EP4331237A1 - Microphone array - Google Patents

Abstract

Microphone arrays contain multiple microphone capsules, the output signals of which are electronically connected together in order to capture sound in a directed manner. The direction and frequency properties of the microphone array are based on the number and positions of the microphone capsules. The aim of the invention is to provide a microphone array which is as small as possible and comprises only a few microphone capsules while still having a substantially uniform direction and frequency dependency over a vocal frequency range and which has a scalable size and is robust against a slightly incorrect positioning of the capsules. This is achieved in that fifteen or twenty-one microphone capsules (K15,11 - K15,35, K21,11 - K21,37) are arranged on a support (T, T') such that the microphone capsules lie on three identical branches, each of which is rotated relative to the other branches by 120°, in such a manner that the same number of microphone capsules lies on each branch. In a flat isometric coordinate system with three axes (L0, L1, L2), each of which is rotated relative to the other axes by 120° and which form an L2 grid of equilateral triangles, each of the microphone capsules lies on a corner of a triangle of the L2 grid.

Description

Sennheiser electronic GmbH & Co. KG Am Labor 1, 30900 Wedemark,

microphone array

The invention relates to a microphone array, in particular an arrangement of a plurality of microphone capsules which interact as an array for recording sound.

background

Microphone arrays are often used, for example, for beamforming, noise suppression or for acoustic source searches. They contain multiple microphone capsules whose output signals are electronically interconnected to work together to pick up sound in a directed manner. A preferred direction can be generated by the type of interconnection, in which the sensitivity of the microphone array for audio recordings is particularly high. Due to the electronic combination of the individual microphone signals, this preferred direction can be set electronically, which means that the preferred direction can be changed with a very short response time. However, a microphone array does not necessarily have good directivity for all directions, but often has one or more fixed preferred directions that depend on the arrangement of the microphone capsules. In addition, microphone arrays do not have the same effect for all frequencies, but show a frequency dependency. This depends, among other things, on the distances between the microphone capsules. A very important aspect of a microphone array is therefore the geometric arrangement of the microphone capsules on the microphone surface: With a fixed number of microphone capsules, they should cover as many inter-element distances as possible, i.e. distances between individual microphone capsules of an array, in as many different directions as possible.

There are different strategies regarding the type, number and positioning of the microphone capsules. A large number of microphone capsules are often combined with one another, for example for microphone arrays that can be mounted on room ceilings, in order to be able to record as many different preferred directions and a specific frequency range as possible. This is often the range of speech frequencies, eg 100Hz-10kHz. Typical procedures in this field are heuristic and therefore very complex searches by "trying out" all conceivable, analytically describable manifolds, such as lines, circles, spirals, etc. and numerical simulation.

For example, in US Pat. No. 6,205,224 B1, at least 63 sensor elements such as antennas or microphone capsules are arranged on concentric circles and, at the same time, on spirals in order to enable largely direction-independent and broadband detection with high directivity. The directional and frequency properties of a sensor arrangement are represented by means of a so-called coarray, which shows inter-element distances and the direction of these distances. In US2013/0101141 A1, thirty microphone capsules are also distributed evenly over the surface of a hexagonal printed circuit board for direction-independent and broadband detection, several of which can then be interconnected. In US2016/0323668 A1 too, numerous microphone capsules are connected together to form a microphone array and are distributed largely evenly over a number of circuit boards. A central circuit board contains 64 microphone capsules, while each of 7 circuit boards arranged in a circle around it contains a further 8 microphone capsules, resulting in a total of 120 microphone capsules. In all of these cases, there is a high computational effort due to the large number of microphone signals and a large microphone array overall.

