Speaker Pop

[rschultz]

Wayne,

Yes. I don't know why DBX has me gain the system to clipping. I guess I understand the rationale to have everything clip at the same level. But it's easier to setup with passive speakers than powered. With passive speakers, you can adjust the amp to clipping with the speakers off. But with powered, you can't do that.
I agree with you and Cory, gain the system to unity.

Also, looking at gain, I have been taught/read that ideally all the faders should run at unity for average levels... this is easy enough on each individual channel. But I thought it also including the main faders. To do this, I thought you turned down the amps to get the right volume. But now I don't think that is right because it sacrifices headroom. You are suggesting to open up the amps more and run the main faders less than unity... is that right? This would give more headroom right?

Thanks.
Ryan

[cmchamp]

Again, I can't find my notes, and I'm pretty sure they're at home anyway.
From what I remember, the Allen & Heath boards do not provide any attenuation in the summing busses or the main output from the channel strip fader.
For example, the Mackie 8-Buss has provides -6dB attenuation of channel signal to group buss or main output buss. This means that 0dBv PFL (pre fader level) input on the channel strip, fader at Unity results in a -6dB signal PFL at the group or at the L/R fader.
Because there is no attenuation like this on the Allen & Heath GL series, I regularly set my client's boards up so that channel PFL peaks read no more than 0dBv on the channel meter and the AFL/PFL meters. This practice after years (almost 20) of working with quartet style vocalists who regularly under sing on a sound check. (regularly, with these guys, I'll set up the input gain at -6dB to -12dB in order to keep some headroom,.)
Back to the GL. . . . If you were to mix your 0dBv "Unity" inputs all at Unity on their respective channel strips, the summing amps (op amps) on the busses and main outputs can become saturated and creating clipping.
So, yes, open the U15P's all the way and run the mix on the channel strips less than Unity. You should still have plenty of headroom and volume.
C.

[rschultz]

Originally Posted by cmchamp

So, yes, open the U15P's all the way and run the mix on the channel strips less than Unity. You should still have plenty of headroom and volume.
C.

Cory,
Wow, that is a radical departure from what I have read... especially in the GL2400 manual. Quote from GL2400 manual, pg 23 of 40, last paragraph.

"It is a common mistake to set amplifier trims to max sensitivity when this results in the console master faders being operated at very low positions, with low meter readings and reduced dynamic range and therefore audible residual system hiss."

I understand the rationale for opening up the amps to prevent their clipping, but practically as the manual says the meters will read low. But, I'm just a rookie, so I'm listening. Maybe there is a happy medium in there somewhere.

Ryan

[cmchamp]

I read that too, and something I didn't find in the manual was their directions for setting input gain.
There is a happy medium somewhere, and you do want to run your output meters (not necessarily faders) around unity.
When I said to mix channel strips less than Unity, I don't mean at drastic levels below Unity. If you're mixing channel strips at less than -12 to -18dB, then yes, trim the amps back so you can bring those up. What should probably better be said is try not to mix with channel faders above Unity.
After trial and error, you'll find the sweet spot with your system.
C.

[rschultz]

Today at lunch I did 2 things:

1) I adjusted the post Xover gain on the 260 by -3.5 dbu. This made the input and output meters on the 260 read the same using pink noise.

2a) I removed the 260 from the chain. But first, I did a loudness check with the 260 inline. I put the iPod into ch16, fader at unity, adjusted gain to get 0 dbu, speaker gains at 2 o'clock. Then I took the master fader to unity... 0dbu on the meter. Listened for a few minutes to get a good feel for the volume with some full range rockin' music (Fireflight). It was a comfortable listening level, not too much though.

2b) Then I took the 260 out, basically removed the inputs and output connectors and connected them together. Ch16 still at unity, speaker still at 2 o'clock. To get the same perceived volume, I had to put the main faders at -35 dbu !!! barely above infinity. THAT is the volume I've been talking about all week, the volume I'm used to in our old building and old system... blow your hair back and make your ears bleed loud.

When I first hooked up the mixer to the speakers the very first time on Tuesday, I thought it was really hot. But after 10 minutes or so I stuck the 260 in and didn't think much about it again... except it always seemed soft from where I thought it should be. But now I know that the 260 is doing something serious to affect it that much.

Obviously I have some questions for DBX tech support. But one would think that if the Driveware meters show the same in and out... that the signal would be the same.

[rschultz]

I went over tonight to measure the output voltage. Speakers were all ready in the trailer for tomorrows finale, but I didn't need them. Unfortunately I grabbed my cheapo meter, only reads VAC in 0.1 increments.

First I measured the mixer output using a 1kHz tone with main faders at unity and 0db on the main meter. I used a XLRF to TRS cable, easier to pick off voltages.
1-2 = 0.3 VAC
1-3 = 0.25
2-3 = 0.8

Next I plugged in the DR260 and checked it's output... 0db in, 0db out on the Driveware meters. Measured the voltage... nothing... or at least less than 0.05 VAC on my meter. I created a new program from scratch, made sure all EQ/comp/limit/etc. was off... still nothing. Then I did a hard reset of the unit, same thing. I even upped the output on the mixer to +5 db:
1-2 = 0.7 VAC
1-3 = 0.6
2-3 = 1.6

Still nothing on the output of the 260. Meters see it, but nothing comes out. I'm not sure where the meters are in the chain, but my guess is after the A/D and before the D/A... sounds like a bad D/A circuit to me.

[rschultz]

So slightly different topic, but still relevant to my situation: assuming I get an EQ to output roughly what the mixer outputs... how to I gain down the system 20-30 db? Those U15P's are killers in our room when I take the board directly to them.

My limited experience suggests I still want to run the board channels and mains at close to unity so all the metering works right. And I think I want to run the U15P's at no less than unity to provide adequate headroom. So the only thing left is to take attenuate it down at the EQ. Is this the right way to do it?

Thanks.
Ryan

[prochlea]

And I think I want to run the U15P's at no less than unity to provide adequate headroom. So the only thing left is to take attenuate it down at the EQ. Is this the right way to do it?

yeah... although not exactly at the EQ. In the DR260 you can attenuate the input signal right at the input stage. It's in the software - on each input you have level control.

We have ours backed down in there - so we're running the board with full output, and then backing it down in the drive rack. If we decide we need some more volume, which I can't see us needing it in our current situation, but if we need it - we can just open it up a little more in the driverack.

[rschultz]

Pat,

Ah yes, true. My 260 is out being serviced... until it gets fixed I'll have to use a 31 band analog GEQ. The one I have only has 5 db of cut on the main... and +/- 12 on each band... so I probably can get it close to what I want with that.

Ryan

[prochlea]

have you found out what the problem was with the 260?

[rschultz]

Pat,

I am running it over to Lombard tomorrow at lunch to an authorized service center. He said 3-5 days on the phone. From my measurements, I think the D/A circuit is bad. The meters work in the driveware, but nothing is coming out.

Ryan