ABSTRACT
There are many types of crossover, classified in various ways. In discussions of crossover design, and in filter design generally, the terms "pole" and "zero" tend to be freely scattered through the text. An all-pole crossover is composed entirely of all-pole filters. The so-called Solen split 1st-order crossover is a variation on the standard 1st-order crossover. Symmetric crossovers have filters with the same slope at the crossover point. For example, a 2-way 2nd-order crossover has 12 dB/octave slopes for both HF and LF filters. Asymmetric crossovers have differing slopes at the crossover point; the HF filter might have a 18 dB/octave slope while the LF filter has a 12 dB/octave slopes. Crossovers are classified as either "allpass crossovers" (APC) or "constant-power crossovers" (CPC) in accordance with the way that the outputs recombine. An allpass crossover has filter outputs that sum in the air in front of the loudspeaker to create a sound pressure level (SPL) with a flat amplitude/frequency response.
