EP0065810A2 - Elektro-akustisches Wandlersystem mit fortschreitender Welle sowie Mikrophon und Lautsprecher mit einem solchen System - Google Patents

Elektro-akustisches Wandlersystem mit fortschreitender Welle sowie Mikrophon und Lautsprecher mit einem solchen System Download PDF

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Publication number
EP0065810A2
EP0065810A2 EP82300302A EP82300302A EP0065810A2 EP 0065810 A2 EP0065810 A2 EP 0065810A2 EP 82300302 A EP82300302 A EP 82300302A EP 82300302 A EP82300302 A EP 82300302A EP 0065810 A2 EP0065810 A2 EP 0065810A2
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EP
European Patent Office
Prior art keywords
transducer
electrical
stages
acoustic
signal
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.)
Withdrawn
Application number
EP82300302A
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English (en)
French (fr)
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EP0065810A3 (de
Inventor
Terry D. Beard
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BEARD, TERRY D.
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Individual
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Publication date
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Publication of EP0065810A2 publication Critical patent/EP0065810A2/de
Publication of EP0065810A3 publication Critical patent/EP0065810A3/de
Withdrawn legal-status Critical Current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
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more 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
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/12—Circuits for transducers, loudspeakers or microphones for distributing signals to two or more loudspeakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2440/00—Bending wave transducers covered by H04R, not provided for in its groups
    • H04R2440/01—Acoustic transducers using travelling bending waves to generate or detect sound

