Q&A: Coverage Concerns
Usual disclaimers apply: This post is part of a series based on questions received from readers and colleagues.
Questions may be edited for clarity, general applicability, or to protect the anonymity of the individual.
If you would like to ask a question, please email me via the Contact page.
Q: When you do arenas, what is the normal range you would be ok with front fills covering, for example, front 20'? I have a show where the artist didn’t want a full system because he wouldn’t sell the upper balconies, but they still sold some seats up there so trying to find best compromise.
You have two separate issues to consider here - the extent of the coverage of the mains, and the coverage depth of the front fills.
First, a standard arena stage being 5 feet (1.5m) means that a crowd of people standing along the barricade will obstruct the fill energy from reaching further back into the pit.
This is not obvious when walking the system in an empty room, where you can hear the fill energy 20 or even 30 feet back from the stage. If you can try go find a way to safely push yourself forward into the pit during a show, you’ll find that the fills are usually nowhere to be seen (heard) after about row 2 or 3 of standing humans. So the folks in Row 1 get a good experience, but further back, we’re out of coverage from the front fills and also falling into the center gap between left and right mains, an area I have taken to calling the Triangle of Sadness (see The Front Row Experience).
So in general, if you are expecting the face-height fills on the edge of your stage to penetrate more than one or two rows into the standing crowd, you’re setting yourself up for failure. As for the mains coverage, since you’re asking about this in the context of a touring application, you should be able to access current Sold Maps from your tour’s production manager or promoter rep, so you can see which areas of the audience need to be covered. The winning strategy here is to cover everything you need to cover with the mains, from back row to barricade, and don’t rely on front fills to pick up any of that coverage slack.
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Q: In some of these concrete arenas, I've struggled getting tight kick because of the Low frequency resonance that stays. The problem is the room acoustics, but is there any methodology to fight this?
Yes, low directivity. Long lines of flown subs, in cardioid configuration. The line length gives you vertical pattern control, and the cardioid gives you front-back pattern control. This keeps energy from going backwards, up, down, and only concentrates it forward onto the listening audience. I often fly more subs than people think you might need in terms of output (7 - 9 units per side typically) and end up attenuating them quite a bit, But they give me the vertical polar I need, and is “less lousy” than many other approaches in hostile environments.
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Q: You mention in your book that you often overshoot 2 boxes for the top of the PA. I just had great success doing that in a 3 tiered theater, for a concert/corporate type show. I'm now currently in a standard corporate ballroom (it's a big rectangle room, 130' wide by 120' long) and that has me wondering - do you still overshoot 2 boxes in a room like this? I'm getting quite a bit of slapback which I understand is parallel flat surfaces interacting, but would your approach change for a room like this? I'm wondering if that overshoot in the back is making this slap any worse off the back wall.
The tradeoff is between uniformity within the coverage area and unwanted energy onto non-listener surfaces. For a ticketed event, my philosophy is generally that the decision is made for us: if the seat has been sold we have to cover it. However in extreme cases rolling off HF on a few seats in the rear to improve the situation for everyone may be worth the tradeoff. That is your call to make as a designer.
In the geometry in your example, I don't think you would notice much difference either way, because the low trim height and the long throw mean a very very shallow angle of incidence onto those rear seats in either case. Since you’re using d&b PA, you can test this by making yourself an EQ2 group that contains just the top box, and drop an aggressive hi shelf cut, then see if you notice much difference in the back wall reflection. I am betting you will not as you are hitting it at such a shallow angle.
If a primary design goal was to minimize the rear wall reflection, I would do the following:
1) drape the rear wall with 12" heavy pipe and drape
2) fly the main hangs high and dive the coverage into the ground about 2/3 of the way into the room
3) transition coverage to a set of delay hangs at that point, also with small splays at the top to put a hard edge of the high frequency, and carefully limit coverage to the last row.
This gives you a better solution in two ways. Mechanically, because hitting the rear wall with more downtilt means more ability to keep energy off the wall while still adequately covering the listening plane. And also acoustically, because the inverse squared law tells us that when the source hitting the rear wall is closer to that wall, the level of the reflected energy will drop off more quickly as it bounces back into the space, and be less objectionable as a disturbance.
Another consideration is that you should be very careful intentionally rolling off HF coverage in the rear rows if that's where the event is being mixed from. And finally, make sure to check your prediction in 3D at HF, as downtilt + toe-in means making some potentially unexpected bendy borders at the edges of coverage.
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Q: My design includes main hangs that are toed in pretty aggressively. I know that you also use this technique; what tips/tools do you like to use to accurately toe in the speakers to a desired position? I definitely gave it my best of just eyeballing it into position.
With a two-point hang, I manage toe-in by physically moving the rigging points. I have an excel solver that gives me the proper amount of point shift for the desired toe-in. For example, a three-foot deep flybar and a desired 3 degrees of toe-in means moving the front rigging point on stage by 1.9 inches. See this article for more: https://www.precisionaudioservices.com/blog/quick-solvers-3-pa-toe-point-calculator
Realistically speaking I usually do this with choker hitches around the beam on the downstage point so I get about 2.5 to 3 inches of offset which translates to about 4 degrees of toe in.
If you are rigging as a single point, you will still have some toe from the weight of the PA loom and cabling pulling off the back of the frame, so usually in a small-PA situation you can get the toe you need by tugging the loom one way or the other. If you have inclinometers and lasers on your flybar you can nail it exactly, otherwise you sort of have to do it visually by standing at the centerline of the venue and looking for the row in which the horns impact, and making sure that matches your prediction.