US 3246321 A
Description (OCR text may contain errors)
Aprii 12, 1966 J. DOGGART 3,246,321
ELECTRICAL SIGNALLING DEVICES Filed Feb. 28, 1962 4 Sheets-Sheet 1 INVENTOR Joy/v Does/1 RT r4 TTORNEYS April 1966 J. DOGGART 3,246,321
ELECTRICAL SIGNALLING DEVICES Filed Feb. 28, 1962 4 Sheets-Sheet 2 INVENTOE Jbf/N D0 an er .4 TTOEN E Y5 ApriE 12, 1966 J. DOGGART 3,246,321
ELECTRICAL S IGNALLING DEVICES Filed Feb. 28, 1962 4 Sheets-Sheet 5 INVENTOQE Jim/v DOGfiABT WIM w 44 TTOENEYS April 12, 1966 Filed Feb. 28, 1962 J. DOGGART ELECTRICAL S IGNALLING DEVICES 4 Sheets-Sheet 4 INVENTOE Joy/v Ewe/2e7- ATTORNEYS for the tone bar.
United States Patent 3,246,321 ELECTRICAL SKGNALLING DEVICES John Doggart, Macclesfield, England, assignor to V. 8: E. Friedland Limited, Macclesiield, England, a British company Filed Feb. 28, 1962, Ser. No. 176,887 Claims priority, application Great Britain, Mar. 1, 1961, 7,522/61; June 7, 1961, 20,64-0/61 7 Claims. (Cl. 340-396) This invention relates to electrical signalling devices.
According to one aspect of the invention there is provided for an electrical signalling device, a base adapted to carry a tone bar and means for striking the tone bar, which base has formed integrally therewith an open mouthed chamber cooperating or adapted for cooperation with a sealing plate to form a resonating chamber Preferably the resonating chamber has one wall adjacent the tone bar, which wall has a sound aperture therein and another wall which is comprised by the sealing plate which seals with the other walls of the resonating chamber. Conveniently the base is adapted to receive thereon an apertured cover so as to enclose the tone bar and the striking means.
Preferably the base is provided with means for supporting two tone bars, two resonating chambers are provided respectively for the one bars and formed integrally with the base, and means are provided for striking bot-h tone bars.
Preferably each tone bar is suspended on members projecting dlrom the wall of the resonating chamber having the sound aperture formed therein.
Conveniently the tone bar, which is to be supported verticallyyis tuned and is provided with apertures'for supports passing therethrough which apertures are so located that when the tone bar is held vertically by the supports, at least the upper of the supports will be abutting the periphery of its associated apertures at the preselected node points. Preferably also only the upper support abuts the edge of its associated aperture, the periphery of the lower aperture being spaced from the support means passing therethrough so that the upper support locates the tone bar against longitudinal movement whilst the lower support is provided only to prevent undue oscillations in the transverse direction of the tone ber having a nose part of smaller dimension, which nose part is received Within a plastic striker cap. In this way,
'we believe we can obtain a harder note on striking of the tone bar. Alternatively the plastic striker may fit in an'apertu-re in the end of the plunger member. In this way the electromagnetic efficiency of the striking means may be improved.
According to yet a further aspect of the invention there is provided an electrical signalling device comprising a base as described in the preceding paragraphs in combination with a cover received on the base and enclosing the tone bar and striking means. The cover is preferably apertured. Preferably the cover is held slightly spaced from the base so that a sound aperture is formed between the base and the cover.
Two embodiments of the invention in the form of socalled door chimes will now be. described, by way of example, with reference to the accompanying-drawings, in which:
FIGURE 1 is a plan of an electrical signalling device of the invention with part of the cover removed;
FIGURE 2 is a section on line 2-2 of FIGURE 1; FIGURE 3 is a section on line 3-3 of FIGURE 1;
FIGURE 4 is a view in the direction of the arrow 4 in FIGURE 1;
FIGURE 5 is an underplan of the signalling device with parts broken away for greater clarity;
FIGURE 6 is a section on line 6-6 of FIGURE. 5;
FIGURE 7 is a detail of FIGURE 6;
FIGURE 8 is :a view of an alternative plunger assemy;
FIGURE 9 is a plan of a modified electrical signalling device of the invention with part of the cover removed;
FIGURE 10 is a section on the line 10-10 of FIG- URE 9;
FIGURE 11 is a section on line 11-11 of FIGURE 9;
FIGURE 12 is an enlarged section on line 12-12 of FIGURE 9;
FIGURE 13 is a scrap section on line 13-13 of FIG- URE 9;
FIGURE 14 is a perspective view from above of the electrical signalling device of FIGURE 9; and
FIGURE 15 is a circuit diagram of the device of FIG- URE 9.