Definitions

  • This invention relates to electrical/acoustic transducers, and more particularly to a traveling wave transducer in which electrical and acoustic signals are transmitted in coordination with each other through the transducer system.
  • Electrical/acoustic transducers can be used either as speakers to transform input electrical signals into output acoustic signals, or as microphones to transform input acoustic signals into output electrical signals.
  • One variety of electrical/acoustic ,transducer is an electrostatic transducer which consists of a pair of parallel plates, between which a flexible membrane is positioned. An electrical charge is estsalished on the membrane, which is cause to vibrate between the plates as a result of either input electrical signals applied to the plates, or input acoustic waves striking the membrane. Functioning as an audio speaker, a voltage differential corresponding to the input electrical signal is applied across the plates.
  • Another object of the invention is the provision of a novel and improved electrical/acoustic transducer which appears as a substantially resistive load to an input signal, thereby reducing reactive losses associated with prior transducers.
  • a further object of the present invention is the provision of a traveling wave electrical/acoustic transducer in which electrical and acoustic signals are propagated through the transducer in sychronism, enabling energy to be coupled between. the electrical system and the acoustic wave, and resulting in an energy efficient transducer device.
  • Impedance means in the form of inductance elements are connected to the various stages and together with the transducer capacitances form an electrical delay line which matches the propagation of an electrical signal through successive stages to a speed which is substantially synchronous with the propagation speed of an acoustic signal through the transducer.
  • each-transducer stage comprises a pair of opposed, substantially acoustically transparent plate members which are spaced apart from each other and establish an equivalent stage capacitance, and a flexible charge- supporting membrane supported midway between the plates.
  • Each successive stage shares a plate with the previous stage, so that each plate except for the one at each end of the array forms a part of two stages.
  • Inductance networks are connected in circuit with the plate members to form an electrical delay line which matches the electrical propagation speed to the acoustic propagation speed through successive stages.
  • the transducer thus appears as a non-reactive load to the driving source, If a greater membrane excursion is desired, the spacing between successive plate members can be enlarged by adding a plurality of intermediate inductive-capacitive delay stages to the various transducer stages, thereby slowing down the electrical signal propagation speed, If, on the other hand, the acoustic signal falls within a frequency spectrum characterized by wavelengths which are much greater than the spacing between successive plate members, synchronization of the electrical and acoustic propagation speeds can he adequately achieved by simply making the inductance elements substantially short circuits,
  • Fig. 1 an electrical delay line is shown which forms one of the theoretical underpinnings of the present invention.
  • a general reference on delay lines is provided in Chapter 22 of the text "The Feynman Lectures on Physics," Feynman, Leighton and Sands, California Institute of Technology.
  • Connected across input terminals 2 and 4 are a series of inductance elements of substantially equal value, except for the first and last elements which are half the inductance value of the others, and a plurality of capacitors connected between each successive pair of inductors and terminal 4.
  • the delay line is terminated by a resistor R1 in series with the last inductance element.
  • the characteristic impedance of the line is approximately the square foot of L/C, L being inductance in henrys and C capacitance in farads.
  • L being inductance in henrys and C capacitance in farads.
  • the characteristic impedance of the circuit would be about 1,000 ohms within the given frequency range, That is, for frequencies of up to about 20kHz, the circuit would act as a 1,000 ohm register across terminasl 2 and 4, when terminated with a matching 1000 ⁇ resistor RI,
  • the propagation of an electrical input signal at terminals 2 and 4 through the delay line would be delayed by the square root of LC at each successive LC stage, or in the above example by about 10 -5 seconds per stage.
  • the invention utilizes the fact that sound traveling at 330 meters per second would travel about 3,3 mm in a 10 -5 second interval, thereby making it theoretically possible to synchronize the propagation of electrical and acoustic signals through a transducer system by constructing the system to emulate a delay line, with each stage of the delay line physically spaced 3,3 mm apart from the next succeeding stage,
  • a series of electrostatic electrical/acoustic transducer stages are electrically and mechancially connected in succession to propagate electrical and acoustic signals through successive stages, and appropriate impedance means such as discrete inductance elements are connected to synchronize the travel of the elelctrical signal through the system with the traveling acoustic waves, It has been found that, when the propagation of the electrical and acoustic signals are substantially synchronized through a succession of electrostatic electrial/acoustic transducer stages, the resulting signal energy output of the coupled set of stages taken together exceeds the arithmetic sum
  • FIG. 2 An implimentation of the invention as a plurality of electrically and mechanically coupled electrostatic electrical/ acoustic transducer stages is shown in Fig. 2.
  • a plurality of plate members in the form of grids or wire mesh screens 6, 8, 10, 12, 14, 16, 18, 20 and 22 (shown with exaggerated widths in Fig. 2) are supported in a parallel array by a plurality of non-conductive spacing and support members 24 which support the periphery of the screens and space them equidistantly apart. Spacing and support members 24 also hold a plurality of flexible membrane members 26, 28, 30, 32, 34, 36, 38 and 40 equidistantly spaced between each successive pair of screens, respectively.
  • the membranes are preferrably formed from a thin mylar material which has been lightly aluminized sufficiently for the membrane to support a static electrical charge, whereby the membranes flex towards one or the other of their adjacent screens in response to applied electrical field forces which accompany electric signals applied to the screens.
  • Each membrane together with the adjacent screens on either side form an electrical/acoustic transducer stage capable of transducing electrical signals on the screen to an acoustic signal from the resulting membrane movement, or of transducing an acoustically induced movement of the membrane into an output electrical signal on the screens, Except for the outermost screens 6 and 22, it can be seen that each screen is common to two transducer stages, thereby saving both materials and space.
  • a plurality of electrical/acoustic transducer stages are made to 3 perform as an electrical delay line to enable a sychronization between electrical and acoustic signals propagated through the transducer system.
  • a plurality of impedance elements in the form of inductors L are connected respectively between each screen and the screen once removed, with half value inductors L/2 connected between screen 8 and an electrical input, and between screen 10 and a termination resistor R1.
  • the entire transducer system be as acoustically transparent as practicable, to minimize losses in the propagation of acoustic signals.
  • fairly open screens for example of 1 mm mesh, formed from wire are used, along with thin lightly aluminized mylar membranes of about 6 micrometers thickness or less.
