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Author Topic: Pink Noise - Gain staging an active sub  (Read 3446 times)

Ross Davey

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Pink Noise - Gain staging an active sub
« on: May 05, 2019, 10:45:18 am »

Hi all,

I have some new RCF 8004-AS Subs that I'm looking to gain stage.

I use a DBX PA2 processor for my system.

The method I follow from the PA2 instructions on youtube is the following (please advise if this is wrong or there is a better method!) -

If you would rather watch the video - https://www.youtube.com/watch?v=rSv6nxw2T9M

  • Disconnect the amp from the speaker (Active speakers so I cant do this)
  • Turn down the attenuator on the amps and play pink noise through the mixer
  • Set the fader of the pink noise channel to Unity Gain
  • Raise the master fader of the mixer until the input signal level is just under the clip point of the Driverack (0) on the drive rack.
  • If you can achieve that with the master fader, raise the pink noise channel fader till you are at this point
  • If you still cant reach this point raise the gain/trim pot of the channel till you are just under 0
  • Turn up the attenuator on the amp until its just under clipping (at this point the subs will be making a lot of noise)
  • Mark where the attenuator dial is set, you do not want to exceed this when running the system
  • Increase the attenuator of the amp till it just starts to clip
  • Open the drive rack limiter control for that channel and adjust the limiter threshold till the clip LED of the amp just about turn off.
  • Set the amp attenuator back to the mark you made earlier and turn off the pink noise
  • Turn down the master fader of the mixer and play a music CD through the mixer and adjust it to unity gain
  • Turn on your amplifiers and slowly raise the master fader till you reach 0vu on the mixers meter or -12 for digital
  • Turn up the amplifiers attenuator till you reach the desired level but do not exceed the mark you made earlier


Because the Subs are active I have no way of disconnecting the speaker from the amp without opening them up and I don't want to do that.

Is there any downside or damage I can cause to the speakers by running pink noise through them till the point the limit light comes on on the sub amp so I can get the right gain staging and set the limiters as per the instructions above. Is there a way I can accuratly calculate the limiter settings without having to pink noise the crap out of them and purposely clip the system?

Noise isn't a problem as I'm going to be doing this in a studio practice room for the evening which is sound proofed so annoying neighbours isn't an issue. Im more concerned about the health of my new speakers.

Ive seen many articles on here about gain staging but never know which one is right as everyone has their way of doing it or opinions.

The way I understand from the drive rack instructions is that my system should be clipping when my meters are almost at clip on the mixer. That way I know from the mixer when I'm near the limit of my system without having to keep checking on the amplifiers during a show?

Looking for advice here. I have the studio time on Wednesday 8th so if anyone has advise I can use before then to get this setup properly that would be apreciated.
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Roland Clarke

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Re: Pink Noise - Gain staging an active sub
« Reply #1 on: May 05, 2019, 05:44:33 pm »

This is all very well, but what you need to do is balance your sub output proportionate to your tops.  In different situations this will likely be different, eg inside you are going to get resonances and room gain, not so likely outside.  It may we’ll be that your subs can’t keep up with your tops, then your only choice will be to buy more or run the whole rig quieter or compromise on bass output.  Simply running pink through your desk and trying to see at what point you hit the limit light doesn’t tell you very much in real world music situations.  I would start the rig low and listen too some tracks you know and increase incrementally and keep checking your cabinet gain trims and input level.  If you hear anything untoward I would back off.  If you decide to run pink through your system, I would only run it at lowish levels, enough to get a good coherence reading on SMAART assuming you are using a measurement system of some kind.
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Tim McCulloch

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Re: Pink Noise - Gain staging an active sub
« Reply #2 on: May 05, 2019, 08:22:32 pm »

If your rig is exclusively based on powered loudspeakers I'd submit this is likely a fools errand.

The purpose of gain staging back in Yee Olde Analogue Dayz was to minimize the noise floor by getting all the devices ahead of the power amp to clip at the same point, and then adjust the amplifier input level until the amp output was clipping.  The result was the lowest possible noise floor and the knowledge that seeing a red light anywhere meant red lights everywhere.

Modern mixers, processors and powered speakers do not have the noise floor limitations of stuff made 30, 40, 50 years ago.  That's not to say gain staging is irrelevant (it is, but mostly for other reasons), but that it's far less of an issue than it was in the previous century.
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Ivan Beaver

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Re: Pink Noise - Gain staging an active sub
« Reply #3 on: May 05, 2019, 08:44:06 pm »

If your rig is exclusively based on powered loudspeakers I'd submit this is likely a fools errand.

