Thursday, October 21, 2010

tuning PA - again

Our rig at church consists of 2x JBL VRX 932 and 1x JBL SRX 718S per side.
If you know much about sound gear, you've probably already noticed a problem.

1. VRX boxes have a 15 degree vertical coverage. 2 boxes = 30 degrees coverage.
30 degrees = not anywhere near enough. So essentially, we have all our speakers blasting away into a small, 30 degree wide patch of the congregation. There is a massive, and I mean massive SPL increase in the hotspot.

To make matters worse, the sound booth is against the back wall - where coverage is the worst.
So all the treble you hear there is reflections off walls & floor.
Behind the sound desk is a large glass wall. So most of those reflections sound almost like they are coming from BEHIND you. Which they are.

I've been trying things to fix this situation for ages, and indeed spent some time rewiring stuff to try yet another wacky idea.

First, I aimed the 'array' further back. This means the front two rows are going to lose fidelity, but moves some coverage back toward the sound booth.

Next, I set the VRX boxes to 'Passive' mode. This activates JBL's array shading feature. What this means is that the top box, pointing towards the back of the room, can be run louder than the bottom box, pointing at the centre/front of the room. Before, the speakers were bi-amped, and both running at the same volume.

Has this helped? I think so. I've only listened to it in an empty room, but it seems to me that the hotspot is much less, well, hot. The coverage is no better, sadly.
Surprisingly, I haven't noticed a lack of audio quality, there's a tiny bit of comb filtering that wasn't there earlier, but that's only in a very small area.

I also set the 31 band graphic master EQ flat, and did all the room tuning on the DSP parametric filters. For some reason, the DSP filters have never been used, weird, because that is the correct tool for tuning a system. We'll keep the graphic around for fast tweaks.
It did need some pretty full on para EQ, (filters at 41, 61, 2.7K, 6K, 10K) but, seems to be sounding ok now. I've also delayed the subs to try to get better fidelity.

Might still be too bright, but it's hard to tell from a mastered CD. We'll try it out this weekend


if you understand what I'm talking about, good work. If you don't, fair enough. We can't all be nerds :p)

1 comment:

  1. Cool Ben, sounds like an improvement! Maybe we could get some fill speakers sometime?