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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Leonardo Wood on March 31, 2014, 12:52:19 AM
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Greetings to all! I've never posted here before, but I have a sound problem that needs solving and didn't even consider posting elsewhere. I knew I'd get good responses here!
If there's such a thing as a good problem, then that's what I've got. I have an excessive amount of low-end capability---that is, relative to the FOH volume levels that we typically run at the church where I oversee sound. In short, we have a pair of JBL PRX615M powered speakers for FOH and two JBL STX828S subs. One sub is powered by a Crown XTi4002 (3,200 watts bridged) and the other by a Crest Pro8200 (4,500 watts bridged). For the time being, we set up each week in a school auditorium that seats around 800 or 900, and the acoustics are decent, but not great.
I'd like to be able to feel the bass (up front near the subs, not in the back...we're not aiming to be that loud). The only two sources that really drive the subs are kick drum and bass guitar. I DO NOT want either the kick or electric bass to overtake the mix at the expense of everything else, since I'm looking for balanced sound. I've considered acquiring 1/3 octave EQ's or perhaps parametric EQ's so that I can boost a narrow band of specific low frequencies for the kick and bass, with the hope of creating a palpable low frequency thump while keeping the overall (or apparent) volume of the overall mix at reasonable levels.
Am I on the right track, or is there a better way to put this subwoofer power to good use? Or, do I just have a lot more bass capacity than I can use?
Thanks in advance for your suggestions.
Leonardo
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Leonardo,
One option is to try feeding the subs from a post fader aux send. Mix your mains as you would normally; then, you can add whatever channels to the subs while keeping everything else out (by using the aux send). You can add thump to taste this way. This may fix your problem of them being out of balance with the mains, as you'll have separate control.
When you do this, pay careful attention to how things sound around your crossover point; you may find yourself needing to do some cuts around here if you are adding lots of sub, as you can somewhat easily change the acoustic crossover point...
Anyway, there are a lot of solutions to your problem, this is just one that I like... I'm sure others will chime in with a pile of other opinions. Certainly it is worth trying to see if you like it.
Cheers,
Nils
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By using these two amplifiers you are getting different output from both speakers.
XTI has a DSP unit in it, and will have some latency. Crest doesn't have this. Have you ever tried running both subs form one of these amps in stereo mode ? You will loose som power of course, but it may be much beter sounding.
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Greetings to all! I've never posted here before, but I have a sound problem that needs solving and didn't even consider posting elsewhere. I knew I'd get good responses here!
If there's such a thing as a good problem, then that's what I've got. I have an excessive amount of low-end capability---that is, relative to the FOH volume levels that we typically run at the church where I oversee sound. In short, we have a pair of JBL PRX615M powered speakers for FOH and two JBL STX828S subs. One sub is powered by a Crown XTi4002 (3,200 watts bridged) and the other by a Crest Pro8200 (4,500 watts bridged). For the time being, we set up each week in a school auditorium that seats around 800 or 900, and the acoustics are decent, but not great.
I'd like to be able to feel the bass (up front near the subs, not in the back...we're not aiming to be that loud). The only two sources that really drive the subs are kick drum and bass guitar. I DO NOT want either the kick or electric bass to overtake the mix at the expense of everything else, since I'm looking for balanced sound. I've considered acquiring 1/3 octave EQ's or perhaps parametric EQ's so that I can boost a narrow band of specific low frequencies for the kick and bass, with the hope of creating a palpable low frequency thump while keeping the overall (or apparent) volume of the overall mix at reasonable levels.
Am I on the right track, or is there a better way to put this subwoofer power to good use? Or, do I just have a lot more bass capacity than I can use?
Thanks in advance for your suggestions.
Leonardo
Welcome to PSW.
It's unclear to me what your problem is - what is happening now that is undesirable? Too many subs and/or too much power can be solved easily by moving the fader down slightly.
Reading between the lines, it seems that you are having trouble with low-frequency definition. There could be several components to this:
- Channel EQ - you may need to learn how to adjust the board channel EQ for more punch. A parametric EQ with variable frequency and Q is very helpful here.
- As mentioned, using aux or group-fed subs can help by only sending the items to the subs that need to be in the subs
- System alignment and/or placement. As Mark mentioned, you're running different gear on different sides. I agree that one amp with one sub per channel is probably better for you guys.
