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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB Lounge => Topic started by: Nathan Riddle on October 07, 2018, 08:55:52 PM
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I know we seem to talk about limiters every few months. But I don't believe we've spoken about this.
I am NOT talking about RMS voltage to peak conversions (1.414 multiplier). [Though I imagine it could be this easy for some 'under the DSP's hood calculations]
Specifically, I have an amp (QSC PLD 4.5) that has two limiters:
RMS
3-100v
attack: 1ms - 9.951s
release: 10ms - 59.01s
Peak
5-155
attack: 0.1ms - 20ms
release: 1ms - 1000ms
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The RMS is used as a thermal limiter (~1/4 power) 40v 3s attack & release.
The peak is wasted as a peak limiter as the amp can't send more voltage than the woofer can handle (given a properly set HPF) it can't physically pop the cone. Thus it would be best used as a RMS limiter of some sort (if it's needed at all).
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I know we seem to talk about limiters every few months. But I don't believe we've spoken about this.
I am NOT talking about RMS voltage to peak conversions (1.414 multiplier). [Though I imagine it could be this easy for some 'under the DSP's hood calculations]
Specifically, I have an amp (QSC PLD 4.5) that has two limiters:
RMS
3-100v
attack: 1ms - 9.951s
release: 10ms - 59.01s
Peak
5-155
attack: 0.1ms - 20ms
release: 1ms - 1000ms
---
The RMS is used as a thermal limiter (~1/4 power) 40v 3s attack & release.
The peak is wasted as a peak limiter as the amp can't send more voltage than the woofer can handle (given a properly set HPF) it can't physically pop the cone. Thus it would be best used as a RMS limiter of some sort (if it's needed at all).
Is there a question?
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Is there a question?
In the title?
Obviously, there are assumptions we would take on the DSP's part. [is the peak limiter measuring peak or RMS, is the RMS (thermal) limiter measuring RMS or some other value, eg. Vavg (under the curve)?]
Can we come up with a method of determining what type of limiting algorithm it is using for peak or RMS?
What is typical?
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In the title?
Obviously, there are assumptions we would take on the DSP's part. [is the peak limiter measuring peak or RMS, is the RMS (thermal) limiter measuring RMS or some other value, eg. Vavg (under the curve)?]
Can we come up with a method of determining what type of limiting algorithm it is using for peak or RMS?
What is typical?
I have done extensive measurements of amplifier limiters in order to copy presets from on amp to another. ITechHD, Lab Gruppen D series, Powersoft X, and QSC CXD-Q are the ones I have tested. There is by far no hard and fast rules for how any of them behave. My method involved hours, upon hours of time in front of an oscilloscope in “roll” mode in order to capture the actual peak voltage values and time constants. Any ole DMM should allow you to set the RMS values, but peak takes some work.
The QSC CXD-Q doesn’t allow you to enter values at all, so nothing I measured would carry over to your amps. The CXD-Q settings want voice coil size, power rating and if it’s a compression driver or not. I was thoroughly disappointed in the results of the CXD-Q though. There were no provisions to let through any transient peaks. Everything was brickwalled to the RMS calculated voltage... with a very long term limiter coming in at 10-30 seconds. Also, don’t even get me started in how wrong the limiter settings are when you put those amps in bridge mode. I had to tell the amp to limit to a “100watt driver” to get a 700W equivalent limitation. Had I blindly typed in values and not measured, it would have been a service nightmare.
Sent from my iPhone using Tapatalk Pro
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I have done extensive measurements of amplifier limiters in order to copy presets from on amp to another. ITechHD, Lab Gruppen D series, Powersoft X, and QSC CXD-Q are the ones I have tested. There is by far no hard and fast rules for how any of them behave. My method involved hours, upon hours of time in front of an oscilloscope in “roll” mode in order to capture the actual peak voltage values and time constants. Any ole DMM should allow you to set the RMS values, but peak takes some work.
The QSC CXD-Q doesn’t allow you to enter values at all, so nothing I measured would carry over to your amps. The CXD-Q settings want voice coil size, power rating and if it’s a compression driver or not. I was thoroughly disappointed in the results of the CXD-Q though. There were no provisions to let through any transient peaks. Everything was brickwalled to the RMS calculated voltage... with a very long term limiter coming in at 10-30 seconds. Also, don’t even get me started in how wrong the limiter settings are when you put those amps in bridge mode. I had to tell the amp to limit to a “100watt driver” to get a 700W equivalent limitation. Had I blindly typed in values and not measured, it would have been a service nightmare.
