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Crossovers circuits are intended for use when extending an existing audio system with a subwoofer. This additional speaker is often one that has been dormant for a long time. If the frequency response is down enough, that's fine, but then you'd need a filter that cuts off all frequencies above, say, 150Hz. Subwoofer networks are often active filters, which require additional power supplies. Current networks are passive and designed so that existing system speaker signals can be used as input signals. Bass information is present in both (stereo) speakers, so the signal for the subwoofer can easily be tapped from either one.
Subwoofer Bass Filter Schematic Circuit Diagram:
This network is a first order lowpass filter with a variable input (P1) and a preset cutoff frequency (P2). The signal from the speaker is input to the "LSP" terminal. The R1-R2-P1 voltage divider is designed for use with an average output amplifier output signal of approximately 50W. P2 allows you to change the network crossover frequency between 50 Hz and 160 Hz. The values for R3, P2, and C1 are calculated assuming the typical input resistance of the subwoofer amplifier connected to K1 is 47kΩ. If this value is low, the value of C1 should be increased slightly.
It is recommended to maximize the volume of the subwoofer amplifier and adjust the volume with P1. This ensures that the input of the subwoofer amplifier cannot be overloaded or damaged. Make sure the speaker signal wire ground is connected to the subwoofer amplifier ground. If you need phase reversal, swapping the wires to the subwoofer is the best option. However, if your subwoofer amplifier input requires additional protection, the best place to look is the Overload Protection section of this site.