anyone know anything about coupling inductors?

[mondogenerator]

basically i want to test a sub x over...butterworth at about 80Hz. From calcs its needs about 170uF and 22mH inductor. ANyone have an idea how to use a tranformer as a coupled inductor in cases like this?

[davygrvy]

air-core is the chosen method as air won't saturate, iron could.

Shavano Music Online - Cross-Over Network; Air Core Inductor Calculator
Inductor Designer / Calculator

22mH looks big, especially if you want a low DCR. I see why you're asking about modding a transformer. You can increase the inductance of a smaller air-core just by sticking a screwdriver (or nails, etc..) through the center if you have any to play with.

Parts-Express.com - Iron Core Inductor Index: Super Q, Laminated "I" Core, C-Core Toroidal

[mondogenerator]

Originally Posted by davygrvy

air-core is the chosen method as air won't saturate, iron could.

Shavano Music Online - Cross-Over Network; Air Core Inductor Calculator
Inductor Designer / Calculator

22mH looks big, especially if you want a low DCR. I see why you're asking about modding a transformer. You can increase the inductance of a smaller air-core just by sticking a screwdriver (or nails, etc..) through the center if you have any to play with.

Parts-Express.com - Iron Core Inductor Index: Super Q, Laminated "I" Core, C-Core Toroidal

LOL strangely enough 22mH is big, and air core is defo out of the question.

[mondogenerator]

oh and yes...air WILL saturate...albeit at a higher current that ferrite or iron cores...just wondered if anyone had any experience of using transformers as coupled inductors in xovers really, and what sort of things i should look for. Really just to save me the hassle of working it all out. As i work in an EM test facility i could get these made cheap and painlessly and my general knowlege of EM stuff is good as a result, however coupled inductors are not common within the power generation industry...or at least not in my field of experience.

[davygrvy]

I mostly see iron-core inductors used for tube rectifier power supplies, not in speaker x-overs. The DCR is the important part as it determines the power loss and to the same effect is the saturation point which is usually given as a current rating.

A Hammond 159ZE will get you 28mH@3A with a DCR of 0.43 and weighs under 3lbs. I believe the behavior of iron-core inductors is the inverse of electrolytic caps. At low currents, the inductance is higher than the rated value. As the core becomes more saturated, the inductance will diminish. No charts at the hammond site for L vs I, sorry.

If this was me, I'd chose a line level x-over instead for many reasons. For the price of the copper alone for an air-core 22mH inductor, you could probably get a plate amp and you're halfway there.