QSC GX3 - Is it enough for my horns?

Re: QSC GX3 - Is it enough for my horns?

Marjan Milosevic said:
Hmmm, i think that the shape of the waveform certainly do has something with it.
Clipped (or chopped off) peaks looks more like a flat line then a waveform and with it the amp is putting our more like a dc current, meaning it is heating the vc a lot more then a pure sine wave (or a waveform).
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Nope. When roasting drivers, what matters is energy delivered to the driver minus what the driver can dissipate as heat. So the energy delivered by the waveform matters, but the exact shape does not. A squarewave delivers double the energy of a sinewave with the same magnitude (or the same energy as a sinewave with a magnitude 1.4 times as great). So when you drive an amplifier into clipping, you end up delivering more power to the driver than the amplifier's rated sinewave output.
 
Re: QSC GX3 - Is it enough for my horns?

Gary Weller said:
The boxes are SR4732A's with 2445's on 60x40 horns (2385?) and have a 4731 x-over with baby cheeks disabled. mids are on a pl230. Unfortunately, I only have a DRPA for DSP. No good limiters available in those.
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Everyone telling Gary to disable the low-pass on the 2445, he clearly states that he is using the crossover from the 2-way box, and therefore the 2445 is running all the way up already.

The 2445 is not going to do above 10k all that pleasantly at all.
 
Re: QSC GX3 - Is it enough for my horns?

Marjan Milosevic said:
Hmmm, i think that the shape of the waveform certainly do has something with it.
Clipped (or chopped off) peaks looks more like a flat line then a waveform and with it the amp is putting our more like a dc current, meaning it is heating the vc a lot more then a pure sine wave (or a waveform).
Click to expand...

Marjan,

If this were true, then any time someone played a square wave keyboard synth the PA would catch on fire.
 
Re: QSC GX3 - Is it enough for my horns?

I am not trying to argue about this but the clipped signal (as a flat line) will make the voice coil heat a lot more. Simply when the line is flat (constant voltage) the cone (diaphragm) is not moving. It stays at one point for a fraction of a time. Meaning no cooling.
Sure there is a lot more in to it, but this certainly adds to the problem.
 
Re: QSC GX3 - Is it enough for my horns?

Marjan Milosevic said:
I am not trying to argue about this but the clipped signal (as a flat line) will make the voice coil heat a lot more. Simply when the line is flat (constant voltage) the cone (diaphragm) is not moving. It stays at one point for a fraction of a time. Meaning no cooling.
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No - the waveform is not an absolute position map of the driver, but rather an accelerating force. For the brief clipped part of the wave, the driver doesn't stay "stuck all the way out" - it's still moving, assuming the square wave is in the audio frequency domain.

Also, if we are speaking about woofers that have a crossover, the crossover will filter out the high frequency elements in the square wave signal to some degree, making it "not DC" again.
 
Re: QSC GX3 - Is it enough for my horns?

Marjan Milosevic said:
I am not trying to argue about this but the clipped signal (as a flat line) will make the voice coil heat a lot more. Simply when the line is flat (constant voltage) the cone (diaphragm) is not moving. It stays at one point for a fraction of a time. Meaning no cooling.
Sure there is a lot more in to it, but this certainly adds to the problem.
Click to expand...
With a clipped music signal, the diaphragm is moving at all times.

Even with a 10KHz square wave the diaphragm moves 10,000 times a second, as opposed to DC, where it is held in place.

An actual square wave will have 3 dB more average power than a sine wave, and a sine wave a lot more average level than music.
Bennett wrote in post 23:
"If this were true, then any time someone played a square wave keyboard synth the PA would catch on fire."

Bennett is ignoring the fact that if someone played a square wave with an equal peak magnitude of any normal music transient, the average power delivered would be an order of magnitude higher than usual music.

Bass speakers sometimes do catch on fire with full tilt boogie square waves, but HF drivers voice coils generally melt through too quick to catch fire.

So you are both wrong, glad to help :^).

Art
 
Re: QSC GX3 - Is it enough for my horns?

