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Author Topic: System limiters in series  (Read 1199 times)

David Allred

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System limiters in series
« on: February 22, 2018, 11:06:27 am »

I plan to use the compressor on the LR output of my MR18 as a limiter.  I can set as RMS or peak.  I also use a Venu360 for zoning, monitor, and its other capabilities, including limiting.  It also has the choice of RMS or peak.
I want to use one for peak and the other for RMS.  Is there a preferred order as to which is in line first? Any considerations?

The follow-up question concerns attack times.  From what I've read, horn drivers need faster attack and subs need a slower attack (if I remember right).  Is that correct?

If so, this is my conundrum... My top and subs are processed by the manufacturer's processor (Yorkville), so I am stuck with single attack, etc settings for tops and subs.  Any settings recommendations?

thanks
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Nathan Riddle

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Re: System limiters in series
« Reply #1 on: February 22, 2018, 11:29:39 am »

I'm no expert. & I don't usually use the board or input limiters only output limiters.

But I'd say set the mixer limiter to RMS and the Venu360 INPUT limiting to peak & the Venu360 output limiter to Thermal.

You'd be best to limit the passbands so you can set attack/release times accordingly.

For the main RMS limiter - set to long attack/release times (say 100ms (maybe even .5 or 1s attack) & 2x-8x release) set the level to limit the entire system to whatever SPL you don't want the system going pass (whether for hearing protection or thermal transducer protection) (long term thermal limit of HF/MF drivers).

For the main peak limiter - set to uber short attack & med release (20uS & 5ms) & set at a level that protects the HF driver from blowing itself up (peak voltage).

For the pass-bands, (thermal limiter) limit to the 1/4 power of RMS (program) power of the driver. Use 3s & 8s (attack & release) for the subs.

etc.

http://www.brightonsoundsystem.co.uk/calculator/powersoft-k10-limiter.php
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David Allred

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Re: System limiters in series
« Reply #2 on: February 22, 2018, 12:00:17 pm »

I'm no expert. & I don't usually use the board or input limiters only output limiters.

But I'd say set the mixer limiter to RMS and the Venu360 INPUT limiting to peak & the Venu360 output limiter to Thermal.

You'd be best to limit the passbands so you can set attack/release times accordingly.

For the main RMS limiter - set to long attack/release times (say 100ms (maybe even .5 or 1s attack) & 2x-8x release) set the level to limit the entire system to whatever SPL you don't want the system going pass (whether for hearing protection or thermal transducer protection) (long term thermal limit of HF/MF drivers).

For the main peak limiter - set to uber short attack & med release (20uS & 5ms) & set at a level that protects the HF driver from blowing itself up (peak voltage).

For the pass-bands, (thermal limiter) limit to the 1/4 power of RMS (program) power of the driver. Use 3s & 8s (attack & release) for the subs.

etc.

http://www.brightonsoundsystem.co.uk/calculator/powersoft-k10-limiter.php

Thanks, I hadn't considered using the compressor on the pre-x-over side in the 360 as a limiter.  That is just like using the one on the MR18 output, except (I assume) peak only.  Nice suggestion.
Unfortunately, I have made a conscious decision to use the Yorkville processor to do the band-pass work, so having individual limiters for them is not in the cards.

That means I can have 3 type of limiting :
MR18 main comp - RMS or Peak
360 input comp - Peak
360 output Limiter - RMS or Peak

So, if the subs and highs are sharing limiters... any thoughts?
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Nathan Riddle

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Re: System limiters in series
« Reply #3 on: February 22, 2018, 12:08:19 pm »

Thanks, I hadn't considered using the compressor on the pre-x-over side in the 360 as a limiter.  That is just like using the one on the MR18 output, except (I assume) peak only.  Nice suggestion.
Unfortunately, I have made a conscious decision to use the Yorkville processor to do the band-pass work, so having individual limiters for them is not in the cards.

That means I can have 3 type of limiting :
MR18 main comp - RMS or Peak
360 input comp - Peak
360 output Limiter - RMS or Peak

So, if the subs and highs are sharing limiters... any thoughts?

Band limited compressors/limiters would work, like Linea Research's VX audio output limiters. But those are out as the Venue360 doesn't have that.

