Like I said before, how much of it you can hear will vary. My amp, a QSCRMX2450 produces 0.03% distortion up full at 1.0khz. Sounds good doesn't it. What they don't tell you is Total Harmonic Distortion quadruples for every octave you increase the frequency. Every doubling of the frequency basically so at 2.0khz the distortion is 0.12%. By the time I get up to 16.0khz distortion is 7.68%. In contrast, at 10dB below full power it only produces 0.03% distortion across the whole 20hz-20khz spectrum.

Why would I want to add that much distortion when I could achieve the same volume levels with a cleaner signal and no distortion ?

That's exactly the point of setting the gain structure correctly! That's why you do it!

Oh I certainly agree that getting the gains right throughout the system is the correct and best way to do it. But everything else I disagree with. If you want to run your amps at less that unity gain (ie less than flat out for most amps) then I'd say go ahead. There's probably more noise generated in the cables from mixer to an amp when the amp's turned up full than there is from an amp turned down and a mixer turned up.

If you only want the system to run quietly then i cant see it matters whether the mixer is turned down or the amp or both. The gains on an amp are signal attenuators at the input of the amp and the master and channel levels on a mixer are attenuators at music source...they're all in the same signal chain.

Many amps in racks in nightclubs and bars are run at much, much less than flat out..its like equalising radiators in a house. The main dancefloor amps will usually be up full and the ones feeding the bars are tweaked so as not to drown out people placing drinks orders. The ones by the bar will not only be quieter but will have less noise as a result.

I dont think anyone really cares or knows about the amount of noise generated by mixers unless it's in the form of distortion..which is a different thing and will usually involve driving the mixer so hard that its output stage starts to clip...it usually only happens if all the LEDs on the meter are on and everything's turned up to number eleven! And who runs their rig like this? (think before you answer)..

I think we agree with each other! I don't run my amps flat out as, having set up the gains on the mixer to peak at 0dB, if I did have the amp up full, it would be far too loud.



Not many people know or care about "heel & toe"-ing or double de-clutching whilst driving, but that doesn't mean that it's not the better way to do it.



DJs with no respect for the gear they are using.

I guess the original topic of this thread has been lost! It was meant to be about the pro's and con's of running your amp with the knobs full-up or not. But interesting thrashing about nontheless!


I wouldn't worry about THD (total harmonic distortion) in your amplifier..unless your trying to trace a fault. Any way in which a waveform differs in its form (rather than amplitude) across the bandwidth of the processing device is distortion....including any EQ or graphic equaliser. In the absence of other data, we engineers use distortion of the waveform through an amp to align a recently repaired one and to check it's working ok, using a signal generator and oscilloscope. This analysing of the waveform soon shows up any subtle fault or misalignment, such as cross-over distortion or clipping. Slight distortion manifests in many audible ways such as a toppy sound, sibilance or muddiness. Many devices are noisy but dont distort!

Well, anyway i'm rambling.

I never said that, not sure if you were talking about me or not.

I'm actually saying the amp shouldn't be up full. The mixer gains should be at 0dB and the amp volume should be set according to how loud you need it for the size of the room you're in.



I don't need to. I set my gear up properly

I've read this thread with interest, especially the technical stuff and to be honest, some of it...ok a lot of it is over my head.
But I can't recall either being told at point of sale, or reading an amp manual that says the amp never / shouldn't be up full! Perhaps it's something I've overlooked?

At the end of the day, if the mixer is not attenuated correctly to the amp in the first place, I'm sure a lot of damage can be done to your system regardless of how much gain you apply to you amps volume knobs!!!

Anyway, off-topic question - I don't know how much of all this applies to digital OP mixers and digital IP amps...but if there's leads going from such an amp to the speakers, it can't really be 100% digital....can it?
Anyone with experience with using the digital mixers / digital inputs and outputs?

Seems to be lots of slightly differing and confusing views here.

The term noise is usually used to represent the total sound present when no signal is being passed and how loud this is being the noise floor. A lot of pieces of equipment specs quote a signal to noise ratio.

