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Author Topic: Too much power, too many subs?  (Read 12964 times)

Leonardo Wood

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Re: Too much power, too many subs?
« Reply #10 on: April 01, 2014, 11:20:44 AM »

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.
« Last Edit: April 01, 2014, 11:27:23 AM by Leonardo Wood »
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Taylor Hall

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Re: Too much power, too many subs?
« Reply #11 on: April 01, 2014, 11:55:53 AM »

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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Leonardo Wood

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Re: Too much power, too many subs?
« Reply #12 on: April 01, 2014, 12:55:41 PM »

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?
« Last Edit: April 01, 2014, 01:01:45 PM by Leonardo Wood »
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Taylor Hall

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Re: Too much power, too many subs?
« Reply #13 on: April 01, 2014, 02:07:44 PM »

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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Conrad Muzoora

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Re: Too much power, too many subs?
« Reply #14 on: April 08, 2014, 04:19:51 AM »

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.
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TJ (Tom) McDonald

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Re: Too much power, too many subs?
« Reply #15 on: April 08, 2014, 09:26:35 AM »

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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Bryan Flick

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Re: Too much power, too many subs?
« Reply #16 on: April 08, 2014, 09:41:56 AM »

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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TJ (Tom) Cornish

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Re: Too much power, too many subs?
« Reply #17 on: April 08, 2014, 10:22:41 AM »

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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TJ (Tom) Cornish

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Re: Too much power, too many subs?
« Reply #18 on: April 08, 2014, 10:25:35 AM »

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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Travis.Riddle

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Re: Too much power, too many subs?
« Reply #19 on: April 08, 2014, 11:51:01 AM »

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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Re: Too much power, too many subs?
« Reply #19 on: April 08, 2014, 11:51:01 AM »


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