GB666705A - Improvements in or relating to public address apparatus - Google Patents

Abstract

666,705. Public address systems. TAYLOR, P. H., and PAMPHONIC REPRODUCERS, Ltd. March 30, 1950 [Jan. 19, 1949], No 1559/49. Class 40 (iv). [Also in Group XL (c)] In a public address system comprising one or more downwardly-directed loud-speakers which are fastened under chairs, pews, &c., and inductively coupled to an audio frequency source over adjacent primary and secondary coils, the use of intermediate amplifiers between the secondary coils and the loud-speakers to provide an adequate power output is avoided by reducing the self-inductance of each coil and hence improving the coupling coefficient, either by spacing each coil turn apart or by forming the coils from a single loop of strip or tubular metal. As shown, the primary coil 1 is located beneath the floor 2 with each turn vertically spaced about 10 inches apart, while the secondary coil comprises a single loop of verticallymounted strip metal 5 embracing a row of chairs and having a narrow portion 8 accommodating a coupling transformer 7 for a loudspeaker 9. Several primary coils may be used, each coil enclosing an area of about 1000 square feet and connected so that the currents in adjacent coil sides are in the same direction. In an alternative arrangement, the coils may be constituted by a metal coating on a wall or other surface. Where suspended loud-speakers are used, the secondary coil may be a square tunnel of copper sheet or a large diameter sheetmetal ring, and the primary loop may be wound outside the building. The primary coils are fed from an amplifier 3 and the lowfrequency coil loading is reduced by a high-pass filter or constant-impedance network. Preemphasis of the high frequencies may also be provided.