Referring now to FIGURES l to 8 of the drawings, a door chime comprises a rectangular base 11 having a removable cover 12, a pair of tone bars 14 and 15 and a striker mechanism 16.
The base 1 1 is formed by injection moulding and is provided along its opposite edges with a pair of substantially rectangular sect-ion resonating chambers 17, 18. Three sides 21, 22 and 23 of the resonating chambers as well as the two ends '24 thereof are formed integrally with the base. The [fourth side of each chamber, which side is in line with the major part of the bas 11, is'constituted by an air tight sealing plate 2 5 also formed by injection moulding and cemented in position. The sides of each chamber are recessed to receive the edges of the sealing plate 25. This sealing plate 25 is provided with ribs 26 (see FIGURE 6) running along its longer edges to bear-against the inner faces of sides 21 and 23 of the resonating chambers. On the opposite sides, the plates 25 have levelling projections 27 to compensate for slightly uneven mounting surfaces.
The tone bars 14 and 1-5 are tuned respectively to emit the notes Flt (739.99 cycles per second) and D (587.33 cycles per second) when struck. A pair of circular suspending apertures 28 and 29 are provided for each 'bar. These apertures 28 and 29 are located centrally of the tone bars and are spaced from the nodes 3 1 and 32 by a distance equal to one-half their diameter so that when the tone bars are carried in a vertical position by two pins of smaller diameter and spaced apart by the distance of the nodes, the points of contact between the pins and tone bar will be at the nodes. The tone bars 14 and 15 are mounted respectively on two pairs of support pins 33 and 34 which are formed integrally with the inner walls 2-1 of the resonating chambers 17 and v18. These support pins are of a diameter slightly less than half the diameter of the supporting apertures and are surrounded in the usual way by soft rubber gong supports 35 and 36 (having a Shore hardness of 35) the outside diameter of which are also less than the diameter of the apertures. The support pins are located at a distance apart slightly greater than the distance between the nodes31 and 32. Thus for each tone bar the rubber gong support 35 surrounding the upper supportpin 33 will bear on the'edge of the upper aperture 28 at its point tangential to the node 31 whilst the rubber gong support 36 surrounding the lower support pin 34 will be located centrally in the lower aperture 29. The gong supports 35 and 36 have flanges 37 to prevent lateral movement of the tone bars and the only contact between the lower gong supports 36 and the tone bars are through these flanges.
The support pins 33 and 34 are so located that the tone bars 14 and '15 are parallel to the resonating chambers 17 and 18 and the anti-nodes of maximum vibration of both tone bars 14 and 15 oscillate along the same line. Sound apertures 30 are formed in the walls 21 of the resonating chambers adjacent the anti-nodes. The resonating chambers -17 and 18 are tuned to the frequencies of tone bars 14 and 15 respectively so as to give the maximum period of sound emission.
Located in line with the anti-nodes of maximum vibration is a two headed striker mechanism 16. The mechanism 16 comprises a pair of coaxial coils 42 and 43 each carried in a pair of closely butting soft iron U frames 40 and arranged side-by-side. The coils 42 and 43 surround a common hollow hard brass tube 44. The ends of the tube 44 are covered respectively by centrally apertured plastic retaining caps 45 (see FIGURES 6 and 7). A soft iron plunger or armature 46 is reciprocable within the tube 44. The plunger 46 has at each end a frustoconical boss 47. An axial blind bore 48 eners each end of the plunger 46. This bore 48 is enlarged at 49 where it passes through the boss 47. A nylon striker 51 is carried at each end by the plunger 46. Each striker 51 has a cylindrical stub 52 which fits in the bore 48 .and a tapered nose portion 53 having a rounded end. This nose portion 53 commences with a short cylindrical part which fits in the enlarged part 49 of the bore 48 A pair of springs 58 and 59 extend between each retaining cap 45 and bosses 47 on the adjacent ends of the plunger 46. The spring 58 is somewhat longer and stronger than spring 59 and the springs are arranged to keep the plunger 46 biased into coil 42 and away from coil 43.
