DE102008014299A1 - Microphone i.e. UM930-Twin microphone, has microphone capsules in housing, and acoustical impedance sensor staying in connection with processor i.e. digital signal process, for signal processing and displacement determination - Google Patents

Abstract

The microphone has microphone capsules in housing and an acoustical impedance sensor integrated into the microphone. The sensor determines individual acoustic field components in displacement (r) and direction to an acoustic source. Value and phase of acoustical impedance (Z) are indicated. The acoustical impedance is provided as a vector value of direction of sound waves incident on the microphone. The sensor stays in connection with a processor i.e. digital signal process, for signal processing and displacement determination. An independent claim is also included for a method for processing of measured acoustic signal for displacement measurement of an acoustic source using a microphone.

Description

The The invention relates to a microphone with distance-dependent Selectivity and a method of processing measured Sound signals for determining the distance of sound sources, wherein the microphone contains a housing with two microphone capsules.

For use can be in the 1 and 2 shown, known microphone 1 , the UM930-TWIN, which has two outputs, are used, the outputs provide the signals of the sound pressure and the sound pressure difference simultaneously for digital further processing. internally contains the housing 2 of the microphone 1 two complete microphones with two microphone capsules 3 . 4 , which are mounted close together at a distance Δx.

Out The physics of sound radiation is known to be at close range a spotlight, the sound pressure level not the sound velocity level equivalent. In addition, there is a sound source in the vicinity a phase difference between the sound velocity and the sound pressure.

In addition, the structure of the microphone allows 1 in conjunction with a digital signal processing device to form directional characteristics and to evaluate sound field components according to their sound incidence angle, as in the document Fellbaum, K .: Proceedings of the 18th Conference ESSV2007 Cottbus is described.

Other microphones and functionalities are in the publications Görne, T .: Microphones in Theory and Practice, 1994, Elektor-Verlag GmbH Aachen , and Eargle, J .: The Microfone Book, 2001, by Butterworth-Heinemann , described.

at The sound recording with microphones often interfere with unwanted Noise, often from sound sources from larger ones Distances come.

Of the Invention is based on the object, a microphone with distance-dependent Selectivity and a method of processing measured Indicate sound signals for distance determination of sound sources, which are formed so suitable that by digital signal processing the sound field components from a close range of a microphone of those can be separated from a remote area. The differences Between sound pressure and Schallschnelle should be exploited, the To analyze microphone signals, the distance to the sound source to determine and according to the analysis result in their amplitude to rate. It should also improve the distance between Speech and interference signal can be brought about.

The The object is achieved by the features of claims 1 and 4 solved.

In the microphone with distance-dependent selectivity with at least two microphone capsules containing a housing with at least two microphone capsules, is according to the Characteristic part of claim 1 additionally a sound impedance sensor integrated, over the individual sound field components in their distance and direction to the sound source are determinable, wherein the magnitude and the phase of the acoustic impedance indicate in which Distance the microphone is from the sound source, where. the sound impedance as vectorial magnitude the direction indicates the incident on the microphone sound waves, wherein the sound impedance sensor with a processor in the form of a digital signal processor - DSP - to Signal processing and distance determination is related.

• – nur der Schalldruck (Kugel) oder
• – nur die Schallschnelle (Acht) oder
• – Schalldruck minus Schallschnelle (Niere nach hinten).

A first analog signal preprocessing can already take place in the microphone, the sum of the signals from sound pressure and sound velocity (kidney forward) always being present at a first output of the microphone, and a variety being configured at a second output, optionally

• - only the sound pressure (sphere) or
• - only the speed of sound (Eight) or
• - Sound pressure minus sound velocity (kidney to the back).

• – eine kontinuierliche Einstellung der Richtcharakteristik zwischen Kugel, breite Niere, Niere, Superniere, Hyperniere und Acht,
• – eine Drehung der Nullstellen im Richtdiagramm auf unerwünschte Störgeräusche,
• – eine Veränderung der Übertragungsfunktion des Mikrofons wahlweise Linearisierung der Frequenz- und Phasengänge,
• – eine Klangveränderung durch nichtlineare Übertragungsfunktionen z. B. durch die nichtlineare Kennlinie einer Vakuumröhre oder Berücksichtigung der Hysteresiskurve eines Ausgangstransformators und
• – eine Analyse der Schalleinfallsrichtung und Bewertung der Mikrofonsignalanteile je nach Schalleinfallswinkel.

