US2179361A - Condenser microphone - Google Patents

Condenser microphone Download PDF

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Publication number
US2179361A
US2179361A US71792A US7179236A US2179361A US 2179361 A US2179361 A US 2179361A US 71792 A US71792 A US 71792A US 7179236 A US7179236 A US 7179236A US 2179361 A US2179361 A US 2179361A
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microphone
sound
membrane
condenser
electrode
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US71792A
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English (en)
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Hans Joachim Von Braunmuehl
Walter Weber
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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

Definitions

  • This invention relates to'improvements in or relating tp microphones, und mute particularly to electrtatic er condenser microphotxes.
  • the hast known microphones are so-called sound pressure recelvers, since only one slde of the membrane or diaphragm is exposed to the sound fleld. Since the sound pressure is a scalar quantity all sound pres- 10 sure receivers possess the property that thelr sensitivity is not dependent on the direction of incidence of the sound but is the same for sound waves coxning from difierent directlons, at least for the low and mlddle frequencies.
  • the pressure microphone shows a characteristlc, which represents the sensitlvlty according to the dlrection of the sound (known in short as the directional response characteristlc) which is in the form of a circle.
  • Such pressure microphones are certainly advantageous for many purposes, e. g., for picking up conversations of a plurality 015 speakers guthered around the microphone.
  • a microphone having the best possible directional response characteristic i. e., having a decided maximum sensitivity for one particular direction.
  • auxiliary devices of karge dimenslons e. g., reflectors
  • the employment of such devices is, however, possible only to a limited extent.
  • a microphone which is sensitive for a precedeular direction of sound can, however, be constiucted if, instead of uslng the scalar property of the sound pressure, the vectorial quantity of the difference in pressure for two neighbouring points ofthe sound field is used for actuating the microphone.
  • the quantity of the efiect cf the sound on the membrane er a corresponding member of the microphone is represented by the sound pressure gradient.
  • 'Ihis principle has been rea1i seg i for an eleetrodmmi mlcrophone by the ribbon microphone exposed on both sides to the action of the sound.
  • the object of the present invention is, however, to provide a pressure dlfference microphone operating 011 the capacltative principle.
  • a condenser microphone in which the membrane acting as the movable p1ate or electrode of the condenser is exposed on both sides to the sound by the provision of perforatlons in the fixed plate. Further, the distance 15 between the membrane and the perforated platze is arranged to be small in proportion to the size of the perforations a11d the spacing thereof, in
  • Condenser microphox1es of this kind have the property of converting into electrlcal oscillations only those sound waves which come from a particular directions, whilst sound waves from cer- 25 ta.in other directions are transmitted electrically to a, considerably lesser extent or not at all.
  • Figure -2 is a curve illustrating the dependenee on frequency of the response of the pressure difference microphone
  • Figures 3a and 3b illustrate in side sectional 40 elevation and rear p1an view respectively a. microphone according to the invention
  • Flgure 4 illustrates a. microphone according another embodiment cf the invention
  • FIGS 5, 6 and 7 illustrate diagrammatically the membrane displacements of a microphone according the invention under the action of the sound pressure anal sound pressure difference for diflerent directions of sound incidence.
  • Figure 8 shows the directional response characteristic of a microphone according to the invention.
  • Figures 9 and 10 illustrate in froni; and side View respectively a microphone provided with mea.ns 1'or increasing the sound pressure difference.
  • the circle D represe'znts the directional response characteristic of the pressure microphone and shows that the sound, which acts on a microphone located at the DC1tre of the circle, infiuences the membrane to an equal extent from all directions.
  • the microphone 1s 01' the above-mentioned construction such that the membrane is influenced on both sides by the sound
  • the directional response characteristic obtained consists of two circles G, which touch at; the line in whlch the microphone can be regarded as located.
  • the directional response characteristic of the pressure gradient microphone has, therefore, the form of flgure 8.
  • This characteristic of the pressure gradient microphone shows that the membrance is most strongly influenced by sound incident; in a. direction at; right angles to its plane., i. e., at right angles to the horizontal 1ine of the diagram, that is to say from the front or rear, whi1st the membrane is not influenced by sound ineident in a direction parallel to the membrane.
