Hi efficient speaker, bass problems

In that case it is prolly a function of amp output impedance and not
power. Tube amps, especially set amps are of high out put
impedance. When this reacts with a speakers impedance which can be low in the bass and higher in the treble (without a zobel network which
wil lower efficency) the result is a less controlled and responsive
bass.

In my opinion a fairly high output impedance (low damping factor) amplifier actually works extremely well with proper loudspeaker matching. In the bass region, a high output impedance has the effect of raising the woofer's electrical Q, which reduces electromagnetic damping. But if we start out with a woofer + box that would "normally" be overdamped, the net result with the low-damping-factor amplifier is a properly damped system... but in addition, you get a "free lunch": You end up with deeper bass extension than you would have gotten with a high-damping-factor solid state amp! If done right, you can get as much as 1/3 octave deeper extension. To put this in perspective, this is more than you'd normally get from doubling the box size while maintaining the same efficiency. I exploit this "free lunch" routinely.

Duke

Extension, dampning and efficiency are the tradeoffs. The vectors go in different directions. The op questions grip vs eff. The extension is not. as I understand. part of the query. But I'm all in for a free lunch of any kind. Elucidate

Tmsorosk,
It looks like you have answered your own question. When listening to high sensitivity speakers your friends were using low powered tubed amps. We have all talked all around your question.There are some tubed amps with very good control, but many low powered amps, even though they play adequate and at times good bass, often they don't have the control of higher powered tubes or most solid state amps. It is typically not caused by a well designed speaker. Tim

My gut instinct tells me that even any well designed speaker, high or low efficiency, is likely to have bass deficiencies unless setup properly and matched to the right amp and associated gear.

Also, I would not expect most amps to deliver equally excellent bass performance on both high and low efficiency speaker designs.

Other than these things, I would say the devil is all in the details....