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Live sound in a concrete gymnasium?


I looking for any help I can get on an upcoming venue. My church is going to have a thanksgiving celebration on Nov.22nd as we have had every year for some time now. However, this year it's being held in a new building. The room is a gymnasium with poured concrete walls, a wood basketball floor and metal roof. The dimensions of the room are 120' x 100' with 25' from floor to the steel roof trusses and another 10' to the steel roofing.
My worries are the obvious reverberence of the room. We plan on having worship services and dinner in the building with about 450 people seated at round cafeteria tables. We will have a stage(perhaps 15' x 30') for musicians and singers. We can assemble the stage at any position but my real question is... what is the best way to position speakers to allow the fullest coverage to the audience and minimizes reverberence? I don't know as of yet what they plan to use for speaker cabinets. As I'm only the drummer(though I ran sound at my previous church for about 20 years, volunteer position) and not the sound tech, I'm just trying to help out with research. I've offered to loan them my Carvin 832 cabinets which have 15" drivers and a 90H x 45V horn. I run those with a Carvin DCM1000 amp. The church has a beringer mixer they use for video mix that they've used at previous events and are in the process of buying a dsp speaker management controller for the sanctuary sound system that could be used for this one night event. I've even given thought about selling my 832's and buying some Carvin LM15's and LSx1801 subs and DCM2000 amp. I'm trying to find out what their budget is for the event, but considering the economy it probably will be "as little as we can spend". The band will probably consist of 3 to 6 vocals, bass guitar(Carvin RC210 amp), 1 or 2 acoustic guitars(direct or through SWR California Blonde), 1 keyboard(roland amp) and 1 electric guitar(Line6 spider210).
If we had only the mixer, mics and outboard gear and had to rent the speakers, can you give me what would be the easiest/lowest cost way to fill the room but not have excess volume or reverberence? Any other info you need to make suggestions, just ask.
Are we just asking for disaster?
October 25, 2008 @04:57pm

Are we just asking for disaster?

Metal plus concrete plus a hardwood floor plus lots of parallel dimensions means you're in for a rough time in terms of acoustics.
The only real ways to mitigate this effectively from a live sound perspective are to absolutely control the stage sound via in-ears and a strict control on stage volume, coupled with an adequate PA that has a lot of tight pattern control down to as low a frequency as possible to keep sound off the structure (meaning either good horn-loaded high-Q trap boxes or a good line array).
Carvin "anything" PA-wise is borderline in quality for what it is, is not really designed for large-scale deployment regardless of what their marketing lit says, and does not generally exhibit the necessary characteristics. (I'm beginning to believe that Carvin is a Christian subculture phenomena- decent guitars and basses, but beyond that, I've never seen their gear outside of church setups).
If I were you, I'd spend my rental budget on as much pipe and drape as I could find (the thicker the better) for the perimeter, and hope lots of people show up to absorb sound. This is the inexpensive way to try to improve the acoustics to any practicable degree in a portable situation.
Overall, the gig sounds like a job for a proper sound company. You should at least investigate the costs and options before dismissing it out of hand- PA companies and the rates they can charge have also been affected by the economy in a downward manner, and the amount of time, effort, and grunt-work it may take you and other church volunteers to cobble together a marginal PA may actually be a false economy in the long run.
Also, adjust yours and everyone else's expectations accordingly. This is not going to be a banner event in terms of sound quality in all likelihood. If everyone understands that going into it, you can live with it.
October 25, 2008 @05:58pm

Good luck getting anything to work well in that echo chamber. Why "Echo" and not "Reverberation?" Reverberation is diffuse, meaning that it is difficult to hear the individual flutter echoes. You're going to be dealing with slap-back and horrid acoustics no matter what equipment you bring in.
The best solution would be to reduce the number of sound amplification sources and mix everything through an adequately sized mixing console then amplify through line arrays.
I think your least headache solution would to to call a live sound production company and have them gear and tech your event.
Yeah, expensive, and probably more expensive than if the building had been designed and acoustically treated for use other than a gymnasium.
October 25, 2008 @05:59pm

so I'm going to start making some phone calls. But I noticed "parallel dimensions" were mentioned and I've seen that as a bad thing more often than not. Another question if you don't mind. Would there be any advantage in setting up the stage in a corner of the room which would put the room in a diamond shape, so to speak?
Just wondering,
October 25, 2008 @10:10pm
Dave Burris

Your best bet is line arrays covering the audience area in as limited an angle as possible and as near to direct radiation for everyone in the room as possible. Speakers placed above and pointing down will help some. What you do not want is firing directly into a parallel concrete wall.
October 26, 2008 @12:26am

The guy says he is expecting an audience of 450+ people, that is a sizable amount of people that will help change the acoustics in the direction wanted.
As people usually wear fluffy/woolen clothes in the winter, the presence of sweaters, coats and the sheer body mass of the audience should definitely help with both absorption and diffusion. Many concert halls sound very different when empty vs full, obviously full having much less echo present.
Actually my guess is that with some proper speaker positioning you should be able to get the job done.
If not you should come to Boston to hear the acoustics of the Orpheum theatre. Even when full, it has flutter echoes with a half second delay. Personally listened to a concert there until utter disbelief.
October 30, 2008 @04:40am

As people usually wear fluffy/woolen clothes in the winter, the presence of sweaters, coats and the sheer body mass of the audience should definitely help with both absorption and diffusion.

Turn the heat off in the venue. This will help all the people retain their wearable acoustic treatments better.
Yes, I'm joking.
October 30, 2008 @04:44am