Re: JBL SRX / QSC PL236 underpowered?
I'd be wholly inclined to agree with you there.
I'd be wholly inclined to agree with you there.
JBL SRX / QSC PL236 underpowered?
- Thread starter Andrew Prince
- Start date
Re: JBL SRX / QSC PL236 underpowered?
Crown I-Techs already monitor and store a variety of fault conditions including clipping (owner-defined parameters), load (high/low/nominal set by owner), AC line voltage, thermal errors...
Crown I-Techs already monitor and store a variety of fault conditions including clipping (owner-defined parameters), load (high/low/nominal set by owner), AC line voltage, thermal errors...
Re: JBL SRX / QSC PL236 underpowered?
I'm going for 'rock' as Genesis are a rock band, albeit one of the prog genre.
This comes back to what a previous post said - the system should be designed for the application, not the other way around. Again I agree. So I guess what I'm asking here is, "what should I expect if I use 4 subs and 2 tops?" I only did that once, back when the band had 4 subs. It sounded muddy to me. Ergo, you're suggesting that as sound engineer for this band, my preference is 2 tops and 2 subs.
I agree. I'm beginning to think I was unwise to trust the band when they told me the DriveRack PA was properly configured and didn't need touching. The amps were incorrectly configured when I got to them because they had a 50Hz LCF switch in on the tops. I think possibly the amps were switched around in the rack when the rack was changed to a better flight case.
I'm more than happy to check the settings against the tunings sheet myself though. So, good advice. Thanks.
I'm going for 'rock' as Genesis are a rock band, albeit one of the prog genre.
This comes back to what a previous post said - the system should be designed for the application, not the other way around. Again I agree. So I guess what I'm asking here is, "what should I expect if I use 4 subs and 2 tops?" I only did that once, back when the band had 4 subs. It sounded muddy to me. Ergo, you're suggesting that as sound engineer for this band, my preference is 2 tops and 2 subs.
I agree. I'm beginning to think I was unwise to trust the band when they told me the DriveRack PA was properly configured and didn't need touching. The amps were incorrectly configured when I got to them because they had a 50Hz LCF switch in on the tops. I think possibly the amps were switched around in the rack when the rack was changed to a better flight case.
I'm more than happy to check the settings against the tunings sheet myself though. So, good advice. Thanks.
Re: JBL SRX / QSC PL236 underpowered?
This is the standard with the JBL SRX system? Or PA systems in general? I can't see how it would be a standard across the board.
Worrying! I frequent a venue that has an old desk and the master fader has snapped off which means, "we can't turn the bands down!" Seriously.
This is the standard with the JBL SRX system? Or PA systems in general? I can't see how it would be a standard across the board.
Worrying! I frequent a venue that has an old desk and the master fader has snapped off which means, "we can't turn the bands down!" Seriously.
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Re: JBL SRX / QSC PL236 underpowered?
Sorry if I'm rehashing old ground. I did originally start with a search for all posts regarding JBL SRX and power requirements. Kudos to the JBL marketing department though.
I'm more than happy to see a healthy bit of clipping as it were. The annoyance with this system comes mainly from the fact that the tops clip occasionally but the subs never come close. This is what brought me to look up all the data on the components and start this thread.
What's more, prior to my involvement with this band, I had to replace one of their compression drivers. See the attached picture. I know not how they managed to do this kind of damage with those QSC amps. I'm not surprised that the amps CAN damage a compression driver. I am merely surprised that they can damage it in this way. That was a £280.00 repair bill and a 14 day wait for a JBL replacement because they don't stock those parts in the UK.
With internally powered speakers, the manufacturers have mostly chosen to replace clip lights with "peak" or "limit" lights. Sometimes you see the light long after you've begun to hear the limiting...[/quote]
Actually, the QSC amps have limiters in them. I'm going to check whether they're enabled.
Sorry if I'm rehashing old ground. I did originally start with a search for all posts regarding JBL SRX and power requirements. Kudos to the JBL marketing department though.
I'm more than happy to see a healthy bit of clipping as it were. The annoyance with this system comes mainly from the fact that the tops clip occasionally but the subs never come close. This is what brought me to look up all the data on the components and start this thread.
What's more, prior to my involvement with this band, I had to replace one of their compression drivers. See the attached picture. I know not how they managed to do this kind of damage with those QSC amps. I'm not surprised that the amps CAN damage a compression driver. I am merely surprised that they can damage it in this way. That was a £280.00 repair bill and a 14 day wait for a JBL replacement because they don't stock those parts in the UK.
With internally powered speakers, the manufacturers have mostly chosen to replace clip lights with "peak" or "limit" lights. Sometimes you see the light long after you've begun to hear the limiting...[/quote]
Actually, the QSC amps have limiters in them. I'm going to check whether they're enabled.
Re: JBL SRX / QSC PL236 underpowered?
The picture shows both over-excursion and overheating. My first guess is the cabinet was bi-amped and crossover settings were wrong. Another possibility is DC (for the heat) from the amp. The diaphragm destruction, though, is from the dome hitting the phase plug. It only takes a few strikes if the crossover point is low (or missing), but it can happen from extreme over-driving use, too. This damage was not caused by the occasional flickering of clip lights... it was caused by too much power for too long.
From your description of the amplifier operation, I'd say the band does not own "Enough Rig for the Gig®" at least as it applies to their top boxes, or there is something very amiss regarding system setup.
The picture shows both over-excursion and overheating. My first guess is the cabinet was bi-amped and crossover settings were wrong. Another possibility is DC (for the heat) from the amp. The diaphragm destruction, though, is from the dome hitting the phase plug. It only takes a few strikes if the crossover point is low (or missing), but it can happen from extreme over-driving use, too. This damage was not caused by the occasional flickering of clip lights... it was caused by too much power for too long.
From your description of the amplifier operation, I'd say the band does not own "Enough Rig for the Gig®" at least as it applies to their top boxes, or there is something very amiss regarding system setup.
