EP0413086B1 - Electro-acoustic transducer - Google Patents
Electro-acoustic transducer Download PDFInfo
- Publication number
- EP0413086B1 EP0413086B1 EP90107295A EP90107295A EP0413086B1 EP 0413086 B1 EP0413086 B1 EP 0413086B1 EP 90107295 A EP90107295 A EP 90107295A EP 90107295 A EP90107295 A EP 90107295A EP 0413086 B1 EP0413086 B1 EP 0413086B1
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- European Patent Office
- Prior art keywords
- plate
- microphone
- boundary area
- membrane
- sound
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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.)
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- 239000012528 membrane Substances 0.000 claims description 8
- 230000015572 biosynthetic process Effects 0.000 claims 1
- 238000009434 installation Methods 0.000 abstract description 10
- 230000005484 gravity Effects 0.000 abstract description 6
- 230000001419 dependent effect Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000002775 capsule Substances 0.000 description 2
- 101100390736 Danio rerio fign gene Proteins 0.000 description 1
- 101100390738 Mus musculus Fign gene Proteins 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000002845 discoloration Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R1/00—Details of transducers, loudspeakers or microphones
- H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
- H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
- H04R1/34—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by using a single transducer with sound reflecting, diffracting, directing or guiding means
- H04R1/342—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 for 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
- H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only
- H04R1/222—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only for microphones
Definitions
- the invention relates to an interface microphone according to the preamble of claim 1.
- Such an interface microphone is known from DE-A-3 334 945.
- the reverberant plates used in known interface microphones are either circular, square or rectangular.
- the transducer element is usually attached centrally.
- the edge of the panel usually has a phase of approximately 45 °, while in the case of thin panels, the edge is usually only broken.
- the plate is irregularly rounded or flattened towards the edge.
- the transducer element is attached outside the center of the plate at a peripheral point. It has been shown that the frequency responses of the interface microphones with circular, square or rectangular plates have strong peaks and dips in the case of vertical sound.
- these microphones show strong irregularities in the polar diagram in the front half space, so that the result is strong and direction-dependent discoloration of the sound.
- These inadequacies can be explained by the fact that, in the case of an interface microphone, the wave front just incident produces a secondary sound field. This secondary sound field is created by sound diffraction at the edge of the plate. A so-called “creeping wave” arises, which spreads from the edge of the plate over its surface. The phase position of the creeping wave in relation to the incident wave depends on the phase jump at the plate edge. This phase jump is different depending on the nature of the edges and the impedance of the surfaces of the microphone body and the interface.
- the creeping wave thus generates a more or less complicated interference pattern.
- the superposition of the incident wave with the creeping wave at the installation location of the transducer is decisive. Negative effects on the frequency response and the directional characteristic can only be avoided if creeping waves are either completely avoided or if they have an overall frequency-independent phase position and a frequency-independent level at the installation location of the converter.
- the creeping wave can only be avoided if the mounting plate were infinitely thin or infinitely extended.
- a thickness of 1 to 2 mm which would be sufficient in practice to avoid creeping waves, is technically not feasible, since no electrostatic converter is available for installation in such a thin mounting plate.
- the object of the invention is to achieve a frequency-independent, hemispherical directional characteristic with a high sound fidelity in the case of an interface microphone of the type mentioned at the outset, even with vertical sound incidence.
- the interface microphone according to the invention is optimized with regard to the geometric shape of its mounting plate and the mounting position of its electroacoustic transducer in the mounting plate so that creeping waves have an overall frequency-independent phase position and a frequency-independent level at the mounting location of the transducer. For every angle of incidence, it is thus ensured that the superposition of the incident wave with the secondary sound field at the transducer location, which is caused by diffraction at the microphone plate there is no linear influence on the frequency response.
- the path lengths from each edge point of the plate to the membrane center are evenly distributed in a length range, the upper limit of which is determined by the sound wavelength of the upper limit frequency of the electroacoustic transducer, and the lower limit of which is determined by half the sound wavelength of the crossover frequency, at which A sound pressure build-up begins to form in front of the microphone area.
- the plate is designed as an oblique-angled triangle.
- the embodiment of an interface microphone according to the invention shown in plan view in FIG. 1 and in section in FIG. 2 has a triangular carrier plate P with the side edges or triangular legs a, b and c.
