It really depends on how insensitive or sensitive your speakers are (efficiency is a different concept, and almost all speakers are very inefficient). I haven't seen speakers below 78 dB/W myself (doesn't mean they don't exist!), and even those can take the paint off the walls with <10W coming in, assuming you aren't trying to run a concert hall. On the other hand, if we look at something like a Khorn, 1W is a very scary concept in practice (>100dB @ 1M - that's hearing-damage-inducingly-loud).
I'm not aware of any domestic setting where 200W continuous begins to make sense (Aside from LFE drive in a theater).
Just remember, 85 dB should be your top-end for any length of time. Any louder and you're really risking your hearing. And we (as humans) aren't really capable of judging if we're "just over" that threshold (the threshold of pain is well over 100 dB and once you've gone that far it's way too much, it's like breathing chlorine gas - if you see the white dots, it's too late). I do agree with the audition/research point very much - figure out what speakers you want (which is your own choice), figure out how sensitive they are, figure out how far you want to sit away from them, and then figure out how much is needed to get you to around 80-90 dB continuous, and then multiply by ten to ensure that you have headroom. Very often the "continuous" value will be around 1W-10W, and the "peak" value will be in that 50-200W range. Most amplifiers can do that (at least on paper).
Here's a neat online calculator:
http://myhometheater.homestead.com/splcalculator.html
Again, I'm not disagreeing with you - I entirely think people should figure out what they really need before making a purchase. Otherwise you can spend time going in circles. If you've got very insensitive speakers, they need power. If you pick something that comes out of the box grinning and saying "oh just you wait, you're gonna be DEAF!" then I would be a bit leery to suggest huge amplifiers (and that doesn't seem to stop most Klipsch fans from hooking up 500W McIntosh blocks to their speakers, which has never made sense to me).
Quote:
I would say that power "needs" should be truly auditioned first (if possible, its not always easy/convenient to try out different gear) because listening habits/behavior vary from person to person. If you are like me, then its hard to get enough power. If you are more normal than me and prefer typical listening levels, then the amps mentioned should work great.
obobskivich gives good advice, but I am certainly one of the few who that uses a substantial amount of power (granted, my speakers aren't very efficient.)
But yeah, perceptually, the human ear generally detects a 10dB increase in power as twice as loud. A 10dB increase in power translates to 10 times the power. So a 10dB from 20W would be 200W. There are diminishing returns on power.
It's a double-edged sword. It takes a lot of power to get very high levels, and it very little power to reach low levels. It is good or bad depending on how you look at it.
Agreed.
Quote:
For $40-$50 more you can get a A/V receiver (Yamaha or Pioneer).
Check Techbargins.
To the overall question:
I'd suggest figuring out what speakers you want, and then sorting out an amplifier for them. If you're getting active speakers, the amplifier is built-in, and it's simple as pie once you pick an active speaker that you like (personally I like Mackie and Genelec, but there's lots of options from KRK, M-Audio, BlueSky, Yamaha, and so on). If you're getting passive speakers, the amplifier is not built-in, and you need to select one. For most passive speakers they're going to be between say 85 and 95 dB/W (there are models that go above or below this, as headfinoob rightly notes), so more or less any suitable amplifier will be good. I wouldn't hamstring yourself with a 5W amplifier, grab an A/V receiver that gives you 20-100W/ch and you'll be more than good enough (and probably never take the thing "to 11"). Also, with passive speakers, consider their nominal impedance relative to what your amplifier can drive. Many cheaper amps cannot handle 4 ohm nominal speakers (it demands too much current and makes them run hot, it risks damage to both speaker and amp), and 4 ohm nominal speakers are not a unicorn. So keep that in mind too. Basically, match like with like: if the amp says it can handle XYZ, get something labeled XYZ. If you need ABC amount of power, get something that says it can provide ABC amount of power (or more, but not too much more because eventually you're wasting money (in other words, if you only need 5W/ch continuous, a 50W or 100W channel amplifier is probably what you'll end up with (they're very common), but there's no need to buy a 1000W amplifier).