The striker mechanism 16 is mounted in a housing 60 formed integrally in the base 11 and having an opening 61 at the underside of the base. This opening 61 is covered by a paper-based Bakelite cover plate 62 of corresponding shape which snaps into position with a pair of noses 63 formed thereon passing into the base 11 to hold the cover plate 62 thereon.
The housing 60 is also formed with a shelf 64 at one side. Four, self-retaining, Phosphor bronze terminal strips 65, 66, 67 and 68 are provided in the shelf 64 and four self-tapping terminal screws 71, 7-2, 73 and 74 respectively pass through these strips 65, 66, 67 and 68. The terminal strips 65, 66, 67 and 68 are provided both sides with small projections 69 to aid retention of the external wires which are hereinafter described. The terminals of the coils 42 and 43 are connected respectively to contact strips 66 and 67 and contact strip 65. The fourth contact strip 68 is a blank contact. The striker mechanism 16 is connected for operation to the mains through a transformer 75 (see FIGURE 1) and to front door and rear door pushbuttons 76 and 77 by three pairs of wires 78a and 78b, 79a and 79b and 81a and 8 11). These wires lead to the shelf along a wiring channel 82 formed on the underside of the base 11 and an opening 83 through the base of the channel 82. One wire 78a, 79a and 81a of each pair is connected to the common blank terminal 68 whilst the other Wires 78b, 79b and 81b are connected respectively to the terminals 65, 66 and 67. Thus when the rear-door push button 77 is actuated, the coil 42 is energised drawing in the plunger 46 causing the striker 51 to strike the tone bar 15. On release of the pushbutton 77, the coil 42 is deenergised and the plunger 46 is returned by the weaker spring 59 into the initial position. Thus a single note only is emitted because the plunger cannot overcome stronger spring -8. When the front-door pushbutton 76 is depressed, the coil 43 is energised causing the plunger to strike the tone bar 14. On release of the pushbutton 76, the coil 43 is deenergised and the plunger 46 is returned by the spring 58 which overcomes spring 59 so that the plunger strikes the tone bar 15. Thus the chime emits two notes when the front-door pushbutton 76 is actuated and only one when the rear-door pushbutton 77 is actuated.
Four bosses 83a, 83b, 84a and 84b are provided projecting through the channel 82. Two of these bosses 83a and 84a have bores 85 which are counter sunk at each end (a) to retain fixing screws during transit and (b) to locate the screws when the chime is being mounted.
The base is also formed with four elongated apertures 86 located below the support pins 33 and 34. These facilitate the fitting and removal of the tone bars as the latter may be inserted or removed at an angle to the base 11 as shown in dotted lines in FIGURE 2.
Two cross pieces 87 of about half the height of the resonating chambers 17 and 18 join the ends of these chambers. Further the resonating chambers are provided with projections 88 running along the outer edges of the surfaces 22. These projections 88 may be hollow to increase the volume of the resonating chambers. The cover 12 is of square edged U shape having a front part 89 and two end arms 90. Short flanges 91a and 91b are provided along the free ends of the front part 89 and the arms 90. The front part 89 of the cover 12 is formed with parallel rows of sound openings 92 (see FIGURES 1, 2 and 3). The louvres 93 defining these openings 92 have a part annular portion and rectangular portion to assist in reflecting the sound waves and to close off the interior of the chime from view when the chime is mounted from 6 feet to 7 feet from ground level. The rows of openings 92 are equispaced from one another and are all the same length.
Three support lugs 94 are formed integrally with the top surfaces 22 of the resonating chambers at a short distance (e.g. inch) from the projections 88. The width of the cover 12. which is slightly less than the distance between the projections 88 is such that the flanges 91a can rest on the support lugs 94. Similarly the length of the arms is such that they end short of the base 11. Thus the cover 12 can be positioned on the base 1 1 with its edges spaced therefrom, except where the flanges 91a rest on the support lugs 94, so as to provide an additional aperture 95 for the release of sound. The cover and base are provided with cooperating latches so that the cover may be firmly but releasably held in position.
The base part and cover 12 are of contrasting colors to give a pleasing appearance. The plunger assembly may be modified if desired. In the modified assembly, which is illustrated in FIGURE 8, the plunger 246 is stepped down twice at its ends at 247 and 248. Respectively surrounding the two larger stepped parts 247 are a pair of ground felt washers 249 which fit in the hard brass tube 44 toallow for free reciprocation of the plunger 246 in the tube 44 and to prevent the former coming into contact with the latter. A nylon cap 251 fits onto each of the smaller stepped parts 248. Each cap 251 has a cylindrical part 252 (see FIGURE 8) leading to a frustoconical part 253 having a rounded striking nose 254. At its other end, the cylindrical part is provided with a flange 256. A blind bore enters the cap 251 through the flange 256. The smaller stepped part 248 is a heavy force interference fit in the bore so that the cap 25-1 will be very securely held thereon by the resilience of the nylon.
