Hello and some live PA setup questions

[RossvanWyk]

Hi all

I'm a live sound engineer from South Africa. I do a lot of theatre/musical work as well as a lot of corporate work. Lately, I have been doing quite a bit with a local band and a few international tours and would like to learn more about PA system setups and getting the most out of a DSP.

My first question relates to a DSP being used in conjunction with an installed PA. In the venue in question, they have got a Beta 3 C2402 DSP. The PA is an HK Audio PA, 2 x IL 15.2 over 1 x IL 218 sub per side and a Beta 3 15" box as a C cluster.

The IL 15.2's consist of a 15" inch driver and a horn. The PA is hung such that the boxes are hung one below the other, on each side of the stage. The top box firing towards the back of the room, the bottom box a little steeper. Now, my question is this, sending from the main console, L and R goes into the DSP, of which it then has 6 outputs : Low L and R, Mid L and R, High L and R. I feel like it's a stupid question, but surely I would only use the Low output for subs and then the High L and R to go to all 4 boxes? I can't figure out how to incorporate the Mid L and R output, as it is essentially a L C R system, the tops not being a Mid/High combination firing at the same area. I hope this makes sense? Please if someone could clarify that for me I would be so grateful.

Secondly, I have a question about the sub placement in the room. Currently the subs are on either side of the stage, essentially in the corner of the room, a little behind the main PA, but further to the outside. I've noticed that where the mixing console is, is the sweet spot for the low end but there are considerable dead spots throughout the room, the only real other bright spots are to be found on the outsides once you approach the subs themselves.

There is obvious cancellation going on, my question would be, what would a better alternative be in terms of placement? Would it be better for them to be center, coupled side by side? They would then be a little in front of the PA, as the stage is solid and I can't tuck the subs underneath.

Sorry for the lengthy post but hoping for a little insight as to a better set up for the PA.

Thanks in advance.

Ross

[albee1952]

Posting a photo of the stage and speakers might help
Re the DSP, I assume this is a digital crossover? You have left and right speakers so the 3 outputs of the crossover(aka "system controller") would go:
low L/R to the subwoofer amps
mid L/R to the amps powering the 15" speakers
hi L/R to the amps powering the horn drivers.

Re subwoofer placement; sticking them in the corners will increase efficiency, BUT with 2 boxes, split left and right, there will be "power alley" up the middle and the response off-center will vary all over the room. Coverage would be best with the 2 subwoofers placed close together and in the center Also, with the subs BEHIND the mid/hi speakers, the mid/hi speakers should be delayed to align with the subs. If the subs were in front of the mains, then the subs would need to be delayed.

[RossvanWyk]

Hi Albee

Thanks for the response.

Sorry, I should have been more clear. So the amps are powering subs, bottom set of tops, top set of tops. There is no amp that powers the 15" driver separate to the horn. So the top PA consists of two 15" speakers with a horn, the top speakers L and R pointing to back of room, the set of speakers hanging just below them firing a little steeper to catch the front etc. So, what I am trying to understand regarding the DSP is, do I just set the Mid L and R setting the same as the High L and R, because I do not want those bottom hung speakers pushing out mid range, as it doesnt make sense, it's firing to a different area, it needs to push the same freq range and the top set. Otherwise, I can just run out of High L into amp powering top set, and link L and R on the amp, and the same from High R, into amp powering bottom set, and link L and R.

I hope that makes sense. I would totally understand if I had separate signal to the 15" driver and the horn but I don't. It's 2 different sets of speakers firing at different areas of the room, they both need to push Highs really.

Thanks again.

Ross

[albee1952]

I'd need to know exact models of speakers, processor and amps to offer the best advice. Traditionally, a 3-way crossover feeds 3 separate sections (woofers, mids, horns) but it sounds like your top boxes(with the 15 and horn) are passive, so you should see if the processor offers a 2-way mode so you can feed the subwoofers properly(like from 90Hz, down) and the top boxes(from 90Hz, all the way up to 20KHz).

[RossvanWyk]

Hi Albee

Sorry for the late reply, have been traveling for work.

The PA is made up of IL 15.2, HK Audio.
2 of these per side, one on top of the other, hung.
The bottom box slightly angled lower to cover the front area.

The processor is the Beta 3 C2402.

All I am trying to understand better is how to utilise the Mid output from the DPS. It doesn't make any sense to me. Reason being, each of the tops should be pushing out the same range, as they are essentially firing to different areas of the room. It makes no sense to run the bottom 2 hanging tops from the Mid L and R with a respective EQ over it, as those boxes are NOT acting as the midrange. They should be full range, same as the top hanging boxes. So, should I run the bottom hanging boxes out of Mid L and R and set the X-over and EQ the same as the top boxes which run out of High L and R. Or should I rather just run out of High L and R and link the amps which run the 2 sets of tops?

Thanks

Ross

[albee1952]

So it looks like the top boxes are passive. so the system processor should be configured for stereo two-way. In truth, there are a few ways to deal with this. Refer to the manual for the C2402 and look to see if it allows this, or see if the crossover points can move either way up(to 20KHz) or way down(to 20 Hz). That would allow you to configure it as a 3-way, where you would only use the mid-high outs, or the low-mid outs. I would start with the subs crossed over around 80Hz(top boxes would get 80Hz and up).

Option 1: since you only need 2 ways from the C2402, if it can't be set as above, is it possible to set crossover frequencies so the the mid output is simply not used? IOW, the low out would be crossed over at 80Hz, the high out would run from 80Hz and up, with the mid out not used(in any case, you only need 2 way for the speakers you have). Its seems a bit like the system designer may have not chosen the best combination of gear

Variation: If you have other means of tuning the top boxes(like some third-octave EQ's at or in the console), you could feed L&R directly to the amp channels powering the top boxes. Then use an AUX send off the console feeding an input of the C2402 and set a single output for a sub out(to the amp and subs). Using an AUX send to feed subs is quite common

If none of this helps, its time to call in some professional help from a local audio expert