for 16 ohms drivers at 800Hz. would take 4.5mH coils and 8.8uF caps. At 1600Hz. use 2.25mH/4.39uF values. The values are not set in stone.
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Hey, a while back I snagged a pair of 4.25mH 18ga. coils at the ratshack on clearance, if you can come up with 4 of those you could just cross a little higher, and use a different cap value to match the coils. In lieu of a fixed pad, you might want to TEMPORARILY use mcm's 16 ohm lpads so you can vary the levels while listening.
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Once you find the sweet spot for overall tonal balance, measure the ACTUAL relative difference between the HF and LF, then work out the fixed pad values. Samremember, altec clones are different animals than pi speakers:)