Art Welter said:
Bennett is ignoring the fact that if someone played a square wave with an equal peak magnitude of any normal music transient, the average power delivered would be an order of magnitude higher than usual music.
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I am not ignoring it, but the voice coil is not destroyed because the waveform has a certain shape. It is destroyed because of delivered heat. Yes, a square wave or even more extremely pure DC will burn up a voice coil a lot faster because they have low (or zero) peak to average ratio, but if they were only a volt or so they would not do any damage. Any waveform with equal peak to average ratio would do as much damage.
 
Re: QSC GX3 - Is it enough for my horns?

My understanding is that a "square wave" signal is actually comprised of many odd order sine waves jammed together so that the peaks form what appears to be a line when viewed on an o-scope. The large number of odd order harmonics is what makes that clipping sound harsh as well as generate the extra power that must be dissipated. From that I gather that there is no raw dc component involved since all components of a square wave are actually sinusoidal.

Greg
 
Re: QSC GX3 - Is it enough for my horns?

Gary Weller said:
The boxes are SR4732A's with 2445's on 60x40 horns (2385?) and have a 4731 x-over with baby cheeks disabled. mids are on a pl230. Unfortunately, I only have a DRPA for DSP. No good limiters available in those.
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Gary,
I use SR4732 bi-amped with a PLX1602 on the tops all the time.That's 600 watts each cabinet at the horn's rated 16 ohm load. Never blown a horn, and we've had the amps up not quite to clipping several times. For us, that's enough horn for all but the loudest concerts. I'd be concerned that the GX3 isn't going to have the git-up-and-go needed to use those horns to their fullest ability.
 
Re: QSC GX3 - Is it enough for my horns?

Matt Tudor said:
Gary,
I use SR4732 bi-amped with a PLX1602 on the tops all the time.That's 600 watts each cabinet at the horn's rated 16 ohm load. Never blown a horn, and we've had the amps up not quite to clipping several times. For us, that's enough horn for all but the loudest concerts. I'd be concerned that the GX3 isn't going to have the git-up-and-go needed to use those horns to their fullest ability.
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Are you bridging the 1602 into one cabinet or both cabinets for the high end or running the amp in stereo with one cabinet per channel?
 
Re: QSC GX3 - Is it enough for my horns?

Mike Caldwell said:
Are you bridging the 1602 into one cabinet or both cabinets for the high end or running the amp in stereo with one cabinet per channel?
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Stereo. And yes, I just realized that I just misread the spec sheet and the 16 ohm rating is for bridge mode. :blush: my goof :blush: my apologies. There's a lesson in this somewhere....
 
Re: QSC GX3 - Is it enough for my horns?

Matt Tudor said:
Stereo. And yes, I just realized that I just misread the spec sheet and the 16 ohm rating is for bridge mode. :blush: my goof :blush: my apologies. There's a lesson in this somewhere....
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The lesson is that you're using the same power I am thinking of using with the GX3. ;) I may look for something a little more powerful and keep the qsc gx3 as the spare monitor amp it is now.
 
Re: QSC GX3 - Is it enough for my horns? Something else to consider

Evan Kirkendall said:
I completely forgot about that when I was browsing the specs! Looking back at the specs again, the x-over points are 1.2k and 6k. And, the 4732a does in fact use the 2445J. http://www.jblproservice.com/pdf/SR-Series/SR4732.pdf Do what Mike says, and you'll experience clarity like you've never heard out of those cabs(at least since you disconnected the VHF)! I have some very nice sounding EQ settings for that horn somewhere... I just need to find them, and I will post them. Evan
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Evan, did you happen to find those EQ settings for the 2445J? And will a DRPA have enough PEQ to use the settings?
 
Re: QSC GX3 - Is it enough for my horns?

Bennett Prescott said:
I am not ignoring it, but the voice coil is not destroyed because the waveform has a certain shape. It is destroyed because of delivered heat. Yes, a square wave or even more extremely pure DC will burn up a voice coil a lot faster because they have low (or zero) peak to average ratio, but if they were only a volt or so they would not do any damage. Any waveform with equal peak to average ratio would do as much damage.
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Is a simpler way of saying this that it is not just the waveform or just the amplitude, it is the combination of those two factors?

