A method for direction-dependent correction of the frequency response of an acoustic wavefront.

Abstract

The present invention relates to a method of operating and / or configuring a two-dimensional acoustic transducer assembly (1) comprising a plurality of individually controllable acoustic transducers (9), each of which generates superimposed elementary waves according to the principles of wavefield synthesis and / or according to beamforming methods to form at least one acoustic wavefront, the local propagation direction of the at least one acoustic wavefront being known or determinable at each transducer (9) of the transducer assembly (1).

Description

[Technical Field]

[0001] The proposed solution describes a method for direction-dependent correction of the frequency response of an acoustic wavefront generated in a two-dimensional acoustic transducer assembly according to the principles of wavefield synthesis, or beamforming method. Summary of the Invention [Means for solving the problem]

[0002] Using multiple, individually controlled acoustic transducers, it is possible to simultaneously radiate several acoustic wavefronts in different directions. A vector-based method known from German Patent Application DE 10 2021 207 302 A1 adapts the shape and level of each wavefront generated from multiple elementary waves to the audience area, thereby minimizing the excitation of undesirable reflections in the reproduction space, even under adverse acoustic conditions. This results in very high speech intelligibility throughout the entire audience area. Furthermore, because the signal level is adapted by the described method, very balanced sound pressure levels are achieved throughout the entire audience area, even when the audience area has an irregular shape and the listener's distance from the acoustic transducer surface varies greatly.

[0003] For this purpose, the delay times and levels of each of the acoustic transducers of the acoustic transducer assembly and the individual wavefronts are calculated separately. Mathematical methods for calculating the delay times are described, for example, in patent application DE 10 2021 207 302 A1. In one embodiment, each acoustic transducer of the acoustic transducer assembly is associated with a coordinate in the audience area. A vector calculation of the distance between the acoustic transducer and the associated point in the audience area allows, with appropriate level correction, to obtain a very uniform sound pressure distribution in the audience area for each individual input signal.

[0004] According to the principles of wavefield synthesis (AJ Berkhout, A Holographic Approach to Acoustic Control, J. audio Eng. Soc, Vol. 36, No. 12, 1988), multiple acoustic transducers generate a wavefront that achieves a very uniform level of high quality sound in a given audience area without excessive unwanted radiation on adjacent reflecting surfaces.

[0005] As the size of audience areas for major events increases, demands on sound systems increase. In many cases, the low directional radiation of sound waves means that sound pressure differences between individual audience stations are unacceptable, and reproduction, frequency response and speech intelligibility suffer from level reduction, airborne sound insulation and undesirable reflections.

[0006] For this reason, loudspeaker assemblies from several individual sound sources direct sound more strongly towards more distant audience areas. A typical application is the so-called line array, which is placed for example on the left and right of the upper part of the stage front. Its curvature is adapted to the audience area, so that the radiating wavefront in the elevation plane is directed towards the more distant audience areas. Around this part of the loudspeaker assembly, an approximately cylindrical wave is generated.

[0007] The surface area of ​​a cylinder increases linearly with its radius, so that the sound pressure decreases by 3 decibels for every doubling of distance.

[0008] In the lower region of the acoustic transducer assembly, the increasing curvature of the transducer surface results in a larger vertical opening angle. In this region, the wavefront is approximately a spherical segment. Here, the spherical surface, which increases quadratically with radius, causes a sound pressure drop of 6 dB with every doubling of distance. The rapid drop in nearby sound pressure and the resulting wider cylindrical shaft at greater distances significantly reduce the difference in sound pressure between the front and rear audience areas.

[0009] Recently, acoustic lines have also been employed with electronic control of individual acoustic transducers. Each transducer has its own amplifier controlled by a signal processor. Mathematical methods allow radiation to be adapted to the audience area much better than would be possible with mechanical placement of the individual acoustic transducers. The curvature of the acoustic transducer assembly can be simulated and adapted electronically according to Huygens' principle, with a small delay in the control of the individual transducers. However, with the available acoustic lines, these possibilities are limited to the elevation plane.

[0010] The directivity can also only be adapted in the elevation plane with this improved radiation, so the sound field can only be roughly tailored to a given audience area. In the azimuth plane, radiation is given only by the mechanical placement of the loudspeaker groups. Here, the audience area can only be adapted by selecting loudspeaker elements with wider or narrower horizontal directivity.

[0011] Loudspeaker fields, such as those available for audio reproduction according to the principle of wave field synthesis (e.g., WO2015036845A1), are much more flexible. Here, each acoustic transducer is operated with a separate final amplifier. According to Huygens' principle, the wavefront is constructed from the superposition of elementary waves from each acoustic transducer, which reconstructs a spherical segment of the wavefront of the real sound source. The center of this spherical segment is the virtual sound source of the wavefield synthesis. The limits of the spherical segment are determined by the size of the acoustic transducer field in relation to the position of the virtual sound source.

[0012] The individual acoustic transducers of the at least one acoustic transducer assembly radiate elementary waves during operation, which are superimposed to form a common wavefront. Whenever reference is made below to the radiation of elementary waves from an acoustic transducer, it is the acoustic center of the acoustic transducer that is meant.

[0013] The at least one acoustic transducer assembly and the audience area are associated with a common coordinate system, in particular a Cartesian coordinate system.

[0014] As will become apparent below, the coordinate system on the side of the at least one acoustic transducer assembly is particularly defined by a direction vector r i and a position vector s that determines the acoustic radiation from at least one acoustic transducer assembly. i The coordinate system thus links at least one acoustic transducer assembly with at least one audience region.

[0015] Position vector s i There is a spatial association between the position vector s and the physical location of the transducer. In the simplest case, the acoustic center of the acoustic transducer is i The acoustic transducer is located at the origin of the position vector s i If the acoustic center of the acoustic transducer is not located exactly at the intersection of the auxiliary grid, the resulting changes in delay time and level can be corrected by spatial interpolation or other methods. i can be stored, for example, in the form of a list.

[0016] By introducing a coordinate system, points in the audience area and points on at least one sound transducer assembly, and therefore indirectly also the sound transducer itself, can be simply geometrically related to one another, for example when calculating the distance from a sound transducer to a point in the audience area.

[0017] The method begins by relating points in a coordinate system to points in at least one audience region, and correspondingly generating a position vector r i Therefore, the position vector r i refers to a specific location within the audience area 3.

[0018] A position vector s that allows the position of each individual acoustic transducer to be determined indirectly or directly. i from the direction vector that determines the radiation direction of the wavefront within the area of ​​each acoustic transducer.

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[0019] Here, the position vector s i Depending on the spatial relationship between the transducer and the delay time τ j is determined and then used to emit acoustic elementary waves. j are respectively the local directions of the common wavefronts in the direction of the direction vector, in particular, the normalized direction vector

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[0020] Thus, each acoustic transducer of the at least one acoustic transducer assembly has a specific delay time τ j The delay time τ of the acoustic transducer is j determines the generation time of the elementary wave at the corresponding acoustic transducer. In particular, the delay time τ j can be determined for the input signal. In other words, each acoustic transducer has an individual delay time τ j Although the delay times of individual acoustic transducers may differ radically, some acoustic transducers may also be assigned the same delay time τ j It can also be operated with

[0021] The sum of the delay times at which the individual acoustic transducers of the acoustic transducer assembly are operated affects the shape of the common wavefront composed of the elementary waves generated by the individual acoustic transducers. In particular, the shape of the common wavefront depends on the delay time τ j can be determined by the sum of

[0022] In particular, a complex wavefront has a delay time τ j As a result, different delay times τ in the acoustic transducer assembly can be generated. jThis results in wavefronts of corresponding shapes, e.g., with different curvatures. The wavefronts formed by the elementary waves are not spherical segments, since they are generated by a virtual sound source using a two-dimensional wave-field synthesis acoustic transducer assembly. Depending on the shape and size of the supply area (i.e., at least one audience area), there will be areas of stronger curvature and areas of flatter curvature. In the direction of the farther away audience areas, the convex curvature of the wavefront is usually small, while the stronger the curvature in the direction of the front audience areas, the more rapidly the sound pressure level decreases with distance and the energy is distributed over a wider audience area.

[0023] Delay time τ of each acoustic transducer j can be determined so that the common wavefront fits the geometry of the audience area. In particular, the local direction of the wavefront is determined by the delay time τ j The irregularly shaped wavefronts created in this way can, in principle, be associated with the same number of grid points of the acoustic transducer assembly (i.e., a coordinate system within the domain of the acoustic transducer assembly), and therefore with the same number of acoustic transducers, with the same size of the audience area. In this respect, such wavefronts are fundamentally different from the spherical segments of point-like virtual sound sources of wavefield synthesis, where the audience surface served by the same number of acoustic transducers increases continuously with distance.

