This is a simple but effective wall support for soundbar, made of two parts: a fixed wall mount and the supporting part which slides nicely in place. I made it parametric so it can be adapted universally using Fusion 360.

My advice is to print horizontally for maximum strength, although this will need a more supports to print properly. You may stretch the PRINT_BED parameter to your maximum if your soundbar looks very heavy. 175mm with 5 walls and 20% infill should be enough, anyway (even in PLA).