Not sure what you're getting at here. Are you suggesting that the
(theoretical) 3dB increase occurs only when the total system power is
doubled, but not when the cone area is doubled?

NEITHER!!!

You get the 3db for the simple reason that two like sounds combine.
it has nothing to do with doubling the power or doubling the cone area!
(other than the power or cone area make the sound in the first place.)

This is the same thing though. Two like sounds combining is the same thing
as doubling the cone area (note: all else being equal, which as you pointed
out before, is a difficult proposition in the real world). Oftentimes,
modeling loudspeaker output consists of treating the cone as an infinite
amount of point sources. Whether you double cone area or double the number
of cones, you're doubling the number of "point sources". In effect, you've
got the same thing going on. So to say it has nothing to do with doubling
the power or cone area is not correct. It has everything to do with it.

I can have a speaker with an 8 inch cone and a speaker with a 15 inch
cone, the 15 may not be louder... so cone area alone is not a factor...

That's correct. There are other variables at play. But there's an
interdependence between all of them.


I can have a speaker being driven with 100 watts and when I increase it
to 200 watts I may not get 3dB more ...

You probably won't. Power compression is a key reason.

BUT, if I have one sound and add another sound the same SPL then I
WILL get 3db!!!

Assuming the wavelength is long enough.

See your way of doubling the cone or doubling the power MIGHT NOT
GIVE ME 3DB.... But my way ALWAYS DOES!!!!!

Not sure what you mean here. Doubling the power or cone area WILL ALWAYS
yield a 3dB increase, assuming everything else is held the same. That is,
same power output, same enclosure size/tuning characteristics, etc.

And, if I were to add two like sounds that were correlated
(in phase perfectly, very likely for bass in a car) then we would
increase
6db!!

the 3db for cone doubling and another 3db for power doubling is a MYTH.

It most certainly is not a myth. You're simply failing to keep the other
variables constant.

Mark Zarella wrote:

Not sure what you're getting at here. Are you suggesting that the
(theoretical) 3dB increase occurs only when the total system power is
doubled, but not when the cone area is doubled?

NEITHER!!!

You get the 3db for the simple reason that two like sounds combine.
it has nothing to do with doubling the power or doubling the cone area!
(other than the power or cone area make the sound in the first place.)

This is the same thing though.

No its not.... you cant double the cone area without doubling the motor
and the cone mass and a whole bunch of other variables.... You cant magicly
double the cone area and even if you did it would not guarantee a 3db
increase.... SO its NOT the same thing... Doubling the cone area MIGHT
give you 3db... doubling the sounds WILL give you 3db increase!! (correlated
gives you 6db)..

See the difference??
your way is MIGHT
my way is WILL
!!!!!!!!!!!!!!!!!!!!!

Not the same thing at all..

Two like sounds combining is the same thing
as doubling the cone area (note: all else being equal, which as you pointed
out before, is a difficult proposition in the real world).

all of what being equal???
Equal voice coil, equal magnets, equal suspension, equal cone weight???
???? Equal power??? How do you know its equal???

And what if it is NOT EQUAL???
What if one speaker is an 8 inch and one speaker is a 15 inch???
it could still be a 3db increase if they combine sounds!!
Then again it might not be!!

The common myth that doubling the cone area gets you 3db is
all full of holes!!

On the other hand 2 equal sounds however is not all full of holes...
it WILL get you 3db or 6db if correlated...

Oftentimes,
modeling loudspeaker output consists of treating the cone as an infinite
amount of point sources. Whether you double cone area or double the number
of cones, you're doubling the number of "point sources". In effect, you've
got the same thing going on. So to say it has nothing to do with doubling
the power or cone area is not correct. It has everything to do with it.

NO!
Its not the fact that the cone area doubles.
Its the fact that the sound doubles!!

MAYBE (and maye not) when you double cone area you get 3db!
But ALWAYS when the sound doubles you get 3db!

Not sure what you mean here. Doubling the power or cone area WILL ALWAYS
yield a 3dB increase, assuming everything else is held the same.

Everything else??
Your statement is missleading and flawed!
doubling the INPUT power to the speaker is likely to not give you
a 3db increase, you just said it as well....

Cone area IS NOT WHY the sound is louder!!
We could do it with a smaller cone or a larger cone or NO CONE AT ALL!

