Somebody who's actually opened up their M3s and examined the high-pass filter on their M3 tweeter would know(2x6?), but a simple capacitor in series with the tweeter would form a first-order filter and roll it off at 6dB/octave, while also adding an inductor in parallel with the tweeter would form a second-order filter and roll it off at 12dB/octave.

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Enjoy the music, not the equipment.