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[Mike Krill]

I need advice setting a peak stop limiter for my mid/high drivers. I have a set of Behringer B1520 Pro (I know their Behringer so please no grief) rated at 300W continuous 1200W peak ran in mono so it's a 4 ohm load. I'm using a Yamaha P2700 amp rated at 500W per channel on a 4 ohm load. I'm using one side of the amp for the behringers and the other side for our monitors. So how do I go about setting a peak stop limiter to properly protect my drivers? I have either a DBX 166XL or a behringer deq2496 for the limiting capacity just need to know the proper way of doing this. Thanks!!

[Greg_Cameron]

I have either a DBX 166XL or a behringer deq2496 for the limiting capacity just need to know the proper way of doing this.

The peak stop limiter in the DBX sounds like crap. It may also not be fast enough and allow punch-through. It's possible the limiter in the DEQ is good enough for a basic setup. But it's lacking attack speed & ratio controls. It has threshold, hold, and release controls. As long as the attack speed is very fast and the ratio large, like 20:1 or more, it may be adequate. The release speed should also be fairly fast and the hold very short or off.

Basically you want to set the limiter threshold so that it doesn't allow the amp to clip, or clip very slightly. Do this first by running the amp without a load connected. Play a test track with solid, percussive content like dynamic bass and drums. crank the level until the amp starts to clip. Then back the threshold down on the limiter until it starts limiting and prevents the amp from clipping. Then up the level and see what happens. If the amp starts to clip again, try lowing the threshold a bit more. Up the level again. If you find that you cannot prevent the amp from clipping, the the limiter is not adequate for true protection. You might investigating getting a known solid limiter used like an Aphex Dominator 720.

Once you set up the limiter without the speakers connected, you then need to retest under load. Amps tend to clip at a lower level with a connected load vs. unloaded. So once you've connected the speakers, starting bringing the level up again. If the amps starts to clip, back the limiter threshold down accordingly. If you hit the limiter and the amp is not clipping, you're good to. Keep in mind that a peak limiter will not protected against excessive rms power into your speakers and can actually cause higher rms levels if you are hammering the the limiter. It's the same thing as sending a highly compressed, low crest factor signal to the speakers. Since your speakers are rated at 300W continuous and the amp can put out 500W continuous, it is possible to still cook the drivers if you are into constant limiting and the amp is just below the point of clipping. So it's still prudent to keep and eye on things. If you see a lot of limiting going on, back off on the levels.

Greg

[Chris Carpenter]

I need advice setting a peak stop limiter for my mid/high drivers. I have a set of Behringer B1520 Pro (I know their Behringer so please no grief) rated at 300W continuous 1200W peak ran in mono so it's a 4 ohm load. I'm using a Yamaha P2700 amp rated at 500W per channel on a 4 ohm load. I'm using one side of the amp for the behringers and the other side for our monitors. So how do I go about setting a peak stop limiter to properly protect my drivers? I have either a DBX 166XL or a behringer deq2496 for the limiting capacity just need to know the proper way of doing this. Thanks!!

You can use this calculator to get an idea where you should set your threshold. Just plug in the information about your speakers, amplifier, and setup and it should give you a limiter value.

http://www.poulpetersen.dk/Appn/gblimthc.html

[Greg_Cameron]

You can use this calculator to get an idea where you should set your threshold. Just plug in the information about your speakers, amplifier, and setup and it should give you a limiter value.

http://www.poulpetersen.dk/Appn/gblimthc.html

A handy link no doubt. However, that particular calculator appears to be for rms limiting rather than peak limiting. Definitely useful though for the finer processors out there which utilize real 2-stage limiting.

Greg

[Mike Krill]

The peak stop limiter in the DBX sounds like crap. It may also not be fast enough and allow punch-through. It's possible the limiter in the DEQ is good enough for a basic setup. But it's lacking attack speed & ratio controls. It has threshold, hold, and release controls. As long as the attack speed is very fast and the ratio large, like 20:1 or more, it may be adequate. The release speed should also be fairly fast and the hold very short or off.

Basically you want to set the limiter threshold so that it doesn't allow the amp to clip, or clip very slightly. Do this first by running the amp without a load connected. Play a test track with solid, percussive content like dynamic bass and drums. crank the level until the amp starts to clip. Then back the threshold down on the limiter until it starts limiting and prevents the amp from clipping. Then up the level and see what happens. If the amp starts to clip again, try lowing the threshold a bit more. Up the level again. If you find that you cannot prevent the amp from clipping, the the limiter is not adequate for true protection. You might investigating getting a known solid limiter used like an Aphex Dominator 720.

Once you set up the limiter without the speakers connected, you then need to retest under load. Amps tend to clip at a lower level with a connected load vs. unloaded. So once you've connected the speakers, starting bringing the level up again. If the amps starts to clip, back the limiter threshold down accordingly. If you hit the limiter and the amp is not clipping, you're good to. Keep in mind that a peak limiter will not protected against excessive rms power into your speakers and can actually cause higher rms levels if you are hammering the the limiter. It's the same thing as sending a highly compressed, low crest factor signal to the speakers. Since your speakers are rated at 300W continuous and the amp can put out 500W continuous, it is possible to still cook the drivers if you are into constant limiting and the amp is just below the point of clipping. So it's still prudent to keep and eye on things. If you see a lot of limiting going on, back off on the levels.

Greg

Thanks for the info gentlemen its will help me utilize and manage my system much better.

Mike

[Chris Carpenter]

A handy link no doubt. However, that particular calculator appears to be for rms limiting rather than peak limiting. Definitely useful though for the finer processors out there which utilize real 2-stage limiting.

Greg

It is; you caught me. However, it does give a nice number to someone who has no idea where to begin.

[Chuck Simon]

Do this first by running the amp without a load connected.

I always thought that running an amp to clip levels without a load connected could somehow damage it.  Am I mistaken?

[Tim McCulloch]

I always thought that running an amp to clip levels without a load connected could somehow damage it. Am I mistaken?

Your info isn't "wrong" per se, it's just out of date.  Back in the old days when amps had tubes, the output stages really needed a load (preferable of a specified target impedance) or they'd fail.  Transistors are, relatively speaking, infinitely more tolerant of no-load situations.

That said, making amp measurements of power, distortion, thermal characteristics, etc require the amp be loaded.  Real Langston Holland's test methods in his review of the SpeakerPower amp module here: http://www.soundforums.net/live/threads/1735-Amp-Tests-%281-of-2%29  Finding 'dummy loads' that can dissipate the output of high-current amplifiers is a challenge, and Langston builds his own with heating elements and large containers of water.  You'll enjoy the read.

Have fun good luck.

Tim Mc

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