Referring now to FIGURES 9-15 of the drawings, the electrical signalling device is generally similar to the door chime described above and those features of the door chime which are identical with corresponding features in the aforesaid door chime will not be hereinafter described in detail. The door chime comprises a rectangular base 111 having a removable cover 112 a pair of tone bars 114 and 115 (tuned respectively to Fit, i.e., 739.99 cycles per second and D, i.e., 587.33 cycles per second), a striker mechanism 116, and a pair of rectangular section resona ting chambers 117 and 118 tuned respectively to the adjacent tone bars and each having hollow projections 119 running along the outeredges of the'upper andend faces 121 and 122 respectively. A number, conveniently three, lugs 123 are formed on the upper faces 121 of the resonating chambers 117 and 118and are spaced about A1. inch away from the projections 119. Two cross pieces 124 of about half the height of the resonating chambers 117 and 118 join the ends'of the latter. H-shaped projections 125 are formed approximately centrally on the cross pieces 124.
The cover 112, which is also generally similar to the cover 12 described above, is of U shape in section with short arms'109. The flat center piece 129 of the cover 112 has a large central circularopening 131. A disc 132 is concentrically located within the opening 131 by means of a concentric flat ring 133. This ring 133 is spaced from the central portion 129 and the disc 132 and is of somewhat greater width than the annular gap 135 between the surround of the opening 131 at the edge of the disc 132 so as to cover the gap. The ring 133 has three pairs of projecting lugs 136 each having bosses 137 which are received in and cemented to rimmed recesses 138 in the rear faces of the central portion 129 and the disc 132. A sound path thus exists from within the cover 112 around the ring 133 and through the gap 135.
The cover 112 has flanges 126a extending along the free edges of the flat part 168 of the cover 112. The flanges 126a merge with flanges 12617 on the free edges of the arms. The width of the cover 112 is slightly less than the distance between the projections 119 so that the flanges 126a may rest on the lugs 123. Catches 127 are provided at the midpoints of the arms of the U-shaped cover 112 to engage the H-shaped projections 125. The cover 112 may thus be held spaced from the base 111 except where the flanges 126a rest on the lugs 123 so that an additional aperture 128 between the periphery 'of the cover and the base is provided for the release of sound.
In this embodiment the striker mechanism 116 includes a single coil 146 mounted between two, soft iron U frames 140 which are closely butted together. The U frames 140 are received in a hollow solenoid chamber 141 formed integrally with the base. Barbed projections 142 are formed on the U frames 140 to improve the grip of the U frames onto the internal walls of the solenoid chamber 141. The coil 146 is energisable to move a soft iron plunger or armature 148 against the influence of a spring 147.
The plunger 148 has frusto-conical end pieces 143 with reduced diameter portions 144 immediately adjacent them. In one of these reduced diameter portions 144 is received one end of the spring 147. Axial blind bores 145 enter each end of the plunger 148. These bores 145 have enlarged diameter portions 145a passing through the end pieces 143. Nylon strikers 190 and 191 are respectively carried at the end of the plunger 148. The strikers 190 and 191 have cylindrical stubs 192 which fit in the bores 145 and, adjacent the stubs, cylindrical parts 192 which fit in the enlarged diameter portions 145a of the bores. The striker 190 has a tapered portion 193 leading from the cylindrical part 192 and terminating in a rounded strikingnose 194. The striker 191 has a long cylindrical portion 195 of smaller diameter than part 192 to which it is joined by a tapered portion 196. The cy lindrical portion 195 terminates in a rounded striking nose 197. The solenoid chamber 141 has a shelf 151 at one side. Four, self-retaining, Phosphor bronze terminal strips 152, 153, 154 and 155 are provided in the shelf 151 and four self-tapping terminal screws 156, 157, 158 and 159 respectively pass through these strips 152, 153, 154 and 155. The terminal strips 152, 153, 154 and 155 have small projections 160 at their edges to aid the retention of external connecting wires. The terminal strip 152 provides a blank common terminal. Terminal strips 153 and 154 are connected by means of wires 161 to a makeand-break mercury switch 162, Terminal strips 154 and 155 are connected by wires 164 to the ends of the coil 146. The mercury switch 162 isdetachably mounted ina thermoplastic support 166 having Phosphor bronze con tact sockets 167 and being carried between the arms of a one-piece, I-shaped, Phosphor bronze rocker 168. The rocker 168 has a brass bearing bush 169 riveted thereto. A brass stud 170 having a reduced diameter threaded end portion 171 passes through the bush'169 and is mounted in a recessed part 172 of the base 111 by means of nut 173 engaging the portion 171. The axis of' stu'd 170 passes through the centre of the mercury switch 162. The longer arm 1770f the rocker 168 is forked at its free end to receive between the forks the cylindrical portion 195 of the nylon striker 191. Felt washers 178 are mounted on the striker 191 on each side of the arm 177. A retaining ring 179 holds the washers 17 8 on the striker 191. A central wiring channel 181 runs the Whole length of the underside of the base 111 and the shelf 151 lies above and extends'entirely over this channel 181'. The various visible parts of the door chime are conveniently made in contrasting colours. Conveniently the base 111 and the ring 133 are one colour e.g black whilst the cover 112 and the disc 132 are another colour e.g. white.
