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Author Topic: Voltage limiting questions  (Read 8601 times)

Taylor Dubois

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Voltage limiting questions
« on: September 03, 2013, 08:31:06 pm »

Does anyone have a tutorial on limiting your system by monitoring the amplifiers voltage, and adjusting your processor accordingly? This is to supply only a certain amount of power to a speaker so that a processor will limit before a driver is ever blown.

Do you calculate the voltage based on the speakers rms, program, or peak?
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Spenser Hamilton

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Re: Voltage limiting questions
« Reply #1 on: September 03, 2013, 08:57:36 pm »

Does anyone have a tutorial on limiting your system by monitoring the amplifiers voltage, and adjusting your processor accordingly? This is to supply only a certain amount of power to a speaker so that a processor will limit before a driver is ever blown.

Do you calculate the voltage based on the speakers rms, program, or peak?

1. This will likely get moved to the lounge.

2. A lot of people will use a DMM on an unloaded amp to set their limiters. I'll defer to Ivan or Art to fill in the math, but a few pitfalls to watch out for are:
 - Limiter may not have instantaneous attack time, the DMM won't show a very small peak getting past the limiter circuitry, whether or not this matters depends on how conservative you are with your crossover/limiter settings.
 - Very few manufacturers publish voltage ratings for their loudspeakers, you can approximate using simple Ohms Law. You are also at the mercy of how the manufacturer rates their speakers, some are more conservative while others are more liberal.
 - Some amps with built-in DSP - namely Crown iTechs - let you enter voltage limits. Research "iTech Voltage Limiter" on this forum for a whole pile of threads on the subject if you feel like being discouraged.

3. I think it was Tim McCulloch who proposed this idea recently: Find the limits of your rig the hard way (blow something up), adjust your limiters accordingly, add more PA if necessary and repeat.
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Tim McCulloch

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Re: Voltage limiting questions
« Reply #2 on: September 04, 2013, 12:29:24 am »

1. This will likely get moved to the lounge.

2. A lot of people will use a DMM on an unloaded amp to set their limiters. I'll defer to Ivan or Art to fill in the math, but a few pitfalls to watch out for are:
 - Limiter may not have instantaneous attack time, the DMM won't show a very small peak getting past the limiter circuitry, whether or not this matters depends on how conservative you are with your crossover/limiter settings.
 - Very few manufacturers publish voltage ratings for their loudspeakers, you can approximate using simple Ohms Law. You are also at the mercy of how the manufacturer rates their speakers, some are more conservative while others are more liberal.
 - Some amps with built-in DSP - namely Crown iTechs - let you enter voltage limits. Research "iTech Voltage Limiter" on this forum for a whole pile of threads on the subject if you feel like being discouraged.

3. I think it was Tim McCulloch who proposed this idea recently: Find the limits of your rig the hard way (blow something up), adjust your limiters accordingly, add more PA if necessary and repeat.

My comment was more about the Ye Goode Olde Dayz when we didn't have the internet and what we were able to read had to have fact and science sifted from the fiction.  Often that meant proving or disproving ones thesis the old fashioned way:  you didn't get the result you wanted, which meant recones, diaphragm replacements and rebuilding amplifier output sections.  And back then we saw a certain amount of that as the cost of tuition at the Ye Olde Skool of Audible Harde Knocks®.

I also think it's wise to push your rig stupid hard so to hear what it sounds like before it breaks.  You need to internalize that sound so it wrenches your gut instead of your wallet the *second time* you hear it starting.  Why?

Because it's about system limiters, Taylor.

There ain't no stinkin' silver bullet that will let you get the maximum potential from your rig while making your drivers 100% failure proof.

The best system limiters are digital... the 10 digits on your hands.  Those, coupled to your ears and tighter gut/lighter wallet will help keep you from blowing up shit.  Here's the deal:  any operator who insists on driving your rig into the ground will do so unless YOU stop him; no electronic device will preserve your rig, long term.  System limiters are there to buy you enough time to stop the madness, but they can't stop it for you.
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Nicolas Poisson

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Re: Voltage limiting questions
« Reply #3 on: September 04, 2013, 03:06:28 am »

Indeed, there are limiters that will both make the system pretty unbreakable AND will not apply such a safety margin that the system would be used at 10% of its capacity. For that, you need a processor that estimates the voice coil temperature, the excursion of the cone, and the amp clip point. This means it has to be adpated to every single speaker model, by a R&D department that will blow a few speakers during verification (oooops, test failed). This is the way speakers processors such as L'Acoustics LLCa or APG SPDS work. It can use a sense return, or need a specific gain for the amp.