Re: JBL SRX / QSC PL236 underpowered?
I did an outdoor band last year with my old EAW JFL system (roughly comparable to VRX). 4 main speakers 2 per side, two single 18" subwoofers centered. I ran out of gas on my mains and was fine with my subs.
That's not a standard that I've ever heard. What kind of top are you referring to? What kind of sub? Single 18"? Dual 18"? A single Danley TH118 produces the same output as about 4-6 typical single 18" subs. For some genres that may indeed be correct, but not an axiom.
I did an outdoor band last year with my old EAW JFL system (roughly comparable to VRX). 4 main speakers 2 per side, two single 18" subwoofers centered. I ran out of gas on my mains and was fine with my subs.
Silas Pradetto
Graduate Student
Re: JBL SRX / QSC PL236 underpowered?
There is way too much calculating and theorizing going on in this thread. Here's how you figure this out:
1. Set up the DSP with the JBL-provided tunings. They suggest an 80Hz lowpass on the subs, which I would NOT increase, and a 80Hz highpass on the tops, which you could increase depending on how much buildup in the 80Hz range you end up with. There are significant implications to changing the crossover. It's not a bad thing to do, but will change phase alignment between tops and subs. Try to keep things where JBL suggests and use input EQ to tune the PA. (You want to use the input EQ as using output EQ will only equalize one passband, and therefore also change the phase alignment between passbands).
2. Set up amps stereo on the tops and bridged on the subs. Take note that bridging an amp immediately adds 6dB of gain, so unless the amp offers bridged gain compensation, you will need to gain the amp down 6dB to keep things even.
3. Run the rig at a gig.
This leaves the question: does it get loud enough?
If it does, leave it.
If it doesn't, get more rig.
After using the SRX stuff pretty regularly, it will take pretty much all the peak power you can throw at it. However, purchasing an amp that can deliver 3000 watts per box doesn't really make any sense, because all that extra power could only be used on peaks, and depending on limiters, melt the coils pretty easily. The money spent on a huge amp could be spent on more subs, and more cones is always better than more power. (Still, I was hitting my SRX subs with a LOT of power and it does make a difference. I was right at the limit of what could be done with 4 double 18s though).
Regarding clarity:
This is called mixing. I would not consider it a bad thing.
Regarding crossover:
There is only a recommendation for the crossover point. Note that subs have a high pass (low cut) and a low pass (high cut) to limit their passband. The 31Hz is the highpass and is to prevent overexcursion below box tuning. Do NOT change or ignore this. The low pass is the 80Hz spec, and this is subject to adjustment. Higher is possible, but they need EQ otherwise there is significant buildup in the 80-100 range. I like my SRX subs at 80Hz, and I still end up cutting 80 usually. See above for some other crossover implications.
There is way too much calculating and theorizing going on in this thread. Here's how you figure this out:
1. Set up the DSP with the JBL-provided tunings. They suggest an 80Hz lowpass on the subs, which I would NOT increase, and a 80Hz highpass on the tops, which you could increase depending on how much buildup in the 80Hz range you end up with. There are significant implications to changing the crossover. It's not a bad thing to do, but will change phase alignment between tops and subs. Try to keep things where JBL suggests and use input EQ to tune the PA. (You want to use the input EQ as using output EQ will only equalize one passband, and therefore also change the phase alignment between passbands).
2. Set up amps stereo on the tops and bridged on the subs. Take note that bridging an amp immediately adds 6dB of gain, so unless the amp offers bridged gain compensation, you will need to gain the amp down 6dB to keep things even.
3. Run the rig at a gig.
This leaves the question: does it get loud enough?
If it does, leave it.
If it doesn't, get more rig.
After using the SRX stuff pretty regularly, it will take pretty much all the peak power you can throw at it. However, purchasing an amp that can deliver 3000 watts per box doesn't really make any sense, because all that extra power could only be used on peaks, and depending on limiters, melt the coils pretty easily. The money spent on a huge amp could be spent on more subs, and more cones is always better than more power. (Still, I was hitting my SRX subs with a LOT of power and it does make a difference. I was right at the limit of what could be done with 4 double 18s though).
Regarding clarity:
This is called mixing. I would not consider it a bad thing.
Regarding crossover:
There is only a recommendation for the crossover point. Note that subs have a high pass (low cut) and a low pass (high cut) to limit their passband. The 31Hz is the highpass and is to prevent overexcursion below box tuning. Do NOT change or ignore this. The low pass is the 80Hz spec, and this is subject to adjustment. Higher is possible, but they need EQ otherwise there is significant buildup in the 80-100 range. I like my SRX subs at 80Hz, and I still end up cutting 80 usually. See above for some other crossover implications.
Regarding the 50hZ high pass on the amps. For the tops it does no harm. For the subs I would turn it off and set the proper HP in the DSP.
Sent from my iPad HD
Sent from my iPad HD
Re: JBL SRX / QSC PL236 underpowered?
These are the tunings from the DR 4800, very similar to the DR 260. I use these settings as a starting point with Crown ITechs.
My bandpass gains are a little different than the ones listed below
718:
HPF 30Hz But 18
LPF 88Hz LR 48
715 low/mid (.208ms) delay
-1.7db gain
HPF 91Hz LR 48
LPF 1.14kHz LR 48
Mid/high
Invert polarity
-16db gain
HPF 1.12kHz LR 48
Eq filters
718:
44.71 Hz 1.5db Q 4.915
68.82Hz 2db Q 4.915
715:
Low mid
93.64Hz 3.5db Q2.922
183.72Hz 3db low pass shelving 6db octave filter
250Hz -2db Q 2.922
500Hz -1.5 db Q 0.92
Highs
1.62kHz -1.8db Q 1.738
2.38kHz -3db Q 4.133
5.55kHz -3db Q 4.13
12.7kHz 6.5db Q 2.457
These are the tunings from the DR 4800, very similar to the DR 260. I use these settings as a starting point with Crown ITechs.
