I had a lot of high-spec plywood left over from my attempt at mounting the TV with it. I also needed to raise my speakers off the floor. So I took some cinder blocks and some of that wood to raise them off the floor.
I used a Bosch jigsaw to cut the wood planks and put felt strips along the bottoms of the cinder blocks. I put small rubber feet on the bottom of the speakers to provide some slip resistance and to isolate vibration.