Douglas Self 
Design of Active Crossovers [PDF ebook] 

Active crossovers are used by almost every sound reinforcement system and every recording studio monitoring set-up; but the use of active crossovers is rapidly expanding. This new edition, presents all the updates to loudspeaker technology and crossover design. The edition expands on loudspeaker configurations and design issues, sound reinforcement issues, more on lowpass and highpass filters, and may other filters. This new edition is a must read for anyone wanting comprehensive practical knowledge.