Consider the circuit connections to the speaker amplifier with two bridge outputs channels (Fig. 18). Dynamic heads BA1, BA2 form loudspeakers left and right stereo channels. They are depicted using broadband. Low-frequency head BA3 connected between the outputs of the amplifiers left and right channels, the signals are summed and head reproduces the monophonic signal.
In this connection scheme is definitely the presence of two high-pass filter to the stereo and LPF for the total channel. Their goal is to eliminate parallel heads, and overloading of the amplifier. Typically, for a stereo channels are used, the filters of the first order (C1, C2), for total - second (C3L1) or third. The calculation is performed in the usual way.
The frequency partition and the order of the LPF is chosen in the range of 80...200 Hz depending on the location of low-frequency drivers. If it is placed in the rear compartment, the frequency partition must be selected as low as possible and the procedure above to avoid playback subwoofer "voice" range. However, this requires the manufacture of relatively large inductors. To use in their design ferromagnetic cores is undesirable because of the distortions caused by the unavoidable magnetization of the core, greatly diminish the sound quality.
Fig. 18
Author: A. Chechetov; Publication: www.bluesmobile.com/shikhman, www.cxem.net