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Author Topic: Running 2 PA systems side by side, pros and cons?  (Read 2420 times)

Justice C. Bigler

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #20 on: August 13, 2019, 12:48:56 am »

Apparently, I'm going to be running FIVE PA systems on this tour.

There are 5 hangs of Karas (54 cabinets): Left, inner Left, Center, inner Right, Right, with 2 hangs of SB18 subs somewhere. Yes, there are seven arrays hanging from our mother truss.

I'll start seeing all that stuff on Tuesday and figure out wtf it's all about. Something, something, L-ISA and spatial imaging...something.
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Douglas R. Allen

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #21 on: August 13, 2019, 06:39:45 am »

Apparently, I'm going to be running FIVE PA systems on this tour.

There are 5 hangs of Karas (54 cabinets): Left, inner Left, Center, inner Right, Right, with 2 hangs of SB18 subs somewhere. Yes, there are seven arrays hanging from our mother truss.

I'll start seeing all that stuff on Tuesday and figure out wtf it's all about. Something, something, L-ISA and spatial imaging...something.

Wow! I wouldn't recommend that junk thrown together at all. What you need is a point source , single speaker. I would recommend 1 of these , properly and safely hung. You should be able to do 25 to 30,000 people no problems. It has Blue Tooth to for the D.J.'s during break ! ;-)

https://www.idjnow.com/gemini-as-15blu-lt-powered-15-inch-speaker-with-led-array-and-bluetooth.html


Douglas R. Allen
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Michael Lawrence

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #22 on: August 13, 2019, 07:46:22 am »

Wow! I wouldn't recommend that junk thrown together at all. What you need is a point source , single speaker. I would recommend 1 of these , properly and safely hung. You should be able to do 25 to 30,000 people no problems. It has Blue Tooth to for the D.J.'s during break ! ;-)

https://www.idjnow.com/gemini-as-15blu-lt-powered-15-inch-speaker-with-led-array-and-bluetooth.html


Douglas R. Allen

And it lights up too! Great, I can leave the GrandMA on the truck.
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Caleb Dueck

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #23 on: August 13, 2019, 08:40:12 pm »

Apparently, I'm going to be running FIVE PA systems on this tour.

There are 5 hangs of Karas (54 cabinets): Left, inner Left, Center, inner Right, Right, with 2 hangs of SB18 subs somewhere. Yes, there are seven arrays hanging from our mother truss.

I'll start seeing all that stuff on Tuesday and figure out wtf it's all about. Something, something, L-ISA and spatial imaging...something.

L-ISA is pretty cool, that plus Digico means you should be in for a great time.  All you need now is Klang:Fabrik!
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Brad Jekko

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #24 on: August 14, 2019, 04:15:00 am »

It seems that splaying identical speakers side by side as opposed to stacking them vertically with the horns together is the less favoured option. So I might do neither, or use an outfill to get width if required.

I want to know more about, for example; different branded 12+1s over 15subs on each side, assuming they are crossed over at the same frequencies...what pros and cons are there with this? Could it actually reduce phaseyness and add more stereo image to the sound? Because the sounds coming out will not be identical?

Thanks for those who suggested hard panning vox and instruments, I was leaning in this direction, but I didn't want to go 100%, now I know it is an option I might try it.
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Luke Geis

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #25 on: August 14, 2019, 08:55:20 am »

The rules don't change. Any more than 1 source of sound and you start running into phase issues, PERIOD. The only reason to add more speakers is coverage. DO NOT do it to try and add SPL for the sake of adding SPL. In larger arena's and venues, you eventually have to supplement the main PA with delays, fills and other distributed speakers not so much to add SPL, but more to maintain it. Fills and delays are not really used to increase SPL, they are used to maintain or keep a desired level of SPL over larger distance. Out fills and front fills are typically not really loud as much as just there to fill in the missing frequency content at the same relative level as is needed for the area they cover.

The " Dual PA " concept is a little different. With this technique, each PA has its own specific content. One is for vocals only, while the other supports everything else. The main advantage of this is that you can tailor each system to be optimized for the content it reproduces. This changes the frequency response between the two enough that the systems, for the most part, stay out of each other's way. Because both systems are not truly reproducing the same sonic content, the interaction between the PA's is minimized. As would be obvious, each PA covers the same area, so there is no increase in that regard. Another potential advantage is that because each PA has specific content, it can be optimized further to increase potential SPL output. Especially for vocals, because you can really tune the PA to enhance vocals, it can get significantly louder than only using a single system for everything. The last and probably best asset to this deployment is that intermodulation distortion is significantly reduced. This means less harmonic distortion and increased intelligibility. More or less, you can acquire higher levels of clarity and intelligibility with less overall SPL!

