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[Adam Schaible]

My amps have this built in - not sure what your budget is, but they are I-Tech HD's

[Phil Lewandowski]

Adam Schaible wrote on Tue, 16 June 2009 15:00

My amps have this built in - not sure what your budget is, but they are I-Tech HD's

Haha, yes I have read and heard much about the Itech's amazing built in limiters, unfortunately, besides the budget problem, it would be going in a rack with all QSC's so that wouldn't be the best for cooling.


So I am hoping Bennett will be able to suggest me something.

Thanks!
Phil

[Greg Cameron]

That was my point previously, you can't get rms limiters in all but the most expensive amps and/or processors. It pretty much rules out that type of setup with budget conscious purchasing unless you go with self-powered and processed boxes. Even the lower cost ones seem to provide rms limiting. In lieu of self powered boxes, the other choice is to try and size amps correctly to match the speakers, use peak limiting, and don't push too hard.

Greg]

[Bennett Prescott]

Phil Lewandowski wrote on Tue, 16 June 2009 14:51

Any suggestions on a limiter or device to do just this?   I have been searching for a long time and all I have found is finding a limiter that has a long enough attack and release times to achieve this.

Try using a compressor instead of a "limiter". Any of the quality units should do it, or any DSP that lets you really slow down the limiter. Getting that time constant correct can be the difference of a few dB in output capability.

[Stephen Dranger]

Chris Strack wrote on Tue, 16 June 2009 12:46

My only additional advise to Stephen Dranger who started this thread is "Gain Structure". It took me some time to understand this concept but it is really important that you read all you can on setting up the proper gain structure for your mixer/amps/speakers. By doing this you will be able to get the most headroom out of your PA system and run it the safest way possible. Turning up the gain control as high as it can go on your amp does not give you the most head room, having a proper gain structure set up between you mixer and amps does. Proper Gain structure also helps you protect your amps from clipping. So if you haven't read about this concept, you need to before you just use your amp bridged and then turn the amp all the way up.

I come from Recording Land so I am at the very least familiar with the idea of gain structure. What I'm not getting is that even with proper gain structure, how can I make sure I don't overheat the speakers if I'm pumping 1300W into 600W RMS speakers, especially since some of my inputs are going to be sine-wave-like? Is there something I can listen for? Do I just need to make sure not to turn it up all the way?

[Art Welter]

Stephen,

If your hearing ability is like your reading comprehension, then no, there is nothing you can listen for.

Smoke 'em if you got 'em.

[Phil Lewandowski]

Bennett Prescott wrote on Tue, 16 June 2009 15:07

Phil Lewandowski wrote on Tue, 16 June 2009 14:51 Any suggestions on a limiter or device to do just this?   I have been searching for a long time and all I have found is finding a limiter that has a long enough attack and release times to achieve this. Try using a compressor instead of a "limiter". Any of the quality units should do it, or any DSP that lets you really slow down the limiter. Getting that time constant correct can be the difference of a few dB in output capability.

What slow attack and release times do you think are good points to start with?  

I believe I remember seeing the Itech average limiter with an attack time of several seconds.

[Adam Schaible]

If you've got a 1300w amp, you'd have to be riding -3db to be pushing 650w continuous.  That's very very high.


What's the sensitivity of your cabs?  Do the math to figure out what 1300w continuous would do compared to say, 130w continuous.  It's a 10db difference, which is significant - but chances are 130w will be plenty of power for you RMS.

On that note, most of the time I try to run the amps at -20db on average.  In your case, that would be 65w (18ishdb gain over stated loudspeaker sensitivity).  Lets say your loudspeaker is rated at 100db 1w/1m - 118db is pretty darn loud.

It sounds like you're small potatoe's, as am I.  Run the amp at -20db and you should be solid.


Side note - is there a way to calculate at what voltage the loudspeaker reaches xlim/xmax?  I believe it's an exponential formula right?  My gut feeling is that this cannot be calculated by T/S specs and has more to do with construction materials.

[Greg Cameron]

Stephen Dranger wrote on Tue, 16 June 2009 12:18

What I'm not getting is that even with proper gain structure, how can I make sure I don't overheat the speakers if I'm pumping 1300W into 600W RMS speakers, especially since some of my inputs are going to be sine-wave-like?

Stephen, if you know for a fact that you're going to be running true sine wave signals through your amp for extended periods, get an amp that has a continuous output rating that is equal to or less than the rms rating of the speakers rather than one that is 2x the rms rating and never hit the clip lights on the amps. This is the only way without an rms limiter that you can ensure you won't cook your speakers. Also be aware that a lot of amps don't like running full power sine waves for extended periods of time and will ramp the output down if you're running full tilt. This is especially true with the newer class D style amps and low impedance loads. Older designs will tend to just overheat or pop their internal breaker if you're running low impedance loads with full power sine waves.

Greg

edit: fixed quote

[Art Welter]

The voltage that is required to reach Xlim/Xmax varies with frequency.

The voltage ratio between Xlim/Xmax varies with suspension and motor design.