How much Power do speakers really use ???????

Though the following is oversimplified, it's what I use when thinking about this issue.

I use a speaker with an 89dB/w sensitivity (and ignore how it was measured). I assume that peaks on the order of 15dB must be accommodated (a figure I remember for the human voice, one of the most demanding instruments). One watt will provide a listening level of 89dB and the peaks will require 32w (with a doubling of power as 3dB). Therefore these speakers require the following:

dB---w------peak w
80---.125---4
89---1------32
98---8------256

Using this as a ballpark, my 8w SET into 89dB/w speakers should be capable of about 83dB (.25w with 8w peaks) at one meter. My listening position is twice that, so somewhere around 80dB would be right (neglecting room effects - and my system is in a really small room). Since I listen exclusively to classical music and nearly always to small ensembles and solo instruments, this level suites my listening habits just fine. YMMV

For most applications...a quality 40 or 60w amp will suffice...and be able to drive even difficult loads to surprising levels of volume...I heard Maggies on a 40w Rega at my local dealer...and it sounded good....granted...if you want to "rock the house" or get evicted...you might need more juice...Im no expert...but even doubling your power is a marginal improvement...to really hear a gain...a factor of 3 or 4 is necessary...others will provide more technical answers...but unless you have a very large room with very inefficient speakers...I wouldnt worry about...

All of it!

I have compared the Cello Grand Masters (96db sensitivity) driven by one of their Performance amps which puts out about 1500 watts into this speaker, vs. a bridged pair that puts out about 6000 watts (per Cello). The difference was quite impressive.

You can NEVER have too much power!

Richard

Let's say you have two amps - one at 50 wpc and another at 5,000 wpc - with identical speakers and listening rooms. If you play both at a certain volume level, say 80 db SPL, both amps will provide the same power. However, during transient peaks, BOTH amps will clip. The 50w amp may distort at clipping while the 5,000w amp will recover much quicker where you would not notice the discontinuity. That's one rationale for mfr's pumping up the amp power - to tackle clipping.

So, the best way I can answer the questions is just how much quality you want for a particular listening level. You can get there with a 2 wpc SET as well as a 600w monoblock; "depends" is the answer - because a particular SPL level is dependent on room size, speaker sensitivity and physical comfort, etc. but the quality comes from both the electronics and the power capability. The SET uses its ability to produce a symmetrical waveform to recover from clipping while the SS beast uses brute force.

Pbb- Sean is certainly not the only person on this forum with useful knowledge, as I'm sure he'd agree, and Twl is quite right. The nominal power required for a nominal speaker in an average room for at a nominal spl is quite low, < 5 watts, many at only 1 watt. Much of the subtle inner detail heard during a listening session would be at 1/10 watt or lower. This is why so many experienced audio-lovers claim that the first watt is the most important! As has been stated, it is the dynamic peaks that necessitate greater power reserves. Of course, not all watts are created equal. The ability for an amplifier to gracefully handle these transient conditions can greatly effect the perception of the relative power between amps.

I seem to recall having read about a demonstration that utilized 10,000 watts (ss, of course) in an attempt to reproduce the sound of scissors cutting a piece of paper, and there was still distortion/clipping of the signal. Certainly, if there is no compromise in the quality of power, then more is better. However, given practical limitations in packaging, layout and component power handling, higher power normally requires significant sonic tradeoffs compared to their smaller siblings. This is typically true of both ss and tube designs.

The approach chosen by Twl and many others offers some unique advantages over the more traditional approach of the last 30 years (low impedance, moderate to low efficient speakers with high power amps). Very high efficiency speakers coupled with a couple or a few very high quality watts is in many ways a far more elegant approach, and allows the user greater choice of amplification to match his/her preferences. Fewer compromises in the amplification topology in low power designs can yield amazing detail and musicality at the same time. Most who have followed this approach strongly embrace SET or OTL topologies, but there are some that use low power ss amps as well.

At the other end, if one works on the assumption that an amplifier is routinely asked to reproduce peaks that produce higher levels of distortion up to clipping, it often comes down to how gracefully the amplifier clips and recovers from these conditions. Fast recovery and harmonic distortion products -softening or rounding of the waveform during clipping with minimal ringing- are often far less annoying in tube amplification than the behavior of some ss amplifiers in this region.

I've heard 12wpc amps produce far better, and more dynamic sound than highly touted 350wpc behemoths. I've also heard 75wpc amps sucked dry by low efficient and difficult speaker loads. In the end, use your ears to determine if an amplifier is appropriate for you in the context of your system and listening habits. Just one man's opinion.