US2787675A - Microphone - Google Patents

Description

- April 1957 Y D. D. MESHIRER ETAL 2,787,675

I MICROPHONE Filed April 2, 1954 4 Sheets-Sheet 1 FIGS.

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INVENTORS. DAV/D D. MESH/QEQ" DALE quL/cK BY 3 w ATTIOEMFX April 2, 1957 D, D, s m ET AL 2,787,675

' MICROPHONE Filed April 2, 1954 4 sheets-sheet 5 54 INVENTORS 7 Y" DAVID oar 55am DALE 11s BY 6 JTTQQNEX April 2, 1957 I D. D. MESHIIARER ETAL 2,787,675

MICROPHONE Filed April 2 1954 I 4 Sheets-Sheet 4 INVENTORJ'. DAV/D 0. MESH/25.2

0A4: quuc/r' ATTOQME'X United States Patent MICROPHONE David D. Meshirer, Jackson Heights, and Dale Gulick, Farmingdale, N. Y.

Application April 2, 1954, Serial No. 420,698

18 Claims. (Cl. 179-179) This invention relates to microphones, and more particularly, to a microphone for use in aircraft and for similar purposes.

An object of the invention is to provide a microphone of the character described having a novel construction whereby the cover may be taken off and the switch unit or transmitter unit removed for replacement or repair by quickly and easily sliding said cover and units out of the casing and without requiring any time-consuming unscrewing or other disassembly operations.

Another object is to provide a microphone construction wherein all the parts, except the switch and transmitter units may be made of non-metallic material, preferably plastic, and completely eliminating screws or other metallic fastening elements.

A further object is to provide a microphone comprising a casing for housing the operating components, said casing being completely closed and sealed off from the atmosphere so as to protect said components from moisture, dust, and the like.

Still another object is to provide the casing with a wall portion having an opening therethrough, switchactuating means extending through said opening, and means sealing said opening for preventing dust and moisture from entering the interior of the casing therethrough.

A further object is to provide in a microphone of the character described, a non-metallic bushing secured in said opening, said switch-actuating means comprising a push button member reciprocally slidable within said bushing and having an inner end engaging the switch and an outer end outwardly of the casing, said sealing means comprising a flexible non-metallic sealing element surrounding said button member and having one end in sealed relation to said bushing and the opposite end in sealed relation to said button member.

Another object is to provide a' novel means for retaining the transmitter unit in fixed position within the casing but permitting said unit to be easily removed there from for replacement or repair.

Still another object is to provide a novel electrical cord construction and mounting means in the casing therefor to permit rapid and easy insertion or removal of the electrical cord with respect to the casing.

A further object is to provide a novel arrangement for mounting the cover member in sealed engagement with the open end of the casing and permitting the cover to be quickly and easily removed or reassembled.

Another object is to provide a microphone of the character described, said open end of the casing being of cylindrical configuration, said cover member having a cylindrical portion'extending Within said cylindrical casing end and removable therefrom, and resilient annular sealing means engaging said cylindrical casing end and said cover cylindrical portion.

Still another object is to provide a microphone of thecharacter described, wherein the casing has a wall portion with an opening therethrough, a resilient nonice metallic sleeve extending through said opening and in sealing engagement therewith, and an electric cord extending through said sleeve and comprising a plurality of electrical wires connected to the transmitter unit and the switch, whereby the opening will be sealed so as to prevent dust, moisture and other deleterious substances of the atmosphere from entering the interior of the casing.

A furtherobject is to provide the sleeve with an enlarged non-circular head, thecasing having a non-circular recess receiving said head to prevent rotation or twisting of the sleeve and the electrical cord relative to the casing.