- the capsule of a transducer W is recessed so that the diaphragm M of the transducer W is flush with the surface of the plate P facing the incident sound.
- the exact location of the transducer W is in the example shown on the line of gravity s1 between its base point F and the center of gravity S.
- the transducer W is connected through the plate with a microphone cable K, which installs at the base of the line of gravity s2 or the shortest leg b is and ends at its other end in a cable connector St.
- the section according to FIG. 2 shows the flush installation of the membrane M and the mounting of the transducer W in a recess in the mounting plate P.
- An electrostatic, pressure-calibrated transducer can preferably be provided as the transducer W, i.e. a transducer that delivers a constant voltage in the listening area at constant sound pressure.
- the frequency response of the interface microphone according to FIGS. 1 and 2 were measured at different sound incidence angles of 0 °, 30 °, 60 ° and 90 °, based on the plane of the mounting plate P.
- the results are in the figures 3a to 3d shown using the solid curve # 1.
- the corresponding frequency responses of known interface microphones with a rectangular carrier plate (dashed curve # 2) and a circular carrier plate (curve # 3) are shown in FIGS. 3a to 3d drawn.
- the flat frequency response achieved with the boundary microphone according to the invention at all sound incidence angles ideally means a frequency-independent, hemispherical directional characteristic. Direct sound and diffuse sound do not result in different sound colorations, as occurs, for example, with a microphone in the free sound field due to the diffraction and shadowing effects on the microphone body.
- the surface-flush installation of the transducer in the plate avoids sound colorations, such as occur with conventional microphones due to delayed reflections at the space boundary surfaces and the associated comb filter effects.
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- Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
- Diaphragms For Electromechanical Transducers (AREA)
- Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)
- Measuring Fluid Pressure (AREA)
- Details Of Audible-Bandwidth Transducers (AREA)
- Piezo-Electric Transducers For Audible Bands (AREA)
Abstract
Description
Die Erfindung bezieht sich auf ein Grenzflächenmikrofon gemäß dem Oberbegriff des Patentanspruchs 1. Ein derartiges Grenzflächenmikrofon ist aus der DE-A-3 334 945 bekannt.The invention relates to an interface microphone according to the preamble of claim 1. Such an interface microphone is known from DE-A-3 334 945.
In einem Raum bilden sich stets durch Überlagerung des direkt eintreffenden Schallfeldes mit den an den Wänden reflektierten Schallwellen stehende Wellen aus, was zu frequenz- und ortsabhängigen Schalldruck-Maxima und -Minima führt. Direkt vor einer schallharten Fläche haben Schallwellen ein Druckmaximum, wobei die senkrecht zur Fläche gerichtete Schnellekomponente verschwindet, da eintreffende und reflektierte Wellen gleichphasig überlagert werden. Der Schalldruck vor der Grenzfläche ist daher doppelt so groß wie im freien Schallfeld. Dieser Effekt wird bei einem bekannten Grenzflächenmikrofon (Zeitschrift "Funkschau", Heft 16, 1985, Seiten 43-45) ausgenutzt, bei weichem auf der Oberseite einer ebenen, dünnen und schallharten Montageplatte ein Miniatur-Elektretwandler angebracht ist. An der Unterseite der Montageplatte befinden sich elastische Füße, um die Montageplatte auf den Fußboden, einer Wand oder einer anderen, schallharten Grenzfläche zu fixieren. Infolge der Erhöhung des Schalldruckes unmittelbar an der Grenzfläche bis auf den doppelten Wert wird die Nutzspannung des Wandlers um 6 dB gegenüber dem Freifeld angehoben. Diese Schalldruckverdoppelung tritt jedoch nur für solche Frequenzen ein, für welche die Grenzfläche groß im Vergleich zur Schallwellenlänge ist.Standing waves are always formed in a room by superimposing the directly arriving sound field on the sound waves reflected on the walls, which leads to frequency and location-dependent sound pressure maxima and minima. Directly in front of a reverberant surface, sound waves have a pressure maximum, whereby the fast component directed perpendicular to the surface disappears, because incoming and reflected waves are superimposed in phase. The sound pressure in front of the interface is therefore twice as large as in the free sound field. This effect is used in a known boundary surface microphone (magazine "Funkschau", issue 16, 1985, pages 43-45), when a miniature electric converter is attached to the soft side of a flat, thin and hard-wearing mounting plate. There are elastic feet on the underside of the mounting plate in order to fix the mounting plate to the floor, a wall or another hard-surface interface. As a result of the increase in the sound pressure directly at the interface up to twice the value, the useful voltage of the converter is raised by 6 dB compared to the free field. However, this doubling of sound pressure only occurs for those frequencies for which the interface is large compared to the sound wavelength.