My bandpass gains are a little different than the ones listed below
718:
HPF 30Hz But 18
LPF 88Hz LR 48
715 low/mid (.208ms) delay
-1.7db gain
HPF 91Hz LR 48
LPF 1.14kHz LR 48
Mid/high
Invert polarity
-16db gain
HPF 1.12kHz LR 48
Eq filters
718:
44.71 Hz 1.5db Q 4.915
68.82Hz 2db Q 4.915
715:
Low mid
93.64Hz 3.5db Q2.922
183.72Hz 3db low pass shelving 6db octave filter
250Hz -2db Q 2.922
500Hz -1.5 db Q 0.92
Highs
1.62kHz -1.8db Q 1.738
2.38kHz -3db Q 4.133
5.55kHz -3db Q 4.13
12.7kHz 6.5db Q 2.457
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Re: JBL SRX / QSC PL236 underpowered?
It doesn't have to be difficult to factor what you should be powering a speaker with. Take the information given and run with it. If the speaker says it will handle X amount of continuous, program and peak power that is all you can go by. The manufacturers will sometimes divulge what they feel is an appropriate amp. In general it is usually an amp that is rated right about where the program power is for said speaker. Others ( people ) will say to simply double the continuous power rating and there you have it. I prefer a slightly different approach, but then again I prefer to run my equipment at around 70-75% of what it can do.
The more scientific way ( the way I like to do it ) is to factor the speakers sensitivity and my desired SPL level. I want some room left over, so I spec for equipment that will acquire the desired results and still be within a reasonable safety margin. The peak SPL listed by manufacturers is not going to happen. So I rely more on the continuous SPL listed ( if it is ), if it is not listed then I subtract 6db from the peak as a safety margin. I want the continuous SPL to be above my desired SPL. Next I do the math. Speaker sensitivity is rated at 1W/ 1 meter. Easy enough, I just start doubling the wattage over and over till I reach the desired amount of gain needed, relying on the old adage that every doubling of power is = to 3db of possible gain. 1w, 2w, 4w, 8w, 16w etc. until the desired SPL at distance is achieved. You will run into one of two things? You will either reach your desired SPL, or you will run out of speaker/amplification...... Don't forget to factor distance for your desired SPL level....... The SPL that will be reached based on the 1 watt/ 1meter rule will be the SPL at 1 meter! So at 50-100' it will be of course much lower by 6db for every doubling of distance. Inside an indoor venue you will not loose as much energy, but that is another issue all together.
If you have more than 1 sub you can add 3db for every doubling thereof. But this is really only true if they are side by side. Placing the subs on the ground will net another 1-3db to that total. I don't rely heavily on half space loading addition, so I add 2db as it is a safe addition to the figures. This should give you a rough idea of what your capable of providing if you do the math on your current rig. It's not an exact science, but it can give you general idea of what you can provide. As long as you intend to work below the factored max ratings you can provide, you should get the results you desire. Once you want to go above the factored potential, your on borrowed time. This is why I shoot to run at 70-75% of potential. My amps, speakers and everything related to it should be able to provide what I need with a good margin left over for the unknown........
If you have done the math and you factor you need X power to get the desired SPL result, the next step is finding an amp with at least that amount of power and not exceeding the speakers peak power rating. I find that the optimal amp power rating usually exists somewhere between the program and peak power rating. Power compression is tough to calculate, but wattage loss over X cable distance is another thing to consider. This should be factored into your decision as well. Just when you thought you had it nailed......... You will more than likely need an amp rated for higher than the manufactures recommended amp power, but that is dependent upon your needs? I prefer to run on the high end and use DSP/ speaker management to reduce speaker damage. So now comes the next issue.
Diminishing returns......... At some point you will either get to where there is no appreciable amp that will provide the exact needed power and stay within budget. To get that last 3db and still be within the speakers peak power rating may cost more than that 3db is worth? You have to spec within a margin that will also appease a budget. You may find that getting that last 3db of desired SPL may cost you more than the speaker your powering? So you may end up having to run with an amp that is running near it's limit if you have to run your system that hot? It's something to consider. What you need, what you can acquire and what you can afford are all part of the big picture. So is your 1K watt amp enough for your current speakers? That depends on if you already have enough to get there and if not, will getting there cost you more than it's worth? If getting the last 3db is not possible then you will have to settle for the next best thing that you can afford. This difference may only result in a couple db loss in potential, but you will be working the system that much harder for more time. If you spec your system to have more than the needed levels you will have little to worry about. The goal is to spec a system that can easily achieve what is needed and within budget.
It's not very black and white, but it's also not very difficult. Simple math will give you an idea and reasoning will finish the job. I prefer to run at 70-75%, but on occasion I have to run beyond that. It's all about needs, not what is truly right, or wrong. Is your amp under-powered? Only if it doesn't meet your current demands.......
It doesn't have to be difficult to factor what you should be powering a speaker with. Take the information given and run with it. If the speaker says it will handle X amount of continuous, program and peak power that is all you can go by. The manufacturers will sometimes divulge what they feel is an appropriate amp. In general it is usually an amp that is rated right about where the program power is for said speaker. Others ( people ) will say to simply double the continuous power rating and there you have it. I prefer a slightly different approach, but then again I prefer to run my equipment at around 70-75% of what it can do.
The more scientific way ( the way I like to do it ) is to factor the speakers sensitivity and my desired SPL level. I want some room left over, so I spec for equipment that will acquire the desired results and still be within a reasonable safety margin. The peak SPL listed by manufacturers is not going to happen. So I rely more on the continuous SPL listed ( if it is ), if it is not listed then I subtract 6db from the peak as a safety margin. I want the continuous SPL to be above my desired SPL. Next I do the math. Speaker sensitivity is rated at 1W/ 1 meter. Easy enough, I just start doubling the wattage over and over till I reach the desired amount of gain needed, relying on the old adage that every doubling of power is = to 3db of possible gain. 1w, 2w, 4w, 8w, 16w etc. until the desired SPL at distance is achieved. You will run into one of two things? You will either reach your desired SPL, or you will run out of speaker/amplification...... Don't forget to factor distance for your desired SPL level....... The SPL that will be reached based on the 1 watt/ 1meter rule will be the SPL at 1 meter! So at 50-100' it will be of course much lower by 6db for every doubling of distance. Inside an indoor venue you will not loose as much energy, but that is another issue all together.
