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Nice article on passive filters for metal drivers here:
That's quite interesting. I wouldn't have thought one notch filter would have more or less distortion than another.
I wonder if those results would apply to filters in other octaves, say woofer notches at or near 1k hz?
The filter doesn't "have distortion", it reduces the distortion induced by the driver (by induction modulation or motor hysteresis) by providing electrical damping. Specific frequencies of interest are unimportant.