Die bei bekannten Grenzflächenmikrofonen benutzten, schallharten Platten sind entweder kreisförmig, quadratisch oder rechteckig. Das Wandlerelement ist in der Regel zentrisch angebracht. Bei dickeren Platten besitzt die Plattenkante in der Regel eine Phase von etwa 45°, während bei dünnen Platten die Kante in der Regel nur gebrochen ist. Bei kreisförmigen Platten ist die Platte zum Rand hin unregelmäßig verrundet oder abgeflacht. Bei einem weiteren, aus der DE-A-3 334 945 bekannten Grenzflächenmikrofon mit kreisförmiger Platte ist das Wandlerelement außerhalb der Plattenmitte an einer Umfangsstelle angebracht. Es hat sich gezeigt, daß die Frequenzgänge der Grenzflächenmikrofone mit kreisförmigen, quadratischen oder rechteckigen Platten bei senkrechtem Schalleinfall starke Überhöhungen und Einbrüche aufweisen. Ferner zeigen diese Mikrofone starke Unregelmäßigkeiten im Polardiagramm im vorderen Halbraum, so daß im Ergebnis starke und richtungsabhängige Klangverfärbungen auftreten. Diese Unzulänglichkeiten erklären sich dadurch, daß bei einem Grenzflächenmikrofon die eben einfallende Wellenfront ein sekundäres Schallfeld erzeugt. Dieses sekundäre Schallfeld entsteht durch Schallbeugung an der Plattenkante. Es entsteht eine sogenannte "Kriechwelle", die sich vom Rand der Platte über deren Fläche ausbreitet. Die Phasenlage der Kriechwelle in bezug auf die einfallende Welle ist vom Phasensprung an der Plattenkante abhängig. Dieser Phasensprung fällt je nach Beschaffenheit der Kanten und der Impedanz der Oberflächen von Mikrofonkörper und Grenzfläche unterschiedlich aus. In Abhängigkeit von der geometrischen Gestalt des Mikrofonkörpers und der Montageplatte erzeugt somit die Kriechwelle ein mehr oder weniger kompliziertes Interferenzmuster. Für den Frequenzgang eines Grenzflächenmikrofons ist somit die Überlagerung der einfallenden Welle mit der Kriechwelle am Einbauort des Wandlers entscheidend. Negative Beeinflussungen des Frequenzganges und der Richtcharakteristik können nur dann vermieden werden, wenn Kriechwellen entweder völlig vermieden werden oder wenn sie am Einbauort des Wandlers eine in der Summe frequenzunabhängige Phasenlage sowie einen frequenzunabhängigen Pegel besitzen. Die Kriechwelle kann theoretisch nur dann vermieden werden, wenn die Montageplatte unendlich dünn oder unendlich ausgedehnt wäre. Eine Dicke von 1 bis 2 mm, welche in der Praxis zur Vermeidung von Kriechwellen genügen würde, ist jedoch technisch nicht realisierbar, da zum Einbau in eine derartig dünne Montageplatte kein elektrostatischer Wandler verfügbar ist.The reverberant plates used in known interface microphones are either circular, square or rectangular. The transducer element is usually attached centrally. In the case of thicker panels, the edge of the panel usually has a phase of approximately 45 °, while in the case of thin panels, the edge is usually only broken. In the case of circular plates, the plate is irregularly rounded or flattened towards the edge. In a further boundary microphone with circular plate, known from DE-A-3 334 945, the transducer element is attached outside the center of the plate at a peripheral point. It has been shown that the frequency responses of the interface microphones with circular, square or rectangular plates have strong peaks and dips in the case of vertical sound. Furthermore, these microphones show strong irregularities in the polar diagram in the front half space, so that the result is strong and direction-dependent discoloration of the sound. These inadequacies can be explained by the fact that, in the case of an interface microphone, the wave front just incident produces a secondary sound field. This secondary sound field is created by sound diffraction at the edge of the plate. A so-called "creeping wave" arises, which spreads from the edge of the plate over its surface. The phase position of the creeping wave in relation to the incident wave depends on the phase jump at the plate edge. This phase jump is different depending on the nature of the edges and the impedance of the surfaces of the microphone body and the interface. Depending on the geometric shape of the microphone body and the mounting plate, the creeping wave thus generates a more or less complicated interference pattern. For the frequency response of an interface microphone, the superposition of the incident wave with the creeping wave at the installation location of the transducer is decisive. Negative effects on the frequency response and the directional characteristic can only be avoided if creeping waves are either completely avoided or if they have an overall frequency-independent phase position and a frequency-independent level at the installation location of the converter. Theoretically, the creeping wave can only be avoided if the mounting plate were infinitely thin or infinitely extended. However, a thickness of 1 to 2 mm, which would be sufficient in practice to avoid creeping waves, is technically not feasible, since no electrostatic converter is available for installation in such a thin mounting plate.
