ABSTRACT
This chapter shows a 1st-order subtractive crossover. Higher-order subtractive crossovers can be implemented by replacing the 1st-order filter with a higher-order version. Subtractive crossovers are also called derived-crossovers, as one output is derived from the other instead of being filtered independently, and constant-voltage crossovers because of the way that their outputs sum to reconstruct the original waveform. The constant-voltage crossover, first properly described by Dick Small, one of the great pioneers of scientific loudspeaker design, is a subtractive crossover. Subtractive crossovers promise—and indeed deliver—perfect waveform reconstruction. The subtractive process also offers perfect matching between the crossover characteristics of the HF and LF paths. An intriguing aspect of the subtractive crossover is the prospect of saving some serious money on filter capacitors. A 3rd-order subtractive crossover can be made in just the same way by replacing the 2nd-order lowpass filter with a 3rd-order one and carrying out the same subtraction.
