[Tim Sprout]

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

Tim Sprout

[William Sommerwerck]

"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.

[PStamler]

What William said. That's roughly how sound levels (dB-SPL) add. If the two levels aren't identical it gets a little more complex.

Peace,
Paul

[geoff]

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, as in phase-locked.

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

geoff

[William Sommerwerck]

"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.

[Sean Conolly]

"William Sommerwerck" wrote in message
...
"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.

My precarious and aging memory agrees with Geoff. If the signals are
correlated with zero phase difference you add 3db. If they are out of phase
then less, or even attenuation.

But if we sum equal levels of random noise, I'd guess at any given moment
you'd have slightly less than 3db, but when averaged over time the signals
are would still would add 3db when summed.

Then again, I've been having my share of 'senior moments' today.

Sean

[Scott Dorsey]

Sean Conolly wrote:

My precarious and aging memory agrees with Geoff. If the signals are
correlated with zero phase difference you add 3db. If they are out of phase
then less, or even attenuation.

This is correct for powers, which is what we are talking about when we
talk about SPL.

But if we sum equal levels of random noise, I'd guess at any given moment
you'd have slightly less than 3db, but when averaged over time the signals
are would still would add 3db when summed.

I believe it is 1.5dB for adding uncorrelated noises with the same spectra
and the same average amplitude.

All of this is fairly clumsy, because Bels, being a logarithmic scale, are
not really intended for summing. They exist to make multiplying easier.
Often if you have to sum values it's easier just to work back from SPL to
pressure level in pascals and sum pressures (or back to volts or watts or
what have you).
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

"Sean Conolly" wrote in message ...

But if we sum equal levels of random noise, I'd guess at any given
moment you'd have slightly less than 3dB, but when averaged over
time the signals are would still would add 3db when summed.

If they were always "slightly less than 3dB", then they could never be 3dB
over the long term.

[Adrian Tuddenham[_2_]]

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 and in-phase, they will add to give an increase of 6dB

Correlated and out of phase, they will cancel, the degree of
cancellation depending on the accuracy of the phasing and amplitude.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[geoff]

On 1/09/2014 10:46 p.m., Adrian Tuddenham wrote:
k.

Correlated and in-phase, they will add to give an increase of 6dB

Yes - that's double the voltage = +6dB, double the power = +3dB.


Correlated and out of phase, they will cancel, the degree of
cancellation depending on the accuracy of the phasing and amplitude.

[Don Pearce[_3_]]

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

"geoff" wrote in message
m...
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

[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

[Tim Sprout]

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