A post-processing of the microphone signals with a DSP can optionally be realized:

• A continuous adjustment of the directional characteristic between sphere, broad kidney, kidney, supercardioid, hypercardioid and eight,
• A rotation of the zeros in the directional diagram to unwanted noise,
• - a change in the transfer function of the microphone optionally linearization of the frequency and Phase transitions
• A sound change due to non-linear transfer functions z. B. by the non-linear characteristic of a vacuum tube or taking into account the hysteresis of an output transformer and
• - An analysis of the direction of sound incidence and evaluation of the microphone signal components depending on the sound incidence angle.

• – Ermittlung des Schalldrucks,
• – Ermittlung der Schallschnelle indirekt über den Schalldruckgradienten durch Berechnung,
• – Berechnung der Impedanz aus Schalldruck und Schallschnelle,

wobei aus einem Vergleich zwischen Schallschnellepegel und Schalldruckpegel eine Bestimmung der Entfernung des Mikrofons zu mindestens einer Schallquelle durchgeführt wird.The method for processing measured sound signals for determining the distance of sound sources by means of the aforementioned microphone according to claims 1 to 3,
according to the characterizing part of patent claim 4 has the following steps:

• - determination of the sound pressure,
• - determination of the sound velocity indirectly via the sound pressure gradient by calculation,
• - calculation of the impedance from sound pressure and sound velocity,

wherein a determination of the distance of the microphone to at least one sound source is performed from a comparison between sound velocity level and sound pressure level.

festgelegt wird, wobei
der Schalldruckgradient grad p durch die zwei in der Distanz Δx angebrachten als Mikrofonkapseln ausgebildeten Druckmikrofone erfasst wird, wobei für die diskrete Mikrofondistanz Δx die Bedingung eingehalten wird, dass sich der Schalldruckgradienten dp / dx durch den Schalldruckdifferenzenquotienten Δp / Δx näherungsweise

darstellen lasst, wobei meist eine Distanz von Δx ≤ λ6 für die höchste Signalfrequenz ausreicht, und
wobei durch zeitliche Integration der Schalldruckdifferenz die Schallschnelle aus der Gleichung [V] nach folgender Gleichung berechnet wird:

und mit dem Schalldruck p zwischen den zwei Druckmikrofonen in den Mikrofonkapseln

und der Schallschnelle v die Impedanz Z einzelner Schallfeldanteile berechnet wird.The sound pressure gradient in the sound field results from the forces necessary to accelerate the "air particles" (F = ma), with the density of the air ρ _{0 being} the acceleration according to equation

is set, where
the sound pressure gradient grad p is detected by the two mounted in the distance .DELTA.x trained as microphone capsules pressure microphones, wherein for the discrete microphone distance .DELTA.x the condition is met, that the sound pressure gradient dp / dx by the sound pressure difference quotient .DELTA.p / .DELTA.x approximately

let represent, being usually a distance from Δx ≤ λ 6 is sufficient for the highest signal frequency, and
whereby, by temporal integration of the sound pressure difference, the sound velocity is calculated from the equation [V] according to the following equation:

and with the sound pressure p between the two pressure microphones in the microphone capsules

and the sound velocity v the impedance Z of individual sound field components is calculated.

By a digital signal processing, the microphone signals in their spectral components decomposed and from the analysis result the direction and determines the distance of individual sound field components to the sound source, being from the information about the distance and the direction the individual sound field components, the signal components unwanted Sound sources suppressed or particularly desired Signal components are highlighted.

The Equality and the differences between the microphone signals decide about which signal analysis method the signal components be separated from each other.