Other objects and advantages will be apparent as the description proceeds in connection with the accompanying drawings wherein:

Fig. 1 is a front elevational view of an embodiment of the invention;

Fig. 2 is a sectional view on line 22 of Fig. 3;

Fig. 3 is a rear elevational view with the cover member removed for clarity in illustration;

Fig. 4 is a detail view of the cover member;

Fig. 5 is a detail view of the switch-actuating push button member;

Fig. 6 is a detail sectional view of an O-ring;

Fig. 7 is a partially sectioned view of a guide bushing for the push button member;

Fig. 8 is a partially sectioned view of a tubular sealing element for the push button member;

Fig. 9 is a detail sectional view of another O-ring;

Fig. 10 is a detail sectional view of a spacer element;

Fig. 11 is a perspective view of another embodiment of the invention and shows the several components in disassembled relation;

Fig. 12 is a front elevational view of the device of Fig. 11;

Fig. 13 is a vertical sectional view on line 1313 of Fig. 12;

Fig. 14 is a rear elevational view of the second embodirnent with the cover member removed;

Fig. 15 is a detail view of the push button member; and

Fig. 16 is a detail perspective View of a cylindrical support member for mounting several of the components of the second embodiment.

Referring to the drawing in more detail, reference numeral 11 indicates generally a first form of a microphone embodying the present invention and comprising a casing 12. The latter is preferably formed of plastic or similar non-metallic material and comprises an outer cylindrical wall 13. At one end of casing 12 is a mouthpiece portion 14 comprising a relatively thin wall 15 extending transverse to the axis of casing 12 and surrounded by a peripheral annular ridge 16.

A conical wall 17 connects wall 15 to cylindrical wall 13. A plurality of projections 18 to 24 extend from wall 17 parallel to the axis of casing 12 to the opposite open end thereof and have end faces lying approximately in a transverse common plane with the end face 25 of cylindrical Wall 13. It will be seen that projections 18-24 are arcuate in transverse section and extend in annular form parallel to wall 13 but spaced inwardly therefrom to provide an annular space 26 between wall 13 and projections 18-24. The latter are also spaced from each other to provide radially extending slots therebetween.

The inner arcuate surfaces 18'-24' of projections 18-24 cooperate to form a substantially cylindrical but discontinuous interior wall surface 33 enclosing a cylindrical interior space within casing 12. Mounted within this space is a carbon button diaphragm unit or transmitter unit 27 of well-known construction, such as the 'Western Electric Co. transmitter unit. This unit 27' serves the function of converting sound waves into electrical impulses.

Mouthpiece wall is provided with a plurality of apertures 28 therethrough. A diaphragm 29 of thin plastic sheet material is mounted against the rear or inner surface 36 of wall 15 to seal apertures 23 and thereby prevent dust or moisture from entering the interior of casing 12. The front face 31 of transmitter unit 27 abuts against diaphragm 29.

Transmitter unit 27 comprises a first cylindrical portion 32 slidably engaging the cylindrical interior wall surface 33. Extending rearwardly from portion 32 is a reduced second cylindrical portion 34 forming a shoulder 35. An annular O-ring 36 of resilient material such as rubber surrounds portion 34 and abuts against shoulder 35. Au annular spacer element 37 of similar material abuts against O-ring 36 to retain transmitter unit 27 securely in its assembled position as will be explained in more detail below.

As seen in Fig. 3, the arcuate inner surfaces 18', 19', and 23 of projections 18, 19, 20, 23 are each provided with an axially extending notch at 38, 39, 40, 41, respectively, for slidably receiving the four corners of an enclosed switch unit 42 such as the standard No. 1 General Electric Co. Switchette. The front surface 43 of switch unit 42 abuts against the rear edge 37 of spacer element 37 to retain the latter against outward movement relative to casing 12. The rear surface 44 of switch unit 42 is substantially co-planar with end face of outer cylindrical wall 13.

Referring to Fig. 4, a circular cover member 45 of plastic or other non-metallic material is provided with a planar surface 46 from which extends a hollow cylindrical portion 47. The latter is provided on its exterior surface with a first peripheral groove 48 adjacent planar surface 46 and a second peripheral groove 49 adjacent the forward end 50 of cylindrical portion 47. 1

As shown in Fig. 2, the interior wall surface 51 of outer cylindrical wall 13 is enlarged or counterbored at 52 adjacent the rear end of casing 12 to provide an annular shoulder 53. When cover member 45 is to be assembled to casing 12, a second resilient O-ring 54, preferably of rubber, is first placed in groove 49 and cylindrical cover portion 47 is inserted into the annular space 26 until shoulder 53 abuts O-ring 54 to snap the latter rearwardly from groove 49 into its final position within the rear groove 48 in which position O-ring 54 will tightly engage the counterbored surface 52 to seal the rear end of casing 12 from the atmosphere and to retain cover member 45 securely in place.