[0024] Each local direction of the common wave front at a location on the wave front represents the direction in which the common wave front propagates at the respective location. Each local direction of the common wave front can be represented by a direction vector perpendicular to the respective point on the common wave front. The direction vector represents the local direction of propagation of the common wave front as the wave front moves perpendicular to the direction vector.

[0025] The adaptation of the common wavefront to the geometry of at least one audience region is in each case determined by the position vector s i (which can be associated with individual wave transducers, for example) into the position vector r i to a position in the audience region corresponding to the normalized directional vector

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[0026] The acoustic transducers of at least one acoustic transducer assembly may be arranged on or within a plane. Alternatively, the acoustic transducers of the acoustic transducer assembly may be arranged on or within an at least partially curved surface. The assembly may be, for example, grid-like. In particular, the distance between the acoustic transducers may be uniform. For example, the distance in a first direction, particularly a vertical direction, and / or the distance in a second direction, particularly a horizontal direction, may correspond to each other, or a regular sequence of distance variables may be obtained. The geometry in or on which the acoustic transducers are arranged may be complex. For example, an acoustic transducer may be placed on a plane within an area, while other acoustic transducers of the same acoustic transducer assembly are placed on a curved surface. Also, different portions of the surface may have different radii of curvature.

[0027] Alternatively, the acoustic transducers of the at least one acoustic transducer assembly may be arranged in a three-dimensional region, in particular in space, and the individual acoustic transducer assemblies may be determined relative to a reference plane, e.g., a flat or curved surface, with at least some of the acoustic transducers of the at least one acoustic transducer assembly being arranged on the reference plane, and the positions of the remaining acoustic transducers of the at least one acoustic transducer assembly being determined by spatial offsets in the three-dimensional region.

[0028] Position vector s i Associated with the delay time τ j The operation of the acoustic transducer with the delay time τ j The delay time can be in the order of milliseconds. For adjacent acoustic transducers, the time difference is usually only a few microseconds, so the whole system requires a very stable system clock.

[0029] Additionally or alternatively, the delay time at which the acoustic transducer operates may be influenced mechanically or geometrically, for example, the delay time of an acoustic transducer may be controlled by the spatial offset of the acoustic transducer assembly relative to other acoustic transducers, particularly in the radial direction of the acoustic transducer assembly.

[0030] An audience area can have an at least partially planar or concave and / or at least partially convex shape. An audience area can be described as a continuous area or as a discontinuous area consisting of at least two continuous parts. Examples of an audience area consisting of several areas are the Great Hall of the Berlin Philharmonic, or an opera hall with several ranks. However, an audience area can also be represented by several coordinate points.

[0031] In the coordinate system, the position vector s associated with the acoustic transducer of the acoustic transducer assemblyi may generate a regular grid.

[0032] Additionally or alternatively, the position vector r i can generate a regular grid on a reference surface R associated with the audience region.

[0033] Each position vector s in the acoustic transducer array i Let r be the position vector i The association associating a point in the audience area corresponding to s can be determined by a connecting line from the acoustic transducer assembly to the audience area. In particular, the connecting line is a position vector s that cuts the audience area or a reference plane R associated with the audience area. i The position vector r obtained from the intersection of the ray with the audience area or a reference plane R associated with the audience area i can be associated with the acoustic transducer.

[0034] Additionally or alternatively, the level at which the acoustic transducers of the at least one acoustic transducer assembly are operated may be determined by a relative amplification factor, particularly in accordance with the provisions

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[0035] Relative Amplification Factor

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[0036] Furthermore, the proposed solution requires a delay time τ to sonify at least one audience area. j The delay time τ of an acoustic transducer assembly having a plurality of acoustic transducers j that generate elementary waves according to j This includes a method for determining

[0037] The method includes the steps of determining a coordinate system that at least one acoustic transducer assembly approximately describes as a reference plane S and an audience area approximately describes as a reference plane R; determining a position vector s on the reference plane S of the at least one acoustic transducer assembly, from which a position of the acoustic transducer of the at least one acoustic transducer assembly can be determined; and determining a normalized direction vector originating from the position vector s.

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[0038] In other words, the common wavefront is represented by the normalized direction vector

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[0039] For sound level adjustment, a relative amplification factor for at least some position vectors s

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[0040] The position vector S may correspond in whole or in part to the location of the acoustic transducers on the acoustic transducer assembly, and in either case, the physical location of the individual acoustic transducers within the at least one acoustic transducer assembly and the position vector s for establishing coordinates within the area of ​​the at least one acoustic transducer assembly. i There is a spatial relationship between

[0041] The number of position vectors S may correspond to or differ from the number of acoustic transducers in the acoustic transducer assembly. In particular, the number of position vectors S may be greater than the number of transducers on the acoustic transducer assembly.

[0042] The position vector S can represent the intersections of an auxiliary grid described on the reference plane S of at least one acoustic transducer assembly, although the position vector S need not lie at all intersections of the auxiliary grid. For example, the auxiliary grid can represent a rectangular plane.

[0043] The number of horizontal and / or vertical grid lines may correspond to the number of rows and / or columns of acoustic transducers in the acoustic transducer assembly, respectively, although the number of horizontal and / or vertical grid lines may be greater than the number of rows and / or columns of acoustic transducers in the acoustic transducer assembly.

[0044] The method may further comprise determining a position vector R on a reference plane R of the audience area, each of the position vectors R being associated with a position vector S. The association may be made by a connecting line from the position vector S to the position vector R, based on which the respective normalized direction vectors

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[0045] In one embodiment, the entire set of connection lines are such that they do not cross or intersect in pairs, in particular, no connection line crosses each other connection line.

[0046] The association of the position vector S with the position vector R can be performed automatically, in particular by means of a 3D CAD file of the audience area. This can be done according to a suitable mapping method. In particular, points and / or areas of the reference plane of the audience area, e.g. points and / or areas corresponding to areas of the audience area not hit by the common wavefront, can be omitted during the association.

[0047] The position vectors R can be uniformly distributed on the reference plane R of the audience area, which allows them to correspond to evenly distributed points within the audience area. The uniform distribution of points is ensured, for example, by the fact that two adjacent points are at the same distance from each other.

[0048] The reference plane R of the audience area may be represented by an auxiliary grid, and the position vector R may correspond at least in part to an intersection of the auxiliary grid.

[0049] Similarly, the reference plane R of the acoustic transducer assembly can be described by an auxiliary grid whose intersection points correspond at least in part to the position vector S. Such auxiliary grids are particularly important for numerical processing, since numerical integration can be easily performed on the auxiliary grid, for example, by the trapezoidal rule.

[0050] The auxiliary grid on the reference plane S of the at least one sound transducer assembly and the auxiliary grid on the reference plane R of the audience area may be interchangeable. In particular, they may have the same number of lines in the horizontal and / or vertical planes. By connecting the intersections of the auxiliary grids, a suitable connection can be established between the reference plane S of the at least one sound transducer assembly and the reference plane R of the audience area.

[0051] The reference surface S of at least one acoustic transducer assembly may be planar or may be at least partially curved, for example. In particular, the horizontal curvature of the reference surface S of the acoustic transducer assembly may be different from the vertical curvature.

[0052] In one embodiment, the reference plane S of the acoustic transducer assembly is parameterized by the coordinates s(u,v)=[x(u,v)y(u,v)z(u,v)], where u and v are real, continuous variables.

[0053] Each individual delay time τ of the acoustic transducer j j To determine the delay time τ(u,v), first a scalar function of the delay time τ(u,v) for a finite number of position vectors of the form s=s(u,v) may be determined, and then the delay time τ of the acoustic transducer j may be calculated. j The determination of can be done, at least in part, by interpolation of at least two values ​​of the form τ(u,v).

[0054] The delay time τ(u,v) is, in one embodiment, a discrete 2D vector field

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[0055] tangent vector s u and s v is the partial differential

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[0056] The value of the function τ(u,v) represents the delay time at the position vector s(u,v), which is the individual position s for each unique combination of parameters u and v. i Then the delay at the driver position can be determined by spatial interpolation.

[0057] The calculated time is then executed to the nearest sample time as predetermined by the overall system sampling frequency.

