Designed this mount to hold a mini soundbar behind the monitor, turning it into a completely hidden, down-firing speaker.

The top holes attach to a VESA mount and have a separation of 10cm.
The bottom slits are to attach the soundbar using a pair of zip ties.
The long (vertical) side of the mount measures 5.5cm from the holes to the edge.

The soundbar ends up hidden behind the monitor, firing downwards at a 30 degree angle towards the front so the sound bounces off the desk better.

For best results print with the long side on the print bed.
Used with a cheap Elegiant PC speaker, a Viotek 29" Ultrawide and an Amazon Basics monitor arm.