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Author Topic: Funky QRX212 Measurments  (Read 1130 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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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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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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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #10 on: May 18, 2017, 11:16:55 pm »

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.

Stelios and Arthur,
Thank you for your replies.  I was told that some diaphragms have been replaced in the past, maybe about 6 years ago.  So you may be onto something.   Sure seems odd it would be that different (given they were reconnected in the proper polarity).    After seeing the initial L-R differences (First Picture) and how the phase trace wraps on the one side, I really suspected an out of polarity driver, but wouldn't that out of polarity driver shown itself when I measured each HF individually?   I did perform a delay find between each HF measurement, but I wouldn't think that would mask a polarity difference.
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Stelios Mac

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Re: Funky QRX212 Measurments
« Reply #11 on: May 20, 2017, 04:48:12 pm »

I don't really think it's polarity on the HF - If it was, I'm guessing there would be a pretty sizable notch right on 1.5k where the crossover is (Wouldn't be as deep as reversed polarity between on a 2-way box, but there would be something), as well as some phasing weirdness.

All the variations start at 1.5k as well, and the response below that is almost identical between the L&R stacks, so it's definitely got to do with the HF, not the room.

I'm not familiar with any QRX speakers, but does the signal go through an analog crossover when biamped? If so, make sure it's in one piece.  ;D
I was once working with some old EV S1202s - Once side sounded way different than the other, no extention past 8k what-so-ever. I got a torch and looked through the bass port, only to find out an inductor had self-desoldered and dropped off.
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Ivan Beaver

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Re: Funky QRX212 Measurments
« Reply #12 on: May 20, 2017, 05:20:42 pm »

I don't really think it's polarity on the HF - If it was, I'm guessing there would be a pretty sizable notch right on 1.5k where the crossover is (Wouldn't be as deep as reversed polarity between on a 2-way box, but there would be something), as well as some phasing weirdness.


Not every time does a polarity reversal result in a notch in the response.

I have seen a case where 2 cabinets were arrayed side by side but sounded really weird when you stood in the middle.  They were totally passive cabinets.

I flipped the polarity on one of them, but the low freq cancelled.

So I pulled out my measurement rig and looked at each one.

Individually the responses were just fine, but one of them had a 180*phase shift around the HF crossover.

We pulled the cabinet down and found the HF driver to be wired out of polarity.

We flipped it and all was fine.

YES, in many cases if the polarity is reversed on an adjacent freq range, there will be a notch in the response, but not always.  It all depends on the particular design.

In many cabinets, the response may be nice and flat, but there is a phase shift of 180* around crossover.  In those cabinets, if you flip the polarity (to fix the 180* phase shift), you will end up with a flat phase, but have a dip in the magnitude response.

Sometimes you get flat phase and magnitude, other times you don't.  DO NOT ASSUME that all cabinets have flat phase.  I would "argue" that many/most do not have flat phase.
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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #13 on: May 20, 2017, 05:50:07 pm »

Not every time does a polarity reversal result in a notch in the response.


Wouldn't a polarity reversal show up on the phase trace though?  I measured each HF individually, and he phase traces are all nearly alike.




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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #14 on: May 20, 2017, 05:59:20 pm »



I'm not familiar with any QRX speakers, but does the signal go through an analog crossover when biamped? If so, make sure it's in one piece.  ;D


I can't say I know for sure either... but.... wouldn't you see some serious differences in the complex impedance curves? 

Maybe addressing those, there are some differences.

Of course I didn't record the exact location of each one (the numbers on the plot indicate the last three digits of the serial number). But from the time stamps of the measurements I can say that 850 and 941 were on house right (the side I think has the problem) and 851 and 902 were on the left, the side I think sounded better.





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Ivan Beaver

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Re: Funky QRX212 Measurments
« Reply #15 on: May 20, 2017, 06:10:27 pm »

Wouldn't a polarity reversal show up on the phase trace though?  I measured each HF individually, and he phase traces are all nearly alike.




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Yes, a polarity reversal will show up as a 180* change in phase.

I would "argue" that if the phase traces are "close enough", then the driver is "in proper polarity" with the intended design.

Maybe I missed it, but are you sure the drivers are the correct ones for the cabinet?

People very often swap out drivers for various reasons.  Often times it is because of a failure, and they needed "something" to make sound.  Even the wrong sound is better than no sound.

I actually had a JBL (brand not important) cabinet brought to me for repair back in the 90s.  The complaint was "the highs don't work".

