Power amp for PA subs

[Barisaxman]

Having subs SL and SR isn't automatically a bad thing, as it is sometimes made out to be. This is where some extra reading in phase cancellation would do you well. The cancellations/summations caused by having left and right subs are only going to be at frequencies where the physical dystance between subs dictates it to be. It's up to the individual user if the power alley effect is something they can live with, or whether pursuing another deployment option is preferable.

 

[s0c9]

[In most cases], if you have SL and SR subs, the amp(s) or self-powered subs should be fed a summed mono signal from your DSP (if you are using a DSP). If you do, there's no such thing as phase cancellation from the subs.. can't happen as they both get the same in-phase signal. It might be room nodes, but that's not the same thing.
IF you don't have a DSP, then how the OP fed the subs might be part of the perceived volume loss and MIGHT be due to phase cancellation.

Center clustering subs (power alley) is not really relevant in the average club/bar venue.. rooms are not large enough, unless your subs are grossly under-powered. The perceived benefit is mentioned in other posts is likely due to collective (combined, single source) volume, not because it's "better". Larger churches, auditoriums, outdoor gigs and the like will benefit from a power alley config vs SL/SR - depending on sub power (wattage). Center clusters in restaurant/bars is not sonically better than SL/SR and (if your subs are setup correctly) you should not notice any difference. Bass is omni-directional.

I'd be curious to see the OP report back on trying to power ONE LS808 with that amp bridged and hear the results.

 

[AndyPanda]

This is how you get phase differences depending on listening position (even if you are summed to mono and have your speaker polarity matched). Any listening position other than center will get the signal from the two speakers at different times

 

[walterw]

Because I dont want to have to buy another 3000 watt poweramp to drive 2 subs. The LS808s only work well if coupled together.

That's the part that makes no sense, they work just as well split apart as any other subs, and better than most in that price/size range. Different sub designs don't magically cancel the same frequencies at the same distances differently.

I've heard two of these crush in a club split a good 20 feet apart, utterly "underpowered" with maybe 7-800 watts each.

 

[s0c9]

This is how you get phase differences depending on listening position (even if you are summed to mono and have your speaker polarity matched). Any listening position other than center will get the signal from the two speakers at different times
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AndyPanda..
Sorry.. but that's not a phasing issue you are showing for bass. That's a (stereo) listening position issue best corrected by running the PA in MONO PA (whole other topic).

 

[s0c9]

That's the part that makes no sense, they work just as well split apart as any other subs, and better than most in that price/size range. Different sub designs don't magically cancel the same frequencies at the same distances differently.

I've heard two of these crush in a club split a good 20 feet apart, utterly "underpowered" with maybe 7-800 watts each.

I own TWO LS800P's.. I have NEVER used more than one in a club for up to 500 people (I'm guessing that #).
They are VERY, VERY LOUD..

 

[Downunderwonder]

Someone up there ^ is misusing "power alley" This effect is a split sub phenomenon. Only in the middle do you get pure bass. Either side you get comb filtering dropouts of 1/2 wave distance differential.

This is most noticeable at 80hz. Moving left or right 3 and a bit feet puts you 1/2 wavelength closer to one than the other. Up the middle of the dead zone is an alley of strong 80hz.

Clustering the subs in the middle, or at a wall, the bass drops off uniformly from there.

 

[Downunderwonder]

AndyPanda..
Sorry.. but that's not a phasing issue you are showing for bass. That's a (stereo) listening position issue best corrected by running the PA in MONO PA (whole other topic).

That's incorrect.

 

[AndyPanda]

AndyPanda..
Sorry.. but that's not a phasing issue you are showing for bass. That's a (stereo) listening position issue best corrected by running the PA in MONO PA (whole other topic).

Sorry but you are incorrect ...

 

[s0c9]

That's incorrect.

It's not incorrect.. comb filtering and phasing are 2 different issues.. and your explanation of comb filtering was good, but it's not caused by phasing.. unless the speakers are incorrectly wired, you don't use a crossover and run subs in stereo (bad idea). With a crossover, there should be no phasing or comb filtering with split stacks (assuming same size speakers/models) and a mono feed. If you have a stereo feed to your subs, different or multiple sub sizes per side, all bets are off.

 

[AndyPanda]

It's not incorrect.. comb filtering and phasing are 2 different issues.. and your explanation of comb filtering was good, but it's not caused by phasing.. unless the speaker are wired out of phase, you don't use a crossover and run subs in stereo (bad idea). With a crossover, there should be no phasing or comb filtering with split stacks (assuming same size speakers/models) and a mono feed. If you have a stereo feed to your subs, different or multiple sub sizes per side, all bets are off.

what do you think causes the comb filtering? It is the phase relationship of the wave coming from the two different sources that are traveling at the same speed but to different distances.

 

[AndyPanda]

In the picture to the right, wherever the two waves intersect they will be in phase and in all other areas there will be some degree of phase shift. Does it matter? To some it does and to some it doesn't. But it definitely exists and is why a single point source sub is my preference.

 

[s0c9]

what do you think causes the comb filtering? It is the phase relationship of the wave coming from the two different sources that are traveling at the same speed but to different distances.

It NOT due to the phase relationship. Comb filtering is due to a delayed version of the primary signal that is produced when two or more speakers are playing the same signal at different distances from the listener. Acoustical interference (what many folks THINK is comb filtering ) is caused by 2 (or more) drivers producing the same frequency ranges.
That's why we use crossovers to split frequencies to equal size drivers.
In a properly configured sub set up, comb filtering should be relatively inaudible.

 

[AndyPanda]

The crossover doesn't come into it - As a simple test try sending a 80 cycle sine wave from two subwoofers (leave the crossover and high freq cabinets out of this test) just a sine wave sent to two subs on opposite sides of the stage. The only place they will be in phase with each other is down the center line where the listener is equidistant from both speakers ... in ANY other location the wave will be in some state of "out of phase" (there will be places where the peaks line up again even though they will be 360 degrees, or 720 degrees out of phase they will sound in phase for all practical purposes - the center line will be actually "in phase") ... do the same test with a single subwoofer.

 

[Zooberwerx]

Another good representation:

Riis

 

[seamonkey]

A great article

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And now you know why consumer audio systems only come with one subwoofer.
By the way, the whole article left off the stage, it should show low frequency as circular full 360, the power alley is on stage also. "I can't hear my bass"

With good sub placement, many times to quiet stage bass you'll see a backfired sub to create a cardioid pattern for the subs.

 

[Downunderwonder]

Side by side subs act as one, in the sub frequency range.

 

[seamonkey]

And the sub frequency range radiates omni directional - 360

 

[frnjplayer]

"It NOT due to the phase relationship. Comb filtering is due to a delayed version of the primary signal that is produced when two or more speakers are playing the same signal at different distances from the listener."

What you are describing here IS interference due to phase differences. AKA comb filtering.

 

[okcrum]

It NOT due to the phase relationship. Comb filtering is due to a delayed version of the primary signal that is produced when two or more speakers are playing the same signal at different distances from the listener. Acoustical interference (what many folks THINK is comb filtering ) is caused by 2 (or more) drivers producing the same frequency ranges.
That's why we use crossovers to split frequencies to equal size drivers.
In a properly configured sub set up, comb filtering should be relatively inaudible.

Delay = phase change. That's just physics. It's not a belief system.

To the topic, I have seen touring acts using a rack of iNukes to drive the sub cluster. The application does not seem too critical as long as the amp has the response and an HPF.