Sound shielding by means of sound

TLDR: An air permeable sound grating for sound shielding as discussed by the authors consists of, or includes, volume changing elements which are controlled by properly positioned means, such as a microphone orientated toward the noise source, to effect change in volume of an adjacent noise transmitting medium such as air.

Abstract: An air permeable sound grating for sound shielding. The grating consists of, or includes, volume changing elements which are controlled by properly positioned means, such as a microphone orientated toward the noise source, to effect change in volume of an adjacent noise transmitting medium, such as air, to effect such a anticyclic change in volume as to cause interference attenuation of the sound at the side of the grating facing away from the noise source. Such volume changing elements are spaced apart a distance less than the wavelength of the highest frequency sound to be shielded and may comprise a variety of means such as spaced heating wires, conductive coating upon a thermal and electrically insulating base, a closed capsule with membrane surfaces having vibration generating means operatively associated with said membrane, radiation generating means for discharging medium heating radiation of energy into the sound transmitting medium together with controls and reflectors for directing the volume changing means or energy to the desired zone to be shielded.