Graphic EQs are fairly useless. System issues should be solved in some kind of DSP with parametric EQ and delay alignment. Channel EQs should also be parametric for the most control. You may be wise to hire a local professional to come and help you do a system setup and run sound for one Sunday service. A small investment in some help from a pro will likely teach you a lot.
If you post your location, there may be someone here local to you that could help.
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By using these two amplifiers you are getting different output from both speakers.
XTI has a DSP unit in it, and will have some latency. Crest doesn't have this. Have you ever tried running both subs form one of these amps in stereo mode ? You will loose som power of course, but it may be much beter sounding.
Actually, no, I haven't tried running both subs on the Crest in stereo mode. In fact, I haven't even run one on the Crest! Let me explain...
We started out with just the Crown amp and one STX828, in addition to using a PRX618S (single 18" driver, self powered) that we had from an earlier purchase. Via an Architectural Acoustics signal processor, I sent one feed to the little sub at 0dB and a separate signal to the STX828 at -6dB, since this sub combination was so lopsided power-wise. I soon realized this was a really bad mismatch in terms of power and quality, and also for various acoustical reasons. (The PRX618 is not terrible on its own, but it's quite inferior to the STX828 when compared side by side.)
While waiting for the second STX828 to arrive---the one that has not even been used yet---I tried just the existing STX828 without the PRX sub, and I increased the feed from -6dB to 0dB. That's when I realized I was going to have a challenge harnessing the power of two of these things! With just the one and the 6dB input increase, the LF output was massive relative to everything else.
Standing close to the sub operating at that level, I'm sure a listener could feel the bass. But to make the overall mix useable, I'd have to bring up the top end by quite a bit, and that would be too loud for our purposes, which brings me back to my original dilemma.
Perhaps by selectively boosting some very low frequency from the kick or bass guitar (probably kick, I would think), I'd be able to get a powerful thump from the subs but without having to raise the higher frequencies too much. I've also thought about a sub-harmonic synthesizer. I've never used one, and I'm doubtful that such a thing is going to help. Another thing I've considered doing is using the Architectural Acoustics processor to cut everything below 50Hz. Our music doesn't have any significant content below that frequency anyway, and I believe that signals below 50Hz from the kick and bass guitar just add to the boominess. But there goes my idea of boosting very low frequencies!
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Going out on a limb... Sounds like this is an issue of improper (or incorrect) mixing technique. It's true you can have too much power, but I think that's only if you don't have the mix setup properly (either gain levels are too high, channel EQ not set appropriately, FOH EQ being used, etc...)
Also - depending on the size of the room and where you are standing when testing, you could be feeling a standing wave; which can skew your observations.
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+1 What Mark Rombouts said.
Can't say this is the only problem, it sure seems like contributing factor.
Secondly, driving subs from an aux bus is an excellent way to control your low end, try that too.
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What settings are you using for the crossover between the PRX615M mains and the subwoofers? Have you gone through the system gain structure? Where are the front panel input attenuators on the amps set? If you're using something like the VSX26 for the processing with the subwoofer output at 0 and +24dBu maximum level outputs then you might want something like 16dB to 19dB of attenuation at the amplifier inputs.
Have you considered how much low frequency sound may be coming from the bass amp and drums on stage? Might you need to control those levels in order to get the low frequency control and sound that you want?
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We started out with just the Crown amp and one STX828, in addition to using a PRX618S (single 18" driver, self powered) that we had from an earlier purchase. Via an Architectural Acoustics signal processor, I sent one feed to the little sub at 0dB and a separate signal to the STX828 at -6dB, since this sub combination was so lopsided power-wise.
While waiting for the second STX828 to arrive---the one that has not even been used yet---I tried just the existing STX828 without the PRX sub, and I increased the feed from -6dB to 0dB. That's when I realized I was going to have a challenge harnessing the power of two of these things! With just the one and the 6dB input increase, the LF output was massive relative to everything else.
Perhaps by selectively boosting some very low frequency from the kick or bass guitar (probably kick, I would think), I'd be able to get a powerful thump from the subs but without having to raise the higher frequencies too much. I've also thought about a sub-harmonic synthesizer. I've never used one, and I'm doubtful that such a thing is going to help. Another thing I've considered doing is using the Architectural Acoustics processor to cut everything below 50Hz. Our music doesn't have any significant content below that frequency anyway, and I believe that signals below 50Hz from the kick and bass guitar just add to the boominess. But there goes my idea of boosting very low frequencies!