Sent from my iPhone using Tapatalk Pro
This is yet another reason to MEASURE and DO NOT assume the "simple numbers" are what they think they are.
There is one MAJOR manufacturer whos "thermal limiter" does not make any sense to me.
To me, a limiter should start to act whenever the threshold is exceeded. Not hard limit to that value quickly, but rather "bring the level" down to that level over the time period specified. If you just barely exceed the level, then it is a very slow attenuation. Exceed it a whole lot and it is a faster attenuation.
In this case, the thermal limiter does NOTHING, until the attack time has passed, and THEN is starts to reduce, at the time period specified.
What is really strange, is that the manufacturer recommends (in several places) for subs to be around 3 seconds of thermal, but yet HF drivers be 10 Seconds of thermal.
That is AN ETERNITY for HF drivers. That provides NO protection what so ever to the HF driver.
As much as we "want" the digital numbers to all be the same, very often they are VERY far off, not even close, unless you count a ratio of 2:1 to be "close". Not me.
It amazes me the "blind assumptions" people take as gospel these days.
Just because somebody says something, many take it as the truth, yet do nothing to try to figure out if it is actually fact or not.
-3dB, -27dB- Hey close enough to "believe" -right?
I better stop now--------------
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Thanks, guys.
David, seems you're the one to talk to about learning to test DSP (amidst others, Ivan/Langston)
I knew everything in DSP can be/is different from previous posts from Ivan/others. But I was hoping there might be some uniformity in the general application of a peak limiter vs RMS limiter. Seems as though there isn't :/
Next on the chopping block would be walking me through testing one. I know how to find thermal limiters well enough via DMM's. But I'd like to learn more advanced techniques of testing such as the thorough reports by Langston on the interfaces or from others on amps/dsp.
https://forums.prosoundweb.com/index.php/topic,154105.msg1553151.html#msg1553151
http://www.bennettprescott.com/downloads/DSP_Differences.pdf
https://www.poweraudio.ro/diy/albums/userpics/10001/BENCH_COMPARISON_TEST.pdf
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I think I'd need some tools/test equipment,
I have a BK Precision 1474, but it's too old to be of any real use.
I'm looking into budget o'scopes (Siglent Technologies SDS1202X-E) to help facilitate this.
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I know we seem to talk about limiters every few months. But I don't believe we've spoken about this.
I am NOT talking about RMS voltage to peak conversions (1.414 multiplier). [Though I imagine it could be this easy for some 'under the DSP's hood calculations]
Specifically, I have an amp (QSC PLD 4.5) that has two limiters:
RMS
3-100v
attack: 1ms - 9.951s
release: 10ms - 59.01s
Peak
5-155
attack: 0.1ms - 20ms
release: 1ms - 1000ms
---
The RMS is used as a thermal limiter (~1/4 power) 40v 3s attack & release.
The peak is wasted as a peak limiter as the amp can't send more voltage than the woofer can handle (given a properly set HPF) it can't physically pop the cone. Thus it would be best used as a RMS limiter of some sort (if it's needed at all).
There are 3 things that you need to protect - Xmax, thermal and mechanical stress limits.
The RMS limiter is usually used to stop the voice coil being overheated. The peak limiter is usually set to protect a mechanical limit. i.e. from a dangerous transient that could rip a cone, shatter a diaphragm, damage the voice coil, or result in early fatigue failures. You can also set it just to stop the amp clipping.
If you get these correct and subject to the speaker design they can also protect Xmax, but there are other more sophisticated ways to model and protect Xmax ... and thermal limits for that matter.
How these are set will depend on the characteristics of the device you are trying to protect, what its peak/transient limit is compared to long term thermal limit.
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There are 3 things that you need to protect - Xmax, thermal and mechanical stress limits.
The RMS limiter is usually used to stop the voice coil being overheated. The peak limiter is usually set to protect a mechanical limit. i.e. from a dangerous transient that could rip a cone, shatter a diaphragm, damage the voice coil, or result in early fatigue failures. You can also set it just to stop the amp clipping.
If you get these correct and subject to the speaker design they can also protect Xmax, but there are other more sophisticated ways to model and protect Xmax ... and thermal limits for that matter.
How these are set will depend on the characteristics of the device you are trying to protect, what its peak/transient limit is compared to long term thermal limit.
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?
