Please note that this crossover (although it will work very well) is usually not as good as the Linkwitz-Riley alignments. The slope of the filters shown here is 18dB/octave, and in common with all odd-order filters there is a 90° phase shift at the crossover frequency. L-R crossovers are available on the Projects Page in both 12dB / Octave and 24dB / Octave. They are completely phase coherent, and offer better overall performance than this version. PCBs are also available for the P09 (one of the most popular).
An improved version of this crossover is shown in Project 123. The later article also has quite a bit more information and gives you more options than the one shown here. This is a completely traditional circuit, where the P123 alternative uses extra opamps to achieve a better overall result with fewer odd resistor values.