Why do speakers improve with more powerful amps?

It's the old DQ 10's analogy I hear in the DQ 10 group I read info in.  "You need a minimum of 200wpc 'to make them sing' " Garbage.....  Mine sound fabulous with a 40 wpc Proton D540. Sister company to the early NAD company. But it's capable of 160 wpc for music transients when called for.  That's at 8 ohms. It's all about the current it was explained to me. I don't listen loud....so no need for a heat producing beast.

I agree with the posters who indicate "it depends". My current Revel speakers are rated at 6 ohms with 87db sensitivity. They were initially being driven with a 50 WPC Arcam and I needed to push the amp pretty hard to get the speakers to sound their best. I switched to an 80 WPC Cambridge Audio amp and the speakers came alive. I noticed it especially in the lower frequencies. But there was also the matter of synergy. The CA amp, being a little more forward sounding, meshed better with the laid back sound of the Revels.

I had been using the Arcam with a pair of Paradigms that were rated at 92db at 8 ohms. That was another great synergy system. 50 watts was more than enough to make those sound great. 

It depends.

The efficiency of the speaker and how the amp reacts to the load. It's as simple as the amp asking the speaker to move, or telling it to move. We talk about watts as if they are all the same. !00 volts at 1 amp is 100 watts, but 25 volts at 4 amps is also 100 watts. P = I X E. The more amperage an amp can put out the more control it has over a driver, specially large drivers with heavy cones.

@jumia   Why buy low efficiency speakers?

Because like everything else in life, it's a tradeoff.  It is easier to build drivers with high sound quality if they are inefficient.  It's against engineering principles as well as natural logic to have the best SQ and the best efficiency in the same design.  Think about it - if it were possible, everyone would be doing it.

Through the years I've went from 80 watts, to 140, to 200, to 300 and now at 600 and 1000 Amps. (Legacy IV 2 and IV 5 Amps). At normal listening, like a movie at slightly spirited volumes there is a difference, although slight. TURN it up, like listening to a Video Concert, and there is no comparison. One sounds like a recording, and one sounds like your THERE!