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Author Topic: Height to Fly JBL VRX  (Read 17991 times)

Dewald Du Plessis

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Height to Fly JBL VRX
« on: March 31, 2011, 03:49:28 AM »

Hi,

Hope someone can help me with some advice. I am building a mobile stage with a small flat bed. The scaffolding towers will be 6 meters apart and JBL recommends to fly the VRX lapīs 8 meters high when using four speakers per side. This is quite high so I would like to know from other peoples experience what is the lowest that I can build these towers and still get good vertical coverage?

Thanks
Dewald Du Plessis
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Ian Stuart

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Re: Height to Fly JBL VRX
« Reply #1 on: March 31, 2011, 06:39:59 AM »

I know very little about line-array stuff but what would happen if you removed 1 or 2 of the boxes per side? I know that you would lose some much needed SPL but would that allow the rig to be lowered and have the same dispersion?

8 meters is pretty damn high. If I owned the rig I would probably just run them at the available height and deal with the consequences later.

It's a sticky situation man, Have you tried calling JBL for some extra advice?
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Dewald Du Plessis

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Re: Height to Fly JBL VRX
« Reply #2 on: March 31, 2011, 08:33:26 AM »

Thanks! I have not yet called JBL for this. We can easily place 2 x boxes per side without the towers as they would then go onto the riser pipes on top of two subs next to the stage.

The towers will be specifically designed for situations where one needs to add more boxes. Eight meters is way to high for me to work with so I am hoping that 4 x boxes per side will function just fine on lets say a 6 meter tower as this is a reasonable height to work with. I will probably need to tilt the array a few degrees backwards to balance out the throw using less height but with little experience on this I would rather get more advice first!

JBLīs recommendation for 3 x boxes per side is 5.5 meters so that will work just fine but why waste extra speakers if they are available  :)
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Dave Bigelow

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Re: Height to Fly JBL VRX
« Reply #3 on: March 31, 2011, 08:41:54 AM »

You could always go 3 a side and then use the last 2 for front fills.
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Dewald Du Plessis

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Re: Height to Fly JBL VRX
« Reply #4 on: March 31, 2011, 08:48:52 AM »

Correction: JBL recommends 7.7 meters with 4 boxes a side, but still....

Tnx Dave that certainly something to consider!
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Tim McCulloch

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Re: Height to Fly JBL VRX
« Reply #5 on: March 31, 2011, 09:23:16 AM »

Thanks! I have not yet called JBL for this. We can easily place 2 x boxes per side without the towers as they would then go onto the riser pipes on top of two subs next to the stage.

The towers will be specifically designed for situations where one needs to add more boxes. Eight meters is way to high for me to work with so I am hoping that 4 x boxes per side will function just fine on lets say a 6 meter tower as this is a reasonable height to work with. I will probably need to tilt the array a few degrees backwards to balance out the throw using less height but with little experience on this I would rather get more advice first!

JBLīs recommendation for 3 x boxes per side is 5.5 meters so that will work just fine but why waste extra speakers if they are available  :)

Adding more boxes doesn't increase your SPL, rather it increases your vertical coverage angle.  The VRX is a fixed-curvature array and "flattening" the top of the array is not possible.

Play with coverage predictions using the JBL VRX array calculator.  You can see the effect of trim height on coverage with it.

Have fun, good luck.

Tim Mc
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Brad Weber

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Re: Height to Fly JBL VRX
« Reply #6 on: March 31, 2011, 11:27:26 AM »

Hope someone can help me with some advice. I am building a mobile stage with a small flat bed. The scaffolding towers will be 6 meters apart and JBL recommends to fly the VRX lapīs 8 meters high when using four speakers per side. This is quite high so I would like to know from other peoples experience what is the lowest that I can build these towers and still get good vertical coverage?
Good coverage of what?  The critical components not stated are what size and shape listener area you are trying to cover and what you define as good coverage.  As Tim said, you could use the VRX array calculator to get an idea of the effect of the trim height on the coverage for various listener areas.
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Ian Stuart

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Re: Height to Fly JBL VRX
« Reply #7 on: March 31, 2011, 08:01:43 PM »

Adding more boxes doesn't increase your SPL, rather it increases your vertical coverage angle.  The VRX is a fixed-curvature array and "flattening" the top of the array is not possible.

Play with coverage predictions using the JBL VRX array calculator.  You can see the effect of trim height on coverage with it.

Have fun, good luck.

Tim Mc

Okay cool, so basically if you had a set SPL for 3 a side then changed it to 4 a side, you'd still have the same SPL but the added boxes would only add SPL to a specific coverage zone? I wish I knew more about arrays, The only thing I do know is that I get all excited when I get to work on one  ;D
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Bob Leonard

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Re: Height to Fly JBL VRX
« Reply #8 on: March 31, 2011, 08:22:31 PM »

Hope someone can help me with some advice. I am building a mobile stage with a small flat bed. The scaffolding towers will be 6 meters apart and JBL recommends to fly the VRX lapīs 8 meters high when using four speakers per side. This is quite high so I would like to know from other peoples experience what is the lowest that I can build these towers and still get good vertical coverage?
Good coverage of what?  The critical components not stated are what size and shape listener area you are trying to cover and what you define as good coverage.  As Tim said, you could use the VRX array calculator to get an idea of the effect of the trim height on the coverage for various listener areas.