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Specifically, I have an amp (QSC PLD 4.5) that has two limiters:
RMS
3-100v
attack: 1ms - 9.951s
release: 10ms - 59.01s
Peak
5-155
attack: 0.1ms - 20ms
release: 1ms - 1000ms
---
Nathan, I've looked at the PLD4.5's limiters on a scope, and AFAICT both the rms and peak work exactly the same, other than the different ranges for attack and release. They seem to simply compress the signal, in hardwall fashion base on attack and release.
But I should add that I'm not all that experienced with a scope....
The only thing I know how to do, is look and see if the waveform is clipped or compressed, after the limiter is fully engaged.
I do not yet know how to look at the time it takes to engage or release a limiter, and whether there is any voltage ramp to on or off.
David, what do you mean by oscope "roll mode" ? Any tips on how to look at attack and release?
Peter, can you describe the more sophisticated ways to model and protect xmax, ..and thermal ?
I know how to use hornResp to model displacement with HFP in place, but that's about it.....
I gotta keep learning here....despite it all, I still managed to lunch a sub driver last week during testing :-[
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Nathan, I've looked at the PLD4.5's limiters on a scope, and AFAICT both the rms and peak work exactly the same, other than the different ranges for attack and release. They seem to simply compress the signal, in hardwall fashion base on attack and release.
But I should add that I'm not all that experienced with a scope....
The only thing I know how to do, is look and see if the waveform is clipped or compressed, after the limiter is fully engaged.
I do not yet know how to look at the time it takes to engage or release a limiter, and whether there is any voltage ramp to on or off.
David, what do you mean by oscope "roll mode" ? Any tips on how to look at attack and release?
Peter, can you describe the more sophisticated ways to model and protect xmax, ..and thermal ?
I know how to use hornResp to model displacement with HFP in place, but that's about it.....
Do you recall if the peak works on peak or rms voltage? [I know, I know... measure; I don't have one to test and I'm creating presets for a friend]
I think he means single where it waits for a signal to cross the trigger threshold and measures from that point forward?
I gotta keep learning here....despite it all, I still managed to lunch a sub driver last week during testing :-[
While you might be bummed (sorry), I busted out laughing and thoroughly enjoy the candor :D
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You can't "convert" Peak limiting to an RMS value; those have to be independently created as they are based on different criteria.
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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.
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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
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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 :)
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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 :D
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 !
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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)
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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.
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I had no problems looking at peak attack times down to the individual cycle. I am on the same DS1054Z.
Thanks David, I see.
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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.
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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.
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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?
I think there is some conflation of terms as used... but almost all of those criteria have a direct influence on the transducer holding together physically and thermally. The interaction a fixed HPF filter and *any* type of voltage limiter is just that, a fixed relationship. When one gets into processing that uses variable HPF or other filters, one must be able to measure the acoustic result of the electrical variables and decide if the protection is sufficient, too aggressive or ineffective... or too audible/inaudible.
What is your goal here? Protection against stupid operation - i.e. DJ-proof, or squeezing the last couple of dB out of a pass band, when operated by mindful mixerpersons?
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What is your goal here? Protection against stupid operation - i.e. DJ-proof, or squeezing the last couple of dB out of a pass band, when operated by mindful mixerpersons?
This is a VERY important statement. With different settings.
But many people want to "squeeze every last watt" and also drive the system as hard as it can be, compression/limiting be damned.
Those are NOT things that happen at the same time.
Often choices have to be made for specific situations.
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I was trying to stay manufacture & limiter values agnostic as I was mostly curious about the differences between RMS & peak limiting circuitry/algorithms.
My goal is to implement the manufacture recommended limiting values.
RMS Limiter: 80 Volts
Thermal Limiter: 40 volts, 3.0 Seconds Attack, 1.0X Release (multiplier of Attack)
XMax Limiter: 60 Volts at 25 Hz
I just thought of a way to do the XMax limiter. Grab the impedance chart and calculate @ that frequency the...nevermind.
Would a limiter set at 60 volts with Attack of 40ms (25hz) work for XMax?
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with Attack of 40ms (25hz) work for XMax?
I keep my peak voltage limiters set to essentially zero attack time. They're there to protect against dropped mics, phantom power pops, and similar accidents. I never expect to hit them during normal operation. But that's just me.
I also fail to see the distinction between RMS limiters and thermal limiters. What's the purpose of an RMS (or other average power proxy) limiter if not to prevent overheating of the voicecoils?
--Frank
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I was trying to stay manufacture & limiter values agnostic as I was mostly curious about the differences between RMS & peak limiting circuitry/algorithms.
