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Tim Sprout Tim Sprout is offline
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Default How do sound decibels add together?

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

Tim Sprout
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William Sommerwerck William Sommerwerck is offline
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"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.
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PStamler PStamler is offline
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Default How do sound decibels add together?

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
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Default How do sound decibels add together?

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
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William Sommerwerck William Sommerwerck is offline
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Default How do sound decibels add together?

"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.



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Sean Conolly Sean Conolly is offline
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Default How do sound decibels add together?

"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


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Adrian Tuddenham[_2_] Adrian Tuddenham[_2_] is offline
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Default How do sound decibels add together?

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
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Default How do sound decibels add together?

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
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Default How do sound decibels add together?

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."
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"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.



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Default How do sound decibels add together?

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


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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.


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Default How do sound decibels add together?

geoff wrote:

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.


Just to avoid confusing the uninitiated:

Double the voltage = quadruple the power = +6dB

Always relate dB back to power and then it will make sense with less
chance of an error. I know it's pedantic, but it avoids a lot of the
misunderstandings which can occur if the 'power' step is left out of the
reasoning.

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

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.


Just to avoid confusing the uninitiated:

Double the voltage = quadruple the power = +6dB

Always relate dB back to power and then it will make sense with less
chance of an error. I know it's pedantic,


Avoiding burning something up is hardly pedantry.

but it avoids a lot of the
misunderstandings which can occur if the 'power' step is left out of the
reasoning.


--
Les Cargill


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Default How do sound decibels add together?

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



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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.


Just to chuck a spanner in the works, it depends what you mean by
"loudness".

The power of a sound is the oscillating pressure change multiplied by
the oscillating particle velocity. The capsule of a SPL meter measures
the pressure change and then assumes the velocity change is proportional
to that. Therefore, if the sound power is calculated by multiplying the
pressure change by the velocity change, the power is proportional to the
square of the pressure change (or proportional to the square of the
velocity change if you measured it with a ribbon mic). This is why the
scale on a common-or-garden analogue SPL meter is not marked linearly:
it has to take account of the square-law relationship.

If you used a pressure capsule on a voltmmeter or oscilloscope to
measure the pressure, you would have to square the readings to make them
proportional to power.


To come back to your cheering people, the power of their voices does add
up linearly (assuming they are uncorrelated and all exactly the same
distance from the mic), but the mic voltage from 50,000 people will be
SQRT(50,000) times the voltage of one single person.


Now to throw another spanner in the works. Suppose you had a single
loudspeaker generating a given sound power and you added a second
loudspeaker giving the same power but uncorrelated - you would expect
double the sound power (+3dB) and you would be correct. Now drive the
second speaker in exact correlation with the first and the theory says
you would get +6dB, which is four times the power - "but that's
nonsense!" I hear you say. However, each loudspeaker is now working in
the pressure field generated by the other, so it is having to do twice
as much work; which means that the theory stands up to reality.

In practice, most loudspeakers are so inefficient that the actual sound
power they deliver is just a tiny proportion of the total electrical
power they absorb, so you you wouldn't notice much change in the loading
on the amplifiers. You might find there isn't a 6dB increase in
practice, because the increased loading on each loudspeaker may mean
that it can no longer deliver as much sound power as when it was
unloaded.


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

So... loudness is power based, logarithmic.


No. Loudness is a subjective measurement. It is not exactly related to SPL.
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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


A rough rule of thumb - all else being equal - is that you need about
a 10dB increase in SPL for a subjective doubling of perceived
loudness. This comes with a multitude of caveats.

d
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Default How do sound decibels add together?

Don Pearce wrote:

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.


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.


In an open stadium this is definitely the case; you can think of the top
of the stadium as being infinitely absorptive. Sound just goes up and keeps
on going. But in a closed reverberant basketball court it's not!
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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On Tue, 2 Sep 2014 20:23:51 +0000 (UTC), Jeff Henig
wrote:

Don Pearce wrote:
On 2 Sep 2014 14:39:09 -0400, (Scott Dorsey) wrote:

Don Pearce wrote:

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.

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.

In an open stadium this is definitely the case; you can think of the top
of the stadium as being infinitely absorptive. Sound just goes up and keeps
on going. But in a closed reverberant basketball court it's not!
--scott


We don't bother with basketball over here, but a large public swimming
pool certainly proves this. Why do people insist on screaming when
they swim?

d


Maybe you should stop throwing Babe Ruth bars into the pool, Don.

(One of my fave movie pranks, BTW. Caddy Shack was a classic.)


Okay, not seen that movie, but | looked up Babe Ruth bars - couldn't
find them. But I did find Baby Ruth bars, and even before I realised
what the swimming pool prank must have been, I got what they looked
like.

