US3118979A - Electrostatic transducer - Google Patents

Electrostatic transducer Download PDF

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Publication number
US3118979A
US3118979A US129629A US12962961A US3118979A US 3118979 A US3118979 A US 3118979A US 129629 A US129629 A US 129629A US 12962961 A US12962961 A US 12962961A US 3118979 A US3118979 A US 3118979A
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United States
Prior art keywords
back plate
layer
layers
diaphragm
conductive material
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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
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US129629A
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English (en)
Inventor
Gerhard M Sessler
James E West
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AT&T Corp
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Bell Telephone Laboratories Inc
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Filing date
Publication date
Priority to NL281794D priority Critical patent/NL281794A/xx
Application filed by Bell Telephone Laboratories Inc filed Critical Bell Telephone Laboratories Inc
Priority to US129629A priority patent/US3118979A/en
Priority to US196670A priority patent/US3118022A/en
Priority to DEW32709A priority patent/DE1190040B/de
Priority to GB29679/62A priority patent/GB1014781A/en
Priority to FR906234A priority patent/FR1330592A/fr
Priority to DE19631437486 priority patent/DE1437486B2/de
Priority to GB19468/63A priority patent/GB1033001A/en
Application granted granted Critical
Publication of US3118979A publication Critical patent/US3118979A/en
Anticipated expiration legal-status Critical
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
    • H04R19/00—Electrostatic transducers

