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US3082298A - Frequency independent directional condenser microphone - Google Patents

Frequency independent directional condenser microphone Download PDF

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Publication number
US3082298A
US3082298A US10718A US1071860A US3082298A US 3082298 A US3082298 A US 3082298A US 10718 A US10718 A US 10718A US 1071860 A US1071860 A US 1071860A US 3082298 A US3082298 A US 3082298A
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US
United States
Prior art keywords
diaphragm
microphone
directional
frequency
sound
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
US10718A
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English (en)
Inventor
Gorike Rudolf
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.)
AKG Acoustics GmbH
Original Assignee
AKG Akustische und Kino Geraete GmbH
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Filing date
Publication date
Application filed by AKG Akustische und Kino Geraete GmbH filed Critical AKG Akustische und Kino Geraete GmbH
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Publication of US3082298A publication Critical patent/US3082298A/en
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Expired - Lifetime legal-status Critical Current

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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
    • 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
    • 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

Definitions

  • condenser microphones which have a diaphragm area of about 40 square centimeters and a capacity of up to about 1000 picofarads.
  • these microphones designed as pressure transmitters do not have a frequency-independent directional pattern. Owing to their high self-capacitance they may be arranged at a distance from the amplifier and may be connected to the latter by a long cable (up to meters and more).
  • the invention relates to a directional condenser microphone which has a frequencyindependent directional pattern as well as a high selfcapacitance and which for this reason is particularly suitable for use with portable tape recorders because, as in the case of a dynamic microphone, it may be connected to the recording apparatus by a long cable whereas, compared with the dynamic microphone, it has the advantage that sound phenomena taking place at high speed (transients) are transduced more accurately.
  • the directional condenser microphone according to the invention belongs to the type in which the diaphragm is exposed to the sound field on both sides and at least one phase shifting member is provided to provide for directional effect.
  • the microphone according to the invention is characterized in that the diaphragm has an area of at least 10 square centimeters and that the maximum dimension of the diaphragm, that is, the largest side of the diaphragm, in the case of a rectangular diaphragm, or the diameter of the diaphragm, in the case of a circular diaphragm, is much larger than the wavelength of the highest frequency of the transmitted range and that the upper limiting frequency of the phaseshifting element approximates the frequency at which the pressure gradient reaches its highest value.
  • frictional acoustic resistance is provided between the diaphragm and electrode either alone or in combination with frictional acoustic resistance disposed directly on the rear of the cathode.
  • FIG. 1 shows the directional pattern of a condenser microphone which is designed as a pressure transmitter and has a large diaphragm in accordance with the prior art
  • FIG. 2 shows frequency response curves of the conventional condenser microphone for various angles of sound incidence
  • FIG. 3 is an exploded view showing an illustrative embodiment of the invention having a unidirectional pattern
  • FIG. 4 shows the microphone formed from the parts of FIG. 3 in assembled condition
  • FIG. 5 shows an illustrative embodiment of the present invention having two diaphragms
  • FIG. 6 shows a microphone according to the invention having a bidirectional pattern
  • FIG. 7 shows a microphone according to the invention having a prearranged diaphragm for protection against moisture
  • FIG. 8 shows a microphone embodying the inventionwhich can be changed over from a unidirectional pattern to an omnidirectional pattern
  • FIG. 9' shows a microphone according to the invention for stereophonic recording
  • FIG. 10 shows the directional pattern of the microphone illustrated by FIG. 9,
  • FIG. 11 shows a modification of the microphone shown in FIG. 9,
  • FIG. 12 shows the directional pattern of the micro phone of FIG. 11,
  • FIGS. 13 and 14 show frequency response curves in rectangular coordinates for microphones in accordance with this invention
  • FIG. 15 is a showing of the frequency response curves in polar coordinates
  • FIG. 16 shows a microphone in accordance with this invention having an elongated, narrow diaphragm.
  • FIG. 17 shows the associated directional pattern for higher frequencies
  • FIG. 18 shows a microphone embodying the invention in the form of a hexagonal pencil.
  • FIG. 1 shows in polar coordinates, for different frequencies, the directional pattern of a microphone having a diaphragm size of 4.5 X 9 centimeters. It is apparent that the directional effect increases with an increase in frequency.
  • FIG. 2 shows the frequency curves of the same microphone for various angles of sound incidence in polar coordinates.
  • the sound character of the sound recording will depend on the distance of the sound source from the microphone because the ratio of direct to indirect sound becomes dependent on distance. Besides, the sound recordings made with such microphone are unnatural owing to an exaggerated reverberation. For this reason it has become generally accepted that the transmitter must be small relative to the wavelength of the highest frequency to be transmitted in order to obtain a frequency-independent directional pattern.
  • the invention discards this opinion because the measures according to the invention, which will be described hereinafter, enable even a condenser microphone having a relatively very large diaphragm to be designed for a frequency-independent directional pattern.
  • the invention relates to a-microphone the diaphragm of which is exposed to the sound field on both sides and which has a sufliciently frequency-independent directional pattern in spite of the large area of the diaphragm. For this reason a perfect sound recording can be made even in rooms having poor acoustic characteristics. It has also been found that cables having a length of up to 20 meters resulted in a loss of only about 4 decibels. This does not involve a modification of the frequency response, as is known, because only a voltage division occurs between the microphone capacitance and the cable capacitance.
  • the invention provides further the use of a second diaphragm, which may be electrically effective or ineffective.