Couple things come to mind. As soon as you as say Architectural Acoustics processor, I have to wonder if you have the skills to set this up. I don't mean to be condescending but it's like those rich folks who buy exotic cars that have lots of power and promptly wreck them (e.g. Paul Cares, who totaled a Lambo LP640 five miles from where I live, racing a Toyota pickup), vs. those who buy them and learn how to drive them really fast (e.g. folks like the late Paul Newman). You can dig yourself quite the hole with a powerful DSP unit, or make a beautiful sounding rig...
So: I am wondering if you are running proper crossover points, and the reason it's so boomy is because the crossover is too high. If it is, when you turn up the sub, you get all this mid bass mud/boom from other instruments mucking things up. It should be 80Hz, no higher. The high pass (cutting everything below some frequency) should be based on the limits of the speaker, and not anything like 50 Hz -- you need more like 40 Hz to get a decent kick sound anyway. The sub's manufacturer recommended high pass is 30Hz -- use that.
Ed Walters
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Greetings to all! I've never posted here before, but I have a sound problem that needs solving and didn't even consider posting elsewhere. I knew I'd get good responses here!
If there's such a thing as a good problem, then that's what I've got. I have an excessive amount of low-end capability---that is, relative to the FOH volume levels that we typically run at the church where I oversee sound. In short, we have a pair of JBL PRX615M powered speakers for FOH and two JBL STX828S subs. One sub is powered by a Crown XTi4002 (3,200 watts bridged) and the other by a Crest Pro8200 (4,500 watts bridged). For the time being, we set up each week in a school auditorium that seats around 800 or 900, and the acoustics are decent, but not great.
I'd like to be able to feel the bass (up front near the subs, not in the back...we're not aiming to be that loud). The only two sources that really drive the subs are kick drum and bass guitar. I DO NOT want either the kick or electric bass to overtake the mix at the expense of everything else, since I'm looking for balanced sound. I've considered acquiring 1/3 octave EQ's or perhaps parametric EQ's so that I can boost a narrow band of specific low frequencies for the kick and bass, with the hope of creating a palpable low frequency thump while keeping the overall (or apparent) volume of the overall mix at reasonable levels.
Am I on the right track, or is there a better way to put this subwoofer power to good use? Or, do I just have a lot more bass capacity than I can use?
Thanks in advance for your suggestions.
Leonardo
Leonardo - as mentioned previously, let us know where you are. Maybe someone on the forum is close to you and can stop by to give you some support.
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Thanks for all the responses so far.
Regarding the crossover point, I'm using a VSX26 to set the sub's high pass at 30Hz (Linkwitz-Riley 36dB/octave) and the crossover point between the STX828S and the PRX615M is set at 80Hz (Linkwitz-Riley 24dB/oct).
I used the VSX26's RTA function to flatten the system's response in the auditorium we use, with additional reductions around 2-4kHz because the PRX615's sound a bit harsh in the upper mids.
I think it would be helpful to clarify this point: Up to this point I have not had issues with too much bass or boomy bass. In fact, the system sounds pretty good as is. The bottom end just doesn't sound as authoritative as I'd prefer. I'm just trying to figure out if it's possible to boost some portion of the bass so it can be felt as well as heard but without the bass being overwhelming to the point of sounding obnoxious. I think the next thing I'm going to try is giving the kick drum a generous boost at various frequencies between 40Hz and 60 or 70 Hz and see if a band of frequencies somewhere in that range doesn't create the authoritative low-end sound/feel that I am looking for without ruining the balance of the overall mix. If what I'm looking for isn't possible without also increasing the FOH to the point that it becomes uncomfortable for the average listener, then it looks like we may have made a mistake buying an additional STX828. I hope that's not the case, though.
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It sounds like you need to restructure your board to work with an aux fed sub as TJ suggested. If you want more kick from your kick drum, give it more presence in your mix. Alternately, you may need to actually dial things *back* as they may be covering up some of the low frequency punch you're looking for.
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I believe I have one aux send that's not being used. I think I'm going to try running the subs on an aux feed. That's not the complete solution, but I think it's a move in the right direction.