In this final assembled position planar surface 46 of cover member 45 abuts against end face 25 of casing wall 13 and also against rear surface 44 of switch unit 42 to retain the latter against outward movement with respect to casing 12 and thereby also retaining spacer element 37. O-ring 36, and transmitter unit 27 in proper assembled position. It will thus be seen that cover member 45 may be quickly and easily removed, preferably by prying it with a screw driver, and switch unit 42 and transmitter unit 27 may be slidably removed and replaced by other units. Thus the operative electrical components may be easily replaced without time-consuming unscrewing or other disassembly operations.

Cylindrical wall 13 is provided with an opening 56 extending radially therethrough. A cylindrical guide bushing 57 of plastic or similar non-metallic material is press-fitted within opening 56. The outer surface 58 of wall 13 is counterbored at 59 around opening 56. The lower or inner end of guide bushing 57 is provided with a peripheral groove 60.

A plastic push button 61 is provided with an enlarged head portion 62 integral with a cylindrical shaft portion 63 reciprocally slidable in guide bushing 57. Shaft portion 63 is provided with a peripheral groove 64 receiving 4 an annular clip 65 adapted to abut the lower end face 66 of bushing 57 to limit upward movement of push button 61.

A tubular sealing element 67 of flexible non-metallic material is provided with an upper lip 68 bent inwardly to engage within groove 60 of bushing 57. The lower end of element 67 is bent inwardly at 69 and then upwardly at 70 in direction parallel to but spaced inwardly from the cylindrical wall 71 of element 67. The inner cylindrical portion 70 of sealing element. 67 is in sealed gripping engagement with the lower end of push button shaft portion 63. It will thus be seen that air, dust and moisture which may pass through the inevitable clearance space between button shaft portion 63 and bushing 57 will be prevented from entering the interior of casing 12, thereby protecting the several operative components therein.

Push button head portion 62 is provided with an integral peripheral flange 72 received by counter-bore 59 when the button 61 is depressed. The lower end face 73 of shaft portion 63 engages a button 74 of switch unit 42 to actuate the latter in a conventional manner well-known in the art.

Wall 13 is further provided with a cylindrical radial opening 75 diametrically opposite to opening 56. A flexible plastic or rubber strain relief sleeve 76 is provided with a. cylindrical portion 77 extending through opening 75 and having an enlarged square head 78 on the inner end thereof to retain sleeve 76 against outward movement relative to casing 12. Sleeve 76 is fixedly secured to an insulated electrical cord 79 having a plurality of electrical wires which are connected to the terminals of units 27 and 42 in the usual manner to form the desired electrical circuit.

The inner surface of casing outer wall 13 is provided with a rectangular recess receiving head 78 so as to prevent sleeve 76 and cord 79 from rotating and twisting relative to casing 12. Sleeve 76 is preferably made of rubber and is molded around cord 79 to provide a durable assembly therewith. Sleeve 76 also sen/es to seal opening 75 so as to prevent dust, moisture and other deleterious substances of the atmosphere from entering the interior of casing 12.

Referring now to Figs. 11 to 16 inclusive, the reference numeral 111 indicates generally a second form of microphone embodying the present invention.

It will be noted that those parts of microphone 111 which are similar to the parts of microphone 11 described above, will be given corresponding reference numerals raised by units over the reference numerals of the first form of the invention.

Microphone 111 comprises a casing 112 preferably formed of plastic or similar non-metallic material, and having an outer cylindrical wall 113. At one end of casing 112 is a mouthpiece portion 114 comprising a relatively thin wall 115 extending transversely to the axis of casing 112, and surrounded by a peripheral annular ridge 116. An approximately conical wall 117 joins transverse wall 115 to cylindrical wall 113.

