relatively flat curve is very favorable to low power tubes.Sensitivity determines ultimate sound pressure levels but in terms of ease of driving a speaker its impedance.

My speaker has a 14 ohm load(10 watt minimum) and my 8 watt 300b amp just seems effortless driving them with any genre of music. Clio09`s experience with the Fritz speaker makes sense to me.

Another point associated with Al's is that not all amps will drive reactive loads properly.
Some amps which are good into resistors will fall flat on the face when confronted with reactive loads....especially at lower impedance.

So, couple a 'powerful' (into resistors) amp with a hi-sensitivity speaker which really is a bad/reactive/lo-impedance load and there 'ya go......oooops.

For the OP example? Let's see some phase data.

Al nailed it dead on. Most solid state amps will not have a problem. Many tube amps have a 4 ohm tap and have zero problems driving a non capacitive load. If you can get a frequency and phase chart, you will see rises and drops in the phase angles, the rises are inductive, tube amps don't mind these, the drop in phase angles are capacitive loads. When you have a steep phase angle, especially in the bass frequencies, most tube amps, just can't handle that. Try to get a copy of the frequency and phase curves for both the Harbeths and the VA Mozart, your questions will be quickly answered.