[quote author=CWatters link=1121999756/0#9 date=1122213586]A spot of googling and it looks like for best sound insulation you should:
Use laminated glass (rather than regular or toughened).
Use two panes of slightly different thickness.
Use a "large" airgap (75-125mm seems to be suggested)
Fit sound absorbent material to the walls inside the air gap.
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Yep, nail-on-the-head.
That's the way to go, I'll be using a 200mm airgap, which will help me somewhat, and with rockwool filling the space between the walls. The only problem is acquiring the glass on a tight budget, that's where my idea of using salvaged security screens comes into play. Hence my appeal to all you building types.
I've a chippy mate who has done post offices/banks in the past, and says that the old screens usually end up getting skipped
...but he's got neither lined up, at least none in the next 6 months anyway.
The vacuum idea has already been suggested elsewhere, and was poo-poo'd by acousticians, plus it would be technically challenging, even my dyson doesn't have that much suction! 8)