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JBL PRX future expansion


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I'm looking to start a conversation on how the JBL PRX line can be expanded upon for larger gigs. Our current system (pair of 612's over a pair 618XLF, one stack per side) is perfect for a majority of the gigs we have. This summer seems to be the year of outdoor gigs. The system performs ok outside, but I've noticed a tendency to push the speakers into limiting (which I get very vocal about when I'm not running the board).

 

Since I've made my bed with the PRX line, I'd like to get some advice on how it can be expanded upon for larger gigs. Moving up to another line of speakers (STX) for example, is out of the cards. I can't foresee having to provide PA for more than a couple hundred. My focus would be on renting speakers for these larger gigs, and then moving up to purchase as budget permits.

 

The first and most obvious choice is to add more subs. Noted and on the list. We've also center clustered the subs. I'd like to direct the conversation more to improving the mid/high range, and how to achieve more throw/depth.

 

I can think of a couple of options:

 

- Increase the PRX612 / 712 to two per side. Concern with this is because of the 90 degree dispersion, it would cause loss/comb filtering

 

- Increase PRX612 / 712 to two per side, but run in a dual PA fashion (for example, instruments in one speaker per side, vocals in the other). My understanding is that this method would reduce comb filtering / loss because the speakers are reproducing different signals, hence not stepping on each other. It may provide more throw because more energy can be directed in each speaker to the specifics sounds sent to them, rather than the whole mix.

 

- Add additional PRX612 /712, but position them in the crowd or at FOH and run them with delay. My mixing board (X32 Compact) allows delay processing. Main downside as I understand it is the additional power/signal cabling and runs.

 

- Choose another speaker from the PRX line to use for FOH, such as the PRX635/735. The ideal is to have as few speakers reproducing the same sounds as possible, but would the 635/735 provide more throw as a 3 way box?

 

Thank you in advance for your suggestions.

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Splay your cabs and think about coverage and overlap. If you have a vox and a guitar in the same bandwidth does is matter if they come out of separate cabs next to each other? Isnt comb filtering a result of identical frequencies no matter if its guitar, vox, drums etc?

I dont see how running a vox out of one box and instruments on the other box next to it will cure comb filtering?

If you get identical boxes you can scale down or up and have more options with your setup(s).

If im wrong on the comb filtering thing someone correct me plz.

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Comb filtering is the result of identical signal (including any bleed) eminating from multiple speaker sources that are not time coherent to the same acoustic center. It's made worse where ther frequency response at the fringes of the pattern vary wildly as the comb filter effect will have additional peaks and valleys due to the ragged pattern.

 

Most of today's horns are quite forgiving of comb filtering as the off axis response is more even. The horns and cabinets in general are also smaller so the time offset is smaller. This is something that we had to worry about more in the good 'ol days where exponential/radial horn flairs were used (better efficiency but at the cost of off axis uniformity) along with large horn mouths.

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Thanks for the responses. The Dual PA idea comes originally from the Grateful Dead's Wall of Sound, and was, as I understand, resurrected by Dave Rat. A google search for Dual PA will explain the concept much better than I can here.

 

Age, thank you for the suggestion. It is very easy to take what is written on internet forums as truth, especially when there seems to be a consensus. But then, the consensus could be result of repeating what was written rather than true live experience. There can be a lot of conflicting information.

 

I'm glad that doubling up a good option, as it's the easiest solution.

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Hey Vort Running a dual system doesn't necessarily get you any more level. It is done for clarity. Think about it. With any source ( let's say a guitar) hitting full on one speaker it would only be hitting half if the signal was split to two identical speakers.

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Thanks for the clarification on the dual PA scenario. You established that doubling up would not be the doomsday scenario most people state it would. How would doubling up on PRX612's compare to setting up delays? What would be the tradeoffs (from a sound point of view) between these two methods?

 

Thanks again for helping me to understand and get a little more from my PRX system.

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Delays involve, well, a delayed signal to bring the delayed speakers back into relative time alignment with the speakers closest to the stage. There is considerably more effort required, more cabling, and the speakers need to be more or less in line with the main speakers for best (or at least believable) effect.

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With a conventional system that's generally the best way to minimize he comb filtering effect, at least in the horizontal plane (which is usually the most important). With a dual system it probably won't make a difference one way or the other since the sound will be different from each cabinet.

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