[0058] In detail, the desired delay time is described by a function τ(u,v), whose gradient is a two-dimensional vector field [Δ u τΔ v τ] and the component Δ u τ and Δ v τ is as given above. The wavefront can be thought of as a three-dimensional structure that associates with each grid intersection a height at this location. The gradient at that location is a vector that points in the direction of the maximum elevation. The magnitude of this vector indicates the maximum slope at this point.

[0059] The speed of sound c may be location dependent, for example, higher temperatures are common in higher regions of the sound propagation region, which affects the speed of sound. The speed of sound may also be location dependent, which is then included in the calculation.

[0060] Numerical integration methods can include the complex trapezoidal method, Simpson's method, Romberg's method, or more advanced inverse gradient methods.

[0061] If the reference plane S of the acoustic transducer assembly is parameterized by the function s(u,v)=[x(u,v)y(u,v)z(u,v)] as above, then the normal n to the reference plane S of the acoustic transducer assembly that can be used to determine the sound level correction is given by s = s(u,v) at the point s u and s v Cross product of n=s u ×s v where s u and s v is given by partial differentiation as above.

[0062] Embodiments will now be described, by way of example, with reference to the drawings in which: [Brief explanation of the drawings]

[0063] [Figure 1] An embodiment for operating an acoustic transducer assembly is described. [Figure 2] 1 illustrates a schematic diagram of a method for directionally dependent correction of frequency response. [Figure 3]1 illustrates a schematic diagram of a wavefront of a virtual sound source for wavefield synthesis in a two-dimensional acoustic transducer assembly. [Figure 4] 1 illustrates a wavefront schematic of a wavefront shape of a two-dimensional acoustic transducer assembly adapted to an audience area. [Figure 5] Determination of a normal vector on a curved reference surface of an acoustic transducer assembly is described. [Figure 6] The association of the auxiliary grid of the acoustic transducer assembly with the auxiliary grid in the audience area is described. [Figure 7] It describes the formation of local direction vectors of wavefronts that arise from the acoustic transducer into surrounding elementary waves and point to the audience area. [Figure 8] The formation of a normalized direction vector of length 1 is described. [Figure 9] An embodiment is described in which the audience region is divided into individual sub-regions with different signal content. [Figure 10] A matched acoustic transducer population for a non-variable audience area is described. [Figure 11] An embodiment is described having a mechanically curved acoustic transducer surface. [Figure 12] Illustrates the frequency response of the boofer (left) and tweeter (right) without signal processing, with and without a translucent plate. [Figure 13] The spatial transfer function of the MDI strong panel is explained. [Figure 14] The transfer functions of a 120° beam optimized at angles of 0°, 30°, and 60° are described. DETAILED DESCRIPTION OF THE INVENTION

[0064] In Figure 1, an embodiment of the method of [1] is represented simply as an example for the purposes of explanation. The method is based on the fact that each sound transducer 9 in the sound transducer assembly 1 is associated with a point in the audience area 3. The procedure is carried out separately for each sound transducer 9, for each intersection of the grid in the audience area 3, and for each input signal of the system that is to be reproduced simultaneously. Thus, the mathematical method described in [1] assigns, for each input signal, a delay time τ and a relative amplification factor τ to each sound transducer.

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[0065] The superposition of elementary waves with those of adjacent acoustic transducers creates each desired local direction in the wavefront. The local propagation directions combine to form a wavefront, the shape of which can be irregular depending on the shape and structure of the listener area. This is the only way to achieve level stability across a large, irregularly shaped audience area.

[0066] The individual input channels Ch 1 to Ch n are processed in the same way as their associated data, and the sum of all signals gives the contribution of each acoustic transducer to a wavefront that is radiated simultaneously in different directions and into different audience areas with independent signal content.

[0067] In the method according to [1], the local propagation direction vector d of each wavefront can also be obtained, from which the distance can be determined for each individual acoustic transducer. Thus, the system knows the path that the corresponding wavefront must travel from the acoustic transducer to the listener. The polar coordinates φ and θ (i.e., spatial / 3D polar or spherical coordinates) from which the local radiation direction of each individual wavefront is determined are also obtained from the calculation.

[0068] The proposed solution explains how the spectral balance of the spatial radiation of the acoustic transducer assembly 1 can be significantly improved.

[0069] In principle, the proposed solution can be used whenever the local radiation direction resulting from the superposition of elementary waves from surrounding loudspeakers is known for each radiating wavefront. This radiation direction is known from the direction of the vector d according to the method described in [1]. However, it may also be derived from the geometric position of the corresponding acoustic transducer relative to the virtual sound source from which the corresponding wavefront originates, or determined by other methods.

[0070] In addition to uniform level distribution, the goal of each audio reproduction is to maintain the audio spectrum throughout the entire audience area. However, in practice, several factors significantly hinder the achievement of this goal. First, the spatial radiation characteristics of the acoustic transducers used must be mentioned. Their diameter and other factors result in directional and frequency-dependent level variations, leading to position-dependent spectral errors in the reproduction area. Furthermore, grids or other structures upstream of the radiation, such as acoustically transparent LED walls as described in [2], can significantly alter the reproduction spectrally depending on the direction of radiation. In very large audience areas, airborne sound insulation, which depends on relative humidity, air pressure, and temperature, significantly limits reproduction, especially in the higher audio frequency ranges, as the distance from the acoustic transducer assembly increases. Furthermore, targeted, directional changes in the frequency response have not been possible until now, for example, to specifically design for the specific preferences of individual audience groups, to compensate for individual hearing loss, or to expand the artistic possibilities of sound field design.

[0071] An embodiment of the proposed solution, which takes the form of a method for correcting the direction-dependent frequency response of an acoustic wavefront generated by a two-dimensional acoustic transducer assembly according to the principles of wavefield synthesis, or beamforming, is illustrated in Fig. 2. This diagram is limited to exemplary signal processing for an individual acoustic transducer. The method shown in Fig. 2 can be applied to the method described in [1], for example, by adding software, if the hardware resources are sufficient for this purpose.

[0072] The signal lines of channels 1 to n transmit the input signals of the system to all acoustic transducer units and all modules. They can also be associated with individual groups of acoustic transducers provided for radiating different frequency ranges. In that case, a corresponding frequency response drop in the crossover range is already realized, and the total signal of all frequency ranges is already equal to the linear frequency response of the entire system in its main radiation direction.

[0073] After a delay by τ and a level adjustment by a relative amplification factor dn for each individual acoustic transducer, each input channel is fed to the sum before the signal controls the loudspeaker. The system's extensions for correcting the direction-dependent frequency response are added before the signal delay in each input channel for the corresponding acoustic transducer. The order in which subsequent corrections are performed is not important. Also, individual corrections can be omitted or additional corrections can be added.

[0074] In an exemplary representation, corrections for the direction-dependent frequency response changes of individual acoustic transducers are placed first in the signal path. As with other frequency response corrections, these are compensated for by forward corrections. For this purpose, the 3D polar coordinates of each acoustic transducer installed in the module are determined individually and stored in a low-reflection space. In principle, it is also possible to use manufacturer-provided half-space radiation data or measurement data for an infinite acoustic wall. However, due to the inhomogeneity of the module's acoustic wall surface, radiation into a flat acoustic wall differs significantly, especially when a multipath assembly is used.

[0075] The measurement data are stored in angular steps in a spherical coordinate system with a radius of 1, and the associated frequency response can be read from the memory obtained from the acoustic transducer using the polar coordinates φ and θ, which determine the local radiation direction of each wavefront. Thus, the data on the local direction of the wavefront from the relationship G(f,φ,θ), known from [1], is used to calculate the frequency response of the wavefront in the subsequent inverse filter G. invIn (f), a frequency response curve is provided that can correct as much as possible the frequency response error of the corresponding acoustic transducer in the local radiation direction of the corresponding wavefront.

[0076] At the second point in the signal path, compensation for an acoustic obstacle in the signal path is presented as an example. This can be a loudspeaker grid with a low-pass function and forming standing waves in the acoustic wall, or a perforated projection surface used as a projection surface in front of the acoustic transducer module. In practice, there are also much more complex requirements, such as larger projection surfaces with only local openings for the sound exit, or very complex and roughly structured obstacles such as the LED structure described in [2] in front of the acoustic transducer module.

[0077] Here too, the compensation is based on a forward correction of the acoustic transducers. In the case of the measurement of the polar radiation of the acoustic transducers, only the difference between the measurement of the individual acoustic transducers without an acoustic obstacle and the measurement of the polar radiation with a preceding obstacle is stored. A further step is similar to the correction of the acoustic transducers and involves the calculation of the function H inv (f) is compensated and normalized in the subsequent elements of the inverse filter.

