US3223782A - Directional microphone with distance control - Google Patents

Directional microphone with distance control Download PDF

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Publication number
US3223782A
US3223782A US201958A US20195862A US3223782A US 3223782 A US3223782 A US 3223782A US 201958 A US201958 A US 201958A US 20195862 A US20195862 A US 20195862A US 3223782 A US3223782 A US 3223782A
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Prior art keywords
transducer
sound
distance
capacitance
frequency
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Expired - Lifetime
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US201958A
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English (en)
Inventor
Weingartner Bernhard
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AKG Acoustics GmbH
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AKG Akustische und Kino Geraete GmbH
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; 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; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers
    • H04R3/005—Circuits for transducers 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; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R2410/00—Microphones
    • H04R2410/01—Noise reduction using microphones having different directional characteristics

Definitions

  • the same effect can be achieved by electrically combining a pressure transducer having a spherical (omnidirectional) pattern with a pressure gradient transducer having a bidirectional pattern.
  • Such a microphone will have an optimum effect in the field of substantially plane sound waves, i.e., at a relatively large distance from the sound source.
  • the sound field thereof can no longer be considered to consist of substantially plane sound waves (plane sound field) but of spherical sound Waves (spherical sound field).
  • the value of the pressure gradient increases strongly with a decrease in frequency in the case of an approach toward the sound source, whereas, in a plane sound field, the pressure difference between two points lying in the direction of propagation of the sound waves increases approximately linearly up to that frequency at which half the wavelength equals the distance between the two points.
  • a microphone arranged for receiving plane sound waves and for actuation by the pressure gradient will have a preferential response to the low frequencies, compared to medium and high frequencies, in a spherical sound field (sound from nearby source).
  • a sound transmitter having a preferably unidirectional pattern, which may be adjustable, and comprising one or more transducers operating on the electrostatic principle
  • this object is achieved in that at least one of the incorporated transducer systems has variable, frequency-dependent electrical and/or acoustic attenuating means associated with it, which are adjustable by adjusting elements associated with distance-graduated scales, marks, symbols or the like, for ensuring an optimum effect at different distances from the sound source.
  • a sound transmitter which comprises a pressure transducer and a pressure gradient transducer has the frequency-dependent, adjustable, electrical and/or acoustic attenuating means associated with the pressure gradient transducer so that the increase of the gradient at the low frequencies in the spherical sound field (sound from nearby source) can be compensated. This will enable an adjustment of both the rear attenuation and the output level in dependence on the distance from the sound source.
  • a further feature of the invention resides in pro viding an acoustic frictional resistance which is connected in parallel to the acoustic capacitance or arranged in a series connection with this capacitance. This will enable an adjustment of the rear attenuation in dependence on the distance from the sound source.
  • an adjustable, frequency dependent electrical attenuating element preferably a resistance-capacitance element, may be inserted in the electrical circuit of this transducer system. This will enable an adjustment of the output level in dependence on the distance from the sound source.
  • FIG. 1 is an electrical circuit diagram in which a pressure transducer and a pressure gradient transducer are combined and which provides only for an electrical control.
  • FIG. 2 is a transverse sectional view showing diagrammatically a pressure gradient transducer which comprises acoustic attenuating means arranged according to the invention.
  • FIG. 3 shows the corresponding equivalent-circuit diagram.
  • FIG. 4 illustrates another embodiment of the invention, FIG. 5 the corresponding equivalent-circuit diagram and FIG. 6 an external view of a sound transmitter according to the invention.
  • the object of the invention may be accomplished by purely electrical methods, or by purely acoustical means, or by a combination of both.
  • FIG. 1 shows an electrical circuit diagram of a sound transmitter which comprises two individual systems, one transducer of which is a pressure transducer 1 having an omnidirectional pattern. Feeding an amplifier stage 3, the transducer 1 is perfectly decoupled from the pressure gradient transducer 2. The latter feeds the amplifier 4, the output of which is connected to that of amplifier 3.
  • a frequency-dependent electrical attenuating element is disposed between the output of the pressure gradient transmitter 2 and the input of the amplifier 4. As shown in FIG. 1, this element may consist of a resistance-capacitance element, which can be switched over.
  • This attenuating element consists of the source impedance of the transducer 2 having the capacitance C and the three resistors R R and R one of which can be connected by means of the changeover switch U to the capacitor C.
  • the resistors R R R enable an adjustment of the rear attenuation and of the output level in dependence on the distance from the sound source.
  • the resistors may serve at the same time as a grid leak for the amplifier tube.
  • the circuit according to the invention differs in that a separate amplifier is provided for each transducer and the frequency-dependent electrical attenuating element is not inserted in the common amplifier output but in the circuit of the pressure gradient transducer, preferably between the microphone output and the amplifier input.
  • the known arrangement effects only a correction of the frequency response
  • the invention achieves that the transducers combined in the sound transmitter have the same sensitivity and the same rear attenuation for any frequency and any distance from the sound source.
  • the invention distinguishes from another previous proposal to arrange frequency-dependent electrical means in the circuit of an individual system of such a combination of transducers.
  • These elements had only the function of correcting the frequency response in the plane sound field and at those high frequencies at which half the wavelength is equal to the sound detour (defined as the sound path from the center of the front face to the center of the rear face of the diaphragm) so that the gradient microphone has a very great, undesired phase/ frequency response.