Die Aufgabe der Erfindung besteht darin, bei einem Grenzflächenmikrofon der eingangs erwähnten Art auch bei senkrechtem Schalleinfall eine frequenzunabhängige, halbkugelförmige Richtcharakteristik bei einer hohen Klangtreue zu erzielen.The object of the invention is to achieve a frequency-independent, hemispherical directional characteristic with a high sound fidelity in the case of an interface microphone of the type mentioned at the outset, even with vertical sound incidence.
Diese Aufgabe wird erfindungsgemäß durch die kennzeichnenden Merkmale des Patentanspruchs 1 gelöst.This object is achieved by the characterizing features of claim 1.
Vorteilhafte Ausgestaltungen und Weiterbildungen des erfindungsgemäßen Grenzflächenmikrofons ergeben sich aus den Unteransprüchen.Advantageous refinements and developments of the interface microphone according to the invention result from the subclaims.
Das erfindungsgemäße Grenzflächenmikrofon ist hinsichtlich der geometrischen Form seiner Montageplatte und der Einbaulage seines elektroakustischen Wandlers in der Montageplatte so optimiert, daß Kriechwellen am Einbauort des Wandlers eine in der Summe frequenzunabhängige Phasenlage und einen frequenzunabhängigen Pegel besitzen. Für jeden Einfallswinkel ist damit gewährleistet, daß durch die Überlagerung der einfallenden Welle mit dem durch Beugung an der Mikrofonplatte entstehenden sekundären Schallfeld am Wandlerort keine lineare Beeinflussung des Frequenzganges stattfindet. In erfindungsgemäßer Weise sind hierzu die Weglängen von jedem Randpunkt der Platte zur Membranmitte gleichmäßig in einem Längenbereich verteilt, dessen obere Grenze bestimmt wird durch die Schallwellenlänge der oberen Grenzfrequenz des elektroakustischen Wandlers,und dessen untere Grenze bestimmt wird durch die halbe Schallwellenlänge der Übergangsfrequenz, bei welcher sich ein Schalldruckstau vor der Mikrofonfläche auszubilden beginnt. In besonders günstiger Weise ist die Platte als schiefwinkliges Dreieck gestaltet.The interface microphone according to the invention is optimized with regard to the geometric shape of its mounting plate and the mounting position of its electroacoustic transducer in the mounting plate so that creeping waves have an overall frequency-independent phase position and a frequency-independent level at the mounting location of the transducer. For every angle of incidence, it is thus ensured that the superposition of the incident wave with the secondary sound field at the transducer location, which is caused by diffraction at the microphone plate there is no linear influence on the frequency response. According to the invention, the path lengths from each edge point of the plate to the membrane center are evenly distributed in a length range, the upper limit of which is determined by the sound wavelength of the upper limit frequency of the electroacoustic transducer, and the lower limit of which is determined by half the sound wavelength of the crossover frequency, at which A sound pressure build-up begins to form in front of the microphone area. In a particularly favorable manner, the plate is designed as an oblique-angled triangle.
Die Erfindung wird anhand eines in den Zeichnungen dargestellten Ausführungsbeispieles näher erläutert. Es zeigt:
- Fig. 1
- eine Draufsicht auf ein Grenzflächenmikrofon gemäß der Erfindung ;
- Fig. 2
- einen Schnitt durch das Grenzflächenmikrofon gemäß Fig. 1 längs der Schnittlinie II - II, und
- Fign. 3a bis 3d
- Frequenzgänge des Grenzflächenmikrofons nach Fig. 1 (Kurve #1), eines Grenzflächenmikrofons mit rechteckförmiger Montageplatte (Kurve #2) und eines Grenzflächenmikrofons mit kreisförmiger Montageplatte (Kurve #3).
