slew rate and rise time

Dazzdax: For the most part the slew rate of just about any amplifier you are using at home is going to be a non-issue. Any signal, no matter what it looks like, can be broken down into a series of sine waves at different amplitudes and phases (Fourier analysis is the mathematical method for proving this). You can only hear the components out to 20 kHz. The max rate of change of a 20 kHz sine wave is 7.5 v/ usec

If you go through the calculations and then double the value for a safety factor, you arrive at an amplifier with a slew rate of 10 v/usec a capable of accurately reproduce a 20kHz sine wave while providing 400 W rms into 8 ohms. So whether you have an amplifier with a slew rate of 10 v/usec or 10000 v/usec, makes no difference.

If you want to get extreme, an amplifier with a 80 kHz bandwidth and providing 1000 W rms for an 8 ohm load will accurately reproduce all of the frequencies in that bandwidth if it has a 64 V/usec slew rate.

In short, slew rate is not something to brag about in an amplifier. Unless the design is simply terrible, there is not going to be a difference in the sound - the amplifier will be fast enough. The placebo effect is of course another story. More important are such specs as output impedance, distortion, and current capability. Find an amplifier that has low output Z, a low distortion spec and a wattage rating for driving 8, 4, and 2 ohm loads that comes close to doubling for each halving of the load Z.

Pay attention to the specs that make a difference. High slew rates and high damping factors are meaningless.

"Find an amplifier that has low output Z..."

What is "low output Z" and how do you find it? Jeff

Musicnoise- I was always under the impression that damping factors are important for controling the woofer and being able produce tighter bass;would that be correct?

'Z' means impedance in 'electronic speak'

Amps damping factor is another one of those minimal specs.
Above a certain minimal value they don't mean much except to the advertising copywriting guy.
Besides, the amp doesn't 'absorb' or 'Damp' or 'control' the Back EMF from the woofer. Rather, the woofer controls itself.
You can test this idea by thumping the edge of a woofer with a finger. Than, short out the leads to the driver with a piece of wire. Thump again and the sound changes lots. this is the woofer damping itself. Low input impedence of an amps outputs just allow the current to pass thru, back to the woofer.
More (arguable) is the speaker systems design 'Q', which also is an expression of damping. What is called 'critically damped' design of Q=.7 will give nice tight bass even with a minimal damping factor amp. A speaker with a hi 'Q', say 1.2 or so, will sound sloppy, even with a high damping factor amp.

Jj2468 & Rleff : In general, the specs for output Z will be listed in the owners manual of the amplifier or on the manufacturer’s web site. One should also note the input Z as this can come into play when interfacing a preamp or source to the amplifier.

As to damping factor, a damping factor of 200 or 2000 will be indistinguishable in practice. The damping factor is just Zspeaker / Zout amp. One could say that this is equivalent to specifying Zout of the amplifier, and, technically that is true. The problem that I have with paying a lot of attention to the damping factor is that it is a step removed from the fundamental parameter, the output Z of the amp. One must keep in mind a caveat - the damping factor has to be stated with regard to a given load impedance, usually this is 8 ohms. But, no “speaker” has a constant impedance from 20Hz to 20 kHz. In deciding whether the changes in speaker impedance over frequency will affect the sound, it is simpler and more straightforward to look at speaker impedance curve or the minimum and maximum speaker impedance specs and then compare those to the amplifier output Z. So long as the ratio is better than 100 or so, you should be fine. Whether it is 200 or 2000 is not going to matter. When it comes to figuring out how to select components for a system and what could cause problems in a system, thinking in terms of base parameters rather than derived parameters makes life easier because it lessens the tendency to unnecessarily complicate the the issue.