ABSTRACT
The elliptical filters used in the crossover are the usual combinations of notch filters and all-pole filters. The two deep notches symmetrically placed on either side of the crossover point are at 529 Hz and 1.84 kHz, less than an octave away from the crossover point. It is obvious that their presence greatly increases the initial roll-off slope, making it more effective than a 4th-order Linkwitz-Riley alignment from this point of view. A 4th-order crossover design based on the use of elliptical filters was published by Bill Hardman in Electronics World in 1999. The original Hardman crossover used Bainter filters to create the notches followed by 2nd-order Sallen & Key filters. The highpass notch response has a passband gain of 0 dB at high frequencies, and at frequencies below the notch comes back up to -10.8 dB. One of the better-known notch crossovers is that known as the Neville Thiele Method crossover.
