US2340604A - Sound signal apparatus - Google Patents

Description

J. R. MaCKAY SOUND SIGNAL `APPARATUS Feb. 1, 1944.

,Original Filed March 14. 1938 2 Sheets-Sheet 1 Feb. 1, 1944. J, R, MaCKAY l2,340,604'

SOUND SIGNAL APPARATUS Original Filed March 14, 1938 2 Sheets-Shaq?. 2

Patented Feb. 1', 1944 i SOUND lSIGNAL APPARATUS John R. MacKay, West Caldwell, N. J., assignor to Wallace & Tiernan Products, Inc., Belleville, N. J., a corporation of New Jersey Original application March 14, 1938, Serial No. 195,893. Divided and this application April 11, 1940, Serial No. 329,059

6 Claims.

This invention relates to sound signal apparatus, and more particularly to signalling or alarm devices of electrically operated type, such as horns, and to control means for signalling apparatus of the character stated. The present application is a division of my -co-pending application Serial No. 195,893, led March 14, 1938, for Sound signal apparatus, now Patent No. 2,306,819, granted December 29, 1942. An especially advantageous use or embodiment of the invention is in fog horns, wherein'ruggedness, power of sound, and dependability overlong periods of time are important criteria. Such horns are often used on floating buoys, and the requirements of a satisfactory horn for such use are particularly severe. All parts must be of a type suitable for use on buoys, where they will be subject to continuous operation, exposure to the elements and to frequent submergence, and to operation at all angles due to the swinging and listing of the buoy. As buoys are frequently collided with, all parts -of the horn and program mechanism must be of such construction that they will not be vdamaged -or operation affected by any jar or bump which the buoy may receive, other than one where the horn or mechanism is actually hit and damaged in consequence. It is a common requirement of horns so used, that they must sound from two to four blasts of about one second per minute, and that this operation is continuous for 24 hours per day for each day of the year.

In general, sound signals such as fog horns have comprised an electromagnet, an armature, a diaphragm associated with the armature, and make-and-break contacts operated, buzzer fashion, by the armature. Certain difliculties, however, have been found with devices heretofore known or available. For example, the pitch of the horn depends on the stiffness of the diaphragmY and inversely on the weight of the armature; and attempts to obtain a pitch high enough for -good carrying quality have either required a sacrifice of power or involved a tendency to break on the part `of the relatively stii diaphragm used,

when flexed with suincient amplitude to create a powerful signal. Furthermore, although it is usually desirable to space .the diaphragm relatively far away from the armature, with a connecting member, it has been found that the spring then employed to support the end of the armature distantfrom the diaphragm, is very apt to break upon continued vibration of otherwise desirable power.

The present invention is particularly designed to remedy one or more of these and other difficulties inherent in prior art devices, and a further object of the invention is to provide apparatus of the character described having satisfactory power and pitch characteristics, which is at the same time highly reliable and adapted for operation over extremely long periods of time Without even partial failure or appreciable reduction in its output due to wear. Another object is to provide more satisfactory contact structures in sound signals, and likewise eflicient arrangements for preventing or greatly reducing Wear of the contacts.

A still further and notably important object is tov provide an improved structure in sound signal devices whereby the amplitude of vibration may be accurately adjusted or set, and a like important object is the provision of novel means for maintaining a constant yamplitude of vibration over long periods of operation.

Other objects are to provide, relative to fog horns and like signal apparatus; an improved and long-Wearing diaphragm structure; a simpler and more efiicient assembly of vibrating parts; and generally sturdier and more reliable arrangement of loperating and control elements.

Other objects' and advantages include those which are hereinafter stated or apparent, or which are incidental to the invention. The nature of the latter will be conveniently explained by reference to the following description and accompanying drawings, which set forth, by Way of example, certain presently preferred embodiments of the invention.

In the drawings:

Fig. 1 is an elevation yof a complete fog h-orn and control unit embodying the invention;

' Fig. 2 is an enlarged longitudinal section of the horn and its operating parts;

Fig. 3 is an elevation of the upper end of Fig.2;

Fig. 4 is a section on line 4-4 of Fig. 2; and

Fig. 5 is a general wiring diagram.

