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Author Topic: Using Compressor as Limiter on FOH  (Read 7099 times)

sam saponaro

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Using Compressor as Limiter on FOH
« on: June 03, 2013, 12:55:41 pm »

I have a spare compressor channel that I have been thinking of using as a limiter for FOH driver protection.Especially as I have allot of headroom with my amps and lower wattage older design speakers.
I'm thinking as I will have approx 3-3.5X the wattage as my speakers cont. rating,I would set a limiter at approx +6Db. Sound OK??
As this unit does NOT have a dedicated limiter,could I achive this by setting the compressor to maximum ratio and threshold to +6Db

Also how would I wire this in??
 In series after my FOH EQ??
As a 1/4" device would I have to go, XLR out of EQ to TRS into the compressor,then TRS back out of the compressor to XLR in to my crossover?? Not sure as I've only used compressors on inserts befor.
Thanks
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RYAN LOUDMUSIC JENKINS

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Re: Using Compressor as Limiter on FOH
« Reply #1 on: June 03, 2013, 01:03:22 pm »

I have a spare compressor channel that I have been thinking of using as a limiter for FOH driver protection.Especially as I have allot of headroom with my amps and lower wattage older design speakers.
I'm thinking as I will have approx 3-3.5X the wattage as my speakers cont. rating,I would set a limiter at approx +6Db. Sound OK??
As this unit does NOT have a dedicated limiter,could I achive this by setting the compressor to maximum ratio and threshold to +6Db

Also how would I wire this in??
 In series after my FOH EQ??
As a 1/4" device would I have to go, XLR out of EQ to TRS into the compressor,then TRS back out of the compressor to XLR in to my crossover?? Not sure as I've only used compressors on inserts befor.
Thanks

Regardless of whether it would help protect your gear or not, where did you come up with +6dB....I assume you mean +6dBu.   Ave you done the math to see how much output your amps would give you at +6dBu input.  Some amps give full output at +4dBu.  Others at 0dBu.  What amps do you have?  What is the gain of your amps.  Are they run stereo or mono bridged...ie an extra 6dB of gain for bridged?
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Jason Lucas

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Re: Using Compressor as Limiter on FOH
« Reply #2 on: June 03, 2013, 01:04:02 pm »

I wouldn't personally trust that for driver protection. Using anything short of a brick wall limiter for that makes me uneasy.
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sam saponaro

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Re: Using Compressor as Limiter on FOH
« Reply #3 on: June 03, 2013, 01:20:27 pm »

Regardless of whether it would help protect your gear or not, where did you come up with +6dB....I assume you mean +6dBu.   Ave you done the math to see how much output your amps would give you at +6dBu input.  Some amps give full output at +4dBu.  Others at 0dBu.  What amps do you have?  What is the gain of your amps.  Are they run stereo or mono bridged...ie an extra 6dB of gain for bridged?
Limiting FOH is a new thing for me.But reading up on Crown's webpage they suggest running 2.5X your continuous rating if you limit to 3-6Dbu if I understand correctly. I am installing fuse holders on all my cabs perhaps this is all I need??
I am currently rewiring my system for 3 way and at the same time took the higher wattage JBL 2225s out(way wrong TS)of my old EAW top boxes for the original lower wattage RCFs. RCFs rated at 100W Cont./200W prog,EAW rates the cabs @ 350W AES with original drivers and crossover network(which I don't have which is why I'm 3 way crossing active).
I am planning on running a Crown CE2000 per side on mains,amp split in stereo one side running midbass other side running Horn and a CE1000 perside in bridge mono running subs,Pair of EVM 18B per side.(one set has proline rated 400W other set has series II rated 200W)I use one of each on each side.
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Jason Lucas

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Re: Using Compressor as Limiter on FOH
« Reply #4 on: June 03, 2013, 01:49:47 pm »

Limiting FOH is a new thing for me.But reading up on Crown's webpage they suggest running 2.5X your continuous rating if you limit to 3-6Dbu if I understand correctly. I am installing fuse holders on all my cabs perhaps this is all I need??
I am currently rewiring my system for 3 way and at the same time took the higher wattage JBL 2225s out(way wrong TS)of my old EAW top boxes for the original lower wattage RCFs. RCFs rated at 100W Cont./200W prog,EAW rates the cabs @ 350W AES with original drivers and crossover network(which I don't have which is why I'm 3 way crossing active).
I am planning on running a Crown CE2000 per side on mains,amp split in stereo one side running midbass other side running Horn and a CE1000 perside in bridge mono running subs,Pair of EVM 18B per side.(one set has proline rated 400W other set has series II rated 200W)I use one of each on each side.

Brick wall limiting right before the power amp stage can limit the amount of voltage that will reach the drivers of your passive cabs (too much voltage can of course damage your drivers).