  • a second diaphragm which may be electrically effective or ineffective.
  • different directional patterns can be adjusted in a manner known per se by a change of the polarizing voltage.
  • the microphone may be converted to a stereophonic microphone operating on two separate channels.
  • the microphone may also be used as a speaker, e.g., for dictating apparatus.
  • a transformer may be connected thereto or a transistor amplifier may be used which is assembled with the microphone to form a unit and which may also generate the polarizing voltage and which generates such a high audiofrequency output voltage that the alternating voltage can be transmitted on unshielded lines.
  • the directional pattern of a pressure transmitter is spherical as long as the wavelength of the sound is small relative to the dimensions of the transmitter. Beyond this range the pressure builds up to provide a directional effect which increases with the frequency. It is also known that the pressure gradient as a driving force in a diaphragm exposed to the sound field on both sides rises linearly until half the wavelength of the sound approximately equals the sound detour around the microphone, i.e. the sound path from the center of the front side of the diaphragm to the center of the rear side of the diaphragm. The two effects described are obtained almost at the same frequency so that the microphone begins to show a directional effect due to a build-up of pressure where the pressure gradient reaches its highest value. As the limits are not definite, the transition is not strictly defined so that it appears to be more suitable to consider the phenomena which occur considerably above and below the critical frequency and then to draw conclusions regarding the behavior at the limiting frequency.
  • FIG. 3 a first illustrative embodiment of the invention is shown.
  • the figure shows the components of a condenser microphone having a unidirectional pattern.
  • One or more layers of a sheetlike acoustic frictional resistance 2, e.g., filter paper, are inserted in a sheet metal casing 1 having a perforated bottom.
  • a trough 3 consisting, e.g., of plastic and having also a perforated bottom is placed on this resistance.
  • An elastic sealing frame 4 of plastic is inserted in the trough.
  • the perforated electrode 5 with parallel spacing threads 6 consisting, e.g., of beads having a thickness of about 20 microns, rests on tional pattern for 0, 90 and 180.
  • the diaphragm 7 is placed on the electrode 5 and stressed by being adhesively connected at its rim. On the side facing away from the electrode the diaphragm is vapor-coated with a metal.
  • the front cover 8 of the housing with the protective grid or with openings forms the closure.
  • FIG. 4 the microphone of FIG. 3 is diagrammatically shown in assembled condition.
  • the diaphragm 7 is supported by the threads 6 and by the rim of the electrode 5.
  • the cavity 13 and the frictional acoustic resistance 2 form the phase-shifting member, which according to the invention is effective at frequencies below 2000 cycles per second and provides for a unidirectional pattern in this range.
  • FIG. 5 shows a microphone having two diaphragms 7a and 7b.
  • One or both of said diaphragms may be electrically effective. It is known that different directional patterns can be set by electrical remote control where two electrically conducting diaphragms are provided. A frictional resistance 1:) may be arranged between the electrodes 5a and 51').
  • a microphone having a bidirectional pattern is shown in FIG. 6.
  • the diaphragm 17 of this microphone contains only a perforated electrode 18 as an acoustically effective element.
  • the frictional resistance is formed between the diaphragm and the perforated electrode.
  • An additional frictional resistance 19 may be provided.
  • a microphone as shown in FIG. 4 may be provided with a slack, thin resilient diaphragm 20 (FIG. 7).
  • a mechanically actuable slide 21 FIG. 8
  • the latter pattern has the above-described disadvantages of being dependent on frequency, although this may he desirable for achieving certain acoustic effects.
  • the mechanism may also serve to obtain the highest fidelity.
  • the microphone according to FIG. 5 may also be used for stereophonic recording if the two diaphragms are connected to separate transmission channels I and II, as is shown in FIG. 9. En this case the microphone is oriented so that the diaphragm surfaces face the sound source.
  • the directional pattern is shown in FIG. 10.
  • two individual microphones according to the invention may also be used which are disposed close to each other for intensity recording and for AB stercophonic recording are spaced from each other and arranged at an angle of relative to each other.
  • the diaphragms may be inclined relative to each other. This is an arrangement which has already been provided in small microphones (FIG. 11). The patterns will obviously also be inclined, as is shown in FIG. 12.
  • FIG. 13 the frequency response curves are shown which are obtained with the microphones according to the invention for a sound incidence at 0, 45, 90, and whereas FIG. 14 shows the frequency response curves for a microphone according to the invention having a bidirec-
  • FIG. 15 shows in polar coordinates the characteristics of a unidirectional microphone according to the invention. Without departing from the invention the diaphragm may have any desired proportions.
  • FIG. 18 is an enlarged view showing a condenser microphone in the form of, a hexagonal pencil.
  • a hexagonal sleeve 21 is perforated on all side faces and serves as an electrode. It is wound with spacing threads 22 and the diaphragm 23- is stretched on the outside over these threads on three adjacent side surfaces.
  • the three side faces opposite to the diaphragm 23 are lined inside the sleeve with filter paper 24, a textile insert or the like forming an acoustic resistance. The ends of the sleeve are closed by plugs, not shown.
  • a directional condenser microphone for transmitting a predetermined frequency range; comprising at least one diaphragm having front and rear faces with a minimum area of square centimeters and a maximum dimension substantially larger than the wavelength of the highest frequency of said range, both of said facesbeing exposed to the action of the sound field; support means carrying said diaphragm; means constituting a frictional acoustic resistance; said support means, said rear face of the diaphragm and said means constituting a frictional acoustic resistance defining a cavity; and said cavity and said frictional acoustic resistance being operative as a phase-shifting element only up to a predetermined frequency in said range at which one-half of the wavelength of sound is less than the effective length of the sound path from the center of said front face of the diaphragm around the microphone to the center of said rear face of the diaphragm.

