Watts! How many do we need?

Normal to loud-side for most speakers is around 1 - 2 watts.  Figure out what it is for your speakers and multiply by 100 to 200 to cover the peaks without capping out the amp's capacity.  And YES, momentary peaks can take that amount of power.

I have an original Schitt Aegir (20 w/ch 8 ohms) and a pair of Ohm 1000 speakers in a 15' X 24' room with a vaulted ceiling -- absolutely no problem reaching my desired listening level (85 dB average) with no hint of clipping or compressed dynamics.  Two caveats, however.  First I use a powered subwoofer and roll off the deep bass to the Ohms. Deep bass can be a power hog  Second, as many know, the relationship between watts and volume level is logarithmic, not linear. Doubling the power gets you 3 dB more volume. Doubling the perceived volume takes 10 times more power. So, if you are a headbanger, and have medium or low sensitive speakers, or have a large room, you're going to need a lot more power than I do.

But, as others have noted, lotsa watts are an attractive advertising carrot. And Class D amps have made it easier to offer that carrot these days.

@ghdprentice 

I’m puzzled by your experience. I don’t doubt it but since current x volts equals watts. What you are describing is that lower current sounds better. So something else is going on when you switch to high watts. 

From my experience with solid state, current was the primary determinant if the amp was up to the task, the more the better. From my tube amp experience, it is far, far less important. So I went from high current 350 wpc solid state to 70 wpc tube amplification and my system sounds so much better it is amazing. It is a high quality amp… I am sure there is a difference between 70 wpc with an inexpensive light weight tube amp and a good one.

I happened to be looking at the meters the other day and noticed they were peaking at 1.5 watts output. I realize analog meters are slow and will not capture the full extent of what is going on and perhaps the meters use a proxy parameter to measure watts… but still interesting. Seems there is some truth in the saying “it’s the first watt that is most important.”

I can switch my amp between 70 wpc and 140 wpc. I noticed the same average power output in either mode but the peaks in sound would send the meters quickly far to the right (higher output) in 70 wpc mode… which makes sense. Even at deafening volume my tube amp does not run out of power. While my past experiences with 75 - 150 wpc solid state either never had good solidity or loss it when pressed to higher volumes (not necessarily ear splitting). The other thing I notice is that my amp sounds much more natural and musical without loss of dynamics in the 70 wpc triode mode vs the 140 wpc ultra linear mode.

One. Million. Watts. (Max total peak)

FYI

there are several Stringrays at a good price here in Audiogon.

as well as a great pair of Snappers; if you have a little extra and want 100wpc.

I keep going down in watts. I do have high-efficiency Klipsch Cornwalls.

My amp voyage has been....

NAD M23 200 wpc

to 

Threshold CAS1 75 wpc

to

Manley Stringray switchable between 20 wpc (triode) or 40 wpc (ultra-linear) 

All have sounded great, but each has been a step up in quality; in my opinion.

I love the sound of the Manley in ultra-linear mode.

It is FAR easier to sell something on more-is-better because that is easy to understand. If the extra power does not come at an expense in terms of sound quality, that would mean no harm in having way too much power in reserve.  But, that is not really the case.  Of curse it is a matter of taste, but, I generally prefer the sound of low-powered tube amps over other types.  Often, my least favorite amps are high-powered tube amps running multiple KT88, KT150, KT170, etc. tubes (the sound is "hard" and harsh sounding to me).  These days, most good solid state amps are smooth and not harsh sounding at all, but, they tend to sound a bit lifeless and unengaging unless the volume is push up higher than one would play the speakers running good tube amps. 

I know Harbeth advocates for a lot of power and their speakers are somewhat inefficient, but, the best I have heard them sound was with medium powered amps.  A good 20-100 watt pushpull tube amp would be my choice.

How about this? Or this?

Or maybe that? Or that?

And who could forget this?

Search engines...I wuv you.

Current uber alles.

Looking at my own meters, it’s movies that are going to push the amps.

For the record, every meter I’ve seen is really a voltage meter in disguise. A low impedance speaker won’t push the needle further up. Perhaps someone has invented a smarter meter though. :)

On a slightly different angle than the OP has asked Nelson Pass has long advocated that the performance of an amp in the first few watts is what matters most.