Subwoofer low pass filter with amazingly flat response

Flat response subwoofer filters are a bit difficult to design.

I happened to find this subwoofer low pass filter, as a surprise, while testing and configuring my home subwoofer with different crossover frequencies. It sounded amazingly great with this filter.

Why i got amazed with this filter is that, i was able to pinpoint each bass notes with greater clarity using this filter.

The filter is actually a combination of 2nd order butterworth (approximate) and 2nd order sub-bessel filter in sallenkey topology.

The main speakers crossover can be best set at around 90Hz. This subwoofer filter is more suitable for 3 inch drivers (that has no dynamic range in the lower bass region say 100-150hz). See also why i chose subwoofer crossover frequency below 100Hz.

Subwoofer low pass filter

The first stage has Q=0.605 and calculated cutoff frequency fc=92Hz. The second stage has Q=0.5 and calculated cutoff frequency fc=107Hz.

I also experimented some RC values for various other crossover frequencies, but none sounded good than this filter.

Variant1: Use 0.056uF instead of 0.068 for a cutoff frequency of 100Hz. (This one is not so better than the previous one)