ABSTRACT
The desirable characteristics of a crossover system are easy to state but not so easy to achieve in practice. There is a general consensus that there are five principal requirements that apply to all crossovers: adequate flatness of summed amplitude/frequency response on-axis; sufficiently steep roll-off slopes between the output bands; acceptable polar response; acceptable phase response and acceptable group delay behavior. Crossovers that sum to a completely flat amplitude response include the 1st-order crossover, the 2nd-order Linkwitz-Riley crossover, the 3rd-order Butterworth crossover and the 4th-order Linkwitz-Riley crossover. There are many crossover types that can be made to sum very nearly flat by tweaking the filter cutoff frequencies. In addition to the general requirements for all crossovers given earlier, there are further special requirements for active crossovers. Some further requirements for active crossovers, in no particular order, are: Negligible extra noise; negligible impairment of system headroom; negligible extra distortion; negligible impairment of frequency response and negligible impairment of reliability.
