In message , Jim Lesurf
writes
The advantage of higher orders is they can cut down to size of the region
where we have an (unwanted) array effect. However you can do this using my
approach, and it saves money as you only need one high-order LPF and then
get the HPF that matches it 'for free'. :-)

Slainte,

Jim


But even if your HPF (say) is a 4-th order, the LPF you get by
subtraction is still only a first order. The phase shift of the summed
output is zero, and it does sum flat of course, so it still is a good
thing.

(It took me ages to work this out, but it is correct, and a quick SPICE
simulation shows it)

As I said in an earlier post, I do this on a homemade two-way (M-T-M)
that I use. A second order HPF for the tweeter, and the subtractive LPF
for the Bass units. I put the main filter as the HPF to roll-off the
tweeter reasonably quickly, whereas I wasn't too worried about the
low-order roll-of of the subtractive LP output.


--
Chris Morriss