What assumptions or facts do we know about the Yorkville processor? Is it doing any limiting at all?
What music do you typically do? I'd say spectral content would change our 'protection' methods.

EDM = thermally limit -3dB below whichever component is the weakest link
Rock = peak limit -3dB below whichever component is the weakest link

You can create thermal limiters from rms limiters by measuring the voltage and doing 1/2 or 1/3 or 1/4 power calculations.
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David Allred

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Re: System limiters in series
« Reply #4 on: February 22, 2018, 01:19:47 pm »

Band limited compressors/limiters would work, like Linea Research's VX audio output limiters. But those are out as the Venue360 doesn't have that.

What assumptions or facts do we know about the Yorkville processor? Is it doing any limiting at all?
What music do you typically do? I'd say spectral content would change our 'protection' methods.

EDM = thermally limit -3dB below whichever component is the weakest link
Rock = peak limit -3dB below whichever component is the weakest link

You can create thermal limiters from rms limiters by measuring the voltage and doing 1/2 or 1/3 or 1/4 power calculations.

Sorry.  The Yorkville processor does the band passes and corrective & protective EQ.  No limiting.

The main situation that is a threat is during DJ-ing for HS age kids.  So mostly rap and pop.  EDM has not made itself popular where I am yet.  Everything else is talking head, amateur talent (no bands) etc.

Thanks for the feedback.
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Nathan Riddle

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Re: System limiters in series
« Reply #5 on: February 22, 2018, 02:23:02 pm »

Sorry.  The Yorkville processor does the band passes and corrective & protective EQ.  No limiting.

The main situation that is a threat is during DJ-ing for HS age kids.  So mostly rap and pop.  EDM has not made itself popular where I am yet.  Everything else is talking head, amateur talent (no bands) etc.

Thanks for the feedback.

Ahh okay.

So if it were me. Page 53/54 of the venu360 manual detail the limiting/gain staging section. [it's fairly lacking IMO, and I've grown to hate dbx's when real processing isn't too far away in price.]

After gainstage & all processing setup is done. I'd do what Ivan taught me.

Disconnect the speakers. Calculate the 1/3 power voltage for the average impedance for the sub amp output.

Then play a ~60hz sinewave into the input. Grab a voltmeter & measure the amp output. Raise the input until the output voltage is +10v or so above whatever you need to limit to.

Turn down the limiter threshold until it brings the voltage down to the calculated voltage limit.

Play some music, season overeasy to taste (~5)
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Mike Monte

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Re: System limiters in series
« Reply #6 on: February 22, 2018, 02:31:33 pm »

Sorry.  The Yorkville processor does the band passes and corrective & protective EQ.  No limiting.

The main situation that is a threat is during DJ-ing for HS age kids.  So mostly rap and pop.  EDM has not made itself popular where I am yet.  Everything else is talking head, amateur talent (no bands) etc.

Thanks for the feedback.

What Yorkville processor are you using?? 
I use TX processors for my TX3/4/8/9s rigs (the TX processors have limiters built in)
I also use e152p and e10p processors (with e152/e10 cabs) that have no limiting....

In the case of the e10p/e152p processors do not send more to the cabs than they are rated for....
 

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David Allred

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Re: System limiters in series
« Reply #7 on: February 22, 2018, 02:50:44 pm »

What Yorkville processor are you using?? 
I use TX processors for my TX3/4/8/9s rigs (the TX processors have limiters built in)
I also use e152p and e10p processors (with e152/e10 cabs) that have no limiting....

In the case of the e10p/e152p processors do not send more to the cabs than they are rated for....

EP1215 for passive use.  Am I missing something here?
Yeah, the TX series sense and adapt, I believe. 
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David Allred

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Re: System limiters in series
« Reply #8 on: February 22, 2018, 03:04:19 pm »

Ahh okay.


 Calculate the 1/3 power voltage for the average impedance for the sub amp output.



Can you expound on this? 