The following first signal analysis method can be used:
The signals of the sound velocity are dependent on the angle, wherein by level comparison with the angle-independent sound pressure signal, a separation of the signal components from the front and from the side is performed and the individual signals are broken down into their spectral components and evaluated depending on the direction or frequency depending on the frequency band.

The following second signal analysis method can be used:
The signals differ in their transit time between the individual microphone capsules, whereby by a Cross-correlation, the delay difference is determined, wherein a temporal structure of the signals is provided to cause a signal separation.

The following third signal analysis method can be used:
The coherence of the signal components determines whether the signals are dominated by direct sound or by disturbing diffuse reverberation.

The following fourth signal analysis method can be used:
A phase comparison between sound pressure and sound velocity distinguishes between plane and standing waves, whereby in a plane wave, in direct sound, the phase angle between sound pressure and sound velocity is 0 degrees and in a standing wave there is a phase angle of 90 degrees.

A Tightening of the directional characteristic over the Hypercardioid can only do so by analyzing the signals and the separation the signals are achieved in individual components.

The Separation of the signals can be time or frequency be performed.

The Sound incidence direction of individual signal components can be analyzed by signal analysis be determined.

By a subsequent directional rating Single signal components can be amplified or attenuated become.

With The microphone according to the invention can simultaneously for sound pressure the sound velocity are recorded, being off a comparison between sound velocity level and sound pressure level a determination of the distance of the microphone to the sound source performed can be.

at multiple sound sources with digital signal processing the microphone signals are decomposed into their spectral components and these are evaluated according to the determined distance to the sound source.

The Microphone signals from sound sources may be in close range of the microphone of signals from sound sources larger Distance to be separated.

With The microphone provided with two microphone capsules are the hardware ones Conditions created, at the same time sound pressure and sound pressure difference take. From these two sizes can in a subsequent signal processing the impedance of the individual Sound field components are calculated and according to their impedance be separated from each other, so that out of dependence the impedance of the distance, the distance of the sound source can be determined by the microphone.

further developments and further embodiments of the invention are in subclaims specified.

The Invention is based on an embodiment by means of explained in more detail several drawings.

It demonstrate:

1 a complete microphone system with holding device according to the prior art,

2 a microphone with two microphone capsules and outgoing terminals according to the prior art after 1 and

3 an impedance-distance characteristic of the acoustic impedance sensor.

In 1 and 2 is a microphone 1 with distance-dependent selectivity with at least two microphone capsules 3 . 4 in a housing 2 shown.

According to the invention, a sound impedance sensor is additionally integrated in the microphone, via which individual sound field components can be determined in their distance and direction to at least one sound source, wherein the magnitude and the phase of the sound impedance indicate at what distance r the microphone 1 is located from the sound source, where the sound impedance as a vectorial magnitude the direction of the microphone 1 indicating incident sound waves, wherein the acoustic impedance sensor with a processor in the form of a digital gnalprozessors for signal processing and distance determination is in communication.

• – nur der Schalldruck (Kugel) oder
• – nur die Schallschnelle (Acht) oder
• – Schalldruck minus Schallschnelle (Niere nach hinten).

In the microphone 1 already takes place a first analog signal preprocessing, wherein at a first output of the microphone 1 always the sum of the signals of sound pressure and sound velocity (kidney forward) is present and on a second output contrast manifold configuration, optional

• - only the sound pressure (sphere) or
• - only the speed of sound (Eight) or
• - Sound pressure minus sound velocity (kidney to the back).

• – eine kontinuierliche Einstellung der Richtcharakteristik zwischen Kugel, breite Niere, Niere, Superniere, Hyperniere und Acht,
• – eine Drehung der Nullstellen im Richtdiagramm auf unerwünschte Störgeräusche,
• – eine Veränderung der Übertragungsfunktion des Mikrofons wahlweise Linearisierung der Frequenz- und Phasengänge,
• – eine Klangveränderung durch nichtlineare Übertragungsfunktionen z. B. durch die nichtlineare Kennlinie einer Vakuumröhre oder Berücksichtigung der Hysteresiskurve eines Ausgangstransformators und
• – eine Analyse der Schalleinfallsrichtung und Bewertung der Mikrofonsignalanteile je nach Schalleinfallswinkel.

