Scanspeak speaker (help!)

My answer might be a little bit useless but I will say that crossover design is the hardest thing to do in speaker building. There is no magic rule to associate a type of driver/loudspeaker combination with a type of crossover. Each type of crossover has advantage and disadvantage. Part quality has also an influence.

I suggest you to search for crossover design in google and you will find a lot of useful information.

When I have time and enough parts, I try different crossover topology and I tweak the system until I get good measurements and a good sound.
 
if i remember it correctly it is a simple netwrok. there is an Lapd using i think 4ohms series and 10 ohms parllel.

other than that the impedance correction is built into the network. it is a lot fo trial an error on site.

since we are DIY we have the advantage of using the XO to compensate for room abnormalities too. the cabinet as I mentioned earlier is not a cuboid but maybe this network will give you a good starting point.