US2126566A - Acoustic device - Google Patents

Acoustic device Download PDF

Info

Publication number
US2126566A
US2126566A US759679A US75967934A US2126566A US 2126566 A US2126566 A US 2126566A US 759679 A US759679 A US 759679A US 75967934 A US75967934 A US 75967934A US 2126566 A US2126566 A US 2126566A
Authority
US
United States
Prior art keywords
case
diaphragm
passage
groove
acoustic device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US759679A
Other languages
English (en)
Inventor
Robert N Marshall
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
AT&T Corp
Original Assignee
Bell Telephone Laboratories Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to NL43957D priority Critical patent/NL43957C/xx
Priority to BE412830D priority patent/BE412830A/xx
Priority to NL45821D priority patent/NL45821C/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US759679A priority patent/US2126566A/en
Priority to GB31677/35A priority patent/GB464996A/en
Priority to FR799518D priority patent/FR799518A/fr
Application granted granted Critical
Publication of US2126566A publication Critical patent/US2126566A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/222—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  for microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
    • H04R1/38—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means in which sound waves act upon both sides of a diaphragm and incorporating acoustic phase-shifting means, e.g. pressure-gradient microphone

Definitions

  • I'his invention relates to acoustic devices; and, more particularly, to microphones or transmitters of the moving coil or electrodynamic type.
  • An object of this invention is to improve the structure and operating characteristics of acousl means for enhancing the low frequency response of the device.
  • Still another feature comprises an enclosure or case for an acoustic device in which the case interior is divided into at least two chambers conv nected by a passage that may be open or closed at the will of the user to control the effective volume of the case.
  • an acoustic device comprises a case open at its ends of different sizes, and enclosing a devicecomprislng a diaphragm, moving coil, and magnet structure,
  • the diaphragm being in alignment with and closing the ysmaller end of the case.
  • the larger end of the case is closed by a plate or wall member, supporting the magnet structure and. diaphragm in position, andv containing a passage.
  • a cover member forming part of the case is secured tothe remaining lportion of the case by a plurality of plug pins, each projecting at one end from the 'l cover and threadably engaging the wall member at the other end.
  • the cover and wall members comprise another air chamber in which is positioned an elongated, open-ended tubular member, one open end of which is secured to the cover and in alignment. with an. apertured portion, thereof.
  • the tubular member may replaced by an elongated groove in the case, either on the inner or outer surface thereof, a closure member overlying vthe groove, the closure member and case containing passages connecting the interior of the case and' the atmosphere through the :30V groove.
  • the closure member may be adjustable in position to vary the effective length of the i groove.
  • the passage connecting the chambers in the case may be covered with anacoustic resistance material, means being provided to vary the 'I 55 effective area thereof,
  • Fig. 1 is an enlarged cross-sectional view of anx 5 acoustic device constructed in accordance with this invention
  • Fig. 2 is a cross-sectional view of the device of Fig. 1, taken along the line 2-2 thereof;
  • Fig. 3 is-an end view of the device of Fig. 1, 10 taken along the line 6-3 thereof;
  • Fig. 4 is a view of the cover orclosure member of the device of Fig. 1, taken along the line 4--6 thereof:
  • Fig. 5 is a sideelevation, substantially actual 15 size, of the device of Figs. 1-4, a jack or connector being shown associated with it;
  • Y Fig. 6 is an enlarged cross-sectional view of another acoustic device constructed in accordance with this invention; 20
  • Fig. 'l is an end view of the device of Fig. 6, taken along the line 1-1 thereof with the cover or closure member removed, and partially broken away to show the cord; Y
  • Fig. 8 is a cross-sectional view, apprczdmately 25 actual size, of the device of Fig. 6, taken along the line 6-6 thereof;
  • Fig. 9 is an enlarged, cross-sectional view of still another acoustic device constructed in accordance with this invention.
  • Fig. 10 is a cross-sectional view, approximately actual size, of the device of Fig. 9,y taken along the line IO-ll thereof; f A
  • Fig. 11 is a front viewsubstantially actual size, of another acoustic device in accordance with 35 this invention. i A
  • Fig. 12 is a side elevational view of the device of Fig. 11;
  • Fig. 13 is an enlarged, cross-sectional view of me device of ng. 11,1:axen along me une n n 40 thereof, and with the front screen and associated frame removed; y
  • Fig. 14 is'a cross-sectional view of the device of Figs. 11 l3, taken 'along the line II-Il of Fig. 13;
  • Fig. v15 is a plan view of afragment of the device of Fig. 11.
  • the acoustic device of l'lgs.' 1-5 comprises an electrodynamic microphone or transmitter, designated generally, Il. -It comprises a hollow housing, container, enclosure or case Il, of insulating material, for instance, phenol linen, inwardly curved'to present a substantially hemispherieal outer surface at its front end 22, which contains acircularopening inwhichanaperturcdplate 5';
