beaverd, Here is a link to an article on amplifier efficiency.
http://sound.westhost.com/efficiency.htm It is generally considered by many people that a good amplifier should behave like a pure voltage source. As the the load decreases ,say from 8ohms to 4ohms the amplifier should double its output. 50w to 100w and so on forever.
This would mean that infinite current from the amplifier would be available to be supplied into the load. If your voltage supplied from the amp stays constant regardless of the load than you have no limit on the current that the amp can supply. Volts X Amps = watts The amperage doubles when the load is halved. If the amp can behave as an ideal voltage source
at least down to 4ohms it has a chance to sound better driving real world loudspeakers,2ohms is even better. This ability requries two things,a power supply large enough to do this and an output stage with transistors that have high power ratings. One of the single most expensive items in a power amp is the power supply the second is the number of high current devices in the output stage. Amplifiers that approach ideal voltage source behavior with realworld loudspeakers cost more money.
Now for the downside, even if the amplifier can double its output
into lower impedance loads it can still sound like crap. The amp should be designed to sound good first and it should be given an adequate power supply to deal with low impedance loudspeakers.Unfortunately designing a good sounding amplifier is not a simple engineering exercise in power delivery.
I hope this has been helpful, Scotty
