Amp & Speakers (exeeding power ratings)

[jcmbowman]

In all seriousness, a fast-acting peak limiter is not the right tool for the job in protecting speaker cabs in 99% of cases.

And a home-built DIY horn-loaded sub designed by Bill and operated by a weekend warrior is the other 1%. Please stop telling people otherwise.

[BrentEvans]

In all seriousness, a fast-acting peak limiter is not the right tool for the job in protecting speaker cabs in 99% of cases.

And a home-built DIY horn-loaded sub designed by Bill and operated by a weekend warrior is the other 1%. Please stop telling people otherwise.

You're both right, in different ways.

Phil, you are right that heat from RMS power destroys drivers. You are right that turning down and bringing enough rig, etc, are good ways to handle the problem. You are wrong that peak limiters are ineffective. We've been through this enough times that you ought to know that horn subs are different. Further, the peak limiter prevents over-voltage which, combined with setting the limiter at or a few percent below the driver's RMS rating will keep the heat at a manageable level, that's why its called "continuous" power rating. It can take that with no problems. This is especially valuable if you are not in complete control of the rig as many times the owner isn't.

I give +1 to jcm. You need to stop passing advice that is contrary to the designer's intent, or get off your tail and build a set of these subs so your advice will have more weight from experience.

[Zack Brock]

Well said Brent, thank you!

[Adam Schaible]

I can appreciate advice that Instructs one to be cautious and smart. Only problem there with your advice Phil is in tradional speaker cabs you can hear distortion and turn it down. In horn subs you can't so you could easily blow drivers and not even realize until you see magic smoke and hear no more bass.

And why is a peak limiter not effective?

One thing to help out the original poster - the volume knobs on a power amp are input attenuators, not output adjuster. So even with the amp vol knob turned half way down the amp can be inadvertantly driven to its full output power with the right high input voltage from a mixer.

Hey Zack,

Pretty much the peak limiter is not the right too for the job because your main enemy is the heating power, like I mention to Turntablist above. A peak limiter will only raise the heating power when it starts to actually do something.


Here is a decent article going through some things:

http://campuspa.com/downloads/Loudspeak ... entals.pdf


Take Care!
Phil

Hi Phil,

The thought that a peak limiter will actually increase VC heat is simply a myth. Think of it this way.... Heat added to the VC can more-or-less be calculated by average voltage over time. It's like your electric oven. High voltage for a long time makes it hot. A peak limiter simply shaves off the peaks - meaning a lower overall voltage over time.

What you are referring to is something different. When peak limiters are set too low transients aren't produced with accurate dynamics, thus causing the engineer to turn up the gain in response. This means more average voltage, thus more voice coil heat. In your example, you're blaming the limiter when it's really the engineer (who either set the limiter incorrectly, or doesn't understand how it works).

RMS limiters are more effective in managing VC heat but are more rare and complex due to the time averaging that takes place. They need more robust circuitry/etc. The combination of peak and RMS limiters is more effective than one or the other. Some elaborate systems actually have thermal limiters that will measure RMS over a larger period of time. The combination of these three limiting systems will allow you to effectively control damage to the system. Peak limiters are a good tool, but not the right one for managing VC heat.

Anyway, what you're saying isn't true - plain and simple. It's like if punch a brick wall and bloody your knuckles, don't blame the wall -- know what I mean?

Best wishes

[CafSentryGnome]

so is bill saying limit to stop the driver from going past xmax, xlim or to stop it from cooking? cos if hes is saying limit for to stop it hitting xlim wouldnt that make any arguement about losing dynamics pretty stupid cos you would be killing the driver by causing mechanical damage if you let it go past that point.

[Bill Fitzmaurice]

so is bill saying limit to stop the driver from going past xmax, xlim or to stop it from cooking? cos if hes is saying limit for to stop it hitting xlim wouldnt that make any arguement about losing dynamics pretty stupid cos you would be killing the driver by causing mechanical damage if you let it go past that point.

We limit at the displacement power rating (xmax) because any additional power applied won't give more usable output, it will just end up as additional heat in the motor. Limiting at the xlim power rating is closing the barn door after the horses have left, the driver is already dead. The argument about losing dynamics if you limit is totally specious. A dead driver has no dynamics.