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[Kevin Maxwell AKA TheMAXX]

When I installed the GL2400 in the church as I mentioned in my previous post, I had to keep telling them to use your ears and not your eyes. They kept trying to set the levels and trims to the same points as they used to. I had to turn the system down after the board so they wouldn’t drive it too far. At first I was talking into the mic and I could hear them pushing it too far and then ringing a little. I was speaking at a moderate level and I could tell from the stage that they were pushing it too far. It got to the point that I was almost yelling at them to “use your ears and not your eyes”. Then I turned the DSP down. They had more then enough level and have commented to me after they had been using the system for a while how natural the system sounds.

I went to a funeral service there recently and one of the church secretaries was running the sound because none of their sound people were available and I wasn’t there to work. I just had to tell her at one point not to have the wireless and the lectern mic on at the same time for the person speaking. She was grateful for the help. Probably no one else noticed the slight problem.

[Winston Gamble]

Quote:

Ivan Beaver   And if you had simply turned down the trim knob, you could have achieved the same thing, with less loss of signal/noise ratio-as the pad will generally give.

How does one affect signal to noise ratio and not the other? Aren't they both just methods of adjusting the gain?

Winston

[John Roberts {JR}]

Winston Gamble wrote on Fri, 23 December 2005 01:16

How does one affect signal to noise ratio and not the other? Aren't they both just methods of adjusting the gain? Winston

A pad, "pads down" or attenuates the signal before it reaches the gain stage.

The net effect to noise already present in the input source is similar, but added noise from the preamp gain will be increased by by the amount of the pad if the pad wasn't needed.

FWIW this preamp input noise isn't strictly linear with gain but a large enough part of it is that such analysis is useful.

JR

[Jeff White]

Last year our church replaced a Mackie 1604VLZ-PRO with a GL2200-32.   We EQed the room using our Driverack PA's Auto EQ Wizard, which we re-ran after the boards were swapped.  Not the most elegant choice, perhaps, but it's served our small system well.  Yet, after resetting the gain structure on all the board channels, I couldn't push the volume to our previous levels without it starting to ring hollow and sound, um, sucky.

In our case, it turns out the main speaker amps had the input gains set oh-so-high.  The amp's clip lights were dancing whenever the sound was near worship levels.

I'm just a volunteer at my church with no formal training, so I can't tell you why the problem wasn't so bad with the Mackie, but thought I'd mention this in case it helps you in your quest.  In my case, I assumed that the previous sound "experts" at my church knew what they were doing, and since the amps are locked away under the stage, the settings were safe and correct. Oops.

the Appendix A article in the Driverack PA manual had a nice over-simple summary of system gain structure that helped me find our problem.  The manual can be found here:
http://www.dbxpro.com/ftp_mirror/PDFs/Manuals/English/PA%20D riveRack%20Manual.pdf
Appendix A is on pages 48-49

Blessings

[Andy Peters]

Jeff White wrote on Fri, 23 December 2005 21:59

Last year our church replaced a Mackie 1604VLZ-PRO with a GL2200-32.   We EQed the room using our Driverack PA's Auto EQ Wizard, which we re-ran after the boards were swapped.  Not the most elegant choice, perhaps, but it's served our small system well.  Yet, after resetting the gain structure on all the board channels, I couldn't push the volume to our previous levels without it starting to ring hollow and sound, um, sucky.

Here's a concept that I think isn't clear to many people.  Try to follow this.

When you set up a console's gain structure, you usually hit the PFL button, have the musician make some noise, and trim the gain until the PFL meter reads unity.  This setting is what the console design engineer feels is the best compromise between signal-to-noise ratio, input headroom, summing bus headroom, and various other considerations.

Note that the particular voltage on the summing bus that corresponds to "unity on the PFL meter" isn't specified, or even important.  Here's what IS important--that value may be different from console model to console model.  Trim the input to unity and put the channel and master faders at unity, and look at the master meters.  Guess what?  The A+H's output may be more or less than the Mackie's output.

If the A+H output is hotter than the Mackie output, the simple fact that there's more gain means the potential for feedback is increased.

Turn that around.  If the Mackie output is less than another console, you may hear the complaint of "this console doesn't have enough 'drive,' and worse, input trims are are pushed up and the console clips.  Or maybe the drive levels out of the crossover get pushed up to get enough level out of the system.  Now swap in a console with more gain without readjusting the crossover drive, and perhaps you get feedback.

-a

[Jeff White]

Andy-
The concept you outlined is quite easy to follow, and it explains a number of the little differences I've noted since we've switched boards. It's just not something that those of us in church sound have to wrestle with very often, since most of us in smaller churches have been "married" to one or two boards for longer than we'd like.

In my case, with nobody around to ask (except this forum!) I read the specs on both boards.  Max output to mains on the 1604 is quoted at +28dBu, max on the GL2200 is +25dBu, so I figured that I shouldn't expect a hotter signal (at equivalent master fader settings)going to the amps with the GL2200 after the channel gains were dialed in.

My day job is physician, and I love it most because I'm always learning something;  sound reinforcement is shaping up the same way!  Thanks for the mini-lesson!

[Ivan Beaver]

The funny thing to me is the fact that apparently several people have made the swap and complain about feedback.  BUT what they fail to mention is that the system is louder than it was before (causing the feedback), and they don't seem to relate the two issues.

[Andy Peters]

Jeff White wrote on Sat, 24 December 2005 09:58

In my case, with nobody around to ask (except this forum!)

That's why this forum exists!

Quote:

I read the specs on both boards.  Max output to mains on the 1604 is quoted at +28dBu, max on the GL2200 is +25dBu, so I figured that I shouldn't expect a hotter signal (at equivalent master fader settings)going to the amps with the GL2200 after the channel gains were dialed in.

That's exactly it.  A console's max output spec is provided, and the console "nominal" output is given as +4 dBu.   But it's not obvious how much one input trimmed to unity contributes to that nomimal output.  I'm not even sure how to spec this (although it's easy to determine), and worse, it's the kind of spec that can be spun in two different ways.  One is that "our console has lots of mix-bus headroom;" the other, opposite line is "our console drives hot! (louder is better)"  

"Console drive," to my mind, at least, isn't a determining factor in console quality.  It is, however, something to be aware of and consider when setting up a system.

The usual system set-up methods (see the study hall) attempt to make everything in the system clip at the same time, but this doesn't take into account console "drive."

I guess this is just one more point to consider when setting up a system.  It's also a point that I haven't seen discussed around here much at all (which is truly interesting, as we tend to beat dead horses on a weekly basis).  An old LABster, Michael Tamas, used to talk about "console drive" but I don't think we'd ever actually explored the concept.

-a

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