Charles, reflections from room surfaces cause partial cancellations at roughly a quarter wavelength from those surfaces. The dip around 70Hz may be a wall bounce at about a four foot distance(1130 ft. per sec/70 Hz= 16 ft.). Are your speaker drivers about four feet from one or both walls? The dip around 280Hz appears to be a floor bounce similarly calculated arising from about a one foot distance. You need to move your walls and floor.

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Enjoy the music, not the equipment.