  • ls mounted in one chamber 2i, and comprises a Ushaped permanent magnet 32, preferably of cobalt steel or cobait-molybdenum steel; an outer pole member 3l, preferably of magnetic iron; an inner or central and substantially cylindrical pole member 24. preferably of cobalt steel or cobalt-molybdenum steel; and a dome-shaped or cap member l5, preferably of magnetic iron.
  • the outer pole has an annular, central portion 28, and a pair of radially outwardly, downwardly projecting extensions 21, Il, one extension 31 containing a circular passage II, and the other a slot Il ex tending inwardly from its periphery, the passage Y and slot receiving pin members 4
  • Pole member 24 has a central passage '4I for a clamping member or bolt Il, the central pole and the cap member being fastened to the central and straight portion 45 of the permanent magnet by this bolt, the threaded end I6 of which is engaged by a pair of nuts l1.
  • '111e diaphragm 4I is of any suitable material, for instance, a light-weight, high-strength material, such as duralumin. It comprises a centrally stiiiened, dome-shaped portion 49; an outer, annular peripheral portion Si; and an-in termediate, flexible, tangentially'corrugated portion Il.
  • the annular portion is secured to the annular ridge or flange $2 of the outer pole, preferably by cement, and such that the coil 53, which may be of edge-wound, insulated, aluminum ribbon or tape and secured to the diaphragm at the junction Il of the portions 49 and 5
  • the coil leads (not shown) are connected to terminal members (not shown) carried by arcuate-shaped terminal strips Il of insulating material, that are fastened to the inner surface 5l of the pole member 23.
  • Acoustic damping means is positioned under the air-gap and comprises an annulus 58 of damping cloth, preferably silk. It is supported by a plate or ring member l! of non-magnetic material, for instance, brass, containing a pluralityof elongated passages 8
  • the ring 59 is maintained in position by a resilient sleeve or ring Il, preferably of soft rubber, that encircles the central pole and is carried by the ring member Il supported on the shoulder or ledge I2, and ls spaced from the under surface il of the outer pole by a resilient washer or ring Il, preferably of soft rubber.
  • the diaphragm end of the unit ll closes the case opening 23, a resilient washer il, for instance, rubber, being interposed between the outer portion of the diaphragm and the radially extending nange portion to provide an air proof seal.
  • the partition member 21 is of insulating material and contains a frusta-conical shaped opening or passage 01 connecting the chambers 2l, 2i,
  • the smaller end opening into chamber 2B It has embedded in it a pair of internally threaded bushings 8l, and a cup-shaped member 69, each of which may be of brass.
  • the cup member contains a helical spring 10, for instance, of phosphor bronze.
  • the clamping nuts 41 bear against the spring 10, which with the partition member in place, is under compression, whereby the unit 3
  • the bushings 62 are electrically connected by suitable conductors (not shown) with the coil lead terminals on the members 5B.
  • the second chamber 26 is defined by the partition member and a removable portion or cover 1
  • This cover supports on its inner surface, an elongated, coiled tubular member 72, open at each end, and one end 'i3 of which is secured to the cover by a clamping plate 14, screws 92 and gasket l5, in line with the multiaperture portion l! thereof.
  • This tubular member is provided in accordance with the teachings of A. L. Thuras Patent 1,869,178, issued July 26, 1932, and in a device constructed in Vaccordance with Figs, 1-5 was approximately six inches long and one-eighth inch in inner diameter.
  • the cover contains an elongated slot or recess l1 adapted to receives jack 'i8 for engagement with three pins or contacts 19 which are supported by the case and project into the slot.
  • the pins have threaded extremities all, which thread into the bushings and cup member to secure the cover to the remaining portion of the case.
  • a suitable sealing compound Il for instance, sealing wax.
  • the chambers 25, 26 and the passage El permit wave propagation from the rear of the diaphragm when the microphone is being used.
  • the tubular member of course, causes the response of the microphone to be enhanced in the region of the low sound wave frequencies.
  • a screen comprising a double layer 85 of cloth, preferably, silk. It is mounted between a pair of protective brass screens I6, within a channeled ring l1, together with a ring member Il having three equally spaced projecting portional! having rivets Sl at their extremities for engagement with three equally spaced recesses S2 in the case.
  • I'his screen is provided in accordance with the teachings of the pending application of F. F. Romanow, Serial No. 729,759, filed June 9, 1934, Patent No. 2,106,813, issued Feb. 1, 1938, to render the open field response characteristic of the microphone substantially uniform regardless of the microphones position with reference to the sound wave source.
  • the acoustic device of Figs. 6, 7 and 8 comprises an electrodynamic microphone or transmitter, designated generally,
  • the casev is curved at one end
