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At a recent gig we experienced some clipping in the subs, which made me question my confidence in my XTi2 amps' limiters. The track which caused the clipping has a particularly low kick going at the same time as a heavy bass line in the low 30Hz, and we were approaching max volume with the rig. Incidentally, I've not noticed any "limiter engaging" indication/limit lights on the XTi2 amps, even when setting up the limiter, so I had the DCX limiter on as well, and we were not showing any limit lights, until this particular track. Limit light flashed on and off, and we heard the subs clip, so turned the gain down straight away.

Did some testing after the fact just recently. I unplugged the speakers, got my DMM out and rechecked my XTi limiters were set correctly for the subs, using the 60hz sine wave method. No problem, couldn't make it read higher than 49.3V. I then played "Reso - Hemisphere" which is known for its constant bass notes and low sweeps to 29Hz. And was dismayed to see readings of up to 51V on the DMM once the basslines started to play. 51V, no wonder we were getting clipping in the subs! Lucky we didn't do any damage.

So I did some more experiments. Deactivated the limiters on the XTi. Set the limiters on the DCX using the 60Hz sine method. The setting turned out to be -20.5dB. Played the track again, and hey presto, nothing over 48V.

Reactivated the XTi limiter, turned off DCX limiter, and ran the sine wave again. I found, that by rapidly turning the master gain to max repeatedly, I could get the voltage to read higher than 50V, sometimes as much as 53V!. Tried the same thing with the DCX limiter, nothing over 49V (it was going slightly over the static setting when doing the rapid max thing, but never over 50V).

My problem with the DCX limiter is this: using the sine wave method, that required setting of -20.5dB means the limit lights are coming on when my master gain knob is at just over half way, but the voltage is showing only around 46V. Does this mean that the limiter will be coming on before I hit max volume in the real world?

I had a play around with having both the XTi2 limiter and the DCX limiter active. I found that with them both on, the required setting on the DCX goes back up to -11.5dB. This means I'm now engaging the limiter at 3/4 position on the master gain knob.

I guess I need to play around more, but my main question is this: is it ok to have both limiters active? or should I just ditch the crown limiters and trust the DCX limiter setting of -20.5dB?

As a side note, I really don't like the fact that there seems to be no visual indicator of limit lights activating on the crown amps.

commander_dan wrote: I found, that by rapidly turning the master gain to max repeatedly, I could get the voltage to read higher than 50V, sometimes as much as 53V!. Tried the same thing with the DCX limiter, nothing over 49V (it was going slightly over the static setting when doing the rapid max thing, but never over 50V).

You are measuring slightly higher than 50v on the xti during rapid ascents because it has an attack time greater than 0. That means short transients above the setting will get through but anything longer than that gets clamped. The idea here is that it keeps long term heat build up from occurring but will allow short transients to get by. The DCX has a zero attack time limiter which means that no transients or anything else for that matter gets by. If the limit of your cab is its RMS power rating (tops usually) than the xti probably sounds better but if the limit of your cab is x-max (subs), then the DCX zero attack limiter would be safer.

commander_dan wrote:
My problem with the DCX limiter is this: using the sine wave method, that required setting of -20.5dB means the limit lights are coming on when my master gain knob is at just over half way, but the voltage is showing only around 46V. Does this mean that the limiter will be coming on before I hit max volume in the real world?

Master gain knob of the amplifier or the mixer? Always keep the amplifiers at full gain for gigging. That way nobody can bump them up higher on you destroying your limiter settings and your speakers.

If it's the mixer then that is an easy fix:

(For the DCX and no speakers attached and limter already set)

1 - Play your sine wave through your mixer and then set the mixer master faders/VU meters at the volume where you want the system to limit at. For some people that will be zero dB or you may want the limiters to come on at the first red light or maybe the second one. You decide.

2 - Set the input gains on the DCX to be at or near 0 dB

3 - adjust the output gain on your subwoofer channel on the DCX up or down so that the orange limit light just comes on.

Don't fret about losing a few volts (48 instead of 50). You won't hear the difference.

4 - verify amplifier voltage with DMM , adjust limiter if necessary.

5 - adjust top boxes output gain to match sub levels.

Now, whenever your mixer lights the first or second (whatever you chose) red light, the dcx is limiting at the exact same setting.

I like the line of thinking CO, and I'll have a play around with setting that up tomorrow. Unfortunately it's often not just my mixer that gets used on my system; other ones get plugged in and used sometimes (always under my direct supervision). It sounds like I shouldn't be trusting the Xti limiters alone for sub use though.

I seem to have found safe ground with the current subs settings; Xti limiters active , dcx limiters also active. Combined, I can't get anything above 49V, sine wave or otherwise. I'm assuming it's fine to have both limiters active?

Another question/possibility. What does running into the XTi2 limiter (not the dcx limiter) sound like through subs? Could it be mistaken for clipping? I only ask because the only 2 times I've heard clipping in the T30's were when I was close to or at Max volume. Just wondering if I've mistaken clipping (very subtle "catch" in the sound of the subs, listening closely) for the sound of limiting?

you are likely mistaking "subs clipping" for the sound of the xti limiter.

hearing the "subs clip" would either be a large dose of distortion or the voice coil smashing the backplate (total failure).

"Subs clipping" ?? Huh? I thought AMPS clip? Subs just, as you alluded to, max out.

Rich4349 wrote:"Subs clipping" ?? Huh? I thought AMPS clip? Subs just, as you alluded to, max out.

Yah sorry, by "subs clipping" I meant I could hear clipping in the subs, ie distortion. It can't be amp clip, so it's either the sound of the signal getting squashed by the limiter, or the sound of the driver breaking up as it approaches xmax, in much the same way as a driver in a main cab begins to break up in the same situation. It's just harder to hear in a folded horn, but it's quite distinctive.

Sine, if it is indeed the sound of the xti limiter I'm hearing, could I emulate this at a lower volume to prove it? Ie, could I set the limiter to say, 30V, crank it up into the limiter with music playing and see if it's the same sound?

Yep give that a shot

I have nothing to add here but Reso Hemisphere is so good.