As generally shown in Fig. l, the sound signal device and its associated control instrumentalities may be conveniently combined in a single unit, comprising an open-mouthed trumpet or bell 20, bolted to a housing 2l for the horn-driving elements, the housing being in turn secured to a case 22. The latter encloses an electric motor unit 23, having associated program cams and contacts as hereinafter described, and also encloses fuses and a relay 24 for operating the horn. Certain adjustable elements of the horn proper, generally designated 25, may be disposed within the casing 22, and the face of the latter shown in Fig, 1 may conveniently comprise a door or cover plate hinged (at 26a) to open upon release of the toggle bolts 26, for access to the enclosed parts, including the elements 25. For convenience of access and adjustment the parts generally designated 23 and 24 are mounted on the inside of the door and are swung out of the casing with it. It will be understood that particularly where the apparatus is to be used at sea or off shore, as on a floating buoy, or where it is otherwise to be exposed to weather or moisture, the entire assembly of casing 22, housing 2| and the inner end 2l of bell 20, must be thoroughly water-tight. To that end, the peripheries of diaphragms, interposed gaskets, and other joined elements, may be embedded in waterproof plastic material, such as glyptol lacquer. A coneshaped or other deflector a may be disposed below the mouth of bell 29, and may be vertically adjusted on its supporting bolts to permit some change of the resonant length of the air column in the bell or trumpet.

Referring now to Figs. 2 to 4 inclusive, there is supported within the housing 2| an electromagnet generally designated 3|), and comprising a laminated iron or preferably laminated steel core, having a central pole 3| and flux-returning portions 32 terminating in the same plane as the pole 3|, to provide adjacent pole elements of opposite polarity, for powerful signal action; the magnet winding 33 is conveniently disposed about the central pole member 3|, as shown. The central portion of the iield core, viz. the pole member 3|, is conveniently provided with a longitudinal hole or tunnel, to admit a tubular shaft or connecting member 34 which is part of the vibrating assembly hereinafter described. The hole or tunnel is conveniently lined with a copper tube 34a, pressed in place, to prevent displacement of the laminations of the member 3| and to guard against an accumulation of rust in the hole, which might otherwise interfere with free movement of member 34.

The diaphragm structure of the horn advantageously comprises a plurality of relatively thin diaphragms disposed in parallel and preferably arranged so that the distance between the diaphragms at the respective ends of the entire set is of substantial extent. For example, in the construction shown, there are provided two groups of diaphragms 35, 36, separated by a substantial space; the inner diaphragm group 35 conveniently comprises three diaphragms 35a spaced slightly apart, while the group 36 comprises two diaphragms 36a, likewise spaced slightly apart. The diaphragms are peripherally retained to the housing 2| by a plurality of bolts 3l, circumferentially spaced around the assembly. Thin supporting rings 38 serve to space the diaphragms within the respective groups, and the groups are separated by a cylindrical spacing member 39, and all parts are preliminarily retained in place by the bolts 3l and securely clamped to the housing' 2| by a plurality of bolts 40 spacedvaround and passing through a flange on the bell or trumpet J, whereby the latter is also clamped against the diaphragm assembly and housing 2|. It will be noted that the annular face of the bell which abuts against the diaphragm assembly, specifically the outer diaphragm group 36, is provided with a relatively wide annular groove 4|, so that the area of contact between the bell or horn proper, and the diaphragm assembly, is confined to a pair of spaced, concentric and relatively narrow annular paths 42, 43, affording an extremely close iit of the bell 20 against the diaphragm assembly and the housmg.

The several diaphragms 35a, 36a are centrally pierced by and secured to a sleeve 45, having its interior in threaded engagement with the oui-,- side of tube 34. Intermediate the several diaphragms of each group on the sleeve 45, central spacing washers a are provided for accurately spacing the diaphragms at the center, and when the assembly is made up, the ends of the tube 45 are advantageously upset or riveted against the heavy terminal washers 45h, whereby each diaphragm group is firmly secured against its corresponding shoulder 45o on the tube 45. The opposite end of the tube 34 on the other side of the electro-magnet 3|), is seated in an armature 46, which comprises laminations of iron or preferably steel in the same plane as laminations of the field core 3|, 32, and which is disposed in proximity to the poles of the latter. A long bolt 4l extends through the tubular` shaft 34 into threaded engagement with a member 43, which provides an extension for the shaft 34 beyond the armature 45, and into which the bolt 41 may be tightened so that the head of the latter engages a lock washer 49a against a large knurled washer sie which is keyed to and abuts the end of sleeve 45, and the sleeve is locked in adjusted position on the shaft 34. Before the bolt 4l is tightened, the knurled washer 49 may be turned to screw the sleeve 34 longitudinally in the sleeve ll so as to adjust the air gap between armature 45 and the core lil-32.