A strategy different from that in the documents mentioned is therefore to use as few microphone capsules as possible for an array. In order to reduce the noise in this case or to obtain a high signal-to-noise ratio (SNR), the microphone capsules must produce as little noise as possible, ie be of high quality. The electro-acoustic properties of all microphone capsules in an array must also be largely identical within tight tolerances. A number-theoretic approach to minimizing the number of microphone capsules and their positioning is pursued in DE10 2010 012388 A1 by positioning them on intersections of Golomb rulers. Although this leads to a reduction in the number of microphone capsules, it also results in a directional characteristic that is not uniform in all directions due to the asymmetrical distribution. In addition, the microphone capsules are distributed almost evenly over the entire surface. US Pat. No. 9,894,434 B2 describes a microphone array with 17 microphone capsules, which are arranged on the diagonals of a relatively large square area of approximately 60×60 cm. This size is typical for most of the arrays mentioned. Furthermore, most of the arrays mentioned have the problem that they are susceptible to even small incorrect positioning of the microphone capsules and cannot be scaled in size without disturbing non-linear effects occurring. In the field of seismology, investigations into sensor arrays have been carried out for a long time. The article "Array Design" by R. Haubrich in the "Bulletin of the Seismological Society of America", Vol.58, June 1968 describes how arrays for detecting seismic waves, ocean waves or electromagnetic radio waves are constructed with as few sensors as possible be able. The directional and frequency properties of different sensor configurations are assessed using coarrays. Various sensor configurations that are considered "perfect" or "optimal" according to this criterion are proposed, including isometric arrays whose sensors lie on the intersection points of an isometric coordinate system. Summary of the Invention

The invention is based on the object of specifying the smallest possible microphone array with as few microphone capsules as possible, but which is more robust against small incorrect positioning of the capsules, has a high and direction-independent directivity and a substantially uniform frequency dependence over a voice frequency range and can be used as a ceiling microphone. The object is achieved by a microphone array according to claim 1.

It has been found that the structures of some of the arrays of seismic sensors proposed by R. Haubrich many years ago are also suitable for arrays of microphone capsules. In particular, isometric arrays with fifteen or twenty-one microphone capsules have particularly good acoustic properties, such as good localization of sound sources and high directivity, as well as other advantages, such as low manufacturing costs. This applies even if the size of the arrays is scaled down according to the language frequencies to be recorded, so that smaller arrays than before are possible. According to the invention, a microphone array has a small number of microphone capsules, in particular fifteen or twenty-one microphone capsules, and a circuit arrangement which is connected to the microphone capsules and is suitable for receiving the microphone signals and for their joint processing. The microphone capsules are arranged in a plane at specific positions on a carrier, namely on three similar branches, each with the same number of microphone capsules, with the branches being rotated by 120° relative to one another about a common center, and with, in a plane isometric coordinate system with three axes rotated by 120° against each other, which form a so-called L2 grid (L2 lattice). form equilateral triangles, each of the microphone capsules lies on a corner of a triangle of the L2 grid. The use of electret capsules is particularly advantageous here, since they typically have less intrinsic noise and lower intrinsic resonance and can record a higher sound pressure level range. However, other microphone capsules can also be used, eg MEMS.

An advantage of the array according to the invention is the good and uniform directivity over the entire relevant voice frequency range and in all directions, as can be calculated using coarrays. However, further advantages of the array according to the invention also include the relatively high level of robustness with regard to small incorrect positioning of microphone capsules, the small size of the array and therefore lower costs, and the relatively free possibility of size scaling.

Further advantageous embodiments are described in claims 2-11.

