He had known his apartment was sound-proofed.
"Tangle Hold"
F. L. Wallace
Modifications of the construction above mentioned include the use of sound-proofed steel panels or insulation board for partitions and walls with an exterior of painted steel.
"A Living from the Land"
William B. Duryee
The woman lay back upon the water-proofed pillow, and her murderous tumour lay revealed.
"Round the Red Lamp Being Facts and Fancies of Medical Life"
Arthur Conan Doyle