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  #1 (permalink)  
Old Tuesday, April 21st, 2009, 01:11 PM
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Red face Help positioning JBL VRX Speakers in our church.

Hi. I was assigned to install the new audio equipment in our church.
The FOH consist of the following:
  • 2 arrays: 4 JBL VRX928 and 2 VRX915 subs per array
  • 4 Crowns XTi 6000
  • dbx PA DriveRack
  • Mackie TT24 w/Digital Snake
The equipment will be arriving in the next 2 weeks and I'm getting a real headache figuring out where to place the speakers in the right spot. I tried to get some 3d simulation software but i haven't found one in my budget. I used the Yamaha YS3 to get some idea trying to match speaker specs to the VRX.

The church specs are:
  • Area 80' x 80'
  • Ceiling: 28' height
  • Stage: 34' wide x 20' deep centered at front side inside the 80' x 80' area.
  • Second floor mezzanine: 80' wide x 20' deep at 9' above the first floor and inside the 80' X 80' area.
I will appreciate any help that i can get. Thanks in advance.
Blessings!
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Old Tuesday, April 21st, 2009, 02:46 PM
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I would contact JBL directly. Many times they will do an analysis for you for free. I know I have EAW and they have a software that I used for speaker placement. Hope this helps.
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Old Tuesday, April 21st, 2009, 03:29 PM
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http://jblpro.com/products/portables...rraytool2.html

This is pretty basic, but it is a 2d tool for the VRX series...
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Old Tuesday, April 21st, 2009, 03:40 PM
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Not to touch on a potentially sore subject, but it would be more typical to perform any modeling and identify the speaker locations prior to selecting and ordering the equipment. Since you already have the equipment the exercise instead seems to be trying to do the best you can with what you have. This can potentially become more a matter of putting the speakers where practical and then adjusting the aiming in the field to optimize the results.

I agree with the suggestion to see if JBL or the party that sold you the speakers can help you and there is a VRX928 'array calculator' on JBL's site, although like most array calculators it looks only at the vertical aspect and does not address the horizontal coverage. You effectively have two high output, nominal 90x60 (I know JBL says 100 degrees horizontal, but the product data actually shows it to be more like 90 degrees) speakers and thinking of it that way may simplify it.

There can often be significant differences between where it would be theoretically best to locate the arrays and where it is practical to locate them and were to actually locate the speakers typically includes considering a number of other factors. Physical conditions such as structural members to hang from, avoiding interference for sightlines/projectors/lights and so on may prohibit or define potential locations. Whether the seating wraps around the stage, whether the balcony is routinely filled, how the actual seating sections are arranged, whether the system is mono or stereo, where the mics are on stage, whether you plan to fly or ground stack the speakers and/or subs and so forth can also be important factors. I find that it is usually best when discussing speaker locations for an existing space to first identify any such relevant issues. Pictures of the space can often help tremendously, but any additional information you can provide on any potential limitations or options would certainly help people offer more effective recommendations.

As I understand what you posted, the room from front to back is 20' of stage, 40' of flat main floor and then 20' of Mezzanine (flat floor?). Side-to-side it is 23' of space (seating?) then 34' of stage and then another 23' of space across the stage area, 80' of seating across the main floor space and an 80' wide balcony with the floor 9' above the main floor. The ceiling is 28' above the main floor and is apparently a flat ceiling with the same height everywhere. If this is true, then some of the above issues, such as what happens off to either side of the stage, whether the system is mono or stereo and any potential interferences, could impact the preferred speaker locations.

And of course, I have to mention the general comment that flying speakers or any devices overhead should be only be attempted by properly trained and experienced parties using appropriate hardware with attachment to structure that has been verified can support the loads involved.
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Old Tuesday, April 21st, 2009, 03:57 PM
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also - i don't know if it's possible to change anything at this point, but the Driverack PA probably isn't the best processor for this system. I wouldn't do anything less than a 260 for this...
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Old Tuesday, April 21st, 2009, 04:46 PM
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Well, I tried the JBL's array tool but I'm more concerned about the horizontal coverage. I don't get to cover all the needed areas without affecting the vertical.

I made a drawing of the top view. I read the blueprints a couple of hours ago and i made an scaled drawing based on the blueprints. Hope this help to a better understanding.

This is the drawing (PDF):
phaserkb.com/misc/topview.pdf


The seats on the center are flat, also the ceiling.
The left, right and mezzanine seats are kinda bleachers.
(I don't like this structure either )

At this moment i can't change the order, just pray to get a nice sound with what I'm about to receive and yes, we have the trained personnel to do the installation. We are also contacting a structural (civil) engineer to verify and certify all the work, following the insurance company policies.

Thanks for your fast response guys.

God Bless U!
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Old Tuesday, April 21st, 2009, 06:00 PM
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ok, I think I'm caught up on everything. I'll just ditto what Brad has said already and go from there.

First, if you have professionals that are coming in to install everything; do they not have someone on staff that can help you figure out where the best place is to hang the arrays? Like Brad said, there is the theoretically best and then the realistic best...

Just a rough, shoot from the hip, estimate (and without any plotting); From your dimensions and pictures I would hang the arrays about 1/4 of the way in on each side of the stage with maximum vertical splay allowed that won't allow holes in the vertical plane.

And with that I need to take a brief time out, also known as pulling a Cory to cook the dinner.
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Old Tuesday, April 21st, 2009, 06:27 PM
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I did a rough plot in illustrator(the only thing i have to work with here at home) and I agree with Les' shot from the hip. - 1/4 of the way in on each side, 1/3 back from the front of the stage at about a 5 degree down angle. I'm sure someone will chime in later with a better plot, but based on my rough one, it looks like you have two options... Hang them straight forward in stereo, and you'll have some dead spots in the front of your right and left sections - or go mono and splay them out to the right and left 30 degrees or so to get more uniform coverage and you'll probably have some comb filtering down the center.


