I'm getting ready to bi-amp my tops. The horn drivers are JBL 2445's. I have a QSC GX3 available. Is it enough power? It's rated 300w @ 8 ohms. The driver is 16 ohms and rated @ 150w RMS. Classic rock band and we're not a quiet band. The mids 2x12 JBL 2206's will be getting 1000W\box. Will the GX3 be enough or should I look for a GX5 or PL1804?
QSC GX3 - Is it enough for my horns?
- Thread starter Gary Weller
- Start date
Re: QSC GX3 - Is it enough for my horns?
GX3 is going to put out around 150w @ 16ohms. That JBL driver is a pretty beefy 2" if I recall correctly. It should theoretically take around 600 watts peak, which is a lot more then your GX3 can put out @ 16ohms! I'm personally a big fan of putting the most power possible into HF drivers. I want those HF transients to come through cleanly, without clipping the amp. You're actually risking more damage to drivers with a smaller amp that runs out of gas, than a bigger amp that can deliver the peaks. Sending those square waves is going to burn coils and do the damage. Those loud peaks last only a few milliseconds, but will make a huge difference in overall clarity, without hurting the drivers. As long as you have a DSP that can offer some form of RMS limiting, you'll be fine with a larger amp.
Of course, the GX3 could very well be enough for you. Depends how much volume you really want...
Evan
GX3 is going to put out around 150w @ 16ohms. That JBL driver is a pretty beefy 2" if I recall correctly. It should theoretically take around 600 watts peak, which is a lot more then your GX3 can put out @ 16ohms! I'm personally a big fan of putting the most power possible into HF drivers. I want those HF transients to come through cleanly, without clipping the amp. You're actually risking more damage to drivers with a smaller amp that runs out of gas, than a bigger amp that can deliver the peaks. Sending those square waves is going to burn coils and do the damage. Those loud peaks last only a few milliseconds, but will make a huge difference in overall clarity, without hurting the drivers. As long as you have a DSP that can offer some form of RMS limiting, you'll be fine with a larger amp.
Of course, the GX3 could very well be enough for you. Depends how much volume you really want...
Evan
Re: QSC GX3 - Is it enough for my horns?
For Christ's sake, Evan, you know better than this. Yes, clipping sounds bad, so I am a big proponent of big power as are you. But the shape of the waveform has nothing to do with whether it burns up your voice coil or not.
For Christ's sake, Evan, you know better than this. Yes, clipping sounds bad, so I am a big proponent of big power as are you. But the shape of the waveform has nothing to do with whether it burns up your voice coil or not.
Re: QSC GX3 - Is it enough for my horns?
Shhh. I'm just trying to get people to avoid clipping.
We all know there's a million different ways to kill a driver, and clipping is toward the bottom of the list, but you know as well as I do that amps do some nasty things when you nail them into clip!
Evan
Shhh. I'm just trying to get people to avoid clipping.
We all know there's a million different ways to kill a driver, and clipping is toward the bottom of the list, but you know as well as I do that amps do some nasty things when you nail them into clip! Evan
Re: QSC GX3 - Is it enough for my horns?
There are three ways to kill a driver. Over power, over excursion, and dropping it. If your amp has enough power to do one of those things while clipping then you may destroy the driver, but the shape of the waveform has nothing to do with it.
Shhh. I'm just trying to get people to avoid clipping.
There are three ways to kill a driver. Over power, over excursion, and dropping it. If your amp has enough power to do one of those things while clipping then you may destroy the driver, but the shape of the waveform has nothing to do with it.
Silas Pradetto
Graduate Student
Re: QSC GX3 - Is it enough for my horns?
Clipping may actually be a convenient way to know when you're out of gas - it will be extremely obvious when the HF driver amps clips, and it would be an easy indication to turn it down. Using a giant amp with no limiter would likely be worse, since the driver won't really start crying until it's dead.
Of course, I'm also a proponent of giant amps on horns - I always use Itech amps no matter what - and they are 1250 watts @ 8 ohms. They have great limiters, though, and knock on wood, I've never blown anything up.
