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Author Topic: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai  (Read 3100 times)

Jared Payne

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Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« on: October 15, 2016, 01:12:10 pm »

I have done a TON of searching and opinions seem to range from wide open to unity.

I don't want to screw up my speakers or anything else for that matter so I looked around for a sound forum and ended up here!

This is my first PA system. I am hoping its a good system and I made a wise choice.

Setup:
-RM32ai
-2x PRX715
-2x PRX718xlf

using the crossovers in the subs. I'll research and learn AUX fed later.

Anyways,

I am just wondering how I should have the gain setup:
-output gain (small knob on the front of the RM32ai, just left of the Left/Right Outputs)
-Input Gain on the back of the speakers


I have been running these all at 12 o'clock assuming this is unity.

I ran sound for another group one time and got some pretty nasty pops through one of the speakers and suddenly stopped output. I shut the speaker down.
The next morning I plugged it in at home and sure enough it was making horrible static, popping noises. I found that this was only on channel 2 on one of the PRX715s. It made this noise with absolutely nothing plugged in to the speaker and the volume increased/decreased with the gain knob. Again Channel One on the speaker worked just as it should. I needed to play that evening so we used channel one. A little while later I went to reproduce the sound... Gone.... speaker seems to be working just as it should.

I did not have the system very loud by any means. It was a very small room that it was setup in. It was my hope with this purchase that I shouldn't have to worry about pushing it too hard as it seems to be a powerful enough system for small to medium venues. Though sometimes I find the main fader nearly red lining bringing me to the option of increasing gain (since the incident I have reduced all gain below 12 o'clock).

Basically I want to make sure that I am not going to screw up this new system with silly mistakes and ignorance. I understand I have a TON to read and have been reading so much about this over the past 6 months I believe my wife is surely going to go mad.

I have looked through the manuals several times and have not found any advice for setting gain on any of the units.

Also are there preventative measures I can take using the compressor/limiter feature on the board? If so what would the proper setting be?

I'll attach an image of the User Interface for the board showing the compressor/limiter/eq options available.

Thank you very much and my apologies if this topic has been covered. I have searched "Jbl prx gain" "prx715 gain settings" etc etc etc to no avail.

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jesseweiss

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Re: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« Reply #1 on: October 15, 2016, 03:57:46 pm »

Search "setting gain structure". I'm not a pro but you shouldn't need to push your mixer master fader to red. You might not be setting input gain for mics and instruments correctly.

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Jared Payne

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Re: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« Reply #2 on: October 17, 2016, 10:10:06 am »

Search "setting gain structure". I'm not a pro but you shouldn't need to push your mixer master fader to red. You might not be setting input gain for mics and instruments correctly.

Sent from my LG-V410 using Tapatalk

Hey Jesse, Thanks for the reply!

I have done a lot of searching on that as well and reading through manuals. Heck as well as tuning the system, phase alignment, polarity, coverage, standing waves, power alley (we now always center subs!!). As a result of this reading I want to get a couple laser pointers to put on top of the mains for coverage angle. I also read that its a bad idea to have any sound reflecting off of the rear of the venue, what I have been doing is setting the polls up as high as possible and then placing the speakers in the angled post hole so they are slightly pointing down. Is this a good idea or not?

Here is an one example of setup from The Dock at Bay view . Happy guy in the middle there is Mr B himself, the singer   8)    ;)



^^ still a few more things to purchase. Next big investment after I have finished paying down the PA system (yeah I went interest free loans - wife is really happy with me!!) is a nice computer controlled automated lighting system... another $5k at least I am sure!! Go big or go home, right?

Coming back to the gain settings:

What I have been doing (or at least trying to, will need to get better about consistency) is setting the channel gain so the level indicator (technical name?) is about half way or basically high enough that the loudest signal sent to that channel doesn't clip. I was trying to do this with the main fader off, we don't need volume to set the preamp gains. Do that on every channel and then mix using the faders from there. Main fader for over all volume.

I have the board gain and the speakers gain setup at 12 o'clock. From reading, the old school of thought was to run the speakers wide open, but with newer active systems to run at unity and only push if necessary.

From talking to Nick over at sweetwater, who works as a sound engineer, he had also mentioned that the general rule of thumb with union based sound companies is to always have twice the power to the subs. With the mains and subs being 1500 watts I have been running all speaker gains at the same level. Placing the subs, centered, next to each other coupling their power to create the 3000 watts.

The problem presented:

We were booked into a bowling alley for an event run in October... It was rather interesting... We were quite literally setup on the bowling lanes themselves. Saturday night we played out and the system definitely felt quiet with the speakers and board set to noon. I had hoped in the purchase of this system that it should have been loud enough to blow the windows out of that place (quoted from our singer).

When I stated that we were nearly red lining the main fader. I assume the level indicator there is a result of how high I have the main faders slider set; of course in combination with the channel faders/sliders. Meaning it shows nothing if its all the way down even when the rest of the channels are bouncing around. Then raise the main fader for over all volume.

At this point the only way to increase volume without clipping the main fader, regardless of channel gain settings, would be to raise the output gain on the board and/or input gain on the back of the speakers.

With it sounding as quiet as it did I raised the gain on the speakers to about 2 o'clock (why do they not put any numbers on these things? I couldn't tell you what dB that is by looking at it.) I also raised the output gain on the board to about the same number.

I suppose my biggest worry is clipping the speakers. It is a pretty new system and I have about $7000 into it so far between the mixer, computer for firewire control, cables, stands, etc.... So I am trying to be REALLY REALLY careful to not ruin the investment rather than stupidly assuming I know everything and then blow something out. I do feel, and know feature wise, that we are not taking advantage of its full capabilities.

One interesting bit I had read was to run pink noise through the system for output and input gain between the board and the speakers. He runs the pink noise and then brings the master fader up just before it clips. Then he raises the gain on the speakers until they start to hit limit and backs it off a little bit. His thought with this was that the main fader was now a good indicator of whether or not the speakers where about to hit limit.

The issue I saw with that was not taking frequency spikes into account.... I would also think that it isn't accounting for an instrument stressing the speakers in a different frequency, but wouldn't this be a mute point being that pink noise is supposed to be all of the frequencies anyways?

Any who ... two pages is enough damn typing. Just trying to cover all basis and make sure to provide enough info for proper feedback (Punny).


After seeing everything that goes into making a system sound truly perfect I want to take some classes on this and intern with a real pro for a bit!
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jesseweiss

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Re: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« Reply #3 on: October 17, 2016, 03:45:14 pm »

Sounds like you know as much or more than I do. If you are running input gain in channels just below clipping, faders at 0, master at 0, and speakers at unity you should be getting plenty of volume. You definitely won't blow the doors off the place but I would think it would be fine.

Where are the channel faders roughly?

We run 2 SRM550s and a srm1850 sub for a 4 pc pop rock band and it's plenty but won't blow the doors off anything.

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jesseweiss

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Re: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« Reply #4 on: October 17, 2016, 07:24:11 pm »

FYI if you repost or move this thread to the Lab Lounge will probably get a lot more, and more knowledgeable, responses.

I think the AV is more for AV installs than PA rigs.

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ProSoundWeb Community

Re: Question - How to set gain JBL PRX715 + PRX718xlf + RM32ai
« Reply #4 on: October 17, 2016, 07:24:11 pm »


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