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Controlling natural reverb
Posted: Fri Dec 07, 2018 3:55 pm
Hi, Folks. I am working in a medium sized auditorium that is a concrete shell at the moment with no wall treatments or sound baffles and an unfinished ceiling. Needless to say, I get tons of natural reverb which is nice for some things but can be a bit troublesome with feedback when I'm trying to get higher gains on stage mics, choir mics and such. I have been experimenting with gates, compression, and LPF's to see if I can cut some of that reverb and feedback out, and I can isolate some of the more troublesome frequencies and drop them out of the mix but I am wondering what suggestions you might have for gate settings or any other tricks I could try. Thanks.
Re: Controlling natural reverb
Posted: Fri Dec 07, 2018 4:20 pm
You are going to struggle without getting some damping into the actual space itself.
Have you tried a backcloth on the stage area? Even something as simple as that can help reduce reflected sound back into mics. allowing a bit more gain before feedback. Also cuts down on reflected sound from any monitors pointing backwards.
Also mic selection and their polar patterns will play its part. What have you got available, and if multi-pattern, what pattern are you selecting?
Compression is probably the last thing you want to use here. A high compression ratio and high threshold to use them as limiters is fine provided there's no make-up gain used. But add make-up gain and you are making a feedback-prone situation worse.
I'd be looking at high-pass rather than low-pass filters, co clear up what is likely to be a muddy bottom end. Ideally this would be on a per-channel basis, but if you've only got an analogue desk with a fixed frequency/slope HPF, then it's going to be hard to optimise it except for turning it on for any channel that actually has a proper bass element to it e.g. bass guitar or kick drum.
Gates can only really stop reverberant sound being re-amplified by the PA, butaren't really going to be any use on say a choir, where the sound can go from quiet to loud and back again quite quickly. All main effort should really be spent into getting absorption into the space. And you'll need properly certified fireproof/resistant materials.
Re: Controlling natural reverb
Posted: Fri Dec 07, 2018 6:09 pm
Wonks has identified the key priority... get the room sorted! :)
It seems like you're trying to provide live sound in an unfinished building - or am I misunderstanding?
Are the speakers already permanently installed or have you got them on temporary stands or resting on the stage?
If the building is unfinished tell those who have responsibility for it to get the job done to get on with it as soon as possible. Let them know that until that's done the sound will always be a compromise. And I'm assuming that something in the way of acoustic treatment/drapes will form part of the finished room.
A few simple things to try...
* If you can, get the loudspeakers off the stage and away from the walls.
* Cut virtually all of the bass and much of the low mids between 200-400 Hz
* Forget about amplifying choirs...
*Make sure speakers and performers are working the mic really close.
* Back-off the levels. Better to have some amplification rather than enough but with constant feedback issues.
* If using stage monitors be very careful about positioning in relation to performers and mics and speak firmly to those of the 'more me' brigade.
* If you're inexperienced be very careful about compression - probably better not to use.
If you have to use gizmos to try and control feedback something's seriously amiss... the priority is to get the room finished/fixed.