Patent GB-327689-A (GB)
Title: Improvements relating to sound re-producing devices
IPC: H04R7/00
Filed: 1929-01-05
Abstract: 327,689. McDonald, R. Jan. 5,1929. Diaphragms; loud-speakers.-In a sound-reproducer such as a loud-speaker or gramophone the vibrations of the vibratory member such as the reed or stylus are transmitted to a conical or flat diaphragm through the medium of tensioned strings &c. which are caused to vibrate in sympathy with the vibratory member and are connected to the diaphragm through distancemembers. As shown in Fig. 1, the strings c are connected to a frame d which supports the diaphragm a and vibrations imparted to the strings are transmitted by the distance-member e. The strings may be of metal, catgut, hair, parchment &c. and may be of different thickness and tensioned to different degrees, so as td be responsive to different ranges of frequency. In the arrangement shown in Fig. 2, the diaphragm is divided radially and concentrically into sections which are conected together by strips of flexible material such as leather or canvas and may be formed so as to respond to different notes. The sections of the diaphragm may be strengthened by ribs a<2>, a<3> and the outer sections may also be supported from a sleeve e by adjustable arms i<3>. The strings c are secured to adjusting pegs c<1> and vibrations are transmitted to the outer sections of the diaphragm through members e while the inner sections are vibrated from the same or a separate reed through strings c<2>. Direct connection may also be provided between the operating unit and the apex of the diaphragm. The separate tensioned strings c may be replaced by a single flexible string which is carried around pulleys disposed upon the frame d and the central plate f and may serve as an aerial or a counterpoise. In the arrangement shown in Fig. 9, a flat diaphragm k is employed in conjunction with a resonator or reflector o. The diaphragm has openings k<1> at which are positioned smaller sound-reproducing units p serving to give directional effects. The units p may be connected to the diaphragm k by flexible rings k<2> and may be adjustable relatively to the plane of the main diaphragm. The main diaphragm k may be supported entirely by the members e instead of being suspended in the frame. In a further modification, a flat diaphragm is supported by a flexible element interlaced between a rigid frame and the upper edge of the diaphragm and is impulsed by parallellyarranged tensioned strings supporting a member extending diagonally across the diaphragm and connected to a pair of vibratory units. The members e mav be secured to the diaphragm by nuts or by adhesive and the diaphragm may be pinned or nailed to the frame d. In addition to the tensioned strings serving to receive the vibrations of the vibratory unit there may be provided other tensioned strings which are set into sympathetic vibration; or the vibratory member may impart vibrations to an intermediate member serving as a sound-board which in turn sets into vibration the tensioned strings which then operate the diaphragm. A number of vibratory units may be used to operate a diaphragm, the units being distributed over the surface and the tensioned strings being of any desired lengths. The tensioned strings may be of single or multiple strands and of varying thickness. They may be enclosed in a covering, e.g. cotton, or coated with paint. The magnetic reed u, Fig. 16, of the vibratory unit may be pivoted or mounted by strands or strips u<1> which may vary in thickness so as to respond to different frequencies. Alternatively, the reed may be constructed of a number of parallel strips which may be connected by resilient material. The diaphragm may be made of wood, e.g. cedar, spruce, balsa wood, pine, &c., and the central portion may be made of metal which is covered on both sides with silk etc.; alternatively, the diaphragm may be constructed of metallic wood or non-metallic thread, or strips woven together. One of the Provisional Specifications refers to an arrangement wherein the loud-speaker may be attached to a stringed instrument so that the sound vibrations are transmitted through the strings to the body of the instrument. The other Provisional Specification also states that the tensioned strings may be connected directly to the diaphragm.