Abstract: A public address system having a microphone, an amplifier which amplifies the output from the microphone and a speaker assembly which receives the output from the amplifier and reproduces a sound, in which the microphone is provided with a transmitter generating an electromagnetic wave and the speaker assembly has two receiving coils disposed perpendicular to each other. The outputs from the receiving coils are used to control the level of an audio signal applied to the speaker assembly and thereby to avoid the occurrence of howling.

Abstract: For improving the sharpness of images produced on the screen of a cathode ray tube in a television receiver or other video signal reproducing device, a control signal is produced to vary in response to transient changes in the level of a video signal by which each electron beam in the cathode ray tube is density-modulated, and such control signal is supplied to a beam focusing electrode of the cathode ray tube so as to control the shape of a beam landing spot on the screen and thereby to prevent the image on the screen from becoming vague at its contours.

Abstract: In a color cathode-ray tube of the plural-beam type wherein the beams originate on a horizontal or vertical straight line and are directed into fields produced by a horizontal-vertical electromagnetic deflection yoke at predetermined incident angles to each other so as to converge at a color screen, magnetic shielding means, for example, secured to electron beam convergence plates, are disposed for selectively shielding at least one of the beams from the leakage flux produced by the horizontal-vertical electromagnetic deflection yoke in deflecting the beams in the direction of the line of origination thereof, whereby such leakage flux acts selectively on only the unshielded beam or beams for correcting a deviation between the positions of rasters on the color screen produced by the plural beams.