  • 03 is substantially the same as the unit like parts bearing like identifying numerals.
  • 00 are secured together by a screw
  • 0 is interposed between the magnet and partition member.
  • the unit is maintained in position by the partition member, which, in turn, is held in place by a lock or clamping rin'g
  • the case contains a circumferentially arranged groove, channel or receas
  • 1 contains an opening or aperture
  • are circular and of approximately the same area as the crosssectional area of the channel or groove
  • 1 is rotatable such that the position of the aperture
  • the low fre vquencyresponse may be varied at will.
  • 20 is provided for closing the passage
  • 02 is connected at one end to the pad end of the member
  • 20 is engaged by one end of a link
  • ' are electrically connected by suitable conductors (not shown) with the terminal members on the insulators 55.
  • the devices of Figs. 6, '1 and 8 and Figs. 9 and are substantially alike, like parts bearing likereference numerals, that of Figs. 9 and 10, however, embodying a different arrangement of the low sound wave frequencies enhancing means.
  • contains a groove, channel or recess
  • 'I'he case contains an aperture or passage
  • 55 are preferably circular and of approximately the same area as lthe cross-sectional area of the groove.
  • the case outer surface contains a groove
  • 12 prevents the closure n-iem-v ff ber from shifting toward the front of the transmitter.
  • the closure member contains an aperture 20
  • one edge is provided with spaced notches
  • This rod extends -through a passage
  • 15 is pushed rearwardly to move the end of th'e rod out of the notch against the restoring action of the spring.
  • Theclosure member is then turned to the desired degree, the pressure on'the member
  • the partition member contains a plurality of 75 spaced passages
  • of damping material, for instance, silk, is secured to one surface
  • the opening 28 is closed by a multi-apertured plate or grid I 85 which fills the cavity in front of the diaphragmand increases the normal range of the electrodynamic unit at high frequencies by preventing resonance by the air in the opening 28 until, for example, about 12,00015,000 cycles per second, or by leaving unaffected the normal reso nant effect of the air of the opening, but adding another resonance at a higher frequency.
  • a multi-apertured plate or grid I 85 which fills the cavity in front of the diaphragmand increases the normal range of the electrodynamic unit at high frequencies by preventing resonance by the air in the opening 28 until, for example, about 12,00015,000 cycles per second, or by leaving unaffected the normal reso nant effect of the air of the opening, but adding another resonance at a higher frequency.
  • 88 Supported on the case
  • 80 is integral with a plurality of spaced supporting arms
  • 88 projects from the case, specifically, from the closure member
  • An acoustic device comprising a case having anopen end, a sound wave translating unit in said case and including a diaphragm and a magnet, said diaphragm closing said open end, means in said case between said magnet and the other end of said case dividing it into two chambers and bearing against said magnet to hold it in position so that the diaphragm closes said case open end, said means containing a restricted. small area passage connecting said chambers, and means constituting a restricted sound wave passage for enhancing the low frequency response of the de# A slide
  • An acoustic device comprising a case having an open end, a diaphragm in said case and closing said open end, and means supported by said case and defining with the case a variable length,
  • a n acoustic device comprising a case having Van open end, a diaphragm in said case and closing said open end, said case having an elongated groove in one surface, and a closure member over said groove, said member and said case containing passages for connecting the interior of the oase and the atmosphere through said groove.
  • An acoustic device comprising a hollow enclosure having an open end, a diaphragm closing said open end, said enclosure having a groove in one surface, and a closure member over said groove, said member and enclosure containing passages of substantially the same area as the cross-sectional area of the groove for connecting the interior of the enclosure and the atmosphere through said groove.
  • An acoustic device comprising a hollow enclosure having an open end, and a diaphragm closing said open end, said enclosure comprising a wall containing an elongated, restricted sound wave passage and having an aperture connecting the passage with the atmosphere outside the enclosure and another aperture connecting the passage with the interior of the enclosure on the inner side of the diaphragm.
  • An acoustic device comprising a hollow enclosure having an open end, a diaphragm closing said open end, said enclosure comprising a wall containing an elongated, restricted sound wave passage and having an aperture connecting the passage with the atmosphere outside of the enclosure and another aperture connecting the passage with the interior of the enclosure on the inner side of the diaphragm, a partition member in said ⁇ enclosure dividing it into two chambers with one of which said passage connects, said partition ⁇ member containing a passage connecting said chambers, and means for closing said last-mentioned passage.
