Air or a steel core inductor

[mondogenerator]

There isn't any until the iron core saturates. With good iron core or ferrite this will not hapen until the speaker is so stressed you wouldn't notice anyway. Buy cored inductors when they are more than 1mH, it only makes sense. Cored inductors have lower DCR, better "Q".

at last a realistic, sensible answer!

to the OP air cores are technically better, but will saturate too eventually. this takes more current to cause though since the generated field is much larger and less densely packed than a ferrite/iron core. this can cause interesting situations where a pair of air cored coils can cross couple to eachother, if they are too close to each other and not perpendicular in one plane.

As Ron wrote, anything over 1 mH go ferrite/iron core or the filter Q will be naff, esp if like me, you wound 1mH AIR COR with a dcr of about 3 Ohms..................and thats on a good day.......

In general, air cores are preferred. I prefer to use foil inductors, but unless you're pretty picky they're not necessary. A coil in series with the woofer especially, and to a lesser extent the mid, should usually be as low in resistance as possible.

yeah ive been there. used some american maybe 6 gauge foil chokes. damned expensive, HUGE coupling field, AND not actually any noticable difference, when compared to large current ferrite cored chokes. the only real bonus i can see to foil chokes is an odd one: the foil is very thin and folded, in this way the 'gauge' means that unlike some wire wound chokes, 'skin effect' at HF is less pronounced. THATS IF its important at all in the intended application. clearly in an LP filter it is NOT, but conversly to their normall application, foil chokes are probably better in this regard, in notches etc at higher frequencies

using a M20 bolt to physically join 2 together thru the centre makes for an intersting trannie though

When mounting the coils on the XO board, if they are close (within 2 inches?) mount them at right angles to each other to minimize coupling.

haha as above, IMHE 2" is still too close


in my home speakers have 5 amp rated ferrites in tweeter HP xover, and 10 amp rated ones in LP, dcr 0.15 OHM, they may rarely saturate, but only on the highest of reactive current peaks , and at higher volumes than i am capable of driving them so im happy with this school of thought.