The purpose of gain staging back in Yee Olde Analogue Dayz was to minimize the noise floor by getting all the devices ahead of the power amp to clip at the same point, and then adjust the amplifier input level until the amp output was clipping.  The result was the lowest possible noise floor and the knowledge that seeing a red light anywhere meant red lights everywhere.

Modern mixers, processors and powered speakers do not have the noise floor limitations of stuff made 30, 40, 50 years ago.  That's not to say gain staging is irrelevant (it is, but mostly for other reasons), but that it's far less of an issue than it was in the previous century.

Very True.

I remember my first PA digital delay.

It only had choices in 5ms increments.  This was back in the 80s

It was VERY noisy.

I had to drive the input right up to clip, and then turn own my amps downstream because of the noise.

Things have come a long way over the years
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Paul G. OBrien

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Re: Pink Noise - Gain staging an active sub
« Reply #4 on: May 05, 2019, 10:12:30 pm »


I have some new RCF 8004-AS Subs that I'm looking to gain stage.

I use a DBX PA2 processor for my system.

Ross what are you mains? If they are also powered then your DRPA just became redendant... it will not add any protection except perhaps in certain extreme conditions like dry rentals to EDM DJs where you would set a limiter at well below the subs maximum output.

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Luke Geis

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Re: Pink Noise - Gain staging an active sub
« Reply #5 on: May 05, 2019, 10:20:23 pm »

I concur with Ivan and Tim, that in the modern era, gain staging is less of a need; especially with powered units.

Some modern powered units have a noise gate built into them as well for the purpose of noise floor reduction.

I would go on to say that dependant upon what you have going on with your mains and the type of mixer you have, the dbx PA2 is possibly an unneeded tool. I am nowadays all about removing as much from the signal chain as possible. If you have a digital amp, why use another digital tool that does the same things the amplifier does? If you have a digital mixer that has most if not all of the digital processing you need built-in, why use another device? The less stuff that is in the signal path, the fewer chances for failure and other anomalies to happen. Less is more. Not knowing exactly what you have going on though, I couldn't say for sure what to do.

The short answer is to turn the subs up until the system sounds the way you would like it to. Without a SMAART rig, anything you do is pretty much guessing anyway. The subs have a delay built into them as well as other features designed to make it less dependent upon other digital tools.
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Ross Davey

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Re: Pink Noise - Gain staging an active sub
« Reply #6 on: May 06, 2019, 04:27:24 am »

Hi all

Thanks for the comments so far.

The main purpose of this exercise for me isn't about removing the noise floor as you all mention. I agree with your points on the noise floor in modern equipment.

I also use the DRPA as my crossover rather than the one built into the subs.

The poster above mentioned that I would ned to balance the subs with the tops (don't disagree) but I set the system so everything clips at the same time when I'm near clip on my mixer. I know that will off balance the subs and probably make them too loud above the tops. I balance everything then from the mixer. If I need less sub I just send less Kick and less bass guitar to the system by turning the fader down, or if I don't want to compromise on the high frequencies going to the tops by turning the fader down I will EQ out some of the bass instead to keep the balance.

The purpose of the exercise for me (and tell me if I'm doing this ass backwards) is to know when my system is near its max. So if I gain stage my equipment I know that when I'm near clip on my mixer I'm near clip on the PA2 and and also the speakers attached to it and know that I cant get any more out of the system and also know that I'm not running it into clip the whole gig from FOH.

If I were to follow the advise of some other posts where by the posters run their mixer at around -12 for digital then just turn the system up till it gives them the level they want, how do I know if I go above -12 that I'm not then running the system into clip without going back and forth to the speakers during the gig to check the clip lights aren't flashing away?

I swap between mains depending on the venue I'm working. I either use HK L5 112 Passive tops with a QSC GX7 amp, 1 per side or I also have two per side RCF HDL6-A (speaker on poles above sub jobs) or centre cluster the subs and put the mains on poles L&R.

The system is only ever used by me and isn't dry hired.
« Last Edit: May 06, 2019, 04:31:49 am by Ross Davey »
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Chris Grimshaw

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Re: Pink Noise - Gain staging an active sub
« Reply #7 on: May 06, 2019, 11:28:57 am »

The poster above mentioned that I would ned to balance the subs with the tops (don't disagree) but I set the system so everything clips at the same time when I'm near clip on my mixer. I know that will off balance the subs and probably make them too loud above the tops. I balance everything then from the mixer. If I need less sub I just send less Kick and less bass guitar to the system by turning the fader down, or if I don't want to compromise on the high frequencies going to the tops by turning the fader down I will EQ out some of the bass instead to keep the balance.

