In message , Wally
writes
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




What frequency are you intending to crossover at between the B139 and
the B110? (I guess its around 600Hz or so).

At this frequency the capacitors will be around 20 to 25uF, and the
inductors around 2 to 3mH.

I detest bipolar electrolytics, and its not too difficult to get good
quality film capacitors in 10uF and 4.7uf values to parallel up to get
the value you need. Polypropylene dielectric will be the best (and the
dearest.)

No point going to working voltages over 100V on the caps though.

You could wind (or buy from Wilmslow) air-cored inductors rather than
open-bobbin ferrite ones, but remember: an air-cored inductor will have
a higher resistance than a ferrite-cored one (more turns as the
permeability of air is a lot less than typical ferrites), and the
external field will extend further. People often forget that the
inductors on the crossover will interact via their mutual-inductance if
they are aligned the same way and close enough. Try if possible to have
the axes of inductors that are close oriented orthogonally to each other
to reduce the transformer action.


--
Chris Morriss