Version 1 of these shelves (https://www.printables.com/model/134832-bose-companion-2-speaker-wall-shelf-shelves) has shorter sides such that the cantilever dips 1-1.5mm. They hold up for at least 10 months in service but I wanted to make some improvements. The longer sides provide a better support for the cantilever while still angled to minimize visually. I've also created shadow lines, improved the screw holes, and used one large hole for wires so one model is used for left and right speakers.
Version 2 is just an extension of the side. Version 3 incorporates connected letters to form the sides. Version 4 embosses the sides with those letters. I've not measured any cantilever dip upon initial use of these models. Version 3 is the only model needing supports to print.
I printed with 0.2 quality with PLA. I used an infill of 15% which is a reduction of the original model where I thought more infill would prevent cantilever dip. The shelves take some time to print at about 12-15 hours for each shelf on an Mk3S+ or an MK3S+ (MMU2S modified).
Because of the print time and the large base of each shelf, I sometimes ran into issues of corner lifting with some combinations of filament and printer without changing other printer conditions (1 out of 4). If this is an issue, you could try printing with the back down, different filaments, addition of a brim, or other printer conditions like varying table temperature.
The author remixed this model.