But what if the manufacturer of your speakers does not provide such a 3 stage limiter ? Then you need to accept a tradeoff between safety and level.

A speaker can handle a great amount of power during short time. This is cool because live music contains many short duration peaks. So basically you will allow the signal to exceed the speaker long time power capacity. But if you compressed heavily the signal, the average signal power is much higher, the mean/peak ratio is low, and the speaker may burn because this average is too high. This is why peak limiters are considered bad speakers protectors. RMS limiters are considered better.

On the other hand, short time power capacity of a speaker is high, but not infinite. It is still possible to launch the cone into space if excursion is too high.

The way I did: my EV DC-one processor claims to have both a RMS and a peak limiter. I set the RMS limiter at a voltage corresponding to the AES (long term) power handling of the drivers. I use a basic ohm's law for that. This means I consider the speakers to be resistive, which is false. But I cannot do better. I have no access to the peak limiter threshold. It is set automatically by the processor according to the RMS threshold. I do not know what rule is used. If you have th luck to own a processor with both threshold, then you should set the peak threshold to correspond to the peak power handling of your speaker, usually like 6db higher.
Of course, this means thet the amp is capable of delivering adequate power. Otherwise, you can set the peak limiter to the clip point of the amp. It is a little bit conservative because an amp can deliver slightly more power than its average during short duration. But you will not loose much (1 or 2dB on peaks ?).

Also, if you run your speaker passive, the tradeoff is even rougher: you will set a limiter for the overall power handling of the speaker. But if the signal is a 5kHz sine, the tweeter will burn long before this power handling is reached.
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Jordan Wolf

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Re: Voltage limiting questions
« Reply #4 on: September 04, 2013, 07:49:40 am »

Does anyone have a tutorial on limiting your system by monitoring the amplifiers voltage, and adjusting your processor accordingly? This is to supply only a certain amount of power to a speaker so that a processor will limit before a driver is ever blown.

Do you calculate the voltage based on the speakers rms, program, or peak?
Taylor,

Here's a good thread from another forum that might help you.  I could've sworn there was a sticky about it on the PSW forums, but I couldn't find it.

Read up!  It only rabbit-trails from here. :-)
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Ivan Beaver

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Re: Voltage limiting questions
« Reply #5 on: September 04, 2013, 12:09:25 pm »

Does anyone have a tutorial on limiting your system by monitoring the amplifiers voltage, and adjusting your processor accordingly? This is to supply only a certain amount of power to a speaker so that a processor will limit before a driver is ever blown.

Do you calculate the voltage based on the speakers rms, program, or peak?
It is not that simple-and the way the limiters respond is not always what you think.

I am working on that very "project" right now.  The limiters in a very popular amp (accepted on every rider) are NOT responding the way an external DSP setup with the same measured voltages (on the same amp with no limiters engaged).

I am finding as much as 4dB difference-so don't want to go into any details until I do more testing.

So it is not just a matter of "measuring" but rather HOW you measure and WHAT you measure.
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Taylor Dubois

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Re: Voltage limiting questions
« Reply #6 on: September 05, 2013, 03:03:15 am »

First, thanks everyone for throwing some information in this thread.
Now I have collected some websites with information on the subject. Here they are:

http://www.poulpetersen.dk/Appn/gblimthc.html
http://forum.speakerplans.com/one-more-limiter-settings-thread_topic80209.html
http://www.funktion-one.com/settings/
http://soundforums.net/junior-varsity/1086-help-me-understand-system-limiting-setting.html
http://soundforums.net/hub/149-loudspeaker-fundamentals.html

If there is any more information on the subject, post it here.
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Steve M Smith

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Re: Voltage limiting questions
« Reply #7 on: September 05, 2013, 03:30:35 am »

3. I think it was Tim McCulloch who proposed this idea recently: Find the limits of your rig the hard way (blow something up), adjust your limiters accordingly, add more PA if necessary and repeat.

Sounds like my father's advice for doing up cylinder head bolts.

"do it up until it breaks then back it off a quarter of a turn!"