If you have more than 1 sub you can add 3db for every doubling thereof. But this is really only true if they are side by side. Placing the subs on the ground will net another 1-3db to that total. I don't rely heavily on half space loading addition, so I add 2db as it is a safe addition to the figures. This should give you a rough idea of what your capable of providing if you do the math on your current rig. It's not an exact science, but it can give you general idea of what you can provide. As long as you intend to work below the factored max ratings you can provide, you should get the results you desire. Once you want to go above the factored potential, your on borrowed time. This is why I shoot to run at 70-75% of potential. My amps, speakers and everything related to it should be able to provide what I need with a good margin left over for the unknown........
If you have done the math and you factor you need X power to get the desired SPL result, the next step is finding an amp with at least that amount of power and not exceeding the speakers peak power rating. I find that the optimal amp power rating usually exists somewhere between the program and peak power rating. Power compression is tough to calculate, but wattage loss over X cable distance is another thing to consider. This should be factored into your decision as well. Just when you thought you had it nailed......... You will more than likely need an amp rated for higher than the manufactures recommended amp power, but that is dependent upon your needs? I prefer to run on the high end and use DSP/ speaker management to reduce speaker damage. So now comes the next issue.
Diminishing returns......... At some point you will either get to where there is no appreciable amp that will provide the exact needed power and stay within budget. To get that last 3db and still be within the speakers peak power rating may cost more than that 3db is worth? You have to spec within a margin that will also appease a budget. You may find that getting that last 3db of desired SPL may cost you more than the speaker your powering? So you may end up having to run with an amp that is running near it's limit if you have to run your system that hot? It's something to consider. What you need, what you can acquire and what you can afford are all part of the big picture. So is your 1K watt amp enough for your current speakers? That depends on if you already have enough to get there and if not, will getting there cost you more than it's worth? If getting the last 3db is not possible then you will have to settle for the next best thing that you can afford. This difference may only result in a couple db loss in potential, but you will be working the system that much harder for more time. If you spec your system to have more than the needed levels you will have little to worry about. The goal is to spec a system that can easily achieve what is needed and within budget.
It's not very black and white, but it's also not very difficult. Simple math will give you an idea and reasoning will finish the job. I prefer to run at 70-75%, but on occasion I have to run beyond that. It's all about needs, not what is truly right, or wrong. Is your amp under-powered? Only if it doesn't meet your current demands.......
Re: JBL SRX / QSC PL236 underpowered?
Indeed, so when JB state 800/1600/3200 then the 800 is continuous.
So this is represented by JBLs 1600 in the above spec. Therefore for typical program (a rock band), I need to drive the speakers with 1600W correct?
And this number is therefore 3200.
So in that case, how do these three numbers relate to my amp spec?
FTC 8 Ohms per channel (20-20kHz, 0.033% THD) 725W
FTC 4 Ohms per channel (20-20kHz, 0.033% THD) 1100W
EIA 1kHz @ 1% THD 8 Ohms per channel 800W
EIA 1kHz @ 1% THD 4 Ohms per channel 1300W
EIA 1kHz @ 1% THD 2 Ohms per channel 1850W
I read the FTC figures to be the real world performance of the amp (in other words, program) and the EIA figures to be not so real world (in other words peak).
Basically, I'm readying the JBL spec like this:
1. They run at around 800W continuously / RMS / normal / safe.
2. They should be driven at 1600W because the difference between 800W and 1600W is where you should be at.
3. If you're an idiot and play cricket with your mics, chances are you will hit 3200W and still be safe, but really you shouldn't be an idiot.
Hence, I conclude, 725W into 8 Ohms with a speaker rated at 800/1600/3200 is not enough power to do the job properly? Am I reading this incorrectly?
The VRX system is similarly priced to the SRX system. In my world, idiots buy 'DJ Speakers' and drive them with Peavey amps, wondering why they blow their HF drivers. Therefore I'm a little lost as to why JBL feel the need to totally idiot proof their VRX boxes. The fact is, an idiot wouldn't spend £5,000.00+ on a VRX system with amps. After all, Ferrari don't limit their cars to 70mph so that idiots don't kill themselves and Rolls Royce don't remove all the leather just in case an idiot spills his coffee.
I don't know about that. It was before my time. I just assumed that they would run all their amps at 1/4 power which would mean the amp is in a very comfortable place. The PA company I heard was doing this was SSE and their typical gigs at the time were arenas (10,000+ people in the UK).
Indeed, so when JB state 800/1600/3200 then the 800 is continuous.
So this is represented by JBLs 1600 in the above spec. Therefore for typical program (a rock band), I need to drive the speakers with 1600W correct?
And this number is therefore 3200.
So in that case, how do these three numbers relate to my amp spec?
FTC 8 Ohms per channel (20-20kHz, 0.033% THD) 725W
FTC 4 Ohms per channel (20-20kHz, 0.033% THD) 1100W
EIA 1kHz @ 1% THD 8 Ohms per channel 800W
EIA 1kHz @ 1% THD 4 Ohms per channel 1300W
EIA 1kHz @ 1% THD 2 Ohms per channel 1850W
I read the FTC figures to be the real world performance of the amp (in other words, program) and the EIA figures to be not so real world (in other words peak).
Basically, I'm readying the JBL spec like this:
1. They run at around 800W continuously / RMS / normal / safe.
2. They should be driven at 1600W because the difference between 800W and 1600W is where you should be at.
3. If you're an idiot and play cricket with your mics, chances are you will hit 3200W and still be safe, but really you shouldn't be an idiot.