Brief description of the drawings

Further details and advantageous embodiments are shown in the drawings. In it shows

1 shows an arrangement of fifteen microphone capsules in a first embodiment of the invention;

2 shows an arrangement of fifteen microphone capsules in a second embodiment of the invention, which is mirror-symmetric to the first embodiment;

3 shows a coarray of an arrangement of microphone capsules according to the first or second embodiment;

4 shows an exemplary arrangement of printed circuit boards for an arrangement of the microphone capsules according to the first embodiment;

5 shows an arrangement of twenty-one microphone capsules in a third embodiment of the invention;

6 shows an arrangement of six microphone capsules in a fourth embodiment of the invention; and

7 shows a block diagram of a microphone array. Detailed description of the invention

1 shows, in a first embodiment of the invention, an arrangement of fifteen microphone capsules on a carrier T. The microphone capsules are arranged in three equal groups on congruent branches which are each rotated by 120° with respect to one another. For example, the first branch includes the capsules Kis,n, Kis,i2, Kis,i3, Kis,i4, and Ki5,is. The second branch includes the capsules Kis,2i - Kis,25 and the third branch the capsules Kis,3i - Kis,35. A Cartesian coordinate system X,Y is given for orientation, but the capsules lie on the intersection points of an isometric coordinate system which is also given in FIG. The isometric coordinate system has three axes L0, L1, L2 offset by 60° in one plane and consists of equilateral triangles. The sides of each of these triangles are each parallel to one of the axes L0, L1 or L2. The center of the entire arrangement, about which the three congruent branches are rotated relative to each other, is the zero point of the Cartesian coordinate system (i.e. X−0, Y=0). This is also at the same time the center of gravity of a middle triangle DM of the isometric coordinate system. As the reference point R of the isometric coordinate system, that corner of the central triangle DM is chosen arbitrarily, which is opposite its side parallel to the L0 axis.

Positions in the isometric coordinate system are specified as multiples of the side lengths of the equilateral triangles. For example, the upper right corner of the middle triangle DM is shifted from the reference point R only by one side in the direction of the L1 axis, which is given in isometric coordinates as position (L0,L1,L2) = (0,1,0). Correspondingly, the upper left corner of the central triangle DM is shifted from the reference point R by only one side length in the direction of the L2 axis, i.e. in isometric coordinates at the position (L0,L1,L2) = (0,0,1). Starting from the reference point R, the microphone capsules are in the following positions: In Cartesian coordinates (X, Y), depending on the scale, the following values result (e.g. for a side length of the triangles or isometric unit of length of 0.05 m, as shown in Fig. 1; unit: meter):

The scale should be chosen so that the smallest distance between two microphone capsules corresponds to the length of the sides of the triangles of the isometric coordinate system. The microphone array shown in FIG. 1 therefore has a diameter of approximately 35 cm.

The positions apply to the coordinate systems indicated in FIG. 1 and naturally deviate numerically when the coordinate systems or the array are rotated or when a different reference point is selected. Also, in the isometric coordinate system, the positions can be reached in different ways (since the axes are not orthogonal to each other), resulting in different but equivalent coordinates. For example, (1 ,1 ,0), (0,2,-1), (2,0,1), (3,-1 ,2) and other other coordinates define the same point. Some equivalent variants can be mapped onto the arrangement shown in FIG. 1 by rotation about the center point. 2 shows an arrangement of fifteen microphone capsules on a carrier T' in a second embodiment of the invention, which is mirror-symmetric to the first embodiment. It has the same acoustic and geometric properties as and is equivalent to the arrangement of the first embodiment. The mirror symmetry here is along the Y-axis. However, identical but rotated variants can be produced by mirroring the arrangement according to the first embodiment on any axis. Because the sensitivity of the array can be set largely uniformly in all directions, all of these variants are equivalent, ie result in the same coarray, and are therefore identical to either the first or the second embodiment. The isometric coordinate system can e.g. B. for a given arrangement or a given base area, in that three external positions lie on a straight line (e.g. Kis,n, Kis,i2, Kis,i3 or K'15,21 , K'15,22, K'15,23) which is parallel to one of the axes L0,L1,L2 of the isometric coordinate system. The distances between two adjacent positions in this Groups of three correspond to the side lengths of the triangles and thus to a unit of the isometric coordinate system.

