Number of drivers, power, and db output

Archived from groups: rec.audio.tech (More info?)

Computer Prog wrote:

> Lets say we have a subwoofer driven off a 500W amp and it can output
> 120db at a specific distance.
>
> Lets now assume that we have the same sub driven off a 250W amp and it
> now produces 117db at the same distance. (120db – 3db for half the
> power).
>
> Finally lets add another identical sub driven off another identical
> 250W amp and it also produces 117db.
>
> What will produce more output, the single 120db sub driven off the
> 500W amp or the two 117db subs driven off the two 250W amps?

In theory the output will be the same, in practice you may be able to get
better loading with the pair, in particular if you are using horn loaded
boxes then the increase in effective mouth area can be a big win.

Also voice coil heating may be less of an issue with the pair of 250W units.

I would be careful of comb filtering issues if I was using a pair of subs
which were less then 10 feet apart but were too far apart to couple.

Regards, Dan.

Archived from groups: rec.audio.tech (More info?)

computer_prog@hotmail.com (Computer Prog) wrote in message news:<455714d5.0410201132.697705c4@posting.google.com>...
> Lets say we have a subwoofer driven off a 500W amp and it can output
> 120db at a specific distance.
>
> Lets now assume that we have the same sub driven off a 250W amp and it
> now produces 117db at the same distance. (120db ? 3db for half the
> power).
>
> Finally lets add another identical sub driven off another identical
> 250W amp and it also produces 117db.
>
> What will produce more output, the single 120db sub driven off the
> 500W amp or the two 117db subs driven off the two 250W amps?

Here's my convoluted way of thinking about it. Acoustical power is
proportional to the square of cone acceleration * area. Cut the power
in half, and you have 70% of the cone motion. Now add the second amp &
speaker, and you have the same cone motion but twice the area, so now
you have effectively 140% of your original cone motion. Squaring this,
you get twice the acoustical power.

This is why a lot of musical amplifiers have really huge cones, or
multiple drivers.

Archived from groups: rec.audio.tech (More info?)

"dangling entity" <randycat99@earthlink.net> wrote in message
news:54258935.0410222139.363b4580@posting.google.com...
> Yes, I was thinking somewhere along the line, doubling up on woofers
> actually gives you +6 dB, instead of +3 dB. I haven't used it in a
> while, so I'm pretty rusty.

It's true that two woofers at 50% drive power produce more output than one
at 100% drive; this is because of 'mutual coupling'. For this to work, the
drivers must be in a cabinet configuration that benefits from mutual
coupling.
I can attest from personal speaker building experience that it gives more
bang for the buck to have two drivers instead of one, AND you improve
reliability by lightening the burden on either driver.


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
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-

Archived from groups: rec.audio.tech (More info?)

On Wed, 20 Oct 2004 16:30:17 -0400, "Arny Krueger" <arnyk@hotpop.com>
wrote:

>"Computer Prog" <computer_prog@hotmail.com> wrote in message
>news:455714d5.0410201132.697705c4@posting.google.com
>> Lets say we have a subwoofer driven off a 500W amp and it can output
>> 120db at a specific distance.
>>
>> Lets now assume that we have the same sub driven off a 250W amp and it
>> now produces 117db at the same distance. (120db - 3db for half the
>> power).
>>
>> Finally lets add another identical sub driven off another identical
>> 250W amp and it also produces 117db.
>>
>> What will produce more output, the single 120db sub driven off the
>> 500W amp or the two 117db subs driven off the two 250W amps?

I think we have been here before. . .

>
>Presuming that the subs are linear, the amount of energy transferred into
>the environment is the same due to conservation of energy.

Well yes, 500 watts of power in, 500 watts of heat out. The room
warms up just the same.

>
>However, two identical subs will not have the same radiation pattern as
>either sub. Two subs radiate their energy over a slightly smaller region,
>because the larger effective diaphragm will be more directional. If the
>measurement position is some distance from the subs, the SPL at the
>measurement mic will be higher for the two identical subs, presuming
>conventional side-by-side mounting and otherwise normal use.
>
>