  • An acoustic device comprising a hollow case having an open end, an electrodynamic unit in said case and including a diaphragm closing said open end but exposed to sound waves therethrough, means for varying the effective volume of the case on the rear side of the diaphragm, means for varying at will the response of the device at the lower end of the audio frequency range, and means to vary at will the response of the device at the upper end of the audio frequency range.
  • An acoustic device comprising a hollow case having an open end, a sound translating unit in said case and including a diaphragm closing said open end and being exposed therethrough to sound waves on one side, said case having a groove in its outer surface connected through an aperture in the case with the interior of the case on the other side of the diaphragm, and a closure member on said case and disposed over said groove, said member having an aperture therein connecting the groove with the atmosphere outside the case and being slidable relative to the case to vary the distance between the two apertures.
  • An acoustic device comprising a hollow case having an open end, a sound translating unit in said case and including a diaphragm closing said open end and being exposed therethrough to sound waves on one side, said case having a groove in its outer surface connected through an aperture in the case with the interior of the case on the other side of the diaphragm, and a closure member on said case and disposed over said groove, said member having an aperture therein connecting the groove with the atmosphere outside the case and being slidable relative tothe case to vary the distance between the two apertures, and means to hold said closure member against movement after adjustment of the closure member for the desired spacing of the aperture.
  • An acoustic device comprising a hollow case having open ends, a diaphragm within the case in alignment with and closing one of said open ends, a coil attached to said diaphragm, magnet structure for said coil, said case including a cover member for its other end and supporting an elongated open ended tubular member in the case, one open end of the tubular member being in alignment with an apertured portion of the cover, and a single wall member in said case dividing it into two chambers and supporting the magnet structure, diaphragm and coil in one chamber, said wall member having a restricted aperture dening a passage connecting said chambers.
  • An acoustic device comprising a hollow case having an open end, a sound wave translating unit in said case and including a diaphragm, a disc partition member slidably insertable in said case and dividing it intotwo chambers and having its central portion only bearing against said unit to hold the latter in position so that the diaphragm closes the case open end, means engaging the interior surface of said case and bearing against the peripheral portion of said partition member to maintain the latter in position, said partition member containing a small area, off-center passage connecting said chambers, and means independent of said partition member constituting a restricted sound wave passage for enhancing the low frequency response of the device, connecting one of said chambers with the atmosphere outside of the case.
  • An acoustic device comprising a case having open ends, a diaphragm within the case closing one open end, a coil attached to said diaphragm, a magnet structure for said coil, said case including a cover member for its other end and supporting an elongated open ended tubular member in the case, one open end of the tubular member being in alignment with an apertured portion of the cover, and a wall member in said case dividing it into two chambers connected by a passage in the wall member, one of said chambers containing the diaphragm, coil and magnet structure and the other chamber containing said tubular member.
  • Anacoustic device comprising a hollow case having a substantially hemispherical section having an apertured Wall portion extending across its region of greatest diameter, and containing a sound wave passing opening in its curved surface portion, a diaphragm closing said opening, a cover member dening an air chamber with said wall portion, said member containing a passage ,connecting the chamber with the air outside the case, and a tubular member between said wall portion and cover member constituting a continuation oi the passage.
  • An acoustic device comprising a casing having openings at its front and back ends, a transmitter including a diaphragm and a magnet disposed within said casing, said diaphragm being positioned adjacent the front end of said casing, an apertured partition within said casing between said magnet and the back end of the casing, and a tubular member entirely within ⁇ the chamber nearest the back end of the casing and cooperating with an opening in the rear of the casing to acoustically connect they open air with the back side of the diaphragm solely via the apertured partition.
  • An acoustic device comprising a casing having an opening at its front and back ends, an apertured partition within said casing, dividing the interior into two chambers, a transmitter unit disposed in the chamber adjacent the front end of the casing, a tubular sound passageway member disposed in the chamber adjacent the back end of the casing and supported thereon, and means on said partition for holding said unit in place.