- Fig. 1
- a plan view of an interface microphone according to the invention;
- Fig. 2
- a section through the boundary microphone according to FIG. 1 along the section line II - II, and
- Fig. 3a to 3d
- 1 (curve # 1), an interface microphone with a rectangular mounting plate (curve # 2) and an interface microphone with a circular mounting plate (curve # 3).
Das in Fig. 1 in der Draufsicht und in Fig. 2 im Schnitt dargestellte Ausführungsbeispiel eines erfindungsgemäßen Grenzflächenmikrofons weist eine dreieckförmige Trägerplatte P mit den Seitenkanten bzw. Dreiecksschenkeln a, b und c auf. Die von den Schenkeln a, b und c eingeschlossenen Winkel α, β, γ betragen im dargestellten Beispielsfalle α = ca. 45°, β = ca. 75° und γ = ca. 60°.The embodiment of an interface microphone according to the invention shown in plan view in FIG. 1 and in section in FIG. 2 has a triangular carrier plate P with the side edges or triangular legs a, b and c. The angles α, β, γ enclosed by the legs a, b and c are in the example shown α = approx. 45 °, β = approx. 75 ° and γ = approx. 60 °.
Auf der relativ dünnen, schallharten Trägerplatte P ist in der Nähe des Schwerpunktes S des Dreiecks, d.h. des Schnittpunktes der drei Schwerlinien s1, s2 und s3, die Kapsel eines Wandlers W vertieft angebracht, so daß die Membrane M des Wandlers W bündig mit der dem einfallenden Schall zugewandten Oberfläche der Platte P ist. Der genaue Einbauort des Wandlers W liegt im dargestellten Beispielsfall auf der Schwerlinie s1 zwischen deren Fußpunkt F und dem Schwerpunkt S. Der Wandler W ist durch die Platte hindurch mit einem Mikrofonkabel K verbunden, das am Fußpunkt der Schwerlinie s2 bzw. am kürzesten Schenkel b installiert ist und an seinem anderen Ende in einem Kabelstecker St endet.On the relatively thin, reverberant support plate P is in the vicinity of the center of gravity S of the triangle, i.e. the intersection of the three lines of gravity s1, s2 and s3, the capsule of a transducer W is recessed so that the diaphragm M of the transducer W is flush with the surface of the plate P facing the incident sound. The exact location of the transducer W is in the example shown on the line of gravity s1 between its base point F and the center of gravity S. The transducer W is connected through the plate with a microphone cable K, which installs at the base of the line of gravity s2 or the shortest leg b is and ends at its other end in a cable connector St.
In dem Schnitt nach Fig. 2 erkennt man den oberflächenbündigen Einbau der Membrane M und die Halterung des Wandlers W in einer Vertiefung der Montageplatte P besonders deutlich.The section according to FIG. 2 shows the flush installation of the membrane M and the mounting of the transducer W in a recess in the mounting plate P.
Als Wandler W kann in bevorzugter Weise ein elektrostatischer, druckkalibrierter Wandler vorgesehen werden, d.h. ein Wandler, der im Hörbereich bei konstantem Schalldruck eine konstante Spannung abgibt.An electrostatic, pressure-calibrated transducer can preferably be provided as the transducer W, i.e. a transducer that delivers a constant voltage in the listening area at constant sound pressure.
Der Frequenzgang des Grenzflächenmikrofons gemäß Fign. 1 und 2 wurde unter verschiedenen Schalleinfallswinkelnvon 0°, 30°, 60° und 90°, bezogen auf die Ebene der Montageplatte P,gemessen. Die Ergebnisse sind in den Fign. 3a bis 3d anhand der ausgezogenen Kurve #1 dargestellt. Zum Vergleich sind die entsprechenden Frequenzgänge bekannter Grenzflächenmikrofone mit einer rechteckförmigen Trägerplatte (gestrichelte Kurve #2) und einer kreisförmigen Trägerplatte (Kurve #3) in den Fign. 3a bis 3d eingezeichnet.The frequency response of the interface microphone according to FIGS. 1 and 2 were measured at different sound incidence angles of 0 °, 30 °, 60 ° and 90 °, based on the plane of the mounting plate P. The results are in the figures 3a to 3d shown using the solid curve # 1. For comparison, the corresponding frequency responses of known interface microphones with a rectangular carrier plate (dashed curve # 2) and a circular carrier plate (curve # 3) are shown in FIGS. 3a to 3d drawn.
