Basic inductor question

[paint guy]

Hi guys, I was registered on here years ago and couldn't remember my UN or password, so I re-registered here recently. I'm planning on building some LCR speakers using an older design from when I was last on here.

Anyways, to my question. I realize that inductors should have careful attention in their placement on the crossover board in relation to their X, Y, and Z axis' to prevent interference between them. However, if I am adding two inductors in series to achieve a particular value, do these rules still work or can those two be mounted parallel (literally) to each other? I didnt think it would be a problem and mounting them in a different orientation would not be any real issue, but I never had any need to do this before, so never thought about it.

Thanks,
Brad

[Evil Twin]

Actually, it's a problem even then. You can find the reason in looking at the equations for calculating inductance, and the relationship to turns- with coupling, if you double the turns, it quadruples the inductance. So putting two inductors together of the same value, say, stacking them on top of each other in phase (don't do out of phase, that creates a different problem) would result in a higher value.

The conventional wisdom about avoiding coupling is both in relationship to net values and to coupling unwanted signals into other parts of your network. So, keep them reasonably separate, and rotated with the magnetic axis of each at 90 degrees to each other in some plane...

[paint guy]

Thanks, that shouldn't be a problem. I have not built many crossovers, but this is the first time I have ever had to couple inductors to achieve a value (2.0 mH and .24 mH) to get as close as possible to a 2.75 mH. The only one I found in stock for 2.75 was a foil one at Madisound ... and I'm just not willing to pay that price. Especially times 3 for all three speakers.

Also, now that you brought it up, why would inductors ever be wired out of phase? Just curious. Never seen that particular topology in a crossover circuit. I appreciate your advice and input.

Brad

[Evil Twin]

Thanks, that shouldn't be a problem. I have not built many crossovers, but this is the first time I have ever had to couple inductors to achieve a value (2.0 mH and .24 mH) to get as close as possible to a 2.75 mH. The only one I found in stock for 2.75 was a foil one at Madisound ... and I'm just not willing to pay that price. Especially times 3 for all three speakers.

Also, now that you brought it up, why would inductors ever be wired out of phase? Just curious. Never seen that particular topology in a crossover circuit. I appreciate your advice and input.

Brad

By out of phase, I was referring to the electrical coupling due to the orientation of the two coils- there are to possibilities, and to the novice, they will look similar, with two coils stacked up. One would be such that the flux linkages unit and build together, resulting in a higher than expected value. Flip one of the inductors over, and it looks pretty much the same to the untrained eye, but then you have flux cancellation, and a substantial drop in inductance.

Yes, when much younger I used to design magnetics systems and power conversion for standard Seinar systems air to air interceptors and early Tie Fighter prototypes.... I find speaker building to be far more relaxing...

[Bear]

Some pictures....

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

[paint guy]

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

Very informative. Thank you!