Budg, that's pretty much it: a doubling of power results in only a 3dB increase in the maximum sound level possible on brief peaks. The increase in level is logarithmic, not linear, so exactly the same 3dB increase occurs between 1 and 2 watts, 10 and 20 watts, 100 and 200 watts, etc. Also note that the sound level using 1 watt is actually quite loud, and is what might be used for a typical average listening level. The peak power required might vary from practically nothing more in the case of some almost uniformly loud pop music recordings to 100 times or more for very dynamic material, such as some classical items that I have.
Yeah, Bernard, the term "subjectively twice as loud" is seen fairly often, but nobody knows what it really means.