Hence, I conclude, 725W into 8 Ohms with a speaker rated at 800/1600/3200 is not enough power to do the job properly? Am I reading this incorrectly?
The VRX system is similarly priced to the SRX system. In my world, idiots buy 'DJ Speakers' and drive them with Peavey amps, wondering why they blow their HF drivers. Therefore I'm a little lost as to why JBL feel the need to totally idiot proof their VRX boxes. The fact is, an idiot wouldn't spend £5,000.00+ on a VRX system with amps. After all, Ferrari don't limit their cars to 70mph so that idiots don't kill themselves and Rolls Royce don't remove all the leather just in case an idiot spills his coffee.
I don't know about that. It was before my time. I just assumed that they would run all their amps at 1/4 power which would mean the amp is in a very comfortable place. The PA company I heard was doing this was SSE and their typical gigs at the time were arenas (10,000+ people in the UK).
Re: JBL SRX / QSC PL236 underpowered?
That's exactly what I thought too. However, I know that the band have never touched the crossover after it was configured by the store that sold them the system. I then thought maybe they connected the subs amp to the tops and that went a little awry, but the damage is in the HF driver and the tops have a passive crossover which would have protected the HF component. Remember, the amp is rated 725W into 8 Ohms or 1100W into 4 Ohms. Whichever way they connected it, I don't see how they could have pumped enough power into the box to cause driver excursion.
No, this damage was caused by wannabe sound engineers and / or musicians. In all seriousness, I'm thinking it's more likely the compression driver was faulty from new and driving it hard tipped it over the edge.
So we've gone from "bi-amp your subs for more power" to "get more tops because they can't keep up with your subs"? Crikey.... I can't keep up!
I will be checking the crossover settings next time I have the rig set up though.
That's exactly what I thought too. However, I know that the band have never touched the crossover after it was configured by the store that sold them the system. I then thought maybe they connected the subs amp to the tops and that went a little awry, but the damage is in the HF driver and the tops have a passive crossover which would have protected the HF component. Remember, the amp is rated 725W into 8 Ohms or 1100W into 4 Ohms. Whichever way they connected it, I don't see how they could have pumped enough power into the box to cause driver excursion.
No, this damage was caused by wannabe sound engineers and / or musicians.
In all seriousness, I'm thinking it's more likely the compression driver was faulty from new and driving it hard tipped it over the edge.So we've gone from "bi-amp your subs for more power" to "get more tops because they can't keep up with your subs"? Crikey.... I can't keep up!
I will be checking the crossover settings next time I have the rig set up though.
Re: JBL SRX / QSC PL236 underpowered?
I know. It's good init?
Do you think this will cause the subs amp to clip at the same time as the tops amp with pink noise? As I previously mentioned, the subs amp never clips, unlike the tops amp. In terms of program, this is Genesis so I often have bass and bass pedals going at the same time. I would expect fairly heavy load on the subs!
This is entirely my purpose in posting here. I want to maximise the potential of this PA so that I have to hire in less.
Indeed.
Thanks very much for the in depth info.
I know. It's good init?
Do you think this will cause the subs amp to clip at the same time as the tops amp with pink noise? As I previously mentioned, the subs amp never clips, unlike the tops amp. In terms of program, this is Genesis so I often have bass and bass pedals going at the same time. I would expect fairly heavy load on the subs!
This is entirely my purpose in posting here. I want to maximise the potential of this PA so that I have to hire in less.
Indeed.
Thanks very much for the in depth info.
Re: JBL SRX / QSC PL236 underpowered?
I did exactly that several weeks ago. Thanks Rob.
I did exactly that several weeks ago. Thanks Rob.
Re: JBL SRX / QSC PL236 underpowered?
Two things to address, both based on the first part of the quote.
First, an amplifier with a larger current reserve will not inherently raise the noise floor of the system simply because it has more available current.
VOLTAGE GAIN will raise the level of whatever is presented to the input of the amp.
There is no "1/4 power." The amplifier is still capable of the same amount of output voltage and current. One can attenuate the input sensitivity, thereby requiring a bigger input signal to drive the amp to full output. The plus to this a reduction in the quiescent noise from devices upstream to the amp.
Two things to address, both based on the first part of the quote.
First, an amplifier with a larger current reserve will not inherently raise the noise floor of the system simply because it has more available current.
VOLTAGE GAIN will raise the level of whatever is presented to the input of the amp.
There is no "1/4 power." The amplifier is still capable of the same amount of output voltage and current. One can attenuate the input sensitivity, thereby requiring a bigger input signal to drive the amp to full output. The plus to this a reduction in the quiescent noise from devices upstream to the amp.
Re: JBL SRX / QSC PL236 underpowered?
The more complex stuff you discussed, I would agree with. However, as I've said before the band are just going to use the PA if it's capable and if not, hire a bigger PA. So regardless of calculations, that's what happens. They either have enough SPL and they turn it down to suit or they don't, in which case they hire.
The more complex stuff you discussed, I would agree with. However, as I've said before the band are just going to use the PA if it's capable and if not, hire a bigger PA. So regardless of calculations, that's what happens. They either have enough SPL and they turn it down to suit or they don't, in which case they hire.
Re: JBL SRX / QSC PL236 underpowered?
It's a numbers game. If you give a band twice the horse power they need for the gig, That is great! But if you give them less than what is needed, your going to see a lot of red lights!!!!!!! There comes a point when, as an engineer you need to stand up and say NO, you can't have any more.......If you are consistently acquiring gigs where you don't have enough RIG FOR THE GIG, then your going to have problems with equipment life and acquiring new gigs. If you at some point tell the band I only have this much, you can't have any more for this price, you may find a bit more mileage? The bigger the rig the bigger the price. At some point a band will realize that they are going to have to pay for the more part.
