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

Personally, i think that a system built for Classical music should be able to sustain a peak of at least 110 dB's at your seated listening position. Obviously, different radiation patterns from various speakers, how far you sit from them and the size of the room will vary how much power you need.

For a "jammin" system that is built for hard rock / metal, the system should be capable of sustaining 110 dB's average at the seated listening position. All of the variables above apply here just like they did above.

As you can see, there is a BIG difference as to what "loud" is in both circumstances. While both systems should be capable of doing 110 dB's at your seated listening position, one of those figures is peak while the other is average. Obviously, a "rock & roll" system that someone tries to achieve "concert level" spl's with will take a HELLUVA lot more of a beating on an average basis. This is NOT to say that everyone listens at these levels, but that the systems should be capable of doing so if one desired. At lesser levels, the systems will be coasting and should sound like it.

I would think that average listening levels at the seated listening position would be somewhere between 70 and 95 dB's on an average for most all types of music. It is only when one really wants to "let loose" or has highly in-efficient speakers that one needs a gob of power. Most of the time, an amp will be producing under 10 watts RMS with peaks below 50 - 100 watts ( depends on the type of music and amount of compression ). Some large scale bass peaks may require hundreds upon hundreds of watts though, so system requirements and what you want to achieve with your specific system and its' limitations will dictate how much power you really need. Look for quality first and "big numbers" later. Sean
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Weiserb:
This is antectdotal;guys with physics degrees,please cut me some slack.
The softest sound,at the softest pitch,(a flute)is about 50 decibels. On a music score,that is notated pp. Each time you double the loudness,add 10 decibels. That is p is 60db,mp is 70db,mf is 80db,f is 90db,and ff is 100 db. A modern orchestra with everybody playing as loudly as they can at the same time is 100 decibels. Some rock bands play at 110db.
If your speaker is rated at 8 ohms resitance, count 1,2,4,8,etc. If your speakers is rated at 4 ohms,count 2,4,8,16,etc. If it's rated at 6 ohms,count 1 1/2,3,6,12,etc. Everytime you move up a "Counting step" add three decibel watts.
Say your speaker is rated 90db at 8 ohms. At one meter,the speaker will have a loundness of 90 decibels being fed one watt. At 2 watts,93 db;at 4 watts,96 db;and so forth. At 90 db into 4 ohms,it would be 90db at 2 watts;93db at 4,and so forth.
It's true,as Sean says, that different speakers have different rates of change at different distances,but anecdotaly,I'd allow 6 db'ds of headroom.

Ok, I've got a question. I've got a pair of B&W 803's in a 12x20ft room. Moderately furnished. I play classical, jazz and hard rock almost about evenly. I like my music at concert levels some of the time and others loud enough so I have to say "what" when someone interrupts me. I rarely listen to music below that, but on occasion.

I am interested in buy a CJ MW60 or Premier 11a. Enough power? How about a Rogue 120 Magnum?

Busaganashi:
To double check my facts,I looked up the B&W Nautalis 803s on their web site;they are rated 90db into 8 ohms.
So 90db would require 1 watt,93db-2 watts,96db-4 watts,99db-8 watts,102db-16 watts,105db-32 watts,108db-64 watts,and 111 db-128 watts.
Sounds to me as if 110-120 Clean watts would fill the bill-with headroom to spare.

So it sounds like the Rogue 120's or perhaps a CJ Premier 12 or 8 is what I need then. Thanks.