Capacitors

The capacitor is the heart of the high-pass filter: it shields the tweeter from low frequencies and smooths impedance in Zobel and notch networks. The part sitting in a tweeter's signal path passes every note, so both type and quality are audible.

Film capacitors (MKP, MKT, paper-in-oil, copper foil) belong in the signal path, bipolar electrolytics suit high-value bass sections, and power capacitors go into supplies. For crossovers, choose at least a 100 V rating and a tolerance of 5% or better.