I blew a speaker on Saturday! Help me learn Gain, db's, levels...etc.

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Enyko

Member
Ok, it didn't really "blow" but my k12 went into 'protection mode' I guess. Where it shuts off to protect itself? That's what I'm thinking. Here is what happened and what I'd like to understand.

Dj-ing a wedding as usual. I feel the levels were at my normal settings when one of my QSC K12's shut off. I waited a while and turned it back on. It came on played for a second and shut off again. Did this twice. I then replaced it with my backup K8 and played music at a lower level because I was obviously nervous of it happening again.

My level settings which I stated are "normal" are pretty much setting all my gains to 12 O'clock. Starting with my DJM-5000, the "trim" as well as the "master" is set to 12. I set the back of my K12's also to 12. As the party needs more volume, I usually increase the "trim" on the mixer channel. This is what I"m assuming happened (and what I shouldn't have done).

Also, I use Traktor Scratch Pro which also has some gain settings. It is "auto-gain", so I don't touch anything.

My question is, what could have happened? And more importantly, what should my settings be? and if I want to increase volume during my performance, is it best to increase the volume on the K12, the "master" on the mixer, the "trim" on the mixer or somewhere in the software?

Thanks for your help guys!
 

adjtogo

Well-Known Member
I'd try the speaker again at home. Set it up and see if it turns back on. If not, call QSC tech support. Is it still under warranty? QSC is well known and has a fantastic support team that can help you out further.
 

Conanski

Active Member
The fader and knob settings are irrelevent, the ONLY thing that matters is the signal level as shown on the meters, and that should always be below clipping(red) at all stages throughout the audio system.
 

Enyko

Member
@Ron - Thanks for the reply. not that concerned about the speaker. Yes, if it's not working any longer, it is under warranty. I'm more concerned with not recreating this problem and learning where my levels should be.

@Paul - I understand the faders are irrelevant but the knob settings? Do you mean the EQ knobs? Yes, I know those are irrelevant as well but I'm talking about the "trim" knob (gain). I'm pretty sure that's relevant. I did forget to mention that my levels were definitely not in the red. I keep them in orange at the most.

http://hotdjgear.com/wp-content/uploads/2009/08/top.jpg
 

Jason Cathcart

New Member
I've got K12's too, and you can push those pretty hard.

What Paul means is that saying that your knobs are at 12 o'clock is irrelevant. It is and it isn't. Your K12's should be set at 12, and it will click in. Anything above that and you're risking your warranty. Telling me the knobs on your mixer are at 12 doesn't tell us anything though. Knowing you weren't running in the red there is helpful though.

Were the red limit lights on the back of the K12's lighting up when this happened? Was the fan in the speaker on or off at the time?

Protection mode is really "Thermal Protection Mode" to prevent the electronics from overheating - in theory you could still push the speaker to the point of it blowing apart as long as you weren't overheating the electronics. Overheat and the speaker goes into Protection mode, and shuts down until its at a safe temperature again. I'd check the fan operation.
 
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Conanski

Active Member
@Paul - I understand the faders are irrelevant but the knob settings? Do you mean the EQ knobs? Yes, I know those are irrelevant as well but I'm talking about the "trim" knob (gain). I'm pretty sure that's relevant. I did forget to mention that my levels were definitely not in the red. I keep them in orange at the most.

http://hotdjgear.com/wp-content/uploads/2009/08/top.jpg

You pretty much got it but when I say fader/knob I'm talking about any and all gain or trim controls.. because they all do the same thing.. control the signal level.

