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Author Topic: JBL PRX 812 wtf  (Read 777 times)

Dan Richardson

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JBL PRX 812 wtf
« on: May 19, 2022, 08:34:59 PM »

My venue came with JBL PRX712s as monitors. They're OK, don't need much EQ, get plenty loud. We run 6. When one amp failed, we went for more, but they'd been discontinued. OK, says I, we'll get a couple PRX812, slot one in, and carry on with our day.

First off, the gain structure is different, way hotter, so we can't just match the knobs. OK, says I, we'll turn down their inputs to match. Then we run them. First thing we discover is the limiter is pre the gain knob, and it's on at even moderate levels. OK, turn up the inputs and back off the sends on those mixes.

Holy shit, these things have no output. They crap out so early. It's embarrassing. Unusable. My old QSC K10s easily outrun them.

Anybody else got experience with them? Am I missing something?
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Thomas Le

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Re: JBL PRX 812 wtf
« Reply #1 on: May 19, 2022, 09:17:10 PM »

My experience: https://forums.prosoundweb.com/index.php/topic,175411

yeah they're quirky cabinets, why couldn't they just leave it alone ala if it ain't broke (other than the annoying "power saving" feature).
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Keith Erickson

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Re: JBL PRX 812 wtf
« Reply #2 on: May 20, 2022, 02:12:23 PM »

My venue came with JBL PRX712s as monitors. They're OK, don't need much EQ, get plenty loud. We run 6. When one amp failed, we went for more, but they'd been discontinued. OK, says I, we'll get a couple PRX812, slot one in, and carry on with our day.

First off, the gain structure is different, way hotter, so we can't just match the knobs. OK, says I, we'll turn down their inputs to match. Then we run them. First thing we discover is the limiter is pre the gain knob, and it's on at even moderate levels. OK, turn up the inputs and back off the sends on those mixes.

Holy shit, these things have no output. They crap out so early. It's embarrassing. Unusable. My old QSC K10s easily outrun them.

Anybody else got experience with them? Am I missing something?

Couple things...

1. There are 2 sensitivity and 2 voicing presets that you can select via the app for them.  When they were originally built they had a lower input sensitivity and a very flat frequency response.  Since many customers for that speaker went into a GC or other music store and plugged a phone directly into speakers, it always seemed that the QSC was louder so they did a firmware update that gave the option to have a higher sensitivity and built a preset that that had more of a DJ smile built into it so it demo'd more like the QSC did.

2. Something is not right in regards to the output.  In my independent testing and measurements of the PRX812W, QSC K12.2, EV EKX12P, and because i had it, the EON612, i found that the PRX812 literally plays over 2x as loud as the K12.2 and the EV if you stop turning the speaker up when the frequency response becomes nonlinear and starts to change.  in fact the EON612 plays about as loud as the QSC and EV.  if you disregard the performance, sound quality, response linearity, and just turn it up till it doesn't get any louder, the K12.2 does play within 3dB of the PRX812 but at that point the QSC is highly distorted and in to massive limiting and driver break up while the PRX remained linear even when in limit.

Measurements taken at 2M and referenced back to 1M.  So SPL is 6db more than the SMAART display.  All SPL data is measured A weighted slow.
Speakers were started at 96DB and turned up 10dB at a time or till the limiter light became active.  Once limiter was active a final measurement was taken pushing +2dB into the limiter .

The chart shows the Max SPL as listed on the spec sheet as well as:

Measured Max linear SPL                      - This is how loud the speaker got with no change in the frequency response
Measured Max linear SPL @ limit           - This is how loud the speaker got when the limiter light came on
Measured Max linear SPL @ limit +2      - You guessed it..volume when pushed +2dB into limit
Corrected Max SPL @ Limit +2              - This is how loud the speaker would play if you applied EQ to the response of Limit +2 to make its response curve have the same     
                                                            response as it did at 96dB.  This can also be looked at as the max volume that the speaker can play while maintaining a linear
                                                            response.

These all show the A-Slow SPL as well as the unweighted Peak SPL with the 12dB crest pink noise.

You can see that while the PRX stopped getting linearly louder (meaning if I asked for +3 I only got +2 etc..) after it was in limit, it maintained the same response and sound quality while the others did not.
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Keith Erickson

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Re: JBL PRX 812 wtf
« Reply #3 on: May 20, 2022, 02:13:54 PM »

Sorry guys...had issues with the images
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Keith Erickson

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Re: JBL PRX 812 wtf
« Reply #4 on: May 20, 2022, 02:14:29 PM »

Sorry guys...had issues with the images
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Bob Stone

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Re: JBL PRX 812 wtf
« Reply #5 on: May 20, 2022, 03:29:50 PM »

Keith - can you please disclose who you work for?
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Dan Richardson

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Re: JBL PRX 812 wtf
« Reply #6 on: May 20, 2022, 03:59:26 PM »

Couple things...

1. There are 2 sensitivity and 2 voicing presets that you can select via the app for them.

2. Something is not right in regards to the output. 

I'll see what I can see in the app.

I'm not getting anywhere near the output you've charted.

Thanks.
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The best sound system is no sound system. Everything else is compromise.

ProSoundWeb Community

Re: JBL PRX 812 wtf
« Reply #6 on: May 20, 2022, 03:59:26 PM »


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