This is a mount for the UE Megaboom 4. It is easy to both insert and remove it and it holds onto the speaker pretty tightly. There is also room to slip a 1 inch wide velcro strap into the base to be extra secure.

Print 2 of the clips and one of the base. You need to print with something somewhat flexible. I did ABS but perhaps PETG would work too. To assemble you need 4x M5x16 button head bolts and 4x M5 nuts (regular or nyloc). The mounting holes are 2 inches apart and sized for M5 with a counterbore.

Original CAD model: https://cad.onshape.com/documents/95aeb737d106ad708c396606/w/ef2997f737f5423ced0be56d/e/15e4c28f195a8a8b3c0a0b54