725w 20-20k (775w 1k) into 8 ohms (sub nominal, 600/1200/2400)
Amp volt data from a spreadsheet I acquired a few years back:
75 v rms
111 v peak

Sub:
63v/98v/126v
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Nathan Riddle

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« Last Edit: February 22, 2018, 03:35:52 pm by Nathan Riddle »
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David Allred

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Re: System limiters in series
« Reply #10 on: February 22, 2018, 04:24:13 pm »

http://forums.prosoundweb.com/index.php/topic,160926.msg1479766.html#msg1479766

http://forums.prosoundweb.com/index.php/topic,159553.msg1465845.html#msg1465845

http://forums.prosoundweb.com/index.php/topic,158775.msg1464129.html#msg1464129

http://forums.prosoundweb.com/index.php/topic,159553.msg1465725.html#msg1465725

All good info, but I am still confused by the 1/3rd power.  (1/3rd of what?)

From one of Ivan posts....
"Since the cabinets are 1700W @ 4 ohms, that would be 82V.

I would run the thermal around 1/3rd power  with a attack around 3 seconds.

This would be around 50 volts"

The math (82 * 1/3 = 27) does not equal 50.
82 down 1/3rd = 54.  That's close, but obviously not 1/3rd power of 82.
Help me understand, please.
thanks
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Ivan Beaver

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Re: System limiters in series
« Reply #11 on: February 22, 2018, 05:17:57 pm »

All good info, but I am still confused by the 1/3rd power.  (1/3rd of what?)

From one of Ivan posts....
"Since the cabinets are 1700W @ 4 ohms, that would be 82V.

I would run the thermal around 1/3rd power  with a attack around 3 seconds.

This would be around 50 volts"

The math (82 * 1/3 = 27) does not equal 50.
82 down 1/3rd = 54.  That's close, but obviously not 1/3rd power of 82.
Help me understand, please.
thanks
Voltage and power are different.

1/2 the VOLTAGE =1/4 the power.

For 1/2 power, you would use the continuous voltage x .707=V

I have since updated my "opinion" on thermal limiters.  I now say 1/4 power (1/2 voltage) for "abusive" situations.  Typically 3 seconds attack time for large powerful woofers, down to 1 second for moderate powered woofers.

This is based on the CONTINUOUS rating of the loudspeaker, which should be 6dB down from the peak rating.

mids and highs are MUCH shorter.

The main reason for the change of opinion is the long term usage, not just signal levels.  1/4 to 1/3 power is fine for extended points in the signal, but you can run into issues if this goes on for hours and hours.

Some events are 72 hours straight with NO break in the music.  This can be HELL on drivers.

So far, the 1/4 continuous power (NOT music power) seems to be a better choice for thermal limiters.

I still like to have program limiters (set at the continuous rating of the driver with an attack time equal to the highpass filter duration) and a peak limiter.  I usually set this at the program voltage, rather than the peak voltage.

In my opinion trying to get a couple of extra dB out of a short peak is simply asking for trouble.

NOTE: some amplifiers have a peak voltage setting, but it is NOT measured by the RMS value of the signal but rather the peak of the signal. 

So if you want a RMS peak to be 100V, you need to set the "peak" limiter to be 140V.

It is important to understand which way YOUR particular amp determines this voltage.

Of course the BEST way, is to simply measure and set accordingly.
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Nathan Riddle

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Re: System limiters in series
« Reply #12 on: February 22, 2018, 05:20:41 pm »

Ivan beat me to it. His voice is superior. Listen to the master ;)

Ivan...

Sorry,

Thermal limiter = 1/3rd of the continuous power.
RMS limit (rms power doesn't exist) = continuous rating (or program, if not as worried about protecting the speaker(s))
Peak = xMax (@ lowest impedance)

For the sub in question (TH118):
7200w (peak)
3400w (program)
1700w (continuous)
566w (1/3rd of continuous)

V = Sqrt( P * R )

[Thermal Limiter] 47.6 (50v) = Sqrt (1700w / 3  * 4ohm)

[RMS limiter] 82.46v = Sqrt(1700w * 4ohm)

[Peak Limiter] 169v = Sqrt (7200w * 4ohm)

[Real Peak Limiter, lowest impedance] 146.9v = Sqrt (7200w * 3ohms)
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David Allred

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Re: System limiters in series
« Reply #13 on: February 22, 2018, 05:56:55 pm »