It will be understood that in the preferred construction shown, the passage of shaft 34 through the hole in pole 3| (strictly speaking, through the tube 34a) is completely free,-i. e., there is no contact anywhere,-and indeed the shaft is entirely clear of supporting engagement or abutment at any point above the diaphragm assem bly as seen in Fig. 2. That is, the spaced groups of diaphragms 35, 35, serve alone, and very satisfactorily, to support the remainder of the vibrating assembly, including shaft 34 and the driving armature 46. Frictional, spring or other supplementary supports for the vibrating instrumentalities are thus entirely eliminated, and at the same time the arrangement is such that the respective positions of the various parts carried by or connected to the shaft 34 may be readily adjusted and the parts accurately locked in adjusted position. Furthermore, by virtue of the inclusion of a plurality, and preferably a multiplicity, of spaced parallel diaphragms which are each relatively thin, an eminently desirable stiffness is obtained for the diaphragm structure without tendency of breakage on the part of its individual constituents. In other words, the diaphragm arrangement may safely be stiff enough to provide a desirably high pitch, although a relatively heavy armature 4B is used to obtain powerful driving action. For example, a horn of the type shown has been satisfactorily constructed to produce a note of 205 to 210 cycles per second, yet strong enough to be heard clearly for several miles, under average listening conditions.

The outer end of the member 48 carries one contact 50a of a pair of contacts generally designated 5G, and arranged to open or close in accordance with longitudinal displacement of the shaft 34. The other contact 50o of the set is mounted on a spring 5|, conveniently secured to but insulated from the casing 22. To avoid exing of its end portion, the spring 5| may have a reinforcing plate, or it may preferably have integral upwardly turned ears 52 along its sides, which not only reinforce the end of the spring, but enlarge its end area so as to prevent breakage adjacent the hole where contact 50h is mounted. The contact 5017, moreover, preferably has a tubular shank 50c whereby it is riveted in the hole of the spring, so that when the contact heats up in use, the shank may expand inwardly and avoid straining the spring The outer end of the spring 5| extends beyond the contacts and is adapted to strike an anvil member 53 which is thus arranged to limit the motion of the spring downward as seen in Fig. 2. The anvil member 53 advantageously comprises a worm wheel mounted on a shaft which is threaded into a cross member 54 that is suitably insulated from the housing 2| and case 22 (it being understood that the housing and case are conveniently bolted together at 55a, as shown). The lower end of the worm wheel shaft has threaded on it a leaf spring 53a, which has its ends abutting the under side` of the member 54 and which strongly biases the worm gear in a downward direction to prevent play and chatter. A pin 53h, carried by member 54, engages a slot in the leaf spring 53a to prevent rotation of the latter.

A worm 55 is journaled in suitable supports on the member 54, for rotative engagement with the wheel 53, and is provided with a milled or toothed wheel 56, and an operating shaft 51 having a slotted head. A check spring 58 releasably engages the teeth of the wheel 56; and the arrangement is such that by inserting a screw driver in the slot of member 51, and turning the same, the Y worm 55 will rotate the gear 53 and raise or lower the upper or anvil face of the latter with respect to the outer end of spring 5|. During such adjustment the check 58 clicks over the teeth of wheel 55, but serves to lock the assembly in any adjusted position. The slotted shaft or head 51 is preferably insulated from the assembly of wheel 58 and worm 55, so as to prevent electric shock to the operator making adjustments, or inadvertent grounding should his screw driver also touch the metal casing. Preferably both the anvil 53 and contact spring 5| are of hardened steel construction, for maximum wear resistance. It will now be explained that the parts generally designated 25 in Fig. 1 may comprise the elements 5 1-55-53-5I-50, which are thus readily accessible, through the door of casing 22, for inspection and adjustment.

It will be understood that the lower contact 5to may be mounted for vertical adjustment in f' member 48, as by a shank threaded into the latter and carrying a lock nut 48a, so that the contact may be locked in position of best alignment with Contact 58h.

