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Author Topic: Funky QRX212 Measurments  (Read 1881 times)

David Sturzenbecher

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Funky QRX212 Measurments
« on: May 17, 2017, 07:05:30 pm »

Hello,
I was called in to mix a show at a local casino.  The system consisted of two EV QRX212 speakers per side, using an EV DC-One processor.  Not sure if the tunings are from EV or not.  Once the system was setup, I noticed that the left side sounded nothing like the right, especially in the HF.   So I setup my testing equipment to take a look.  With the mic in the center isle, a few feet in front of FOH, here is the L vs R measurement. (See LRStart.JPG)


I had suspected something in the DSP was different between the two so I then took a transfer function from the input of the mix console, to the input of the speakers (plugging the NL4 from the speaker into a VIbox). The transfer functions for the Left was identical to the Right. I can post these...but all 4 amp channels were the same.

Thinking there may be an HF polarity flip inside one of the boxes I took a TF of each HF section.  As you can see, they are pretty similar, especially on the phase trace. (See Individual HF.JPG)


One more piece to this puzzle is that I experienced this with the same rig, in the same venue a month prior.  I wasn't able to track if all 4 speakers were deployed in the exact same location.   It seems really odd to me that the difference heard, and measured could be a venue anomaly.

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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #1 on: May 17, 2017, 07:07:02 pm »



Here is what the venue looked like.


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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #2 on: May 17, 2017, 07:08:29 pm »



Another shot


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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #3 on: May 17, 2017, 07:10:20 pm »

And Lastly here are the four complex impedance sweeps of the drivers




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Rob Spence

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Re: Funky QRX212 Measurments
« Reply #4 on: May 17, 2017, 07:28:54 pm »

Did you check that the left and right outputs of the mixer were correct?
Might not be the speaker system?


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John Ferreira

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Funky QRX212 Measurments
« Reply #5 on: May 17, 2017, 07:50:07 pm »

How about going to the power amp and use the LHS cables to measure and test separately LHS and RHS? Then use the RHS cables and test and measure also on both LHS and RHS.

It may not be the speakers, and it may be the mixer chain.
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John Ferreira

David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #6 on: May 17, 2017, 07:51:38 pm »

Did you check that the left and right outputs of the mixer were correct?
Might not be the speaker system?


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The transfer function was the same from the input of the mixing console, to the input of each speaker, on both the left and the right side. If there were any differences along the way, including internal to the mixer, between mixer and DSP, or internal to the DSP, it should really have shown itself in this measurement. My goal was to determine the input signal to each speaker was the same.



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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #7 on: May 17, 2017, 08:07:23 pm »

How about going to the power amp and use the LHS cables to measure and test separately LHS and RHS? Then use the RHS cables and test and measure also on both LHS and RHS.

It may not be the speakers, and it may be the mixer chain.

If there was a difference, anywhere along the line between the Left and the Right, wouldn't it have shown itself as differences in the input-of-mixer/input-of-each-speaker transfer functions? My thought is, yes. 

I reference the "measurement" side of the transfer function as being "input-of-speaker", and not "the output of the amplifier" on purpose.   The same cable that plugged into the speaker, was the same cable used for the measurement. 

The input-of-mixer to input-of-each-speaker transfer function can be seen below,  I didn't save all 4...because...they were all the same.

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Stelios Mac

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Re: Funky QRX212 Measurments
« Reply #8 on: May 18, 2017, 07:06:23 am »

Maybe a diaphragm was blown at some point in the past and replaced with a cheaper clone?
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Arthur Skudra

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Re: Funky QRX212 Measurments
« Reply #9 on: May 18, 2017, 08:46:34 pm »

Maybe a diaphragm was blown at some point in the past and replaced with a cheaper clone?
Or maybe someone swapped a diaphragm out with an OEM replacement, and swapped the wires around?  Discovered it in a cluster of two identical speakers, contractor asked me if it really mattered (I think he was being lazy and trying to get out of setting up 30 ft of scaffolding).  I gave him a dumbfounded look of disgust, so he went to setup the scaffold and fixed his mistake!  The phase trace is an invaluable tool to find this kind of problem, which is what I'm suspecting with the OP.
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