[Don Pearce[_3_]]

On Tue, 02 Sep 2014 08:35:32 -0800, Tim Sprout
wrote:

On 9/1/2014 4:25 AM, 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

d

So...loudness is power based, logarithmic. A stadium of 50,000 cheering
people generates power, which increases the loudness, with some
attenuation depending on phase, and is not 50,000 X the loudness of 1
person cheering.

Thanks. I have always wondered about this.

Tim Sprout

And bear in mind that most of those 50,000 are a long way from you.
Only the nearest twenty or so people contribute in meaningful way to
the loudness you hear. The rest just add the background sussuration.

d