Wie man aus dem Vergleich der Kurven #1 bis #3 erkennt, sind die Frequenzgänge unter allen Schalleinfallswinkeln bei dem erfindungsgemäßen Mikrofon nach Fign. 1 und 2 sehr eben und ausgeglichen. Bei dem Grenzflächenmikrofon mit rechteckförmiger Platte (Kurve #2) und kreisförmiger Platte (Kurve #3) zeigen sich insbesondere bei den 0°-Frequenzgängen deutliche Abweichungen von dem ebenen Verlauf bei höheren Frequenzen . Diese Frequenzgangverzerrungen erklären sich dadurch, daß die Kriechwellen, die durch Beugung an der Mikrofonplatte entstehen, am Einbauort des Wandlers eine frequenzabhängige Phasenlage sowie einen frequenzabhängigen Pegel besitzen.As can be seen from the comparison of curves # 1 to # 3, the frequency responses at all sound incidence angles in the microphone according to the invention according to FIGS. 1 and 2 very even and balanced. With the boundary microphone with a rectangular plate (curve # 2) and circular plate (curve # 3), there are clear deviations from the flat course at higher frequencies, particularly in the 0 ° frequency response. This frequency response distortion can be explained by the fact that the creeping waves, which are caused by diffraction at the microphone plate, have a frequency-dependent phase position and a frequency-dependent level at the installation location of the converter.
Wesentlich ist, daß der anhand eines Ausführungsbeispiels mit dreieckförmiger (schiefwinkliges Dreieck) Montageplatte erläuterte Erfindungsgedanke allgemein dahin umschrieben werden kann, daß die geometrische Form der Platte P und der Einbauort der Membrane M bzw. Kapsel W so zu wählen sind,daß sich bei Überlagerung des einfallenden primären Schallfeldes mit dem durch Schallbeugung an den Plattenkanten entstehenden sekundären Schallfeld (Kriechfeld) ein ebener Frequenzgang am Einbauort der Membrane M ergibt. Dies läßt sich dann erreichen, wenn die Weglängen von jedem Randpunkt der Platte P zur Membranmitte gleichmäßig in einem bestimmten Längenbereich verteilt sind. Die obere Grenze dieses Längenbereichs wird bestimmt durch die Schallwellenlänge der oberen Grenzfrequenz des Wandlers. Die untere Grenze dieses Längenbereichs wird durch die halbe Schallwellenlänge derjenigen Frequenz (Übergangsfrequenz) bestimmt, ab der sich ein Schallstaudruck vor der Platte P ausbildet.It is essential that the inventive concept explained using an exemplary embodiment with a triangular (oblique triangle) mounting plate can generally be described in such a way that the geometric shape of the plate P and the installation location of the membrane M or capsule W are to be selected such that when the incident primary sound field with the secondary sound field (creep field) resulting from sound diffraction at the plate edges results in a flat frequency response at the installation location of the membrane M. This can be achieved if the path lengths from each edge point of the Plate P to the membrane center are evenly distributed in a certain length range. The upper limit of this length range is determined by the sound wavelength of the upper limit frequency of the transducer. The lower limit of this length range is determined by half the sound wavelength of that frequency (crossover frequency) from which a sound pressure builds up in front of the plate P.
Der mit dem erfindungsgemäßen Grenzflächenmikrofon erzielte ebene Frequenzgang bei allen Schalleinfallswinkeln bedeutet in idealer Weise eine frequenzunabhängige, halbkugelförmige Richtcharakteristik. Direkt - und Diffusschall haben keine unterschiedliche Klangfärbungen zur Folge, wie sie beispielsweise bei einem Mikrofon im freien Schallfeld aufgrund der Beugungs- und Abschattungseffekte am Mikrofonkörper auftreten. Zudem werden durch den oberflächenbündigen Einbau des Wandlers in die Platte Klangfärbungen vermieden, wie sie bei üblichen Mikrofonen durch verzögerte Reflexionen an Raumbegrenzungsflächen und den damit verbundenen Kammfiltereffekten auftreten.The flat frequency response achieved with the boundary microphone according to the invention at all sound incidence angles ideally means a frequency-independent, hemispherical directional characteristic. Direct sound and diffuse sound do not result in different sound colorations, as occurs, for example, with a microphone in the free sound field due to the diffraction and shadowing effects on the microphone body. In addition, the surface-flush installation of the transducer in the plate avoids sound colorations, such as occur with conventional microphones due to delayed reflections at the space boundary surfaces and the associated comb filter effects.