Gary, it sounds to me like you have one of the original SR4731A boxes with the dual 12s and 2445. That 2445 is a beast of a loud driver, and with 150 watts should still blow right past the double 12s with 1000 watts. You could probably amp those 12s up to about 2500 watts and still be safe, and at that point you might need a bigger amp on the 2445.
What are you doing for DSP? It's not like you can just go ahead and biamp a speaker blindly. If you don't have DSP settings for your box, designed on the DSP you're using, I wouldn't bother. Shot-in-the-dark biamping may get louder but it certainly won't sound better.
Clipping may actually be a convenient way to know when you're out of gas - it will be extremely obvious when the HF driver amps clips, and it would be an easy indication to turn it down. Using a giant amp with no limiter would likely be worse, since the driver won't really start crying until it's dead.
Of course, I'm also a proponent of giant amps on horns - I always use Itech amps no matter what - and they are 1250 watts @ 8 ohms. They have great limiters, though, and knock on wood, I've never blown anything up.
Gary, it sounds to me like you have one of the original SR4731A boxes with the dual 12s and 2445. That 2445 is a beast of a loud driver, and with 150 watts should still blow right past the double 12s with 1000 watts. You could probably amp those 12s up to about 2500 watts and still be safe, and at that point you might need a bigger amp on the 2445.
What are you doing for DSP? It's not like you can just go ahead and biamp a speaker blindly. If you don't have DSP settings for your box, designed on the DSP you're using, I wouldn't bother. Shot-in-the-dark biamping may get louder but it certainly won't sound better.
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Re: QSC GX3 - Is it enough for my horns?
Oh poo. I thought the heart shaped waveforms when the amp was within normal operating range sounded better. But, I guess you just shattered those.
Evan
Oh poo. I thought the heart shaped waveforms when the amp was within normal operating range sounded better.
But, I guess you just shattered those. Evan
Silas Pradetto
Graduate Student
Re: QSC GX3 - Is it enough for my horns?
My waveforms are happy faces
Oh poo. I thought the heart shaped waveforms when the amp was within normal operating range sounded better.
Evan
My waveforms are happy faces
Re: QSC GX3 - Is it enough for my horns?
IIRC, the older SR-A boxes had a 2447 in them, which is a 1.5" driver. Still beastly, but not quite the 2445. That does bring up a good point.. What boxes are you using Gary, and what do you have for DSP(if any)?
Evan
IIRC, the older SR-A boxes had a 2447 in them, which is a 1.5" driver. Still beastly, but not quite the 2445. That does bring up a good point.. What boxes are you using Gary, and what do you have for DSP(if any)?
Evan
Re: QSC GX3 - Is it enough for my horns?
Oh poo. I thought the heart shaped waveforms when the amp was within normal operating range sounded better.
Re: QSC GX3 - Is it enough for my horns?
To be clear, the 2445 and 2447 were both 150 watt, 4 inch diameter compression drivers. The 2445 had a 2 inch exit throat diameter, whilst the 2447 had a 1.5 inch exit. Both were specified with a 118 dB SPL sensitivity at 1 mW on a plane wave tube. Mileage on any given horn may vary.
To be clear, the 2445 and 2447 were both 150 watt, 4 inch diameter compression drivers. The 2445 had a 2 inch exit throat diameter, whilst the 2447 had a 1.5 inch exit. Both were specified with a 118 dB SPL sensitivity at 1 mW on a plane wave tube. Mileage on any given horn may vary.
Re: QSC GX3 - Is it enough for my horns?
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.
Re: QSC GX3 - Is it enough for my horns?
Well, then start with the GX3 and see what happens. If you find yourself running out of gas, then I'd look at other options.
Evan
Well, then start with the GX3 and see what happens. If you find yourself running out of gas, then I'd look at other options.
Evan
Re: QSC GX3 - Is it enough for my horns? Something else to consider
That box does have the 2447, basically same thing as a 2445 without the extended throat that opens up to a two inch. The diaphragm most likely is also the ribbed version for extra stiffness.
