Crossover For Subwoofer


The crossover network is
intended for use when an existing audio installation is to be extended
by the addition of a subwoofer. Often, this additional loudspeaker is
one that has been lying around for some time. If its frequency response
extends down far enough, all is well and good, but a filter is then
needed to cut off any frequencies above, say, 150 Hz. Often, a subwoofer
network is an active filter, but here this would necessitate an
additional power supply. The present network is a passive one, designed
so that the speaker signal of the existing system can be used as the
input signal.

Crossover Circuit For Subwoofer

Crossover Circuit Diagram For Subwoofer

Since the bass information is present in both (stereo) loudspeakers,
the signal for the sub woofer can simply be tapped from one of them.
The network is a 1st order low-pass filter with variable input (P1) and
presettable cut-off frequency (P2). The signal from the loudspeaker is
applied to terminal ‘LSP’. Voltage divider R1-R2-P1 is designed for use
with the output signal of an average output amplifier of around d 50 W.
The crossover frequency of the network may be varied between 50 Hz and
160 Hz with P2. The values of R3, P2, and C1, are calculated on the
assumption that the subwoofer amplifier to be connected to K1 has a
standard input resistance of 47 kΩ.

If this figure is lower, the value of C1 will need to be increased
slightly. It is advisable to open the volume of the subwoofer amplifier
fully and adjust the sound level with P1. This ensures that the input of
the subwoofer amplifier cannot be overloaded or damaged. Make sure that
the ground of the loudspeaker signal line is linked to the ground of
the subwoofer amplifier. If phase reversal is required, this is best
done by reversing the wires to the subwoofer. If notwithstanding the
above additional protection is desired at the input of the subwoofer
amplifier, this is best effected by ‘overload protection ’ elsewhere in
this site.


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