Blaming it on CONE AREA or POWER or BOTH is a flawed
way of looking at something thats very simple....

IF! and I stress IF!
your second speaker is the same size and IF it puts out the
same dB as the first one which is already playing then you
would get 3db, and you would be doubling your cone area.

BUT, and I stress BUT!
you could also get the same3dB without doubling your cone
area! You could get it if a smaller or larger speaker was
playing the same sound or you could get 3dB if a fat lady
was singing the same song at the same level... See, it has
nothing to do with cone area!!!

You COULD!
You MIGHT!
But it wont always!!
read this http://www.installer.com/tech/conearea.html

Eddie Runner

You get the 3db for the simple reason that two like sounds combine.
it has nothing to do with doubling the power or doubling the cone
area!
(other than the power or cone area make the sound in the first place.)

This is the same thing though.

No its not.... you cant double the cone area without doubling the motor
and the cone mass and a whole bunch of other variables.... You cant
magicly
double the cone area and even if you did it would not guarantee a 3db
increase....

I never claimed you could. In fact, I agreed with you on this point earlier
in the thread. But, in order to understand what's going on, it's often
useful to analyze the output of a system, any system, when changing just one
variable. The real life consequences may or may not reflect this analysis.
In this case, I think there is an application where this analysis reflects
the real world - for instance, adding the second sub, even if total system
power remains unchanged, is illustrative of this effect. However, you can't
use your oversimplified "adding an identical second source" analysis,
because it doesn't apply - the two sources aren't identical.

SO its NOT the same thing... Doubling the cone area MIGHT
give you 3db... doubling the sounds WILL give you 3db increase!!
(correlated
gives you 6db)..

See the difference??
your way is MIGHT
my way is WILL
!!!!!!!!!!!!!!!!!!!!!

Not the same thing at all..

Your way is "will" only under certain circumstances. It's not applicable
for others (see above). That's why it's useful to know the underlying
cause, rather than simplified shortcuts that aren't generalized for all
cases.


Two like sounds combining is the same thing
as doubling the cone area (note: all else being equal, which as you
pointed
out before, is a difficult proposition in the real world).

all of what being equal???
Equal voice coil, equal magnets, equal suspension, equal cone weight???
???? Equal power??? How do you know its equal???

In real situations, it's difficult to keep everything equal. But in the
case of adding second sources, you can keep everything you listed above
equal. You can selectively vary power in the process and arrive at all
kinds of answers - answers which you have a more difficult time predicting
using your one nongeneral way of looking at things.


And what if it is NOT EQUAL???
What if one speaker is an 8 inch and one speaker is a 15 inch???
it could still be a 3db increase if they combine sounds!!
Then again it might not be!!

Not only might it not be, but it's highly unlikely that it would be! First
of all, the freq response would probably be entirely different. If it was
not, then the sensitivity would probably be entirely different.


The common myth that doubling the cone area gets you 3db is
all full of holes!!

I agree that it's misused, but it's not full of holes. The theory stands
true. The problem is that many people apply it in the wrong way.

Oftentimes,
modeling loudspeaker output consists of treating the cone as an infinite
amount of point sources. Whether you double cone area or double the
number
of cones, you're doubling the number of "point sources". In effect,
you've
got the same thing going on. So to say it has nothing to do with
doubling
the power or cone area is not correct. It has everything to do with it.

NO!
Its not the fact that the cone area doubles.
Its the fact that the sound doubles!!

So then you're pointing out the obvious. All you're saying is
dB=10log(P/P0). You've said nothing but doubling a quantity is going to
yield a 3dB increase in that quantity. That applies to anything. I'm
talking about speakers. I'm talking about WHY the sound doubles. The
physical cause of the sound doubling. Quibbling over whether your units are
differential or logarithmic does not address this at all.

"Mark Zarella" pam
wrote:

Gosh isn't it interesting at how some folks need to argue things that might be
better spent on more productive issues. Mark is right but there is one area in
this discussion, not Mark's that needs a minor correction:

....sigh.....
SO its NOT the same thing... Doubling the cone area MIGHT
give you 3db... doubling the sounds WILL give you 3db increase!!
(correlated
gives you 6db)..



I think Eddie means combined "coherently". Two identical sounds will always be
"correlated". They can be nothing else if the are the 'same.'