This is at its greatest when the music signal is highest before clipping. If you run a mixer at 50% then it makes sense that the S/N ratio is going to be lower than at 100%. How much difference this makes is debatable in modern equipment.

With the advent of digital equipment, resolution comes into play, and lots of system techs now try to maximize the resolution being utilized by using as much of the digital range as possible (often by running very hot into the initial A/D stage).

It is correct to say that you should really set gain structure where all pieces of kit are hitting 0db at the same time (esp digi kit to make best use of resolution) and that amp gains/input sensitivity are adjusted accordingly so that the amp clips at this point, however in practical terms its often safer to sacrifice some of the perfect gain structure and run the amp gains on full, in order to prevent people being able to turn it up further.

Modern kit tends to have very good ways of limiting the signal at most points prior to the amps, whilst leaving simple gain knobs handily available to the uninformed. Ask most general public how turn up the volume and most will point to the amp....



No it can't, but the quest should be to try to minimize the number of A/D conversions that take place. If your mixer has digi outs and your crossover/EQ has digi ins then use them.

Imagine a relatively simple setup using mixer, EQ, crossover, amps, speakers.

digi to analogue from mixer
analogue to digi into the EQ
digi to analogue out of EQ
analogue to digi into crossover
digi to analogue out of crossover to amps

If you were using a digi mixer and say a Behringer DEQ2496 and DCX2496 you could go digital all the way until you had to go analogue into the amps.

I was really agreeing with Djgorey, but the gain structure being set correctly I recommend to anyone who has the knowledge to do it. But on the other hand, if you do want to run your amps with the knobs turned down, I say go ahead. The problem (as has been suggested) is when you want to run the amps harder and you try to do it by increasing mixer output over the 0db level to force the amps up higher. I think this is what people have tried to say can be problematic..in that you run the risk of distorting the mixer when running over unity gain into an attenuated amp. The answer's yes, of course, and different mixers and amps will distort more or less readily (depending on their designed-in headroom).

Norty's pretty much clarified my point in that noise and distortion arent the same thing. Turning down an amp and increasing the mixer may actually reduce the noise audible from the mixer until you have to turn it up so much that it distorts..if you see what I mean!!! The difference is that relatively little distortion will still sound very bad...but you can get away with alot of noise before it's audible above the general din you hear in a disco (respect where due..)!

Noise = The stuff you can hear when its not doing anthing.
Distortion = The stuff you can hear when its doing too much of something.
Sound/signal/program = The (sometimes) nice stuff in the middle.

I don't think anyone said they're the same. But yes, gain structuring is about getting the best balance between the 2 and amps up full with gains up half is not going to achieve that.

If by the term 'amp' you mean the gain on the front of the amplifier then I'm afraid thats incorrect as written.

Distortion is only introduced when either the input signal is distorted or the amp output is pushed past the point of clipping, where upon the THD will increase. How much THD is present at 0db is dependant on how the manufacturers rate their amp.

Whether you turn the gain knob down or not, you can still drive the amp to this level, therefore achieving distortion.

But as a standalone item, an amp with its gain up full is still doing nothing, therefore no distortion.

Thanks for that - appreciated.

I think this could be made a sticky!

It's been a good discussion with points on both sides and, in the end, agreement.

However, and a couple of people have said before, those of us that are arguing about this sort of thing generally know about it (maybe with some polishing of knowledge needed for me) and care about it. A lot of people don't know so don't care so don't know and, probably more importantly, won't bother to find out. As long as it goes loud, they're happy!

So, D.X., Superstar and Norty - it's been a pleasure thrashing this thing out with you! May your systems never have red lights!

On a lighter note I have a Behringer DEQ1024 on the repair bench and Ive never seen so many red lights darting about.

i normally go half and half been using for a year now and no problems :S
i always use it for house entertainments and gigs. should i change that?

well if you have an amp that is rated more than your speakers so say you had 700 watt speakers nd a 1000 watt perside amp you should run it anywhere between 3/4 of the way and full.
but ideally you need your amp ticking over nicely run it at full becuase other wise you will push you mixer into the red and clip the signal

but you should work on this saying: you can turn a high rated power amp down but you cant turn a low rated power amp up[u][/b].