[0078] The third correction element in the signal path serves to compensate for the airborne sound insulation within the signal path. Its influence on the frequency response depends on relative humidity (%), air pressure (kPa), and temperature (K), and increases with increasing distance from the sound transducer to the listener. In principle, a data set containing the values ​​could be created here as well, but each of the three factors mentioned changes the curve in a different way, and for this purpose, data sets for individual distance steps would need to be created for each of the values. Therefore, it is more appropriate to provide values ​​of relative humidity (%), air pressure (kPa), and temperature (K) valid for the entire system, calculate the resulting frequency course of the airborne sound insulation at 1 meter directly from the known mathematical relationship for a distance of 1 meter, and multiply this value by the distance from the sound transducer to the listener, which is known by the length of the vector d described in [1]. The resulting value A invUsing (f), the inverse filter then compensates for the airborne sound insulation of the relevant wavefront in the direction of the audience area.

[0079] To be able to calculate the compensation filters for each of the three filter blocks, the data must be preprocessed. First, the data is normalized to vary the overall amplitude in all directions by a fixed value to reach the desired level. The data is then regularized, which involves frequency limiting and spatially and spectrally smoothing the data. The degree of smoothing depends on the required quality of compensation and the available filter resolution. Finally, the normalized and regularized frequency response data for a given angle φ and θ (or d in the third block) is inverted to obtain the final inverse filter.

[0080] Because compensation can lead to undesirably high filter amplification at certain frequencies or in certain directions, the maximum amount of compensation is determined by the adjustment factor w G , w H , and w A may be limited by

[0081] For this purpose, a limit value for maximum compensation of, for example, +12 dB can be entered for the entire system. In principle, this limit value can also be adapted to the current level of the corresponding input signal, so that the maximum available headroom is always used for compensation.

[0082] For example, a reduction of less than one-third of the width of a narrowband frequency response, such as that caused by the directional null position of a sound transducer, is subjectively insignificant. This differs from a reduction in the entire high-frequency range, which can be clearly heard even at long distances, especially in dry ambient air. It is important here to make the most of the available headspace. One possibility for increasing it for more distant areas has already been described in patent specification [1]. As the distance from the sound transducer assembly increases, an audience area of ​​the same size is associated with more sound transducers. The described extension of the method described in [1] allows a very balanced level transition to be achieved over large, irregularly shaped audience areas without significant acoustic discoloration.

[0083] The described method allows for further refinements: as an example, the initially mentioned directionally dependent frequency response variations may be inserted as an additional correction factor in order to specifically design for the particular preferences of individual audience groups, to compensate for individual hearing loss, or to expand artistic possibilities.

[0084] Alternatively, the system can operate autonomously as individual modules with permanently programmed directional effects and permanently programmed direction-dependent corrections of the frequency response. In fixed installations, a given audience area can then be sounded to very high quality using one or more correspondingly programmed modules.

[0085] The use of such modules in the home, with permanently programmed directional effects and corresponding permanently stored values ​​for correcting the directional dependence of the frequency response of the sound transducer, is also conceivable. Thus, when a single input channel is employed as a stereo loudspeaker, a spectral constancy of reproduction is achieved by the specially set emission angle, which is never achievable when separate loudspeakers are used for each frequency range.

[0086] Further improvements and / or modifications are possible.

[0087] Figures 3 to 11 illustrate aspects for operating the acoustic transducer assembly 1, which may be operated, for example, using the proposed solution (method, computer program product, acoustic transducer assembly).

[0088] In FIG. 3 a given audience area 3 is represented, which is sonicated with a planar acoustic transducer assembly 1 according to the principle of wave field synthesis (WFS).

[0089] In operation, the acoustic transducers of the acoustic transducer assembly 1 generate elementary waves 8 that are superimposed to form a common wavefront 4. The common wavefront 4 is designed as if it were emanating from a virtual sound source 12. Thus, the surface of the wavefront 4 formed from the elementary waves 8 of the acoustic transducers 9 corresponds to a spherical segment. For illustrative purposes, the common wavefront 4 is divided into rectangles 105, which represent the proportion of elementary waves 8 generated by each of the approximately same number of acoustic transducers of the acoustic transducer assembly 1 on the common wavefront 4.

[0090] In the spherical segment 4, each sub-area 105 associated with a given number of acoustic transducers of the acoustic transducer assembly 1 is approximately the same size. Correspondingly, the sound pressure is uniformly distributed over the surface of the wavefront 4 at the same time.

[0091] However, the audience areas 106 associated with these partial sections have very different sized surfaces over which the same energy of the associated spherical shaft section is distributed, and accordingly the sound pressure levels in different parts of the audience area 3 will be different.

[0092] 1, the virtual sound source 12 is positioned behind the acoustic transducer assembly 1. The position of the virtual sound source 12 determines both the curvature of the common wavefront 4 and the direction in which it propagates. If the virtual sound source 12 is positioned close to the acoustic transducer assembly 1, the feed area is large and the curvature of the common wavefront 4 is large. The surface of the common wavefront 4 increases rapidly with distance, and therefore the sound pressure level decreases rapidly.

[0093] The farther the virtual sound source 12 is from the WFS acoustic transducer assembly 1, the narrower the radiation angle and the smaller the curvature of the spherical segment. At very long distances, the wavefronts become nearly parallel, and their level decays little with distance. However, as a result, the supply area 10 becomes narrow enough that only a portion of the audience area 5 is supplied. The location of the virtual sound source 12 is therefore a compromise between a wide supply range and an acceptable sound pressure drop in the rear rows of the sounded audience area 3. As is also evident from FIG. 1 , the same number of acoustic transducers in the acoustic transducer assembly 1 supply a significantly larger portion of the sounded audience area 3 with increasing distance, with a correspondingly steeper drop in sound pressure. Furthermore, it becomes apparent that the common wavefront 4 of the entire supply area 10 will unintentionally impinge on surfaces outside the sounded audience area 3.

[0094] The possibility of supplying a given audience area with several virtual sound sources having the same signal content is known. A method for this purpose is described in WO 2015 / 022579 A3. A three-dimensional further development of this method is described in patent application DE10 2019 208 631 A1. The combination of several wavefronts emanating from different virtual sound sources enables a very balanced level transition across a large audience area 3. Reflective surfaces can be intentionally omitted, and the level can be adjusted separately for each individual wavefront. Even in acoustically challenging environments, a high direct sound level with correspondingly good speech intelligibility can be achieved throughout the entire audience area 3. This method, according to the principles of wavefield synthesis, approaches the goal of completely and extremely uniformly sonicating a given audience area 3 with a two-dimensional acoustic transducer assembly 1.

[0095] However, due to the different positions of the virtual sound sources, these methods introduce a time offset between the individual beams (e.g., acoustic radiation in a specific spatial angle range). This results in a comb-filter effect in the frequency response at the beam boundary region if the time difference between the beams is not compensated for. This time compensation is possible because the individual virtual sound sources can be controlled independently of each other in time. However, at the boundary region of the individual beams, the offset can only be fully compensated at one point; at other positions, when the wavefronts of coherent signal content overlap in the transition region, a perceptible comb-filter effect is unavoidable in the upper playback frequency range.

[0096] The audience area 3 in an event hall is, as a rule, predetermined, and its shape and size can hardly ever actually be adapted to the acoustic requirements for high-quality sound. In rare cases, the area to be supplied is a flat rectangle. In many cases, the area is asymmetric, with the rear area elevated to ensure a clear view of the stage. The position of the two-dimensional acoustic transducer assembly 1, which can operate according to the principle of wavefield synthesis, is also, as a rule, predetermined, since the sound source is to be placed in the stage area.

[0097] 4 to 11, an embodiment of a method for generating a closed wavefront without transitions between individual beams using a substantially two-dimensional acoustic transducer assembly 1, as known from wavefield systems, whose shape in the azimuth and elevation planes is designed to ensure a uniform distribution of sound pressure levels over a given audience area 3. This can be achieved if the spatial angle Ω of the proportions of a given number of acoustic transducers on the generated wavefront is adapted to supply a given portion of the audience area 3, each equally large portion of the audience area 3. This would not be possible with discrete virtual sound sources in wavefield synthesis.

[0098] 4 shows an acoustic transducer assembly 1 having multiple acoustic transducers. The acoustic transducer assembly 1 is used to sonicate an audience area 3. In operation, the individual acoustic transducers 9 of the acoustic transducer assembly 1 radiate elementary waves 8 that overlap to form a common wavefront 4.