3 shows the co-array of the arrangement, which is basically known from the theory of R. Haubrich, according to the first as well as the second embodiment, but adapted here for sound waves of speech sound or for speech frequencies. The points represent the relative position of two microphone capsules in the array to one another, i.e. the distances between them and the directions of these distances. In other words, each point in the coarray means that there is at least one pair of microphone capsules in the array whose relative position to each other is the same as the position of this coarray point relative to the coarray center CM. Each point thus also represents a possible direction of incidence and wavelength of sound waves, which can be processed by the microphone array with precise direction, i.e. can be used to locate a sound source and generate a directivity. It is important here that no holes occur in the coarray at points of the isometric coordinate system. This is given here. A hole in the coarray would mean that the microphone array would not be able to process sound waves with the appropriate direction of incidence and wavelength in the correct direction. However, it is generally not possible to infer a unique associated microphone arrangement directly from a coarray.

The coarray of the microphone arrangement according to the invention has the advantageous property that (at least in the interior of the coarray) each coarray point has six neighboring points arranged evenly around it and each at the same distance from itself. This allows the size of the microphone array to be scaled to the wavelengths of interest. The coarray points with the smallest distance to the origin (smallest inter-element distances) indicate the highest spatially unambiguously resolvable frequency before undersampling sets in, ie below the so-called "spatial aliasing". Accordingly, the coarray points with the greatest distance to the origin determine the performance of the beamformer for low frequencies. This allows the smallest inter-element spacing of the microphone array to be scaled to the smallest wavelength or highest frequency of interest while still maintaining dense coverage of all wavelengths for all larger inter-element spacings or longer wavelengths. For example, scaling the microphone array of the first or second embodiment to a diameter of 35 cm (L=5 cm) leads to a highest frequency (below spatial aliasing) of about 6.9 kHz. An advantage of the invention is that the microphone capsules are not evenly distributed over the entire area of the array, but form groups. This means that relatively large parts of the area do not have to be covered by circuit boards or printed circuit boards for contacting the capsules. In particular, it is not necessary to provide a circuit board or group of circuit boards in the size of the entire arrangement. This further reduces the production costs for the array, which are relatively low simply because of the small number of microphone capsules, and its weight. In addition, due to the distribution of the microphone capsules over three congruent branches, the same circuit boards can also be used for each branch. FIG. 4 shows an exemplary arrangement of three identical circuit boards P1, P2, P3 for an arrangement of the microphone capsules according to the first embodiment. The circuit boards P1-P3, each containing five microphone capsules of a branch, are rotated by 120° and arranged on a carrier. Other components such as a processing unit with one or more processors, AD converters, etc. can also be arranged on these boards. In particular, it is also possible to accommodate at least some of these further components on an additional circuit board (not shown), which is located in the middle and is connected to the capsule-carrying circuit boards P1-P3. Another advantage of this arrangement is that there is no microphone capsule in the middle, so there is enough space for a central circuit board. As a result, no stacking of circuit boards is necessary in this area, which would make the array thicker, more complex to manufacture and therefore more expensive. In addition, the fundamentally symmetrical design ensures that the center of gravity of the entire array is in the middle, which makes assembly easier. In addition, it is possible to replace each of the three boards P1-P3 with, for example, two sub-boards P1 I, P12, P2I, P22, P3I, P32 in order to further reduce the overall board area. This is advantageous when the total area of the array and thus the (sub)boards is large compared to the area required for the components. Here, too, at least three sub-boards are the same, e.g. B. P1i, P2i and P3i. Depending on the space requirements of the other components, it is possible that the boards (or at least the capsule-carrying boards) make up less than half of the total area of the array.