You said the 2404 baby cheek tweeters were disconnected. The crossover network is still inline for the the 2447 and 2404 when switched into the bi-amp mode and it is low passing the 2447 somewhere around 6000hz or 7000hz as it assumes the 2404 is active to pick up at that point and go on out. The 2447 will work fine running all the way out on the top end with a little CD horn EQ applied at the DSP but since the internal passive crossover that will need to be physically by passed in the cabinet. You would want to put a blocking cap in series with the 2447 driver, something about 10uf to 12uf would work well for some low frequency and DC protection. When bi-amping play with a crossover frequency around 1,200hz to 1,500hz and see what you like.
Believe it or not when those boxes are ran in the full range mode there is no crossover filtering on the 12's, they get all of the full range signal and run all the out till they just naturally roll off. I guess they did that to save money on using really big high power inductors on the crossover network!
With some simple mods and basic bi-amping they will sound better.
With your set up you'll run out headroom first on the 12's with the PL230, the 2206 is a good sounding 12 but not the most efficient when used as a mid driver.
One more thing, as your cabinets are with the disconnected 2404 tweeters even when in the full range mode the 2447 is still low passed in the 6k to 7k range.
That box does have the 2447, basically same thing as a 2445 without the extended throat that opens up to a two inch. The diaphragm most likely is also the ribbed version for extra stiffness.
You said the 2404 baby cheek tweeters were disconnected. The crossover network is still inline for the the 2447 and 2404 when switched into the bi-amp mode and it is low passing the 2447 somewhere around 6000hz or 7000hz as it assumes the 2404 is active to pick up at that point and go on out. The 2447 will work fine running all the way out on the top end with a little CD horn EQ applied at the DSP but since the internal passive crossover that will need to be physically by passed in the cabinet. You would want to put a blocking cap in series with the 2447 driver, something about 10uf to 12uf would work well for some low frequency and DC protection. When bi-amping play with a crossover frequency around 1,200hz to 1,500hz and see what you like.
Believe it or not when those boxes are ran in the full range mode there is no crossover filtering on the 12's, they get all of the full range signal and run all the out till they just naturally roll off. I guess they did that to save money on using really big high power inductors on the crossover network!
With some simple mods and basic bi-amping they will sound better.
With your set up you'll run out headroom first on the 12's with the PL230, the 2206 is a good sounding 12 but not the most efficient when used as a mid driver.
One more thing, as your cabinets are with the disconnected 2404 tweeters even when in the full range mode the 2447 is still low passed in the 6k to 7k range.
Re: QSC GX3 - Is it enough for my horns? Something else to consider
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
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
Re: QSC GX3 - Is it enough for my horns?
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).
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).
Re: QSC GX3 - Is it enough for my horns?
I am sure someone with more design experience will chime in but I tend to think this explanation (the flat top DC thing) is the application of an overly simple model to a complex situation. I would tend to think that clipping the peaks means the whole RMS average is at a higher level which would cause heating, not what is happening to the shape of the peak at the top.
How about a little thought problem? At 5000 hz, if the top 50% of each peak is cut off, how long do each of those "DC" pulses last? I would argue that they do not last long enough to be considered DC.
I am sure someone with more design experience will chime in but I tend to think this explanation (the flat top DC thing) is the application of an overly simple model to a complex situation. I would tend to think that clipping the peaks means the whole RMS average is at a higher level which would cause heating, not what is happening to the shape of the peak at the top.
How about a little thought problem? At 5000 hz, if the top 50% of each peak is cut off, how long do each of those "DC" pulses last? I would argue that they do not last long enough to be considered DC.
Re: QSC GX3 - Is it enough for my horns?
Marjan,
Two things:
1. The waveform that you "see" graphed by something like DAW software does not represent the movement of the driver. To get an idea of what the drivers' real displacement is you need to double integrate that signal.
2. In practice in the modern era the DC offset voltages that can be produced in clipping are small, so the aren't contributing as much to heating as you might think. A large DC offset would indeed be bad for driver heating.
Marjan,
Two things:
1. The waveform that you "see" graphed by something like DAW software does not represent the movement of the driver. To get an idea of what the drivers' real displacement is you need to double integrate that signal.
2. In practice in the modern era the DC offset voltages that can be produced in clipping are small, so the aren't contributing as much to heating as you might think. A large DC offset would indeed be bad for driver heating.