The interior of casing 112 is hollow and is formed with a cylindrical interior wall surface 133 adjacent mouthpiece portion 114. A transmitter unit 127 similar to unit 27 described above, is mounted within the space enclosed by wall surface 133, and comprises an enlarged cylindrical portion 132 slidably engaging the cylindrical interior wall surface 133. Extending rearwardly from portion 132 is a reduced second cylindrical portion 134 forming a shoulder 135 at its junction with portion 132.

Mouthpiece wall 115 is provided with a plurality of apertures 128 extending therethrough. The transmitter unit 127 comprises a diaphragm 129 of thin plastic sheet material adapted either to abut or to lie adjacent the rear inner surface 130 of mouthpiece wall 115. Diaphragm 129 serves to seal off apertures 128 and thus prevent dust or moisture from entering the interior of casing 112. However, diaphragm 129 is suificiently flexible so as to permit sound waves to'pass therethrough.

As best seen in Fig. 16, a cylindrical support member, indicated generally at 201, is formed of non-metallic material, preferably plastic, and serves in microphone 111 substantially the same function as the annular means comprising O-ring 36 and annular spacer element 37 of microphone 11. The internal diameter of support member 201 is slightly larger than the external diameter of reduced cylindrical portion 134 of transmitter unit 127 whereby the front end 202 of support member 201 extends around the transmitter portion 134 and slidably receives the latter so as to abut against the shoulder 135.

A pair of rectangular slots 203, 204 extend longitudinally of support member 201 from the opposite end 205 thereof. Slots 203, 204 are disposed diametrically opposite each other and are adapted to receive a switch unit 142 which is substantially similar to switch unit 42 described above with respect to microphone 11. It will be seen that switch unit 142 is of rectangular shape in cross-section and snugly fits within slots 203, 204 so as to abut against the inner surfaces 203', 204 of the latter.

As best seen in Fig. 14, switch unit 142 is of a length greater than the external diameter of cylindrical support member 201 whereby the opposite ends of switch unit 142 project radially outwardly from the latter. A pair of contacts 207, 208 project upwardly from one of the outer ends 209 of switch unit 142 and the opposite end 210 thereof is provided with a projecting contact 211. Soldered to contacts 208, 211 are a pair of electrical wires 213, 214, respectively. A third wire 212 is soldered at one end to contact 207 and at its opposite end to one of the contact terminals (not shown) of transmitter unit 127. A fourth wire 215 is soldered at its inner end to the other contact terminal of transmitter unit 127. As best seen in Fig. 11, wires 212, 214 and 215 are enclosed by a sheath of insulation 216 so as to comprise therewith an electrical cord indicated generally by the reference numeral 179.

The electrical cord 179 extends through a hollow rubber sleeve 176 similar to sleeve 76 described above, and preferably molded of rubber and fixedly secured around cord 179. The sleeve 176 is slightly conical in shape and projects through a circular opening 217 extending radially through the cylindrical wall 113 of casing 112. The inner end of opening 217 communicates with a square recess 218 formed in the interior surface 113 of wall 113.

. The inner end of sleeve 176 is formed integral with an enlarged square head 178 which fits within recess 218 so as to prevent rotation or twisting of sleeve 176 and cord 179 relative to casing 112. The engagement of head 178 with the bottom of recess 218, and also the engagement of sleeve 176 with the interior surface of opening 217 seals off the latter so as to prevent moisture, dust and other atmospheric ingredients from entering into the interior of casing 112.

Referring again to Fig. 16, support. member 201 is further provided with a slot 220 extending from its end 202 for receiving the button shank 234 to be described below. A series .of smaller slots 221, 222 and 223 also extend from the end 202. The intermediate slot 222 receives the inner cylindrical portion 224 projecting from head 178 of sleeve 176 when the various components are in the assembled relation shown in Figs. 13 and 14. Slot 223 receives wires 212, 213 extending therethrough and slot 221 similarly receives wire 214, thereby maintaining wires 212, 213, 214 in properly assembled relation within casing 112.