Definitions

  • This invention relates to electroacoustic transducers and more particularly to such transducers of the electrostatic type.
  • General objects of this invention are to improve the performance and to facilitate the construction of electroacoustic transducers of the electrostatic type.
  • An electrostatic transducer normally comprises a rigid metal back plate and a thin conductive plate or diaphragm stretched or mounted by its edge in a plane parallel to the surface of the back plate and closely spaced and insulated from it.
  • a potential difference is applied between the back plate and the diaphragm the difference in potential therebetween alters the force manifested between the plates thus to cause the diaphragm to move toward or away from the back plate substantially in proportion to the magnitude of the applied electric potential. Movement of the diaphragm produces sound pressure wave counterparts of the applied electrical signal.
  • the dielectric between the two should be reasonably constant and sufficiently thin to permit the desired spacing to be obtained. If the spacing is too small, large signals produce excessively large excursions of the diaphragm and it may physically contact the back plate. Such a contact interrupts the normal mode of vibration of the diaphragm. In effect, it stops all vibration at the point of contact and gives rise to a number of secondary vibrations in the diaphragm. As a result, second and higher order harmonic distortion is produced.
  • the transducer of the present invention avoids many of these difficulties. It employs a thin sheet of flexible metallized dielectric material stretched across a perforated back plate to form a capacitor in which the thin sheet of flexible material acts as a solid dielectric. Ordinarily, considerable care must be exercised in positioning the metallized sheet in juxtaposition with the back plate so that the air gap, which is inevitably present even although a spongy filler is used, is reasonably thin and uniform over the entire back plate surface. In accordance with the present invention, an additional thin layer (or layers) of dielectric material is inserted between the metallized sheet and the back plate to form a multilayer diaphragm.
  • the several air layers are of random configuration such that the total air gap along a given line normal to the quiescent plane of the diaphragm is virtually a constant from point to point along the surface of the diaphragm but distributed unequally from point to point.
  • the air gap between outer conductive layer and the back plate is replaced by a plurality of intermediate air gaps of highly irregular configurations. Since the auxiliary layers responsible for the several air gaps are virtually noncompressible and yet compliant, large signal fluctuations that ordinarily would be sufficient to cause a direct contact of the outer metallized layer with the back plate cause only a contact between two adjacent layers, but not a firm contact from front to back. For example, along a given line normal to the plane of the diaphragm the outer conductive layer may, in its swing toward the back plate, contact the intermediate dielectric layer adjacent to it. However, at this point of contact all vibration of the outer conductor is not stopped.
  • construction of the transducer is simplified because surface irregularities due to normal machine processes are quite satisfactory, and the critical placement of the outer conductor at a specified small distance from the back plate is accomplished automatically by virtue of the auxiliary film layer(s) placed therebetween.
  • the present invention thus furnishes an instrument of simpified construction in which (1) the distance between the two electrodes may be made very small thus to increase substantially the efficiency of the unit; (2) the polarizing bias potential may be made considerably higher without danger of a short-circuit developing through the dielectric; (3) the resonant frequency may be controlled by precision adjustment of the mean volume of the air gap between the diaphragm and the rigid back plate, and (4) the transducer can be constructed cheaply since there are few critical parts and it utilizes inexpensive materials.
  • FIG. 1 is a cross-sectional view of a condenser earphone illustrative of a preferred embodiment of the invention
  • FIG. 2 is a cross-sectional view, on a greatly enlarged scale, of a small portion of the diaphragm layers of a transducer constructed in accordance with the invention
  • FIG. 3 is a group of wave form diagrams illustrating a form of distortion common to electrostatic transducers
  • FIGS. 4 and 5 represent on the frequency scale sound pressure and distortion, respectively, of an electrostatic transducer in accordance with the invention.
  • FIG. 6 illustrates the impulse response of a condenser earphone.
  • FIG. 1 shows in section a condenser earphone constructed in accordance with the invention. It comprises a rigid back plate 10 preferably of metal, for example, a disc of brass about thirty-five millimeters in diameter. If desired, several small ridges 11 about 0.025 millimeter high may be provided on the upper surface of the back plate to aid in shaping the air gap behind the diaphragm. A plurality of small diameter holes or wells 12 in the back plate provide, together with the ridges, a sufilcient air volume to establish a desirable resonant frequency. Approximately two hundred holes each about one millimeter in diameter and about 3.5 millimeters deep have been found to be a sufficient number. If desired, one of the holes may be extended through the back plate or an additional port may be provided to equalize ambient pressure.
  • a rigid back plate 10 preferably of metal, for example, a disc of brass about thirty-five millimeters in diameter. If desired, several small ridges 11 about 0.025 millimeter high may be provided on the
  • a high resonant frequency is desirable in an electrostatic earphone because radiation resistance is constant so long as the earphone radiates into a small closed volume. This is normally the case. Further, in a condenser earphone much less vibration amplitude is required as compared with open air loudspeakers to produce SllfilCiCllt loudness levels.
  • the mass of the diaphragm and the compliance of the air layer yield a resonant frequency of approximately fourteen kilocyoe
  • the resonant frequency of an electrostatic transducer employing a multilayered diaphragm in accordance with the present invention may easily be selected to lie in the audio frequency or ultrasonic frequency range.
