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From the Q&A

With TJ Byers

Woof Woof, No Bow Wow


 I am thinking of building a subwoofer using the signals from my stereo speakers. I want to combine the signals and feed them through a low frequency filter into a high-impedance amplifier. Can you give me some ideas?

Port St. Lucie, FL


Sure, and here it is.

This circuit uses two op-amps to accomplish the task. The first is a low-pass filter with a cut-off frequency of about 150 Hz. The second filter sharpens up the roll-off frequencies so that you don't get a hard boom below 10 Hz or above 200 Hz. Realize that this circuit is designed for use with 15- to 18-inch woofers in a good reflex baffle or horn enclosure. Anything smaller would be speaker suicide.