[0099] The acoustic transducers 9 of the acoustic transducer assembly 1 have individual delay times τ j , i.e. the acoustic transducers 9 emit elementary waves 8 with individual delay times. The common wavefront 4 is j In particular, the common wavefront 4 is formed by the operation of the acoustic transducer assembly 1 with individual delay times τ j It may be shaped by operation at.

[0100] The acoustic transducer assembly 1 and the audience area 3 are arranged such that the positions of the individual acoustic transducers of the acoustic transducer assembly 1 are represented by a position vector s i The exact delay times of the individual acoustic transducers are determined by the position vector s i If the delay time is not exactly located at the origin of the auxiliary grid, it can be determined by interpolation from the calculated delay times of the intersection points around the auxiliary grid.

[0101] These position vectors s iThe acoustic transducers associated with the element waves 8 emit individual delay times τ j Basically, the individual delay times τ of the acoustic transducers 9 are j are different from each other, but may be the same in at least some respects.

[0102] Delay time τ j Determining r is done by associating each intersection of the auxiliary grid 5 with an intersection of the auxiliary grid 6 within the audience area 3. In particular, this association associates the sound transducer 9 with a position vector r i The position vector s with the corresponding point in the audience region 3 i Associate with.

[0103] From this association, a direction vector 7 is obtained that originates from an intersection of the auxiliary grid 5 and points in the direction of the associated intersection of the auxiliary grid 6 in the audience area 3. The normalized direction vectors 7 in the rectangular parallelepiped 60 are each a position vector s i Starting from the clause

number

[0104] Then, the associated position vector s i The delay time τ of the acoustic transducer determined using j is the position vector r i The local direction 50 of the common wavefront 4 in

number

[0105] According to the proposed solution, the normalized direction vectors 61 determine the shape of the common wavefront 4. In particular, the local direction 50 of the common wavefront 4 can be determined by the direction vectors 7. The normalized direction vectors 61 are each perpendicular to the common wavefront 4.

[0106] By appropriate choice of correlation (see Figure 8) and normalized direction vector 61, the common wavefront 4 can be shaped to fit the geometry of the audience area 3. This is done by correlation of grid points.

[0107] The wavefront 4 is then shaped so that the same number of acoustic transducers of the acoustic transducer assembly 1 are associated with equal sub-areas 106 of the audience area 3. The corresponding sub-surfaces 105 of the wavefront 4 then have different sizes. At this distance, the upper sub-area of ​​the sketch is still much smaller than the lower sub-area. Correspondingly, in this area, the sound pressure within the same wavefront is significantly higher than in the lower sub-area intended for nearby audience locations.

[0108] 5 shows a reference surface 30S for modeling the acoustic transducer assembly 1 in the coordinate system 2. On the reference surface 30S of the acoustic transducer assembly 1, a regular curved auxiliary grid 5 is arranged, to which the positions of the individual acoustic transducers 9 of the acoustic transducer assembly 1 are aligned. By means of the reference surface 30S, and in particular the auxiliary grid 5, the coordinates of the individual acoustic transducers 9 of the acoustic transducer assembly 1 in 3D space can be determined.

[0109] The reference surface 30S is parameterized in curvilinear coordinates by the equation s(u,v)=[x(u,v)y(u,v)z(u,v)], where u and v are real variables.

[0110] The normal 202n on the reference surface 101S at s(u,v) is, by definition, a tangent vector 201s u and s v is the normal to the tangent plane spanned by, and the partial derivative of s(u,v)

number

[0111] The acoustic transducers 9 of the acoustic transducer assembly 1 do not themselves need to be attached to the intersections of the auxiliary grid 5; their respective delays and their levels are interpolated to the intersections in three-dimensional space. The curvature of the reference plane 30S and the curvature of the auxiliary grid 5 may be different in the azimuth and elevation planes, and it is also possible to curve the auxiliary grid 5 in only one plane.

[0112] In practice, the reference surface 30S of the acoustic transducer assembly 1 is usually a plane, and therefore the auxiliary grid 5 is a planar auxiliary grid. This corresponds to the case where the acoustic transducer 9 is mounted in a substantially two-dimensional assembly. A plane is considered a special case of a curved surface.

[0113] Figure 6 shows the association of the auxiliary grid 5 of the acoustic transducer assembly 1 with the auxiliary grid 6 in the audience area 3. The solution approach presented here starts not from the location of a virtual sound source (as represented in Figure 3), but from the given geometry of the audience area 3 to be sonified and the shape of the acoustic transducer assembly 1.

[0114] In principle, the sonified audience area 3 can be of any desired shape, such as flat, curved or elevated. Figure 6 depicts a sonified irregularly shaped audience area 3 which is not particularly symmetrical and which is more strongly elevated in the rear region on the right than on the left.

[0115] Conventional approaches, and even wavefield synthesis virtual sources, are inadequate to solve the task of providing very uniform direct sound to an audience area such as that depicted in Figure 6, because the wavefront curvature of wavefield synthesis virtual sources is always a spherical segment.

[0116] On the other hand, the association of the depicted auxiliary grids 5 and 6 can be used to generate a common wavefront 4 whose shape is adapted to the geometry of the audience area 3 to be insonified.

[0117] To solve this problem, coordinate system 2 is determined.

[0118] Coordinate points distributed over the audience area 3 to be sonified are related to coordinate system 2. In Figure 6 these coordinate points within the audience area 3 are located at the intersections of auxiliary grid 6, but they may also be distributed within the audience area 3 by other mapping methods.

[0119] Furthermore, an auxiliary grid 5 is associated with the coordinate system 2, by means of which the position of the acoustic transducer 9 of the acoustic transducer assembly 1 can be determined. The auxiliary grid is represented in FIG. 5 as a planar regular auxiliary grid. However, in principle, the auxiliary grid may also be curved, i.e., have curved lines. In principle, the auxiliary grid 5 could be placed on a reference plane on which the acoustic transducer assembly 1 is modeled.

[0120] The number of coordinate points in the audience area 3 corresponds to the number of intersections of the auxiliary grid 6. Thus, a coordinate point of the auxiliary grid 6 in the audience area 3 may be associated with each intersection of the auxiliary grid 5 in the audience area 3. The distribution of the coordinate points is done across the entire audience area 3 with as uniform a spacing as possible between the individual coordinate points.

[0121] A coordinate point with position r(x,y,z) is associated with each intersection of the grid 5 in the audience area 3. The connecting lines 7 between the intersections of the auxiliary grid 5 and their associated coordinate points in the audience area 3 then form vectors in the coordinate system 2 that are the basis for calculating the duration and level of the audio signal.

[0122] The represented planar auxiliary grid 5 of the acoustic transducer assembly 1 has a rectangular shape with an aspect ratio similar to that of the planned acoustic transducer assembly 1, such as in the form of an acoustic transducer array. There must be at least as many intersection points as there are acoustic transducers 9 provided in the acoustic transducer assembly 1. In principle, since the aspect ratio is not defined, it is also possible to construct a single line of acoustic transducers if this is appropriate for the given spatial situation in the audience area 3.

[0123] The distance between the grid lines of the auxiliary grid 5 may vary in the horizontal and vertical planes, but must at least correspond to the number of rows and columns of the two-dimensional acoustic transducer assembly 1 .

[0124] The acoustic transducers 9 of the acoustic transducer assembly 1 can be mounted so that their acoustic centers are located at the intersections of the auxiliary grid 5. However, their positions can also be offset from these intersections, in which case their respective execution times and levels are determined by interpolation of values ​​calculated for surrounding grid points.

[0125] The more grid lines there are, the more accurate the interpolation. A smaller number of grid lines results in a wavefront that is not uniformly curved but consists partially of planar surfaces. The resulting diffraction effects introduce local irregularities into the frequency response.

[0126] In principle, not all intersections of the auxiliary grid 5 need to be associated with a physical sound transducer 9. This allows for the low-mid-range sound transducers 9 to be suspended in the area where they have their sound outlets. Furthermore, as explained in DE 10 2009 006 762 A1, all sound transducers 9 can be distributed slightly irregularly on the surface. In this way, undesirable aliasing effects in the audience area 3 can be reduced, since the resulting comb filter effects are statistically compensated to some extent in the frequency response.

[0127] An auxiliary grid 6 placed above the audience area 3 completely surrounds it. The shape of the auxiliary grid 6 is adapted to the audience area 3. In principle, this could be done manually. In practice, however, hundreds or even thousands of grid points are required to ensure that the distance between the sound transducers 9 is small enough to achieve a reproduction that is almost free from audible aliasing effects. The few grid lines in the sketch serve to illustrate the functional principle of intelligibility.

