Alesis M1 Active MKII Reference Manual page 34

Surround Sound
W
ALL MOUNTING
Once your have located the general area for the horizontal and vertical
position, you need to find a wall stud. Attach shelving brackets or other
commercial speaker-mounting device into the wall stud, then attach the M1
Active Mk2s to the mount, allowing room for the rear-panel input and AC
connections.
The M1 Active Mk2s weigh 19.5 lbs., so it is vitally important that any
stand they're resting on be securely mounted through the wall material
(usually 3/4" sheetrock, which by itself does not have the strength to
support the speakers) and into a wooden stud using hardened screws
or other fastener rated to hold at least two times that weight.
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M1 Active Reference Manual