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US3031538A - Small-size condenser microphone - Google Patents

Small-size condenser microphone Download PDF

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Publication number
US3031538A
US3031538A US725956A US72595658A US3031538A US 3031538 A US3031538 A US 3031538A US 725956 A US725956 A US 725956A US 72595658 A US72595658 A US 72595658A US 3031538 A US3031538 A US 3031538A
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United States
Prior art keywords
diaphragm
microphone
sound
sleeve
annular
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Expired - Lifetime
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US725956A
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English (en)
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Gorike Rudolf
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—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
    • H04R1/32—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

  • the pressure and pressure gradient components In order to obtain in a unidirectional condenser microphone a suflicient insensitivity to a sound incidence at 180, the pressure and pressure gradient components must be equal in amount and opposed in phase.
  • the sensitivity of the microphone for a constant thickness of the diaphragm is independent of the diameter of the diaphragm as long as the detrimental capacitance is negligible and the working resistance is sufficiently high. For instance, if the diameter of the diaphragm is reduced to one-half, the mass of the diaphragm Will be one-fourth and, for the same resonant frequency, the restoring force will also be one-fourth. Owing to the reduction of the diaphragm area to one-fourth the driving force will also be one-fourth so that the elongation of the diaphragm will be equal and with it the ratio between the change in capacitance and the capacity at rest.
  • the sensitivity varies in direct proportion with the diameter because the driving force depends on the length of the sound path from the front face to the rear face of the diaphragm.
  • the German patent specification No. 924,325 describes a microphone having such action and comprising a diaphragm carrier and a counterelectrode which is separated by an ,air, gap from the diaphragm carrier and behind which an air chamber is preferably provided, the air gap communicating with the outside air through one or more acoustically ineffective openings.
  • the length of the sound path from the front face to the rear face of the diaphragm, which determines the pressure gradient, corresponds only to the diameter of the diaphragm.
  • a reduction of the diaphragm diameter for example, to 1.8 cm., results in a decrease in sensitivity for sound incidence at 0 and 180 that is suificient only in the medium frequency range.
  • the present invention adopts another measure for in: creasing the pressure gradient in condenser microphones without an appreciable increase in the diameter of the microphone. Tests have shown that, the pressure gradient will be increased if the surface of the detour disc is folded rearwardly about the line Where the disc is fixed and a narrow annular air gap is defined between the hollow cylinder formed by the disc and the peripheral surface of the microphone. The width of this air gap must be such that the friction is adequate to prevent the formation of standing waves, on the one hand, and that it provides optimum conditions for the passage of sound, on the other hand.
  • a condenser microphone having a preferential response in one direction comprises a diaphragm having front and rear faces, which are both exposed to the sound field of the microphone, amicrophone body assembled with and extending rearwardly of said diaphragm, and a hollow structure surrounding said microphone body and defining with the periphery of the latter a narrow annular passage having a length which is approximately equal to the diam eter of said diaphragm and which exposes the rear face of said'diaphragm to said sound field.
  • FIGS. 1 and 2 are frequency response curves for known condenser microphones having diaphragms of different diameters
  • FIG. 3 is a-vertical, longitudinal sectional view of a condenser microphone embodying the present invention
  • FIG. 4 is a transverse sectional view taken along the line IV-IV of FIG. 3;
  • FIGS. 5 and 6 are views similar to that of FIG. 3, but showing two additional embodiments of the invention.
  • FIGS. 7 and 8 are frequency response curves for microphones of the kind shown in FIG. 6.
  • FIG. 9 is a view similar to that of FIG. 6, but showing a detail modification of that embodiment of the invention.
  • FIG. 1 the'frequency response curves for a known condenser microphone having a diaphragm diameter of 3.2 cm. show a decrease in sensitivity of at least 12 decibels between a sound incidence of 0 and a microphone While permitting reduction of the dimension of the latter, the embodiment of the invention illustrated in FIGS. 3 and 4 has the rim of the diaphragm 1 affixed, e.g., with adhesive, to the end face of a metal sleeve 2.
  • the electrode 3 is closely spaced from the diaphragm 1 and may consist, e.g., of a plate formed with bores.
  • electrode 3 is held in a sleeve 4 of insulating material inserted in the metal sleeve 2, with the sleeves 2 and 4 forming a hollow structure.
  • a microphone body formed by a cylinder 5 of insulating material is supported in the sleeve 4 by means of spacing arms or radial webs 6 (FIG. 4) to define a narrow annular gap 7, which is interrupted only by the Webs 6 extending parallel to the axis of the cylinder.
  • the sound waves which enter from the rear into the gap 7 can freely reach the air chamber 9 defined between electrode 3 and microphone body 5 and can pass from chamber 9 through the bores in the electrode 3 to the rear face of the diaphragm.
  • annular gap 7, rather than being defined between microphone body 5 and sleeve 4, may alternatively be defined between the outside cylindrical surface of the sleeve 4 and the inside cylindrical surface of the metal sleeve 2.
  • the diaphragm 10 is aflixed to the front end edge of the metal sleeve 11.
  • the electrode 12 defining an internal cavity 13 is held by a bolt 14 and a nut 15 to the insulating plate 16, which may consist, e.g., of quartz.
  • a cylindrical annular clearance 23 forming a radial inner portion of an annular passage is defined between the outside peripheral surface of the electrode 12 and the inside peripheral surface of the sleeve 11.
