High school theatre acoustic treatments?

[took-the-red-pill]

Hello Guys,

Hopefully this doesn't stray too far from the topic of studio acoustics, but my searches here and elsewhere have turned up nothing as far as figuring this out. I will ask the question after some details.

My son's high school theatre group uses a small gym for their productions. The acoustics are pretty awful, and speech is hard to understand. There was a huge issue at 315, 630, 1.25K a,d 2.5K which we have EQ'ed out, but of course, that's just a bandaid. The room is VERY lively.

In discussions with them, they have given me a budget of between $500 and $1000CAN(think US dollars) to buy materials to try to address the issues. I am in construction and would organise a work bee with the lads in tech, and a few dads, to build and install the treatments.

The space is divided into a stage area and the seating area with a cinder block wall between them and, of course, an opening in the wall. This opening is approximately 35 feet wide and 14 feet high

Seating area area: 57'W X 47' front to back X 19.5" high, all surfaces are plumb, level, and square. The sides and back are cinder block. The floor is concrete. The ceiling is corrugated metal. There are 3 metal trusses, about 4' high hanging down going width wise, all currently have theatre lights on them.

Stage area: Also 57' wide X 30' deep. The stage is raised by 32" and as far as I know, is constructed of 3/4" plywood on wood joists, with an empty cavity below.

I'm looking for a starting point. If we are to do panels, I've calcuated that with that budget we could build about 24 panels, 2'x8'X 3-1/2" thick, with 3" Safe And Sound inside, cloth covers in front, and vapour barrier in in the rear. I know it's not going to fix it, but it's a starting point.

If we had these panels, where would be the most effective place to place them?

Is there another method other than these style of panel that would be more effective?

If this is not the forum for this question, please direct me to an online resource where I might find a starting point.

Peace
Keith

[Soundman2020]

Is there another method other than these style of panel that would be more effective?

Keith, to be very honest, you'll need a much bigger budget to treat that place, and probably careful setup of the sound system with distributed speakers would go a long way to help.

I run live sound frequently, and I have found that in places like that, your best bet is to simply distribute a lot of speakers around the room, with suitable signal delay on each one, and keep the levels LOW. That way, you have far more people inside the critical distance for the speakers, and you stand less chance of exciting room modes. I don't want to seem like I'm boasting, but there's one particular hall like this, with dimensions very similar to what you describe, that I have to run live sound in a couple of times per year, and folks who run the place say that the way I do it is the only way they have every heard in their hall that actually works. They say that, with my setup, you can hear the spoken word and music clearly, whereas with all others who come in, it is a mess. They say that other sound engineers try to set up big stacks at the front of the room, on either side of the stage, and that just kills it. Lots of power at the front is a really bad idea in a resonant space. Small amounts of power distributed throughout is what works. That room sounds like an echo chamber anyway, and you can't even hear people speaking normally more than about 5 or 6 meters away when it is empty. But with this distributed speaker method, presenters and bands can be heard quite well.

So try spreading spreading around enough speakers to keep everyone in the audience within about 4 to 5 meters of a speaker, orient the speakers carefully to point away form the walls and at the audience, set up delays on each one individually, keep the levels low, and I'm betting it will improve things considerably, even without treatment.

As you already found out, EQ is useless for correcting that type of problem, since EQ is a frequency domain tool but resonance is a time domain problem. Using EQ to fix resonance is like using a screwdriver to screw in a nail: Wrong tool. Wont work.

Having said all that, if you really do want to try with your acoustic panels, I would make them bigger and deeper: 8' x 4', with six inches of cheap mineral wool or fiberglass, and just checkerboard them on the side and rear walls. Put some right up against the walls, and leave a 6" gap behind the others. And you do not need that "vapour barrier in in the rear". That would reduce the effectiveness, not increase it. Just leave them open at the back.

Theoretically, you need about 4500 sabins of absorption to tame that room, which is the same as 4500 square feet of open window ( ) 24 panels of your 2' x 8' works out to 384 square feet, or less than ten percent of what you need. You'd need 280 such panels, or 140 of the type I suggest.

In a room that size I would also consider some type of diffuser on the walls, maybe even simple poly-cylindricals down with plywood and battens. Intersperse those with the absorption. I'd also hang some panels vertically from the trusses.

Probably with 50 or 60 of the larger, thicker absorption panels, and 20 to 30 polys, you'd be able to hear quite a difference in that room.

(It would be interested to run REW on that room, untreated! I'm betting the RT-60 time is off the scale, way up in the high single digits, or maybe even low double digits.)


- Stuart -