As far as the other questions asked above. You have to do the math. If you feel your under powered, you probably are. An 1100 watt amp for a speaker that will take 1600 watts for a decent period of time ( program power ) is probably under powered if you want top get near rated specs!!!!!!!! It's very simple. Do the math. I have X watts and a speaker capable of producing X DB with 1 watt of power. Every doubling of watts is equal to 3db of potential gain. You will come to a point where you can factor just how much SPL your able to create. If your speaker is 98db at 1 watt and your powering with an 1100 watt amp, you are going to be able to provide about 30db of gain, or 128db SPL at 1 meter from the speaker. That is at best and running the amp at full tilt. So if your going to have any kind of safety margin ( which most pro's factor 10db's for live audio ) your not going to have a lot of possible SPL. That is to say that with a 10db safety factor your actually only able to produce around 118db of usable SPL out of that speaker with another 10db in the tanks for the what if........... That 118db will only translate into around 88db at 50' from the stage in an outdoor setting. If you run closer to your amp max wattage you may be able to acquire another 10db? Indoors this changes a bit.
Being able to get your subs together and centralized can help get some better numbers. You gain 3db when you double the wattage, so placing one sub next to the other nets you another 3db. If you double again you gain another 3db etc. etc. Half space loading, which is what happens when you place the subs on the ground, should get you between 1 and 3db of more gain, but don't count on that. So you ask a second time if 1100 watts is enough? It is if it gets you the needed acoustic volume. If it doesn't, then no it's not enough.
As for bands using up whatever they are given, that is true. If you allow a band to run what you brung, they will. I Have no problem with saying NO................ At some point saying NO is important. If the band is paying for a PA that is only capable of a portion of what they want, that is what they are paying for. If they want to pay for more then that is great. In many cases it's not the band paying for it. So saying no, this is all I can do, can go a long way, if the band realizes that it may come back to them for the bad results. I find it helpful to find out what the client desires as a volume need. Loud rock venue volume, middle of the road private venue volume, or quiet background music volume. This can help you a lot in deciding the appropriate sized PA for the GIG. If the client wants rock venue volume, your looking at a PA capable of providing over 110db at the mix position ( even if it's needed or not ), for mid level it about 110-100db at mix position and for background you should shoot for something capable of at least 100db at mix position. This is a guideline for the bar/private party sound guy and does not apply to the large corporate/ rock show providers who will not be asking these questions. If you are a privately owned small sound company and can provide 110db at 50' or more from the stage, your in a good place and you are probably also not going to be asking these questions. If your a bar/ private party guy that is always wondering why you can't get what is needed, now you know....... You have to have equipment that is first capable of the numbers, then properly deploying it so you can back those numbers up. If you already are finding you need more, it's going to cost money to get more. Either double the wattage, or double the number of boxes used. If this is not a viable option in either case then you should be staying away from those types of gigs until you can.
In most cases there is a reality of what can be acquired. If you do shows that a lot of volume is needed you can generally get more by running less through the PA! I.E. a bar gig where you only run vocals through the PA. The speaker will get more volume for the vocals, than if you try and run everything through it. If you run guitar, drums, keys and everything else your going to eat up headroom. This means that in order to get one instrument over the top of all the others, is going to eat up even more headroom. If your only having to reproduce one thing you can allocate more wattage to it's reproduction. This means more volume. The lower number of frequencies you have to reproduce, the more energy you can reserve for reproduction. If your consistently running out of headroom, try simply mic'ing less instruments. This should open up some headroom for the instruments that really need more level to be heard. Next is to mix subs on an aux!!!!! If you can do this you will allocate a lot of energy robbing low end sound, away from the tops allowing for more headroom to whatever is needed. The subs will also gain more headroom, by only having to deal with frequencies that they are meant to reproduce. This is a nice trick to try if you have self powered subs!!!!
If you send full range signal to your self powered subs you probably find that you have to back the gains down because they start to distort, or the limiter kicks in. But if you run only run bass and kick to them ( via an auxiliary mix ) and even use a crossover before them ( to roll off even more high frequency content ), you should find that you can run the input trims higher and get even more level to those instruments! This can be acquired by doing the same thing for a conventional unpowered system with a x-over. Running the subs on an aux free's up headroom and can allow for more volume of the amplified instruments before clipping. This effect is also helped by the fact that you can tune each part of the system to be optimized for it's intended reproduction. Food for thought.
It's a numbers game. If you give a band twice the horse power they need for the gig, That is great! But if you give them less than what is needed, your going to see a lot of red lights!!!!!!! There comes a point when, as an engineer you need to stand up and say NO, you can't have any more.......If you are consistently acquiring gigs where you don't have enough RIG FOR THE GIG, then your going to have problems with equipment life and acquiring new gigs. If you at some point tell the band I only have this much, you can't have any more for this price, you may find a bit more mileage? The bigger the rig the bigger the price. At some point a band will realize that they are going to have to pay for the more part.
As far as the other questions asked above. You have to do the math. If you feel your under powered, you probably are. An 1100 watt amp for a speaker that will take 1600 watts for a decent period of time ( program power ) is probably under powered if you want top get near rated specs!!!!!!!! It's very simple. Do the math. I have X watts and a speaker capable of producing X DB with 1 watt of power. Every doubling of watts is equal to 3db of potential gain. You will come to a point where you can factor just how much SPL your able to create. If your speaker is 98db at 1 watt and your powering with an 1100 watt amp, you are going to be able to provide about 30db of gain, or 128db SPL at 1 meter from the speaker. That is at best and running the amp at full tilt. So if your going to have any kind of safety margin ( which most pro's factor 10db's for live audio ) your not going to have a lot of possible SPL. That is to say that with a 10db safety factor your actually only able to produce around 118db of usable SPL out of that speaker with another 10db in the tanks for the what if........... That 118db will only translate into around 88db at 50' from the stage in an outdoor setting. If you run closer to your amp max wattage you may be able to acquire another 10db? Indoors this changes a bit.
