Alternating voltage and current are typically symmetrical about zero, so an "average" figure is zero. RMS figures are the solution.
In the context of audio systems, power is either being dissipated, or it's not, and any power measurement should be average power, not RMS. Mathematically, they're probably the same. Sorry, it's a bug-bear of mine...
At least nobody seems to talk PMPO any more...
Speakers are rated in terms of their power handling capacity, and amps are rated for the amount of power they can output. If your speakers are rated to handle less than the amp you run the risk of damaging the speakers (presuming we're talking per-channel ratings).howsie wrote:75w rms speakers will sound best on a 75 rms or higher amp. Most amps are 60 rms so dont go below this.
Impedance is the important rating. If the speaker impedance doesn't adequately match the amp rating, the amplifier can be damaged if it is run too close to its maximum power capacity.
Don't be afraid to put high-power speakers on a low power amp. If the impedances match, the only significant issue is that you've probably paid more for your speakers than you needed. It's no different to running a high-power system at less than maximum volume.