5 shows an arrangement of twenty-one microphone capsules in a third embodiment of the invention. The same applies to this embodiment as to the first and second embodiments described above, in particular it has similar advantages. However, the quality of the sound recording due to the larger Number of microphone capsules can be even better. Starting from the reference point R, which is defined as described above, and with the coordinate systems given in Fig. 5, the microphone capsules are in the following positions (whereby equivalent variants can also be generated here by mirroring on an axis and/or rotation):

The microphone capsules can be distributed very compactly, for example on two circuit boards per branch. A possibility for one of the circuit boards P21, 1 with five capsules K21.11-K21, 15 of the first branch is shown in FIG. The other two capsules K21, ie, K2i, 17 are close together and can therefore also be mounted very compactly on a second circuit board (not shown). The necessary additional electronic components (processor, AD converter, etc.) can be accommodated on one of the two circuit boards and/or on a possible additional, central circuit board (not shown) in the middle of the array. In this case, too, the other two branches are congruent, each rotated by 120° and can use boards of the same type (i.e. boards with the same layout) as the first branch. A possible central board can be shared. In this embodiment, too, it is possible that at least the circuit boards carrying the capsule make up less than half of the total area of the array (depending on the space required by the other components).

It should be noted that only a relative scale is given in FIG. 5 . This results from the fact that the arrays according to the invention (in all embodiments) are scalable in size without the occurrence of disruptive and difficult-to-calculate non-linear effects. For the embodiment shown in FIG. 5, the radius r _max of the outermost capsules is about L*6.11, where L is the side length of the isometric triangles, and the maximum inter-element spacing is about dmax = L*11.79. For example, with a scale of L=5 cm and a circular shape of the array, a diameter D of about 61.1 cm (dmax=58.95 cm) results, with a scale of L=4 cm, a diameter D of approx. 48.9 cm (dmax = 47.16 cm) and with a scale of L=3.5 cm a diameter D of approx. 42.8 cm (dmax = 41.27 cm). Conversely, the diameter of the array or the maximum inter-element spacing can be specified. For example, for an array diameter of about 55 cm, the scale L=4.5 cm must be chosen, and a maximum inter-element distance of eg dmax=40 cm results in about L=3.39 cm. Arrays of different sizes do not fundamentally differ in their frequency response, only the frequency range is slightly shifted. As is well known, the maximum inter-element spacing is important for locatability of sound sources and generation of directivity at low frequencies, while the minimum inter-element spacing (ie, scale L) is important for locatability and generation of directivity at high frequencies. Overall, depending on the embodiment, a scale of L=3-6 cm can be useful for speech frequencies, particularly in the range L=4-5 cm.

Corresponding relationships to scalability also apply to the other embodiments. For example, for the first and second embodiments (rounded) r max = L* _3.512 , D=L*7.024 and d max = L*6.557.

6 shows an arrangement of six microphone capsules in a fourth embodiment. This variant is particularly suitable for very small microphone arrays, which can be placed on a conference table, for example, while the embodiments described above are well suited for mounting on ceilings and walls. With this variant, the quality of the directivity and the localization of the sound sources is not as good as for the variants described above due to the small number of microphone capsules, but better than with other comparable arrangements with only six capsules. Starting from the reference point R, which is defined as described above, and with the coordinate systems given in Fig. 6, the microphone capsules are in the following positions (whereby equivalent variants can also be generated here by mirroring on an axis and/or rotation):

The microphone capsules can in this case be distributed on one board per branch or, due to the small overall size, all together on a single board Rb to be attached. This results in values of (rounded) r _max =L*1.527, D=L*3.054 and dmax = L*2.646.

FIG. 7 shows an exemplary block diagram of a microphone array, which can correspond to the first or second specific embodiment, for example. Other embodiments have a different number of microphone capsules per branch and/or a further subdivision of the boards of each branch into sub-boards. Three circuit boards P1, P2, P3 are each of identical construction and are rotated by 120° relative to one another on the carrier T, as shown in FIG. 1 and FIG. 4, respectively. Each of these boards contains the same number of microphone capsules Ki5,n-Ki5,i5, whose signals are given to respective analog-to-digital converters AD1-AD5, which are also located on the same board. As a result, the connection between the sensitive analogue microphone signal and the AD converter is very short. Optionally, individual digital processing blocks DP1-DP5 and/or common processing blocks SP1 can be present on the board, e.g. B. Processors. These can, for example, filter the digitized microphone signals. Digital output signals S1-S3 of the boards are given to a central board CP, where a processor unit performs the audio processing AP of the array, in particular the beamforming (beamforming). In addition, the array's audio processing AP can perform an acoustic search of a (main) sound source in real time in order to align the resulting array beam in the direction of the (main) sound source. To do this, it can optionally report signals SD1-SD3 back to the boards P1-P3. The resulting digital output signal of the array is output. An analog output signal can also be output as an option.