My goal is to implement the manufacture recommended limiting values.
I just thought of a way to do the XMax limiter. Grab the impedance chart and calculate @ that frequency the...nevermind.
Would a limiter set at 60 volts with Attack of 40ms (25hz) work for XMax?
I'm curious what kind of speaker this is that needs an extra limiter for frequencies that low - I know Ivan pointed out how the HPF could be rendered less effective, but surely unless this is an infra sub or studio monitor, you are going to have an HPF higher than 25Hz in place already, right?
Anyhoo, 40ms is one whole wavelength at 25Hz, therefore if your limiter only kicks in after 40ms you've already let one cycle through to the driver, including one positive and one negative peak (assuming something remotely resembling a sine wave at least).
If you want to prevent the first peak coming through, you'd need to have an attack set to 1/4 wavelength at the longest, depending on how quickly the limiter responds after the attack time has passed.
FWIW,
David.
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I'm curious what kind of speaker this is that needs an extra limiter for frequencies that low
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That quotes 40Hz, not the 25Hz in your earlier post...
But, that wasn't really the point - which was that your limiter would need to kick in at no later than 1/4WL of the frequency of interest.
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That quotes 40Hz, not the 25Hz in your earlier post...
But, that wasn't really the point - which was that your limiter would need to kick in at no later than 1/4WL of the frequency of interest.
The other quote was TH118's suggested limiter preset. TH115 is what I was building presets for.
But good point about the 1/4WL.
The answer to this question is there's no way to convert between the two. And to not use the peak limiter in the PLD as it's useless in this situation (amp self-limits).
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I've seen that table in other literature I've downloaded from Danley. I'm guessing the "x-max limiter" is a peak limiter downstream of a low-pass filter that attempts to model the (approximately inverse square) relationship of excursion and frequency. That relationship gets interesting near the lower cutoff and is very different for different types of speakers -- bass reflex, closed-back horn, other horns, etc.
I'd be happy if Ivan would give us the long, complicated, and correct version of what those limiter settings mean.
--Frank
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I've seen that table in other literature I've downloaded from Danley.
snip
I'd be happy if Ivan would give us the long, complicated, and correct version of what those limiter settings mean.
--Frank
Agreed.
I would like to know what (nominal) impedance the values are for. It would make a difference between an 8 ohm sub and a 4 ohm sub.
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Agreed.
I would like to know what (nominal) impedance the values are for. It would make a difference between an 8 ohm sub and a 4 ohm sub.
As long as the settings are all voltage-based, as opposed to true power, the number of speakers in parallel does not matter as the amplifier is a voltage source. That's the advantage of voltage-based limiters and why Powersoft provides the "Power into 8 Ohms" mode, which is an RMS voltage limiter. But if the speaker in question is available in more than one impedance it certainly would be necessary to know which one the table is referring to.
As an aside, Powersoft has a good guide for coming up with limiter settings based on driver characteristics in their amplifier instruction manuals. If not for questions of fair use I'd reproduce it here. But I think it's available for download.
--Frank
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I'm all ginned up making time measurements now that I *think* I know how...
Here's a PLD4.5 anomaly.....
First pict = C channel alone, 60V RMS with 2s attack
Second = AB channels in parallel, same 60V RMS 2s attack
Scope grid 1sec/division.
C channel has about 2.9s to start of limiting, and at least 7s to full limiting.
AB has about 5.3s to start, and about 10s to full.
Big difference, and again, the attack the setting was 2 seconds.
Somethin aint right with that camel ride.....
Ivan keeps saying you have to test everything...
I honestly hope I'm just screwing up the measurements...I'd like to be able to trust stuff without doubt...
But anyone can tell just by counting off seconds and watching a DMM, that limiting takes much longer than the amp's attack setting.
So I think the scope work is OK. Oh, and there's an 8 ohm dummy load in place...
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As long as the settings are all voltage-based, as opposed to true power, the number of speakers in parallel does not matter as the amplifier is a voltage source. That's the advantage of voltage-based limiters and why Powersoft provides the "Power into 8 Ohms" mode, which is an RMS voltage limiter. But if the speaker in question is available in more than one impedance it certainly would be necessary to know which one the table is referring to.
As an aside, Powersoft has a good guide for coming up with limiter settings based on driver characteristics in their amplifier instruction manuals. If not for questions of fair use I'd reproduce it here. But I think it's available for download.
