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Author Topic: JBL VRX Series Speakers  (Read 35727 times)

Danny Baies

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JBL VRX Series Speakers
« on: December 28, 2010, 04:07:29 pm »

Here's the scenario i stumbled upon...

Few years back i moved to another state and to another church. I got involved with the audio department.
Ever since i was there i noticed that the sound is not right in the church. They remodeled this church and totally overhauled the sound system.

We have JBL VRX932LA and JBL VRX918S. These speakers are mounted in ceiling in array . In front we have 4 VRX932LA and 1 JBL VRX918S. All this speakers are interlinked, so the output from a speaker goes into the input on the next speaker.

The info i got from the ones that installed them is that they connected 2 speakers per pair.

From what i figured out is that these speakers are connected in parallel and they get output from a Crown CE2000. The problem is that is not enough power that comes out of those speakers. They are not loud enough.

The specs on the Crown CE2000 are that they can take load of 2,4,8 Ohms. Since the 2 (8 ohms) speakers are connected in parallel that get a 4 ohms input.

What can be wrong? Anyone any ideas ?

Thank you.
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Ivan Beaver

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Re: JBL VRX Series Speakers
« Reply #1 on: December 28, 2010, 07:46:18 pm »

Danny Baies wrote on Tue, 28 December 2010 16:07

Here's the scenario i stumbled upon...

Few years back i moved to another state and to another church. I got involved with the audio department.
Ever since i was there i noticed that the sound is not right in the church. They remodeled this church and totally overhauled the sound system.

We have JBL VRX932LA and JBL VRX918S. These speakers are mounted in ceiling in array . In front we have 4 VRX932LA and 1 JBL VRX918S. All this speakers are interlinked, so the output from a speaker goes into the input on the next speaker.

The info i got from the ones that installed them is that they connected 2 speakers per pair.

From what i figured out is that these speakers are connected in parallel and they get output from a Crown CE2000. The problem is that is not enough power that comes out of those speakers. They are not loud enough.

The specs on the Crown CE2000 are that they can take load of 2,4,8 Ohms. Since the 2 (8 ohms) speakers are connected in parallel that get a 4 ohms input.

What can be wrong? Anyone any ideas ?

Thank you.

It could be anything, based on your limited description of the problem.  Stating that the sound is "not right" does not tell us anything at all.

Possibilities; Damaged loudspeakers- wrong aiming-not setup properly-wrong design for the room-FOH mixing skills-wiring error and on and on.

More details would help A LOT
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Danny Baies

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Re: JBL VRX Series Speakers
« Reply #2 on: December 28, 2010, 08:59:49 pm »

well, the speakers are not damaged, aiming maybe, room size not proper for sound but it seems not loud as it should be and anything that gets close to 0db amplified it turns into feedback.

The speakers are rated for 800W, at 8ohms. The amp outputs 400W at 8ohms but because we have 2 speakers in parallel at 4ohms the amp outputs 660W and there is no feel at all of 600w from the speakers. My surround system at home is more powerful that the speakers at church. I will make a diagram to explain more on this subject.

Thank you.
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Arnold B. Krueger

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Re: JBL VRX Series Speakers
« Reply #3 on: December 28, 2010, 09:29:01 pm »

Danny Baies wrote on Wed, 29 December 2010 01:59

well, the speakers are not damaged, aiming maybe, room size not proper for sound but it seems not loud as it should be and anything that gets close to 0db amplified it turns into feedback.



If you are saying that the loudness of your system is limited by feedback (howling), then amplifier power is most certainly not the problem.

Before I go on, is your system limited by howling feedback?
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Dick Rees

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Re: JBL VRX Series Speakers
« Reply #4 on: December 28, 2010, 09:31:34 pm »

Danny Baies wrote on Tue, 28 December 2010 20:59

well, the speakers are not damaged, aiming maybe, room size not proper for sound but it seems not loud as it should be and anything that gets close to 0db amplified it turns into feedback.


What does that mean?  The statement "0dB amplified" is meaningless.  What are you trying to say?

Quote:


The speakers are rated for 800W, at 8ohms. The amp outputs 400W at 8ohms but because we have 2 speakers in parallel at 4ohms the amp outputs 660W and there is no feel at all of 600w from the speakers.