Being able to get your subs together and centralized can help get some better numbers. You gain 3db when you double the wattage, so placing one sub next to the other nets you another 3db. If you double again you gain another 3db etc. etc. Half space loading, which is what happens when you place the subs on the ground, should get you between 1 and 3db of more gain, but don't count on that. So you ask a second time if 1100 watts is enough? It is if it gets you the needed acoustic volume. If it doesn't, then no it's not enough.
As for bands using up whatever they are given, that is true. If you allow a band to run what you brung, they will. I Have no problem with saying NO................ At some point saying NO is important. If the band is paying for a PA that is only capable of a portion of what they want, that is what they are paying for. If they want to pay for more then that is great. In many cases it's not the band paying for it. So saying no, this is all I can do, can go a long way, if the band realizes that it may come back to them for the bad results. I find it helpful to find out what the client desires as a volume need. Loud rock venue volume, middle of the road private venue volume, or quiet background music volume. This can help you a lot in deciding the appropriate sized PA for the GIG. If the client wants rock venue volume, your looking at a PA capable of providing over 110db at the mix position ( even if it's needed or not ), for mid level it about 110-100db at mix position and for background you should shoot for something capable of at least 100db at mix position. This is a guideline for the bar/private party sound guy and does not apply to the large corporate/ rock show providers who will not be asking these questions. If you are a privately owned small sound company and can provide 110db at 50' or more from the stage, your in a good place and you are probably also not going to be asking these questions. If your a bar/ private party guy that is always wondering why you can't get what is needed, now you know....... You have to have equipment that is first capable of the numbers, then properly deploying it so you can back those numbers up. If you already are finding you need more, it's going to cost money to get more. Either double the wattage, or double the number of boxes used. If this is not a viable option in either case then you should be staying away from those types of gigs until you can.
In most cases there is a reality of what can be acquired. If you do shows that a lot of volume is needed you can generally get more by running less through the PA! I.E. a bar gig where you only run vocals through the PA. The speaker will get more volume for the vocals, than if you try and run everything through it. If you run guitar, drums, keys and everything else your going to eat up headroom. This means that in order to get one instrument over the top of all the others, is going to eat up even more headroom. If your only having to reproduce one thing you can allocate more wattage to it's reproduction. This means more volume. The lower number of frequencies you have to reproduce, the more energy you can reserve for reproduction. If your consistently running out of headroom, try simply mic'ing less instruments. This should open up some headroom for the instruments that really need more level to be heard. Next is to mix subs on an aux!!!!! If you can do this you will allocate a lot of energy robbing low end sound, away from the tops allowing for more headroom to whatever is needed. The subs will also gain more headroom, by only having to deal with frequencies that they are meant to reproduce. This is a nice trick to try if you have self powered subs!!!!
If you send full range signal to your self powered subs you probably find that you have to back the gains down because they start to distort, or the limiter kicks in. But if you run only run bass and kick to them ( via an auxiliary mix ) and even use a crossover before them ( to roll off even more high frequency content ), you should find that you can run the input trims higher and get even more level to those instruments! This can be acquired by doing the same thing for a conventional unpowered system with a x-over. Running the subs on an aux free's up headroom and can allow for more volume of the amplified instruments before clipping. This effect is also helped by the fact that you can tune each part of the system to be optimized for it's intended reproduction. Food for thought.
Re: JBL SRX / QSC PL236 underpowered?
As I've previously pointed out, the band own the PA. I'm their sound engineer. They do the gig with their PA or with one they hire in if their PA isn't big enough. All I'm trying to do is ascertain whether I'm getting the best out of the PA the band have currently, which will allow the band to hire a bigger PA less and save money.
I didn't think I was under powered. I've always done the gig properly, with the equipment at hand or hired in when I knew it wasn't going to be enough. In both cases, I've not had a problem. It was only when I started looking seriously at the spec of the amps and speakers that I began to wonder what was possible. At that point, I also began to question what the specs were actually telling me. Hence this thread popped up.
I don't see the maths as being important here. I know that's the right way to do it if you're being asked to spec a system for a certain application, but I'm not doing that. I will always use this system if it will do the job. I can't make the system any smaller or bigger. It is what it is, maths or no maths.
Hmmm... Having only got two tops and two subs, I run them one sub either side with the tops on poles. I don't really see how I could centralise the subs like that, so I've not considered it before.
Again, it's a moot point. The band will use whatever I decide. I'm the sound engineer and I'm running the PA.
Again, it's the bands PA. I'm a member of the band as the sound engineer. It's not a case of money or who gets paid what for what.
I'm none of these. I'm just a sound engineer that is confused by the way JBL have specified their numbers in the SRX manual and trying to get the best out of my amps because I'm not convinced the system is set up 'right' or the band will get the most out of it. In other words, all I'm really asking is, three fold:
1. If you had two JBL SRX718 speakers, how many subs would you run alongside them to consider the system 'correct' for rock type bands.
2. What power would you drive them with and how (mono bridged, stereo, what impedance?)?
3. Given the answers to the first two questions, how would you then use a couple of QSC PL236 amps as a best fit for those answers?
The 'application' that people have mentioned is purely; "to get the most out of the system without going daft, so that we can use the PA to its full ability and not hire a PA in as often."
I'm running the system bi-amped. That is, subs and tops. I have a dbx DriveRack PA on crossover duties. I wouldn't expect the subs to have to deal with full range. It's being done properly.
In the interest of spreading some understanding of the band and the type of gigs we are doing, here's the full collection of videos we have online. All were filmed on a Sony Z5E (go look it up - I'm not an amateur). The audio in all cases is straight into the camera mic (which probably costs more than most YouTube style cameras you normally see from amateur or semi-pro bands). So it's not exactly great, but it is more accurate than a lot of stuff out there.
