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[dave moldover]

Need input on how to best arrange (6)QSC KW181s in a cluster. It's for a dance competition with no live music so feedback is not an issue. 14,000 sq/ft ballroom, about 1500 dancers. Ceiling is 18' height. I want to locate the subs behind a drape against the wall. Would they perform best in a horizontal line tight to one another or stacked in (2)stacks 3 boxes high? How far apart should the stacks be? Are there other considerations? Wondering about the pros/cons create by interaction between multiple subs. Suggestions? Thanks!

[Stephen Kirby]

You can download the free Ray End software and get some prediction of the interaction between subs in different placements.

Assuming the dancers are in the middle of the room and spectators around the edges you may want to get them close together.  That will spread the pattern out move and reduce cancellations from each other and as each one reflects off the side walls.  Probably the most even coverage.
If there was a stage, this would also wrap a lot of LF back into the middle of the stage, but if you're able to get them up against the back wall in this situation, you won't have to worry about that and probably get a bit less cancellation from a closer back wall.

[Ivan Beaver]

It depends.

What is the ACTUAL layout of the room? stage, walls, audience etc?

Depending on the levels expected, you might need more "subbage".

One way to get more level would be to pile them all up in a corner.

That may or may not make sense, depending on the particular layout.

[Tim McCulloch]

Need input on how to best arrange (6)QSC KW181s in a cluster. It's for a dance competition with no live music so feedback is not an issue. 14,000 sq/ft ballroom, about 1500 dancers. Ceiling is 18' height. I want to locate the subs behind a drape against the wall. Would they perform best in a horizontal line tight to one another or stacked in (2)stacks 3 boxes high? How far apart should the stacks be? Are there other considerations? Wondering about the pros/cons create by interaction between multiple subs. Suggestions? Thanks!

This topic is where I turn into the cranky old drill sergeant... and ask "you think you're the first person to have this question?  You're not terminally unique, jarhead!"

In a more fraternal way, "did you SEARCH?"  This question or some variation of it gets asked about every 90 days.  This forum (or its predecessors) has been around nearly 2 decades.

The non-answer *answer* is that everything is based on time, there for also on distance.  Summation (such as it is) happens when waveforms are 0° in relative phase and lesser summation will occur until you you reach 180° where cancellation is complete; then as you reach 270° to 360° summation will occur again, albeit 1 full cycle late.

To sum, acoustic sources also need to be within 1/4 wavelength at the frequency summation is desired.  Wavelength is speed of sound (1170 feet per second) divided by frequency, say 80Hz.  That gives a wavelength of 14.625 ft. /4 and you get 3.65 ft.  So long as the acoustic centers of you subs are no further apart than that, you will get coupling and the array will acoustically behave as a virtual single source, at 80Hz and lower.

As Ivan says, "it depends", based on other criteria you haven't disclosed (or perhaps not yet considered).  But for now I've given you enough info that you can probably figure it out.

[dave moldover]

The will be against the rear wall. There is no stage. I'm planning to put them all close together. I was wondering if they couple better stacked vertically or horizontally. If there are placed in 2 clusters of 3 how far apart should they be to avoid cancellation. Thanks.

[Scott Holtzman]

The will be against the rear wall. There is no stage. I'm planning to put them all close together. I was wondering if they couple better stacked vertically or horizontally. If there are placed in 2 clusters of 3 how far apart should they be to avoid cancellation. Thanks.

Tim already answered that for you.

Summation (such as it is) happens when waveforms are 0° in relative phase and lesser summation will occur until you you reach 180° where cancellation is complete; then as you reach 270° to 360° summation will occur again, albeit 1 full cycle late.

To sum, acoustic sources also need to be within 1/4 wavelength at the frequency summation is desired.  Wavelength is speed of sound (1170 feet per second) divided by frequency, say 80Hz.  That gives a wavelength of 14.625 ft. /4 and you get 3.65 ft.  So long as the acoustic centers of you subs are no further apart than that, you will get coupling and the array will acoustically behave as a virtual single source, at 80Hz and lower.

[Paul G. OBrien]

The will be against the rear wall.

Which is the long or the short wall? Or is the room pretty much square? And will that be in the center of the wall or off to one side?

From a purely theoretical standpoint.. which is to ignore the effects a room has on low frequency reproduction.. which are significant, you have some clustering options with 6 boxes that can generate some directivity that may be benificial.

If you were situated in the center of the short wall in a rectangular room then placing all 6 boxes in a row on the floor would narrow the pattern and make it better fit the room, you would get more bass further back in the room.

If however you are situated on the long wall in a rectangular room then 2 stacks 3 high right beside each other will act more like 1 big subwoofer and produce a more symetrical pattern.

[Tim McCulloch]

Tim already answered that for you.

I give them tools, they want a contractor.

[Stephen Kirby]

It's not going to be physically possible to get 6 single 18s to have their acoustic centers less than 3.65 feet apart, so some compromise is necessary.

Once they no longer fully couple, the interference will cause some degree of directivity.  Which will change depending on frequency.  You should play with the software to really visualize this.  One extra row in either direction isn't going to make a huge difference.  If you could model the room you might see whether reflections off the walls or the ceiling affect the frequencies you're worried about more.

2 wide by 3 high would be more of a logistical hassle to keep safe.  Simplest solution would be to ratchet strap them in pairs so the top one can't move, and put them side by side in the middle of the back wall.  If the back wall is the long wall and you find bass isn't spreading widely enough, you can drop the level of the outside two by a bit to reduce the cancellation.

[Dave Garoutte]

3 wide,
2 high.

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