Yes, if there is only one power amp the speakers would be underpowered.  That does not mean that they won't get "loud", though.  From the first part of your post it would seem that the output of the system is limited by the onset of feedback, not by the speakers and amp(s).

Quote:


My surround system at home is more powerful that the speakers at church.



Your system at home does not have open microphones, so you can turn it up as much as you like.  The system at the church has open microphones and the feedback loop from them is what is limiting the output of the system, not the equipment itself.

It is obvious from your attempts at delineating the problem that you have little experience with live sound and a preconceived notion of what's "wrong" with things. That's two strikes right there.

Just exactly what is your role in your church?  Are you officially in charge of anything, part of a team/committee or just a critical listener?  Have you been tasked with assisting with the "problems" or are you just posting here for sympathy and corroboration of your opinions?


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Danny Baies

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Re: JBL VRX Series Speakers
« Reply #5 on: December 28, 2010, 10:58:39 pm »

OK, i will explain more as it seems that its not clear what im trying to say.

Setup
Front row: 4 VRX932LA and 1 sub VRX918S.
Front side rows L & R: 2 VRX932LA

Back row: 2 VRX932LA and 1 sub VRX918S.
Back side rows L & R: 2 VRX932LA

Amps

Speakers: Crown CE2000
Subs: Crown CE1000

The whole system is mono.
We have 2 speakers per output channel.

Im not posting here just for sympathy, but to resolve a problem that i and other guys from the audio dept. think exists.  

I serve at this local church as a tech in the Audio/Video Dept. I'm not a pro in live sound but not a novice either. Ive worked with sound for about 10 years. As far as experience with equipment, im a electronics engineer.

Sorry if i didnt express myself right, and the whole idea with the home theater was just a reflection on speaker power regardless of mics.

The power in the system described is the same with or without mics open.

We output signal from the mixer board on Left channel for the back row and Right channel for the front row.
From the mixer all outputs go thru en EQ and 2 Compressors. We disabled both of them to test the system.

The feedback is achieved mostly with the choir mics and pulpit mic. If we have the full choir seated we cant move the faders more than 0 without getting feedback.

The placement of the mics and speakers may not be ideal but this should not affect the system this bad.

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Sidney.Pilien

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Re: JBL VRX Series Speakers
« Reply #6 on: December 29, 2010, 01:11:09 am »

If you play a cd and bring up that fader, can it get loud? What are the level indicators on the amps on the cd and on mics?

If the amp level indicators are barely registering, the input signal from the board may be  too weak so you need to backtrack.  What is the speaker cable size and run? If too small and too long, the amp won't push out the power needed.

What are the stereo out master meters reading at the board with cd and with mics? If strong with both, the problem is after the mixer.

Where are the subs getting the line feed from? Signal splitter(okay) or Y cable (a no no )from stereo or from an aux master(preferred)?

If the cd plays loud both sides, you may have a gain structure problem (low gain) which may result from poor EQing. You may be cutting at the wrong notch filters which will result in feedback.

Hope this helps.


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Ivan Beaver

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Re: JBL VRX Series Speakers0Diagrams NEEDED
« Reply #7 on: December 29, 2010, 08:38:59 am »

It sounds like you have a lot of loudspeakers in that room.

You say you have multiple rows  (I assume a delay ring?).

Could you draw a diagram of the setup.

Delay subs are generally not a good idea-but can be done-if odne properly.

Improper setup and design is one of the main causes of feedback.  And the mics you describe are most often the problem.

You say it does not sound like 600 watts.  WHY?  Have you checked the polarity of ALL the cables?

Who installed the system?  Who designed the system?  I would go to THEM and voice your complaints and see what they can do about it-because it sounds like the system is unusable.  Did they get paid?

Regarding the 0dB feedback issue.  That says ABSOLUTLY NOTHING.  It is simply a matter of gain structure.  I could setup the exact same system (without moving cabinets or doing an alignment)and you could turn it all the way up and not get feedback (of course it would not be loud-but if if it would make you "feel better" you would be able to turn it ALL the way up. Very Happy .

