Crossover questions

Given that my speaker rebuild fantasy is gradually taking shape, I'm
starting to think about what to do about crossovers. The plan is to bi-amp,
one amp to the B139 drivers, the other to the B110/T27. I'd rather ditch the
orginal KEF DN12 units and make new ones for the mid/top, probably keeping
to the spec crossover frequency. So, I have some questions about
components...

Am I right in thinking that air-cored inductors are better than those with
some sort of ferrite(?) core? For the same value, would an air-cored version
be physically larger? If so, is that because it requires more turns?

What is the best type of capacitor to use wthin sensible cost limits?


--
Wally
www.artbywally.com
www.wally.myby.co.uk/music