Originally Posted by: Lordathestrings[font=trebuchet ms]Doubling the power into the same speaker will produce a barely perceptible increase in the Sound Pressure Level. SPL is expressed in logarithmic units, in this instance an increase of 3 dB. If one speaker is more efficient than the other, this could contribute more than the power difference. If the 15 Watt amp has a speaker rated at 96 dB SPL at 1 Watt (the standard comparison), and the 30 Watt amp is driving a speaker rated at 92 dB SPL, then the 15 Watt amp will be slightly louder than the 30 Watt amp, until both amps are driven flat-out, and then they would become about equal.[/font]