Other people on here can explain it a lot better than I can but I believe that's the gist of it.
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Caleb Dueck

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Re: Using Compressor as Limiter on FOH
« Reply #5 on: June 03, 2013, 01:57:58 pm »

Driver protection is something done in a DSP.  A comp across the main bus is a personal preference, but not a gear protector.

Different pass bands need different attack/release times, and typically mote than one compressor. 
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RYAN LOUDMUSIC JENKINS

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Re: Using Compressor as Limiter on FOH
« Reply #6 on: June 03, 2013, 04:26:09 pm »

We still don't know much about your setup but the CE2000 has either 1.4volt or 2.83volt sensitivity.  At 1.4 volt sensitivity you would reach full output at approximately +5dBu.  At your guess of +6dBu you would be clipping pretty bad and potentially damaging your drivers by over powering them.

Somewhere around here is a post I made with detailed examples of the math to figure out your basic limiter settings.  You are going to need a real DSP to get real protection.  Even something like a DRPA with its soft limiter can give you some protection.  There are plenty of other options to choose from though.
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Don Boomer

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Re: Using Compressor as Limiter on FOH
« Reply #7 on: June 03, 2013, 04:46:57 pm »

Set the comp/limiter for about a 20:1 ratio or higher. In the real world there is almost no practical difference between 20:1 and infinity:1 (because you have almost nothing to drive above threshold. If you set the threshold at "0" you'd have to drive 20 dB more to get the output to rise 1 dB). Anything less than 20:1 doesn't give you much protection. The attack and release will depend of the averaging style of your limiter and the frequencies involved. You probably want the attack on the order of 15ms - 20ms for woofers and maybe 5ms for tweeters (not written in stone). The release is generally set to be 10 times the attack time.

Now comes the tricky part ... how do you set the threshold?

Now you need to know how much voltage your speaker will handle. It will be called the "continuous", "average", or "rms" rating. If it is called "program" then cut that number in half and if "peak" divide by 4 (generally). Understanding the "real" number is a bit difficult ... so setting a limiter like this depends on how good this number really is. Adjust (down) as necessary for your own comfort.

It is helpful to know by which method the manufacturer has used to make this rating. If done by the AES method then it considers the minimum impedance. Speakers have a "nominal" rated impedance e.g. 4 ohms or 8 ohms but the true impedance varies with frequency. It would be typical for an 8 ohm speaker to vary between a low of maybe 6 ohms (at low frequencies) to a high of 20 or 40 ohms at high frequencies. So your amp is delivering varying amounts of "wattage" at different frequencies. You may have to subtract a little bit of power handling ability.

Convert the speaker rating to Volts;

sq root (speaker rating * impedance)

so a 500W 8 ohm speaker looks like this ...

square root (500*8) = 63.24 volts

(just type "square root (500*8) into google and it will do the math for you)

At this point you can simply drive signal through your limiter to your amp and bring down the threshold until you reduce the output of the amp to 63Vac measured on an AC voltmeter (assuming you have proper gain settings)
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Art Welter

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Re: Using Compressor as Limiter on FOH
« Reply #8 on: June 03, 2013, 04:52:41 pm »

Limiting FOH is a new thing for me.But reading up on Crown's webpage they suggest running 2.5X your continuous rating if you limit to 3-6Dbu if I understand correctly. I am installing fuse holders on all my cabs perhaps this is all I need??
Fuses are useless, for them to protect your drivers the fuse will blow on short peaks that would not damage (burn) a voice coil.

Using a compressor for the whole system cutting -3 to -6 dB could actually increase the average level, which can actually burn your speakers more than the higher dynamic range /less average power before compressing or limiting.

By the way, the  Prolines rated for 400W are also 3 dB less sensitive than the series II rated at 200W.
They need twice the power to reach the same level, best to run the series II on their own amp channel set -3 dB compared to the higher rated drivers.
Classic.
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Tim McCulloch

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Re: Using Compressor as Limiter on FOH
« Reply #9 on: June 03, 2013, 05:52:43 pm »

Fuses are useless, for them to protect your drivers the fuse will blow on short peaks that would not damage (burn) a voice coil.

Using a compressor for the whole system cutting -3 to -6 dB could actually increase the average level, which can actually burn your speakers more than the higher dynamic range /less average power before compressing or limiting.

By the way, the  Prolines rated for 400W are also 3 dB less sensitive than the series II rated at 200W.
They need twice the power to reach the same level, best to run the series II on their own amp channel set -3 dB compared to the higher rated drivers.
Classic.

Bingo, +1, etc.

Sam, Art is telling you the gospel truth.  Use your compressor for artistic reasons but do NOT expect it to provide any system protection.
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Re: Using Compressor as Limiter on FOH
« Reply #9 on: June 03, 2013, 05:52:43 pm »


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