I think I’d make it with two posts about twelve inches apart. Make the bottom plate about six inches wider than the speaker and about four inches deeper than the speaker. That will be about right for keeping it stable. Then make the top plate the same dimension as the speaker, or a little smaller if you don’t want it to be viewable. Stick the speaker to the stand with Velcro. I’d use some sort of hardwood and stain it to match whatever colors in your room. I’d make the posts 2 1/4” X 2 1/4” (three laminated 3/4" hardwood boards)and center them between the plates. A little glue and a couple screws should be plenty strong enough. Or, if you have a biscuit cutter, biscuits work very well and don’t take long at all. If you need the speaker to be angle up some, just cut the posts at whatever angle you think you need.
