The speaker cabinets are made of MDF. The material was hastily cut and glued together, and didn't fit perfectly. A lot of filer was added to make corners straight and to cover some mistakes made when routing the large vent-hole.

With all edges straight, I rounded them with a router, which gave them a much more complete appearance.

When spray painting MDF, remember that cut and routed surfaces are "thirsty". A thin layer of filler will remedy that. Even so, other surfaces will also absorb moisture from water based paint, and fibres will rise to make a rough finish. After each coat of primer, I sanded the cabinets with a fine paper.