[0128] It is therefore advantageous to automatically determine the coordinate points within the audience area 3 by means of a 3D CAD file of the audience area 3 using an appropriate mapping method. Areas that are not intended to be directly hit by the common wavefront 4 may also remain without an associated grid point, since undesired reflections would emanate from them. They are therefore not associated with an acoustic transducer 9, and the wavefront is transmitted directly in their direction. From these areas, the coordinate points are moved without changing their number. The surrounding coordinate points are shifted accordingly to maintain a uniform distribution throughout the audience area 3. Each intersection of the auxiliary grid 5 in the plane of the two-dimensional acoustic transducer assembly 1 is associated with a reference point within the audience area 3 to be sonicated.

[0129] The visualization in the 3D CAD file makes it easy to switch off the vacant audience areas 3. In this case, the calculations remain unchanged in principle, but now only the sound transducers associated with the vacant audience areas 3 are not fed with signal. This reduces the diffuse sound field level in the event hall, which contributes to improving speech intelligibility in the occupied audience areas 3.

[0130] Figure 7 shows by way of example how the local curvature 50 of a wavefront 4, which according to the method of explanation does not have to be a spherical segment, arises from the superposition of elementary waves 8 of surrounding acoustic transducers 9. The acoustic centers of the acoustic transducers 9 are, for simplicity's sake, attached in the example to the intersections of an auxiliary grid.

[0131] Each individual acoustic transducer 9, represented in black in the sketch, has an omnidirectional half-space radiation due to the principle of wave field synthesis. Therefore, the elementary waves 8 generated by it alone cannot form a direction vector. The local direction vector d of the associated wavefront is generated only at a certain distance from the acoustic transducer assembly 1 by the superposition of the elementary waves 8 of the surrounding acoustic transducers.

[0132] The direction vector 7d of this intersection can be determined by the term d=rs(3): it is always orthogonal on the local wavefront 50.

[0133] In the exemplary representation of FIG. 7, the point represented by the vector r is at the intersection of the auxiliary grid 6 of the audience area 3 .

[0134] In principle, the direction vector 7d can also be determined without the aid of auxiliary grids 5 and 6. In this case, the direction vector 7d starts from a position vector s on the reference surface 30S that models the acoustic transducer assembly 1 and points to a position vector r in the audience area 3, or to a position vector R that represents a point on the reference surface 30 that models the audience area 3r.

[0135] Below we explain how the delay times and levels of individual acoustic transducers 9 can be derived from a given direction vector 7 so that the superposition of their elementary waves 8 is superimposed onto a wavefront that is consistently aligned with a given audience area 3.

[0136] In FIG. 8, the direction vector 7d selected as an example from FIG. 6 is

number

number

[0137] The desired wavefront generated by the acoustic transducer assembly 1, particularly in the form of a curved or planar array, is directed along a normalized direction vector 61 (i.e., locally along direction vector 61

number

[0138] Delay time τ at each position s(u,v) on the reference plane 30S of the acoustic transducer assembly 1 j is determined by a scalar delay function τ(u,v).

[0139] In vector calculus, the gradient of a scalar function τ of some variables is a vector field ∇τ, whose components can be determined by partial derivatives from τ; in particular, the following applies:

number

[0140] The delay gradient ∇τ(u,v) can be determined in the following way.

[0141] Normalized Direction Vector 61

number

number

number

number

[0142] scalar

number

number

[0143] In the special case of a planar acoustic transducer assembly 1, as represented in FIG.

number

number

number

number

number

[0144] The delayed gradient ∇τ(u,v) and the components of Eq. (5)

number

number

number

[0145] In reality, the distance between the acoustic transducers 9 is finite. Therefore, the differential equations from equations (7a) and (7b) must be rewritten as discrete difference equations. The differential delay in the u or v direction, Δ u τ and Δ v τ is where

number

number

[0146] Several mathematical integration methods are available, such as the complex trapezoidal method, Simpson's, or the more advanced inverse gradient method. The integration constants can be freely chosen. To satisfy causality conditions and minimize system latency, the minimum delay across all drivers is subtracted from the calculated delay.

[0147] Relative amplification factor for each position of the acoustic transducer assembly 1

number

number

number

[0148] Relative Amplification Factor

number

[0149] As the tilt of the radiation increases compared to the normal n, the number of acoustic transducers 9 at a given spatial angle Ω increases, at which the sound pressure level increases.

[0150] The compensation according to equation (9) corrects this according to the cosine function of the angle γ in Figure 6. The uniform distribution of the coordinate points r ensures a very even distribution of the sound pressure throughout the audience area 3 being sonicated.

[0151] FIG. 9 shows that the sonified audience area 3 can also be divided into individual sub-areas 701, 702, 703 with different signal content.

[0152] In principle, these partial areas could also be distributed over partial areas of the acoustic transducer assembly 1. However, clearly more precise sonication is obtained if the high directivity of the entire assembly is used to align the signal content to the desired audience area 3. In each of the partial areas 701, 702, 703, the number of intersections 6 corresponds to the number of intersections 5 of the auxiliary grid of the acoustic transducer assembly 1.

[0153] If the signal content is the same, the division into sub-regions does not make sense if the sub-regions are not sufficiently spatially separated. If the signal content is consistent, the comb filter effect occurs at the region boundaries.

[0154] The individual partial areas may also be smaller than the associated acoustic transducer 9 surface, as long as the intersections of the auxiliary grids are closer to each other within the audience area 3 than the auxiliary grid of the acoustic transducer assembly 1. In this case, a concave wavefront is created whose sound pressure level is higher within the audience area 3 than the generating radiating surface itself.

[0155] It is also possible to reduce the size of the auxiliary grid in the audience area 3 to a point. The two-dimensional acoustic transducer assembly 1 then generates, according to the vector-based method described, the same concave wavefront that would arise at the two-dimensional acoustic transducer assembly 1 according to the principles of wavefield synthesis at this point in the virtual sound source.

[0156] Using the coordinates of the grid points 5 on the reference plane of the sound transducer assembly 1 and their associated coordinates 6 in the audience area 3, it is also possible to compensate for sound pressure drops at higher frequencies through airborne sound insulation. At a given humidity, the frequency-dependent attenuation value of air per meter is precisely known. Then, since the distance to the associated audience location (given by the length of the direction vector d in Figure 7) is known, a corresponding inverse equalization curve can be associated with each sound transducer 9.

[0157] In large audience areas 3, the sound pressure drop at the upper end of the audible range can rise to well over 10 dB in dry air. In any case, this frequency range needs to be controlled quite high with the flat acoustic transducer assembly 1, since the level gain due to improved matching of synchronously operating loudspeaker groups is only effective at relatively long wavelengths. Therefore, additional compensation for airborne sound insulation in distant audience areas 3 can bring the system to the limits of its controllability at high signal levels in the upper audible frequency range.

[0158] The solution to this problem is to position the coordinate points r further from the sound transducer assembly 1 closer to each other. In the far audience area 3, the same number of sound transducers 9 are then associated with smaller sub-areas 106. Each time the surface is bisected, the level increases by up to 3 dB, and the control of the associated sound transducers 9 must be reduced accordingly, so that the sound pressure level remains approximately the same throughout the audience area 3. The correspondingly reduced control signals are connected to more headroom in the associated amplifiers. This can then be used to equalize the drive signals to a greater extent.

[0159] In the described method, the localization of sound sources is fundamentally different from the localization of virtual point-like sources in wavefield synthesis, where virtual sources are, in principle, localized to their virtual starting points, equivalent to real sources, regardless of the listener's position in the source area.

[0160] However, the wavefront aligned with the audience area 3 does not start from a defined location of the virtual sound source. It is, of course, created from an extended sound source with many different starting points in the area behind the sound transducer surface. A listener in the left front location in Figure 4 will associate the starting point with the wavefront in the lower left corner of the sound transducer assembly 1, while for a listener in the right rear location, the sound comes from the upper right corner of the sound transducer assembly 1. This is not a drawback for reproduction without optical reference to the sound source, but spatial reproduction is only possible to a limited extent according to Figure 4.

[0161] Nevertheless, the theoretical derivation of wavefield synthesis from the Kirchhoff-Helmholz integral makes it possible to generate wavefronts of any desired shape, so this method can be related to the field of wavefield synthesis (Jens Ahrens: The S i ngle-layer Potential Approach Applied to Sound Field Synthes i s Including Cases of Non-enclos i ng Distr i tions of Secondary Sources, PhD dissertation, Technical University of Berlin, 2010).