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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)
US10718A 1959-03-04 1960-02-24 Frequency independent directional condenser microphone Expired - Lifetime US3082298A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT170659A AT209396B (de) 1959-03-04 1959-03-04 Kondensatormikrophon

Publications (1)

Publication Number Publication Date
US3082298A true US3082298A (en) 1963-03-19

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Family Applications (1)

Application Number Title Priority Date Filing Date
US10718A Expired - Lifetime US3082298A (en) 1959-03-04 1960-02-24 Frequency independent directional condenser microphone

Country Status (5)

Country Link
US (1) US3082298A (de)
AT (1) AT209396B (de)
DE (1) DE1121116B (de)
GB (1) GB911866A (de)
NL (1) NL249090A (de)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3223782A (en) * 1961-06-19 1965-12-14 Akg Akustische Kino Geraete Directional microphone with distance control
US3445595A (en) * 1964-09-11 1969-05-20 Int Standard Electric Corp Electromechanical transducer coupled to a low input impedance transistor amplifier and yielding a flat response over a given frequency range
US3777079A (en) * 1971-10-21 1973-12-04 Willco Gmbh Directional microphone for head mounted midget hearing aids
EP0186388A2 (de) * 1984-12-20 1986-07-02 AT&T Corp. Toroidmikrophon zweiter Ordnung
US4757546A (en) * 1985-11-19 1988-07-12 Kabushiki Kaisha Audio-Technica Narrow directional microphone
US4789044A (en) * 1985-11-19 1988-12-06 Kabushiki Kaisha Audio-Technica Narrow directional microphone
USD444143S1 (en) 1999-10-08 2001-06-26 Telex Communications, Inc. Microphone
USD851633S1 (en) * 2017-06-12 2019-06-18 Toa Corporation Microphone with built-in speaker