The instrumentalities hereinabove described are also diagrammatically shown at the upper part of Fig. 5, except that for purposes of sim-v plicity the diaphragm structure is shown as a single diaphragm member 6U. It will here be seen that the internal wiring arrangement of the horn is simply such that the Winding 38 is connected in series with the contacts 50 across the input terminals 5|, the path from the contacts 50 to the lower one of the terminals 6| being conveniently through ground as diagrammatically indicated. Actually, in the apparatus of Figs. l to 4, this grounded path extends from contact 5ta through the shaft 34 and the diaphragm assembly, to housing 2|. l

VAssume for the time being that a suitable source of current, such as a storage battery, is connected across the terminals 5|. Contacts 50 are normally in closed position, and the winding being thus energized, the armature 46 is attracted by the field poles 3|, 32. The contacts remain closed, i. e., the spring 5| follows the downward displacement of the armature 4E (Fig. 5), until the outer end of the spring strikes the anvil 53. The downward stroke of the .armature and diaphragm assembly 46--60 then continues, as will now be well understood, and upon the return stroke (initiated by the energy stored in the diaphragm), contacts 50 again close, and under a presently preferred adjustment with respect to the natural period of the vibrating system, the spring 5| is flexed back to and past its original position as shown in Fig. 5, and the cycle is repeated. Other things being equal (except the current consumption) the amplitude of diaphragm vibration is dependent upon the space E2 intermediate the upper surface of anvil 53 and the outer end of spring 5| in its neutral or rest position; that is. the wider the space the longer the contacts 5f! are closed during each stroke, and the greater the force exerted on the armature 46. It will now be seen that the described horn structure, including the worm 55 for varying the position of anvil member 53 with respect to the spring 5|, is provided with effective means for adjusting the amplitude of diaphragm vibration, so as to obtain and maintain the desired amplitude at all times and without excess current consumption.

When the horn is used for marine signalling purposes, for which it is notably adapted, it must draw a relatively substantial current in order to produce a signal sufciently powerful to be heard, say, for several miles. Under such circumstances-for example, where the horn is located and hooked up, as on a floating buoy, to operate automatically at frequent intervals-long continued use is apt to wear down the surfaces of the rapidly operated contacts 55 (even though a condenser 63 or a condenser-resistor unit is connected across them, as shown in Fig. 5), or more particularly to carry metal from one contact to the other, thus causing the pitting of one contact and the building up of the other contact so as to disturb their parallelism and their relative positions in operation. Fig. 5 accordingly shows a particularly advantageous arrangement for automatic intermittent operation of the horn, and at the same time, for avoiding or greatly reducing the wear on the contacts.

It has been explained hereinabove that the casing 22 may contain a motor 23, together with an associated cycling mechanism and a horn controlling relay 24. As shown diagrammatically in Fig. 5, the electric motor 23, which may be energized from a pair of storage batteries 65, 6B, connected in series, is adapted to drive a pair of cams 61, 68. Although other` motors may be satisfactorily employed in many cases, I prefer to use a motor of the type described and claimed in United States Patent No. 1,985,357, to Charles F. Wallace, for Electric motor apparatus; it will be understood that where the device is expected to operate continuously for long periods of time and without attention, it is desirable to employ a motor having the low current consumption, constant speed and general dependability characteristie of the patented motor.

Cam E1 is provided, for example, with two oppositely disposed risesor high spots 69, and a pair of normally open cam contacts 10 are arranged to be closed by each passage of a rise ES--thus in the instance shown, twice during each revolution of cam 6l. Cam '68, which may be assumed to rotate at the same speed as cam 6l, is provided with a single rise 1I, which is longer in extent than either rise 69 of cam El, and which is so disposed that it shifts a contact-operating follower 'l2 shortly before contacts ll are closed by one rise @Q of cam l, and keeps the follower in shifted position until after the same rise @Si (on cam 6l) has passed the contacts l@ and permitted them to reopen. When shifted, the follower l2 is adapted to open the normally closed contacts 'I3 and to close the normally open contacts 14.

One of the input terminals 5l of the horn is connected through conductor l5 to the connection T6 between the batteries li and E55; the other input terminal of the horn is connected through conductor 16a, heavy duty contacts 'll (normally open) of the relay 24, to the common contact member 12a of the contacts i3, la. The other sides of the contacts i3, lll, are respectively connected to the opposite ends of the batteries 65, ES, and it will now be appreciated that, assuming contacts ll to be closed, the horn is connected to battery 65 or battery 6% respectively accordingto Whether contacts 'i3 or 'I4 are closed. Furthermore, since the sides of the batteries G5 which are connected together through the common connection l5 are opposite in sign, the current flow through the horn when contacts 'i3 are closed is in the reverse direction from the i'low when contacts 'i4 are closed. The low-current relay 2t is conveniently used to avoid the association of heavy duty contacts with the timing cam 6l (although in some cases heavy duty contacts may be used at 'lll and the relay 2t omitted), and the winding of the relay may be connected, as shown, through contacts 'lil to the midpoint 'i6 of the batteries, and also through the contact arm 12a and selectively through contacts 'I3 or 14, to the other side of one or the other of the batteries in the same manner as the horn itself.

