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Author Topic: will different content in adjacent speakers cause phase issues?  (Read 3640 times)

david collins

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I've done some reading on this website and i *think* i've learned that you can't just line up more speakers side by side by side, because the sound beams will interfere with each other and create odd filter effects. so it would be ill advised to set up, say, two 15" 2 way boxes with 90 degree horizontal dispersion on either side of your target to get more loudness, or just more headroom so the speakers can each work less hard and sound better.

but what if you produced music with different content in each pair? 2.2.1 perhaps. B left, A left, C sub, A right, B right.  if the B speakers are playing piano and and the kicks high information, but the guitar, snare, and hats are in the A speakers, would there be unwanted coupling effects?

if that would even work, does anyone think there'd be any possible benefit or advantage to producing/performing music for and on a setup of this nature? i'd like to think that you'd get more volume and clarity, and i've read that some sound guys will have speakers in the center that do vocals. would that be a similar concept, or is this a dumb idea?
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Brian Jojade

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Re: will different content in adjacent speakers cause phase issues?
« Reply #1 on: December 08, 2021, 07:00:09 PM »

Any time you have multiple sources they impact each other to some degree. As you move through the pattern there may be slight areas of interference. But, since the material from each speaker is different, it will become unnoticeable.

As far as getting louder, that may not be so dramatic. Each speaker still can only produce the same peak SPL. Splitting that across 2 speakers doesn’t change that. Overall volume may end up higher when both are producing sound at the same time, but not by a lot.
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Riley Casey

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Re: will different content in adjacent speakers cause phase issues?
« Reply #2 on: December 08, 2021, 07:40:34 PM »

Phase cancellation is an issue when the same information ( waveform ) arrives at different times. Just because a snare drum and an electric guitar happen to produce sound at the same frequency at a given instant such cancellation as might occur is insignificant and in fact an integral part of the whole sound. Just imagine that the same thing happens without amplification. In the scenario you describe there would be no measurable phase cancellation

david collins

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Re: will different content in adjacent speakers cause phase issues?
« Reply #3 on: December 08, 2021, 08:02:26 PM »

Phase cancellation is an issue when the same information ( waveform ) arrives at different times. Just because a snare drum and an electric guitar happen to produce sound at the same frequency at a given instant such cancellation as might occur is insignificant and in fact an integral part of the whole sound. Just imagine that the same thing happens without amplification. In the scenario you describe there would be no measurable phase cancellation

Any time you have multiple sources they impact each other to some degree. As you move through the pattern there may be slight areas of interference. But, since the material from each speaker is different, it will become unnoticeable.

As far as getting louder, that may not be so dramatic. Each speaker still can only produce the same peak SPL. Splitting that across 2 speakers doesn’t change that. Overall volume may end up higher when both are producing sound at the same time, but not by a lot.

thank you both for taking the time to reply. would it be correct to say that the reason pairs wouldn't be louder is because each speaker is equally likely to be pushing or pulling at any given time, so you'd have an equal amount each of both pulling, both pushing, and contradictory motion? so, virtually no cancelling, but virtually the same amount of air pressure?

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Corey Scogin

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Re: will different content in adjacent speakers cause phase issues?
« Reply #4 on: December 08, 2021, 11:38:53 PM »

thank you both for taking the time to reply. would it be correct to say that the reason pairs wouldn't be louder is because each speaker is equally likely to be pushing or pulling at any given time, so you'd have an equal amount each of both pulling, both pushing, and contradictory motion? so, virtually no cancelling, but virtually the same amount of air pressure?

Two speakers side-by-side producing the exact same content will constructively couple at lower frequencies where the wavelength is long relative to the distance between the speaker centers, resulting in higher SPL at those lower frequencies.
If you listen to a sine wave tone at various frequencies while walking around in front, as the frequency increases, you'll hear alternating areas of constructive and destructive interference, resulting in higher SPL at some locations and lower SPL at others. That's what is referred to as having phase issues. As the frequencies increase further, the pattern of where constructive and destructive interference occurs will change.
Here's a visual that may help: falstad.com/interference

Two speakers producing different content side by side will not increase the SPL overall but may result in better sound. You might think of it as each speaker having to do less work, though that's an imprecise description.
What you describe in the original post is referred to as "dual PA". It's used not for increased SPL but for increased clarity. I don't know it well enough to explain it concisely but I believe the reason is that it avoids some instruments/frequencies modulating others. Dual PA is occasionally used on large tours too. I believe the U2 360 tour from years ago utilized dual line arrays.

