The Reconstruction Finance Corporation (RFC) was established during the Hoover administration with the primary objective of providing liquidity to, and restoring confidence in the banking system. The banking system experienced extensive pressure during the economic contraction of 1929-1933.
Typical materials used for electromagnetic shielding include sheet metal, metal screen, and metal foam. Any holes in the shield or mesh must be significantly smaller than the wavelength of the radiation that is being kept out, or the enclosure will not effectively approximate an unbroken conducting surface.
An electromagnetic (EM) wave is not a sound wave. A sound wave is mechanical energy, and an electromagnetic wave is electromagnetic energy. The EM wave could be a radio or light wave, but in any case, it is composed of moving electric and magnetic fields. This electromagnetic wave can move through air or the vacuum of space, but sound (or any mechanical wave) must have a medium to travel through.