  • Such a. microphone is diagrammatically illustrated in Figures 3 and 3".
  • the fixed condenser platze E has a plurality of openings n, and at the other side cf the membrane M is located a plate E similar in shape and arrangement to the fixed plate E.
  • This platze either does not take part electrically in the operation of the microphone, or is connected in a particular manner known in connection with difi'erential microphones.
  • the function o1 the parts K and L will be referred to later.
  • a. capacitive microphone may possess a horizontal frequency curve, it is necessary that the amplitude of the membrane be constant over the audible range. Since the membrane of the microphone is exposed to the sound fleld on both sides, the difierence in sound pressures at the tront and rear sides is proportional to the drive of the membrane. This sound pressure difierence has, however, a rising frequency characteristic up to that frequency at which the half wave length corresponds the difierence in path between the front and rear sides of the microphone button.
  • the frequency is plotted as abscissae F and the amplitude 01 the membrane as ordinates A.
  • the resonance curve is shown by a full line. Its flat course with a weak maximum at the point W: shows the high degree of damping.
  • the arrangement of a, flat air cavity in front of the membrane brings about an increase in the driving force.
  • the position and the degree of this increase can be suited to the falling characteristic of the frequency curve (right band part of the curve, Figur-e 2).
  • the irequency curve (left band part of the curve, Figure 2) can be compensated by coupling one or more closed air cavities with parts of the mem brane.
  • Figure 3 shows such a construction by way of example.
  • a completely closed cavity L is coupled. by means of a tube K with the space between the membrane M and. the fixed electrode E.
  • By suitable shaping and dimensioning this coupled closed air cavity the strength and progress with frequency of the desired compensatlng increase can be dimensioned for the fall at lower frequencies.
  • a microphone constructed in accordancc with the invention is of such dimensions that its diameter is not greater than the wave length u! the highest frequency 1:0 be transmitted, there is obtained a microphone which is extremely satisfactory in operation, since the satisfactory properties of directional response are further supplemented by a good frequency curve.
  • the upper limit of the diameter lies a.t about 3 cms. corresponding to a wave length of 10.000 Hertz (cycles per second).
  • F01 the lower limit the consideration arises in connection with the construction that with reduction 015 the diameter the sensitiv ity of the microphone is reduced. It follows from this that the most satisfactory dimension of the microphone described is such that even having regard to the lower limit of sensitivity the diameter is approximately 3 cms.
  • the basic form cf the pressure gradient microphone which as above described possesses a fixed perforated platze, can be altered by mounting a second membrane on the rear side cf this fixed plate. The action obtained thereby will be explained more detailed in the following.
  • the resultant movement of the operative membrane c is in thls case zero, as S1 and s1 are oppositely directed. Movement of the ele :trically inoperative membrane d only occurs.
  • Such a microphone possesses on this a.ccount a. directional response characteristic in the form of the cardioid shown in Flgure 8. In this case the microphone is to be regarded as being on the horizontal line parallel with the membrane, so that the vertical line in Flgure 8 is perpendicular to the electr ically operative membrane.
  • the condition for a decrea.sing or vanishing sensltivity for sounds from rearward directions is the equality of the membrane displacements under the influence of the sound pressure and under the influence o1 the sound pressure diflerence.
  • the displacement of the membrane caused by the sound pressure diflerence is determined by the properties controlling the movement of the membrane and the magnitude of the sound pressure difierence. The latter ls determined by the length of path between the front and real sides of the membrane, i. e. simply by the diameter of the microphone.
  • the movement of the membrane mu.st be principally determined by friction.
  • the driving force must increase with the frequency, i. e. the pressure diflerence must ipcrease as fax as the upper limiting frequency of the transmission range. This requirement is fulfilled if the length of path between the front and rear sides of the membrane for the upper llmlting frequency is smaller than a half wave length.
  • the dlameter is preferably arranged to be about 3 cm., as above explained.
  • the electrode b possesses, accordlng to Figure 4, besides the hores a extending through lt a number of shorter bores e not extending through it. Their number, size and arrangement influences the membrane displacement caused by the action of the sound.