Thanks Ivan and Nathan.
I had a bit of an aha moment on the way home, and thought that I should not be dividing volts by 3, but watts, then converting to volts.  Turns out I was right.
I dove into the limiter and compressors in the MR18 and 360, and hit a stumbling block.
The max attack time in the 360 is 200ms, and the MR18 is 120ms.  How much does that limit (PUN) me.  What are my best options, considering?
2 to 3 hrs is about as long as I go in dance mode. 
As a reminder my sub amp (PLX3602) is 775w into a 600w cont sub (UCS1).
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Ivan Beaver

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Re: System limiters in series
« Reply #14 on: February 22, 2018, 07:49:37 pm »

Thanks Ivan and Nathan.
I had a bit of an aha moment on the way home, and thought that I should not be dividing volts by 3, but watts, then converting to volts.  Turns out I was right.
I dove into the limiter and compressors in the MR18 and 360, and hit a stumbling block.
The max attack time in the 360 is 200ms, and the MR18 is 120ms.  How much does that limit (PUN) me.  What are my best options, considering?
2 to 3 hrs is about as long as I go in dance mode. 
As a reminder my sub amp (PLX3602) is 775w into a 600w cont sub (UCS1).
As usual, it is a matter of "it depends", and "specifics matter".

In YOUR particular case, I would turn the clip eliminators on the amp ON.  That should take care of the "peaks".

Since the rating of the amp is just a little bit (1.1dB) over the continuous rating of the driver, I would not worry about a continuous limiter.

So that leaves a thermal limiter.  But you don't have a long enough attack time.

I would set the attack at max (200ms).  The continuous voltage for 600 watts @ 8 ohms = 69V.  The 1/4 power point would be half that voltage, so 34V.

But since you don't have a long attack time, I would suggest a higher voltage/power, so maybe around 45V.  This is a balance between voltage and time.

If you wanted, you could set the limiter in the MR18 as a continuous limiter.  An attack time of 20ms and voltage of 69V would be a good start.

The problem with setting a limiter in the MR18 is that if there are any changes or boosts of freq in the DSP, the limiter voltages can be pretty meaningless.

It is for this reason the limiters should be the LAST thing in line.

If given a choice, I prefer to have the longest attack time (lowest voltage) first, and the peak limiter last.

NOTE: the attack time I suggested for the MR18 is based on a 50Hz highpass (or there abouts.

Some people prefer to set the attack time for twice the time for the xover freq

So that would be 40-50ms.  I would not worry to much about it.
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David Allred

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Re: System limiters in series
« Reply #15 on: February 22, 2018, 09:02:00 pm »

Thanks a ton Ivan.
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Chris Grimshaw

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Re: System limiters in series
« Reply #16 on: February 23, 2018, 03:37:51 am »



I have since updated my "opinion" on thermal limiters.  I now say 1/4 power (1/2 voltage) for "abusive" situations.

Makes sense.
Power ratings are measured with pink noise, clipped to a 6dB crest factor.
That means a square wave with half the peak voltage would have the same power delivery.


When it comes to 72-hour gigs, that's some serious thermal abuse as everthing will end up saturated with heat - driver frames, screws, all that stuff. Things like tapped horns stand a fighting chance since they've got the magnets close to the outside world, with lots of airflow. Sealed mid-high boxes will really suffer.
I guess the solution there is to bring way more rig than would "needed", so you can run well away from the clip lights and keep everything fairly cool.
IIRC, Pi Speakers came up with a good way of getting heat out of the drivers from a front-loaded horn, involving an external aluminium heatsink, and a tube to connect it to the driver's polepiece. Thermal performance was much improved. Could be something to look at for boxes that enclose the drivers completely.

Chris
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Ivan Beaver

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Re: System limiters in series
« Reply #17 on: February 23, 2018, 07:37:54 am »


IIRC, Pi Speakers came up with a good way of getting heat out of the drivers from a front-loaded horn, involving an external aluminium heatsink, and a tube to connect it to the driver's polepiece. Thermal performance was much improved. Could be something to look at for boxes that enclose the drivers completely.

Chris
The problem with aluminum plates is  that when you stack them (on some cabinets), the plates are next to each other can therefore cannot radiate to the outside world.

I did a test on a FLH cabinet that had a 1/4" aluminum plate that was very close to the driver magnet (at one point anyway), vs a wooden cover.