  • the addition of more layers to the diaphragm, or an increase in the volume between the diaphragm and back plate, as by increasing the number and size of the wells in the back plate decreases the resonant frequency of the system.
  • Back plate It ⁇ is supported by an insulating annular frame 13 provided with a raised flange at its periphery.
  • Frame 13 may be made of any rigid insulating material, for example, of the plastic material known commercially as Lucite.
  • Disposed across the face of the back plate It ⁇ and clamped in close proximity to the upper surface thereof is a thin circular diaphragm formed of a number of layers of thin dielectric material.
  • the layer next adjacent to back plate (one such layer lid is shown by way of illustration but several layers may, in accordance with the invention, be used) is formed from a thin sheet of dielectric material, for example, from a thin (0.25 mil) film of plastic material such as polyethylene terephthalate, known commercially as Mylar. A thinner film may be used, if desired.
  • the outer layer 15 is formed from a thin sheet of Mylar which is metallized on one side, for example, with a thin layer of aluminum. Such metallized foil is commercially available.
  • the metallized coating of foil 15 constitutes one element of a capacitor and the back plate 10 constitutes the other conductive element.
  • Insulating frame 13 is supported by an annular metal frame 16 provided with a flange on its outer edge.
  • the several layers of foil are clamped to the frame 16 by means of an annular ring 17 constructed to form a taut fit with the upper portion of the flange of frame ill. in practice, a convex protrusion in ring 17 is formed to fit a corresponding concave groove in frame 16.
  • This arrangement has proved satisfactory for providing sulficiently high mechanical tension for the several layers of the diaphragm.
  • the edge of the diaphragm is thus hel in a taut, smooth condition. More elaborate securing means may, of course, be used if desired.
  • Electrical contact to the outer metallized foil element of the capacitor may be made via frame 16, e.g., through terminal 18.
  • annular support member '19 of insulating material is provided. It is coardally mounted within annular frame H6 and spaced to abut insulating frame 13. If desired, member U may be formed as a boss on frame 13. A metallic member Ztl threaded on its outer surface to engage threads on the inner surface of support member 19 may be advanced to urge, by way of a bearing member 21, back plate it) toward an intimate contact with the diaphragm.
  • Bearing member 21 preferably is of spherical form so that a single adjustment of threaded member 2a suitably tilts the back plate and effects a proper seating of it. With this arrangement it has been found that minute adjustments may be conveniently made.
  • Electrioal contact with the back plate It), e.g., the second capacitor element, is conveniently made via member 20 and bearing 21, e.g., through terminal 22.
  • the entire transducer is preferably enclosed in an outer case 23 formed of a suitable plastic material and provided on its inner surface with a fiange or the like for supporting frame 16. It may be threaded on its outer surface to receive a front cap 24 of similar plastic material. As is usual, the outer case and front cap provide protection for the internal elements both from mechanical damage and dust.
  • front cap 24 is also arranged to form, with ring 17 and the diaphragm, a Helmholtz resonator tuned to about 12,000 cycles per second.
  • the rather high resonant frequency is achieved by providing a large neck cross-section.
  • the resonance of the cavity may be further broadened by filling the cavity with damping material 25.
  • damping material 25 For example, porous paper material may be used. The damping material may touch the metallized' foil layer without noticeable effect.
  • FIG. 2 shows an enlarged small section of back plate 10, nonmetallized foil 14, and metallized foil 15.
  • a single foil layer 14, preferably of 0.15 mil Mylar sheeting is shown placed between an outer foil 15 preferably of 0.25 mil Mylar coated with a thin layer of aluminum on the outer side, and back plate ill
  • additional auxiliary layers may be placed between foil 15 and back plate 10 if desired.
  • the several layers are assembled by forcing them together as tightly as possible to avoid the entrapment of large air bubbles. Under normal manufacturing conditions, and without special effort, minute air bubbles are never theless trapped between adjacent foils and between foil and back plate because of the inherent irregularities of the various surfaces.
  • coated foil 15 is, in usual practice, placed in close proximity to the back plate 10. With such an arrangement, a single air gap only is present and, for reasonably high efficiency, is very thin. Hence, large signal excursions of the foil layer 15 cause the foil to contact the back plate repeatedly, and at many points. The number of points of contact is dependent upon the vibration amplitude and the fluctuation of the thickness of the air layer, i.e., as a result of irregularities in the adjacent surfaces. Contacts of this sort result in mechanical distortion when the applied signal Voltage has the same polarity as the direct current biasing potential and in substantially lower transducer efficiency.
  • FIG. 3 illustrates this condition.
  • An applied sine Wave signal a of low magnitude produces undistorted vibration on both the forward excursion of the diaphragm and on its return to yield a sound pressure wave that closely resembles the signal counterpart.
  • a somewhat larger applied sine wave signal b produces a sound wave that is somewhat flattened on the second half cycle due to a slight contact of the diaphragm with the back plate, while a signal of substantially larger magnitude produces a sound wave, e.g., c, that is considerably distorted on its second half cycle due to a firm contact at many points of the diaphragm with the back plate.
  • predominantly second harmonic distortion is imparted to the emitted sound pressure wave.
  • the combined thickness S(r) of the two air layers in the diaphragm arrangement of FIG. 2 is where S and S denote the thickness of the gaps between layers 14 and 15, and between back plate and layer 14, respectively, on a line normal to the quiescent plane of the diaphragm.