Not to stray off-topic, but Mark Rombouts made a comment that got me thinking. He pointed out that the two subs are being powered by amps with different power ratings; and the Crown XTi4002 has latency due to it's built-in DSP, whereas the Crest Pro8200 is completely analog with no latency.
Even though I am not using any of the Crown's DSP to process the signal, there is still a latency of 1.11 ms, because the signal is still being sampled and converted. I can use the VSX26 to correct that by delaying the signal going to the Crest amp, so that both amps will receive signals with the same amount of delay. But suppose I didn't. Would a difference of 1.11 ms between the two subs make an audible difference (with the subs positioned side-by-side)? The power difference between the two amplifiers (3200W vs 4500W) is only 1.5dB. Would a difference that small be problematic?
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I wager that the difference between power output of your amps will be a bigger "problem" than dialing out 1ms of latency.
The good thing about being afforded a good amount of time beforehand is that you can test multiple scenarios to see which works best, and they're all reversible. Try running both subs off one amp in stereo, try adding in a delay to the crest amp, try adjusting the attenuation of the more powerful amp to "match" the weaker one.
Just be sure to make one change at a time. Much like any other form of troubleshooting, doing every fix all at once can cause more problems than solutions and still leave you with your original underlying issue.
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I think having one amp more powerfully that the other isn't a big problem. Actually the weaker amp may even be putting out more power than the "stronger" one if it has a higher gain. Start by matching the gain of the amps. That way, they will all be putting out the same power for any given input until you clip the weaker amp.
Conrad
www.kooleventug.com
Sent from my iPhone using Tapatalk
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Really sounds like it's just a mix issue, rather than a signal flow or a hardware issue. Perhaps you should consider hooking up an RTA to help mix in your space. That way you can more easily analyze which frequencies in the bass range are being driven to overpower the mix. Often, the bass can feel like it is overpowering simply because whatever instrument is throwing out bass frequencies hits a note that resonates extra loud (the room's resonant frequency). I have to almost completely cut around 125 Hz out of my bassist, because whenever he hits a B, the walls start to crumble a little bit ;).
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I believe I have one aux send that's not being used. I think I'm going to try running the subs on an aux feed. That's not the complete solution, but I think it's a move in the right direction.
Not to stray off-topic, but Mark Rombouts made a comment that got me thinking. He pointed out that the two subs are being powered by amps with different power ratings; and the Crown XTi4002 has latency due to it's built-in DSP, whereas the Crest Pro8200 is completely analog with no latency.
Even though I am not using any of the Crown's DSP to process the signal, there is still a latency of 1.11 ms, because the signal is still being sampled and converted. I can use the VSX26 to correct that by delaying the signal going to the Crest amp, so that both amps will receive signals with the same amount of delay. But suppose I didn't. Would a difference of 1.11 ms between the two subs make an audible difference (with the subs positioned side-by-side)? The power difference between the two amplifiers (3200W vs 4500W) is only 1.5dB. Would a difference that small be problematic?
That 1.11ms of latency will definitely cause you to lose definition from your subs. You can possibly compensate for that delay with your signal processor.
Just my 2 cents, but I sometimes will put a high pass on the bass around 80hz, to help clean things up. This might also give you better definition between the kick and bass.
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That 1.11ms of latency will definitely cause you to lose definition from your subs. You can possibly compensate for that delay with your signal processor.
Just my 2 cents, but I sometimes will put a high pass on the bass around 80hz, to help clean things up. This might also give you better definition between the kick and bass.
You like cutting off the whole bottom octave of the bass??
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I believe I have one aux send that's not being used. I think I'm going to try running the subs on an aux feed. That's not the complete solution, but I think it's a move in the right direction.
Not to stray off-topic, but Mark Rombouts made a comment that got me thinking. He pointed out that the two subs are being powered by amps with different power ratings; and the Crown XTi4002 has latency due to it's built-in DSP, whereas the Crest Pro8200 is completely analog with no latency.
Even though I am not using any of the Crown's DSP to process the signal, there is still a latency of 1.11 ms, because the signal is still being sampled and converted. I can use the VSX26 to correct that by delaying the signal going to the Crest amp, so that both amps will receive signals with the same amount of delay. But suppose I didn't. Would a difference of 1.11 ms between the two subs make an audible difference (with the subs positioned side-by-side)? The power difference between the two amplifiers (3200W vs 4500W) is only 1.5dB. Would a difference that small be problematic?