Microphone 111 is further provided with a circular cover member 145 which is of similar construction to cover member 45 described above and hence the various constructional details of cover member 145 and the means for securing it to the open end of casing 112 will not be described, reference being made to the description of Figs. 1 to inclusive for this aspect of the device so as '6 to avoid repetition. member 145 engages switch unit 142 so as to urge the latter inwardly. Switch 142 in'turn abuts against surfaces 203', 204' of slots 203, 204 so as to urge the opposite end of support member 201 against shoulder of transmitter unit 127 and thereby maintain the latter and diaphragm 129 in assembled relation against mouthpiece wall 115.

It will be seen in Fig. 11 that after removal of cover member 145, switch unit 142 may be removed from slots 203, 204 of support member 201. The latter may then be removed so as to permit the withdrawal of transmitter unit 127 and all of the operative components will then be in the disassembled relation shown in Fig. 11, thereby permitting easy removal and access to the various components for repair or replacement thereof. It will also be seen that sleeve 176 together with cord 216 may be pulled inwardly through opening 217 towards the interior of casing 112 and may then be removed outwardly through the open end of the latter for replacement or repair of cord 216.

As shown in Fig. 13, another cylindrical opening 230 extends through casing wall 113 in a radial direction and is located diametrically opposite opening 217. The interior surface of wall 113 is provided with a radially inwardly projecting boss 231 so as to increase the bearing length of opening 230. The upper end of the latter communicates with an enlarged counterbore 231a extending radially inwardly from the exterior surface of easing wall 113. A cylindrical non-metallic bushing 232 is press-fitted within counterbore 231 and is provided with an outer end projecting outwardly from the exterior surface 113 of wall 113.

A push button indicated generally at 233 comprises a cylindrical shank 234 extending through bushing 232 and also through opening 230 and is reciprocally slidable therein. The lower end of shank 234 engages button 174 of switch unit 142. A circular groove 235 is formed on an intermediate portion of shank 234 and engageably receives an 0-ring 236 which abuts boss 231 so as to' limit the outward movement of push button 233.

Integral with the outer end of shank 234 is an enlarged head portion 237 adapted to be engaged by the finger of the operator in order to depress push button 233 so as to actuate button 174 of switch unit 142. The periphery of head portion 237 is integrally formed with a cylindrical flange 238 extending radially inwardly and adapted to slide over the outwardlyprojecting portion of bushing 232 so as to aid in guiding push button 233 in its reciprocal sliding movement.

An annular sealing element 240 of flexible non-metallic material preferably rubber, surrounds the upper end of a shank 234 and is provided wtih a suitable central aperture receiving the latter. The outer peripheral edge of sealing element 240 is clampingly engaged between the inner end of bushing 232 and the inner surface 231' of counterbore 231, whereas the edge of the central opening of sealing element 240 is fixedly sealed to an upper portion of shank 234. It will thus be seen that sealing element 240 seals off opening 230 so as to prevent dust, moisture and other deleterious atmospheric substances from entering the interior of casing 112.

It is to be understood that the specific embodiment through, a thin flexible non-metallic diaphragm within It will be understood that cover,

answers said casing and lying adjacent the interior surface of said wall and sealing off said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casing having a wall portion with an opening therethroug'h, switch-actuating means :extending through said opening and movable therein for controlling said switch, means sealing said opening for preventing dust and moisture from entering the interior of the .casing therethrough, an end of said casing being open, a non-metallic cover member secured to the casing and sealing off said open end thereof from the atmosphere, comprising a nonmetallic bushing secured in said opening, said switch-actuating means comprising a push button member reciprocally slidable within said bushing and having an inner end engaging the switch and an outer end projecting outwardly of the casing, said -seal ing means comprising a flexible non-metallic sealing element surrounding said button member and having one end in sealed relation to said bushing and the opposite end in sealed relation to said button member, said bushing being provided with an annular groove, the inner end of said button member having a cylindrical shank, said one end of the sealing element being secured within said groove, said opposite end of the sealing element comprising an approximately cylindrical wall and being provided with an annular flange portion spaced radially inwardly from and extending parallel to said cylindrical wall, said flange portion being in sealed engagement with said cylindrical shank of the button memher.