I'm curious how you got this far without figuring this out. Hopefully someone else will have a little better plot that gives better results. Don't get me wrong - I like the VRX speakers - we have them at our church, but based on my quick look, i don't think they're right for the room.
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Old Tuesday, April 21st, 2009, 07:51 PM
Les Les is offline
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Ok, I'm back...

Thanks for the model Pat and "confirming" my shoot from the hip

I would caution the 1/3 of the way back (If I am understanding you) as that would put them over the stage and in serious danger of feedback for anyone downstage. I wold place them on the downstage edge and aim it to cover the balcony and as much from the back to the front of the audience chamber as possible.

Now, with this you'll still leave at least a 1/3 of each side seating areas uncovered (the 1/3 closest to the stage) and you'll likely leave the first several rows uncovered. Most assured the center front of the audience will be lacking coverage.

So, for those areas you will need fill speakers. I would say initially that you'll need side fills for the 1/3 of the side seating not covered, and likely some beefier fills for that. I've seen a VRX turned on it's side once in a situation like this to be used as a side fill and it worked fairly well. That would of course be contingent upon a 15deg angle would be sufficient (which would mean to break out the CAD).

You'll need a Center/Front Fill likely. Something like an EAW JF60 or a JBL AC16 (or similar) if you want to stick with JBL. On the less expensive side I also like the CPL23 from Community.

Now, remember, this is all shoot from the hip kind of stuff. I would still check with the company installing it and see if they can help you figure it out professionally.

Alternatively you can see if you can find a professional Audio designer in your area who can come out and help you make the best of what you have. I've done that before with churches, and though I would rather start from scratch, I have helped them out with the appropriate disclaimers in place.

Honestly, by the nature of the question, I think that you're in a little over your head and the several hundred to a couple of thousand dollars spent to pay a consultant that can be on site and help you sort this out would be well, well, worth the money. It will help you make the most of what you have coming in and be able to sort it out.

A couple of questions though. How is the seating raked on the sides? Which way do the seats face? Honestly I'm trying to figure out how that works... How many are you seating?

And the audio booth in the back of the balcony? I can't think of a worse place to put it. I would really, really, really, push to have that moved. To the very least at to the front of the balcony, in the open. It would be better to move it to the floor but I would take the front of the balcony if that's all I could do.

Last edited by Les; Tuesday, April 21st, 2009 at 07:55 PM. Reason: Clarification
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Old Tuesday, April 21st, 2009, 08:25 PM
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Quote:
I would caution the 1/3 of the way back (If I am understanding you) as that would put them over the stage and in serious danger of feedback for anyone downstage. I wold place them on the downstage edge and aim it to cover the balcony and as much from the back to the front of the audience chamber as possible.

You probably have more experience than me in this situation, but let me ask this - could you get away with having the speakers 1/3 of the way back from the stage since they are line array's with a little more focused coverage than your normal two or three way cabinet? I definitely see feedback potential with LF, but how would it be for higher stuff? A little off the main topic, but still related...

Could he move them to the front of the stage and point them down a little more?
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Old Tuesday, April 21st, 2009, 08:30 PM
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The drawing definitely helps, thanks! I'm assuming from the equipment being expected in a couple of weeks that the building is almost finished. Hopefully you can still get conduit to the speaker locations, you may have planned for that.

Modeling the system in anything other than EASE might be difficult. I think the only modeling data available for the JBL VRX 900 series is an EASE dll file. EASE dll files are basically subroutines provided by the manufacturers and used specifically by EASE to model array speaker systems as a single entity. Since that is apparently the only data available, it might limit any accurate modeling to EASE. And due to the sloped seating, Mezzanine, etc., it would be necessary to have vertical dimensions (room sections or elevations) to model even just the audience areas.

Because of the width of the seating and it being so close to the stage, my first thought would be a mono system with both arrays in the center at the front edge of the stage and one array covering each half of the room. I just don't see a good way to get stereo for much more than a small portion of the room unless the speakers were way out at the outside walls on either side and that would introduce its own problems. The down side of having both arrays in the center is that you could get quite a bit of spill onto the stage below. I'm also a bit worried about getting coverage to the upper row at the rear of the Mezzanine and to the seats up front, including those at the top front of the side 'bleacher' seating.

As far as mounting height, what is the ceiling? If you are flying the entire array (subs and mains) and the ceiling is acoustically reflective, then you typically want the arrays to put the subs either very close to the ceiling or a minimum of 8' or so from the ceiling. Between those two points you can get boundary cancellation due to reflections off the ceiling where certain frequencies from the subs are reduced in level, possibly almost canceled, due to out of phase reflections from the ceiling.

A few other thoughts. If the walls to either side of the stage are full height that could be interesting, it almost looks like it effectively makes the stage more a proscenium or recessed stage. You could also get some flutter echo between the two side walls to either side of the stage. And if the speakers have to cover the main floor and Mezzanine, you are likely going to have a lot of sound energy hitting the big, flat rear walls, although the sloped, tiered seating in the Mezzanine should help prevent a big slap back to the stage from the house speakers, at least when the seating is occupied. Overall, some acoustical treatments might be worth considering.

If the seating in the Mezzanine is like bleachers and the mix position is between two seating sections on the floor level, then it would seem to be in a bit of a canyon. That would be a challenge. I'm not a big fan of remote mixing with a PC or laptop, but this is one situation where you might want to look at it as an option.
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Old Tuesday, April 21st, 2009, 09:05 PM
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We always provide speaker placement when we sell equipment. Go to your dealer or JBL.

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