Crossover Coil Interaction

[Jamier]

How far apart should the inductors in a xover be placed? I have built several and never noticed any problems but I never made more than one version of any particular circuit to make side by side comparisons. Can close proximity of coils be a problem? What are the symptoms of coil interaction?

Jamie

 

[Paul Birkeland]

It's much more commmon to just arrange the coils so that they are unlikely to interact.  Beyond that, you'd need a scope an a generator to see how any two coils might interact with each other.

 

[Josh.G]

I found some tests someone did with inductor positions when I was wondering about that myself.  Maybe this will help you out!

http://www.troelsgravesen.dk/coils.htm

 

[Jamier]

Josh,

    Thanks for that link. Interesting stuff. I have referred to Troel's site often but never saw that article.That guy is so prolific. It would take days and days to review everything he has done.

Jamie

 

[Paul Joppa]

A decade or two ago, there was an article on the subject - possibly in Speaker Builder (?)  If I recall correctly, it tested complete crossovers, not just two coils on various configurations. As I recall, the effect was quite a bit larger than I intuitively expected.

 

[Jamier]

    Considering PB and PJ's comments, perhaps you guys will eval this coil arrangement.As I said before, I don't think I have ever had a problem, but if you don't measure the interaction or try several arrangements and compare, how would you know? For scale, board is 6"x12". The large foil inductor is about 8 inches from the smaller aircores. This is the first time that I have put both woofer and tweeter components on the same board ( due to space considerations). This puts more coils in proximity to each other and thus, my concern.

Jamie

 

[Paul Joppa]

The large foil inductor has the same axis as the small one at the far end of the adjacent long side. It is possible to orient three with mutually perpendicular axes. The 8" spacing is too close to rule out an audible difference without testing it.

As always with speakers, an audible difference may not tell you which will sound better. At some point, if it sounds good then it IS good, and you should enjoy some music!

My two cents.

 

[Jamier]

PJ,

    Thanks for the advice. Have you ever seen anyone cover xover coils with steel boxes or flat shields? It would be easy to do, but probably a little bit of overkill.

Jamie

 

[Paul Birkeland]

    Thanks for the advice. Have you ever seen anyone cover xover coils with steel boxes or flat shields?

This can change the inductance of those coils!

 

[Jamier]

PB,

      I almost forgot about that. I guess that's the reason why you should never use steel screws to secure an iron core inductor(?) ( I've never used one, but I heard that advice some time ago).

Jamie

 

[jdm]

+1 for PJ's suggestion concerning the inductor with the red leads.

Jim

 

[Jamier]

Jim,

    I'm not completely sure, but I think PJ was referring to the coil with the white shrink. This definitely has a problematic orientation with the large foil inductor, but since it is almost nine inches away I'm hoping it doesn't effect things too much. I hope PJ will let me know for sure if that's the one he was referring to.

Jamie

 

[Paul Joppa]

The one with red wires has the same orientation as the foil inductor, and is close enough to be  a potential problem - IMHO.  If you put it on edge (like the white-wire one is) with the axis pointed at the one with white wires, they will all have axes perpendicular to each other, which should minimize interactions.

Whether the difference is audible, or produces a clear preference, can only be determined by experiment.

 

[Jamier]

Well, I guess this is my chance to make those comparisons I was talking about.Since this xover will be mounted externally, changing things will be easy. I'll change one now and see if there is a difference between the two once I have them up and running.Thanks to all for your input.

Jamie

 

[Jamier]

I could not tell a difference between the xover with the reoriented aircore  and the one with the axis parallel to the large foil inductor. My hearing may not be what it used to be, so if any difference exists it isn't apparent to me. I think I will change "wrong" one though, just to keep things consistent.(maybe 8 inches was enough?).

Jamie

 

[Paul Birkeland]

Yeah, I would be equally less surprised if you did hear something.  This stuff can be fiddly, and I've become somewhat dependent on my measuring rig to make me feel less crazy!

-PB

 

[Paul Joppa]

Thanks for posting. A negative result is just as useful as a positive one - maybe even more useful, since you avoid a lot of "confirmation bias" that way!