  • the fluctuation of air gap S(r) is generally much smaller than the equivalent fluctuation experienced by a single air gap between the diaphragm layer and the back plate, i.e., than that ordinarily experienced without the interposition of the auxiliary layers. This results in a more homogeneous vibration amplitude over the whole surface of the outer foil of the transducer diaphragm.
  • the condenser earphone of the present invention exhibits superior frequency response, efficiency and freedom from distortion.
  • Efficiency is a function of the applied biasing potential, tension of the diaphragm, and compliance of the air layer. If the applied signal potential is, for example, a sine wave and is constant over the entire frequency range, the resulting force is also constant. At frequencies lower than the resonant frequency of the system, which as mentioned before is about 14,000 cycles per second, a constant force gives a constant displacement. In a closed coupler whose dimensions are small compared to the wave length, a constant displacement causes constant pressure. Therefore, a flat frequency response for the pressure is experienced. A slight roll-oif at low frequencies has been found to be a result of slight air leaks in the case of the transducer.
  • FIG. 4 shows the frequency response of a condenser earphone constructed in accordance with the present invention as compared with that of a typical dynamic earphone. It is quite evident that the condenser earphone exhibits a considerably flatter response, particularly at higher frequencies.
  • FIG. 5 illustrates the percent of total harmonic distortion produced by an earphone in accordance with the present invention as a function of frequency, and that produced by a high quality condenser transducer constructed in accordance with prior art techniques, i.e., without provision of the auxiliary layers of dielectric material.
  • Curve 1 illustrates the total harmonic distortion of such a prior art condenser transducer at a signal level of db sound pressure level (SPL).
  • Curve 2 indicating substantially lower distortion at all frequencies than curve 1, shows the distortion produced by a transducer with two foils, i.e., a coated outer foil and an intermedi ate foil (as illustrated in FIG. 2) at an identical sound pressure level, i.e., 80 db.
  • Curve 3 shows, for the same multifoil transducer, the distortion produced at a signal level of db SPL. It will be noted that even at this high sound pressure level the total harmonic distortion at all frequencies is considerably below that of a condenser earphone constructed according to the prior art. Although not illustrated, it has been found that the condenser microphone of the invention exhibits lower distortion in the low and middle frequency range than does a high quality dynamic earphone. Tests show, however, that a dynamic earphone is somewhat better at higher frequencies. Nevertheless, distortion of the condenser earphone is still less than one percent over the entire range at sound pressure levels of 100 db or less.
  • FIG. 6 illustrates the impulse response of a condenser earphone constructed in accordance with the principles of the present invention together with the impulse response of a high quality dynamic earphone.
  • a square wave input signal for example, of the sort illustrated in line A
  • the condenser earphone has an impulse response, shown in line B, which is almost a true image of the applied square wave.
  • the dynamic earphone differentiates the input pulse and produces relatively sharp spikes, multiple resonances, and ringing as shown in line C.
  • novel transducer of the present invention may also be employed as a microphone to convert sound pressure variations incident on the diaphragm into voltage variations.
  • the term transducer is for this reason employed to designate the unit structurally, independently of whether it effects a conversion from acoustic energy into electrical energy or vice versa.
  • the back plate element of the capacitor may be dispensed with in favor of a second metallized foil layer pressed in contact with an intermediate layer so that, in effect, the diaphragm supports both elements of a capacitor.
  • the diaphragm may be formed with the metallized surface facing inward toward the auxiliary dielectric layers, thus to allow the plastic backing for the conductive surface to act as a protective membrane. Additional auxiliary layers may then be used to achieve the proper resonant frequency and diaphragm compliance.
  • a condenser earphone comprising a thin flexible layer of a conductive material, a relatively thick metallic back plate of substantially the same surface dimensions as said flexible layer, said back plate having a plurality of spaced wells therein, means for peripherally securing said layer of conductive material in juxtaposition to said back plate, a plurality of layers of substantially noncompressible thin film dielectric material intimately sandwiched between said layer of conductive material and said back plate to form a compliant vibratile member which includes said thin layers of dielectric material and a highly irregular configuration of minute static air layers trapped between said thin layers of dielectric material, insulating covering means for rigidly supporting said several layers and said back plate, said covering means having an opening in proximate relation to the surface of said flexible layer of conductive material, and means for electrically connecting to said layer of conductive material and to said back plate.
  • An electrostatic transducer comprising a thin flexible layer of conductive material, a rigid conductive back plate having a substantially plane surface, means for peripherally securing said layer of conductive material in juxtaposition to the plane surface of said back plate to leave a relatively uniform air gap between said layer and said back plate, means for dividing said air gap into a plurality of relatively nonuniform intermediate air gaps, the dimensions of said intermediate air gaps being highly irregular from point to point in a plane parallel to the quiescent plane of said flexible layer of conductive material but substantially a constant over the entire surface area of said plane in a direction normal to the quiescent plane of said flexible layer, said means comprising a plurality of layers of substantially noncornpressible thin film dielectric material intimately sandwiched together and supported by said peripheral securing means between 5% said layer of conductive material and said back plate, and means for connecting electrically to said layer of conductive material and to said back plate.