  • the resistors of the resistance-capacitance element which can be switched in stages must be dimensioned so that the boosting of the low frequencies caused by the pressure gradient is compensated within certain limits for any distance from the sound source.
  • the sensitivity of each of the two individual transducers will always be the same and the adjusted unidirectional pattern will also be maintained independently of the distance from the sound source.
  • the sound transmitter can .be selectively given an omnidirectional or a bidirectional pattern by using one or the other transducer of the system alone.
  • the changeover may be effected by a simple switch because only electrical circuits must be switched.
  • the use of the arrangement according to the invention will provide for a uniform frequency response under all sound conditions.
  • FIG. 2 Another illustrative embodiment of the invention, in which a frequency-dependent acoustic attenuating element is used, is shown in FIG. 2.
  • This shows a directional microphone having a unidirectional pattern, which is achieved by a phase-shifting acoustic element.
  • a phase-shifting element consisting of a resistance-capacitance element, as are used in most cases in condenser microphones, have shown, however, that the deterioration of the rear attenuation and the increase of the sound energy received from a nearby sound source can be opposed with very simple means.
  • the invention teaches the connection of an acoustic frictional resistance in parallel to the capacitance (restoring force) of the phase-shifting element which is responsible for the undirectional pattern; this resistance may be replaced, if desired, by an equivalent series resistance.
  • the value of the parallel acoustic frictional resistance should be approximately r/A times the frictional resistance of the resistance-capacitance element, where r is the distance of the microphone from the sound source and A the sound detour from the center of the front face to the center of the rear face of the diaphragm.
  • the frictional resistance must be variable. It causes, above all, the maintenance of the rear attenuation at low frequencies in dependence on the distance from the sound source whereas the increase in sensitivity in the case of 0 sound incidence may be compensated, if desired, by a selective attenuating element included in the circuit.
  • the rear attenuation and the output level may be separately controlled, or simultaneously by a single adjusting element.
  • the diaphragm 5 vibrates relative to the highly perforated counterelectrode 6.
  • the phase-shifting resistance-capacitance element responsible for the unidirectional pattern is formed by the capacitance C, constituted by a cavity, and the acoustic frictional resistance R.
  • the duct 7 and the narrow, adjustable gap R provide a communication to the chamber C, the acoustic impedance of which is much smaller than that of the frictional resistance R formed by the narrow gap so that the action of this resistance greatly predominates and results in the desired effect if the dimensions called for by the invention are selected.
  • Z is the acoustic impedance of the diaphragm 5
  • p and p -i-Ap are the actuating forces at two different points of the sound field.
  • the other references denote similar elements as in the circuit diagram of FIG. 2.
  • FIG. 4 is a diagrammatic transverse sec tional view showing such an arrangement and FIG. 5 is the corresponding equivalent-circuit diagram.
  • the counterelectrode 6 consists of a frictional resistance, which together with the annular space C constitutes the phase-shifting element.
  • the low-volume chamber behind the diaphragm 5 is connected to the capacitance C by an acoustic frictional resistance R", which corresponds to the parallel resistance R in FIG. 2.
  • the frictional resistance R" is also formed by a narrow, adjustable slot or gap.
  • an electrical resistor may be connected in parallel to the microphone capsule havinga cardioid directional pattern in a circuit which is analogous to that of the capsule having a bidirectional pattern shown in FIG. 1.
  • the time constant of the resistance capacitance element consisting of said capsule and said parallel resistor should correspond to the period of the lowest frequency to be transmitted.
  • FIG. 6 shows finally how the proposal according to the invention can be practically employed.
  • the sound transmitter in the form of a cylindrical, rod-shaped body has a sound-permeable part 7 and a housing part 10.
  • This housing part may be provided with, e.g., annular setting elements 8, 9, which are associated with distancegraduated scales so that the rear attenuation and the output level may be adjusted to provide optimum transmission characteristics at each distance from the sound source.
  • the adjusting elements may be arranged to be coupled or may be operated by a common member. Either of rings 8, 9 will be sufficient if it is arranged to effect the adjustment of the rear attenuation as well as of the output level.
  • such a transducer having a phase-shifting element may be symmetrical and comprise two diaphragms so as to enable an adjustment of different directional patterns.
  • the components may have the following values:
  • the pressure transducer 1 may have a capsule capacitance of 100 picofarads, and the two resistors shown between the transistor 1 and the tube 3 may have a resistance of 250 megohms each.
  • the coupling capacitor between these two resistors may have a capacitance of 1000 picofarads.
  • the pressure gradient transducer 2 may have a capsule capacitance C of 100 picofarads.
  • the coupling capacitor C between the transducer 2 and the tube 4 may have a capsule capacitance of 1000 picofarads.
  • C capsule capacitance of transducer 2 in farads
  • R resistance of resistor R R or R in ohms
  • r distance of sound source from microphone in meters
  • c velocity of sound in meters per second.
  • a grid leak resistor R having a value of megohms may be used.
  • the value of the acoustic frictional resistance R should comply with the following equation:
  • the capacitance C should comply with the following relation:
  • R frictional resistance of the element R at the rear sound inlet to the transducer in kg./ sec.
  • said frictional resistance is connected in series with said capacitance.
  • a sound transmitter having a unidirectional pattern and comprising at least one electrostatic transducer and frequency-dependent attenuating means coupled to said transducer and adjustable to improve the characteristics of the transmitter for the reception of sound from at least two different distances, said one transducer comprising an acoustic capacitance, and said attenuating means comprising an adjustable acoustic frictional reslstance connected to said capacitance to form a phaseshrfting acoustic system therewith; said attenuating means further comprising an electric attenuating means electrically coupled to said transducer; said electric attenuating means comprising a resistance-capacitance element.