The purpose of the exercise for me (and tell me if I'm doing this ass backwards) is to know when my system is near its max. So if I gain stage my equipment I know that when I'm near clip on my mixer I'm near clip on the PA2 and and also the speakers attached to it and know that I cant get any more out of the system and also know that I'm not running it into clip the whole gig from FOH.

With regards to the first paragraph, pushing channel faders is not the same as balancing the PA system. If you run the subs high and the bass GTR low, you'll have lots of 100Hz and down from the bass GTR, but no midrange definition at all.

Secondly, all you need to do to achieve what you want is connect the desk to the cabinets, run pink noise while tickling the red lights at the mixer, and then set the gain controls at the speakers so that they, too, are just about flashing red.

That way, the red line on your mixer is the same as the red line on your speakers.

Chris
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Ross Davey

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Re: Pink Noise - Gain staging an active sub
« Reply #8 on: May 06, 2019, 11:40:26 am »

Secondly, all you need to do to achieve what you want is connect the desk to the cabinets, run pink noise while tickling the red lights at the mixer, and then set the gain controls at the speakers so that they, too, are just about flashing red.

That way, the red line on your mixer is the same as the red line on your speakers.

Chris

Thanks - thats basically the point I'm getting at in my first post. Am I wrong to get it up this way so that I'm using clip on my mixer to show me when the rest of the system is clipping? That way I know from the desk how much system I have left to play with for that gig. Other posters just seem to run the desk around 0 or -12 for digital and then turn the system up at the amps/active speaker till its where they want it. But in that scenario how do they know what their headroom is? How do they know that if they need to go a bit louder above -12 that they aren't then putting the speakers into clip?

Also one of the other points I mentioned doesn't seem to have been addressed. Do I risk damaging my subs by running pink noise through them and turning them up till they clip so I can work out where the clip point is? Is there any risk to doing this? (a crossover point will have been set in my DRPA first before doing this first)

Thanks
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Riley Casey

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Re: Pink Noise - Gain staging an active sub
« Reply #9 on: May 06, 2019, 02:34:16 pm »

If your active subs don't have optimal crossover and limiting characteristics designed into the box by the manufacturer there probably wasn't any benefit to choosing active versus passive subs to begin with.

...
Also one of the other points I mentioned doesn't seem to have been addressed. Do I risk damaging my subs by running pink noise through them and turning them up till they clip so I can work out where the clip point is? Is there any risk to doing this? (a crossover point will have been set in my DRPA first before doing this first)

Thanks

Dave Garoutte

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Re: Pink Noise - Gain staging an active sub
« Reply #10 on: May 06, 2019, 04:52:48 pm »

With regards to the first paragraph, pushing channel faders is not the same as balancing the PA system. If you run the subs high and the bass GTR low, you'll have lots of 100Hz and down from the bass GTR, but no midrange definition at all.

Chris
+1

The bass gtr is sending frequencies to the sub and the mains.
If you lower the fader to control the sub output, you are also reducing all of the harmonics that come through the tops.

If the tops and subs balanced to each other, but the sub (ie) runs out of steam first (clips), you need more sub.
Making them both clip at the same input just means they are NEVER balanced.
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Luke Geis

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Re: Pink Noise - Gain staging an active sub
« Reply #11 on: May 06, 2019, 05:06:22 pm »

The hard part with gain staging powered equipment from different manufacturers is that the input clip point and the input sensitivity of the amp may be different. Turning one unit down so you can drive another one harder does exactly that, but does nothing for your frequency response and acoustic performance.

If you need/want more sub activity, the acoustic crossover point will shift with it and without being able to actually measure and adjust those settings, the activity of doing so is literally a matter of taste at that point. So if you want more low end and to still be able to gain stage the whole system, you either need more subs, or you turn down the tops. Then we address input sensitivity. If one unit has a 26db fixed gain input sensitivity and another unit has a 1.14v input sensitivity, they will acquire acoustic output slightly differently from one another. One will get louder sooner and clip sooner than another as well. This may completely change how the system as a whole is staged. Most powered units simply have a max input level that is typically around +20dbu. Now if you have similar input sensitivities but different peak input capabilities, you cannot really gain stage per se and adjust the systems acoustic balance as well. Since all the units will be running equally, the difference in peak output is what will determine the base frequency response. If the tops produce 136db and the subs only 130db when clipped, you will always have a deficiency of -6db from the subs. The only way to change the balance is to turn down the tops. Keep in mind however that the inputs of the respective speakers will still clip at the same relative input level, so turning a speaker down simply means you have to drive it that much more in order to clip it. You, in essence, can change the relative outputs to make it so that they all clip at the same time, but as mentioned, you lose the ability to balance the system.

