MoFi,
Don't know why its not more widely used, one explanation could be that you'd need twice the capacitance otherwise required. For an example if your crossover design for the high-pass filter for the tweeter calls for a 5uF capacitor followed by a 15uF capacitor with a .3mH coil to ground from their midpoint (typical values).
To convert this to a actively biased crossover you would need two 10uF (replacing the 5uF) capacitors in series with their midpoint being the bias point followed by two 30uF (replacing the 15uF) capacitors in series with the bias point being their midpoint, so you can see the bill of materials stack up pretty quickly.
Good Listening
Peter
