Looking to make some passive crossovers and I have questions about inductors:
(1) If 2 inductors are wired in series, will the net result be summed? (ie - 4 mH + 4 mH = 8 mH or (3.5 mH + 2 mH = 5 mH)

(2) If 2 inductors are wired in parallel, will the result be similar to what happens to the impedance of speakers when they are paralleled? (ie 4 ohm + 4 ohm + 4 ohm = 1 1/3 ohm so would an inductor similarly be 4 mH + 4 mH + 4 mH = 1 1/3 mH)

(3) This one may be specifically for DUKK. At one point you said you have souped up passive cross overs to increase their slope from 6 db/octave to 12, 18 or 24 . . . how did you do that?

My assumption is that my first two questions are wrong. That if I were to series inductors I would not increase the inductance, but rather steepen the slope - so 3 inductors would steeped the slope to 18 db / octave.

If anyone can help me out for sure on this I would greatly appreciate it. Thanks.

Inductors work like resistors when it comes to value

Parallel= 1/i1+1/i2+1/i3=1/iT

Series = i1+i2+i3=iT


Capacitors work opposite

Parallel= sum of cap's
Series= well, you know what I mean.

^ So indeed the first 2 questions were correct.

As for #3, depending on the crossover you are dealing with it can be pretty easy to turn say a 6db low pass (a simple inductor) into a 12db low pass by adding a cap across the line.

Thanks Furley; I knew that much about capacitors just from playing around with them. I now know how to exactly calculate the value by doing that. Thanks for confirming what I thought in my first 2 questions.

Thanks Dukk - Exactly where "across the line?" From the one end of the inductor to the next? From the + terminal of the woofer to the -? Do you have a schematic, or know of a good site that would have a tutorial?

And, would it be possible to steepen the slope further to 18db?

If this information is necessary: The application is running a 2 channel amp in tri-mode. I don't know if that would effect any of your suggestions for steeping the slope, and placement of the capacitor.

I will be working with a simple inductor / capacitor for the lowpass / highpass.

increasing the slope is obtained by caps and inductors.

for a lowpass filter you'd need two inductors and one capacitor to make 18dB/oct

Pretty decent link, with schematics: http://ccs.exl.info/calc_cr.html

Thanks Jeepbeats! Awesome link.

It confirmed how I understood DUKK's wiring explanation. The question I now have, is Can I steepen the slope while running the amp in tri-mode.

It would seem to me that the high-frequencies which make it through the inductor, get a "free-ride across the capacitor then straight back to the amp. These seems to be somewhat of a "short" in my mind. Obviously it works because people have been using these things for a while. However, since I will be running my fronts LR and my sub mono, would this "free-ride" to those high-frequencies come back to the amp with too low of an impedance - also detrimentally effecting the high-freq out puts going to my speakers?

. . . wait . . . I think I might be getting it.

Does an inductor exponentially increase the impedance the amp sees as the freq. goes up - hence the diminished output? Likewise, does a capacitor exponentially increase the impedance the amp sees as the freq. goes down?
If that is the case then I suppose there would be no supposed "short" as I earlier mentioned . . .

Dukk, you're old-school and have done tri-mode stuff back in the day, what Can I and can't I do?

Your understanding of how an inductor and capacitor perform their jobs is correct - their impedance changes with frequency and that is what causes the attenuation.

I would not worry about going steeper than 12db. The difference in sound really is not that great from 12 to 18db/octave but the cost is. I'd rather face the woofer into the floor or wall and get some free rolloff that way.

Thanks Dukk,
And you still are avoiding the tri-mode question. At this point I will assume your avoidance means it is safe to run tri-mode regardless of slope. I will begin my searach for adequate inductors.

lol - not really avoiding but yeah provided the amplifier is tri-mode capable slope doesn't really matter.