One thing to note: when point-source speakers are built to be arrayable, the high frequency horn patterns overlap roughly at the -6db point and the diaphragm centers are relatively close to each other, minimizing the interference between them. Since the low frequency drivers are also close together and the lower frequencies are more omni-directional, they constructively combine resulting in an increase in low frequency SPL.
« Last Edit: December 08, 2021, 11:41:54 PM by Corey Scogin »
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Chris Grimshaw

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Re: will different content in adjacent speakers cause phase issues?
« Reply #5 on: December 09, 2021, 05:37:47 AM »

thank you both for taking the time to reply. would it be correct to say that the reason pairs wouldn't be louder is because each speaker is equally likely to be pushing or pulling at any given time, so you'd have an equal amount each of both pulling, both pushing, and contradictory motion? so, virtually no cancelling, but virtually the same amount of air pressure?

At some moment, the cones may be moving in opposite directions, or in the same direction. That's largely irrelevant here: if a guitar chord is sustained, and a snare drum is hit, some frequencies will be produced by both instruments at the same time. At 1kHz, for example, the snare may cancel the 1kHz component of the guitar for a very short duration, or it may sum. If the next snare hit is 0.5ms early/late, then the 1kHz component will then do the opposite, but only if the components are exactly in-phase. Chances are they won't be - they might be 10 degrees out, or 348 degrees out. It's almost certainly random, and we're only considering one specific frequency here.

It's important to note that we, as humans, don't perceive this. We hear a guitar chord and a snare hit. The above works for acoustic summation, too.



When it comes to PA systems, harmonic distortion and inter-modulation distortion (which are actually different manifestations of the same mechanism) play a key role.

Let's consider, for a moment, a typical scenario: we're running the PA system at or close to the limiters (because if we're not hitting the red occasionally, we've brought too much rig). The drivers are in their linear region, ish, but the linear region isn't, er, linear. You'll still have a few percent THD (Total Harmonic Distortion). That sounds fine for more sparse mixes (ie, just vocals). A little harmonic distortion can help "warm things up" - look at all the people using valve (tube) amps in their home HiFi systems, often listening to low-channel-count music.

When there are more components to the mix, the PA system can start to sound "congested" and "muddy". This is where the harmonic distortion components start piling up, and you've got the distortion of the bass guitar (for instance) turning the rest of the lower-mids to mush.
The instinct, then, is to push the faders further to get some channels louder than others, and then we're definitely into the limiters, with the overall sound quality suffering further.
What should be done there is reducing the volume a little, and allowing the PA to operate in a more comfortable fashion.

Running a dual PA system, and choosing which instruments go through which speakers, means we can reduce the piling up of harmonic distortion, improving clarity. In extreme cases, it stops the kick drum (for example) making the vocals go "crunch" each hit.

So, while it won't get much louder than a single PA, each cabinet isn't working so hard, so the audience receives cleaner sound overall.


Chris
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Dave Garoutte

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Re: will different content in adjacent speakers cause phase issues?
« Reply #6 on: December 09, 2021, 12:01:14 PM »

The Dead's wall of sound was the epitome of multi channel PA.
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John Roberts {JR}

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Re: will different content in adjacent speakers cause phase issues?
« Reply #7 on: December 09, 2021, 03:13:52 PM »

Do two musicians singing next to each other or two guitar players next to each other cause problems?

JR
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John Bosco

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Re: will different content in adjacent speakers cause phase issues?
« Reply #8 on: December 09, 2021, 03:17:52 PM »

Do two musicians singing next to each other or two guitar players next to each other cause problems?

JR

Not if they are friends, but if they are brothers, well we know how that turns out.
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Tim McCulloch

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Re: will different content in adjacent speakers cause phase issues?
« Reply #9 on: December 09, 2021, 05:48:07 PM »

Not if they are friends, but if they are brothers, well we know how that turns out.

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Re: will different content in adjacent speakers cause phase issues?
« Reply #9 on: December 09, 2021, 05:48:07 PM »


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