Claims (8)
- A boundary area microphone, the electroacoustic transducer of which is built with a membrane into the surface of a sound reflecting plate in such a way that, on superposition of the incoming primary soundwaves with the secondary soundwaves generated through curving of the wave motion at the edge of the plate, an even frequency of motion is formed at the membrane location, positioned so that the distance from any point on the edge of plate (P) to the centre of the membrane is evenly divided within a range, the upper boundary of which is defined by the wavelength of the upper frequency limit of the electroacoustic transducer (W) and the lower boundary is defined by half the wavelength of the lower frequency limit, which is responsible for the formation of a sound pressure build up ahead of plate (P).
- A boundary area microphone as described in (1) characterised by plate (P) being triangular in form.
- A boundary area microphone as described in (2) characterised by plate (P) being of triangular form with unequal angles.
- A boundary area microphone as described in (3) characterised by the sides (a, b, c) of the triangular plate (P) forming angles (α, β, γ) of approximately 45°, 75° and 60°.
- A boundary area microphone, as described in any of claims (2) to (4) characterised by a membrane (M) in the vicinity of the geometric centre (S) of the triangular plate (P).
- A boundary area microphone, as described in (5), characterised by the membrane (M) being positioned approximately on the perpendicular bisector (B) of the longest side (a) of the triangular plate (P), in between its geometric centre (S) and the intersection point (F) of the perpendicular bisector with side (a).
- A boundary area microphone as described in claims (1) to (6) for which transducer (W) is intended to be of the electrostatic type.
- A boundary area microphone as described in claims (1) to (7) for which transducer (W) is intended to be pressure calibrated.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3926884A DE3926884A1 (en) | 1989-08-16 | 1989-08-16 | ELECTROACOUSTIC CONVERTER |
| DE3926884 | 1989-08-16 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP0413086A1 EP0413086A1 (en) | 1991-02-20 |
| EP0413086B1 true EP0413086B1 (en) | 1994-06-01 |
Family
ID=6387125
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP90107295A Expired - Lifetime EP0413086B1 (en) | 1989-08-16 | 1990-04-18 | Electro-acoustic transducer |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5168525A (en) |
| EP (1) | EP0413086B1 (en) |
| JP (1) | JPH0388599A (en) |
| AT (1) | ATE106650T1 (en) |
| DE (2) | DE3926884A1 (en) |
Families Citing this family (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5574794A (en) * | 1995-01-19 | 1996-11-12 | Earmark, Inc. | Microphone assembly for adhesive attachment to a vibratory surface |
| US6421444B1 (en) * | 1995-09-28 | 2002-07-16 | Nortel Networks Limited | Embedded higher order microphone |
| US5684756A (en) * | 1996-01-22 | 1997-11-04 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Noise reducing screen devices for in-flow pressure sensors |
| DE19703311A1 (en) * | 1997-01-30 | 1998-08-06 | Sennheiser Electronic | Interface microphone |
| US7349546B2 (en) * | 2003-09-04 | 2008-03-25 | Kyocera Wireless Corp. | System and method for identifying a headset type in an electrical device |
| US7106875B2 (en) * | 2003-09-09 | 2006-09-12 | King James T | Dual boundary pressure zone three dimensional microphone and hearing aid |
| US7903137B2 (en) * | 2004-10-15 | 2011-03-08 | Lifesize Communications, Inc. | Videoconferencing echo cancellers |
