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Turning Your Amp Down Can Blow Your Speakers?


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it is the square waves that kills speakers.


Yes and no..an 80's synth emits square waves (on certain settings) and there's no evidence that 80's music blows speakers any more than any other! (most electric guitars are heavily clipped but these don't hurt amps either!).

The problem is when the output stage of an amp is clipped, this creates sustained levels of +ve and -ve DC mainly due to the bias and feedback circuits in the power stages of amps being upset or confused. You wont get this by clipping the mixer as the signal is AC coupled from the output of the mixer to the first stages of the amp so can't pass any DC to the speakers by design. Edited by superstardeejay

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The thing with clipping is that most amps never actually 'clip' (in the true sense) because they have onboard limiters to prevent it. So the light may well be flashing, but its indicating limiting rather than clipping which is an altogether different beast. In these situations it is simply the fact that the energy in the signal is higher as the average level is higher (peaks are cut off, but the signal below threshold, where the weight of a tune is, is higher up the scale)

I agree, square waves are a bit of a misnomer, it's more likely the higher energy content present in those heavily limited signals which burns voice coils. And as i said at the top, limiters that aren't dynamic level controls will not absolutely protect speakers as they only affect the signal above the threshold. They don't prevent the signal below threshold rising to damaging levels. High transients way above the rated power of the speaker very rarely kill them, its the sustained high power of very conpressed signals which does it. For HF that's things like feedback from a mic, where the VC's overheat very quickly due to their size and ability to dissipate the heat.

DIY plans and pro audio related technical discussions

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I normally keep my amp on full, Only turning it down for the initial swich on of amp, Mixer ect. The Mixer gain is kept at half and if any more power is needed then I use the master. I always keep an eye on the mixer levels enshurening the levels never go into the red! If they do then thats when to start turning the mixer gains down.
On the Amp if you use a modern Peavey like mine, They have a good built in gadget called DDT protection!

This post has also inspired me!!

Thanks Rich
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The compressor will still allow the average power to rise, even though it will control the peaks.


Yes, thats what compressors do of course, but not the type that are used by PA systems to prevent overdriving. These are compressor-limiters, and work differently to a compressor in a mic channel used to accentuate quiet voices and tame loud voices. Their release time is very short and restores unity gain inbetween individual peaks crossing the threshold....squeezing..or..compressing (!!) the signal.

A compressor-limiter for PA speaker protection will have a long release time (typically over 4 seconds) and an instant attack. Ratio is set so that crossing the threshold takes the limiter immediately into gain reduction (across the entire signal range) well below the threshold and doesn't return it for several seconds after the mixer signal has been taken back below the threshold.

This way, the speakers are protected fully, it's not simply a 'peak' limiter such as the Purple Audio, Urei, Drawmer units etc...but more like the Behringer Ultradrive, BSS Omnidrive, DBX Driverack, Formula Sound AVC etc.



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Just read this again and still can't believe why they said it. If they're supposed to know what they're talking about then they'll understand about signal to noise ratio and gain structure. Turning an amplifier up full will require you to drastically reduce one of the gain levels along the way which will introduce a lot of noise to the signal.

Setting all the gains to unity (0dB) will ensure the cleanest possible signal is sent to the amp. It is then down to the amplifier to set the desired sound level in the room.
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Some interesting theoretical views.

I run my amps flat out. Always have. Always will!

I am extremely careful with the gain stages throughout the chain, NEVER sending anything above Odb to the amps.

Never had any problems at all.

My advice, use your ears!!!!

Remember how I posted sometime ago about working with your speakers slightly to the back of you, that way you can use them to monitor what your playing. It always amazes me to see people with theeir speakers 4 or 5 feet infront of them and regimented in a line. How, from behind your speakers, can you honestly tell what your sound is like?? Amazing.

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QUOTE(Kingy @ Jan 20 2009, 09:04 AM) [snapback]232309[/snapback]

Remember how I posted sometime ago about working with your speakers slightly to the back of you, that way you can use them to monitor what your playing. It always amazes me to see people with theeir speakers 4 or 5 feet infront of them and regimented in a line. How, from behind your speakers, can you honestly tell what your sound is like?? Amazing.


Definitely! Although, feedback can be a problem with them behind you and, of course, you risk more hearing damage, but that's why if you see me at a gig, I spend the first hour of a gig running round the front of the speakers to listen to what they sound like.
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QUOTE(djgorey @ Jan 20 2009, 10:11 AM) [snapback]232311[/snapback]

Although, feedback can be a problem with them behind you



Shouldn't be if you know how to set the mic up properly. That is most people's problem!!

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QUOTE(Lag1Rich @ Jan 10 2009, 10:38 AM) [snapback]231502[/snapback]

The Mixer gain is kept at half and if any more power is needed then I use the master. I always keep an eye on the mixer levels enshurening the levels never go into the red! If they do then thats when to start turning the mixer gains down.


