Why is there a notch filter in series with a planar magnetic driver ?
A passive notchfilter, made out of a parallel combination of a resistor, capacitor and inductor, is the standard way to tame the cavity resonance. The graphs below show the action of the notchfilter as supplied with the B&G RD75 planar magnetic driver. Although a passive notch filter is not a perfect way of eliminating the cavity resonance, it does an adequate job. Since the cavity resonance peak is asymmetric, an active notchfilter, as used in the Clearview active crossover with equalising, does a better job in attenuating the peak under different circumstances while restoring the symmetry in the response. For an overview of passive notch filters for the Radia series of drivers, please take a look in the passive crossover section of the FAQ.
