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Can anyone clarify a discussion I had today regarding distortion within an audio system and what actually distorts. I initially had set up a sound system for a preview of some short films. Now the system is quite old- made up of 4 Crown amp and a home amp for the master output. I had set the levels on the Crown amps at max and then found an output level on the master that would both work with the large space as well as compliment the output of the sound design. It worked very well and I was happy. No noise floor, good distribution throughout the space, no distortion. I was then approached by one of my colleagues who was concerned about the systems set up and mentioned that he had changed the settings on the Crown amps. He reiterated that the main output level on the amps must never go above 11 o'clock or else it will distort. I was quite perplexed at this because I had always set my amp levels between 3 o'clock and max and never had a problem with distortion. He was quite adamant about his settings and refused to budge on the matter.

My question comes in 2 parts, is it correct in assuming that when setting your output levels on an amp that going to max is not a problem because your are simply attenuating the sounds and not affecting the gain at all which would prevent the issue of distortion? Also, can distortion occur in a pre-amp a regular master amp as well as in the speakers themselves or is distortion exclusively the product of a master amp over-loading?

I hope that I am clear regarding my queries.

Thanks.

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2 Answers 2

It is very possible to distort or even permanently damage your speakers by overdriving them. That is, it is possible for your amps to provide more power than the speaker is rated to handle, depending on how well matched your amps and speakers are.

That said, your speakers will distort and make all kinds of nasty noises before burning out that should clue you in to the fact that something is wrong.

You are correct in your understanding that the "gain control" on the amp is actually an input attenuator, that reduces the incoming signal level, but that doesn't mean you can't overdrive either one.

As Shaun mentioned, distortion can happen at any point in the signal chain, if you are pushing too high a signal level to any individual component. The speakers can distort when they are overdriven, the amps will clip and distort if they are pushed too hard, you could clip at your system eq, xover, or speaker management processor (if you have one), or you can overdrive your output stage of your console, or at the mic pres.

This is why good gain structure is very important. I like to build my gain structure from the inputs outward, and set my amp's attenuation where it needs to be to provide the proper level of signal to the room. Specific attenuation knob positions are pretty much meaningless unless the rest of your gain structure is already worked out. It could very well be appropriate to run your amps full-out, if the speakers can handle it, the size of the room calls for it, and the rest of your gain structure requires it.

So, look at the power rating of your speakers, look at the output power for your amps, see how strong your input signal is to the amps. Where is your master fader set on your console? How are your inputs trimmed? Those are all elements of your gain structure and they all play a factor in good clean sound.

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Thanks for the input. I too am i total agreement with you in regards to distortion existing at any part of the chain. –  oinkaudio Jun 17 '11 at 6:01

As far as setting the gain of the master/speaker amps, it really depends on the unit. Technically, yes, you're correct about the behavior of the gain control on them. That doesn't mean there isn't a component somewhere else within the amp's circuit that couldn't be affected by the master gain setting (pretty rare, but it can happen). From my experience in live audio situations, the main reason to keep the master amps away from max was only to help protect the speakers in case of power spikes, signal pops and the like. You have a higher chance of damaging the the speakers when their amp is turned all the way up. This is more of a concern in live venues than it is in studios.

As far as distortion, it can occur nearly anywhere in the chain: mic (that's why they have dBSPL ratings), preamp, mixer, outboard gear, amp or speakers.

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Perfect. Both answers offer some great insights into how an audio system needs to be set up and calibrated. I really appreciate the feed back. –  oinkaudio Jun 17 '11 at 6:04

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