There's several reasons why this is wrong. Firstly, signal to noise ratio. If you set them to 0dB then you're getting the optimum signal to noise ratio. The more you bring it down the more noise you introduce into the signal. You're also sacrificing headroom because the signal sent to the amp is not as strong as it should be so the amp will start distorting when you turn it up high. If you turned the amp down and the mixer gains up you'd achieve a sound level increase but without the distortion.

Think about it. 0dB at every gain stage will give you the cleanest signal. The amp then amplifies the signal until the amp itself starts distorting or the speakers distort if they can't handle it. Now imagine you had set everything right on the limit. 0dB on every gain and the amp up as far as possible without distortion. Now say you turned your mixer gain meter down to half. You'd lose a substantial amount of sound but if you tried to get it back by turning the amp up the amp would start distorting so by only having your mixer up half you're sacrificing a lot of headroom. Edited by D.X
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QUOTE(D.X @ Jan 20 2009, 03:40 PM) [snapback]232335[/snapback]

There's several reasons why this is wrong. Firstly, signal to noise ratio. If you set them to 0dB then you're getting the optimum signal to noise ratio. The more you bring it down the more noise you introduce into the signal. You're also sacrificing headroom because the signal sent to the amp is not as strong as it should be so the amp will start distorting when you turn it up high. If you turned the amp down and the mixer gains up you'd achieve a sound level increase but without the distortion.

Think about it. 0dB at every gain stage will give you the cleanest signal. The amp then amplifies the signal until the amp itself starts distorting or the speakers distort if they can't handle it. Now imagine you had set everything right on the limit. 0dB on every gain and the amp up as far as possible without distortion. Now say you turned your mixer gain meter down to half. You'd lose a substantial amount of sound but if you tried to get it back by turning the amp up the amp would start distorting so by only having your mixer up half you're sacrificing a lot of headroom.


+1
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QUOTE(superstardeejay @ Jan 20 2009, 05:59 PM) [snapback]232350[/snapback]

i dont understand the previous 2 posts



My "+1" was agreeing with D.X.'s post.

D.X.s post was all about setting up the correct "gain structure" for the best signal/noise ratio throughout the signal chain. You want the best signal/noise ratio in order to get the best sound.

If, for instance, the input signal from your CD (Rumours by Fleetwood Mac on CD, for instance, is recorded a lot lower than "Tango in the Night") is too low and you do not adjust the input gain, there will be a lot of noise being sent to the mixer. When you up the mixer level, you up the amount of noise and this then goes to the amp.

Its the same at the next stage - if the mixer is not putting out a good strong signal (peaking at 0dB), the signal going to the amp will be noisy. If you then amplify that signal, you will amplifying a lot of noise just to get the music part of the signal to the right level.

This is why the best way to set-up your rig is to set the input gain, then the mixer, then the processors (if you have them) and then the amp(s). You get the least amount of noise for every "bit" of music.

The amp will introduce noise too (everything does), but by making sure that everything else in the signal chain is set correctly, you make the best use of what you have.

Superstar - does this help (and please forgive me if it sounds patronising; it definitely isn't intended to).

D.X. - that is that what you meant, isn't it?!
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+2 smile.gif

I am a little paranoid about "protection"

From the mixer, first stage is the FBQ3102 with the low cut set to 40hz and the high to 20,000hz. No point sending frequencies to the amp that the speakers can't handle.

Next in the chain is an Ecler FAP30L that is a crossover and compressor/limiter. Has a very short attack time and will instantly kill the volume on any individual channel where the signal gets too hot.

All set at 0db at max volume. Anything above 0db gets cut by the compressor/limiter. Amps are set so that 0db is comfortably below clipping point.

Neither of the amps ever flash the red clipping lights even with feedback when some bright spark points the mic at the speakers.

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QUOTE(TonyB @ Jan 20 2009, 07:19 PM) [snapback]232357[/snapback]

+2 smile.gif

I am a little paranoid about "protection"

From the mixer, first stage is the FBQ3102 with the low cut set to 40hz and the high to 20,000hz. No point sending frequencies to the amp that the speakers can't handle.

Next in the chain is an Ecler FAP30L that is a crossover and compressor/limiter. Has a very short attack time and will instantly kill the volume on any individual channel where the signal gets too hot.

All set at 0db at max volume. Anything above 0db gets cut by the compressor/limiter. Amps are set so that 0db is comfortably below clipping point.

Neither of the amps ever flash the red clipping lights even with feedback when some bright spark points the mic at the speakers.


This way your amps will last forever (probably), the sound will be as good as the system can make it and, even better, you can chuck a hell of a lot at your speakers because the signal is clean.

I'm paranoid too - red means "STOP"!
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if the mixer is not putting out a good strong signal (peaking at 0dB), the signal going to the amp will be noisy


Will it? How noisy? What mixers are that noisy?

