US1750348A - Electric horn - Google Patents

Description

latented Mar. 11, 1930 UNITED STATES PATENT yOFFICE FABNM IF'. DORSEY, 0F ROCHESTER, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO NORTH EAST APPLIANCE CORPORATION, OF ROCHESTER, NEW YORK, A. COR- PORATION OF NEWYORK .ELECTRIC HORN v Application led July'IO, 1925. Serial No. 42,780.\

1,729,281 to William B. Connolly, in which an overtone is produced by the independent res- -onant vibration of the armature by which the diaphragm ismagnetically actuated.

The object of the invention is tovincrease the eiliciency and facilitate the manufacture of horns of this type, and this is accomplished by the use of a magnetic and sonorous armature of the form hereinafter described.

In the accompanying drawings, Fig. 1 is a side elevation, partly in section, of an electric horn embodying the present invention. Fig. 2 isa side elevation, in section approximately on the line 2-2 in Fig. 3. Fig. 3 is a front elevation of a portion of the horn comprising the rear shell, or housing, and the parts attached thereto and enclosed therein. Fig. 4 is an elevation, partly in section, of the circuit-breaker and the' parts immediately associated therewith.

The invention is illustrated as embodied in a horn having an elastic metal diaphragm 5, which is gripped and supported, at its margin, betweena front plate 6 and a cup-shaped metal shell or housing 7. Attached to the front plate 6 is the horn proper or projector 8, which may vary in lengthaccording to the pitch of the note which 1t is desired to produce. The front plate and the housing are secured togetherv by `bolts 9.

The electromagnet comprises a central core 10, which is surrounded by a coil or windin 11. It comprises also a generally U-shape yoke 12 formed of a relatively wide and thin strip of steel, with its extremities bent in wardly, as shown in Fig. 1. The housing and the yoke, are centrally perforated, and the core has a screw-threaded rearwardly projecting extremity 13,- which passes through these members and receives a nut 14 y which the parts may be all drawn and secured tightly to ether. The coil, being embraced by the yo e and particularly by its inturned extremities, is securely fixed in place in a simple and eiective manner. The part 13 of the core is attened, or otherwise vmade non-circular in cross section, and the openings in the yoke and the housing are correspondingly formed, so that these parts are prevented from accidental relative rotation, while the-original assembly of the parts is facilitated.

The armature, which cooperates with the electromagnet, consists chiel of a relatively wide and long bar 15. This har is secured to the middle of the diaphragm by a bolt 16, the necessary space between the armature and the diaphragm being. maintained by a sleeve or spacer 17 surrounding the bolt. The bolt is made of steel, so that its head 18,y lying at the rear of the armature, may be considered as a part of the magnetic circuit, cooperating with the core 10. The circuit iscompleted through the armature and through the lateral members of the yoke, the magnet thus having three poles, all separated by suitable air-gaps from the armature.

In the present construction the principal, or lower, tone of the horn has a pitch due to the relation of the stiffness of the diaphragm to the total load or weight upon the diaphragm. The overtone results from vibration of a higher frequency, imposed also upon 75 the diaphra m, and resulting from local vibrations in t e armature. In order that these local vibrations may be emphasized as much as possible, the armature bar 15 is made longer than necessary to perform its magnetic function, extending substantially beyond the outer poles of the magnet, as shown in Fi 1. For the same reason it is preferably ma e thicker than necessar for the magnetic function, and in order t at this thickness may not give it a rate of vibration too high for the intended purpose, the bar is reduced in thickness for limited portions 19, adjacent its pointof at- `tachment to the diaphragm. This may be tion may be free, the air-gaps between the Aarmature and the outer poles of the magnet are made somewhat greater than the gap at the core, so that no engagement occurs be- 10o tween the armature and the ends of the yoke. ward direction, so as to cause the contacts to The motion of the diaphragm is accordingly the resultant of the relatively slow vibrations, due to its own natural frequency and the load upon it, and the relatively high vibrations transmitted to it from the armature, while the ehect, in accordance with well known phonetic laws, is that of two distinct harmonious tones.