2. A microphone comprising a hollow casing formed of non-metallic material, and one end of said casing having a mouth-piece portion including a wall of said casing, said wall having a plurality of apertures therethrough, a thin flexible non-metallic diaphragm within said casing and lying adjacent the interior surface of said wall and sealing of]? said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casing having a wall portion with an opening therethrough, switch-actuating means extending through said opening and movable therein for controlling said switch, means sealing said opening for preventing dust and moisture from entering the interior of the casing therethrough, an end of said casing being open, and a nonmetallic cover member secured to the casing and sealing off said open ,end thereof from the atmosphere, said casing being provided with a cylindrical hollow interior adjacent said diaphragm, said transmitter unit being located within said cylindrical casing interior coaxial therewith and having a first cylindrical portion adjacent said diaphragm and of a diameter approximately equal to the diameter of said cylindrical interior, said transmitter unit having a second cylindrical portion with a diameter less than said diameter of the cylindrical casing interior, the junction of said cylindrical portions forming a shoulder, annular non-metalic means extending around said second cylindrical portion and having a surface engaging said shoulder and another surface engaging an inner end of said switch, said cover member engaging the outer end of said switch.

3. A microphone comprising a hollow casing formed of non-metallic material, and one end of said casing having a mouthpiece portion including a wall of said casing, said wall having a plurality of apertures therethrough, a thin flexible non-metallic diaphragm within said casing and lying adjacent the interior surface of said wall and sealing off said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casinghaving a wall portion with an opening therethrough,

switch-actuating means extending through said opening and movable therein for controlling said switch, means sealing'said opening for preventing dust and moisture from entering the interior of the casing therethrough, an end of said casingbeing open, a non-metallic cover member secured to the casing and sealing off said open end thereof from the atmosphere, said open end of the casing being of cylindrical configuration, said cover member having a cylindrical portion extending within said cylindrical casing and removable therefrom, and resilient annular sealing means engaging said cylindrical casing end and said cover cylindricalportion, said cover cylindrical por tion being provided on the exterior surface thereof with an annular groove, said annular sealing means lying within said groove and engaging the interior surface of said cylindrical casing open end, said cover cylindrical portion being provided with a second annular groove spaced axially inwardly of the first-recited groove, said annular sealing means comprising a-ring and adapted to be placed in said second annular groove when the cover member is disassembled from the casing and movable into said first-recited groove as said cover cylindrical portion is inserted into said cylindrical casingopen end.

4. The combination of claim 3, the interior surface of said cylindrical easing open end being provided with a radially inwardly projecting abutment means engageable with said ring for moving the latter from said second groove to said firstq-ecited groove as said cover cylindricalportion is inserted into said cylindrical casing open end.

5. A microphone comprising a hollow casing formed of plastic material, one end of said casing having a mouthpiece portion including a wall of said casing, said wall having a plurality of apertures therethrough, a thin flexible non-metallic diaphragm 'within said casing and lying adjacent the interior surface of said wall and sealing off said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casing being provided with a cylindrical hollow interior adjacent said diaphragm, said transmitter unit being located within said cylindrical casing interior and coaxial therewith and having a first cylindrical portion adjacent said diaphragm and of a diameter. approximately equal to the diameter of said cylindrical interior,.said transmitter unit having a second cylindrical portion with a diameter less than said diameter of the cylindrical casing interior, the junction of said cy1indrical portions forming a shoulder, annular non-metallic resilient means extending around said second cylindrical portion and having a surface engaging said shoulder and another surface engaging an inner end of said switch, said cover member engaging the outer end of said switch, said annular means comprising a resilient ring engaging said second cylindrical portion and said shoulder and a resilient annular spacer ring located between and contacting said ring and said inner end of the switch.