To setup your system for best signal to noise ratio follow this proceedure.
Start with the whole system connected and all gains/trims at 0 or the lowest setting. Adjust all tone/EQ controls to 0(no boost or cut) and play a track with lots of high sustained levels ensuring the gains/level controls/faders or whatever it is that controls the output level of your music source(laptop) is as high as it will go without distorting. If the source device(media or CD player) has no output control don't worry about it. Hopefully your mixer has signal meters(LEDs) on each input channel or can be switched to display the input level, and if so adjust the trim control until the signal meter is just below the reds. Now raise the fader on that channel to unity or about 8 of 10. Now raise the mains fader until the outout meters are just below the reds, and finally raise the amp or powered speaker gains until they are just below clipping or the system is producing enough SPL for the event. There is no need to turn the amp/speaker up higher than necessary, doing so just adds more noise(hiss or hum) to the system. Your system is now "calibrated" and if nothing changes you know that red on the main mixer meters means the whole system is out of gas so don't push it any harder. But of course we know the levels on tracks can vary a lot so you will have to keep readjusting the channel trims to keep them out of the red, but the other channel settings should not vary much unless you make large boosts or cuts with the EQ controls. If you do so try to remember to zero them out again before starting the next track.
 

GaryBonaducci

New Member
Enyko, I notice the K12s use Class D amplifiers, which in general requires steady AC power coming in because they don't have huge transformers and capacitors like traditional amps. Did you ever try your speakers out at home? It could be that your problem was with the venue's AC power having imperceptible brownouts, which triggered the amp's protection circuitry to activate and protect the speakers. Rather than problems with your input signal, clipping, or overheating, your problem might have been with the location. Do your speakers work fine now at home?
 

dboomer

Member
I can't believe that simply overdriving the input of your K12 caused it to shut off and not come back. I don't think it possible to get enough output from a mixer to do this. I think you will find that you just had an unrelated failure.

To your question ... You do want to drive your mixer hard BUT always less than clipping its outputs. Then starting with your speaker turned down bring it up until you have enough loudness for your show. At that point just turn your mixer down when you don't want full volume but leave your speaker set. Typically too many people operate with their mixer down and their speaker up when it works much better the other way around.
 

Ballroomdancer

New Member
To setup your system for best signal to noise ratio follow this proceedure.
Start with the whole system connected and all gains/trims at 0 or the lowest setting. Adjust all tone/EQ controls to 0(no boost or cut) and play a track with lots of high sustained levels ensuring the gains/level controls/faders or whatever it is that controls the output level of your music source(laptop) is as high as it will go without distorting. If the source device(media or CD player) has no output control don't worry about it. Hopefully your mixer has signal meters(LEDs) on each input channel or can be switched to display the input level, and if so adjust the trim control until the signal meter is just below the reds. Now raise the fader on that channel to unity or about 8 of 10. Now raise the mains fader until the outout meters are just below the reds, and finally raise the amp or powered speaker gains until they are just below clipping or the system is producing enough SPL for the event. There is no need to turn the amp/speaker up higher than necessary, doing so just adds more noise(hiss or hum) to the system. Your system is now "calibrated" and if nothing changes you know that red on the main mixer meters means the whole system is out of gas so don't push it any harder. But of course we know the levels on tracks can vary a lot so you will have to keep readjusting the channel trims to keep them out of the red, but the other channel settings should not vary much unless you make large boosts or cuts with the EQ controls. If you do so try to remember to zero them out again before starting the next track.
If your trim control on your music channel is just below the red, how do you set the trim on your mic channel? Will the music cover up the mic channel?
 

Conanski

Active Member
If your trim control on your music channel is just below the red, how do you set the trim on your mic channel? Will the music cover up the mic channel?

Mic channel is set the same, you set the trim so that the input isn't clipping when you are speaking loudly into the mic. As for getting the MC/DJ vocals over the music, for the most part you're not normally going to be talking when the music is at it's loudest, but if you did then simply drop the music channel fader(not the trim) a little while talking. Some mixers also have a talkover switch on the mic channel that automatically drops the other channels 6db or so while the mic is on.. very useful for this type thing. One last tool I won't be without ever again is a compressor/limiter for the mic, when setup correctly it allows you to get lots of vocal level without overdriving the mic input on the mixer.. even with loud music playing. To utilize this though you need a mixer with an insert on the mic channel or a mixer with this and possibly other effects built-in.
 
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