A square wave of a certain peak amplitude represents a greater average level and more energy than a sine wave with the same peak amplitude, but that may not be true if the square wave were of a lower amplitude. The issue with clipping is that the peak level remains the same while increasing the average level and the energy represented by the resulting waveform. Take that same resulting waveform from clipping and drop it several dB in level and it may be no problem.
 
Re: QSC GX3 - Is it enough for my horns?

Brad Weber said:
Is a simpler way of saying this that it is not just the waveform or just the amplitude, it is the combination of those two factors?

A square wave of a certain peak amplitude represents a greater average level and more energy than a sine wave with the same peak amplitude, but that may not be true if the square wave were of a lower amplitude. The issue with clipping is that the peak level remains the same while increasing the average level and the energy represented by the resulting waveform. Take that same resulting waveform from clipping and drop it several dB in level and it may be no problem.
Click to expand...

This was already answered further up the thread.

To wit:
Rob Timmerman said:
When roasting drivers, what matters is energy delivered to the driver minus what the driver can dissipate as heat. So the energy delivered by the waveform matters, but the exact shape does not. A squarewave delivers double the energy of a sinewave with the same magnitude (or the same energy as a sinewave with a magnitude 1.4 times as great). So when you drive an amplifier into clipping, you end up delivering more power to the driver than the amplifier's rated sinewave output.
Click to expand...
 
Re: QSC GX3 - Is it enough for my horns? Something else to consider

Gary Weller said:
Evan, did you happen to find those EQ settings for the 2445J? And will a DRPA have enough PEQ to use the settings?
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I'm pretty sure the DRPA can handle this:

x-over: 1.2k, 4th order L/R

EQ1: -6dB @ 2.8k Q3.2
EQ2: -3dB @ 5k Q6.3
EQ3: -2dB @ 1.8k, Q10
EQ4: +6dB @ 9.6k, 12/dB Hi-Shelf (Do this one to taste)

For your 12's, you'll probably want a cut around 250hz, and 500. I can't remember much about the Low section of that box...


If you run out of EQ filters(I forget how many it has), lose the cut at 1.8k.

Let me know how it sounds... I haven't heard those settings in a while!


Evan
 
Re: QSC GX3 - Is it enough for my horns? Something else to consider

Evan Kirkendall said:
I'm pretty sure the DRPA can handle this:

x-over: 1.2k, 4th order L/R

EQ1: -6dB @ 2.8k Q3.2
EQ2: -3dB @ 5k Q6.3
EQ3: -2dB @ 1.8k, Q10
EQ4: +6dB @ 9.6k, 12/dB Hi-Shelf (Do this one to taste)

For your 12's, you'll probably want a cut around 250hz, and 500. I can't remember much about the Low section of that box...


If you run out of EQ filters(I forget how many it has), lose the cut at 1.8k.

Let me know how it sounds... I haven't heard those settings in a while!


Evan
Click to expand...

DRPA only has 3 PEQ per channel, and they have very coarse resolution. You'll likely have to deal with 'almost' there.
 
Re: QSC GX3 - Is it enough for my horns? Something else to consider

Evan Kirkendall said:
I'm pretty sure the DRPA can handle this: x-over: 1.2k, 4th order L/R EQ1: -6dB @ 2.8k Q3.2 EQ2: -3dB @ 5k Q6.3 EQ3: -2dB @ 1.8k, Q10 EQ4: +6dB @ 9.6k, 12/dB Hi-Shelf (Do this one to taste) For your 12's, you'll probably want a cut around 250hz, and 500. I can't remember much about the Low section of that box... If you run out of EQ filters(I forget how many it has), lose the cut at 1.8k. Let me know how it sounds... I haven't heard those settings in a while! Evan
Click to expand...
Thanks Evan for the settings. I'll get them as close as possible and use my ears from there and let you know how they sound. I've got a pre-new years gig next friday.
 
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