Mama - UK 'all era' Genesis Tribute Band on Vimeo
I'm also running an X32 but I've yet to get chance to mix down one of the many multitrack recordings of a gig so that I can use superior audio for the videos. Shame that but I've just got too many wedding edits to complete professionally before I can dabble with the band videos. The videos are mostly of bigger gigs without our PA. The ones filmed at The Diamond are also not our PA. The most recent two are the JBLs, as are the early rehearsal videos. None of them are mixed on the X32. Hope you enjoy.
The band are performing at The Cavern in Liverpool tonight, so if I get chance, I'll grab some static video with X32 multitrack audio.
As I've previously pointed out, the band own the PA. I'm their sound engineer. They do the gig with their PA or with one they hire in if their PA isn't big enough. All I'm trying to do is ascertain whether I'm getting the best out of the PA the band have currently, which will allow the band to hire a bigger PA less and save money.
I didn't think I was under powered. I've always done the gig properly, with the equipment at hand or hired in when I knew it wasn't going to be enough. In both cases, I've not had a problem. It was only when I started looking seriously at the spec of the amps and speakers that I began to wonder what was possible. At that point, I also began to question what the specs were actually telling me. Hence this thread popped up.
I don't see the maths as being important here. I know that's the right way to do it if you're being asked to spec a system for a certain application, but I'm not doing that. I will always use this system if it will do the job. I can't make the system any smaller or bigger. It is what it is, maths or no maths.
Hmmm... Having only got two tops and two subs, I run them one sub either side with the tops on poles. I don't really see how I could centralise the subs like that, so I've not considered it before.
Again, it's a moot point. The band will use whatever I decide. I'm the sound engineer and I'm running the PA.
Again, it's the bands PA. I'm a member of the band as the sound engineer. It's not a case of money or who gets paid what for what.
I'm none of these. I'm just a sound engineer that is confused by the way JBL have specified their numbers in the SRX manual and trying to get the best out of my amps because I'm not convinced the system is set up 'right' or the band will get the most out of it. In other words, all I'm really asking is, three fold:
1. If you had two JBL SRX718 speakers, how many subs would you run alongside them to consider the system 'correct' for rock type bands.
2. What power would you drive them with and how (mono bridged, stereo, what impedance?)?
3. Given the answers to the first two questions, how would you then use a couple of QSC PL236 amps as a best fit for those answers?
The 'application' that people have mentioned is purely; "to get the most out of the system without going daft, so that we can use the PA to its full ability and not hire a PA in as often."
I'm running the system bi-amped. That is, subs and tops. I have a dbx DriveRack PA on crossover duties. I wouldn't expect the subs to have to deal with full range. It's being done properly.
In the interest of spreading some understanding of the band and the type of gigs we are doing, here's the full collection of videos we have online. All were filmed on a Sony Z5E (go look it up - I'm not an amateur). The audio in all cases is straight into the camera mic (which probably costs more than most YouTube style cameras you normally see from amateur or semi-pro bands). So it's not exactly great, but it is more accurate than a lot of stuff out there.
Mama - UK 'all era' Genesis Tribute Band on Vimeo
I'm also running an X32 but I've yet to get chance to mix down one of the many multitrack recordings of a gig so that I can use superior audio for the videos. Shame that but I've just got too many wedding edits to complete professionally before I can dabble with the band videos. The videos are mostly of bigger gigs without our PA. The ones filmed at The Diamond are also not our PA. The most recent two are the JBLs, as are the early rehearsal videos. None of them are mixed on the X32. Hope you enjoy.
The band are performing at The Cavern in Liverpool tonight, so if I get chance, I'll grab some static video with X32 multitrack audio.
Re: JBL SRX / QSC PL236 underpowered?
Hello Andrew, back to the math, maybe this will shed different light on the subject...
As a reference 800W is 10A and 80V into 8 ohms, this can be your continuous spec from JBL
Now for program, suggested is 1600W, which is 14A and 113V into 8 ohms, this equates to 1.414 x the 80V reference voltage, not much - SPLwize the +3db difference is barely noticiable to the average listener. So you are not really gaining anything here.
Peak wattage - which is defined as the max you should momentarially apply to the system is 3200W or 20A and 160V - not many amps can provide this for more than a few tens of milliseconds (thank goodness) This is 2X our 80V voltage and is +6db. You can hear this increase. But you can get the same +6db by coupling cabinets together (mostly low freq) if you drive them with the same power (current x voltage).. You can not run this power into the speakers except for milliseconds.
Most live program has a very wide dynamic range, +16db or more easily. it is difficult for a live PA system to amplifiy that range without compromises. Think about the +6db SPL gain you get with 4X the power, add the cost of amps and cost of power infrastructure to the equation, and thats why a PA is designed around the app. You could use the biggest amps you can find and most effecient speakers designed to handle all scenerios, but it will most likely cost you a lot.
Mike
Hello Andrew, back to the math, maybe this will shed different light on the subject...
As a reference 800W is 10A and 80V into 8 ohms, this can be your continuous spec from JBL
Now for program, suggested is 1600W, which is 14A and 113V into 8 ohms, this equates to 1.414 x the 80V reference voltage, not much - SPLwize the +3db difference is barely noticiable to the average listener. So you are not really gaining anything here.
Peak wattage - which is defined as the max you should momentarially apply to the system is 3200W or 20A and 160V - not many amps can provide this for more than a few tens of milliseconds (thank goodness) This is 2X our 80V voltage and is +6db. You can hear this increase. But you can get the same +6db by coupling cabinets together (mostly low freq) if you drive them with the same power (current x voltage).. You can not run this power into the speakers except for milliseconds.
Most live program has a very wide dynamic range, +16db or more easily. it is difficult for a live PA system to amplifiy that range without compromises. Think about the +6db SPL gain you get with 4X the power, add the cost of amps and cost of power infrastructure to the equation, and thats why a PA is designed around the app. You could use the biggest amps you can find and most effecient speakers designed to handle all scenerios, but it will most likely cost you a lot.
Mike