Power rating for speakers

Worf -- Stan's response led me to realize why you were asking your question about damaging speakers by playing at low volume. Keep in mind that playing a high powered amp at low volume is a very different situation than playing an underpowered amp at a volume level that is more than it can handle (that exceeds its power rating).

In the first case the speakers are fed a clean, undistorted signal. In the second case, as Stan indicates, the speaker may be fed a highly distorted (clipped) signal. It is the clipping distortion that can do the damage, not the low volume.

Clipping distortion will sound like the music is breaking up on peaks. It will have a static-like character whenever the music gets loud.

Stan -- A small correction to your explanation. The damage would not be caused by the clipped waveform causing dc to flow. The danger with a clipped waveform is the sharp transition points where the normal sine wave turns into a flat top or flat bottom. The abrupt transition points contain high frequency spectral components that are not present in the original waveform. Their high frequency causes the speaker crossovers to route them to the tweeters, causing the tweeters to have to handle abnormally high power levels, which leads to overheating and burn-out.

Regards,
-- Al

Al undoubtably has answered this but I'll try to make it simple. When a speaker is rated at 100 watts it should mean 100 continuous watts. Music is composed of peaks. A 100 watt speaker can tale PEAKS of several times this. If you take a low powered amp and drive it into clipping [beyond its capability] it will eventually start to pass DC current through to the drivers and end by burning them out. so you should err on the high side rather than the low. If you are careful you can use ALMOST any amp with any speaker, but matching power output and speaker requirements make life easier.

Would mean if I played the music at a low level (say 10W) for a speaker thats rated 50-150w, I'd be damaging the speaker?

No.

Please also see my response in the other thread in which you posted a similar question.

Regards,
-- Al

Would mean if I played the music at a low level (say 10W) for a speaker thats rated 50-150w, I'd be damaging the speaker?

Essentially nothing. These are approximate power ranges the speaker manufacture thinks are proper for the speaker. But amps vary tremendously in their ability to deliver power at different impedance's. Also remember that far more speakers are damaged by too little power than too much. Get the efficiency of the speaker , measured in db for one watt input. Increasing the output 3db requires twice the power. See if the amp you are considering has more than enough to drive the speaker to its full rated output.