[Gary Eickmeier]

Don Pearce wrote:
On Sun, 31 Aug 2014 17:13:57 -0700, "William Sommerwerck"
wrote:

"geoff" wrote in message
...
On 30/08/2014 9:48 a.m., William Sommerwerck wrote:
"Tim Sprout" wrote in message ...

If you play two sounds simultaneously, each at 100 decibels, what
would a decibel meter [sic- read? 100 decibels?

Assuming the sounds are uncorrelated, the powers add:
100dB + 100dB = 103dB.

Surely you are ARE correlationed [sic], as in phase-locked.

??? Why should they be?


In general terms yes, 103dB, but if not identical in every way,
slightly less than 103.

The powers of two uncorrelated signals simply add -- that's a fact.
100dB + 100dB = 103dB

Correlated signals -- I don't remember. I'd have to dig out a book.

Correlated signals will add to 106dB if in perfect phase - right down
to - infinity dB if perfect antiphase

I don't think all of these scholarly statements apply to loudspeakers
playing in a room, which is what the OP was talking about. For example, two
speakers playing a mono signal out of phase - you would not hear nothing,
you would hear plenty. It would just sound weird.

Gary Eickmeier