I do know what you're suggesting but surely no mixer these days is so noisy as to be audible unless its always run flat out? As a service engineer I see each and every mixer under the sun! The noisiest are the Denon digital by far but even so it's just background hiss that's in any case generated by the master D>A section and isnt affected by the channel faders or input gains...and is masked by the quietest tracks.



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QUOTE(superstardeejay @ Jan 20 2009, 09:23 PM) [snapback]232366[/snapback]

Will it? How noisy? What mixers are that noisy?

I do know what you're suggesting but surely no mixer these days is so noisy as to be audible unless its always run flat out? As a service engineer I see each and every mixer under the sun! The noisiest are the Denon digital by far but even so it's just background hiss that's in any case generated by the master D>A section and isnt affected by the channel faders or input gains...and is masked by the quietest tracks.


As you said, there are few mixers where the noise is audible, but the point about setting up the gain structure is that you minimise the amount of noise so you get the best sound quality and the best efficiency from your equipment.

Whether or not you can hear it, the noise is there (I can't hear 18kHz, but it's there!). By having incorrect gain structure on your mixer, by the time the signal gets to the amp, the amp is amplifying "noise" rather than music, so you are, effectively, wasting the power of your amp.

If you imagine that a good signal has, for example, 80% music and 20% noise (you can find out the specific S/N ratios from manufacturer's specs), then a poor gain structure could do 75% music and 25% noise. You see that you'd have to turn the amp up to get the same volume of music.

It's the same effect as when somebody doesn't have the mic close enough to their mouth - you have to turn it up to get the right sound level and find that you are amplifying "air". Edited by djgorey
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the amp is amplifying "noise" rather than music


Again you're right in theory but surely no s/n ratio is so bad that we have to be concerned with its detrimental effect on its amplifier. Besides, any background noise from a mixer will be present whether there's music running through it or not. Your post suggests that all that's not music is noise and all that's not noise must be music! You can actually have nothing, y'know! Edited by superstardeejay

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QUOTE(superstardeejay @ Jan 21 2009, 05:24 PM) [snapback]232469[/snapback]

Your post suggests that all that's not music is noise and all that's not noise must be music! You can actually have nothing, y'know!


No you can't! In a specific signal going to an amp, all that is not music is unwanted noise (although some music just sounds like noise to me!).

It's not that you have to worry about loud hissing noise drowning out the music (if you have that you do need to worry!); setting the gain structure is about getting the best possible signal out of the equipment you have and maximising amount of music that gets from the CD player to the speakers.
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QUOTE(djgorey @ Jan 21 2009, 06:22 PM) [snapback]232480[/snapback]

No you can't! In a specific signal going to an amp, all that is not music is unwanted noise (although some music just sounds like noise to me!).

It's not that you have to worry about loud hissing noise drowning out the music (if you have that you do need to worry!); setting the gain structure is about getting the best possible signal out of the equipment you have and maximising amount of music that gets from the CD player to the speakers.


That's right, you can't. Background noise will always be present in the signal. Achieving unity gain on all gains will minimise this. At the other end of the scale is distortion which will also be introduced into the signal if an amp is turned up full.

Amps up full and gains up half produces noise and distortion. How much of it you can hear will vary but it's definitely there.
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QUOTE(D.X @ Jan 22 2009, 01:00 AM) [snapback]232512[/snapback]

At the other end of the scale is distortion which will also be introduced into the signal if an amp is turned up full.

Amps up full and gains up half produces noise and distortion. How much of it you can hear will vary but it's definitely there.


You are basing this on what???

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All this talk of hiss/noise etc etc, sleep1.gif

Why not just set up the system with the correct gain structure from mixer to amps including everything inbetween,then turn the source volume up or down with your channel faders.

It can't be that hard can it? 071.gif
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QUOTE(Andy Dunn @ Jan 22 2009, 11:57 AM) [snapback]232538[/snapback]

All this talk of hiss/noise etc etc, sleep1.gif

Why not just set up the system with the correct gain structure from mixer to amps including everything inbetween,then turn the source volume up or down with your channel faders.

It can't be that hard can it? 071.gif


That's what I've been saying!! biggrin.gif

That it's important to set up the correct gain structure!
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QUOTE(Kingy @ Jan 22 2009, 11:39 AM) [snapback]232534[/snapback]

You are basing this on what???



Real life. If you know of a mixer that can send a signal with no noise and an amp that can turn that signal into sound at full volume with zero distortion I'd love to hear about them.

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QUOTE(D.X @ Jan 23 2009, 12:28 AM) [snapback]232612[/snapback]

Real life. If you know of a mixer that can send a signal with no noise and an amp that can turn that signal into sound at full volume with zero distortion I'd love to hear about them.


Are we talking audible or on a scope? If it's the latter you are of course correct, but the former...well there are loads!!

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