  • the quartz plate 16 is secured in the sleeve 11 by means of an annular nut 17 engaging internal threads formed in that sleeve.
  • a hollow structure in the form of a sleeve 18 has an internal annular bead 19, which fits over the sleeve 11 so that an annular gap 20 forming the radially outer portion of an annular passage is formed between the outside surface of the sleeve 11 and the inside surface of the sleeve 18.
  • the sleeve 11 is provided behind the annular head 19 of sleeve 18 with regularly peripherally spaced radial openings 21 which establish communication between the clearance 23 and gap 20 forming the radially inner and outer portions of the annular passage. Sound entering the back end 22 of the narrow annular gap 20 passes along the latter and through the radial openings 21 to the annular clearance 23, and then along the latter to reach the rear face of the diaphragm at 24.
  • the narrow air gap between the diaphragm 10 and the electrode 12 serves as an acoustic frictional resistance.
  • the electrode 12, plate 16 and that portion of sleeve 11 which extends behind electrode 12 form a microphone body, while that portion of sleeve 11 which surrounds the electrode 12 forms a partition between gap 20 and clearance 23.
  • FIG. 6 comprises the same elements as the microphone of FIG. 5 and additional means for connecting the cavity 25 behind the electrode through an acoustic frictional resistance to the outside air at the rear of the microphone.
  • a disc 26 having holes 27 is formed with a forward annular extension 28 screwed into the electrode 30.
  • a disc 31 is disposed in back of disc 26 and has a rearwardly directed screw-threaded sleeve 32 in threaded engagement with the holder 33 for the electrode 30 and an air gap 34 acting as an acoustic frictional resistance is defined between the disc 26 and the disc 31. Sound waves entering from the rear through the opening 35 of sleeve 32.
  • the damping effected by the viscosity influences the velocity of the sound wave.
  • the dimensions of the annular passage for the sound may be selected to provide such an effect that, in the case of sound coming from the rear, the wave which travels around the diaphragm and reaches the front face of the microphone is approximately equal in amplitude and opposed in phase to the wave which passes through the annular passage to the rear side of the diaphragm.
  • the narrow passage for the sound has the additional advantage that standing waves (pipe resonances) are avoided by an adequate friction on the Walls of the sound passage. 7
  • the length of the sound passage is preferably selected to correspond approximately to half the wavelength of the lowest frequency at which the diaphragm has a directional effect. This corresponds to a length which is approximately equal to the diameter of the diaphragm.
  • the internal width of the annular sound passage of a practical embodiment was 0.3 mm. and good results were obtained when the width was varied between 0.5 mm. and 0.1 mm.
  • a microphone constructed according to FIG. 6 has the frequency response curves shown in FIG. 7 for a sound incidence at 0 and respectively.
  • FIG. 8 shows such frequency response curve for a small microphone according to FIG. 6, with existing irregularities.
  • An increase of about 2 decibels is observed at a frequency in the range between 4000 cycles and 10,000 cycles, and a drop of about 3 decibels occurs at a frequency adjacent that of increase.
  • the sleeve which defines the annular passage is formed according to the invention with one or more small radial openings, so that the sound waves may enter the annular passage at the back end and also through these radial openings and the length of the sound path between the front and rear faces of the diaphragm is varied so that the pressure gradient as a driving force is equalized.
  • the sleeve 18 which defines the outer wall surface of the annular gap 20 opening at the back end, as at 22, is formed with radial openings 36.
  • the equalizing effect of these openings is influenced by their number, form, size and arrangement, and the optimum effect can be empirically determined.
  • a condenser microphone having a preferential response in one direction and comprising a diaphragm having a front face directly exposed to the sound field and a rear face, a microphone body extending rearwardly of said diaphragm, a hollow structure surrounding said microphone body and having a front face secured to the periphery of said diaphragm, a perforated electrode spaced behind said diaphragm and rigidly connected to said hollow structure, and means radially spacing said hollow structure from said microphone body to define an annular passage therebetween, said rear face of the diaphragm being exposed to the sound field by way of said annular passage, said annular passage having a length which is approximately equal to the diameter of said diaphragm, and the radial thickness of said annular passage being between 0.1 mm. and 0.5 mm.
  • a condenser microphone having a preferential response in one direction and comprising a diaphragm having a front face directly exposed to the sound field and a rear face, a microphone body extending rearwardly of said diaphragm, a hollow structure surrounding said microphone body and having a front end face secured to the periphery of said diaphragm, a perforated electrode spaced behind the diaphragm and rigidly connected to said hollow structure, and spacing means radially spacing said hollow structure from said microphone body to define an annular passage therebetween, said annular passage having a length which is approximately equal to the diameter of said diaphragm, said rear face of the diaphragm being exposed to the sound field by way of said annular passage, said spacing means including a tubular partition extending between said microphone body and hollow structure and dividing said annular passage into radially inner and outer portions, said tubular partition having radial openings establishing communication between said radially inner and outer portions of the annular passage,
  • said radially inner portion being open at its front end to said rear face of the diaphragm and closed at its rear end, said radially outer portion being longer than said radially inner portion and being closed at its front end and open at its rear end to the sound field.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US725956A 1957-04-13 1958-04-02 Small-size condenser microphone Expired - Lifetime US3031538A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT836959X 1957-04-13

