The lowpass filter LP1 and the highpass filter HP1 may each be independently configured as:
Bessel 6 dB/octave (1st-order)
Bessel 12 dB/octave (2nd-order)
Bessel 18 dB/octave (3rd-order)
Bessel 24 dB/octave (4th-order)
Butterworth 6 dB/octave (1st-order)
Butterworth 12 dB/octave (2nd-order)
Butterworth 18 dB/octave (3rd-order)
Butterworth 24 dB/octave (4th-order)
Linkwitz-Riley (Butterworth-Squared) 12 dB/octave (2nd-order) Linkwitz-Riley (Butterworth-Squared) 24 dB/octave (4th-order)
In addition, the cutoff frequency, attenuation, and polarity in the low band and the high band may be independently adjusted, and the filters in either band may be bypassed entirely.
The cutoff frequency in each filter is continuously variable from 20 Hz to 20 kHz.
The attenuation in each band is continuously variable from -96 dB to 0 dB, plus mute.
The polarity in each band is selectable as + or - (in-phase or out-of- phase).
Each band may be bypassed, in which case all of the crossover filters in that band will be bypassed while the crossover filters in the other band will not be affected.
Two-Way Bessel and Butterworth Crossovers Bessel crossovers utilize Bessel filters. Bessel filters are designed for maximally-flat group delay, meaning that they have nearly linear phase and excellent transient response. Their amplitude response is not as flat and their cutoff is not as sharp as those of Butterworth filters.
Butterworth crossovers utilize Butterworth filters. Butterworth filters are designed for maximally-flat amplitude response, meaning that the amplitude response in the passband is as flat as possible without ripple. Their phase response is not nearly as linear and their transient response is not as good as those of Bessel filters.
The Bessel filters used in the ISP-100 crossovers are automatically scaled so that their amplitude response is -3 dB at the selected cutoff frequency, regardless of the filter order.
The amplitude response of a Butterworth filter is naturally -3 dB at the selected cutoff frequency, regardless of the filter order.