  • the spacing between successive stages that is, the spacing between the center lines of successive membranes or screens, is selected to synchronize the electrical and acoustic propagation speeds. With an inductance network and transducer stages producing a delay of 10 -5 seconds per stage, the distance between stages would be 3.3 mm for an assumed acoustic velocity of 330 meters per second.
  • Fig. 2 illustrates an electrical to acoustic c transducer. Every other membrane 26, 30, 34 and 38 is s charged to one polarity through respective coupling resistors R2 by a first voltage source 42, while the remaining membranes 28, 32, 36 and 40 are charged to the opposite polarity through respective coupling resistors R2 by a second DC voltage source 44.
  • the operating efficiency of the system will increase as the charge on the membrane is increased, but a tendency of the membranes to arc limits the charge that can be applied to them, Immersing the membranes in a non-arcing gaseous environment permits them to be charged to higher voltages.
  • an electrical input signal from an AC source 46 to be transduced to an acoustic signal is applied through the upper inductive network to every other screen 8, 12, 16 and 20, while the polar mirror of the input electrical signal is applied from equivalent AC source 48 through the lower conductance network to the remaining screens 6, 10, 14, 18 and 22; sources 46 and 48 may conveniently be provided from a center tapped transformer.
  • the screens forming the plates of each successive transducer stage are charged to oppostive polarities, creating an electric field which causes the charged membrane between the two screens to flex away from the screen of like polarity and towards the screen of opposite polarity, This in turn creates an acoustic wave which arrives at the next membrane at the same time the electric input'signals have reached the screens.:: surrounding that membrane and set up a similar electric field as in the first transducer stage.
  • the second membrane is acted upon by both a traveling electric field and the acoustic waves set-up by the preceeding membrane, and produces an acoustic wave which is considerably greater than that produced by the first stage.
  • the acoustic wave continues to travel through the system, arriving at each successive membrane at the same time the electrical input signals cause the screens on either side of the membrane to establish an electrical field which cooperates with the arriving acoustic wave in flexing the associated membrane.
  • the output energy with the described transducer should approach the square of the arithmetic sum of the output energies of a simlar number of individual transducer stages acting independent of each other. Analytically, this may be attributed to two factors. First, each transducer stage arithmetically adds to the pressure of the traveling acoustic wave, so that the output pressure from the eight stage device shown in Fig. 2 would be eight times as great as the output pressure from a single stage. However, the energy in an acoustic wave is proportional to the square of the pressure.
  • the transducer system of Fig, 2 appears substantially as a purely resistive load to the input, passing electrical energy stored in the reactive capacitance of one stage on to the next instead of dissipating it immediately in a damping resistor as is necessary with conventional electrostatic speakers,
  • This consideration again increases the efficiency of the system by a factor approximately equal to the number of stages, assuming the efficiency of each stage is low,
  • the combined effect is to increase the efficiency of the described system by approximately the square of the number of stages, compared with a conventional single stage electrostatic transducer. While the above situation applies to a lossless device, and in practice some losses are experienced due to the resistive load and the movement of the indivual membranes, the efficiency of the system will still greatly exceed that of individual single stage electrostatic transducers,
  • the transducer described thus far has an upper frequency limitation of approximately- ⁇ 4/LC.
  • the electrical signal is exponentially attenuated as it progresses through the system.
  • the upper frequency limit would be about 32 kHz. Since the capacitance associated with each stage is directly proportional to the area of the elements and inversely proportional to the distance between stages, the upper frequency limitation can be modified by adjusting the physical configuration of the transducer elements,
  • FIG. 3 An end view of the transducer system illustrated in Fig. 2 is shown in Fig, 3, In this configuration, spacer and support elements 24 are seen to be generally rectangular, Small pads 50 are shown in place between the screens and membranes, limiting the area of membrane movement essentially to the region between pads. Smaller area elements could also be used, and the pads eliminated,
  • FIG. 4 an equivalent circuit of the system of Fig, 2 is depicted, including an equivalent resistance Req associated with each transducer stage.
  • the capacitance associated with each stage is represented by an equivalent capacitor Ceq.
  • the electrostatic elements interact with the acoustic field, they do not appear as pure-capacitances in the equivalent circuit, but rather appear as capacitors Ceq bridged by resistors Req in the case of a speaker, or as capacitors bridged by power sources in the case of a microphone.
  • Req is to the first.order proportional to the square of the spacing; between successive stages, and inversely proportional to the square of the electrostatic charges on the membranes, Req exists, because of and represents the conversion of electrical energy into acoustic energy and is generally small compared to the characteristic impedance Rl of the delay line, if the efficiency of the transducer is fairly low. As the efficiency rises, as-is the case with a well designed example of the invention, Re
  • the above frequency limitation may be alleviated to a great extent by a judicious selection of the spacing between the transducer elements and of the size of the inductors.
  • the relationship stated above whereby Req is proportional to the square of the spacing between successive screens or membranes (which spacings in the preferred embodiment are equal) suggests that the efficiency of the system can be increased by reducing the spacing between the screens and membranes.
  • Ceq increases since it is inversely proportional to the spacing.
  • the efficiency problem may be compensated for by an increase in the size of the inductor elements, thereby making possible the greater efficiency of smaller spacing without limiting the operating frequency of the device.
  • FIG. 5 another embodiment of the invention is shown which.allows for greater membrane excursions and thereby high'er pressure, more efficient acoustic waves,
  • intermediate inductive-capacitive delay stages are connected between successive membranes in the delay line to retard the propagation speed of an electrical signal through the system.
  • a greater spacing between stages and a greater membrane excursion becomes possible.
  • an intermediate inductor L' at the top of the delay line and intermediate screen 8' are added between membranes 26 and 28, while intermediate inductor L' at the bottom of the delay line and intermediate screen 10 1 are added between membranes 28 and 30.
  • Each added screen in effect forms a new capacitive element with its adjacent screen.
  • Similar inductors and screens are added to the remaining stages in the system, the size of each inductor and spacing between screens being selected to achieve the desired slowing of the electrical propagation speed.
  • a single electrostatic speaker stage represented by Ceq is the first element of an immediately terminated delay line.
  • Ceq represents the equivalent capacitance of a conventional electrostatic speaker, and is connected through an inductance element of L/2 value to an input signal source 52.
  • the system is terminated by another inductor element of L/2 value connected in series with a termination resistor R2 across Ceq.
  • R2 is ⁇ L/C.
  • the system shown is capable of efficiencies up to double the efficiency of the electrostatic speaker operating by itself. Again, the system could be used as a microphone by simply replacing signal source 52 with a load.

