GB447749A - Improvements in means for converting electrical energy into sound - Google Patents

Abstract

447,749. Acoustic horns and resonators. VOIGT, P. G. A. H., 53, Church Road, Upper Norwood, London. Oct. 17, 1934, No. 29654. [Class 13] [See also Group XXXIX] In an arrangement for the conversion of electrical currents intc sound, the radiation of the sounds of low frequency is increased by simple longitudinal vibration of an air column in a resonator or "bass-chamber" of rigid construction which is free from openings near the node large enough tc introduce severe losses or to alter the fluidamental mode of vibration at a frequency determined solely by the length of the basschamber. The air column in the basschamber is excited at a distance from the antinode(s) by electromechanical means which do not seriously affect the mode of vibration and which are constituted, for example, by a diaphragm smaller than the sectional area of the chamber at the point of excitation coupled to a speech coil magnet system strong enough relative to the area of the diaphragm to damp it adequately and to prevent the diaphragm opening from acting as a large vent. The air column may be enclosed in a tube of circular or square cross-section, open at one or both ends, and the diaphragm is preferably mounted eccentrically with regard to the central axis of the resonator. As shown in Fig. 5, the resonator or bass-chamber 9 may be slightly tapered and the diaphragm may also operate a horn 8 of normal shape with a cut-off above the fundamental frequency of the "bass-chamber '' 9. Each side of the diaphragm driven by the actuating unit may be associated with a " basschamber," and, as shown in Fig. 7, a directly driven diaphragm 16 drives the air columns in the chambers 12, 13 whilst the sides of a second diaphragm 17 co-operate with the chambers 14, 15. The "bass-chamber" may be folded or re-entrant, and as shown in Fig. 4 may be thickened, as at x, to reduce losses at this point.