Due to the fact that all microphone capsules of a branch are mounted together on a circuit board or group of circuit boards and the positioning of the circuit boards on the carrier T can also take place with very little deviation, the position of the capsules relative to one another is very accurate. The carrier can, for example, comprise one or more fixed or reverberant plates made of metal, plastic or the like. In one embodiment, the carrier is a metal or plastic plate with holes through which the sound can reach the microphone capsules (in the case of the installed ceiling microphone, from the underside). In this case, the plate is sound-reflecting, so that the sound pressure at the microphone capsules is increased by up to 6 dB and the array works as a boundary layer microphone. On the other hand, the arrangement of the microphone capsules according to the invention allows small deviations from the specified position of, for example, up to 0.5 mm, which makes assembly easier and therefore cheaper. Conventionally, higher accuracy is required here in order to achieve a certain audio quality. the Microphone capsules can also be mounted on at least two groups of three similar (sub) boards PCB1 1 - PCB3. ₂ must be attached, with each branch having one circuit board from each group. Each (sub) board can contain at least two microphone capsules. A central area of the array between the three circuit boards or groups of circuit boards rotated relative to one another may contain no circuit board or a circuit board without a microphone capsule. Alternatively, an additional microphone capsule can be located in the middle, increasing the total number of capsules. The other positions remain unchanged. Thus, the modified first and second embodiments have sixteen microphone capsules, the modified third embodiment has twenty-two capsules, and the modified fourth embodiment has seven capsules. Such a central capsule has the advantage that it picks up a sound signal at the position of the highest sound pressure (dynamic pressure) and thus improves the directivity and the signal-to-noise ratio for the entire array. However, such an additional central capsule does not lie on a point of the L2 lattice and therefore leads to an asymmetrical co-array with holes, so that the array has a non-uniform directivity and is no longer easily scalable in size.

Electret capsules are particularly suitable as microphone capsules. Each microphone signal can be individually corrected or normalized, for example by means of filtering in the individual digital processing blocks DP1-DP5. The corresponding filter parameters depend on the properties of the respective microphone capsule, for example phase response and frequency response. Therefore, those electret capsules that have an internal memory element with corresponding correction data from which the filter parameters can be determined are particularly well suited. In addition, the filter parameters can be influenced by the examined or detected direction of the sound source (ie the localization of the sound sources or the beamforming). The localization of sound sources and the actual sound recording of the main sound source can be separate processes. It is possible to use only some of the microphone capsules for localization in order to keep the processing effort low, while all capsules are used for the actual sound recording. An advantage of the microphone arrays according to the invention is the good directivity and the high signal-to-noise ratio, ie good noise suppression. The fewer microphone signals available, the more difficult it is to suppress noise. However, this relationship is non-linear, also dependent on the position of the microphone capsules and is therefore difficult to predict. In particular, the microphone arrays according to the invention with fifteen or twenty-one microphone capsules show a good and uniform directivity over all relevant frequency components and directions of incidence of the sound, or very good noise suppression measured by the small number of microphone capsules, and are particularly well suited for ceiling microphones.

