'Tin foil'? It was actually heavy duty GOLD!! wrapping paper, that consisted of gold foil bonded to paper-I had LOTS of it, once papered a whole wall with it to get a 'golden glow/sun' effect!
I must have thought that the poly needed something inside to retain some frequency.
You're right about rigidity, though using 1+1/2 inch stuff helped-I channeled it out behind the speaker unit, leaving 'piers' to hold the bolts, using big washers to spread the load. Was pretty firm (didn't come apart easily!)
Using PVA helped too, coated it all.
Don't know enough about the varieties of insulation materials, but it's an area to investigate, both in terms of being light; inert, etc.. See Von Schweikert stuff.
I'm just waiting for first coat of stain to dry-Osmo Wood wax finish, Red.
I've used Osmo oil on our pine floor -non toxic/natural oils .Hardwearing.
Might do front in 2 coats, rest in one coat.
Yet to decide what to put on the top (45 degree) slope-something more interesting than wood -tile, maybe or Bamboo iKea tray?
The rather thin unit will be screwed to a small baseplate, glued to a 12" X 12' Terracotta Tile - as before-echoing my love of Iberia
(I could have used Marble that I got from a quarry in Portugal years ago when travelling about there, but....how to cut it (my local Stonemason has retiired)
More when I put it all together!
Oh...PAWO? No idea!
THis doesn't help!
http://frugal-phile.com/tom-zHorn.html
I made one from off-cuts from house renovation bits! Until one fell on to its bullet-bit the bullet! Still have the other-centre speaker? A la Klipsch La scala origin?