By post-processing of the microphone signals with a digital signal processor - DSP - can be realized either:

• A continuous adjustment of the directional characteristic between sphere, broad kidney, kidney, supercardioid, hypercardioid and eight,
• A rotation of the zeros in the directional diagram to unwanted noise,
• A change in the transfer function of the microphone optionally linearization of the frequency and phase responses,
• A sound change due to non-linear transfer functions z. B. by the non-linear characteristic of a vacuum tube or taking into account the hysteresis of an output transformer and
• - An analysis of the direction of sound incidence and evaluation of the microphone signal components depending on the sound incidence angle.

• – Ermittlung des Schalldrucks,
• – Ermittlung der Schallschnelle indirekt über den Schalldruckgradienten durch Berechnung,
• – Berechnung der Impedanz aus Schalldruck und Schallschnelle,

wobei aus einem Vergleich zwischen Schallschnellepegel und Schalldruckpegel eine Abschätzung der Entfernung des Mikrofons zur Schallquelle durchgeführt wird.The inventive method for processing measured sound signals for determining the distance of sound sources by means of a microphone 1 has the following steps:

• - determination of the sound pressure,
• - determination of the sound velocity indirectly via the sound pressure gradient by calculation,
• - calculation of the impedance from sound pressure and sound velocity,

wherein an estimate of the distance of the microphone to the sound source is made from a comparison between sound velocity level and sound pressure level.

in the Generally it is known from the technical acoustics that in an acoustic wave in addition to the sound pressure p and a sound velocity v → present is.

The Invention uses the existence of the two sizes out.

The sound pressure p decreases with a distance radiator with the distance r from the sound source according to equation

On the other hand, the sound velocity v decreases with its distance r to the sound source according to the equation

als Funktion der Entfernung r, wie in 3 betrachtet, müssen zwei Bereiche unterschieden werden:

• 1. kr < 1 Nahbereich N und
• 2. kr > 1 Fernbereich F

Will the specific impedance

as a function of the distance r, as in 3 considered, two areas have to be distinguished:

• 1. kr <1 near-field N and
• 2. kr> 1 long range F

At close range N, the following equation applies: Z = jσ 0 ckr. [III]

The impedance Z is dependent on the distance r to the sound source. In the vicinity grows | Z | with increasing distance to the sound source proportional to the distance r. In the impedance-distance characteristic is a rising straight line available.

The Impedance is purely imaginary.

If the distance r reaches the distance in the range around kr = 0, it completes in 3 a change in the far range F.

In the far range F applies according to equation

The Impedance is real. In the impedance-distance characteristic is a constant straight line parallel to the r-coordinate.

One Microphone, which in addition to the sound pressure and the impedance of the sound field recorded, requires the actual sound pressure sensor another Sensor for the speed of sound. Microphones that speed the sound It is very difficult to realize in practice. Therefore, the speed of sound is usually over indirectly determines the sound pressure gradient.

The sound pressure gradient in the sound field results from the forces necessary to accelerate the "air particles" (F = ma). With the density of air ρ ₀ , the acceleration becomes equation

darstellen lässt. In der Mikrofonpraxis reicht dazu meist eine Distanz von Δx ≤ λ6 für die höchste Signalfrequenz aus.The sound pressure gradient grad p can be detected by the two pressure microphones mounted at the distance Δx. For the discrete microphone distance Δx, the condition must be maintained that the sound pressure gradient dp / dx approximates by the sound pressure difference quotient Δp / Δx

let represent. In the microphone practice, this usually lasts a distance of Δx ≤ λ 6 for the highest signal frequency.