Claims

patent claims 1 microphone array with fifteen or twenty-one microphone capsules (Kis,n - Kis,35, K21.11 - K21.37); and a circuit arrangement (AD1 - ADs, AP) which is connected to the microphone capsules in order to receive microphone signals from the microphone capsules and which is suitable for joint signal processing of the microphone signals; wherein the microphone capsules are arranged in one plane on a support (T, T'), characterized in that the microphone capsules are arranged on the support at the following positions: on three identical branches, each with the same number of microphone capsules, the branches each rotating by 120 ° rotated against each other about a common center; and wherein, in a planar isometric coordinate system with three axes (L0, L1, L2) rotated by 60° relative to each other, forming an L2 grid of equilateral triangles, each of the microphone capsules lies on a corner of a triangle of the L2 grid. 2 microphone array according to claim 1, wherein the side length of each triangle of the L2 grid corresponds to the smallest distance between two of the microphone capsules. 3 microphone array according to claim 1 or 2, wherein the geometric center of the array is in the center of one of the triangles, which is the middle triangle (DM), and wherein positions in the isometric coordinate system are specified as multiples of the side lengths of the triangles in the format (L0, L1 , L2) and relative to a reference point (R) at the corner of the central triangle (DM) opposite its side parallel to the L0 axis. 4 Microphone array according to claim 3, wherein the microphone array contains fifteen microphone capsules (Kis,n - K1535) which, starting from the reference point (R), are arranged at the following positions, or at the corresponding positions of a mirror-image arrangement: - Ki5,i 1 =(0,4,0), K15,12=(1,3,0), Kis,i3=(2,2,0), Kis,i4=(0,2,2) , Kis,i5=(0,2,1 ), - Kl5.21=(0,0,-3), K15.22=(0,-1 ,-2), Kl5.23=(0,-2,-1), K15.24=(2.0 ,-1), K15,25=(1 ,0,-1), and - K15,31=(-3,0,1), Kl5,32=(-2,0,2), KIS,33=(-1 ,0,3), KIS,34=(-2,-1 ,0), KIS,35=(-2,0,0). 5. Microphone array according to claim 3, wherein the microphone array contains twenty-one microphone capsules (K21.11 - K2i,37) which, starting from the reference point (R), are arranged at the following positions, or at the corresponding positions of a mirror-image arrangement: - K _21,21 =(-5,-1 ,0), K _21,22 =(-4,-2,0), K _21,23 =(-5,0,1), K _21,24 =(0 ,-5 ,0) , K _21,25 =(0,-5,-1), _K21.26 =(-1,-2.0), K21.27=(1,-2.0); and - K21 .31 =(2,0,-4) , K21 ,3 ₂ =(3,0,-3), K _{2I ,33} =(0,0,-5), K21 ,3 ₄ =(5, 1,0), _K21,35 =(5,2,0) , _K21,36 ⁼ (3,0,0), K21,37 = (1,2,0). 6. microphone array according to any one of claims 1 to 5, wherein the microphone capsules on three identical, rotated by 120 ° to each other circuit boards (PCB1-PCB3) or Groups of boards are attached. 7. Microphone array according to claim 6, wherein the microphone capsules are mounted on at least two groups of three identical circuit boards (PCB1 1 - PCB3. ₂ ), each circuit board containing at least two microphone capsules and each branch having one circuit board in each group. 8. Microphone array according to claim 6 or 7, wherein a central area of the array between the three mutually rotated circuit boards (PCB1-PCB3) or groups of circuit boards contains no circuit board or a circuit board without a microphone capsule. 9. microphone array according to any one of claims 1 to 8, wherein the signal processing performs a beam forming (beam forming). 10. microphone array according to any one of claims 1 to 9, wherein the microphone array is suitable for mounting on a ceiling of a room; the support is a metal plate with a sound-reflecting surface; and each of the microphone capsules is attached to a hole in the metal plate, so that it picks up the sound through the hole. 11 . Microphone array according to one of Claims 1 to 10, the side lengths of the triangles of the L2 grating being in the range of 3 - 6 cm, in particular in the range of 4 - 5 cm.