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Limiting amplifier output via LMS

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Conanski View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 12:29am
Ok.. I didn't have much time to get into this any deeper earlier but lets see if I can get you started now.

Input sensitivity: This is the amount of voltage required to drive an amp to full output. Power amplifiers are really voltage amplifiers meaning that is what they boost, you put in 1 mV and it gets boosted to 1v for example. A mixer or preamp also contains one or more voltage amplifiers, there is a phono or mic preamp at the very beginning that boosts micro volt signals up to milivolts, then the main preamp boosts miliamps up into volts range, and finally the power amp boost 1-2v signals up to 50-100v signals to drive speakers.

A PA processor or LMS operates on the same level as the mains output of a mixer, it can boost the signal a little bit but that's not really it's function, so with all controls at unity(no boost or cut) it will output the same signal level it receives. And I just remembered this.. the meters on digital devices like the DCX are labelled in dBFS, that scale is totally different than what is found on analog mixer. With a digital device 0dB is digital clipping and you never want to go anywhere near that, unity or 0dB on your mixer equals -18dBFS on the DCX so everything is referenced to this number.

So going back to where I left off, if you drive the main output of your mixer to +2dB the Low output of the DCX will be driving the Low amp channel of the t-amp to about 835w @4ohms which is almost exactly what you want so set the Low output limiter in the DCX there at -16dBFS

That same signal will be driving the Mid output of the LMS to the same voltage which results in about 610w into 8ohms on that channel of the t-amp, but that is double the power you want for the mid drivers so you need to set the mid output level and the limiters at -19dBFS.

Now we come to the High output. The difference in input sensitivity of this amp means that the amp will be close to but slightly under full output with a +2dB input signal, but that is about what you want so set the limiter there at -16dBFS.

Now do a low level listening test to see how the system sounds, try a bunch of different music and listen for balance between the Lows, mids and highs. If the mids or highs need to be backed down then make that level adjustment in the LMS at the outputs and make sure you drop the limiter threshold on that output the same amount.

Also note that the gain controls on all amplifier channels should be set wide open.

Hope this helps.


Edited by Conanski - 20 May 2017 at 12:51am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Futendra Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 1:26am
The out gain on the DCX2496 just says "dB"

What you mean by driving the mixer to +2dB is basically that I should mix everything out on +2dB instead of the 0dB mark? Isn't it easier to add this +2dB on the LMS, so I can mix everything to +0dB as usual?


Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.



This is all so confusing


Edited by Futendra - 20 May 2017 at 1:33am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RoadRunnersDust Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 4:20am
Did nobody mention that the 'dB Decibels' unit of measurement may as well be 'tS Teaspoons' on the DCX? Cry

If you're setting gain and limiters the final stage should really be done with the drivers plugged in and a trueRMS voltmeter and levels at full-whack to account for any non-linearity int the system... Whats the point in setting preventative measures for a level it was never tested at?

Edited by RoadRunnersDust - 20 May 2017 at 7:57pm
Buying myself a TFL-760H... piece by piece >.<
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 4:58am
Originally posted by Futendra Futendra wrote:

The out gain on the DCX2496 just says "dB"
  Yes.. but notice how there are no +dB numbers just -dB? Everything is referenced to digital clipping.

Originally posted by Futendra Futendra wrote:

What you mean by driving the mixer to +2dB is basically that I should mix everything out on +2dB instead of the 0dB mark? Isn't it easier to add this +2dB on the LMS, so I can mix everything to +0dB as usual?
  Yes actually that is a good idea and was going to be my next suggestion.


Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.

This is all so confusing


Yes it can be very confusing, there are several different scales.. dBv, dBu, dBFS that are referenced to different things so you really have to pay attention.

Spend some time with the DCX and you will see what I am saying about the levels.. a signal level of 0dB on your mixer will only light up the bottom 3 leds on the DCX meters, and that is correct.


Edited by Conanski - 20 May 2017 at 5:01am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 4D Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 8:35am
Originally posted by Futendra Futendra wrote:

The out gain on the DCX2496 just says "dB"

What you mean by driving the mixer to +2dB is basically that I should mix everything out on +2dB instead of the 0dB mark? Isn't it easier to add this +2dB on the LMS, so I can mix everything to +0dB as usual?


Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.



This is all so confusing



Which mixer will be used.?

DMZ. "The bass was intense. Girls were literally running up to stand next to the subs"
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Futendra Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 2:03pm
Originally posted by 4D 4D wrote:

Originally posted by Futendra Futendra wrote:

The out gain on the DCX2496 just says "dB"

What you mean by driving the mixer to +2dB is basically that I should mix everything out on +2dB instead of the 0dB mark? Isn't it easier to add this +2dB on the LMS, so I can mix everything to +0dB as usual?


Originally posted by JaKe JaKe wrote:

The levels on the DCX are a little confusing 0dB on the DCX is actually +22dBu.



This is all so confusing



Which mixer will be used.?



Behringer Xenyx X1832USB
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 6:56pm
OK

Without load of comedy maths that just never works, the EP1500 is pretty much exactly the right amp for the tops, so if that never clips you are golden.
HF out 0dB

The 15s and 10s will run from the same power (we used SR707s for both, a 707 is about 2.6 dB lower than a TSA 4-1300, so pull 3dB out for Mid and kik.

Let the subs have what ever you've got, so 0dB gain there.

so 

Sub 30-100Hx LR-24 @ 0dB
15s 80-250Hz LR-24 @-3dB
10s 250-5K3Hz LR 24@-3dB
1s 3K15 >air LR-24 @0dB

then use a limiter on the INPUT to make sure the top amp doesn't clip!!!!

Output limiters are for idiot that want a shit sound!

Also make sure your subs run from the mono sum bus....


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Futendra Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 7:33pm
Originally posted by shagnasty shagnasty wrote:

OK

Without load of comedy maths that just never works, the EP1500 is pretty much exactly the right amp for the tops, so if that never clips you are golden.
HF out 0dB

The 15s and 10s will run from the same power (we used SR707s for both, a 707 is about 2.6 dB lower than a TSA 4-1300, so pull 3dB out for Mid and kik.

Let the subs have what ever you've got, so 0dB gain there.

so 

Sub 30-100Hx LR-24 @ 0dB
15s 80-250Hz LR-24 @-3dB
10s 250-5K3Hz LR 24@-3dB
1s 3K15 >air LR-24 @0dB

then use a limiter on the INPUT to make sure the top amp doesn't clip!!!!

Output limiters are for idiot that want a shit sound!

Also make sure your subs run from the mono sum bus....



Yeah, yeah, the delays and crossovers are set up, we just want to make it so that if we turn the amps all the way up, we don't blow our drivers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 8:25pm
First you always turn all the amps all the way up.....
If you grade your output gains as above and don't let anything clip you will be fine...

:-)

S
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Futendra Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 8:35pm
Originally posted by shagnasty shagnasty wrote:

First you always turn all the amps all the way up.....
If you grade your output gains as above and don't let anything clip you will be fine...

:-)

S

It's basically to prevent any mistakes from happening. We're also thinking about buying an AVC2, just to be safe.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shagnasty Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 8:56pm
An AVC2 is a piece of crap used by people that can't run a rig.

Get a BSS DPR-402 if you must, it craps all over the AVC2 for rig protection, the AVC2 is used in venues with un-manned rigs really, a BSS 402 infront of your DCX will make you system more bombproof than the Formula sound by a long shot, also if the DJ really rags it, it will instantly control the level and ultimately sound shit so you can ask the DJ to re-gain quality by pulling off the level.

having run some VERY big TMS rigs i have never blown a driver or set a limiter in my life.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 20 May 2017 at 11:12pm
Originally posted by APC321 APC321 wrote:

A simple non-technical check to see if you have done things right:

1) Get the DJ mixer that you will be using with your rig.

2) Connect it up to your LMS and amps. Do not connect the speakers.

3) Play some tunes through the DJ mixer and max out all the eq, and red line the masters on the DJ mixer.

If none of the clip lights light up on your amps (or just flash occasionally with the music on bass or sub) then you will be fine.
  

 The problem with this is, yes, if your limiters are set correctly then they will stop the amps from clipping, however, with everything wound up the system may then be into heavy limiting which will increase the average power to your drivers and overheat the voice coils.
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