In use the door chime is normally connected to a source of electric power e.g. a bell transformer 182 (shown diagrammatically in FIGURE 15), a front-door pushbutton 183 and a rear-door pushbutton 184. The transformer 182 is connected to terminal strips 152' and 155, the front-door pushbutton 183 to terminal strips 152 and 153 and the rear-door pushbutton 184 to terminal strips 152and 154. Thus when the rear-door pushbutton 184 is actuated, the plunger 148 is moved backwards under the influence of the coil 146 to strike'tone bar 114. On release of the reardoor pushbutton 184 the' plunger 148 is moved forward under the influence of the spring 147 to strike the tone bar 115. Thus'two' notes are emitted.
When'the front-door pushbutton 183 is actuated, it is connected to the coil 146 via the mercury switch 162. Initially the coil 146 draws in the plunger 148 to strike the tone bar 114. At the same time, the rocker 168 is rocked and the mercury switch 162 so moved that it breaks the circuit of the pushbutton 183 and the" coil 146, deenergising the coil 146. The plunger 1481s therefore moved forwardly by the spring 147 to strike the tone bar 115, the rocker 168 being simultaneously moved forward to make the circuit of the front-'door pushbutton 183 thereby energising the coil 146 and drawing in the plunger 148 until thetone bar 114 is again struck and the mercury switch 162 re-opened. The plunger 148 thus reciprocates back and forth striking the tone bars 114 and until the front-door pushbutton 183 is releaseda This alternate striking of the tone bars 114 and 115 gives a warbling effect.
It will be noted that the base, the resonating chambers and the support pins for the tone bar's and housingfor the striker mechanism are comprised by three parts only, viz. the base part and the two sealing plates. Furthermore, by providing the elongated apertures'in thebase, the depth of the chime under the cover need be only slightly greater than the width of the tone bars.
We have found that by providing the additional apertures 95 and 128 in addition to the central soundapertures 92 or 135, the sound emitted by the door'chimes is considerably increased. Further we found that in the second embodiment the increase in sound emission is greater under these circumstances than was obtained by increasing the'size of the gap until it was of an aesthetically unattractive size or even removing the disc 132 altogether.
The invention is not limited to the precise constructional details hereinbefore described and illustrated in the accompanying drawings.
1. An electric signalling device, comprising: a base and a cover therefor; sound emitting means and electroresponsive operating means therefor between said base and said cover, said base having a composite resonating chamber; and a sound aperture defined between said base and said cover formed by means spacing said cover from said base, said sound aperture being operative to enhance the sound of said sound emitting means.
2. An electric signalling device, comprising: a base and a cover therefor, said cover being provided with at least one sound aperture therethrough; sound emitting means and electroresponsive operating means therefor between said base and said cover, said base having a composite resonating chamber and a second sound aperture defined between said base and said cover formed by means spacing said cover from said base, said second sound aperture being operative to enhance the sound of said sound emitting means.
