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From: Leon on 18 Feb 2010 15:24

If I put 2 equal powered speakers (subs) together, I guess I get 3db more SPL
plus 3db from coupling effects? Or is it 6?

If I add to the bunch, how does it increase?

Does it matter if I put 4 cabs in a line, or 2 on top of 2? What about 2 in each
corner compared to 4 below mid stage? ( I know not to tower them up 1x4!!)

I have some cheap subs ($200) that are rated 118db @ 400 watts (their maximum),
so if I put 4 together what could the rating go up to?

I want to be able to match up with 4 - 450 top boxes.

Thanks!

From: Joe Kotroczo on 18 Feb 2010 15:52
On 18/02/2010 21:24, in article vl7rn5tc815ldfklkj176lncpolu4fqcm5(a)4ax.com,
"Leon(a)nospam.com" <Leon(a)nospam.com> wrote:

>
> If I put 2 equal powered speakers (subs) together, I guess I get 3db more SPL
> plus 3db from coupling effects? Or is it 6?
>
> If I add to the bunch, how does it increase?
>
> Does it matter if I put 4 cabs in a line, or 2 on top of 2? What about 2 in
> each
> corner compared to 4 below mid stage? ( I know not to tower them up 1x4!!)

The short answer: yes it matters.

And by the way: vertical sub arrays are all the rage lately. ;-)

A nice paper on sub arrays is here:
http://www.voidaudio.com/pdf/bass%20guide.pdf

--
Joe Kotroczo kotroczo(a)mac.com

From: Denny Strauser on 18 Feb 2010 16:24
Joe Kotroczo wrote:
> On 18/02/2010 21:24, in article vl7rn5tc815ldfklkj176lncpolu4fqcm5(a)4ax.com,
> "Leon(a)nospam.com" <Leon(a)nospam.com> wrote:
>
>> If I put 2 equal powered speakers (subs) together, I guess I get 3db more SPL
>> plus 3db from coupling effects? Or is it 6?
>>
>> If I add to the bunch, how does it increase?
>>
>> Does it matter if I put 4 cabs in a line, or 2 on top of 2? What about 2 in
>> each
>> corner compared to 4 below mid stage? ( I know not to tower them up 1x4!!)
>
> The short answer: yes it matters.
>
> And by the way: vertical sub arrays are all the rage lately. ;-)
>
> A nice paper on sub arrays is here:
> http://www.voidaudio.com/pdf/bass%20guide.pdf
>
When the Grateful Dead did Stadium shows in the late 80's, their subs
were stacked 1-wide/14-high. By stacking them vertically, the vertical
dispersion is narrowed, and the sub frequencies were sent more into the
listening area & not into the sky. And a 50 foot array gave them a
frequency response down to single digits. AWESOME!

- Denny
From: GregS on 18 Feb 2010 16:29
In article <vl7rn5tc815ldfklkj176lncpolu4fqcm5(a)4ax.com>, Leon(a)nospam.com wrote:
>
>If I put 2 equal powered speakers (subs) together, I guess I get 3db more SPL
>plus 3db from coupling effects? Or is it 6?

6 total.

>If I add to the bunch, how does it increase?

If you add 2 more its another 6.

>Does it matter if I put 4 cabs in a line, or 2 on top of 2? What about 2 in
> each
>corner compared to 4 below mid stage? ( I know not to tower them up 1x4!!)
>
>I have some cheap subs ($200) that are rated 118db @ 400 watts (their maximum),
>so if I put 4 together what could the rating go up to?
>
>I want to be able to match up with 4 - 450 top boxes.
>
>Thanks!
>

I was reading posts from some guy, I think in engineering, that the maximum
addition of sound you can get is just over 10 dB. Maybe 12, from acoustic
gain effect. I'll read the Voidaudio site and see if I archieved the other guys posts.
guys posts.

greg
From: Krooburg Science on 18 Feb 2010 20:33
On Feb 18, 12:24 pm, L...(a)nospam.com wrote:
> If I put 2 equal powered speakers (subs) together, I guess I get 3db more SPL
> plus 3db from coupling effects? Or is it 6?

With a set of subs, doubling power into that set nets a 3dB increase
in output not taking power compression into account. Doubling boxes
but with the same power *dissipated* (half the power per box from the
original number) nets a 3dB increase. Doubling an boxes *and* amp
power nets a 6dB increase. If you have an amp that's putting out 100
watts into 8 ohms and you add another identical 8 ohm box, the amp
power out nearly double from supplying 2x as much current. So
inherently when you double subs connected to an amp or double up subs
& add amp, you're essentially doubling power and boxes for a 6dB
increase in output.

With top (mid/high) boxes, the net increase in SPL for doubled boxes
in an *array* and doubled power is only ~3dB due to a combination of
destructive & constructive interference (comb filtering). Putting
boxes together with a combination of coupling and non-coupling drivers/
frequencies, that is the result. This is because drivers and boxes
need to have their distances within a 1/4 of the wavelength of the
frequencies they're reproducing. After that distance, they start to
comb. Low frequencies have relatively long wavelengths, but upper mids
and highs don't. With subs in clusters, the drivers and frequency
couple very well. Not so with top boxes past the lower frequency
bandpass. Here's a link to an audio frequency wavelength calculator if
you feel like plugging in some numbers:

http://www.sengpielaudio.com/calculator-wavelength.htm

> If I add to the bunch, how does it increase?

As stated before, doubling subs and amp power nets a 6dB increase. So
it's an exponential relationship of box count vs. output:

1 sub = 0dB baseline
2 subs = +6dB SPL gain over 1 sub
4 subs = +6dB SPL gain over 2 subs (12dB more than 1)
8 subs = +6dB SPL gain over 4 subs (18dB more than 1)
16 subs = +6dB SPL gain over 8 subs (24dB more than 1)
32 subs = +6dB SPL gain over 16 subs (30dB more than 1)
and so on....

> Does it matter if I put 4 cabs in a line, or 2 on top of 2? What about 2 in each
> corner compared to 4 below mid stage? ( I know not to tower them up 1x4!!)

With only 4 small subs, it's not going to make much if any difference.
You need a pretty long line of boxes to achieve any real pattern
control. Now the larger the sub array and the arrangement, the more
difference it's going to make on the pattern control & coverage. The
longer the array the more pattern control will be exhibited end to end
due to interference from one end of the array to the other. The
frequency the pattern control is effect to depends on the array
length. This is true in both horizontal and vertical arrays. Depending
on the venue and the array implementation, this can be an asset or a
detriment to audience coverage.

> I have some cheap subs ($200) that are rated 118db @ 400 watts (their maximum),
> so if I put 4 together what could the rating go up to?

Take the SPL ratings with grain of salt, especially with cheap boxes.
There is likely no qualifier of what frequency they're talking about
and calculated specs, the most common, often don't come close to real
world performance. As for the answer based on the "calculated" spec, 4
subs vs. 1 would give you a 12dB increase in level if they're packed
together in an outdoor free field. If you place them in separate
areas, they will comb filter and the average level will be less than
the 12dB calculation. However, in a room things can be much different
due to boundary reflections. It can increase SPL or decrease it
depending on room modes.

>
> I want to be able to match up with 4 - 450 top boxes.
>
> Thanks!

K.
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