Professional loudspeaker systems use the possible less passive filters (crossovers) because of the components' variable parameters and their impacts on each other, the non-linearities and dissipated power. Instead of this active crossovers are placed before the amplifiers. This solution makes possible further corrections, too like equalization and delay according to the loudspeaker's model and placement. These shall be integrated in a device called system processor (or system controller).
System processors in the market are DSP based in general but in this paper an FPGA based solution will be described. The device for it is a Logsys FPGA demo board with a Xilinx Spartan3E chip on it extended with a Wolfson WM8569 stereo audio codec.
The paper introduces some system processors and their features. You can read about the desired filters and transfer functions in details and how they are implemented, for example about the applied wave digital filter structure to achieve smaller required word length for the calculations, about the difference between peaking and shelving equalizers or about the wide-spread Linkwitz-Riley filter and its benefits. Explains a solution to control output signal level before clipping.