What is passive EQ compared to an active EQ circuit?
A passive EQ uses inductors and high value capacitors to filter; there are no amplifiers in the circuit to filter. It uses an amp to match impedances. An active type EQ circuit is different in that the filter (reactive) element is located within the feedback loop of an amplifier. These generally utilize lower value capacitors and resistors instead of inductors. One of the main advantages of passive EQ’s are in the way they sound, which tends to be more musical due to rich harmonic structure inside the inductors. Another huge advantage is the excellent phase coherence exhibited by this type of circuit. Active EQ’s tend to have strange and unpredictable phase discrepancies around the EQed frequencies, making the sound somewhat smeared and unfocused, whereas a passive circuit will not have this effect. Disadvantages for passive circuits include the cost as the inductors need to be very high quality with strict tolerances, the capacitors need to be very high value, and aligning the unit is
