Speaker sensitivity, impedance, and calculating amp power

@tomic601 There sure are!

Thanks, Erik. While this question may have a practical upshot, it’s really a theoretical question. I appreciate your efforts to answer it. 

Excellent. Thank you, all.

I'll go buy the Harley book. I'll try to consult it before asking questions like this. I assumed there were no prereq's for asking a question.
@millercarbon — I'm interested in both. It starts with a practical question but leads into theoretical ones, which I want to get a handle on. I'm not seeking to ask questions with hidden motives. No need to out me.
@erik I'll reconsider my question. 

Another way to have asked the question would have been:

"What role does impedance have, if any, alongside other factors in the calculation of how much power should be used to drive a speaker comfortably?"

@tomic601 How loud? SPL of about 80 db, which I would assume with classical/jazz would have peaks of about 100 SPL?

I have been using various calculators to try to see how all the factors I mentioned in the OP vary. For example, there's this one from Crown: www.crownaudio.com/en-US/tools/calculators#amp_power_required
And a nice sheet linked to here on the Hans Beekhuyzen Channel www.youtube.com/watch?v=itKqSWH07_Y

The reason I asked the question was because the calculators I found do not mention the impedance of the speakers. Again, I'll reconsider my question based on what Erik said and what the Harley book says. If I could delete the question, I would.

Buying it right now. 

Thanks, @tvad 

This was helpful. https://youtu.be/DNfpYncOQRc

@daledeee1 This conversation with Jim Salk has a graph, perhaps of the kind you're asking about? Of course, you're asking about getting graphs for *any* speaker we want to buy. Salk's graph is not in this excerpt but you can find it here:

https://www.innerfidelity.com/content/beauty-sight-and-sound-salk-wow1-mini-monitor-page-2

This part of the Inner Fidelity conversation bears a bit on this topic:
"Q: Tying in with the above - desktop users don't typically have space for a massive amp. They tend to use compact units with relatively low power ratings, with Class D implementations being more and more common. Any comment on amplifier matching with these speakers?

A: Today, the trend in speaker design is to develop smaller and smaller speakers that play deeper and deeper. The problem is, the laws of physics dictate that the resulting speakers will be somewhat insensitive and will require more power to drive. But since that is what speaker manufacturers want to produce, most of the R&D for cutting-edge drivers these days is focused on insensitive drivers that play deeper in smaller cabinets. So if you want to use the cutting edge drivers (which we do), the models you develop will tend to be lower sensitivity. They will require more power to drive, but will be more accurate and exhibit higher sound quality.

At the same time, amps are becoming more powerful to address this need. This is especially true of Class D amplifiers. These provide a lot of power at a very reasonable price and are very efficient as well. While some people feel that Class D amps are not quite ready for prime time and can be a bit analytical, they are certainly accurate and provide a lot of performance for the money. Plus, they run cool which is another advantage.

As for the small class D amps, these are quite attractive cost-wise, but don't work all that well with low sensitivity speakers. Years ago, some friends did some interesting experiments at the Rocky Mountain Audiofest. They set up both average power meters (RMS) and peak-reading meters and monitored the power levels while playing music. While the RMS meter registered 5 - 8 watts, the peak-reading meters hit peaks of 200 - 250 watts during instantaneous transients (drum hits and the like). So while, on average, 5 - 8 watts is sufficient, if you want the cleanest possible performance, the more watts you have, the better. So while these small "T-amps" are quite inexpensive, many of the lower power amps won't have the muscle required to control the woofer in the bass region. So I'd pass on trying to marry them up." (Jim Salk)

Thanks, Doug. I was listening to Paul McGowan on why overkill buys you the benefits of "linearity" in the speakers' response on a video yesterday, but he was careful to point out that *how* you listen makes a huge difference as to whether it will matter. For critical listening, it can make a genuine difference and it's best to know that before purchasing. That's why I'm researching these questions.

And of course the character of the amp's sound is critical. But to make a careful appraisal in the listening, I want to ensure that power levels  are sufficient to do the speakers justice, with perhaps a little to spare. Of course, if I cannot tell, I cannot tell, and then saving money would be my priority, at least to shepard it toward elsewhere in the system.

The larger questions I've raised in a couple threads on this forum — on sensitivity, on impedance, on crossover controls — are seeking a better theoretical understanding so that I can make some good guesses as to what to audition.

If, for example, I know that a 4 ohm/88db sensitivity speaker would benefit from an amp of 200 watts more than 100 watts, I should try to arrange *that* as my auditioning lineup. After all, dealers are patient — they'll give me a chance to try out different combinations — but only to a point. So, in order to try out what might be something I want to actually buy, I need to do as much homework, first. And I want to try my hardest to buy from a dealer, if they carry the gear I actually prefer. I'm convinced that brick and mortar listening opportunities are a value, and if they treat me reasonably and offer reasonable prices, I want to buy with them.

@audiokinesis Right -- and, FWIW, I think the speakers mentioned here are that way because they're small and yet can do bass pretty well. Other speakers Salk makes are not as insensitive, e.g. the  Song3 Beats. 

@tvad Good suggestion. That may be the way to go. I'm going to hear some Atolls tomorrow and some Quicksilver. Just to hear them -- and they'll play through Dyn Evoke 10s, so we'll see how they perform. Later, when I have the Salks, I'll try out some amplification in my home, and maybe via Reno. 

Thanks -- I am so glad to know that, and will go take a look at his speakers.