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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)
US129629A 1961-08-07 1961-08-07 Electrostatic transducer Expired - Lifetime US3118979A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
NL281794D NL281794A (en:Method) 1961-08-07
US129629A US3118979A (en) 1961-08-07 1961-08-07 Electrostatic transducer
US196670A US3118022A (en) 1961-08-07 1962-05-22 Electroacoustic transducer
DEW32709A DE1190040B (de) 1961-08-07 1962-07-31 Elektrostatischer Wandler
GB29679/62A GB1014781A (en) 1961-08-07 1962-08-02 Improvements in or relating to electroacoustic transducers
FR906234A FR1330592A (fr) 1961-08-07 1962-08-06 Transducteur électrostatique
DE19631437486 DE1437486B2 (de) 1961-08-07 1963-04-30 Elektroakustischer wandler
GB19468/63A GB1033001A (en) 1961-08-07 1963-05-16 Electroacoustic transducers

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US129629A US3118979A (en) 1961-08-07 1961-08-07 Electrostatic transducer

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US3118979A true US3118979A (en) 1964-01-21

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US129629A Expired - Lifetime US3118979A (en) 1961-08-07 1961-08-07 Electrostatic transducer

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US (1) US3118979A (en:Method)
DE (1) DE1190040B (en:Method)
GB (1) GB1014781A (en:Method)
NL (1) NL281794A (en:Method)

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3300585A (en) * 1963-09-04 1967-01-24 Northern Electric Co Self-polarized electrostatic microphone-semiconductor amplifier combination
US3418436A (en) * 1964-07-21 1968-12-24 Neumann Georg Unidirectional condenser microphone
US3736436A (en) * 1971-11-04 1973-05-29 Mc Donnell Douglas Corp Electret pressure transducer
US3868624A (en) * 1972-12-29 1975-02-25 Us Navy Apparatus for mapping acoustic fields
US3980838A (en) * 1974-02-20 1976-09-14 Tokyo Shibaura Electric Co., Ltd. Plural electret electroacoustic transducer
US4081626A (en) * 1976-11-12 1978-03-28 Polaroid Corporation Electrostatic transducer having narrowed directional characteristic
US4160882A (en) * 1978-03-13 1979-07-10 Driver Michael L Double diaphragm electrostatic transducer each diaphragm comprising two plastic sheets having different charge carrying characteristics
US4178621A (en) * 1978-01-23 1979-12-11 Motorola, Inc. Electromechanical pressure transducer
US4204244A (en) * 1978-01-23 1980-05-20 Motorola, Inc. Electromechanical pressure transducer
US4598590A (en) * 1984-09-14 1986-07-08 At&T Bell Laboratories Electret transducer for blood pressure measurement
US4885783A (en) * 1986-04-11 1989-12-05 The University Of British Columbia Elastomer membrane enhanced electrostatic transducer
US5395592A (en) * 1993-10-04 1995-03-07 Bolleman; Brent Acoustic liquid processing device
US5450498A (en) * 1993-07-14 1995-09-12 The University Of British Columbia High pressure low impedance electrostatic transducer
EP3200479A2 (en) 2016-01-28 2017-08-02 Sonion Nederland B.V. An assembly comprising an electrostatic sound generator and a transformer
CN109819379A (zh) * 2018-12-29 2019-05-28 瑞声科技（南京）有限公司 振膜及发声器件
US20230164490A1 (en) * 2020-06-30 2023-05-25 Goertek Inc. Diaphragm and sound generating device using the diaphragm

Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1767657A (en) * 1929-08-09 1930-06-24 Ephraim Banning Capacity reproducer
US1777170A (en) * 1928-03-12 1930-09-30 United Reproducers Patents Cor Acoustic device
US1826952A (en) * 1929-10-21 1931-10-13 Ephraim Banning Acoustic condenser diaphragm
US1975801A (en) * 1930-12-15 1934-10-09 Sound Lab Corp Ltd Microphone
US2009520A (en) * 1933-06-29 1935-07-30 Reisz Eugen Electroacoustic device
DE864696C (de) * 1942-04-01 1953-01-26 Telefunken Gmbh Kondensatormikrofon
DE884516C (de) * 1940-12-09 1953-07-27 Siemens Ag Elektrostatisches Mikrophon
US2944119A (en) * 1957-12-20 1960-07-05 Philco Corp Transducers
US3041418A (en) * 1960-01-14 1962-06-26 Rca Corp Transducers