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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)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
US201958A 1961-06-19 1962-06-12 Directional microphone with distance control Expired - Lifetime US3223782A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
AT474961A AT226290B (de) 1961-06-19 1961-06-19 Schallempfänger mit vorzugsweise einseitiger, gegebenenfalls einstellbarer Richtcharakteristik, enthaltend ein oder mehrere nach dem elektrostatischen Prinzip arbeitende Wandlersysteme

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US3223782A true US3223782A (en) 1965-12-14

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US201958A Expired - Lifetime US3223782A (en) 1961-06-19 1962-06-12 Directional microphone with distance control

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US (1) US3223782A (de)
AT (1) AT226290B (de)
DE (1) DE1162415B (de)
GB (1) GB1007891A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3305638A (en) * 1964-02-17 1967-02-21 Steven D Teachout Condenser microphone circuit with solid electrolyte battery polarizing source
US3777079A (en) * 1971-10-21 1973-12-04 Willco Gmbh Directional microphone for head mounted midget hearing aids
JPS5446525U (de) * 1977-09-07 1979-03-31

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2173219A (en) * 1937-05-29 1939-09-19 Rca Corp Electroacoustical apparatus
US2293258A (en) * 1939-11-24 1942-08-18 Bell Telephone Labor Inc Acoustic device
US2309109A (en) * 1937-06-04 1943-01-26 Rca Corp Microphone
US2678967A (en) * 1949-02-22 1954-05-18 Nordwestdeutscher Rundfunk Capacity microphone with variable directional characteristic
US3061690A (en) * 1958-09-15 1962-10-30 Turner Company Acoustically compensated microphone with adjustable acoustic resistance
US3082298A (en) * 1959-03-04 1963-03-19 Akg Akustische Kino Geraete Frequency independent directional condenser microphone

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE912821C (de) * 1935-11-13 1954-06-03 Siemens Ag Einrichtung zur Sprachuebertragung aus geraeuscherfuellten Raeumen
DE924807C (de) * 1936-10-09 1955-03-07 Siemens Ag Einrichtung zur Sprachuebertragung aus geraeuscherfuellten Raeumen
DE927037C (de) * 1949-02-23 1955-04-28 Nordwestdeutscher Rundfunk Kapazitives Mikrophon mit veraenderbarer Richtcharakteristik
DE1044170B (de) * 1952-08-14 1958-11-20 Schoeps Dr Ing Karl Mikrophon-Anordnung zur Erzielung einer Richtcharakteristik fuer bevorzugt einseitige Schallaufnahme

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2173219A (en) * 1937-05-29 1939-09-19 Rca Corp Electroacoustical apparatus
US2309109A (en) * 1937-06-04 1943-01-26 Rca Corp Microphone
US2293258A (en) * 1939-11-24 1942-08-18 Bell Telephone Labor Inc Acoustic device
US2678967A (en) * 1949-02-22 1954-05-18 Nordwestdeutscher Rundfunk Capacity microphone with variable directional characteristic
US3061690A (en) * 1958-09-15 1962-10-30 Turner Company Acoustically compensated microphone with adjustable acoustic resistance
US3082298A (en) * 1959-03-04 1963-03-19 Akg Akustische Kino Geraete Frequency independent directional condenser microphone

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3305638A (en) * 1964-02-17 1967-02-21 Steven D Teachout Condenser microphone circuit with solid electrolyte battery polarizing source
US3777079A (en) * 1971-10-21 1973-12-04 Willco Gmbh Directional microphone for head mounted midget hearing aids
JPS5446525U (de) * 1977-09-07 1979-03-31

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Publication number Publication date
DE1162415B (de) 1964-02-06
GB1007891A (en) 1965-10-22
AT226290B (de) 1963-03-11

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