  • the described microphone arrangement may also be so constructed that it can be used as a directional or non-directional microphone according to the manner in which it is connected. For this purpose it ls only necessary to make both membranes electrically conducting. For a directional m crophone one membrane remains unconnected, and for a non-directional microphone both membranes are used connected in parallel.
  • a condenser microphone a fixed condenser plate having transverse perforations extending from side to side and also having recesses extending from each platte side only partway to the other side, a diaphragm constituting the movable condenser plate and being spaced from said fixed plate by a. distance small compared with the diameter and spaclng of said perforations and recesses and of a value which would render the frictional air damping on said dlaphragm hlgh as compared with its massand elasticity damping and a. second diaphragm disposed on the other side of said fixed platte at a distance similar to the spacing of said first mentioned diaphragm.
  • a condenser microphone having a flxed elentrode and a movable diaphragm electrocle flxed only at its periphery and spaced from sald fixed electrode, said flxed electr0de having a relatively small number of wide-spaced transverse perforations through which the side of the diaphragm electrode facing the fixed electrode is exposed to the effect of the sound waves, tl1e distanoe between the diaphragm and said fixed electrode being small with respect to the diameter and the spaclng of said perforations and of a value which would render the frictional air damping on the diaphragm high as compared with its massand elasticity damping and a plane sheet of material surrounding said fixed electrode in its plane, said material having a sound transmission Which decreases with increasing frequency.
  • a condenser microphone having a fixed electrode und a movable dtaphragm electrode flxed only atlts pertphery and spaced from said flxed electrode, said flxed electrode havlng a relatlvely small number cf wlde-spaced transverse perfora ttons. the dtstance between t;he dlaphragm and said flxed electrode betng small wlth respect t o t;he dtameter and the spaclng 01 said pertorations und.
  • 01 a value whlch would render the h lctlonal alr damplng an the diaphragm hlg'h 9.s compared wttzh ltzs massa.nd elasticttydamping a second diaphragm disposed on the other side 01 said flxed electrode at a distance slmilar to t:he spacing of said flrst-mentloned dlaphragh and adapted to transmtt: the sound waves through said perforations t;o said flrst dlaphragm, and a plane sheet; 01 materlal surroundlng said flxed electrode in lts plane, said materlal having a sound transmisslon whtch decreases wlth lncreasing frequency,
  • a condenser microphone a flxed condenser plate having a relatively small number 01 transverse perforatlons untformly spaced over its area, and havlng a diameter not greater than the wave length 015 sound at the highest frequency to be transmltted, and a.
  • a condenser microphone a fixed condenser platze having transverse perforattons extending from s1de to side and also having recesses extendlng from Vietnamese plate stde only partway to the ot;her slde, a dlaphragm constitutlng t;he movable condenser plate and being spaced froxn said flxed platze by a distance small compared with the diameter and spacing 015 said perforattons a.nd recesses and of a value whlch would render the trictional a.ir damptng on said diaphragm high as compared with it:s massand elasticity damplng,
  • a condenser microphone a flxed condenser pla.te havlng transverse perforatlons extendlng Iro'm side to slde and also havlng recesses extend- Ing trom Vietnamese platze side only partway to t:he other slde, a. dlaphragm constzituttng the movable condenser plate and belng spaced from said fixed platze by a distance small compared wlth the diameter andspacing of said perforatlons and recesses and o! a.
  • a condenser microphone having a fixed electrode and a movable diaphragm electzrode fixed only at; its perip'hery and spaced from said fixed electrode, said fixed electrode having a relatlvely small number of wide-spaced transverse perforations through which the side of the diaphragm electrode faclng the flxed electrode is exposed t:o the efiect cf the sound wavas, the distance between the dlaphragm and said fixed electrode being small w1t:h respect: to the diameter and t;he spaclng 013 said perforatlons and of a va1ue which would render the frictlonal air damping on the diaphragm high as compared wit;h its massand elasticity damping.
  • a second diaphragm disposed on the other side 01 said flxed electrode at; a distance similar t;o the spaclng 0f said first-mentioned diaphragm, and a plane sheet of material surrounding said 'flxed electrode in its plane, said material having a sound transmtssion which decreases wlth increaslng frequency, the diameter of said fixed condenser platze and of said diaphragm being not; greataer than t:he wave length 0f sound at: the highest: frequency t;o be transmitted.
  • HANS JOACHIM vor BRAUNMHL. WALTER WEBER.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US71792A 1935-04-04 1936-03-30 Condenser microphone Expired - Lifetime US2179361A (en)

