Can a 40 watt speaker go where a 25 watt was?

Hollywood it right. Speakers don't make power, they just handle it, or if they're not strong enough, they burn out. If you can find a graph of the response curve of that 40 watt speaker that will tell you more about its performance.

No you wont run into any problems. 40 watts is just what the speaker can handle, however hooking it up to 20 watts is fine.

specific. And here is why: Very not often does the amp positioned out the rated optimal power consistently. All music is intermittent, aside from some bass CDs made to attempt the applications of subs. and extra greater, slightly greater power it quite is sparkling (no distortion) is a few distance greater useful than decrease than powering a speaker and clipping (over making use of) the amp to attempt to attain slightly greater output. This clipping heats up the voice coil (way better than slightly greater sparkling power might ever do) and additionally sends erratic voltage spikes to the speaker. that's what's going to blow the speaker. era.