3. An electrical signalling device, comprising:
(a) a base member including a rear surface, and having a pair of parallel, elongated, cuboidal resonating chambers running along opposite side edges thereof, the front, side and end walls of said chambers being formed integrally with said base member, the rear side of said chambers opening onto said rear surface, and the confronting side walls of said chambers each being formed with a central aperture;
(b) a pair of sealing plates mounted to seal the rear,
open sides of said resonating chambers;
(c) a pair of sounding members mounted in confronting relationship on the confronting side walls of said resonating chambers and having an antinodal vibration adjacent said central apertures in said confronting side walls;
((1) a striker means mounted between said sounding members and movable for alternately striking said members;
(e) electroresponsive actuating means mounted on said base operable for moving said striker means, and including at least one coil;
(f) a cover for said base, said sounding members, said striking means and said actuating means being disposed between said base member and said cover; and
(g) a sound aperture defined between said base member and said cover formed by means spacing said cover from said base member, said sound aperture being operative to enhance the sound of said sounding members.
4. An electrical signalling device as recited in claim 3, further comprising lugs formed integrally with said confronting side walls of said resonating chambers for carrying said sounding members.
5. An electrical signalling device comprising:
(a) a base member, said base member having a pair of composite resonating chambers;
(b) a pair of sound emitting'means mounted on said resonating chambers in confronting relationship;
(c) a solenoid striker mechanism mounted on said base member between said sound emitting means, and including: a coil; an armature; a striker carried on each end of said armature, said armature being movable in one direction by said coil when said coil is energized to cause one of said strikers to strike one of said sound emitting means; and a spring for moving said armature and said strikers in the opposite direction when said coil is deenergized to cause the other of said strikers to strike the other sound emitting means;
(d) a movable switch unit, including: a pair of terminals; and means to connect said terminals in series with said coil when said switch unit is in a first position, said'means being movable to efiect disconnection of said terminals when said switch unit is moved into a second position; i
(e) a cradle for mounting said switch unit on said base member for pivotal movement between said two positions;
(f) linkage means connecting said cradle with said armature, and arranged to pivot said switch unit from said first position into said second position when said armature moves to strike said one sound emitting means;
(g) a power source;
(h) a circuit, including said movable switch unit, for
connecting said coil to said power source;
(i) a cover for said base member, said resonating chambers, said sound emitting means, said solenoid striker mechanism, said movable switch unit, said cradle and said linkage means being disposed between said base member and said cover; and
(j) a sound aperture defined between said base member and said cover formed by means spacing said cover from said base member, said sound aperture being operative to enhance the sound of said sound emitting means.
6. An electrical signalling device as claimed in claim 5, wherein the base member includes a rear surface, and said composite resonating chambers comprise: a pair of parallel, elongated, cuboidal resonating chambers running along opposite side edges of said rear surface,.the front, side and end walls of said chambers being formed integrally with said base member, the rear side of said chambers opening onto said rear surface, and the confronting side walls of the chambers each being formed with a central aperture adjacent the sound emitting means.
7. An electrical signalling device, comprising:
(a) a rectangular base;
(b) a pair of composite elongated cuboidal resonating chambers running along opposite side edges of said rectangular base and each extending between points spaced inwardly from the opposite end edges of said 7 rectangular base;
(c) a pair of sound emitting members, one of said members being associated with each of said resonating chambers;
(d) electroresponsive striker means carried by said rectangular base and arranged to strike said sound emitting members;
(e) an elongated projection extending along the outer edge of each of said resonating chambers;
(f) a U-section cover for said rectangular base, said resonating chambers, said sound emitting members and said striker means being disposed between said rectangular base and said cover, said cover having a base extending parallel to said rectangular base and lying between said elongated projections above said resonating chambers, and including two-Harms depending from the opposite end edges of the base of said cover and extending toward said rectangular base, the width of said cover being less than the distance between said elongated projections; and
(g) a sound aperture defined between said rectangular base and said cover, formed by means releasably se curing said cover to said rectangular base with said cover spaced from said rectangular base and said resonating chambers, said sound aperture being operative to enhance the sound of said sound emitting members.
References Cited by the Examiner UNITED STATES PATENTS 1,940,718 12/1933 Koch 200 ll2.1 2,016,604 10/1935 Karnell 340-392 2,445,406 7/1948 Pollard 200-112 X 2,491,986 7/1948 Larson 200 -112 X 2,820,913 1/1958 Christy 340-393 X 2,844,680 7/1958 Christy et a1. 340-392 X 2,850,724 9/1958 Bassani 340--392 X 2,946,905 7/1960 Jolly 31034 NEIL C. READ, Primary Examiner.