Are These 4312a Control Monitor Crossovers?

[brettMc]

Hello,

Bought a second set of what I think are JBL 4312a Control Monitor Crossovers but not sure the item was properly marked. I figured if I was going to attempt my first ever hands-on upgrade of a crossover network that I should do them on a second set...in case I totally mess it up.

Please take a look at the images and let me know if these are the proper crossovers for these speakers. Your expertise is much appreciated!

Speakers:


Second-hand Crossover:

[grumpy]

yes.

Network 66324 is 3112D and called out on the 4312A Technical Manual (as is network 3112C)

[brettMc]

yes.

Network 66324 is 3112D and called out on the 4312A Technical Manual (as is network 3112C)

Could your recommend where I can find all the replacement parts I might need and a good soldering iron? Also what gear do I need to test the speakers? Tone genrator? Some sort of impedance tester? And maybe a hot air gun to unglue some of the parts from the board?

I could also use some tips on 'do's and fonts' before I do anything....

Thanks so much!

[brettMc]

...also....

Does anyone know if the tweeter and midrange are wired out of phase with the woofer or is it just the midrange that's out of phase?

[Odd]

JBL 4312A Technical Manual

[Doctor_Electron]

Looking at the technical manual the LF and MF are not wired at 180 degrees because the LF to MF section is first order. And also it appears that the HF is also not wired at 180 degrees even though that section is second order. As I think I understand it the MF to HF phase relationship is not as audibly critical as that of the LF-HF transition.

If you've ever had a mid driver such as a 104H connected wrong or happen to do it in the future, you will immediately appreciate the need to wire the mid out of phase with the LF when using a second order network.. It sounds absolutely hideous.