GB278098A - Improvements in horns for acoustic instruments - Google Patents

Abstract

278,098. Voigt, P. G. A. H. July 5, 1926. Sound magnifying and directing appliances.- Gramophone &c. horns are designed so that the sound waves are expanding at any point as if the source wene at a constant distance from the point of expansion. For a straight horn cf circular cross-section, this is obtained by forming the walls to the shape of the curve known as the " tractrix " in which the length of the taugent between the point of contact with the curve and the central axis is a constant. For horns of square cross-section, the central longitudinal section is a tractrix, or alternately, for horns of square or any other cross-section, the area at any point is made equal to the area of the corresponding circular horn based on the traetrix. Bent horns as shown in Fig. 2 are obtained from the basic straight horn a, e by dividing the latter into transverse sections h, g, f, f<1>, f, b, b<1>, j<1>, &c. which are bent separately about centres i<1>,i<2>, &c. in a manner fully described in the Specification so as to form corresponding sections h, g, n, n<1>, n<1>, n, r, r<1>, &c. of the final bent horn. The use of different centres i', i<2>, &c. minimizes the difference of phase introduced by the difference in length of path around the bend. An alternative method of avoiding phase-displacement around the bend is to split the horn into two sections, as shown in Fig. 3, each section being bent about fixed or variable centres (indicated by crosses), and the inner section being bent back on itself so as to provide a length of path equal to that through the other section. In Fig. 3, the lower half of the horn is suppressed and the imaginary centre line of the complete horn is continued in a member 5, 6.