[0162] Further improvements Up to now, it has been assumed that the acoustic transducers 9 of the acoustic transducer assembly 1 are arranged on a regular grid. However, in reality, the distribution of the acoustic transducers 9 may be irregular. First, the running time τ is calculated on a sufficiently dense regular grid, and then the running time is interpolated to the irregularly arranged acoustic transducers.

[0163] FIG. 10 shows a complexly designed audience area 3 having a sub-area 802 and shows the installation of an acoustic transducer assembly 1 having an acoustic transducer 9, which is adapted to the complex design of the audience area 3.

[0164] In the illustrated embodiment, the association between points on the acoustic transducer assembly 1 and points in the audience area 3 is made by association between intersections of an auxiliary grid 5 of the acoustic transducer assembly 1 and intersections of an auxiliary grid 6 of the audience area 3.

[0165] However, not all nodes of the auxiliary grid 5 are associated with acoustic transducers 9 of the acoustic transducer assembly 1; in other words, the nodes of the auxiliary grid 5 are unequipped. Specifically, there are unequipped nodes among the equipped nodes.

[0166] The shape of the sound transducer assembly 1 can therefore be adapted to the complex design and / or geometry of the audience area 3 in a fixed installation, allowing for more efficient use of the sound transducers.

[0167] The auxiliary grid 6 in the audience area 3 may for example be rectangular and in particular may extend beyond the audience area.

[0168] An irregular shape of the auxiliary grid 6 may lead to inaccurate results in the calculations according to the described method.

[0169] Intersections of the auxiliary grid 6 within an audience area 3 that do not have an associated audience, i.e., in this case, intersections of the auxiliary grid 6 that are located outside the sub-areas 5a, 5b, 5c of the audience area 3 that are to be sound-treated, are associated with auxiliary grid points of the auxiliary grid 5 of the acoustic transducer surfaces that are not equipped with an acoustic transducer or are switched off.

[0170] An auxiliary grid 5 of the sound transducer assembly 1 is also optionally aligned with the employed low-mid range sound transducers. Their run times and level calculations depend on nearby grid points. Possible time shifts of depth offsets are compensated for. The phase position of the subwoofer can also be effectively adapted in this way. According to this method, the shortest of all calculated run times for the individual sound transducers is subtracted from all calculated run times, always directly generating a wavefront adapted to the audience area 3.

[0171] A further improvement relates to devices shaped according to the rules of the described method, whereby a single wavefront whose shape is adapted to a given listener area can be generated from a mono signal without electronic time shifting of the signal. This mechanical solution is advantageous for fixed installations in acoustically problematic environments. For example, even under unfavorable acoustic conditions, it is possible with reasonable effort to install an acoustic system that guarantees a high proportion of direct sound with correspondingly good speech intelligibility.

[0172] A mechanically curved acoustic transducer assembly 1 is shown by way of example in FIG.

[0173] A mechanically curved acoustic transducer assembly 90 may provide a cut-to-size common wavefront 4 to a sonicated audience area 3, as described with reference to FIG.

[0174] In this case, the operation of the acoustic transducer 9 of the acoustic transducer assembly 1 is controlled by the delay time τ j All acoustic transducers are fed with coherent signals, i.e. from a mono signal source.

[0175] Mechanical realization is achieved by suitable arrangement of the acoustic transducers 9 on a mechanically curved acoustic transducer assembly 90, in particular by suitable spatial offset of the acoustic transducers 9 relative to each other, in particular offset in the direction of propagation of the common wavefront.

[0176] To determine the respective positions of the acoustic transducers 9 on the surface of the fitted acoustic transducers of the audience area 3 to be sonicated, a unit vector 61 is calculated starting from the associated grid point of the planar auxiliary grid 5.

number

[0177] With the alternating angles α and β thus known, the new coordinates of the acoustic centre of the associated acoustic transducer 9 and its orientation in the right triangle of the rectangular parallelepiped 40 can be determined.

[0178] The delay time calculated according to the method described for each acoustic transducer 9 is calculated along the diagonal S of each rectangular parallelepiped. d This is produced by mechanically offsetting the acoustic centre of each acoustic transducer 9 along the

[0179] The different signal levels of the individual acoustic transducers 9 of this two-dimensional acoustic transducer assembly 1 can be achieved with an approximately common final amplifier by appropriate parallel and series connections of the acoustic transducers 9 or by connecting to different amplifiers each associated with transducers 9 having approximately the same level values.

[0180] The acoustic transducers 9 do not need to be oriented in the diagonal direction of the rectangular parallelepiped, as long as there is no significant degradation in their spatial radiation characteristics. Therefore, this method can also be realized by a device for lateral displacement of the acoustic transducers, as described in WO2015 / 004526 / A2. In that case, the displacement s of the acoustic center of the original acoustic transducer grid from the grid point y Then, the quotient

number

[0181] No single mechanical device can produce spatial sonification of the audience area 3. This makes it feasible to achieve, with manageable effort, sonification in which the distribution of sound pressure levels is very uniform throughout the audience area 3, ensuring a high level of speech intelligibility even in acoustically hostile spaces.

[0182] In the following, several embodiments of methods and devices are presented for sonicating a given audience area 3 by means of acoustic transducer assemblies 1, controlled with individual delay times and levels according to the principles of wavefield synthesis.

[0183] Thus, for example, in method variant 1, the shape of the acoustic common wavefront 4 formed by the superposition of the elementary waves 8 of the acoustic transducers 9 can be determined from the given geometry of the audience area 3 and the acoustic transducer assembly 1 in a common coordinate system 2 such that coordinate points of the audience area 3 are associated with each intersection of a regular, at least partially planar and / or curved grid associated with the acoustic transducers, and vectors are generated from these connecting lines from which the delay times of the associated acoustic transducers 9 can be mathematically calculated, so that the local curvature of the wavefront formed by the superposition of the elementary waves 8 of the surrounding acoustic transducers 9 progresses in the direction of this vector, creating a closed wavefront that can reach the entire audience area 3, and in this wavefront, level corrections from the associated vector are also possible for each acoustic transducer 9, improving the uniformity of the sound pressure throughout the audience area 3.

[0184] In an improvement of variant 1, for example, coordinate points in the plane of the two-dimensional acoustic transducer assembly 1 are intersections of a planar or curved grid to which coordinate points in the audience area 3 are associated in the common coordinate system 2, and the connecting lines between the associated grid points and the points in the audience area 3 respectively do not intersect or intersect.

[0185] In a further refinement, the number of horizontal and vertical grid lines in the plane of the two-dimensional sound transducer assembly 1 corresponds, respectively, to the number of sound transducers installed in the rows and columns of the two-dimensional sound transducer assembly 1. Alternatively, the number of grid lines may be greater than the number of sound transducers 9 in the rows and columns of the two-dimensional sound transducer assembly 1, in which case the acoustic centers of the individual sound transducers 9 may be located at the intersections of the grid lines. Delay time and / or level values ​​may be determined, for example, by interpolating values ​​of surrounding grid points, allowing a reference point within the audience area 3 to conform to the geometric requirements of the audience area 3 in all three spatial dimensions, although care must be taken to ensure that the areas between individual grid points remain approximately the same size throughout the audience area 3, resulting in a relatively uniform distribution of sound pressure levels throughout the audience area.

[0186] In a further refinement of variant 1 or one of the above variants, the vector obtained from the difference between the coordinates of the grid points associated with each acoustic transducer 9 in the plane of the two-dimensional acoustic transducer assembly 1 and the respective positions of the associated coordinate points in the audience area 3 is a unit vector

number

[0187] In principle, physical acoustic transducers 9 radiating the same frequency range do not have to be associated with all intersections of the auxiliary grid, which makes it possible, for example, to interrupt the installation in an area where there is a sound emission part of a low-mid range acoustic transducer 9, or to place a high-frequency loudspeaker in front of the low-mid range acoustic transducer, the difference in execution time being compensated for by a mechanical offset by interpolation at the intersections of the auxiliary grid.

[0188] In a further refinement of the above variant, the effect of the angle of the resultant wavefront at a given grid point relative to the plane of the sound transducer assembly 1 on the perceived signal level at the associated point in the audience area 3 is compensated by compensating the level of the sound transducer associated with each point with a cosine function of the angle, the value of this cosine function being the unit vector

number

number

[0189] In principle, several auxiliary grids within the audience area, each having the same number of points as the grid in the plane of the two-dimensional acoustic transducer assembly 1, could also be associated with the intersections of the planar or curved grid within the two-dimensional acoustic transducer assembly 1, so that partial areas within the audience area could be supplied with different signal content, for example simultaneously.

