Capacitors are among the most-used components in any electronic design, but have particular significance in pro audio applications. The most basic is a simple filter, such as a passive speaker crossover, where a single non-polar capacitor in-line with a tweeter can create a first-order, -6 dB/ octave slope high-pass filter (as shown here) that blocks low frequencies from reaching the tweeter and the impedance of the speaker and value of the capacitor determines the roll-of frequency. For example, in-line with an 8-ohm tweeter, a 10-microFarad capacitor creates a roll-of that’s approximately of 2 kHz; a 20-microFarad cap creates a filter in the 1 kHz range. Conversely, adding a single inductor (coil) inline with the woofer results in a first-order low-pass filter. More complex (second/third/ fourth-order) passive crossovers with slopes up to -24 dB/octave can be created with various combinations of multiple capacitors and inductors.