By temporal integration of the sound pressure difference can be the speed of sound can be calculated from the equation [V] according to the following equation.

und der Schallschnelle v kann die Impedanz Z einzelner Schallfeldanteile berechnet werden.With the sound pressure between the two pressure microphones in the microphone capsules

and the sound velocity v, the impedance Z of individual sound field components can be calculated.

in the The field of microphone technology has become the digital signal processing not yet enforced. First microphones with integrated digital signal processor (DSP) are known, but the DSP has in these microphones in first and foremost the task, the large dynamic range, the classic analog microphones have, in a qualitatively equivalent to convert digital data stream. The best available Analog-to-digital converters (ADC) have a signal-to-noise ratio of about 120 dB, which is not sufficient for high quality microphones. Therefore, the large level range of analog microphones, today up to more than 150 dB, especially with measuring microphones can range to two or more ADCs in their level range and charged to each other via a DSP.

• – nur der Schalldruck (Kugel)
• – nur die Schallschnelle (Acht)
• – Schalldruck minus Schallschnelle (Niere nach hinten).

The two-channel microphone UM930-TWIN has two microphone capsules mounted at a distance of Δx. The signals of both microphone boxes are initially available analogously at two outputs in parallel. For design reasons, it is provided that not the primary sound pressure signals the outputs are supplied, but takes place in the microphone, a first analog signal preprocessing. Thus, the sum of the signals of sound pressure and sound velocity (kidney forward) is always present at the first output of the microphone. On the other hand, the second output can be configured in many ways. For example:

• - only the sound pressure (sphere)
• - only the speed of sound (eight)
• - Sound pressure minus sound velocity (kidney to the back).

By the "accounting" of the capsule signals in the microphone according to the classical method of adding weighted microphone signals the user also has two directional characteristics without DSP at the same time to disposal.

• – eine kontinuierliche Einstellung der Richtcharakteristik zwischen Kugel, breite Niere, Niere, Superniere, Hyperniere und Acht,
• – eine Drehung der Nullstellen im Richtdiagramm auf unerwünschte Störgeräusche,
• – eine Veränderung der Übertragungsfunktion des Mikrofons z. B. Linearisierung der Frequenz- und Phasengänge,
• – eine Klangveränderung durch nichtlineare Übertragungsfunktionen z. B. durch die nichtlineare Kennlinie einer Vakuumröhre oder Berücksichtigung der Hysteresiskurve eines Ausgangstransformators und
• – eine Analyse der Schalleinfallsrichtung und Bewertung der Mikrofonsignalanteile je nach Schalleinfallswinkel.

Only by the post-processing of the microphone signals with a DSP numerous new possibilities become realizable. For example:

• A continuous adjustment of the directional characteristic between sphere, broad kidney, kidney, supercardioid, hypercardioid and eight,
• A rotation of the zeros in the directional diagram to unwanted noise,
• - A change in the transfer function of the microphone z. B. linearization of the frequency and phase responses,
• A sound change due to non-linear transfer functions z. B. by the non-linear characteristic of a vacuum tube or taking into account the hysteresis of an output transformer and
• - An analysis of the direction of sound incidence and evaluation of the microphone signal components depending on the sound incidence angle.

By the signal processing according to the invention is intended to be Separation of signal components from spatially different arranged sound sources can be achieved. This task is focused only on microphones whose mechanical dimensions are small compared the wavelength are.

The The sound signals are recorded with the two-channel microphone UM930-TWIN. The signal processing is done with DSP. Therefore An evaluation board is also available.

• 1) Die Signale der Schallschnelle sind in ihren Beträgen winkelabhängig. Durch Pegelvergleich mit dem winkelunabhängigen Schalldrucksignal kann eine Trennung der Signalanteile von vorn und von der Seite erfolgen. Zweckmäßig ist es, die einzelnen Signale in ihre spektralen Anteile zu zerlegen und je nach Frequenz oder Frequenzband richtungsabhängig zu bewerten.
• 2) Die Signale unterscheiden sich in ihrer Laufzeit zwischen den einzelnen Mikrofonkapseln. Durch eine Kreuzkorrelation kann die Laufzeitdifferenz bestimmt werden. Die zeitliche Struktur der Signale ist dafür verantwortlich, ob eine Signaltrennung möglich wird.
• 3) Über die Kohärenz der Signalanteile kann ermittelt werden, ob die Signale vom Direktschall oder vom störenden diffusen Nachhall dominiert werden.
• 4) Durch Phasenvergleich zwischen Schalldruck und Schallschnelle kann zwischen ebenen und stehenden Wellen unterschieden werden. In einer ebenen Welle, Direktschall, ist der Phasenwinkel zwischen Schalldruck und Schallschnelle 0 Grad. Dagegen verursachen stehende Wellen einen Phasenwinkel von 90 Grad.