Assume now that the motor 23 is rotating the cams 6l, S3 in a counterclcckwise direction, from the position shown in Fig. 5. The rise 'si of cam 5'! rst shifts the follower` 'l2 so as to close oontacts 'i4 and open contacts 'lf-.3. Thereafter one rise 69 of cam 6l causes contacts lil to close and the relay 24 is accordingly energized from battery 65. Energization of relay 2li closes its contacts ll, so that current is supplied to the horn, through its input terminals El, from battery S55-contacts 'lil being now closed. The horn continues to blow until the rise i:3S passes contacts 1G, opening them, thereby de-energizing relay 213 and opening its contacts 'Il in the supply circuit to the horn. Thereafter, the follower '.'2 drops down from the rise H, and contacts 'i3 are closed. They remain closed during the time that the other or opposite rise Eil or cam Eil closes the contacts lil; and it will now be understood that when the contacts 'lll are thus again closed to energize the relay 2d and operate the horn, both the relay and the horn are supplied from battery 65, and current flows through the horn in the reverse direction from that during the immediately previous period of energization. In other words, as the motor 23 continues to drive cams 5'! and 68, the horn is periodically sounded and the direction of current flow through it is reversed each time, so that wear or other disturbance of the horn contacts 53, particularly as occasioned by transposition of metal between these contacts, is very greatly reduced; the action at the contacts 50 is thus, so to speak, a series of brief tendencies to carry the metal rst one way and then back again respectively, so that over a longr period of time the contacts are relatively unai'lected by metal transposition.

It will be noted that the arrangement of cams El and B8 is such that contacts 'E3 and 'M are operated at times when no current is owing, so as to avoid wear of these contacts by arcing. At the same time, it will be noted that the program contacts 'ill and the heavy duty relay contacts 'll both benefit by the same reversal of current flow which is provided for the horn; in conseduence, wear or other deformation of contacts 'le and ll is greatly obviated.

It will be appreciated, ol course, that the number of rises Si) o-n cam El and correspondingly the use of one or more rises H on cam 68 may be varied to suit requirements oi design or operation. In one embodiment of the invention, the arrangement has been that shown in 5, with the rises 69 of such length, and with the motor 23 driving the cam 67 at such rate (2 R. P. l\/I.), that the horn makes four one-second blasts each minute; and with continuous operation of that character for a period exceeding six monthsfour blasts per minute, day and night-there was no appreciable deformation of the contacts 59 and very little appreciable wear.

It will be understood that the capacity of condenser G3 (for ease in mounting, two condensers 53 are shown in Fig. 3 and will be understood connected in parallel) may be readily selected to coordinate the period of the electrical circuit with the natural period of the mechanical elements.

It will now be appreciated that the present invention not only affords a horn which is relatively simple in construction, dependable in operation, and easily built, to have any predetermined pitch within a wide range, but also ailoids distinctively improved control arrangements for such horns so as to avoid contact wear and impairment of normal operation. The advantages realized by the invention are, furthermore, of special importance where the signal device is to be automatically intermittently operated at freo uent intervals and in a location as on a marine buoy) where it must give reliable service without frequent attention. On the one hand, the working vibration of the diaphragm and associated driving assembly is necessarily powerful, and tends to set up disturbing vibrations in every part that is mechanically connected with the apparatus; on the other hand, the electrical parts, notably contacts, are subjected to driving or control operation on each of the many hundred or often several thousand separate occasions on which the signal is operated every day. The invention is particularly eiective in obviating or minimizing the wear or other derangement which would otherwise inevitably result from the strenuous operating conditions just described.

In accordance with the provisions ol the patent statutes, I have herein described the principle of operation of my invention, together with the apparatus which I now consider to represent the best embodiments thereof, but I desire to have it understood that the apparatus disclosed is only illustrative and that the invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combinations and relations described, some of these may be altered and others omitted and some of the features of each modification may be embodied in the others without interfering with the more general results outlined, and the invention extends to such use within the scope of' the appended claims.