6. Amicrophone comprising a hollow casing formed of plastic material and havingan open end, a transmitter unit within said casing, a switch .within said casing and operatively connected to said transmitter unit, a plastic cover member secured to the casing and sealing off said open end thereof from the atmosphere, said casing being providcd with a cylindrical hollow interior adjacent said diaphragm, said transmitter unit being located within said cylindrical casing interior coaxial therewith and having a first cylindrical portion adjacent said diaphragm and of a diameter approximately equal to the diameter of said cylindrical interior, said transmitter unithaving a second cylindrical portion with a diameter. less than said diameter of the cylindrical casing interior, the junction of Said cylindrical portion forming a shoulder, annular nonmetallic resilient means extending aroundsaid second cylindrical portion and having a surface engaging said shoulder and an opposite surface engaging an inner end of said switch, said cover member engagingthe outer end of said switch, said annular means comprising a resilient ring engaging said second cylindrical portion and said shoulder and a resilient annular spacer ring located between and contacting said ring and said inner end of the switch, said switch and said transmitter unit being slidably mounted within the casing for outward movement through the open outer end thereof when the cover member is removed.

7. A microphone comprising a hollow casing formed of plastic material, a transmitter unit within said casing, a switch within said casing and operatively connected to said transmitter unit, an end of said casing being open, and a plastic cover member secured to the casing and sealing ofi said open end thereof from the atmosphere, said open end of the casing being of cylindrical configuration, said cover member having a cylindrical portion extending within said cylindrical casing open end and removable therefrom, and resilient annular sealing means engaging said cylindrical casing open end and said cover cylindrical portion, said cover cylindrical portion being provided on the exterior surface thereof with an annular groove, said annular sealing means lying within said groove and engaging the interior surface of said cylindrical casing open end, said cover cylindrical portion being provided with a second annular groove spaced axially inwardly of the first-recited groove, said annular sealing means comprising a ring and adapted to be placed in said second annular groove when the cover member is disassembled from the casing and movable into said first-recited groove as said cover cylindrical portion is inserted into said cylindrical casing open end.

8. A microphone comprising a hollow casing formed of plastic material, a transmitter unit within said casing, a switch within said casing and operatively connected to said transmitter unit, an end of said casing being open, and a plastic cover member secured to the casing and sealing off said open end thereof from the atmosphere, said open end of the casing being of cylindrical configuration, said cover member having a cylindrical portion extending within said cylindrical casing open end and removable therefrom, and resilient annular sealing means engaging said cylindrical casing open end and said cover cylindrical portion, said cover cylindrical portion being provided on the exterior surface thereof with an annular groove, said annular sealing means lying within said groove and engaging the interior surface of said cylindrical casing open end, said cover cylindrical portion being provided with a second annular groove spaced axially inwardly of the first-recited groove, said annular sealing means comprising a ring and adapted to be placed in said second annular groove when the cover member is disassembled from the casing and movable into said first-recited groove as said cover cylindrical portion is inserted into said cylindrical casing open end, the interior surface of said cylindrical casing open end being provided with a radially inwardly projecting abutment means engageable with said ring for moving the latter from said second groove to said first-recited groove as said cover cylindrical portion is inserted into said cylindrical casing open end.

9. A microphone comprising a hollow casing formed of non-metallic material, and one end of said casing having a mouthpiece portion including a wall of said casing, said wall having a plurality of apertures therethrough, a thin flexible non-metallic diaphragm within said casing and lying adjacent the interior surface of said wall and sealing off said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casing having a wall portion with an opening therethrough, switch-actuating means extending through said opening and movable therein for controlling said switch, means sealing said opening for preventing dust and moisture from entering the interior of the casing therethrough,

an end of said casing being open, and a non-metallic cover member secured to the casing and sealing ofl? said open end thereof from the atmosphere, said housing being provided with a cylindrical hollow interior adjacent said diaphragm, said transmitter unit being located within said cylindrical casing interior coaxial therewith and having a first cylindrical portion adjacent said diaphragm and of a diameter approximately equal to the diameter of said cylindrical interior, said transmitter unit having a second cylindrical portion with a diameter less than said diameter of the cylindrical casing interior, the junction of said cylindrical portions forming a shoulder, annular non-metallic means extending around said second cylindrical portion and having a surface engaging said shoulder and another surface engaging an inner end of said switch, said cover member engaging the outer end of said switch, said annular means comprising a cylindrical support member having the first-recited surface at one end thereof and slots extending from the opposite end thereof for receiving said switch and supportably mounting the latter, said switch projecting outwardly beyond said opposite end of the support member so as to be engaged by said cover member.