We seem to have come round in a circle now.

Running a mixer into the red does not mean it's output is clipping. It just means that the output is increasing the signal by more than unity. (ie theres an overall increase rather than decrease).

The clip light on an an amp is usually red, this is the one you dont want flashing because the circuitry that drives it is telling you that the output-to-speaker waveform is distorting.

If you run the gains ('attenuators') on your amp at full, this usually means that when the mixer is in the red, the amp is clipping because the inputs and outputs are manufactured and calibrated that way. It's not always precise, because of manufacturing tolerances, but its a very good guide.

Turning the amp gains down will mean that the meters on the mixer no longer have a meaningful relationship to the amp levels so that going into the red on the mixer wll happen before the same on the amp. This is not necessarily a bad thing! To present a distorted signal at the output of the mixer, you usually have to drive the mixer very hard past red indeed; how far depends on quality of mixer.

Please note my use of the word 'usually' here and there. There are always weird exceptions.

I think in the case of some of the Pioneer mixers, these seem to be able to be run quite a way past the top RED and they don't distort the output (apparently). Have seen DJs use the DJM-800 like this where the top LED is abotu the only one that goes on/off, probably with the master at full (or very close to it)... But I guess the crossover/speaker management system takes care of high signal input appropriately...

David

I can't believe this thread is still going.

Most (all?) chassis amps arrive with no volume control - no problem, use the one on the mixer, that's what it's for. S/N ratios are of little cosequence these days - mixers no longer use nasty little 741 op amps and carbon resistors in the signal path.

Burning a speaker out by under-powering it?
So if I severely underpower one of my bass bins by attaching a portable CD player's output to it, the speaker will smoke like heck, yes?

No, obviously.
The RMS value of the vaveform supplied (The equivalent DC level which would produce the same heating effect) would have to be higher than the rate at which the speaker's voice coil could dissipate that heat produced, and given thermal inertia this could be quite a bit higher than the speaker's continuous rating for short periods.

Flat-topping the waveform increases that heating effect, which is why heavy distortion might cause damage. Not the distortion itself, but the extra 'invisible' power you are pumping to the speakers.

Worst of all, this clipping of the waveform can be cuased by an overdriven amp, an overdriven mixer or even be in the recorded music. Have a look at some waveforms from R&B pop crap - it might surprise you.

Enough to make you afraid to turn on the PA system at all!

It should be noted that overdriving a mixer into clipping does not in itself produce harmful waveforms at the speaker terminals of an amplifier. It is clipping the amp output that causes this.

The 2 main causes of driver failure are mechanical failure due to over excursion and thermal failure. The 1st mechaznical is from driver over excursion meaning the driver is being pushed past the limits of excursion that it was designed for and the 2 is too much power through the driver which burns out the voic coils in the drivers. You cant blow a driver by turning your amplifier down as long as you turn it down to the point that the driver isn't being put under mechanical stress and as long as you're not putting too much power through the driver. If you set gain structure before an event or gig and then keep levels well below clipping you should be ok 99% of the time.

Yes, the available power will not be reduced - the system gain will be reduced. Gain is the amount of voltage amplification which a signal undergoes. Absolute maximum power available is unaffected. If your mixer/preamp generates a very high signal the speakers will be damaged. In conclusion speakers don't blow because of underpowering but because of pushing amps past there limit which puts out way more power than it's rated and overpowers the speaker. Clipping the amp will not blow the speaker if the amp is not overpowering the speaker.

Match your amps to your speaker sets ( watts and Ohms), run the amps at maximum and make sure the output from your mixer is not permantanly in the red zone.

Running the amps at maximum is only really ideal when you think people might touch the amp's attenuators, so you sart with them on maximum so people cant turn them up anymore, but this reduces dymanic range and so its not something that I ever. I always set gain structure with a pink noise test tone run through the system (make sure you disconnect the speakers first) and then go along the line adusting the gain controls and faders so that each piece of equipment clips at the same level, then all you do is turn the front end gain control down and the rest of the system stops clipping, and bang there you go all your equipment is gain matched. Doing this makes it very easy to make sure you know for definate you're not running the system into clipping.