The circuitbreaker, by which the current through. the winding 11 is controlled and rendered intermittent, comprises a normally staticnary contact 20, and a movable contact 21 cooperating therewith. The movable contact is mounted on a blade spring 22, and this spring projects, at one extremity, into the path of movement of the armature, so that at each rearward vibration of the latter the spring is engaged and pressed rearwardly, thus separating the contacts. Where it is desired to insulate both sides of the circuit from the mass of the horn` a piece ot insulating material 23 is attached to the end ot the bladespring to prevent direct metallic engagement between tue armature and the spring.

ln order that the circuit-breaker may be conveniently adjusted to regulate the current impulses in the magnet, the contact 20 and the blade-spring 22 are mounted upon asupport in the form of a sheet-metal plate 2d, being insulated therefrom in any convenient manner. The plate is bent rearwardly at its lateral edges, so as to provide parallel arms 25, continuous with tlangcs 32. it its rear edge the plate has two rearward projections 2G, which rest against the inner surface of the housing, as shown in Fig. 3. T he plate cooperates witha base-member, formed also ot sheet-metal and comprising a horizontal portion 27 and a vertical portion 28 (referring to Fig. Two lugs 41, projecting from the horizontal portion, are riveted to the housing to secure the base in place. The horizontal portion is cut away at its forward end, as shown particularly in Figs. 2 and li, and formed with lugs 29 which overhang the projections 26 on the plate 24, and thus, through the reaction of the springs and other parts hereinafter described, prcjviding pivotal bearings about whichthe platel may swing on a line adjacent the inner surface vof the housing, and in the general direction of movement of the diaphragm and the armature.

At its inner extremity the part 28 of the base is provided with two forwardly bent projections 30, which constitute supports for coiled springs 31, ressing at thelr forward ends against the anges 32 on the plate 24. The arms 25 rest against the outer surface of a bar 33 into which an adjusting screw 34 is threaded, and this screw projects through an opening in the wall of the housing, so that it is accessible from the outside and may be turned by a screw-driver. The gprings 31 tend normally to rock the plate 2a in a forcbe separated earlier in each rearward motion of the armature. This tendency of the springs is resisted, however, by the arms, the cross-bar and the adjusted screw; and by rotation of the latter the operative position of the circuit-breaker may thus be exactly determined, while the constant pressure of 'the springs 31 not only preventsany accidental movement, but also acts to thrust the projections 26 outwardly and hold them in eective engagement with the housing and with the lugs 29.

The blade-spring, the stationary contact., and the terminals by which they are connected with other parts of the instrument, are secured to the plate 24 by means of screws 37.' Two bindingposts 38 project through the walls of the housing and serve to connect the horn with the exterior parts ot its energizing circuit. A. condenser 39 is connected with the two contacts of the circuit breaker for the usual purpose, as a convenient means for supporting this condenser, it is attached to the middle ot a strip 420 of insulating material, and this strip is secured in place by 'the nuts and washers on the inner ends of the binding posts, as shown in Fig. 3.

rl`hc invention claimed is:

1. ln an electric horn, the combination, with a sonorous diaphragm and an electromagnet, ot a resonantly vibratory armature attached, at its middle point only, to the mid dle of the 'diaphragm and cooperating magnetically with the magnet, the armature being relatively thick and rigid 'for the greater part of its length, but having limited portions ot reduced thickness close to itspoint of attachment, whereby resonant bending ot the armature is substantially restricted to the parts thereof adjacent the point o attachment.

2. ln an electric horn of the type in which a resonantly vibratory armature is attached, at its middle point only, to a sonorous diaphragm, an armature in the form of a bar provided with two parallel transverse slots located near to and on opposite sides of its point of attachment to the diaphragm, whereby the resonant bending of the armature is substantially limited to the positions in which the thickness is reduced by the slots.

FARNUM F. DORSEY.

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