Patent GB-305429-A (GB)
Title: Improvements in or relating to electrically operated vibratory devices such as are used in the recording or reproduction of sounds
IPC: H04R11/00
Filed: 1928-01-30
Abstract: 305,429. Trouton, M., and Wireless Music, Ltd. Jan. 30, 1928. Divided on 293,131. Magnetic instruments.-Relates to an electrically operated vibratory device, more particularly for use in the recording or reproduction of sounds, of the type in which the vibratory motion is at least partially rotational about a real or virtual axis and in which the armature length in a direction perpendicular to the axis is at least as great as the distance of the nearest end of the armature from the axis. The term "armature " is defined as that part of the vibratory member which lies opposite to and co-operates with a magnet pole surface, the end of the, armature nearer the axis of rotation being referred to as the heel and the opposite end as the toe- The invention consists in a vibrator device of the above type in which the portion of the vibratory member between the axis of rotation and the heel of the armature is made stiff in relation to the armature itself. Fig. 1 shows a construction in which the vibratory member comprises a cross-bar b clamped at its ends to pillars e screwed to the base of the instrument. Projecting at right angles to the cross-bar is an armature a and a stiff portion j interposed between the cross-bar and armature. The armature can be regarded as vibrating about an axis i coincident with the centre line of the cross-bar which is adapted to twist when the armature vibrates and thus furnish the required restoring force. The stiffening may be provided in the form of webs or, as shown, by using a greater thickness of metal. The contour of the stiffened portion instead of ending at the heel g of the armature as shown may be carried in a gentle curve into the upper surface of the amature, the curved profile extending from the top of the cross-bar to some distance along the armature or even to the toe f thereof. A rod m connects the armature with a diaphragm, the point of connection of the rod being preferably disposed between the centre and heel of the armature e.g. at a point between one-third and two-fifhs of the length of the armature measured from the heel thereof. Fig. 3 shows a construction in which the armature a and stiffened portion j are mounted on pivots (not shown) for vilbration about the axis i. A blade k projects downwardly from the portion j and bears against a screw l, the blade furnishing the restoring force whilst rotation of the screw l serves to adjust the air gap between the armature and pole-pieces (not shown). In a modified construction, Fig. 4, the supporting pillars e are united by a yoke provided with a lug n, the vibratory member being similar to that shown in Fig. 1. A thin threaded rod p, attached to the upper end of the portion j. passes through a hole in the lug n and is provided with an adjusting knob q. The hole in the lug n is arranged somewhat below the level of the top of the cross-bar b so that the rod p is subjected to bending. In some cases the armature may be provided with slots, saw cuts or corrugations in a direction substantially parallel with the direction of the magnetic flux in the armature. Specifications 293,131 and 299,537 are referred to.