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Author Topic: Nexo PS15 Passive Crossover Woes  (Read 327 times)

Mark Fairchild

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Nexo PS15 Passive Crossover Woes
« on: December 07, 2017, 12:39:40 pm »

So I've been doing some shop work while the gigs have slowed down and decided to go through all of our speaker inventory with systune to look for anything unusual and have definitely stumbled on some problems I wasn't expecting with our Nexo PS15's. 10 out of our 12 PS15's (first version, not R2) have a big dip around the crossover frequency between the woofer and horn as shown in the pics. We always just run them passive with either their controller and Lab Gruppen fp6400's or with Nexo 4x1 amps depending on the application. None of our PS15R2 versions have this problem. The first thing I checked was to make sure the drivers were wired correctly which they were. I then experimented with reversing the polarity of the woofer which removed the cancellation at 1 Khz, but the phase response no longer matched up with a PS15 that measures good which told me something else was going on. So, I figured something might be going on with the passive crossovers. I switched the crossovers between a PS15 that measures good and one that measures bad, and the problem followed the crossover unit. I'm not very knowledgeable about crossovers, but this crossover only consists of about 7 components. I'll try to get a picture of it to upload. Does anyone know what could go wrong in so many crossovers to cause this before we go through the trouble of sending all of them to nexo to fix?


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Ivan Beaver

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Re: Nexo PS15 Passive Crossover Woes
« Reply #1 on: December 07, 2017, 12:54:00 pm »

I would suspect a cap that has either opened or changed value.

Which one depends on the particular circuit layout.

You could take an LCR meter and compare the good circuit to the bad one.

But be sure to disconnect 1 leg of each component being tested, to remove it from the circuit.

You can get an LCR meter pretty cheap these days
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Art Welter

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Re: Nexo PS15 Passive Crossover Woes
« Reply #2 on: December 07, 2017, 01:23:21 pm »

1)10 out of our 12 PS15's (first version, not R2) have a big dip around the crossover frequency between the woofer and horn as shown in the pics.
2)I then experimented with reversing the polarity of the woofer which removed the cancellation at 1 Khz, but the phase response no longer matched up with a PS15 that measures good which told me something else was going on.
3)So, I figured something might be going on with the passive crossovers. I switched the crossovers between a PS15 that measures good and one that measures bad, and the problem followed the crossover unit.
4) Does anyone know what could go wrong in so many crossovers to cause this before we go through the trouble of sending all of them to nexo to fix?
1) 10 out of 12 appear to have the polarity reversed on the HF.
2) Reversing the woofer's polarity would make the phase response 180 degree off from the "normal" woofer. You can easily determine the woofer's polarity with a 9 volt battery "click test", + voltage to the + terminal should make the cone go away from the magnet.  Normally one reverses polarity of the HF driver to correct a "hole" in the crossover region.
3) The difference between the crossovers could as Ivan suggested be due to a problem capacitor, or component changes between crossovers.
4) Some HF diaphragms can be installed "upside down" in relation to the compression cover, resulting in reversed polarity, which could have happened at the factory or if re-diaphragmed.

Art
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Mark Fairchild

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Re: Nexo PS15 Passive Crossover Woes
« Reply #3 on: December 07, 2017, 03:45:47 pm »

If it was a driver polarity problem it should show up on the phase plot though by hovering around 180 and -180 degrees instead of around 0 degrees above 2k like all the units currently do. That's why I chose to experiment with changing the polarity of the woofer, but that was only fixing a symptom of the problem and not the problem itself. The phase and response problem seems to only exist around the crossover frequency and not above or below it. If I take the crossover of one of the units that has the crossover dip and change it out with one of the units that doesn't have the dip then that speaker now has the dip which is how I narrowed it down to the crossover. Here's a peek at the internals to show how simple the crossover is, but my boss will most likely take them to a local repair guy or send them off. I make a better audio guy than I do a bench tech, I hope haha

On a side note I wasn't expecting to see Nexo branded Capacitors.

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Mark Fairchild

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Re: Nexo PS15 Passive Crossover Woes
« Reply #4 on: December 07, 2017, 04:18:32 pm »

Oh I should also note there's an additional board behind the compression driver that it's connected to, but I only switched around the main one shown in the photo. So the second board doesn't appear to be connected to the problem.
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David Sturzenbecher

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Re: Nexo PS15 Passive Crossover Woes
« Reply #5 on: December 07, 2017, 05:54:51 pm »

Oh I should also note there's an additional board behind the compression driver that it's connected to, but I only switched around the main one shown in the photo. So the second board doesn't appear to be connected to the problem.

Mark,
Have you reached out to Nexo?  They have been very responsive in my experience.
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