This was a double driver cabinet, with both drivers getting the same signal. 1 of each type on each driver-that were in different parts of the cabinet.

I put temp probes on the top part of the magnets and ran them outside so I could measure the temp of the magnet housing.

I drove them with two signals at the same time.  pink noise mixed with heavy EDM.  So it was very abusive.

What I found was that the aluminum plate driver ran cooler than the wooden plate driver-about 2 to 3 * C.  This was very consistent from just after the start of the test up to where I stopped the test, which was when the magnets reached around 90*C.

What I found interesting was watching the "cool down".  I had stopped the signal and was just watching the temp on the magnets as they cooled down.

The wooden plate magnet cooled down a good bit faster than the aluminum plate.

There was no air flowing, inside or outside the cabinet.  The cabinet was inside an isolated room, so the ambient temp of the room had risen a fair bit during the test.

The aluminum plate did not provide enough of a temp advantage to make it worth while.  In my opinion anyway.

Something else to consider about aluminum plates.  They can remove heat, just as well as they can transmit heat to the driver in hot outdoor situations.  It is not a one way street.

You need to look at the whole package/usage when considering certain things, not just one part of it.
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Dave Garoutte

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Re: System limiters in series
« Reply #18 on: February 23, 2018, 12:46:36 pm »

If the ambient temperature is very high, the enclosure and driver are likely to be at the same temperature anyway, so the heat sink wouldn't be introducing any extra heat into the driver.  It is interesting that the 'plated' speaker took longer to cool off.  Perhaps the plate was re-radiating back to the driver.
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Ivan Beaver

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Re: System limiters in series
« Reply #19 on: February 23, 2018, 01:06:46 pm »

If the ambient temperature is very high, the enclosure and driver are likely to be at the same temperature anyway, so the heat sink wouldn't be introducing any extra heat into the driver.  It is interesting that the 'plated' speaker took longer to cool off.  Perhaps the plate was re-radiating back to the driver.
At the point of "cool off", there was no signal, so no air movement-inside or outside the enclosure.

I probably should have redone the test, but just lowered the drive level a goo dbit and see what happened.

Oh well, hind sight is 20/20
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Stephen Kirby

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Re: System limiters in series
« Reply #20 on: February 23, 2018, 04:32:04 pm »

Thermal mass.  The more of it, the slower the cooling.  With a wooden cover the magnet was attempting to reach equilibrium with the surrounding air.  With the metal cover the surrounding air was warmer as the plate took time to cool off.

In the PCBA world, the thermal mass of different components substantially complicates the reflow profile used on the in-line ovens used to solder SMT boards.  Smaller scale but same effect.

There's also the ability of something to absorb or radiate heat.  Back in my youth of hot rodding VWs some folks would polish engine parts like the valve covers.  This reduced heat dissipation meant the engines were more likely to run hot or overheat.  Leaving a rough surface meant more radiating area and less internal reflection.  Better yet was painting them crackle black.

Many laptops and such make use of thermal pipes or conduits to get heat from inside the box nearer to an outside surface or some place airflow can be found.  In a speaker this could take the form of copper bars running from the magnet or pole piece to inside a port.  Or the back panel (which does have the disadvantage of absorbing sunlight IR.
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Re: System limiters in series
« Reply #21 on: February 23, 2018, 07:52:06 pm »

I had a really nerdy post about heat transfer that I decided wasn't worth posting so I deleted it.  I'm glad Stephen didn't hold back.


As my brother-in-law the mechanical engineer would say, technically it's "specific heat capacity" and not "thermal mass" if you really want to split hairs, but I don't haha.

Surface area is great (add fins to your heat sink) but even better if you can put a front on it to make a "chimney" to drive some convection air currents and make it a more active heat dump.  Same way a baseboard heater works (or doesn't work if the front panel is removed). 

Keeping the metal out of direct sunlight would be key, paint it white or maybe a chrome finish would reduce direct solar radiation gains that would otherwise very easily make the metal heat sink hotter than the ambient air temp. Then we'd need to figure out how to keep people from stacking them or cutting themselves on the exposed metal.....sorry to wreck a perfectly good conversation about limiters with thermodynamics.
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