OR I could set it up so that when you got to -20 it would feedback.  Is the sound any different-NO-just the fader level.

Disabling the eq's is one surefire way to get the sytem to "misbehave".  They are a part of the system (if they are setup properly) and the system relies on them.

I have not seen any mention of a crossover.  How are the subs being run?

Since you are an Engineer-I would assume it would be realy easy to draw a block diagram of the setup and layout.  Be sure to draw a layout of the room with the positions of the loudspeakers in relation to the audience and the stage and the mics on the stage.  THIS IS IMPORTANT!

THAT would help explain A LOT.

If you want help-you need to supply more information
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Brad Weber

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Re: JBL VRX Series Speakers
« Reply #8 on: December 29, 2010, 11:12:06 am »

Danny Baies wrote on Tue, 28 December 2010 22:58

OK, i will explain more as it seems that its not clear what im trying to say.
Danny Baies wrote on Tue, 28 December 2010 22:58

The power in the system described is the same with or without mics open.
Danny Baies wrote on Tue, 28 December 2010 22:58

The feedback is achieved mostly with the choir mics and pulpit mic. If we have the full choir seated we cant move the faders more than 0 without getting feedback.

I think that these seemingly contradictory comments may be part of the confusion and some clarification may be provided by looking at it on an extremely simple basis.  Is the problem getting sufficient level at all?  Or is the problem getting the system loud enough without experiencing feedback?  As Sidney noted, with only a source like a CD player active can you get the level you desire?  What levels are you able to get for the listeners and what levels are you trying to achieve?

Danny Baies wrote on Tue, 28 December 2010 22:58


We output signal from the mixer board on Left channel for the back row and Right channel for the front row.
From the mixer all outputs go thru en EQ and 2 Compressors. We disabled both of them to test the system.

As Ivan commented, it sounds like you have mains and a delay ring and that both the main and delay rings consist of three arrays and one sub.  It is not clear if the intent of the three arrays is as an exploded cluster or some form of LCR system, however all of the main arrays being on one common output and all of the 'delay' arrays on another common output suggest an exploded cluster arrangement.  However, three 100 degree horizontal arrays for both the main and delay ring would be uncommon for most rooms.  Unless there is something unusual about the application or information missing about the system configuration, this seems like a very unusual speaker and electronics configuration.  Whether that is a result of the initial design and/or installation or from some subsequent modifications is unknown, but it sounds like there may either be some missing information or some other issues potentially involved.

Danny Baies wrote on Tue, 28 December 2010 22:58

The placement of the mics and speakers may not be ideal but this should not affect the system this bad.

If the problem is feedback and especially if the system configuration and adjustments are less than optimal, then yes, this could very well significantly negatively impact the system.


Overall I think you may be getting a bit too focused on the power to the speakers rather than the general system configuration and function.  Run passive full range your VRX932LA mains have a power rating of 800W continuous and a 95dB/1W/1m sensitivity.  The VRX918S subs have the same ratings, but there is one sub versus six to eight mains in each 'ring'.  The CE2000 is rated at 400W per channel into 8 Ohms and 660W per channel into 4 Ohms, but at 1kHz rather than 20-20kHz.  So on the one hand, if you do indeed have two VRX932LA boxes or one VRX918S box on each amp channel and feedback is not an issue then you could indeed probably get 6-7dB more out of the system.  On the other hand, how relevant is that if you aren't getting what you should or don't actually need that additional 6-7dB for the application?

Along with a better description of the system configuration, any information you can provide about the room, speaker locations, sources on stage, etc. would probably be helpful.
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Brad Weber
muse Audio Video
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Danny Baies

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Re: JBL VRX Series Speakers
« Reply #9 on: December 29, 2010, 02:26:18 pm »

Thank you to all for your inputs.
I will supply a diagram to show how the system is put together and all the components involved and a full description of the system.

When i moved to this church i asked the engineer who put together this setup and how did they do it so i could understand it. As time past few thing started to fail or fall apart. This church was fully remodeled in 2007. Apparently they did hire a company to design the AV system. They got their idea of how should it be and what components they should use so they did not get their bid but  took charge and did it themselves.

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