What kind of a mind do I have?

d
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On Tue, 2 Sep 2014 21:09:02 +0000 (UTC), Jeff Henig
wrote:

Don Pearce wrote:
On Tue, 2 Sep 2014 20:23:51 +0000 (UTC), Jeff Henig
wrote:

Don Pearce wrote:
On 2 Sep 2014 14:39:09 -0400, (Scott Dorsey) wrote:

Don Pearce wrote:

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.

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.

In an open stadium this is definitely the case; you can think of the top
of the stadium as being infinitely absorptive. Sound just goes up and keeps
on going. But in a closed reverberant basketball court it's not!
--scott

We don't bother with basketball over here, but a large public swimming
pool certainly proves this. Why do people insist on screaming when
they swim?

d

Maybe you should stop throwing Babe Ruth bars into the pool, Don.

(One of my fave movie pranks, BTW. Caddy Shack was a classic.)


Okay, not seen that movie, but | looked up Babe Ruth bars - couldn't
find them. But I did find Baby Ruth bars, and even before I realised
what the swimming pool prank must have been, I got what they looked
like.

What kind of a mind do I have?

d


Here's your clip. Heh...

http://youtu.be/TPxiXGr9nFM


Yup, I wrote exactly that scene in my head. Somebody had to eat it at
the end.

d
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On 3/09/2014 4:35 a.m., Tim Sprout wrote:


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.


That one must be a really crap team !

geoff

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Don Pearce: Got a problem with basketball? Where is "over here", man?
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On Tue, 2 Sep 2014 16:12:15 -0700 (PDT), wrote:

Don Pearce: Got a problem with basketball? Where is "over here", man?


No problem with it - apart from the extreme tedium of course. Over
here is England.

d
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Don Pearce wrote: "On Tue, 2 Sep 2014 16:12:15 -0700 (PDT), wrote:

Don Pearce: Got a problem with basketball? Where is "over here", man?


No problem with it - apart from the extreme tedium of course. Over
here is England.

d "

Oh, ok, just making sure.
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On 03/09/2014 18:26, Don Pearce wrote:
On Wed, 3 Sep 2014 17:04:19 +0000 (UTC), Jeff Henig
wrote:

BTW, dry humor is NOT a bad thing--it's actually my favorite. Dry sarcasm
is the best.


Yup. The humour I like best is the kind that makes me work a little to
get it.


I quite like the stuff that doesn't seem funny when you hear/ see it,
then a few moments or weeks later hits you. Often while you're in a
situation where you daren't laugh.

That and a good bit of slapstick.
--
Tciao for Now!

John.
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On Wed, 03 Sep 2014 Don Pearce wrote:

We didn't build the world's greatest empire by staying indoors just
because it wa a bit damp and chilly outside.


Quite. Given most of our houses were equally cold and damp inside.


Dead right. I remember as a child in winter there was usually ice on
the inside of my bedroom window. No central heating, and the living
room was the only one with a fire.


Luxury! Further north we had to walk barefoot in the snow to school every
day...10 miles - uphill in both directions.
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In article ,
Tom McCreadie wrote:
On Wed, 03 Sep 2014 Don Pearce wrote:

We didn't build the world's greatest empire by staying indoors just
because it wa a bit damp and chilly outside.

Quite. Given most of our houses were equally cold and damp inside.


Dead right. I remember as a child in winter there was usually ice on
the inside of my bedroom window. No central heating, and the living
room was the only one with a fire.


Luxury! Further north we had to walk barefoot in the snow to school every
day...10 miles - uphill in both directions.


Don't know you were born. We started work down pit at 3 years old. Only
school we had was Sunday school, after the 6 am service. Then had to groom
the pit ponies. We did get Xmas off though - on a leap year.

--
*A woman drove me to drink and I didn't have the decency to thank her

Dave Plowman London SW
To e-mail, change noise into sound.
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Default How do sound decibels add together?

"Gary Eickmeier" wrote in message
...
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


While you were busy dismissing actual technical details as irrelevant
(no surprise, since you apparently can't be bothered to understand
what you're talking about), you forgot to actually read the OP and
misrepresented it. There was nothing specific about speakers.

Regardless, many of the technical details posted on the thread are
explicitly relevant to multiple sound sources in a room, and are
accurate technically. But you think they're "scholarly" so you don't
have to bother understanding. So you don't understand: business as
usual. Even reading the manual seems too tediously "scholarly" for
you, so you don’t bother; and when you make ridiculous claims about
understanding how your own equipment works, you end up with egg on
your face.

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.


Master of the obvious! Boy, you must be some kind of "scholar" to know
that advanced stuff! It's nice of you to come here and explain it to
the experts.




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