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I'm trying to figure out how to match up speakers and amps. To me the math just doesn't make sense. I see some amps that have a peak performance of 1200W at 8 ohms but a maximum power of 170W at the same resistance. Or another an output of 350W at 8 ohms with a peak of 400W.
Why such the difference in peak and output between companies? And it's not a matter of stereo vs bridged mode. Also what are the advantages and disadvantages of bridged and stereo?
Also, how would you match up speakers? In the first case, would you look for 200W or 1000W speakers? In the second would you go for 350W, 400W, or 500w?
Is a higher wattage going to give me a louder sound, or is it just a clearer sound at louder volumes?
Pretend I'm an idiot and let's do this and layman's terms. (No real need to pretend )
I'm sure there's pretty of lurkers out there that would like to get a professional's explanation.

The methods used to measure and report output do vary quite a bit from manufacturer to manufacturer. However, I don't really understand what you're asking here. Are you saying that an amplifier that says it's a 1200W amplifier only produces 200W per channel @ 8 ohms? I'll assume this is what you're referring to and I'll explain. The 1200W peak rating would typically be referring to it's bridged configuration at the lowest nominal resistance that it's capable of handling (usually 4 ohms bridged). This is because you're combining the power of both channels of the amplifer and running it through the lowest possible resistance. As resistance goes up, the amount of power the amp can push through the load goes down. So then if you split it across two channels as well, it drops even further. I hope that make sense and explains it for you.

The advantage of a bridged configuration then is that you can combine the power of the two channels in the amplifier to drive a speaker with a higher power handling capacity. So if you need 1000W to drive you sub, you don't need an amp that can deliver 1000W per channel (which is a big and expensive amp). You can use an amp that may only deliver 400W per channel but when bridged delivers 1000W. Now the disadvantage is of course that now you've only got one channel on that amp. So if you need to drive both left and right signals, like for you top-end cabinets, you need two amps.

Matching your amplifier to your speakers is very important as you can imagine. Speakers usually have 3 ratings for power handling. They are RMS, Program and Peak. A good general rule of thumb is that your amplifer should be capable of delivering 100 - 150% of the Program rated (which is usually double the RMS and half the Peak rating) power. Now the other key here is that speakers have different nominal impedance values. As you've seen the amps are rated based on how much power they can deliver at each resistance measurement. So for an example, if I have a pair of 2-way cabinets that have a nominal resistance of 8 ohms and and RMS rating of 350W, I'd be looking for an amplifier that can deliver 700-1000W per channel at 8 ohms.

More power in your amplifier has two benefits. First, yes it does ultimately translate into higher volume capabilities. Indirectly, it also means less distortion. As you run your amplifiers closer and closer to their peak levels, the more harmonic distortion they introduce in the output. So by having a more powerful amplifier, it allows you to run the amplifier farther below it's peak and still produce the same volume. This means less distortion. It also gives you headroom, which is the ability of the amplifier to respond to extraneous peaks (transients) in the signal without producing additional distortion or going into clipping (what happens when the signal exceeds what the amplifier can reproducel).

I hope that makes sense, it's a lot of information to try to explain in such a brief format, and it's late so I don't know how coherent it was.

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DJ Tony
Let It Rip Karaoke

Amplifier RMS ratings are measured by certain methods established by the FTC and EIA, and you will sometimes see slightly different power ratings for the two measurement methods, for RMS power.

Peak power is not defined by a regulatory or standards body, and the amp companies can pretty much make up whatever crap they want. Crown includes a "20ms burst" spec for some of their amplifiers, while Behringer advertises "peak power" without any definition at all. QSC lists "dynamic headroom" in decibels for some of their products but again does not state anything about how long the amplifier will maintain that output level at any frequency.

As letitrip mentions, buying an amp that states its RMS output is about 1x to 1.5x the speaker "program power" rating is usually a good idea.

I have bought all amps with similar power output so I can interchange them as needed on really busy days. I own (3) EP2500/EP4000, (2) EPX3000, (1) RMX2450, and (3) XTi 2000. These also happen to be about the biggest amplifiers which are useful to me since most venues I am at only have 20A circuits, and nothing larger for audio use.

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Jeff Wheeler, moonlight DJ/KJ

Another bit of math you should know is that it takes 10-times the power to double the loudness to the listener.

It is a common misconception that watts = volume, such as "200 watts is twice as loud as 100 watts" (incorrect). In fact a 1000 watt-amp is only 3db louder than a 500 watt amp...imperceptible to most people. To double the volume of a 500-watt amp you would need a 5000 watt unit!

What you do gain is headroom. You also gain a safety factor as most speakers are damaged not by being overpowered, but underpowered (clipping).