Limiter Question

[CosmicTech]

I wanted my first post on this forum to be about a new build but I will start with a question. I am new to everything I have read on this forum and I am trying to dumb down a few things so I may understand and remember their function better. Case in point, limiters. Are limiters devices or a function of certain devices that more or less "limit" the voltage of the input single to an amplifier?

[Grant Bunter]

I wanted my first post on this forum to be about a new build but I will start with a question. I am new to everything I have read on this forum and I am trying to dumb down a few things so I may understand and remember their function better. Case in point, limiters. Are limiters devices or a function of certain devices that more or less "limit" the voltage of the input single to an amplifier?

Hi CosmicTech,
Welcome to the fourm

When we talk about limiters here, we more often than not mean brick wall limiters.
These allow one to set a voltage limit (notice I say voltage limit and not watts? That's because volts are measurable and watts are a calculation) to protect drivers, most commonly in subs.
So yes, you have it right, limit voltage

The DBX Driverack series, Behringers DCX2496 and a bunch of other brands have this capability, as well as a whole host of other useful functions to make systems sound great and almost bulletproof.

The brick wall limiter is slightly different to the limiter one may see on a compressor/limiter one might insert over a channel on a mixer...

[CosmicTech]

Great. All the gain, level and volume adjustments on PA equipment had me wondering if that is how you keep the input voltage level to an amplifier under control.

[Grant Bunter]

Great. All the gain, level and volume adjustments on PA equipment had me wondering if that is how you keep the input voltage level to an amplifier under control.

Yes.

The brick wall limiter is the last link in the chain before the amps (and in the case of the previously mentioned processors, is the last function).

The goal is to limit the voltage in output from the amplifier to protect drivers.
Of course, without it, the amplifier can put out enough voltage to kill your drivers...

[commander_dan]

Grant, I have some more questions regarding brick wall limiting and thought I may as well continue this thread as the info may benefit the OP as well.

I have a DCX2496 and an XTi 2002 running my T30's and I have set the limiter on the Xti using a volt meter. I did this by running a 60Hz sinewave through the chain (subs not plugged in) with all the gains wide open and amp on max. I then set the limiter at -2.5dB on the amp, as that brought the volts down to 48. Was this method correct, or should I have used a lower frequency sine wave?

Another question, is it better to limit using the DCX or the XTi? (I haven't looked into how to do it with the DCX either, any advice there would be appreciated)

And another question, if setting the limiter with all the gains wide open, doesn't this require one to be clipping the system (via the dj mixer being in the red) to get the full power out of the T30's, or does running in the red not matter once one has set the brick wall limiter with the gains wide open? To that end, could the issue of running in the red be solved by putting a physical barrier on the gain knobs on the DJ mixer which disallows them to be turned up past the first level of red?

Insight and sharing of knowledge greatly appreciated!

Dan

[Grant Bunter]

Hey Dan,
As long as the limiter is brick wall, it doesn't matter I guess.

Most people use non DSP amps with rack DSP to limit. I wouldn't limit using both.
Others just use DSP in amp.

So you can also limit tops (yes, you should, if you can), I would use the DCX if you're using another non DSP amp for tops, or more subs.

60Hz seems often recommended for sub setup.
I adjust channel strip gain to just below clip. And master to just below clip.This gives you a max point of sorts, ie, when you run the system, you don't ever quite want clip, and you now know where that point is on your console.
If you need more volume after that is done, you need more cabs!
Running in the red or no depends on what it sounds like with cabs connected IMHO.
If it sounds distorted in the tops running in the red, try to avoid it.
You add a little safety net when you go from sine wave to setup to music in use anyway.

The last step when setting limits is to max everything out on the mixer/console suddenly (push all relevant faders to max), and see if the voltage rises at all on the amp output. If it does, you need to go back and revisit your limit settings and gain structure, and so on, until you kow that regardless of what happens on you mixer, the voltage limit will never pass the specified amount.

I wrote a setup tutorial for the DCX2496:
http://billfitzmaurice.info/forum/viewt ... =4&t=20833

There's a lot of info there, and some argument lol. It's all healthy learning though...

[commander_dan]

I adjust channel strip gain to just below clip. And master to just below clip.This gives you a max point of sorts, ie, when you run the system, you don't ever quite want clip, and you now know where that point is on your console.

I agree with this but I am thinking of situations where others might be DJ-ing on my setup (while I'm there of course), in that scenario isn't it risky to have the ability to go into clip if the limiter was set at just below clip? What I'm getting at is, is it possible to have a setup so that max volume (ie max volts) is acheived before going into the red on the mixer, AND once pushed into the red, the level stays the same (without the limiter kicking in)? I want to avoid hitting the limiter if possible. More cabs are coming which will help

In my earlier years I owned a set of speakers and an amp and I used to do sound for friends parties and what not. The speakers would distort if the amp was pushed past about half volume, so to stop people cranking the volume up to full (causing terrible distortion, yet they ALWAYS did it!) I hard-limited the volume slider with a piece of metal inside which prevented it going past half (which for the speakers was full volume), and this solved my problem. Since nothing has really changed (in that people inherently always want to turn the volume up past the point of distortion), I want to acheive the same thing with my current system.

Thanks for link Grant, I'll be sure to check it out.

Dan

[escapemcp]

I agree with this but I am thinking of situations where others might be DJ-ing on my setup (while I'm there of course), in that scenario isn't it risky to have the ability to go into clip if the limiter was set at just below clip? What I'm getting at is, is it possible to have a setup so that max volume (ie max volts) is acheived before going into the red on the mixer, AND once pushed into the red, the level stays the same (without the limiter kicking in)?

That's what a limiter does essentially - you cannot avoid hitting the limiter, if you want to keep the volume the same whist increasing the volume control past your 'max' point - that's the limiters very job! If you were just playing a constant (sine wave/coloured noise) output, then once you pushed your mixer above the 'max' level, the downstream limiter would keep the level the same (=the exact behaviour you describe above). However, music isn't a constant level source and the only reference that the limiter can use to limit is the actual music that is being passed through the device. The limiter cannot 'track' the volume control on the mixer, only the mixer's overall output. As such the limiter may be disengaged during quiet sections of music tracks and then on during the louder sections. To avoid it switching on and off on every beat, we use slow release times to smooth out the limiting behaviour.

If you want a situation where DJs cannot go past a certain volume on the mixer, then the sort of physical limiter that you described (mechanically not allowing the volumes faders to go past a set point) seems the only way to go.

Hope that made sense. If not, please hit the "Reply" button

TIP: I initially found that my volumes had to be quite low (well below 0dB) on my mixer to keep the input stage of my DEQ & DCX from clipping (yes, it was at +4dBu). DJs were NEVER going to stick to that level. I therefore soldered some resistors into the XLR connections coming from my mixer, which dropped the voltage that my mixer put out. Now that the mixer's volume levels look half decent to DJs, they don't run into the limiter half as much as they used to.

Something like what's on this page