Jf50 front fill crossover issue

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Chrisfromthepast

Well-known member
Joined
Mar 5, 2018
Messages
265
Hi GroupDIY,
I hope this little repair will be enlightening to members besides being a passive crossover network, this puzzle still has the possibility of requiring homewound inductors, or some discussion of the best electrolytics for a crossover design…
On the bench are (4) EAW JF50 nearfield speakers, 2 of which have radically different phase and frequency responses than the other 2.
The only thing I have to go on is the 1 sheet marketing material. EAW might come through with a layout.
When I’ve been down this road in the past with wedges and traps, I was able to get the crossovers out and lift one side off the turret board connection, and measure every component to brute force and save time.
This is a tight little package, and I can’t quite get the whole thing out, or have an easy time lifting the components inside the box.
So, I need a little help thinking this through.

The marketing suggests a 4th order crossover filter, and I know from the test trace that the 125hz 6db filter at the bottom works fine on all of them. The problem seems to be in between the woofer and the mid range driver. Im guessing an inductor melted, but which one? Inside is a rainbow of wires, and a user facing 4 ohm to 16 ohm switch complicates the maze.
I have no schematic or layout, but can say a little about the topology I learned from sweeping the speaker and probing the terminals unloaded.
One of the 5 inch woofers has a high pass at 125 and is open on top, while the other acts as a midrange driver.
Is this 4th order crossover with silk dome on top, and 2 identical 5inch “woofers” that are at different pick points in the crossover a common topology that I can google?
 
Sounds like a 2.5-way arrangement..? Although the "One of the 5 inch woofers has a high pass at 125 and is open on top, while the other acts as a midrange driver" part is really confusing.

Does the second woofer have a high-pass AND a low-pass? That's what i would understand as "acts as a midrange driver".
 
Sounds like a 2.5-way arrangement..? Although the "One of the 5 inch woofers has a high pass at 125 and is open on top, while the other acts as a midrange driver" part is really confusing.

Does the second woofer have a high-pass AND a low-pass? That's what i would understand as "acts as a midrange driver".
My understanding is one of the woofers is high-passed and low-passed, the other being only high-passed, relying on its natural roll-off to cross-over with the tweeter.
This is not a rare arrangement, actually one of the several possible 2.5-way arrangements.
 
This is a tight little package, and I can’t quite get the whole thing out, or have an easy time lifting the components inside the box.
Can you graph the electrical response of each driver? That should definitely point at which part is duff.
Anyway, in order to fix the problem, you'll have to take apart the cross-over.
BTW, have you checked that all drivers are OK?
 
I have replaced some drivers in the 4 units, and was pretty disappointed that I still had work to do. I checked the polarity of each component, and swapped them around with the same results.
here is one of the units, sweeping each of the speaker terminals unloaded
jf50 unloaded.png
 
This is the same speaker, loaded, and swept 1 meter from the tweeter. Two of the speakers look like this, with some small discontonuity at the hf crossover region, but is flat enough for EAW

Screen Shot 2022-09-23 at 10.48.42 AM.png
 
here is the same crossover test , with 2 different units.
3 is the one I posted before. 2 is a sort of control group, presumed good.
this is a sweep, through an amplifier, with the test done at the speaker terminals with speakers attached.
Impedance test of the drivers will have to happen this afternoon. The woofer and mid range drivers are the same
j50 loaded 2 units.png
 
so, speaker 2 should be considered "right" compared to 3, and the problem is probably in the HF portion of the crossover.
are these reasonable assumptions to start hunting with?

Thanks for helping me think it through!
 
I have replaced some drivers in the 4 units, and was pretty disappointed that I still had work to do. I checked the polarity of each component, and swapped them around with the same results.
here is one of the units, sweeping each of the speaker terminals unloaded
View attachment 98849
Definitely something wrong with the midrange (green plot).
You mentioned a high-pass filter on one of the drivers. Looks like a duff capacitor in the midrange output. Its contribution is close to nil.
The low here is driven full-range except for a 20Hz infra filter.
 
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