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[Tim McCulloch]

You can't "convert" Peak limiting to an RMS value; those have to be independently created as they are based on different criteria.

[David Sturzenbecher]

I think he means single where it waits for a signal to cross the trigger threshold and measures from that point forward?

Correct, Y axis is still voltage, X axis is still time, however the time is continuous

Attached is a rather crude example.  Here is was looking at the time constants for thermal limiters on a bridged amp. 

[Frank Koenig]

You can use a peak voltage limiter with a long attack time as an approximation of an average power limiter, but in doing so you're assuming a constant crest factor (ratio of peak to average value) of the signal. A limiter based on the root-mean-square of the voltage is a better approximation of an average power limiter, assuming only a constant load resistance. To measure true average power you need to average (low-pass filter) the product of the instantaneous voltage and current, and some amps can do this. You get into trouble, however, if you have varying numbers of speakers in parallel, not to mention the problem of one speaker going open circuit and killing the other. We've covered this ground on this forum not long ago.

If you want to verify the differences between limiters on the bench you need to use a test signal with variable crest factor, such as a pulse train of varying duty cycle or variable crest factor noise (now synthesizing that is cool). But you can get pretty far with sine waves, tone bursts, and a little faith in the instruction manual combined with some common sense.

--Frank

[Nathan Riddle]

You can't "convert" Peak limiting to an RMS value; those have to be independently created as they are based on different criteria.

What are those criteria?

If what Mark said about the PLD limiters is true (that they are simple limiters) then wouldn't the time constant (attack/release times) just change to allow for more of an average level?

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Be back later, I gotta prep me home for a hurricane

[Mark Wilkinson]

Do you recall if the peak works on peak or rms voltage?

While you might be bummed (sorry), I busted out laughing and thoroughly enjoy the candor 

Peak works on rms voltage too.   Take a look at max peak voltage setting available, and you'll see it's only 155v.

Yeah, you gotta laugh....I sure did... I'm pretty good at laughing at myself , get lots of opportunities to practice it lol
The spider-to-former ring of glue broke....don't really know what to think...can't pinpoint when it happened....
Help please anybody !

[Mark Wilkinson]

Correct, Y axis is still voltage, X axis is still time, however the time is continuous

Attached is a rather crude example.  Here is was looking at the time constants for thermal limiters on a bridged amp.

Thanks,  OK I see how to use roll mode for checking thermal.  Thermal attack is slow enough to see....

But peak?  With peak's much shorter attack?  vs roll mode's parameter limit?  200ms minimum on mine (ds1054z)

[David Sturzenbecher]

Thanks,  OK I see how to use roll mode for checking thermal.  Thermal attack is slow enough to see....

But peak?  With peak's much shorter attack?  vs roll mode's parameter limit?  200ms minimum on mine (ds1054z)

I had no problems looking at peak attack times down to the individual cycle.   I am on the same DS1054Z.

[Mark Wilkinson]

I had no problems looking at peak attack times down to the individual cycle.   I am on the same DS1054Z.

Thanks David, I see.

[Mark Wilkinson]

What are those criteria?

If what Mark said about the PLD limiters is true (that they are simple limiters) then wouldn't the time constant (attack/release times) just change to allow for more of an average level?

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I think it may be more of a combo of what i think I measure, and what Tim was saying...
Because the rms limiter voltage setting pretty well matches measured amp output, where the peak voltage limiter setting typically measures 5-10 volts lower (rms measurement).   
So there appears to be some kind of algorithm in play....sorry if oversimplified.

[Peter Morris]

I think the terminology gets butchered a bit between manufactureres, publications, forums, etc. I'm trying to see through the veil 

I was trying to state that with the HPF set according to manufacture recommendation over excursion would be taken care of.

Taken from Nick here:
https://soundforums.net/community/threads/help-me-understand-system-limiting-setting-it.1139/page-2

There's also talk of a difference between a true RMS limiter and a thermal limiter.

Perhaps there is no need for an additional rms/peak limiter when using a thermal limiter and the amp can't send peak voltage?

In general a well set HPF will offer protection, but you have to remember that it is not a limiter and if you try hard you can still have issues.

Let’s say the filter is 12 dB per octave at 40Hz (i.e - 12dB @20Hz) .… so if the DJ for example pushes all the LF GEQ faders up by 12 dB to get more bass (as I have seen) then you will still have full drive at 20Hz and Xmax issues.

The trick is to put the limiter before the HPF so you can't get the extra 12dB of drive.

The problem when you exceed Xmax is the voice coil comes out of the gap and the thermal capacity drops dramatically because the coil no longer has the magnet assembly to wick the heat away.  Usually its worse that we think because most driver don’t behave very well at extreme Xmax situations and develop some offset with their cone position. It’s due non symmetrical magnetic flux and suspension behaviour. (Klippel BL measurements) … this is why you see drivers with the coil burn at one end.

Luckily for many subs their impedance over their operating range is quit high, think in terms of twice their nominal rating so the heat build up is not as bad as we might first think.

Generally you see peak limiters come more into play with compression drivers, they often see huge peaks but the average power can be quite low. The peaks can break the voice coil assembly, shatter the diaphragm or blow the first part of the coil winding like a fuse. You usally set the rms limiter time constants to allow the peaks / transients through to the driver so the music still sounds dymanic and real and then catch the dangerous peaks with the peak limiter.

The trick with limiters is finding a solution that still allows you to take full advantage of the speaker’s capabilities but at the same time protecting them from stupid operators.

[ProSoundWeb Community]