An Active Biquadratic Filter for Equalizing Overdamped Loudspeakers
When a bridged-T network is inserted into the feedback path of a voltage follower, it can produce an inexpensive biquadratic filter whose transfer function has first-order coefficients as low as 2.5 (Q = 0.4), often approaching 2 (Q = 0.5), in the numerator when those in the denominator lie in the very useful range between 0.5 and 2. Among its applications, it is peculiarly suited to equalizing "over-damped" loudspeakers, i.e. with exceptionally low Qt's, that are typical of robust, sensitive, drivers with large magnets. The wide range of applications is possible through selection of the more suitable of the two possible configurations of a bridged-T network, described in Figs 2 to 5 as CRRC or RCCR. The work is the subject of intellectual property claims.
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