Re: [Phys-l] decibel dilemma

[John Denker <jsd@av8n.com>]

Kilmer, Skip wrote:
> Does the fact that we aren't just adding power, but power as complex wave forms affect this
> argument?


An excellent question.

I reckon adding power is OK provided the sources are mutually uncorrelated.

This is ye olde question of add-before-you-square or square-before-you-add.
At some deep theoretical level, for waves of the same kind, it is never
wrong to add-before-you-square;  for sound waves this means adding the
pressure values, then squaring to get the power.

However, if the sources are uncorrelated, then when you do the square
the cross terms vanish (on average), so the bottom-line result is what
you would get by simply adding the power values.

In some ways this is related to Parseval's theorem.