I claim:

l. Sound signal apparatus comprising, in combination, an electromagnet, an armature therefor, make-and-break contacts in series with the electromagnet and associated with said armature for causing Vibration of the latter toward and away from the electromagnet, one of said contacts being carried with the armature and the other contact having a supporting spring for maintaining the contacts closed during a substantial part of each cycle of vibration, a supporting member connected to the armature, and a stili diaphragm assembly comprising a plurality of peripherally mounted, spaced diaphragms centrally secured to said member for drive by the armature and arranged in a plurality of sets Widely spaced apart at all points to provide the sole support for said member, armature and firstmentioned contact, said apparatus including means peripherally mounting the diaphragms in the aforesaid spaced relation, and said mounting means comprising means rigidly clamping the diaphragms about their peripheries.

2. In sound signal apparatus, in combination, a plurality of sets of relatively closely spaced, thin, peripherally mounted diaphragms centrally pierced by and secured to a connecting member therefor, an armature spaced from said diaphragms and mounted on an extended portion of said connecting member, said sets of diaphragms being substantially widely spaced and providing the sole support for said connecting member and armature, electromagnetic means associated with the armature for effecting vibration of the diaphragms in unison, supporting structure for the apparatus, and mounting means for the diaphragms, rigidly peripherally clamping said diaphragms to said supporting structure in the aforesaid spaced relations of the diaphragms and sets thereof.

3. In an electric horn, the combination with an electrically vibrated driving element, of a soundproducing assembly adapted for prolonged vibration at a frequency of not less than about 200 cycles and at an amplitude for normal audibility of not less than a mile, and comprising at least several peripherally secured, thin, centrally interconnected diaphragms spaced apart at all points and including two substantially widely spaced diaphragms, all of said diaphragms being disposed together on one side of said driving element and connected to said element to be driven thereby, said horn having a supporting structure and said diaphragms having associated securing means for rigidly peripherally clamping said diaphragms to the supporting structure in the aforesaid spaced relation, and said diaphragms having lll individual nexibllity and combined stiffness cooperating to provide the aforesaid characteristics of frequency and amplitude of vibration of the sound producing assembly.

4. Electric warning signal apparatus comprising, in combination, a stiff sound-producing diaphragm structure comprising at least several peripherally mounted, thin diaphragm spaced apart at all points and centrally interconnected for vibration in unison, and electrical driving means therefor including an electromagnet having a massive armature to be vibrated thereby, for development of substantial driving power, to vibrate the diaphragm structure at a predetermined desired frequency, said electromagnet being disposed intermediate said diaphragms and said armature, said armature being thereby spaced substantially from said diaphragms and said armature 'being mechanically connected to said diaphragms centrally of the latter for drive of and support only by said diaphragms, said diaphragms being spaced and including two which are widely spaced apart, and said diaphragm structure being thereby adapted to support said massive armature for vibration by and with the armature to provide a signal of large amplitude at the desired frequency; said apparatus including mounting means rigidly peripherally clamping said diaphragms in the aforesaid spaced relation.

5. An electric horn comprising, in combination, a relatively stiff sound-producing assembly adapted for prolonged vibration at a predetermined desired frequency and at high amplitude for distant audibility and comprising a plurality of sets of spaced, peripherally mounted, thin diaphragms, said sets of diaphragms being widely spaced apart and all of said diaphragms being centrally interconnected to vibrate in unison, and electrically operated driving means for effecting vibration of said assembly at said desired frequency, said horn including mounting means rigidly peripherally securing said diaphragms in said spaced relation.

6. In an electric horn to be operated on direct current, the combination with electrical driving means comprising an electromagnet, an armature therefor and associated make-and-break contacts for eecting vibration of the armature, of a diaphragm structure to be driven by said armature and adapted to cooperate with the armature to provide a self-excited assembly vibrating at desirably high amplitude and comprising a plurality of peripherally secured diaphragms appreciably spaced apart at all points and disposed together at one side of said driving means, and means fastened centrally to said diaphragms for connecting same to the armature,

. said horn having a supporting structure and said cliaphragms having associated securing means for rigidly peripherally clamping said diaphragms to the supporting structure in the aforesaid spaced relation.

JOHN R. MAcKAY.

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