Audio Systems: various class power amplifier efficiency, audio power amplifier, complex circuitry

Question
hi, i want to ask that "A" class audio amplifier 25% efficient, class "B" is 50% efficient, class "C", "D", and "F" are 90% efficient.
my question is as under.
1 - what is the meaning of various class efficiency and efficiency has to do with what
   (A) - more efficient audio power amplifier give more out put at speaker? or vice a versa.
   (B) - more efficient audio power amplifier draw less ac watt at      electricity supply? or vice a versa.
   (C) - class "H" and "G" audio power amplifier how much efficient?

thanks.

Answer
There is a very good discussion in this paper:

http://www.imws.nuim.ie/publications/documents/sralph.pdf

I suggest you begin reading around page 16.

Class H and G require a feedback to the power supply increasing the rail voltages as the power out increases. It is just a variation of circuitry to get a little more efficiency.  This class of audio power amplifier has not become popular because the benefits do not offset the additional cost of the complex circuitry.

Do you need more?