Steve.
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Brian Jojade

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Re: Voltage limiting questions
« Reply #8 on: September 06, 2013, 05:38:36 pm »

Does anyone have a tutorial on limiting your system by monitoring the amplifiers voltage, and adjusting your processor accordingly? This is to supply only a certain amount of power to a speaker so that a processor will limit before a driver is ever blown.

Do you calculate the voltage based on the speakers rms, program, or peak?

Limiters are not the best tool to use to prevent damaged gear.  Their use is more to limit the maximum volume of the system.  So the best thing to do is make sure your system is capable of getting far louder than the maximum that you need, and use the limiter set conservatively to your max desired SPL.  This will then be a relatively safe setting, although you can still find ways to blow stuff up.
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Re: Voltage limiting questions
« Reply #9 on: September 06, 2013, 08:13:45 pm »

Limiters are not the best tool to use to prevent damaged gear.  Their use is more to limit the maximum volume of the system.  So the best thing to do is make sure your system is capable of getting far louder than the maximum that you need, and use the limiter set conservatively to your max desired SPL.  This will then be a relatively safe setting, although you can still find ways to blow stuff up.

IOW, bring more than enough rig for the gig ;-) 
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Brian Jojade

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Re: Voltage limiting questions
« Reply #10 on: September 09, 2013, 11:46:54 am »

IOW, bring more than enough rig for the gig ;-)

Exactly.  Either you budget now for more gear and it works flawlessly, or you go cheap and bring barely enough and budget for repairs down the road.
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Keith Farmer

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Re: Voltage limiting questions
« Reply #11 on: October 18, 2013, 03:46:22 am »

A simple case of Ohms Law

RMS Voltage limit = Squart(RMS Power limit W * Nominal Impedance)
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Ivan Beaver

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Re: Voltage limiting questions
« Reply #12 on: October 18, 2013, 07:32:02 am »

A simple case of Ohms Law

RMS Voltage limit = Squart(RMS Power limit W * Nominal Impedance)
That works if loudspeakers were lightbulbs.

But since they are not-and the input voltage is very dynamic-it get a lot more complicated.

Yes that would give a "basic" answer", but not one that I would want to "stand behind" and say for sure "this is where you set it".

I have been doing a lot of "research" on limiting-how to set it up-how to easily measure where to set it and so forth.

I am writing a paper that should give some insights on "my" thoughts/procedures etc-but it is not done yet.

But let's just say that my "attitudes" have changed over the last couple of months-a good bit.

I don't want to go into it now-but the "proper procedure" (so far as my testing has lead me this far) is a good bit different than what I did/recommended in the past.

Until I am more "sure" I don't want to say anything as it is not "finalized".
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Ed Walters

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Re: Voltage limiting questions
« Reply #13 on: October 18, 2013, 11:40:00 am »

That works if loudspeakers were lightbulbs.

Well, in a way they are -- their cold resistance is lower than their hot resistance, and along with that comes power compression and all that jazz.

I bet you could make the case for having peak limiting points increase as the average thermal limit is approached -- the coil/motor could probably stand the highest peak drive voltage without mechanical damage just before the average level has melted/burned the coil...

Ed Walters
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Ivan Beaver

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Re: Voltage limiting questions
« Reply #14 on: October 18, 2013, 07:12:09 pm »

Well, in a way they are -- their cold resistance is lower than their hot resistance, and along with that comes power compression and all that jazz.

I bet you could make the case for having peak limiting points increase as the average thermal limit is approached -- the coil/motor could probably stand the highest peak drive voltage without mechanical damage just before the average level has melted/burned the coil...

Ed Walters
I was talking about the fact that light bulbs have a "generally" constant voltage applied to them-so the wattage is constant.

Loudsepakers are not even close to having a constant voltage applied to them.  So the "wattage" is all over the place and FAR from constant.
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Charlie Zureki

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Re: Voltage limiting questions
« Reply #15 on: October 18, 2013, 08:02:01 pm »

I was talking about the fact that light bulbs have a "generally" constant voltage applied to them-so the wattage is constant.

Loudsepakers are not even close to having a constant voltage applied to them.  So the "wattage" is all over the place and FAR from constant.

  +1  Hammer
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Re: Voltage limiting questions
Ā« Reply #15 on: October 18, 2013, 08:02:01 pm Ā»


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