Ben, that illustrates how we can be fooled by a speaker which has a hump in the mid-bass response. Measurements by the NRC showed that the M22 enclosure was actually tuned about 5Hz lower than the M3, giving a slightly better bass extension. The "hump" both makes mid-bass fundamentals louder than normal and increases the relative loudness of the upper harmonic of a low bass fundamental.

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Enjoy the music, not the equipment.