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE350499C (de) * 1922-03-21 Joseph Engl Dr Elektrostatisches Telephon
DE892773C (de) * 1941-04-17 1953-10-12 Siemens Ag Kondensator-Mikrofon

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1777170A (en) * 1928-03-12 1930-09-30 United Reproducers Patents Cor Acoustic device
US1767657A (en) * 1929-08-09 1930-06-24 Ephraim Banning Capacity reproducer
US1826952A (en) * 1929-10-21 1931-10-13 Ephraim Banning Acoustic condenser diaphragm
US1975801A (en) * 1930-12-15 1934-10-09 Sound Lab Corp Ltd Microphone
US2009520A (en) * 1933-06-29 1935-07-30 Reisz Eugen Electroacoustic device
DE884516C (de) * 1940-12-09 1953-07-27 Siemens Ag Elektrostatisches Mikrophon
DE864696C (de) * 1942-04-01 1953-01-26 Telefunken Gmbh Kondensatormikrofon
US2944119A (en) * 1957-12-20 1960-07-05 Philco Corp Transducers
US3041418A (en) * 1960-01-14 1962-06-26 Rca Corp Transducers

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3300585A (en) * 1963-09-04 1967-01-24 Northern Electric Co Self-polarized electrostatic microphone-semiconductor amplifier combination
US3418436A (en) * 1964-07-21 1968-12-24 Neumann Georg Unidirectional condenser microphone
US3736436A (en) * 1971-11-04 1973-05-29 Mc Donnell Douglas Corp Electret pressure transducer
US3868624A (en) * 1972-12-29 1975-02-25 Us Navy Apparatus for mapping acoustic fields
US3980838A (en) * 1974-02-20 1976-09-14 Tokyo Shibaura Electric Co., Ltd. Plural electret electroacoustic transducer
US4081626A (en) * 1976-11-12 1978-03-28 Polaroid Corporation Electrostatic transducer having narrowed directional characteristic
US4204244A (en) * 1978-01-23 1980-05-20 Motorola, Inc. Electromechanical pressure transducer
US4178621A (en) * 1978-01-23 1979-12-11 Motorola, Inc. Electromechanical pressure transducer
US4160882A (en) * 1978-03-13 1979-07-10 Driver Michael L Double diaphragm electrostatic transducer each diaphragm comprising two plastic sheets having different charge carrying characteristics
US4598590A (en) * 1984-09-14 1986-07-08 At&T Bell Laboratories Electret transducer for blood pressure measurement
US4885783A (en) * 1986-04-11 1989-12-05 The University Of British Columbia Elastomer membrane enhanced electrostatic transducer
US5450498A (en) * 1993-07-14 1995-09-12 The University Of British Columbia High pressure low impedance electrostatic transducer
US5395592A (en) * 1993-10-04 1995-03-07 Bolleman; Brent Acoustic liquid processing device
EP3200479A2 (en) 2016-01-28 2017-08-02 Sonion Nederland B.V. An assembly comprising an electrostatic sound generator and a transformer
US20170223464A1 (en) * 2016-01-28 2017-08-03 Sonion Nederland B.V. Assembly comprising an electrostatic sound generator and a transformer
EP3200479A3 (en) * 2016-01-28 2017-08-30 Sonion Nederland B.V. An assembly comprising an electrostatic sound generator and a transformer
US10687148B2 (en) * 2016-01-28 2020-06-16 Sonion Nederland B.V. Assembly comprising an electrostatic sound generator and a transformer
CN109819379A (zh) * 2018-12-29 2019-05-28 瑞声科技（南京）有限公司 振膜及发声器件
US20230164490A1 (en) * 2020-06-30 2023-05-25 Goertek Inc. Diaphragm and sound generating device using the diaphragm

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Publication number Publication date
DE1190040B (de) 1965-04-01
NL281794A (en:Method)
GB1014781A (en) 1965-12-31

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