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Author Topic: Funky QRX212 Measurments  (Read 1776 times)

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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Ivan Beaver
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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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