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AT211394B (de) * 1959-10-09 1960-10-10 Goerike Rudolf Kondensatormikrophon

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1753137A (en) * 1926-08-12 1930-04-01 Seibt Georg Electrostatic loud-speaker
US1776112A (en) * 1929-04-08 1930-09-16 Ephraim Banning Loud-speaker condenser
GB571870A (en) * 1943-12-10 1945-09-12 Otto Kurt Kolb Improvements relating to unidirectional microphones
US2387845A (en) * 1943-06-24 1945-10-30 Bell Telephone Labor Inc Electroacoustic transducer
DE884516C (de) * 1940-12-09 1953-07-27 Siemens Ag Elektrostatisches Mikrophon
US2686847A (en) * 1951-12-12 1954-08-17 Bell Telephone Labor Inc Directional transducer
DE920311C (de) * 1935-11-13 1954-11-18 Siemens Ag Einrichtung zur Sprachuebertragung aus geraeuscherfuellten Raeumen
US2787671A (en) * 1952-10-06 1957-04-02 Schall Technik Dr Ing Karl Sch Microphone arrangement
US2852620A (en) * 1954-08-13 1958-09-16 Schoeps Karl Adjustable condenser microphone
US2920140A (en) * 1958-03-14 1960-01-05 Rca Corp Electrostatic microphone circuits

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1044170B (de) * 1952-08-14 1958-11-20 Schoeps Dr Ing Karl Mikrophon-Anordnung zur Erzielung einer Richtcharakteristik fuer bevorzugt einseitige Schallaufnahme

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1753137A (en) * 1926-08-12 1930-04-01 Seibt Georg Electrostatic loud-speaker
US1776112A (en) * 1929-04-08 1930-09-16 Ephraim Banning Loud-speaker condenser
DE920311C (de) * 1935-11-13 1954-11-18 Siemens Ag Einrichtung zur Sprachuebertragung aus geraeuscherfuellten Raeumen
DE884516C (de) * 1940-12-09 1953-07-27 Siemens Ag Elektrostatisches Mikrophon
US2387845A (en) * 1943-06-24 1945-10-30 Bell Telephone Labor Inc Electroacoustic transducer
GB571870A (en) * 1943-12-10 1945-09-12 Otto Kurt Kolb Improvements relating to unidirectional microphones
US2686847A (en) * 1951-12-12 1954-08-17 Bell Telephone Labor Inc Directional transducer
US2787671A (en) * 1952-10-06 1957-04-02 Schall Technik Dr Ing Karl Sch Microphone arrangement
US2852620A (en) * 1954-08-13 1958-09-16 Schoeps Karl Adjustable condenser microphone
US2920140A (en) * 1958-03-14 1960-01-05 Rca Corp Electrostatic microphone circuits

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3223782A (en) * 1961-06-19 1965-12-14 Akg Akustische Kino Geraete Directional microphone with distance control
US3445595A (en) * 1964-09-11 1969-05-20 Int Standard Electric Corp Electromechanical transducer coupled to a low input impedance transistor amplifier and yielding a flat response over a given frequency range
US3777079A (en) * 1971-10-21 1973-12-04 Willco Gmbh Directional microphone for head mounted midget hearing aids
EP0186388A2 (de) * 1984-12-20 1986-07-02 AT&T Corp. Toroidmikrophon zweiter Ordnung
EP0186388A3 (en) * 1984-12-20 1987-12-02 American Telephone And Telegraph Company Second order toroidal microphone
US4757546A (en) * 1985-11-19 1988-07-12 Kabushiki Kaisha Audio-Technica Narrow directional microphone
US4789044A (en) * 1985-11-19 1988-12-06 Kabushiki Kaisha Audio-Technica Narrow directional microphone
USD444143S1 (en) 1999-10-08 2001-06-26 Telex Communications, Inc. Microphone
USD851633S1 (en) * 2017-06-12 2019-06-18 Toa Corporation Microphone with built-in speaker

Also Published As

Publication number Publication date
AT209396B (de) 1960-06-10
GB911866A (en) 1962-11-28
NL249090A (de)
DE1121116B (de) 1962-01-04

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