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DE472549X 1935-04-04

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FR (1) FR804785A (fr)
GB (2) GB472056A (fr)

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2416557A (en) * 1947-02-25 Electroacoustic transducer
US2627558A (en) * 1946-07-22 1953-02-03 Electro Voice Unidirectional microphone
US2678967A (en) * 1949-02-22 1954-05-18 Nordwestdeutscher Rundfunk Capacity microphone with variable directional characteristic
DE2337078A1 (de) * 1972-07-21 1974-02-07 Ind Res Products Inc Richtungsempfindliche hoerhilfe
EP1891834A1 (fr) 2005-05-27 2008-02-27 OY Martin Kantola Consulting Ltd Appareil, système et méthode pour signaux acoustiques
EP1891833A1 (fr) 2005-05-27 2008-02-27 OY Martin Kantola Consulting Ltd Ensemble de transducteurs acoustiques, et systeme et procede associes
US20130236037A1 (en) * 2005-08-23 2013-09-12 Analog Devices, Inc. Multi-Microphone System
US8666090B1 (en) 2013-02-26 2014-03-04 Full Code Audio LLC Microphone modeling system and method
US10701481B2 (en) 2018-11-14 2020-06-30 Townsend Labs Inc Microphone sound isolation baffle and system

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2416557A (en) * 1947-02-25 Electroacoustic transducer
US2627558A (en) * 1946-07-22 1953-02-03 Electro Voice Unidirectional microphone
US2678967A (en) * 1949-02-22 1954-05-18 Nordwestdeutscher Rundfunk Capacity microphone with variable directional characteristic
DE2337078A1 (de) * 1972-07-21 1974-02-07 Ind Res Products Inc Richtungsempfindliche hoerhilfe
EP1891834A1 (fr) 2005-05-27 2008-02-27 OY Martin Kantola Consulting Ltd Appareil, système et méthode pour signaux acoustiques
EP1891833A1 (fr) 2005-05-27 2008-02-27 OY Martin Kantola Consulting Ltd Ensemble de transducteurs acoustiques, et systeme et procede associes
US20130236037A1 (en) * 2005-08-23 2013-09-12 Analog Devices, Inc. Multi-Microphone System
US9338538B2 (en) * 2005-08-23 2016-05-10 Invensense, Inc. Multi-microphone system
US8666090B1 (en) 2013-02-26 2014-03-04 Full Code Audio LLC Microphone modeling system and method
US10701481B2 (en) 2018-11-14 2020-06-30 Townsend Labs Inc Microphone sound isolation baffle and system

Also Published As

Publication number Publication date
GB472549A (en) 1937-09-24
FR804785A (fr) 1936-11-02
GB472056A (en) 1937-09-16

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