SET amps and speaker sensitivity.

Of course, you must also take into consideration listening room volume, dynamic range of the music you like, impedence curve of speaker and ability of amp to deliver current to that load. For example, I can get ear splitting volume from my 1w Berning Micro-zotl in my small study (70 sq ft; 500 cu. ft.) with 93 dB speakers, but that is not be the case in my living room (300 sq. ft, 2500 cu.ft. with opening into large hallway).

That's right Peter. And dB is a logarithmic scale, so a 10 dB increase is twice as loud! Also FYI, 3 dB is perceptible as an increase in loudness (less than that is often perceived as better but not necessarily louder). So you need to double the power output of an amp to get a significant increase in volume. FYI, sensitivity is generally in units of dB/1 watt/1 meter; 1 watt (or 2.8 volts) of output, producing X dB of sound pressure measured at 1 m from the speaker.