Thanks for the encouragement, both.  The idea came to me as I stared at all my rpg foam, panels and Skylines, admiring their sonic properties but thinking them more appropriate to a studio than a domestic setting.

Penance, what I'm doing is inserting acoustic panels from the leading manufacturer :>) into the back of open weave linen canvases.  I researched 'acoustically transparent paints' and concluded that they are just thin and water-based so I'm using thinned, matt artists acrylics which preserve acoustic properties but improve the artwork.  I'm using box canvases of 50mm thickness (thus giving a 25mm air gap) which doubles the efficacy of a 25mm thick panel.  Of course, all this does increase the cost of an acoustic panel but, hopefully, gets them into people's living rooms more easily.