amplifier/speaker power (Sound level) : eBay Guides

When buying speakers think about the auditorium (room) that they are going to play in. The larger the room the greater the sound intensity they are going to have to provide to give an acceptable volume level. Most speakers will accept power levels far greater than their quoted RMS value but, and this is a big but the output from the amplifier must be clean i.e. undistorted ( a 30 watt amp running flat out will burn out a pair of speaker whereas a 500 watt amp running at 125 watt  is unlikely to do any damage, I have seen the damage an underpowered amp can do to speaker units). This brings us to efficiency (how good is a speaker at converting electrical energy into sound) the pinnacle is Lowther (PM6,7 etc.) an efficient speaker will require far less power (watts) for a given sound intensity level than an inefficient one. Most speakers are quoted as  nn/db per watt, the bigger nn is then the more efficient the speakers are. My speakers are 83.5/db per watt and is about as low as they go, values over 90db/watt is the acceptable norm. The Lowthers are about 96db/watt, 3db represents a doubling of electrical power.

At the end of the day buying an amplifier of greater output than your speakers might suggest taking will provide a better sound and last longer (much longer) than an underpowered amp into power thirsty speakers.