A friend of mine has a rather big black sub which he hates the look of. He built a coffee table out of MDF to measure so that the sub just fits underneath. He then threw a table cloth over it, which reaches all the way to the floor, and put a vase of flowers on it. Casual visitors not in the know don't even realise there is a sub, not that is, until the table cloth starts moving backwards and forwards during more energetic sounds due to the amount of air the sub moves.