Alesis M1 Active Mk2 Reference Manual page 21

Careful consideration should also be given to the physical spacing between
the speakers. Alesis recommends that the distance between the speakers for
stereo applications equal the distance between the listener and either speaker.
In other words, the listener and the two speakers are at the three corners of a
triangle having equal- length sides. The illustration below shows this
concept. Note that both speakers are turned in somewhat, so that the prime
listening position is directly in front of each speaker. Applications that
require monitoring by more than one engineer are accommodated by a
smaller rotation of the cabinets. This will widen the prime listening position
somewhat.
The speakers and
listener should be at
the three corners of
a triangle having
equal length sides
NOTE: On some mounting surfaces the vinyl finish of the M1 Active
Mk2's cabinet may cause it to slip too easily. Included with this
reference manual packet are two pieces of adhesive backed non-skid
foam. If necessary, apply the pad to either the bottom (for vertical
placement) or cabinet side nearest the ports (for horizontal placement).
If you plan on using the M1 Active Mk2s in both modes, simply cut the
pad in half and apply to both the bottom and the side nearest the
ports).
M1 Active Mk2 Reference Manual
Prime Listening Position
Speaker Installation
19