High efficiency is usually considered over 92db. 100db would be extreme high efficiency.
Another important consideration as to how well a speaker can work with a low watt amp (especially tubes) is the impedance curve. The more flat the curve the better for the amp. A 100 db speaker with a curve above 100hz that ranges fro 2-16ohms (not unusual) will likely do less well than a 96db speaker with a near flat curve. So if one is making a judgement based on "specs" one should look at the whole picture.
Of course the best way is to actually audition the speaker with the amp.
For over 30 years the comments about how well Daedalus speakers preform with low watt amps are pretty consistent, especially the last 15 years.
Good morning Lou,
in the forums I frequent and read, especially in Italy and in Europe, I notice that high efficiency is linked to the possibility of using even just 2-3 watts, and people often talk about horns and speakers that are particularly easy to drive, near 100 dB.
Rightly so, efficiency is not the only decisive parameter, since there are also phase rotations and ease of driving; I can have high efficiency, but if I have a minimum of 2.5 Ohms, perhaps, depending on the musical genres, volume, and the size of the listener's room, there can be significant differences. Not only that, but the amplifier's delivery capabilities are also crucial, and I agree that only by listening in one's own system and environment can the true result of a given pairing between a power amplifier and speakers be appreciated. It remains that between 90 dB and 99 dB, to take a simple example, the same amplifier will perform differently in terms of delivery while everything else remains the same.
If an amplifier is rated at 30 watts, speakers with 90 dB sensitivity will produce a certain sound pressure with that power, while speakers with 99 dB sensitivity would produce a sound pressure that doubles every 3 dB, so equivalent to about 240 watts, assuming all other surrounding conditions are identical, meaning the same electrical parameters, which obviously will never happen, but it still gives an idea of what to expect from amplifier-speaker pairings.
I still think that it's not just the watts that determine the final result, that each listener favors certain sound parameters, and that ultimately careful and prolonged listening is the only way to make a fairly complete judgment. And I’ll leave out other surrounding factors, also because if a system sounds good, let’s say you can perceive it already with a handful of well-known audio tracks!
Greetings Dario
P.S.
I apologize for the text; perhaps I am not able to fully express some concepts and my thoughts due to my somewhat limited English! Thank you anyway for the discussion, which allows one to understand and appreciate elements that are not always within one's own knowledge and broadens one's understanding—a key aspect of growing in the Hi-Fi field, combined with listening to audio systems that offer a different musical listening perspective compared to one's own.