I recently purchased a lovely new power amp, a Hafler P4000, and have been making some basic comparisons between that, and my other amp (for sale, by the way). Both amps were bridged and ran through a 4x10 cabinet; the specs indicate 550 watts bridged @ 8 ohms for the Hafler P4000, and 830 watts bridged @ 8 ohms for the Crown Powertech 2.1. Using the levels as a guide, to my ears, the Hafler sounds almost twice as loud as the Crown, even though it's rated output is much less. the question is why do some amps have a higher output than others, if wattage is not a factor, then what is? Help me out here people.