Protecting Your PA System

[SourceRaver]

Ok so you bought the PA system you always wanted and your friends are beginning to ask if they can borrow it. Problem is, your friends are notorious for pushing the levels into the red and you’re afraid they may damage your system...and they probably will!

So how do you protect your PA system when you’re not around?

What you need is a Compressor and/or limiter.

Without getting too technical, a compressor monitors the signal strength going to your PA. When it exceeds a certain threshold as set by you, the ‘extra’ signal above the threshold is compressed and the volume is gradually reduced. If your increase the threshold, the device then acts a limiter and stops the volume going above a certain level. This effectively stops your PA from getting any louder and thus preventing it from being damaged.

"A compressor puts a gentle ‘squeeze’ on excess levels, whereas a limiter hits it on the head with a hammer” (Live Sound Mixing 4th Edition 2005 D.R.Fry)

In this post we will be looking at a typical example of a compressor and I have chosen the Behringer PRO-XL MDX2600. You can find the user manual at:

http://www.behringer.com/EN/downloads/p ... 7_M_EN.pdf

“WOW!...that’s a lot of buttons and knobs!!” you say.

Don’t be worried, you only need half of them! Lets have a look at what they do.

Pushing the Couple button allows you to control both the left and right channels with only the left hand side of the unit. This is better as it provides for a better stereo ‘image’ as any compression applied to the left is also applied to the right (and vice versa)

Pushing the Gate button turns on the gate function. What that does is mute (i.e. get rid of) all the unwanted sounds during a break in the music including noise such as electrical hum or hiss. You can adjust the amount that’s removed by adjusting the trigger knob.

The Threshold knob lets you adjust the point where the unit starts to ‘clamp down’ on the signal.

The Compression Ratio control allows you to set how much compression you want applied when the signal exceeds the threshold. It may be a little or a lot (infinity:1 acts as a limiter and clamps down hard on the signal).

The Attack control determines how quickly the compression is applied once the signal goes above the threshold.

The Release control determines how quickly the compression is removed once the signal drops below the threshold.

The Auto switch disables the attack and release function and the unit decides how much is required by itself.

The Interact Knee changes compression from a hard knee (i.e. instantaneous compression) to a combination of both hard and soft knee (soft knee is a gradual increase in compression)

The IN/OUT button allows you to make a comparison between compressed and uncompressed audio

The Output control allows you to compensate for any drop in gain due to compression.

The Peak Limiter buttons allows you to determine at what point the signal is reduced to prevent damage to your equipment.

So a good way to protect you PA is to install a compressor between the desk and amp (or powered speakers) and then:

1. Use the maximum possible threshold (i.e. experiment for the best sound)

2. Apply a high compression ratio

3. Make the attack time as short as possible

4. Have a medium to long release time

Good Luck!

[Cupe]

Great post

+rep given

[skyblue]

there is one installed in my company car, I try to turn up the tunes and it turns it back dow again... very annoying... awesome if your lending your gear out though!

[pill]

I was looking at getting one of these for a set of speakers I hire out to people. Do you reckon a cheap compressor is going to be much more effective than that which comes built into some amps (if you'd like to know specifically it's the Peavey PV-8.5C)?

[SourceRaver]

It really depends on your speakers. Looks like the compressor on the Peavey amp cant be adjusted and is primarily used to protect the amp (ie stop it working too hard to reproduce the audio signal). If your amp is more powerfull than your speakers, then the amp is protected but the speakers may still get damaged. If your speakers can take more power than your amp puts out, then they will be OK. I think a compressor/limmiter is still a good idea as it allows you to fine tune your system a lot better and gives you a lot more control.

TIP: If your hiring the gear out, make sure you lock up the amp case so no one can have a fiddle if they think it isnt loud enough!

[pill]

Thanks,

I would, but I don't want to have to drill holes for air in the Gator Roadcase :s

A compressor might be the way to go thanks for this article it really explained alot.