And this is the crux of the matter. Hight of the array will be determined by the area to be covered, so until you have that determined there's no answer to the question. Once you have determined the area to be covered, and then used the JBL calculator as suggested above, you may find you don't need the hight or as many boxes. You also need to keep in mind that JBL recommends this rig for 1000 person scenerios.
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Dewald Du Plessis

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Re: Height to Fly JBL VRX
« Reply #9 on: April 01, 2011, 03:03:50 AM »

Thanks for the info this has helped. After looking at the JBL calculator we have decided to build these towers to a hight of 5.5 meters. This is a reasonable hight to work with safely. Three boxes would give us good SPL and coverage for certain venues and should the venue require more vertical coverage than this, we would use four boxes and trim it slightly to add that extra throw! For smaller applications we would not use the towers but in stead use the standard riser pipes.
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tim.j.phillips

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Re: Height to Fly JBL VRX
« Reply #10 on: April 01, 2011, 06:21:45 AM »

JBL's recommendation of 7.7 meters is probably not far off if I had to guess.  I know the 4 VRX a side we have in our theater are too low and they are sitting at maybe 25 feet in the middle of the array, probably a bit lower.  Sadly when they built the theater they put the subs on top of the array which makes them hang even lower then id imagine they should be.

-Tim
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Brad Weber

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Re: Height to Fly JBL VRX
« Reply #11 on: April 01, 2011, 08:45:02 AM »

I wish I knew more about arrays, The only thing I do know is that I get all excited when I get to work on one  ;D
Keep in mind that the VRX is not a line array, it is a constant curvature array.  Adding VRX boxes simply adds greater vertical coverage while with a true line array additional boxes can be used to increase the vertical coverage and/or to provide greater output at various points in the vertical coverage.  And also remember that you can use the three position high frequency shading switch on the VRX boxes to assist in getting the desired HF coverage.
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James A. Griffin

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Re: Height to Fly JBL VRX
« Reply #12 on: May 12, 2011, 07:10:33 PM »

I've flown 4 VRX from my 16 foot Sumners for a venue about 110 feet deep.  Coverage to back of audience was just fine.  Only real issue at that height is that the bottom box points almost straight down at the first 3 rows.    The consensus of several users I've talked to about this is that the bottom box is almost useless in most scenarios.   I'm inclined to agree.   Very few gigs that we can get with a VRX system can actually make good use of the 4th box.   
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Tim McCulloch

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Re: Height to Fly JBL VRX
« Reply #13 on: May 13, 2011, 03:53:52 AM »

I've flown 4 VRX from my 16 foot Sumners for a venue about 110 feet deep.  Coverage to back of audience was just fine.  Only real issue at that height is that the bottom box points almost straight down at the first 3 rows.    The consensus of several users I've talked to about this is that the bottom box is almost useless in most scenarios.   I'm inclined to agree.   Very few gigs that we can get with a VRX system can actually make good use of the 4th box.

If you can use up-tilt on the bumper, you can aim high.

As a constant curve, all you can do by adding boxes is the increase the vertical coverage angle, but you can rotate that arc up or down.  For example, you might use the up rotation to cover a balcony and still give you usable coverage on the floor.  In the situation you describe, I'd fly 3/side and use the remaining pair as front fills.

Brad W. points out the HF switch, and I suggest all VRX users look at the SPL predictions in JBL's VRX array calculator while working with shading.  Shading is the secret sauce to making the most of the VRX.

Ken Freeman has scores of VRX in his inventory and has come up with some clever drive processing to make a VRX array more even in it's vertical coverage, but it requires processing and power on a per-box basis.  He posted about this in the FUD forum a couple of years ago.

Have fun, good luck.

Tim Mc
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Randall Hyde

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Re: Height to Fly JBL VRX
« Reply #14 on: May 13, 2011, 11:09:52 AM »

Hi,

Hope someone can help me with some advice. I am building a mobile stage with a small flat bed. The scaffolding towers will be 6 meters apart and JBL recommends to fly the VRX lapīs 8 meters high when using four speakers per side. This is quite high so I would like to know from other peoples experience what is the lowest that I can build these towers and still get good vertical coverage?

Thanks
Dewald Du Plessis

Which cabinets are you using?
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Dewald Du Plessis

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Re: Height to Fly JBL VRX
« Reply #15 on: June 24, 2011, 06:52:02 AM »

I would like to share a photo of the mobile stage that is complete now and based on the west coast of Namibia!
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Dewald Du Plessis

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Re: Height to Fly JBL VRX
« Reply #16 on: June 24, 2011, 06:53:47 AM »

I would like to share a photo of the mobile stage that is complete now and based on the west coast of Namibia!
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Re: Height to Fly JBL VRX
ÂŦ Reply #16 on: June 24, 2011, 06:53:47 AM Âŧ


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