Seriously - get rid of the second amp. It's not helping you AT ALL, and if the subs are right next to you, the processing delay will goof things up. If the subs are on opposite sides of your room, the 1.1ms isn't a problem, but you are just making your life more difficult - more stuff to set up, more interactions.
As Conrad said, max power capability difference isn't the issue, but rather sensitivity and gain - one sub is probably running louder than the other.
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Greetings to all! I've never posted here before, but I have a sound problem that needs solving and didn't even consider posting elsewhere. I knew I'd get good responses here!
If there's such a thing as a good problem, then that's what I've got. I have an excessive amount of low-end capability---that is, relative to the FOH volume levels that we typically run at the church where I oversee sound. In short, we have a pair of JBL PRX615M powered speakers for FOH and two JBL STX828S subs. One sub is powered by a Crown XTi4002 (3,200 watts bridged) and the other by a Crest Pro8200 (4,500 watts bridged). For the time being, we set up each week in a school auditorium that seats around 800 or 900, and the acoustics are decent, but not great.
I'd like to be able to feel the bass (up front near the subs, not in the back...we're not aiming to be that loud). The only two sources that really drive the subs are kick drum and bass guitar. I DO NOT want either the kick or electric bass to overtake the mix at the expense of everything else, since I'm looking for balanced sound. I've considered acquiring 1/3 octave EQ's or perhaps parametric EQ's so that I can boost a narrow band of specific low frequencies for the kick and bass, with the hope of creating a palpable low frequency thump while keeping the overall (or apparent) volume of the overall mix at reasonable levels.
Am I on the right track, or is there a better way to put this subwoofer power to good use? Or, do I just have a lot more bass capacity than I can use?
Thanks in advance for your suggestions.
Leonardo
If you have two amps and two subs I would suggest trying them in a cardioid setup.
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That seems like a solution to a problem that doesn't exist.
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That 1.11ms of latency will definitely cause you to lose definition from your subs. You can possibly compensate for that delay with your signal processor.
Just my 2 cents, but I sometimes will put a high pass on the bass around 80hz, to help clean things up. This might also give you better definition between the kick and bass.
uhhh… No. 1.11ms of latency will have zero audible effect on the combining through the crossover of a sub. Assuming the sub goes up to 100Hz, the shortest wavelength it reproduces is about 10 feet long. That is about 10ms long. The part of the waveform where summation is always positive is the middle half, or 5', or 5ms of the wave. 1.11ms is not enough time error to be noticed. It could be compensated for by moving the subs 1' downstage.
Mac
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That 1.11ms of latency will definitely cause you to lose definition from your subs. You can possibly compensate for that delay with your signal processor.
Being off 1 ms in the subwoofer range is 1/20-1/10 of a wavelength. Yes, it will have an effect, not nearly as much as other issues with rooms reflections, relative sub/top positioning,...
Edit: should have completed reading the thread and read Mac's post before I said the same thing.
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Thanks for the insight.
The subs are not separated. They're on the main floor, centered directly in front of the stage, one stacked on top of the other. I can add delay with the VSX26 to get both subs in phase, to correct for the Crown's DSP latency. That'll require two different sends to the subs instead of one, but that's what we were doing all along before getting rid of the the little PRX powered sub.
So far, however, I haven't powered the subs with two different amps. Just to see what it sounded like, I used the Crest Pro8200 in stereo mode to run both subs last Sunday. I know that two STX828S subs are really underpowered using that amp for both, but I was curious to hear what it was capable of, since several people have suggested ditching the Crown.
Underpowered as that setup may be, it was more than adequate for our needs. (The music runs a little loud at my church, but we're not loud like an all-out rock concert!) I ran a few different low freq. test signals through the subs and was surprised at how noticeable the difference was between the Crown XTi4002 (from previous tests) and the Crest Pro8200. Specifically, when I muted the signal, the sound stopped noticeably faster, as if the room were a little less reverberant. That's what I was hoping for, to tighten up the bass. Next week I plan to use both amps and A/B the subs to see if the tighter bass response is as pronounced as it I think it is.