| US7720232B2 (en) * | 2004-10-15 | 2010-05-18 | Lifesize Communications, Inc. | Speakerphone |
| US7720236B2 (en) * | 2004-10-15 | 2010-05-18 | Lifesize Communications, Inc. | Updating modeling information based on offline calibration experiments |
| US8116500B2 (en) * | 2004-10-15 | 2012-02-14 | Lifesize Communications, Inc. | Microphone orientation and size in a speakerphone |
| US7970151B2 (en) * | 2004-10-15 | 2011-06-28 | Lifesize Communications, Inc. | Hybrid beamforming |
| US20060132595A1 (en) * | 2004-10-15 | 2006-06-22 | Kenoyer Michael L | Speakerphone supporting video and audio features |
| US7760887B2 (en) * | 2004-10-15 | 2010-07-20 | Lifesize Communications, Inc. | Updating modeling information based on online data gathering |
| US7826624B2 (en) * | 2004-10-15 | 2010-11-02 | Lifesize Communications, Inc. | Speakerphone self calibration and beam forming |
| US7991167B2 (en) * | 2005-04-29 | 2011-08-02 | Lifesize Communications, Inc. | Forming beams with nulls directed at noise sources |
| US7593539B2 (en) * | 2005-04-29 | 2009-09-22 | Lifesize Communications, Inc. | Microphone and speaker arrangement in speakerphone |
| US7970150B2 (en) * | 2005-04-29 | 2011-06-28 | Lifesize Communications, Inc. | Tracking talkers using virtual broadside scan and directed beams |
| DE202009015757U1 (en) | 2009-11-17 | 2010-09-23 | Maier, Andreas | Microphone mount |
| JP5708629B2 (en) * | 2012-02-21 | 2015-04-30 | ヤマハ株式会社 | Microphone device |
| US10419850B2 (en) | 2017-01-18 | 2019-09-17 | Trident Acoustics | Dynamic boundary pressure zone microphone |
| FI20175954A1 (en) * | 2017-10-27 | 2019-04-28 | Teknologian Tutkimuskeskus Vtt Oy | Enclosure for a sound level meter and a sound level meter |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2394221A1 (en) * | 1977-06-10 | 1979-01-05 | Thomson Csf | REVERSIBLE ELECTRO-ACOUSTIC TRANSDUCER DEVICE WITH CONSTANT DIRECTIVITY CHARACTERISTICS IN A WIDE FREQUENCY BAND |
| JPS5859697A (en) * | 1981-10-05 | 1983-04-08 | Matsushita Electric Ind Co Ltd | Plane speaker |
| JPS5957596A (en) * | 1982-09-27 | 1984-04-03 | Sony Corp | Microphone device |
| SE443483B (en) * | 1983-01-14 | 1986-02-24 | Gustav Georg Arne Bolin | RECEIVER MAGNETIC FOR SOUND WAVES CONSISTING OF A RESONANCE DISC AND ANTICULAR CAUSED BY THE SOUND MOVES REACTING PIEZOELECTRIC MICROPHONE TYPE MICROPHONE |
| DE3331657A1 (en) * | 1983-09-02 | 1985-03-21 | Canton Elektronik GmbH & Co, 6395 Weilrod | Loudspeaker |
| JPS60244190A (en) * | 1984-05-17 | 1985-12-04 | Matsushita Electric Ind Co Ltd | Rectangular flat speaker |
| JPS6124399A (en) * | 1984-07-12 | 1986-02-03 | Onkyo Corp | N-angle flat diaphragm |
| US4742548A (en) * | 1984-12-20 | 1988-05-03 | American Telephone And Telegraph Company | Unidirectional second order gradient microphone |
-
1989
- 1989-08-16 DE DE3926884A patent/DE3926884A1/en active Granted
-
1990
- 1990-04-18 DE DE59005896T patent/DE59005896D1/en not_active Expired - Fee Related
- 1990-04-18 EP EP90107295A patent/EP0413086B1/en not_active Expired - Lifetime
- 1990-04-18 AT AT90107295T patent/ATE106650T1/en not_active IP Right Cessation
- 1990-08-13 JP JP2214895A patent/JPH0388599A/en active Pending
- 1990-08-15 US US07/567,572 patent/US5168525A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US5168525A (en) | 1992-12-01 |
| DE59005896D1 (en) | 1994-07-07 |
| EP0413086A1 (en) | 1991-02-20 |
| JPH0388599A (en) | 1991-04-12 |
| DE3926884A1 (en) | 1991-02-21 |
| ATE106650T1 (en) | 1994-06-15 |
| DE3926884C2 (en) | 1991-11-28 |
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