The crossover used within Pi Speakers uses a third order filter for the tweeter and a matching filter for the woofer, with crossover point and slope dependant on the woofer chosen. In addition to the basic crossover frequency-splitting high-pass and low-pass filters, top-octave compensation is employed for compression drivers for response shaping, to make power response flat.

I highly encourage you to download a copy of the accompanying executable Spice models, which are currently available and online. That way you can manipulate the models shown in this document yourself - changing crossover components to modify crossover frequency and filter slope. There are models of the sample filters shown in this crossover document, and there are models of the specific crossover designs I recommend for use in Pi Speakers shown as well.

Be sure to check periodically for additions to this document. When it's done, it will have second-order and a third-order designs and a discussion of the strengths and weaknesses of each. It will also show the power across each part used in Pi crossovers, so a person can know how to select appropriate components.