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Author Topic: Limiter Setting help  (Read 706 times)

Joe Sawaya

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Limiter Setting help
« on: June 27, 2014, 01:11:31 am »

I'm embarrassed to even ask this because I feel like I should know all of this stuff at this point in my career. I know much has been posted about how to properly set up limiters to protect speaker components, but I have to admit, I don't understand the math and terminology and frankly, I'm afraid of blowing up my speakers without proper settings. Is it inappropriate or too much to ask of someone in the know to help me with these settings?

I have a 16 box EAW KF730 rig run from 4 (total) Crest Pro9200 amps. The signal is processed through an Ashly Protea 4.24C. I built the system to match that of another guy in the area for the purpose of cross renting. Not much of that has happened in the last decade of ownership, and I would like to make some changes to my own system.

I've always loved the sound of the system but, while recognizing that it has limitations because it is a smaller array, I believe the system is underpowered. I have been running it as follows (per side):

Crest 1---Channel 1---KF730 Hi/Mid===2200 Watts @ 4 Ohms for 1400 Watt speakers (4 @ 350 Watts each @ 16 Ohms)
Crest 1---Channel 2---KF730 Hi/Mid===2200 Watts @ 4 Ohms for 1400 Watt speakers (4 @ 350 Watts each @ 16 Ohms)
Crest 2---Channel 1---KF730 Low===2200 Watts @ 4 Ohms for 2800 Watt speakers (4 @ 700 Watts each @ 16 Ohms)
Crest 2---Channel 2---KF730 Low===2200 Watts @ 4 Ohms for 2800 Watt speakers (4 @ 700 Watts each @ 16 Ohms)

Roughly going from the EAW general rule of using an amplifier capable of twice the rated speaker power, the Hi/Mid section seems to be great. The lows seem to be greatly lacking.

As a disclaimer, I'm not trying to make the arrays have more SPL as much as I'm just trying to get more headroom, instead of constantly operating at the limits of the amplifier for the entire show.

To set the limiters in the past, I have left the speakers disconnected from the amps and sent a signal through the processor, into the amps until the amps clipped. Back down the limiter until clip light goes out, done. I figure because the amps are the weakest link, that is my limit point.

My idea for more headroom is to keep the Hi/Mids as is and split the lows into two separate amps set to bridge-mono. The setup now looks like this:

Crest 1---Channel 1---KF730 Hi/Mid===2200 Watts @ 4 Ohms for 1400 Watt speakers (4 @ 350 Watts each @ 16 Ohms)
Crest 1---Channel 2---KF730 Hi/Mid===2200 Watts @ 4 Ohms for 1400 Watt speakers (4 @ 350 Watts each @ 16 Ohms)
Crest 2---Bridged---KF730 Low===6500 Watts @ 4 Ohms for 2800 Watt speakers (4 @ 700 Watts each @ 16 Ohms)
Crest 3---Bridged---KF730 Low===6500 Watts @ 4 Ohms for 2800 Watt speakers (4 @ 700 Watts each @ 16 Ohms)

Even doubling the available power (2800W x 2 = 5600W), I'm setting myself up for an amazing fireworks show if I don't keep things limited properly. This is why I am here asking for help.

I already backed off the processor output to the lows by 6dB to compensate for going to bridge mono, but where do I set the limiters on those outputs? I see a lot of input sensitivity/impedance numbers on the equations listed, but I don't know what all of that means.

Would someone be willing to help me figure this out before I repeat the great "Eight 15" Drivers Gone With a Single Tom Hit" of '02?

And not to take a mile from the inch you might give me, but I'm trying to figure the same out for subs:

Crown CE4K---Bridged---EAW LA400 Subs===2800 Watts @ 4 Ohms for 1000 Watt speakers (2 @ 500 Watts each @ 8 Ohms)


Thank you sincerely.

Joe


Ashly Protea 4.24C
http://www.ashly.com/products/protea-system-processors.php

EAW KF730
http://eaw.com/portfolio_page/kf730/

Crest Pro 9200
http://www.peaveycommercialaudio.com/media/pdf/Pro200_specs.pdf

Crown CE4000
http://www.crownaudio.com/media/pdf/legacy/127393.pdf

EAW LA400
http://eaw.com/portfolio_page/la400/
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Brian Jojade

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Re: Limiter Setting help
« Reply #1 on: June 27, 2014, 12:18:04 pm »

Basic limiters will NOT protect your gear.  In fact, having a limiter on the system has the potential to cause MORE damage.  Normal limiting does protect against peak voltage spikes, such as a dropped mic, or a sudden feedback squeal. However, if you're driving the system into limiting, it's only shaving off the peaks. The sound below the threshold stays there and your average RMS value becomes higher.  If you're using an amp with RMS higher than the rated power of the speaker, you're now in danger territory.  The only true protection would be to have an RMS limiter.

You should also be aware that the clip indicator on the amplifier without a load attached may be significantly different than with the speaker connected.  The clip limiters are good warning indicators that you've got to turn things down.  Setting your limiter as you have done only turns off the warning light.  Again, your average RMS value could exceed your driver rating, and with no warning, you can have blown speakers.

So, long story short, the limiters are there for emergency protection, sort of like the emergency brake on your car.  It's there for when things go wrong, but if you are relying on them to stop you from crashing all the time, you're going to be sorely disappointed in the results.
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Brian Jojade

Art Welter

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Re: Limiter Setting help
« Reply #2 on: June 27, 2014, 12:47:18 pm »

Unfortunately, your DSP does not have separate peak and average (RMS) power settings, so your present way of setting the limiters is about as good as any. Since the bridged amps have the potential for a bit more than 3 dB more power than the AES rating, if watching the clip indicators (under load as Brian suggests) you would want to back down an additional 3-4 dB. That said, an additional 3 dB (less when thermal compression sets in)  from 90-200 Hz is not much of a headroom increase.

As far as the LF, even more important to have separate peak and average (RMS) power settings, as some music has as little as 3 dB crest factor below 100 Hz, same as sine waves, double the average power of the 6 dB crest factor AES signal, and 4 times the average of regular pink noise.

This may help you a bit:
http://forums.prosoundweb.com/index.php?topic=132359.10
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Robert Weston

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Re: Limiter Setting help
« Reply #3 on: June 27, 2014, 12:52:39 pm »

Joe - you've got some nice equipment.  Though, your subs appear to be way undersized (in power) for the rest of your rig.  The LA400 is good, but only has a 12" 500watt driver (looks like you are using 2 of these?).  The size of your rig would dictate at a minimum 2 x dual-18" (JBL SRX728 comes to mind).  Head room is about moving air... and it doesn't look the 12" subs can do it the way you want it done.

The issue appears to be not enough power on the low end... and not so much as setting limiters in order to use more of the system (what B. Jojade commented).

For the limiters... only for emergency use.
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Joe Sawaya

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Re: Limiter Setting help
« Reply #4 on: June 27, 2014, 11:02:15 pm »

Thank you for the replies. I will do more research on RMS limiting and update my processing. Emergency protection is primarily what I'm looking for.

And I'm using four LA400s per side. They seem to do well for 95% of what I do. Sorry I wasn't clearer on that.


Sent from my iPhone using Tapatalk
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Doug Jane

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Re: Limiter Setting help
« Reply #5 on: June 30, 2014, 02:39:29 am »

I hope you are using short welding cables to connect the speakers, otherwise you will be losing a lot of power in the cable.
And your distro needs to be hunky with all the primary power this will draw.
I would think you would be better to split your boxes on to smaller amps that are more suited to the box. This also gives you redundancy when the fireworks do occur.
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