The equality and the differences between the microphone signals determine which signal analysis method the signal components can be separated from each other, whereby the following signal analysis methods can be used:

• 1) The signals of the sound velocity are angle-dependent in their amounts. By level comparison with the angle-independent sound pressure signal, the signal components can be separated from the front and from the side. It is expedient to decompose the individual signals into their spectral components and to evaluate them depending on the direction of the frequency or frequency band.
• 2) The signals differ in their transit time between the individual microphone capsules. Cross-correlation can be used to determine the transit time difference. The temporal structure of the signals is responsible for whether a signal separation is possible.
• 3) The coherence of the signal components can be used to determine whether the signals are dominated by direct sound or by disturbing diffuse reverberation.
• 4) By comparing the phase between sound pressure and sound velocity it is possible to differentiate between plane and standing waves. In a plane wave, direct sound, the phase angle between sound pressure and sound velocity is 0 degrees. In contrast, standing waves cause a phase angle of 90 degrees.

In summary can be found that the combination of two or more channels Microphones in connection with digital signal processing numerous new possibilities the recording quality of language opened to improve music. The setting of the directional characteristic through linear operations does not pose any problems. A tightening the directional characteristic beyond the hypercardioic succeeds only by analyzing the signals and separating the signals into individual ones Components. The separation of the signals can be temporal or frequency respectively. The sound incidence direction of individual signal components can be determined by signal analysis. By a subsequent directional evaluation can be individual signal components strengthened or dampened.

From a point sound source, the sound pressure decreases with the distance one through r. On the other hand, the sound velocity decreases with one by r square until the sound pressure level equals the sound velocity level. If the sound velocity is recorded with a microphone at the same time as the sound pressure, a comparison of the sound velocity level with the sound pressure level can be used to estimate the sound pressure level Distance of the microphone to the sound source done. In the case of several sound sources, the microphone signals can be decomposed into their spectral components with digital signal processing and these can be evaluated according to the determined distance to the sound source. The microphone signals from sound sources in the vicinity of the microphone can thus be separated from signals from sound sources from a greater distance.

1

microphone

2

casing

3

first microphone capsule

4

second microphone capsule

N

post set

F

remote area

r

Distance / distance

Z

impedance

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Fellbaum, K .: Proceedings of the 18th Conference ESSV2007 Cottbus [0004]
• - Görne, T .: Microphones in Theory and Practice, 1994, Elektor-Verlag GmbH Aachen [0005]
• - Eargle, J .: The Microfone Book, 2001, by Butterworth-Heinemann [0005]

Claims (18)

Microphone ( 1 ) with distance-dependent selectivity with at least two microphone capsules ( 3 . 4 ) in a housing ( 2 ), characterized in that in the microphone additionally an acoustic impedance sensor is integrated over the individual sound field components in their distance and direction to the sound source can be determined, the amount and the phase of the sound impedance indicate at which distance the microphone is from the sound source, said , the acoustic impedance as a vector quantity indicates the direction of the sound waves incident on the microphone, the acoustic impedance sensor being in communication with a processor in the form of a digital signal processor for signal processing and distance determination. Microphone according to claim 1, characterized, that already in the microphone a first analog signal preprocessing takes place wherein at a first output of the microphone always the sum of Signals of sound pressure and sound velocity (kidney forward) is applied and configured differently on a second output becomes, - only the sound pressure (sphere) or - just the Sonic Speed (Eight) or - sound pressure minus Sonic speed (kidney to the rear). Microphone according to claim 1 or 2, characterized, that by editing the microphone signals with a DSP optional can be realized: - a continuous adjustment the directional characteristic between sphere, broad kidney, kidney, supercardioid, Hypercardioid and eight, - a rotation of the zeros in the directional diagram to unwanted noise, - one Change the transfer function of the microphone optional linearization of the frequency and phase responses, - one Sound change due to non-linear transfer functions, z. B. by the non-linear characteristic of a vacuum tube or taking into account the hysteresis curve of an output transformer and An analysis of the sound incidence direction and Evaluation of the microphone signal components depending on the sound incidence angle. Method for processing measured sound signals for determining the distance of sound sources by means of a microphone according to claims 1 to 3, marked by following steps: - determination of the sound pressure, - Detection the speed of sound indirectly over the sound pressure gradient by calculation, - Calculation of the impedance from sound pressure and sonic speed, being from a comparison between sound velocity levels and sound pressure level an estimate of the distance of the Microphones to the sound source is performed. A method according to claim 4, characterized in that the sound pressure gradient in the sound field from the forces that are necessary for the acceleration of the "air particles" (F = ma), resulting, with the density of the air ρ _0, the acceleration according to equation