When I moved the cabinet to remove the back, I heard a "clunk".  So I figured the driver had broken off the neck of the plastic horn.

But when I got the back off, the driver was still there-but one of the wires was not hooked up.

I looked for the "clunk" and found ANOTHER HF driver in the bottom of the cabinet.

I guess it had ripped the wires from the one on the horn.

The one in the bottom had a blown diaphragm.  So I guess they just put a new driver on the horn and left the old one in the cabinet. Who knows---------

Why they never noticed the clunk when moving it is beyond me.  Oh well.
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David Sturzenbecher

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Re: Funky QRX212 Measurments
« Reply #16 on: May 20, 2017, 06:30:31 pm »


Maybe I missed it, but are you sure the drivers are the correct ones for the cabinet?

People very often swap out drivers for various reasons.  Often times it is because of a failure, and they needed "something" to make sound.  Even the wrong sound is better than no sound.



I mentioned previously that some of the HF drivers got new diaphragms a few years back, maybe 5-6 years ago.  I am told that it was from an authorized EV shop, but I have not opened the boxes up myself. I do know for sure that none of the drivers were intentionally swapped out with non-oem modules on purpose. It looks like i will see this rig again next month, however in a different venue, so the investigation will continue.
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Ivan Beaver

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Re: Funky QRX212 Measurments
« Reply #17 on: May 20, 2017, 07:22:36 pm »

I mentioned previously that some of the HF drivers got new diaphragms a few years back, maybe 5-6 years ago.  I am told that it was from an authorized EV shop, but I have not opened the boxes up myself. I do know for sure that none of the drivers were intentionally swapped out with non-oem modules on purpose. It looks like i will see this rig again next month, however in a different venue, so the investigation will continue.
Maybe there is something wrong with the xovers inside.
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Ivan Beaver

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Re: Funky QRX212 Measurments
« Reply #18 on: May 20, 2017, 07:27:07 pm »

I do know for sure that none of the drivers were intentionally swapped out with non-oem modules on purpose.
Years ago I was working as a bench tech at a "all around" audio shop.

They had some Peavey speakers they would rent out to customers.

One time they came back and I glanced at them the next day (not my job to check them in), and they didn't look right.

I took them apart and the guy who rented them had taken out the Black Widow speakers and 22xt driver and had replaced them with total garbage  drivers, just so they would "make sound" when returned.

I suspect he rented him just for that purpose.

It is amazing what can happen to gear when it is not in your hands.

I'm not suggesting anything, just saying "things happen" and people don't realize it.
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Tim Weaver

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Re: Funky QRX212 Measurments
« Reply #19 on: May 21, 2017, 02:41:31 pm »

Maybe a horn fracture causing a reflection in the throat?
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Kevin Maxwell

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Re: Funky QRX212 Measurments
« Reply #20 on: June 02, 2017, 11:14:51 pm »

Below is something I wrote about the QRX212 speakers and I wonder if maybe one of the horns wasnít put back in the proper way. But looking at the pictures of that room I would either rotate the horns the way I mention below or I would use the dual PA method with the horns in the normal configuration.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
I am writing this part for people that donít know about the horns in the QRX212 speakers. They are asymmetrical in coverage but square in shape so they can be rotated. In normal configuration they are 75-degrees wide by 15-degrees up and 35-degrees down. I spoke to EV about the splay and was told that the boxes with the backs touching had to be 13 1/8Ē apart in the front to minimize the horns interfering with each other. That would get you the 150-degrees wide for 2 boxes. I didnít want 150-degrees of coverage and it seemed to me when I tried that the 12Ē drivers didnít splay well. I used the dual PA method once indoors and it worked great, flat fronted 2 boxes a side and ran vocals in one and instruments in the other, per side. But I needed more than 75 wide (for an outdoor summer concert series we were doing) and less than 150. I have been using them with the fronts splayed 8Ē apart. It was a compromise like a lot of things in sound windup being.

Now to how we rotated the horns. If you look at our setup as boxes 1-4 with boxes 1 and 2 as a pair on house left and boxes 3 and 4 as a pair on house right. If you are looking into the box we rotated the horns so boxes 1 and 3 have the horns, with the 35-degree to the left and the 15-degrees to the right. And on boxes 2 and 4 (if you are looking into the box) the 35-degree angle is to the right and the 15-degrees to the left. So the 15-degree part of the horns are in the middle of each stack, towards each other. This should give you 100 degrees of horizontal coverage from the horns. This orientation seemed to give me a much narrower area of horn interference in the audience area.   

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