In practice, it is advisable to NOT mix brands and models of speakers. Each little difference would, in theory, improve/reduce issues, but in reality, all it does is make one PA sound different from the other. This just diminishes the perceived quality of the show because as a person moves from zone to zone, it will sound different and still be plagued by at least some amount of destructive interference. Objectively, you are trying to make the entirety of the listening space sound the same. I also think it looks tacky to have multiple brands or models of speakers clumped together. When spread out in different areas, at least with different models or vendors of speakers, it at least looks intentional or purposeful.
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Don T. Williams

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #26 on: August 14, 2019, 07:03:19 pm »

It seems that splaying identical speakers side by side as opposed to stacking them vertically with the horns together is the less favoured option. So I might do neither, or use an outfill to get width if required.

I want to know more about, for example; different branded 12+1s over 15subs on each side, assuming they are crossed over at the same frequencies...what pros and cons are there with this? Could it actually reduce phaseyness and add more stereo image to the sound? Because the sounds coming out will not be identical?

Thanks for those who suggested hard panning vox and instruments, I was leaning in this direction, but I didn't want to go 100%, now I know it is an option I might try it.

We are not trying to pop your bubble, but unless the speaker components AND the crossover circuits are identical you are going to have issues.  A 12 dB per octave crossover at 1.5Khz does not have the same phase response as a 18 dB per octave 1.5K cross-over, and crossover filters can be Butterworth, Bessel, L-R, and other types of filters.  It's more than just crossover frequency.  To make matters more complicated, the speaker components themselves affect the cross-over.  Two different 1" throat compression dirvers probably have greatly different phase and frequency response curves even though they have very similar specs.  800 Hz to 15,000 Hz is an almost meaningless specification without a lot of other information.

Take the best advice given:  run it as a "dual" system or just don't bother to add more speakers.  In this audio situatiion 1+1 does not equal 2.  If all were perfect, the maximum increase in level would only be 6 dB. We already know this isn't and won't be a "prefect" situation.  Worst case puts you with a negative increase in level.  If you are worried it doesn't "look" powerful enough, just stack the second system up but don't use it.
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Luke Geis

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #27 on: August 14, 2019, 09:13:10 pm »

I don't give any credit to the whole idea of the +6db notion. In a perfect world right...... It is physically impossible to get the acoustic centers of the drivers close enough to be within 1/4 of a wavelength for any real usable bandwidth with ANY main/top PA system ( subs are a slightly different story ). At best with even a 10" speaker, the acoustic centers will be closer to 12" apart. This means that at best, you can achieve good acoustic coupling at frequencies below 280hz. I ain't no nose picker, but that sure seems useless to me since most 10" speakers will be crossed over around 100hz. So you get 100hz worth of real coupling where a +6db potential MAY be achievable.

Between all the comb filtering nulls and other garbage, the best usable overall ( read it as averaged ) spl gain you could see is +3db, and that is an at best. +3db is how loud a gnat farts when she is trying to lay eggs in your ear at night when the world is asleep. As mentioned and re-iterated, DO NOT use more speakers to increase potential SPL, only use it to increase coverage. If you do a Dual PA setup where vocals are in one system and the rest of the band is in the other, then and only then, you might be cooking with gas.

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Frank Koenig

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #28 on: August 14, 2019, 09:48:13 pm »

This means that at best, you can achieve good acoustic coupling at frequencies below 280hz.

While I'm not for one moment defending random piles of speakers for increasing SPL at the expense of SQ, the situation is not quite that dire. Two co-planer point sources 12 in. apart observed 30 deg off axis, for instance, will be 120 deg out-of-phase at 753 Hz. Plenty of "2-tens-and-a-horn" speakers have their woofers farther apart than that. On axis you will indeed get a 6dB increase in available output as the sound pressures sum (this is neglecting any baffle effect). For uncorrelated sources (random phase) the powers, rather than the pressures, sum and the increase will be 3 dB. Get out your sound level meter and try it -- it really works. --Frank

"Co-planer" was a poor choice of words. Two points are always co-planer. What I was trying to say is that both sources lie in a plane to which the acoustic axis is normal -- as two speakers side-by-side.
« Last Edit: August 15, 2019, 11:11:14 am by Frank Koenig »
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Dave Garoutte

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Re: Running 2 PA systems side by side, pros and cons?
« Reply #29 on: August 15, 2019, 03:14:14 pm »

While I'm not for one moment defending random piles of speakers for increasing SPL at the expense of SQ, the situation is not quite that dire. Two co-planer point sources 12 in. apart observed 30 deg off axis, for instance, will be 120 deg out-of-phase at 753 Hz. Plenty of "2-tens-and-a-horn" speakers have their woofers farther apart than that. On axis you will indeed get a 6dB increase in available output as the sound pressures sum (this is neglecting any baffle effect). For uncorrelated sources (random phase) the powers, rather than the pressures, sum and the increase will be 3 dB. Get out your sound level meter and try it -- it really works. --Frank

"Co-planer" was a poor choice of words. Two points are always co-planer. What I was trying to say is that both sources lie in a plane to which the acoustic axis is normal -- as two speakers side-by-side.
Parallel axes?
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Re: Running 2 PA systems side by side, pros and cons?
« Reply #29 on: August 15, 2019, 03:14:14 pm »


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