I'm trying to teach myself crossover design so that I can build a crossover for a 2-way kit I want to modify. The kit is the SEAS Idunn kit from Madisound. I want to add a second woofer (in parallel) to the design, which should increase overall SPL 3db. It will also change the net impedance of the woofers, so I'll need to modify the crossover. The modified Idunn will be combined in a single enclosure (separate compartments) with a powered sub.

To make sure my method was correct, I tried to derive the values SEAS shows for the unmodified Idunn, using this online calculator:

Passive Crossovers, Capacitor and Coil Calculator

(That is the only one I could find that allows calculation of 1st, 2nd, and 3rd-order filters. The Idunn uses a 2nd order on the woofer, 3rd order on the tweeter).

The calculator gives entirely different values from those SEAS shows (see photo).

I'm assuming the impedance value for the tweeter should take into account the L-pad. That gives a net impedance for that load of 4.75 ohm. I also tried the calculation using the tweeter's nominal 6 ohm value. The values for the tweeter filter I got are:

4.75 ohm

________

C1 10.16 uF

C2 30.46 uF

L1 0.26 mH

6 ohm

_____

C1 8.04 uF

C2 24.12 uF

L1 0.33 mH

Neither of which agrees with SEAS' values.

I also compared the low-pass filter values from the calculator with SEAS' values. They are different also.

The nominal impedance of the tweeter is 6 ohms; 8 ohms for the woofer. Specs are here:

H1571-08 U18RNX/P (woofer)

H1499-06 27TBCD/GB-DXT (tweeter)

Can anyone explain these discrepancies?

Thx!