10. A microphone comprising a hollow casing formed of non-metallic material, and one end of said casing having a mouthpiece portion including a Wall of said casing, said wall having a plurality of apertures therethrough, a thin flexible non-metallic diaphragm within said casing and lying adjacent the interior surface of said wall and sealing ofi said apertures but permitting sound waves to pass therethrough, a transmitter unit within said casing and adjacent said diaphragm, a switch within said casing and operatively connected to said transmitter unit, said casing having a Wall portion with an opening therethrough, switch-actuating means extending through said opening and movable therein for controlling said switch, means sealing said opening for preventing dust and moisture from entering the interior of the casing therethrough, an end of said casing being open, and a non-metallic cover member secured to the casing and sealing off said open end thereof from the atmosphere, said casing having a wall portion with a second opening therethrough, a resilient non-metallic sleeve extending through said second opening and in sealing engagement therewith, and an electrical cord extending through said sleeve and comprising a plurality of electrical wires connected to said transmitter unit and said switch.

11. A microphone as recited in claim 10 wherein said sleeve is provided with an enlarged non-circular head, said casing having a non-circular recess receiving said head to prevent rotation of the sleeve and cord relative to the casing.

12. A microphone as recited in claim 11 wherein said sleeve and head are integrally formed of rubber and said sleeve is fixedly secured to said electrical cord extending therethrough.

13. In a microphone as recited in claim 9, said casing having a wall portion with a second opening therethrough, a resilient non-metallic sleeve extending through said second opening and in sealing engagement therewith, and an electrical cord extending through said sleeve and comprising a plurality of electrical wires connected to said transmitter unit and said switch, said support member having means engaging the portions of said wires within the casing for maintaining said wire portions in assembled position within the casing.

14. A microphone comprising a hollow casing formed of non-metalic material, said casing having a front apertured wall, and an annular wall extending rearwardly from the periphery of said front wall, and integrally formed therewith, said casing being open at its rear end, said casing being formed with an internal cylindrical recess, a transmitter unit fitted in said recess and adjacent said front wall, means Within said casing formed with a pair of horizontally aligned, rearwardly opening notches, a switch unit in the casing having its ends slidably received in-said notches, a non-metallicback cover removably mounted on the rear open end of the casing and serving to retain the switch unit within said notches, and whereby removal of the back cover will permit sliding of said switch unit as a whole, rearwardly, out of said notches and through said rear open end of the casing, and whereby, Withdrawal of the switch unit will permit, pulling out the transmitter, said annular wall having an opening, a switch actuating button member slidably mounted in said opening and depressable to actuate said switch unit, said casing having a second opening, a sleeve slidably passing through said second opening, a cord attached to said sleeve and comprising wiring operatively connected to said switch unit and transmitter.

15. The combination of claim 14, the means formed with the switch comprising a cylindrical member of unmetallic material having one end slidably received in said cylindrical recess and contacting the back of said transmitter, and said cylindrical member extending to said back cover and being formed with an opening through which the "switch actuating button member passes, and an opening through which said sleeve passes.

'16. The combination of claim 14, said sleeve having a non-circulardead non-rotatably engaged within a noncireular recess in said annular wall of said casing at said bottom opening.

17. The combination of claim 16, means to seal said back cover to said casing, means to seal the opening through which said switch actuating button member passes into said casing, and said sleeve and head, and said sleeve having a forward portion adjacent said head to seal the opening in the casing through which said sleeve passes.

18. The combination of claim 14, in combination with a non-metallic diaphragm fitted in said cylindrical recess and interposed between said transmitter and front wall and covering'the operations in said front wall.

References Cited in the file of this patent UNITED STATES PATENTS Blount May 5, 1936 2,267,364 Blount Dec. 23, 1941

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