Landscapes

  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
US759679A 1934-12-29 1934-12-29 Acoustic device Expired - Lifetime US2126566A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
NL43957D NL43957C (enrdf_load_stackoverflow) 1934-12-29
BE412830D BE412830A (enrdf_load_stackoverflow) 1934-12-29
NL45821D NL45821C (enrdf_load_stackoverflow) 1934-12-29
US759679A US2126566A (en) 1934-12-29 1934-12-29 Acoustic device
GB31677/35A GB464996A (en) 1934-12-29 1935-11-15 Improvements in or relating to sound translating devices
FR799518D FR799518A (fr) 1934-12-29 1935-12-14 Perfectionnements aux dispositifs acoustiques ou analogues

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US759679A US2126566A (en) 1934-12-29 1934-12-29 Acoustic device

Publications (1)

Publication Number Publication Date
US2126566A true US2126566A (en) 1938-08-09

Family

ID=25056553

Family Applications (1)

Application Number Title Priority Date Filing Date
US759679A Expired - Lifetime US2126566A (en) 1934-12-29 1934-12-29 Acoustic device

Country Status (5)

Country Link
US (1) US2126566A (enrdf_load_stackoverflow)
BE (1) BE412830A (enrdf_load_stackoverflow)
FR (1) FR799518A (enrdf_load_stackoverflow)
GB (1) GB464996A (enrdf_load_stackoverflow)
NL (2) NL45821C (enrdf_load_stackoverflow)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2490227A (en) * 1941-12-04 1949-12-06 Reslosound Ltd Electrodynamic loud-speaker
US2515031A (en) * 1948-03-31 1950-07-11 Bell Telephone Labor Inc Microphone having controllable directional response pattern
US2702318A (en) * 1951-01-10 1955-02-15 Astatic Corp Unidirectional microphone
US2848561A (en) * 1953-06-02 1958-08-19 Akg Akustische Kino Geraete Dynamic microphone
US3342285A (en) * 1966-12-19 1967-09-19 Standard Systems Comm Corp Combination pillow speaker and control unit
EP0188017A1 (en) * 1984-12-19 1986-07-23 Philips Electronics Uk Limited Electroacoustic calling device

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2490227A (en) * 1941-12-04 1949-12-06 Reslosound Ltd Electrodynamic loud-speaker
US2515031A (en) * 1948-03-31 1950-07-11 Bell Telephone Labor Inc Microphone having controllable directional response pattern
US2702318A (en) * 1951-01-10 1955-02-15 Astatic Corp Unidirectional microphone
US2848561A (en) * 1953-06-02 1958-08-19 Akg Akustische Kino Geraete Dynamic microphone
US3342285A (en) * 1966-12-19 1967-09-19 Standard Systems Comm Corp Combination pillow speaker and control unit
EP0188017A1 (en) * 1984-12-19 1986-07-23 Philips Electronics Uk Limited Electroacoustic calling device

Also Published As

Publication number Publication date
FR799518A (fr) 1936-06-15
BE412830A (enrdf_load_stackoverflow)
NL43957C (enrdf_load_stackoverflow)
GB464996A (en) 1937-04-29
NL45821C (enrdf_load_stackoverflow)

Similar Documents

Publication Publication Date Title
US2037187A (en) Sound translating device
US4258235A (en) Pressure gradient electret microphone
US3095484A (en) Unidirectional microphone
US2126566A (en) Acoustic device
US2401328A (en) Sound translating device
US3053339A (en) Pipe microphone
US2515031A (en) Microphone having controllable directional response pattern
US2058555A (en) Acoustic device
US2702318A (en) Unidirectional microphone
US2042822A (en) Telephone transmitter
US1847702A (en) Sound translating device
US2852620A (en) Adjustable condenser microphone
US3115207A (en) Unidirectional microphone
US2873812A (en) High frequency loudspeaker structure
US1766473A (en) Electrodynamic device
US2400281A (en) Electromechanical signal translating apparatus
US2340777A (en) Throat microphone
US3141070A (en) Electrodynamic microphone
US2260727A (en) Contact microphone
US3061690A (en) Acoustically compensated microphone with adjustable acoustic resistance
US2688373A (en) Sound translating apparatus
US2358099A (en) Tone control for transmitters
US1685766A (en) Support for vacuum tubes
US1954966A (en) Sound translating device
US3482062A (en) Damped electro-acoustic high frequency transducer