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Pink Noise - Gain staging an active sub

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Ross Davey:
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.

Roland Clarke:
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.

Tim McCulloch:
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.

Ivan Beaver:

--- Quote from: Tim McCulloch 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.

--- End quote ---

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

Paul G. OBrien:

--- Quote from: Ross Davey on May 05, 2019, 10:45:18 am ---
I have some new RCF 8004-AS Subs that I'm looking to gain stage.

I use a DBX PA2 processor for my system.
--- End quote ---

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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