Chris Morriss wrote:

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

It depends on what I do with the bass cabs. If I build one-piece 3-way
units, then the xover would probably stay the same as the spec 400Hz. I'm
considering separating the bass cabs from the mid/top so's I can stash the
big boxes out of the way and just have small stand-mounted speakers that are
easier to move and don't dominate the room. I want to keep two bass cabs,
and they'll probably be positioned either side of the listening position,
wider than the mid/top. There's a good chance that they won't be
symmetrical.

Having no direct experience of it, I don't know how much the directional
bass frequencies would suffer with the speakers spread around, so I'm
tending to the view that a separate cab arrangement would entail lowering
the B139/B110 crossover point, to put more of the directional bass into the
easily-positioned B110s. I have a plus in that there will be two bass cabs,
with left/right separation, but a potential minus in how lower bass I can
get out of the B110s in their proposed enclosures. Ideally, I'd like to have
the B110s roll off without any LC, and have some kind of (adjustable?)
filter before the bass amp to fit the low end to the mid roll off. I need to
learn more about the effect of the mid enclosures before I can come up with
a probable number for a bass/mid crossover frequency.



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

Yup, in the ballpark for the DN12.


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.

Okay, I'll troff for polypropylene caps.


You could wind (or buy from Wilmslow)

I'm up for winding them if there's a sensible cost saving (I'll have a look
at Wilmslow's prices).


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. ...

Can I get around the resistance thing by using thicker wire?


... 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.

Duly noted. :-)


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