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US3031538A true US3031538A (en) 1962-04-24

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US725956A Expired - Lifetime US3031538A (en) 1957-04-13 1958-04-02 Small-size condenser microphone

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US (1) US3031538A (de)
DE (1) DE1082298B (de)
GB (1) GB836959A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3261915A (en) * 1961-05-17 1966-07-19 Akg Akustische Kino Geraete Directional sound transmitter
US4258235A (en) * 1978-11-03 1981-03-24 Electro-Voice, Incorporated Pressure gradient electret microphone
US20050190944A1 (en) * 2004-02-25 2005-09-01 Kabushiki Kaisha Audio-Technica Unidirectional condenser microphone unit

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1148118A (en) * 1965-12-10 1969-04-10 Tesla Np Condenser microphone

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB420390A (en) * 1932-07-16 1934-11-30 Neumann Georg Microphone
US2297211A (en) * 1938-07-25 1942-09-29 Gerlach Erwin Condenser microphone
US2445821A (en) * 1944-03-29 1948-07-27 Noble E Brewer Condenser microphone
FR1084139A (fr) * 1952-10-06 1955-01-17 Microphone à condensateur pour réception directionnelle
FR1088157A (fr) * 1953-02-03 1955-03-03 Perfectionnements apportés aux microphones électrostatiques
US2787671A (en) * 1952-10-06 1957-04-02 Schall Technik Dr Ing Karl Sch Microphone arrangement
US2832620A (en) * 1955-01-28 1958-04-29 Orlow Stephen De Latch structure for vehicle rear deck

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE884516C (de) * 1940-12-09 1953-07-27 Siemens Ag Elektrostatisches Mikrophon
GB571870A (en) * 1943-12-10 1945-09-12 Otto Kurt Kolb Improvements relating to unidirectional microphones

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB420390A (en) * 1932-07-16 1934-11-30 Neumann Georg Microphone
US2297211A (en) * 1938-07-25 1942-09-29 Gerlach Erwin Condenser microphone
US2445821A (en) * 1944-03-29 1948-07-27 Noble E Brewer Condenser microphone
FR1084139A (fr) * 1952-10-06 1955-01-17 Microphone à condensateur pour réception directionnelle
US2787671A (en) * 1952-10-06 1957-04-02 Schall Technik Dr Ing Karl Sch Microphone arrangement
FR1088157A (fr) * 1953-02-03 1955-03-03 Perfectionnements apportés aux microphones électrostatiques
US2832620A (en) * 1955-01-28 1958-04-29 Orlow Stephen De Latch structure for vehicle rear deck

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3261915A (en) * 1961-05-17 1966-07-19 Akg Akustische Kino Geraete Directional sound transmitter
US4258235A (en) * 1978-11-03 1981-03-24 Electro-Voice, Incorporated Pressure gradient electret microphone
US20050190944A1 (en) * 2004-02-25 2005-09-01 Kabushiki Kaisha Audio-Technica Unidirectional condenser microphone unit

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Publication number Publication date
DE1082298B (de) 1960-05-25
GB836959A (en) 1960-06-09

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