Higher sensitivity - more dynamic sound?

@lonemountain , I don’t follow your reasoning. You said:

"So your 102dB 1w/1m speaker may not have such good dynamics with a 20W amp if 1W= 102dB SPL then .2W=105, 4W =108, 8W =111, 16W=114dB SPL and that’s it! That’s 12dB of dynamic range.

"86dB 1w/1m, 89dB 2w, 92dB 4w. 95dB 8w, 98dB 16W, 101dB 32W, 104dB 64W, 107dB 128W, 110dB SPL at 256W/1m. 86dB 1/1m speaker on a 250W/ch amp = 24dB of dynamic range! 12dB dynamics is better than 24dB dynamics?"

The dynamic range of a system is the difference between the softest and the loudest sounds the system can produce. Assuming both systems are limited by the same noise floor, the 102 dB system is capable of 114 dB peaks while the 86 dB system is capable of 110 dB peaks. So in your example, the 102 dB system has 4 dB more dynamic range.

But that’s not the whole story. Making another comparison and using 110 dB SPL for both, the 102 dB system will have negligible compression effects from the 7 watts it needs (this may not be true if it’s a single fullrange driver), while at 110 dB/256 watts the 86 dB speaker is far more likely to have thermal compression effects. And since musicians use dynamic contrast to convey emotion, compression effects tend to rob the music of emotion and "life". The use of very high-quality drivers (and/or many drivers) in the 86 dB speaker does make a worthwhile improvement in this area.

Let’s revisit noise floor for a moment: To a crude first approximation the in-room reflection field can be thought of as a "noise floor" which can mask low-level sounds. For a given room, the narrower the loudspeaker’s radiation pattern, the higher the direct-to-reverberant sound ratio, and therefore the lower the "noise floor" imposed by the in-room reflection field. So IF our 102 dB speaker is also highly directional (which is likely), it will probably result in a lower effective "noise floor" and correspondingly greater dynamic range and may result in better retrieval of low-level details.

Edit: Looks like several of us were typing at the same time, and I was the slowest.

Duke

Phusis

I think your post makes my point.  Efficiency alone is not the sole issue or a spec to chase.  Amp power, purpose and many other factors matter a lot.  In live sound, 127dB SPL is important.  In home audio, its damaging to our hearing. 
The 20W limit was only responding the post of the 25W amp mated to an efficient loudspeaker had better dynamics (earlier in this and other threads).   Good amps with high power are very available.

@lonemountain --

I think your post makes my point. Efficiency alone is not the sole issue or a spec to chase. Amp power, purpose and many other factors matter a lot. In live sound, 127dB SPL is important. In home audio, its damaging to our hearing.

The 127dB info only served to prove that eff. + extension is readily possible. I wouldn’t dream of using the max. potential in my home environment, but headroom is your friend, not least in LF, and thus the max. SPL numbers should make more sense in this context. Operating the amps much below full tilt is also worthwhile headroom, I might add.

The 20W limit was only responding the post of the 25W amp mated to an efficient loudspeaker had better dynamics (earlier in this and other threads). Good amps with high power are very available.

But more wattage in low eff. speakers comes with a price eventually, as per Duke’s post just above.

Amp power, purpose and many other factors matter a lot.

Quality wattage where it matters most, and power quantity (and overall quality) ditto; I use 30W class A from ~600Hz on up, ~2kW from ~85 to 600Hz, and 500W below ~85Hz. The pro class D-based amps used below 600Hz are quality amps and more than sufficient for the respective frequency spans - that's one of the beauties of active config. that such a distribution of amp types is possible. 

Valid points all Duke- my point about dynamic range was "system dynamics" not one system vs another.  The 86dB efficiency speaker on a 250W amp has more total dynamics to cover incoming source material of a wider dynamic content than the 102dB/20w amp system. 

Brad

@charles1dad

Thank you Charles, you summed it up wonderfully!

Janos