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Horrible combing at a gig

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frank kayser:
We did a job at a city fair last weekend.  We supplied the sound.  I think we made every mistake in the book.  Overall, vocals could be heard, and there was good balance between instruments and vocals.  The combing in the coverage field was as bad as I ever heard.

The setup: 2 QSC K10 (129dB ea) over a single Mackie SWA1501 per side.  The speakers stacks were deployed about 35' apart, with the two K10s side-by-side on poles with a little splay. So in theory, the two K10s could produce 132dB. Theory vs reality...

I heard the combing close to what I thought the crossover point of the sub was.  I jumped to the conclusion the subs were the major contributor to the combing. I was thinking I should have center-clustered the subs.  Speakers were on the concrete slab apron with no height difference between that slab and the stage -i.e.,one big slab. That would have been quite ugly. Reading some previous posts here and other places, it appears the deployment of the 2 K10s on each side was the problem, not the subs.

So the ultimate answer is "don't do that again".  Yeah, I get it.  Lesson learned. Not enough rig for the gig.  How does one add "rig" to the rig?

Stacking boxes side-by-side is generally a no-no, while stacking speakers one on top of the other, while not perfect, is preferable.

I've seen trap boxes set up side by side, but those would create combing, too, wouldn't they?

So, a single bigger, fatter, heavier box each side with a higher SPL output (i.e.,  JBL SEX812P @136dB) would be a better solution.

Coming up: In two weeks, a new venue. The seating area is about 110 degrees wide, and flat.  Most audience will be between 30' and 65' out.  Most bigger boxes, i.e.,  JBL SEX812P have a coverage angle of 90 degrees horizontal.  To get the necessary width, I could splay the boxes outward, leaving a hole in the middle.  I could use a center fill to compensate.  Wouldn't that create its own combing issue?
- or -
I could angle the mains in to ensure front row coverage.  Could I use "wing" speakers to add to the width?  Isn't that repeating the mistake of last weekend?
- or -
An Evox 8 (128dB) which advertises 120 degree coverage.  I'll plan on assuming the coverage may be 10 degrees optimistic.
I've used the Evox 8 in similar situations, and the sound quality was smooth and even.  Volume was moderate - around 90dBA in the listening area.  I'm not doing EDM, Rap, HipHop with this job.  Audience will be a little older.

A lot of room for comments.  Please feel free...


Caleb Dueck:

--- Quote from: frank kayser on June 12, 2024, 04:10:06 PM ---Stacking boxes side-by-side is generally a no-no, while stacking speakers one on top of the other, while not perfect, is preferable.

--- End quote ---

This depends on the dispersion of the horn (IE, wide horizontal by narrow height), and how close the horn is to the top edge of the box.  Something like a QSC with conical horn, relatively far from the box edge, isn't going to play nice together - either horizontally or vertically arrayed. 

The least bad - mains, with out fills, physically away from the mains a bit, and time delayed - so the mains are directly behind the delay speakers (read: sound propagation doesn't curve).

The only real solution to "enough rig for the gig" is - enough Rig; IE, speakers that can cleanly put out more sound.  Then minimize weaknesses by getting the speakers up high, angled down toward the ears of the back row, get speakers with tighter vertical pattern, get speakers with vertical pattern control (read: better front to rear relative levels down to a greater/lower frequency). 

Keep existing speakers as in/out/delay fills, or B rig. 

How many times a year will you use, meaning be able to charge for, a better system?  That will determine buy vs cross-rent.  If it's a large number (20+), that's where you can look into which boxes to buy. 

Chris Grimshaw:
Time to drag out this old thing:
None of those boxes will hit their rated SPLs and sound good doing it.

+1 to Caleb's comments about renting in.

Since you've got active speakers, and hopefully enough Aux sends left on the desk, how about running a dual PA? Vocals in one, instruments in the other. It improves headroom and removes the problem of side-by-side speakers interfering.



Paul G. OBrien:

--- Quote from: frank kayser on June 12, 2024, 04:10:06 PM ---I heard the combing close to what I thought the crossover point of the sub was. 
--- End quote ---
You heard comb filtering at 80-100hz? The cancellation nodes that would occur at those frequencies are not exactly small... you would have to be moving back and forth 6-10ft side to side to hear it. Maybe try describing in more detail what you heard.

The K10 might have about 120dB of usable output... figure 92-94dB broadband sensitivity of a 10" woofer with 500w applied(27dB gain) equals about 120dB max output for the box. If you didn't know the original K series were powered by a pair of 500w amp for the woofer and one for the CD.. which will never use more than 50w to 100w. It's really a 600w box.

Gordon Brinton:
Meyer makes a nice little point source box called ULTRA-X40. It's dispersion is 110 x 50. Renting them might be feasible. If you wanted two per side for more spl, they also offer a more splayable version, Ultra X42, which is 70 x 50. If you splayed them hard enough, they probably wouldn't comb. (IDK, I haven't used them yet.)


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