Here is a revised version of my MBOW1 3-way design that replaces the discontinued Peerless 850146 CSC-X Line woofer with the Peerless SLS 830668 10" woofer ($56 each at Madisound) in a two Cubic Ft. sealed box. The bass-mid crossover is 450 Hz using a second order acoustic slope. Here is the link for the woofer.
And here are the schematics for the crossovers. Note that the M130 is connected with REVERSE POLARITY. Don't mess that up--it will ruin the sound.
NET 1 (Bass Low Pass Filter)
NET 2 (High Pass and Low Pass Filters for M130 Mid)
NET 3 (High Pass Filter for OW1)
Here is the on-axis response as measured by my Praxis system on the tweeter axis. My upper cabinet had no edge round over, and this introduces diffraction dips around 3 kHz and from 7 kHz-8 kHz. If you use a 3/4" round over, these will largely disappear. No roundover is needed on the woofer cabinet.
The response measured at 30 degrees, 45 degrees, and 80 degrees off-axis horizontally shows no serious irregularities other than the expected changes in diffraction effects and upper treble response.
Finally, here is the predicted impedance. It falls to 3 ohms briefly in the midbass, but this should not be a problem for most amplifiers.
The plans for the MBOW1 upper cabinet can be found here. These plans were meant originally for a larger tweeter than the OW1, so the routing and cutout will have to be adjusted for the smaller OW1 flange and inner diameter. You may also move the tweeter hole down a little so that the bottom of the OW1 flange is where the bottom of the original tweeter flange is indicated. In my prototype, I just used a rectangular 2 cu. ft. box for the bass cabinet, constructed with 3/4" mdf and a single shelf brace. The dimensions are 24 1/4" H, 12" W, 17.5" D. The woofer is mounted toward the top, with a center-to-center distance of 12" between the woofer and midrange. You will need some kind of isolation between the bass and upper cabinets. Simple rubber feet on the upper module will probably do. There really isn't room in the little upper cabinet for the entire Net 2 and Net 3 crossover.
I would plan to mount the whole crossover in the bottom of the bass cabinet, or build a separate hollow base for all those components (some of which will be very bulky). The crossover will be very expensive if you use top-of-the-line poly caps. I used Axon poly caps for the larger values, and think they are a very good value (available from GR Research). Or I'm sure you could use mylar and probably never know the difference.