One way around this is by going with subs on an aux. Since you can gain stage the system, you know that if you see clipping here, it's also clipping there right. Well with subs on an aux you can create balance in the mix directly. Need or want more or less bottom end? Simply turn the sub aux up or down on that given channel. The downside with this approach is that true system linearity is sacrificed in order to create the desired balance. The only way to have system linearity is to have the subs and mains tuned so that at X drive level, the system is performing as desired. If you alter the drive level to either half of the system, you will have a deficiency or an abundance of output from one part or the other. This is not usually a problem but is something to consider. This is why we say simply turning the subs up or down to the desired balance is the easy way to go. If at the very least, the system balance is good, then most of the other shortcomings are less of an issue or at least easier to sort out.

With powered units gain staging is really a moot task. If you balance the system to a desired frequency response, you will almost invariably be turning the tops down to create the desired balance. This means the subs will always clip first. At what level they clip at is typically easier to determine than sending level to them and looking at them. Most all powered units will say what the max input level is. For the RCF 8004 that level is adjustable between -2dbu or +4dbu as best as I can tell. So if you turn the sensitivity all the way up to +4dbu, you already know that when you hit +4dbu on your output meters, the subs will then be clipping. Most mixers are capable of producing around +18dbu to as much as +26dbu; so capable of much more drive level than is required to clip most any amplifier input.

The DRPA is nothing more than a digital tool that could be used to deal with that issue, but so is turning the speaker up or down. I don't suggest using the DRPA as a crossover for the subs. The subs have a selectable crossover and it is non-defeatable, so if you use the crossover in the DRPA for the subs, you would be stacking crossovers on top of one another. This can create several ms of phase shift and create a very unique and interesting slope to that phase shift. Keep it simple. Use the shortest path you can. The tops often don't have a crossover built in and using the DRPA for that purpose then makes sense.

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Paul G. OBrien

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Re: Pink Noise - Gain staging an active sub
« Reply #12 on: May 06, 2019, 07:02:51 pm »

Am I wrong to get it up this way so that I'm using clip on my mixer to show me when the rest of the system is clipping?

IMO Yes, I don't think a digital device should ever be pushed to clipping and the idea of everything in the signal chain clipping at the same time just make no sense to me. I'm of the opinion that the ONLY device that should ever approach clipping are power amplifiers.
Couple points.
It's not likely you could ever push a quality powered speaker into output clipping.. the built-in limiting just won't allow it, but it is still possible to clip the inputs.
I don't think there is a need to push a modern digital mixer to clipping levels, no you don't need to utilize all the ones and zeros to achieve good SQ or S/N ratio, these things are very forgiving these days.
I have a bunch of powered speakers now and the only thing I do is set gains to unity, with the mixer outputs hitting +4dbu or -16dbFS the speaker limiters are active so I know that is all she wrote.






     
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Ivan Beaver

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Re: Pink Noise - Gain staging an active sub
« Reply #13 on: May 06, 2019, 07:17:56 pm »

IMO Yes, I don't think a digital device should ever be pushed to clipping and the idea of everything in the signal chain clipping at the same time just make no sense to me. I'm of the opinion that the ONLY device that should ever approach clipping are power amplifiers.
 
One idea would be to choose a point somewhere BELOW clipping, and by a good margin (say 10dB or more) and let that be where the amps hit limit.

Of course it gets a lot more complicated when you start to consider subs and full range cabinets and the meters does not care what the freq content is, or what the balance of the subs to tops is.

It only cares about the loudest signal, which may or may not be the one that could send one cabinet or the other into clip.

The only way it could be really useful is if the tops and subs "run out of gas" at the same time.

In most cases, this is not what happens.  But it could.
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Douglas R. Allen

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Re: Pink Noise - Gain staging an active sub
« Reply #14 on: July 25, 2019, 08:15:16 pm »

Maybe I missed it as I just skimmed the thread but could you give us a total rundown of your pa system?
Mixer type and what your using for tops and amps if they are not self powered? It may make it easier to answer your question.  Does your new subs have a way to bypass the internal crossovers in them? You may not get a better crossover for your subs then the one's the manufacture has in them.

Douglas R. Allen
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Re: Pink Noise - Gain staging an active sub
« Reply #14 on: July 25, 2019, 08:15:16 pm »


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