M-Audio AV32.1 Guide D'utilisation page 8

Height
Position the monitors so that they are parallel to the ground and that your
ears are between the midpoint of the woofer and the tweeter.
Orientation
If possible, place the monitors in their upright position; avoid laying
them on their sides. The woofer and tweeter are vertically aligned and
will provide the best performance when the monitors are upright.
Placing them on their sides may create strong reflections from nearby
surfaces resulting in spectrally unbalanced sound.
If your monitors must be oriented horizontally due to space or line-of-
sight considerations, place them so that their tweeters are on the
"inside" to improve imaging.
Tweeters
8