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  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • General Health & Medical Sciences (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
EP82300302A 1981-05-15 1982-01-21 Elektro-akustisches Wandlersystem mit fortschreitender Welle sowie Mikrophon und Lautsprecher mit einem solchen System Withdrawn EP0065810A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US26401181A 1981-05-15 1981-05-15
US264011 1988-10-28

Publications (2)

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EP0065810A2 true EP0065810A2 (de) 1982-12-01
EP0065810A3 EP0065810A3 (de) 1983-07-20

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EP82300302A Withdrawn EP0065810A3 (de) 1981-05-15 1982-01-21 Elektro-akustisches Wandlersystem mit fortschreitender Welle sowie Mikrophon und Lautsprecher mit einem solchen System

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EP (1) EP0065810A3 (de)
JP (1) JPS57192195A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4872148A (en) * 1984-03-08 1989-10-03 Polaroid Corporation Ultrasonic transducer for use in a corrosive/abrasive environment
WO2005015948A1 (en) * 2003-07-24 2005-02-17 New Transducers Limited Acoustic device
EP2247120A3 (de) * 2009-01-08 2013-03-06 Harman International Industries, Incorporated Passive Gruppenverzögerungsstrahlenbündelung
US9955260B2 (en) 2016-05-25 2018-04-24 Harman International Industries, Incorporated Asymmetrical passive group delay beamforming

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2014150337A (ja) * 2013-01-31 2014-08-21 Yamaha Corp 静電型スピーカ

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1978200A (en) * 1930-03-24 1934-10-23 Bell Telephone Labor Inc Electrostatic acoustic device
US1983377A (en) * 1929-09-27 1934-12-04 Gen Electric Production of sound
US2496031A (en) * 1947-12-30 1950-01-31 Rca Corp Dual microphone sound detector system
US3136867A (en) * 1961-09-25 1964-06-09 Ampex Electrostatic transducer
JPS5241524A (en) * 1975-09-29 1977-03-31 Sony Corp Condenser speaker driver

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1983377A (en) * 1929-09-27 1934-12-04 Gen Electric Production of sound
US1978200A (en) * 1930-03-24 1934-10-23 Bell Telephone Labor Inc Electrostatic acoustic device
US2496031A (en) * 1947-12-30 1950-01-31 Rca Corp Dual microphone sound detector system
US3136867A (en) * 1961-09-25 1964-06-09 Ampex Electrostatic transducer
JPS5241524A (en) * 1975-09-29 1977-03-31 Sony Corp Condenser speaker driver

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENTS ABSTRACTS OF JAPAN *
PATENTS ABSTRACTS OF JAPAN, vol. 1, no. 108, 22nd September 1977, page 3797 E 77; & JP - A - 52 41 524 (SONY K.K.) (31-03-1977) *

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4872148A (en) * 1984-03-08 1989-10-03 Polaroid Corporation Ultrasonic transducer for use in a corrosive/abrasive environment
WO2005015948A1 (en) * 2003-07-24 2005-02-17 New Transducers Limited Acoustic device
GB2417386A (en) * 2003-07-24 2006-02-22 New Transducers Ltd Acoustic device
GB2417386B (en) * 2003-07-24 2006-09-13 New Transducers Ltd Acoustic device
US7564984B2 (en) 2003-07-24 2009-07-21 New Transducers Limited Acoustic device
EP2247120A3 (de) * 2009-01-08 2013-03-06 Harman International Industries, Incorporated Passive Gruppenverzögerungsstrahlenbündelung
US8971547B2 (en) 2009-01-08 2015-03-03 Harman International Industries, Incorporated Passive group delay beam forming
US9426562B2 (en) 2009-01-08 2016-08-23 Harman International Industries, Incorporated Passive group delay beam forming
US9955260B2 (en) 2016-05-25 2018-04-24 Harman International Industries, Incorporated Asymmetrical passive group delay beamforming

Also Published As

Publication number Publication date
JPS57192195A (en) 1982-11-26
EP0065810A3 (de) 1983-07-20

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