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Author Topic: Converting peak limiter to RMS limiter  (Read 1033 times)

Frank Koenig

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Re: Converting peak limiter to RMS limiter
« Reply #30 on: October 11, 2018, 03:31:46 pm »

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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Mark Wilkinson

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Re: Converting peak limiter to RMS limiter
« Reply #31 on: October 11, 2018, 03:32:21 pm »

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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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #32 on: October 11, 2018, 04:03:35 pm »

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


--

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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Nathan Riddle

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Re: Converting peak limiter to RMS limiter
« Reply #33 on: October 11, 2018, 04:18:42 pm »

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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Frank Koenig

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Re: Converting peak limiter to RMS limiter
« Reply #34 on: October 11, 2018, 04:39:27 pm »

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 Wilkinson

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Re: Converting peak limiter to RMS limiter
« Reply #35 on: October 11, 2018, 05:25:14 pm »

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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Dave Guilford

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Re: Converting peak limiter to RMS limiter
« Reply #36 on: October 12, 2018, 12:27:12 pm »

 OK guys well letís 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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Mark Wilkinson

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Re: Converting peak limiter to RMS limiter
« Reply #37 on: October 12, 2018, 12:41:51 pm »

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....
 
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