http://www.linkwitzlab.com/filters.htm#3

and it is to a page with info on Linkwitz-Reilly filters. This one shows a 24 db/oct two way.

The topology and values are the same as those I sent you from the old Spkr Builder article. The formula is slightly different, but the results end up being the same. For example, in one, caps might me C and C/2, and the other 2C and C, but once you ran all the numbers, the values ended up the same.

For those interested, there is a schematic at that link.

There is a link under the schematic to a plot of the xover.

Also, check out the subsonic filter at the top of that page.