--Frank
True, if we are simply adding subs. I am talking about the 8ohm sub vs 4ohm sub version. We are protecting the speaker's power (heat/ability to do work) not how much voltage the coils can handle without arcing through the insulation. Thus the voltage would change (power stays the same) for the same sub (just different ohms). Unless I'm wrong... I see your sentence stating what I'm saying... lol
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Oh yeah, I've read the Powersoft limiter document a few times. Always learn something new.
http://www.brightonsoundsystem.co.uk/calculator/powersoft-k10-limiter.php
http://www.powersoft-audio.com/en/docman/804-how-to-setup-limiters/file
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I'm all ginned up making time measurements now that I *think* I know how...
Here's a PLD4.5 anomaly.....
First pict = C channel alone, 60V RMS with 2s attack
Second = AB channels in parallel, same 60V RMS 2s attack
Scope grid 1sec/division.
C channel has about 2.9s to start of limiting, and at least 7s to full limiting.
AB has about 5.3s to start, and about 10s to full.
Big difference, and again, the attack the setting was 2 seconds.
Somethin aint right with that camel ride.....
Ivan keeps saying you have to test everything...
I honestly hope I'm just screwing up the measurements...I'd like to be able to trust stuff without doubt...
But anyone can tell just by counting off seconds and watching a DMM, that limiting takes much longer than the amp's attack setting.
So I think the scope work is OK. Oh, and there's an 8 ohm dummy load in place...
Man, I wish that was the case. The more I dive into all of this testing and verifying I keep finding that trusting isn't working. Maybe I should just stick with IT ::)
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I'm all ginned up making time measurements now that I *think* I know how...
Here's a PLD4.5 anomaly.....
First pict = C channel alone, 60V RMS with 2s attack
Second = AB channels in parallel, same 60V RMS 2s attack
Mark, is it possible that what you're seeing is the amplifier's normal thermal limiting and has nothing to do with the limiter settings? That could account for the different results with different amounts of current available. If it's a voltage limiter it should behave the same with no load as with 8 Ohms and with any number of channels in parallel. Also, a normal RMS limiter would start reducing gain as soon as the RMS value exceeds the threshold. Is the final value of the voltage consistent with the limiter setting? Keep experimenting :)
Are you located anywhere near the SF Bay Area? I'd be happy to look at this.
--Frank
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Mark, is it possible that what you're seeing is the amplifier's normal thermal limiting and has nothing to do with the limiter settings? That could account for the different results with different amounts of current available. If it's a voltage limiter it should behave the same with no load as with 8 Ohms and with any number of channels in parallel. Also, a normal RMS limiter would start reducing gain as soon as the RMS value exceeds the threshold. Is the final value of the voltage consistent with the limiter setting? Keep experimenting :)
Are you located anywhere near the SF Bay Area? I'd be happy to look at this.
--Frank
Thanks Frank, for your very friendly offer to help look at things. I wish I could take you up on it ! but alas I'm in Virginia.
The final voltage after limiting has settled in, is consistent with the RMS limiter setting... 60V.
I don't think there can be any other limiting in play, such as a built in thermal protector, because I'm using no more than a 2Vrms drive level (amp set at 32dB gain).
And my tests are very short term...dummy load isn't getting hot...amp signal lights look right.....ect
The amp, when in 'advanced' limiter mode, appears to be blind to any settings other than voltage, attack and release.
Doesn't that imply it's strictly dealing with voltage, independent of load? That's what I've been thinking...
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OK guys well let’s cut to the chase. I have looked this up a bunch of different ways and it only pulls old and outdated threads with no good answers, just speculation that no one ever followed up with
I have itech5000hd and Srx725 running stereo.
What values should I have in place? It would be awesome to have one setting that lets me dummy proof, and another setting to let me squeeze the most out
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Well, I'm happy to say I got my wish....I had screwed something up...sincere apologies.
Starting anew from ground up a single PLD channel measures the same as a pair in parallel.
I would say from the single channel RMS shot below with an attack setting of 2s, that initiation begins as per setting, taking maybe 5s more to fully attenuate.
Peak set at 20ms attack looks spot on, with full attenuation at setting.
Dual channel parallel looked identical for RMS.
Nathan, one other biggie mis-info I gave you earlier.
Peak voltages are just that, peak...not RMS.
Put the two on top each other in Amplifier Navigator and you will see what I mean.
Plus the peak voltage setting matched exactly what i was reading on scope peak.
Again, apologies for bad info....