soundproof

There would have been no birth certificates because Dugard was forced her to give birth in a soundproof structure in the backyard.

They were within ten yards of the plane when a wail of anguish was born—and died—in two soundproof helmets.

The wireless office was soundproof and practically airtight.

The booth was soundproof and all the lad did was to drop coins.

But even if they had time to look it up, which they didn't, the contestant couldn't hear them in a soundproof booth.

I suggested that, folding-doors not being soundproof, I had better wait downstairs.