is determined, wherein the sound pressure gradient grad p is detected by the two mounted in the distance .DELTA.x trained as microphone capsules pressure microphones, wherein for the discrete microphone distance .DELTA.x the condition is met that the sound pressure gradient dp / dx by the sound pressure difference quotient approximate

can represent, where usually a distance of Δx ≤ λ 6 is sufficient for the highest signal frequency, and wherein by temporal integration of the sound pressure difference, the sound velocity is calculated from the equation [V] according to the following equation:

and with the sound pressure p between the two pressure microphones in the microphone capsules

and the sound velocity v the impedance Z of individual sound field components is calculated. Method according to claim 4 or 5, characterized that by digital signal processing the microphone signals in their spectral components decomposed and from the analysis result the direction and determines the distance between individual sound field components to the sound source be, taking from the information about the distance and the direction of the individual sound field components, the signal components suppressed or undesirable sound sources desired signal components are highlighted. Method according to one of claims 4 to 6, characterized in that the equality and the differences decide between the microphone signals over, after which signal analysis method separates the signal components from each other become. Method according to claim 7, characterized, that the following signal analysis method is used: The signals the speed of sound are dependent on the angle, wherein by level comparison with the angle-independent sound pressure signal a separation of the signal components carried out from the front and from the side is and where the individual signals in their spectral components disassembled and dependent on the frequency or frequency band depending on the direction be rated. Method according to claim 7, characterized, that the following signal analysis method is used: The signals differ in their transit time between the individual microphone capsules, wherein determines the transit time difference by a cross-correlation is, with a temporal structure of the signals provided for it is to bring about a signal separation. Method according to claim 7, characterized, that the following signal analysis method is used: about the coherence of the signal components is determined as to whether the signals dominated by direct sound or disturbing diffuse reverberation become. Method according to claim 7, characterized, that the following signal analysis method is used: Through a Phase comparison between sound pressure and sound velocity is between plane and standing waves distinguished, being in a plane Wave, with direct sound, the phase angle between sound pressure and Sonic speed is 0 degrees and in a standing wave a phase angle of 90 degrees is present. Method according to one of the preceding claims, characterized in that a tightening of the directional characteristic over the hypercardioid only by analyzing the signals and the separation the signals into individual components. is reached. Method according to one of the preceding claims, characterized in that the separation of the signals in time or Frequency is performed. Method according to one of the preceding claims, characterized in that the sound incidence direction of individual Signal components is determined by signal analysis. Method according to one of the preceding claims, characterized in that by a subsequent directional Evaluation of individual signal components amplified or damped become. Method according to one of the preceding claims, characterized in that the sound velocity is simultaneously recorded with a microphone to the sound pressure, wherein a comparison of the sound velocity level with the sound pressure level, a determination of the distance (r) of the microphone ( 1 ) is performed to the sound source. Method according to one of the preceding claims, characterized in that at several sound sources with digital Signal processing the microphone signals in their spectral components disassembled and these according to the determined distance be evaluated to the sound source. Method according to one of the preceding claims, characterized in that the microphone signals from sound sources in the near range of the microphone of signals from sound sources larger Distance to be separated.