[0190] The reference points within the audience area 3 may be distributed more tightly as the distance from the two-dimensional acoustic transducer assembly 1 increases, for example with the intention that the area between the reference points becomes smaller with distance from the two-dimensional acoustic transducer, so that the associated acoustic transducers 9 of the two-dimensional acoustic transducer assembly 1 may be controlled at lower levels while the sound pressure in the respective areas remains unchanged, resulting in more headroom to compensate for high frequency attenuation due to airborne sound insulation in these areas.

[0191] The effect of airborne sound insulation on the signal in the auditorium for each individual sound transducer 9 is calculated using the associated vector

number

[0192] In principle, individual audience areas 3 can be excluded from the supply, for example temporarily, for example when not occupied by an event, thereby improving the proportion of direct sound in the remaining parts of the audience area 3.

[0193] In a device for sonifying a given audience area 3, according to one of the variants of the above method, the running times emitted by the individual acoustic transducers 9 of the two-dimensional acoustic transducer assembly 1 are not achieved by electronic delays of the signal content but by mechanical positioning of the acoustic transducers controlled by a coherent signal, and the signal level of each acoustic transducer 9 corresponds to a value determined for the original intersection of the grid.

[0194] In the following, several embodiments of a method for direction-dependent correction of the frequency response of an acoustic wavefront are described.

[0195] Thus, for example, in variant 1a, a direction-dependent correction of the frequency response of an acoustic wavefront generated by a two-dimensional acoustic transducer assembly according to the principles of wavefield synthesis or according to beamforming methods, for example as an extension of the method of German Patent Application No. 10 2021 207 302.6 [1], is performed for sonifying a given audience area, in which multiple input signals can be associated with different audience areas simultaneously and independently of each other, the signal levels being adapted in such a way that a highly balanced sound pressure level is ensured across the entire audience area, and in which non-linearities in the frequency response of the individual wavefronts across the entire audience area can be largely compensated for by additionally inserting corresponding correction elements in the signal path of each input channel of each acoustic transducer, this compensation being performed for each input channel of the system based on an inverse correction of coefficients that physically influence the linearization of the radiation of each acoustic transducer depending on the local radiation direction of the wavefront to be corrected, respectively, in relation to the front surface of the two-dimensional acoustic transducer assembly.

[0196] In an improvement of variant 1a, the nonlinearity of the frequency response depending on the radiation direction is largely compensated by a forward correction, by determining and storing individually in a low-reflection space the data stored under the 3D spherical coordinates of each acoustic transducer installed in the module for each acoustic transducer of the acoustic transducer assembly, so that its frequency response in the radiation direction of each wavefront is retrieved from the memory by the spherical coordinates φ and θ and calculated by the function G inv As (f), the frequency response error of each acoustic transducer in the local radiation direction of each wavefront is largely compensated by an additional inverse filter inserted in each signal path.

[0197] Additionally or alternatively, in one embodiment, frequency response errors caused by acoustic obstructions in the propagation direction of the wavefront can be largely compensated for by forward correction, whereby the difference between the unobstructed radiation and the radiation behind the structure obstructing the propagation of each wavefront in 3D spherical coordinates of the individual acoustic transducers is spatially detected and stored as 3D spherical coordinates, whereby the difference between the two frequency responses in the radiation direction of each wavefront is called by polar coordinates φ and θ and is expressed as a function H inv The inverse filters normalized and inverted as (f) and additionally inserted in each signal path maximize compensation of frequency response errors caused by acoustic obstructions in the local radiation direction of each wavefront.

[0198] Additionally or alternatively, the effect of airborne sound insulation on the frequency response of each wavefront can be calculated by directly calculating the attenuation process at a distance of 1 meter from known mathematical relationships with the actual values ​​of relative humidity (%), atmospheric pressure (kPa), and temperature (K) in the audience area, and multiplying the inverted and normalized value by the distance of the acoustic transducer to the listener area at which the local portion of the relevant wavefront is aimed, to obtain the resulting function A by filtering the signal path. inv (f) can be used to compensate for distance-related level losses of the relevant wavefront in the direction of the audience area, which can be significantly compensated for.

[0199] Additionally or alternatively, an inverse of the frequency response obtained from stored or calculated data can be connected upstream of the filter in the signal path to compensate for the drop in frequency response by a corresponding higher amplification and reduce the increase in resonance by attenuating the signal in the corresponding frequency range, the correction being performed in octave, third or smaller frequency steps, and any shift in the total level of the relevant channels upstream of the filter being compensated for by a corresponding correction of the total level of the correction curve, with the maximum value of the compensation preventing over-control of subsequent stages in individual frequency ranges.

[0200] Additionally or alternatively, additional polar frequency response data and inverse or non-inverse filters that result in direction-dependent frequency response changes of selected wavefronts can be inserted as additional correction elements in the signal path to realize the specific preferences of individual listener groups, to compensate for individual hearing loss, or to expand the artistic design possibilities for the spatial sound field, or other acoustic objectives.

[0201] In principle, the order of the correction elements in the signal path can be freely chosen and individual correction possibilities can be bridged or omitted.

[0202] Additionally or alternatively, if the wavefront direction is fixed within the system, fixed correction values ​​can be stored within the system.

[0203] In principle, a system with permanently programmed directional effects and permanently programmed direction-dependent frequency response corrections can operate autonomously as individual modules or can be combined with additional correspondingly programmed modules to form a permanently programmed acoustic transducer array.

[0204] Additionally or alternatively, directional characteristic data may be stored in the individual modules and read from a central memory during the configuration process and overwritten via the data path.

[0205] Further embodiments are described below. [Example]

[0206] Example 1. A method of acoustically sonicating at least one audience area (3) with at least one acoustic transducer assembly (1) having a plurality of acoustic transducers (9), wherein each individual acoustic transducer (9) of the at least one acoustic transducer assembly (1) emits elementary waves (8) that overlap to form a common wavefront (4); a) at least one acoustic transducer assembly (1) and at least one audience area (3) are geometrically linked to each other by a coordinate system (2); b) the physical locations and position vectors s of the individual acoustic transducers (9) within at least one acoustic transducer assembly (1); i and a spatial correlation between the at least one acoustic transducer assembly (1) for determining its coordinates within the area of ​​the at least one acoustic transducer assembly (1), and c) Point in coordinate system (2) and position vector r i There is an association with a point in at least one audience region (5) corresponding to d) The direction vector, in particular the normalized direction vector (61), is given by

number

[0207] e) Delay time τ of the acoustic transducer (9) j respectively, the local direction (50) of the common wavefront (4) is in the direction of a direction vector, in particular, the normalized direction vector (61)

number

[0208] Example 2. The method according to example 1, characterized in that the acoustic transducers (9) of at least one acoustic transducer assembly (1) are arranged in or on a plane, or in or on an at least partially curved surface or plane (30), in particular in a grid-like manner, and the position of the acoustic center of the acoustic transducers can deviate from the intersection of the auxiliary grid (5), but the associated delay time and level changes are compensated for by the spatial arrangement.

[0209] Example 3. The method according to example 1, characterized in that the acoustic transducers (9) of the at least one acoustic transducer assembly (1) are arranged in a three-dimensional region, in particular in space, in particular that a portion of the acoustic transducers (9) of the at least one acoustic transducer assembly (1) is arranged on a reference plane (30), and the positions of the remaining acoustic transducers (9) of the at least one acoustic transducer assembly (1) can be determined by an offset (91) into the three-dimensional region.

[0210] Example 4. Delay time τ j The method according to at least one of the preceding embodiments, characterized in that the operation of the acoustic transducers (9) having the acoustic transducers (9) is controlled by control via a computer system and / or mechanically, in particular by spatially offsetting (91) the acoustic transducers (9) of the at least one acoustic transducer assembly (1) relative to one another.

[0211] Example 5. The method according to at least one of the preceding examples, characterized in that at least one audience area (3) has an at least partially concave shape and / or an at least partially convex shape.

[0212] Example 6. The method according to at least one of the preceding examples, wherein at least one audience area (3) can be described as a continuous surface.

[0213] Example 7. The method according to at least one of the preceding examples, wherein at least one audience area (3) can be described as a discontinuous surface made up of at least two contiguous surfaces.

[0214] Example 8. Position vector s i 4. The method of claim 1, wherein:

[0215] Example 9. Position vector r i The method according to at least one of the preceding embodiments, characterized in that it provides a regular grid (6) on the surface associated with at least one audience region (3).

[0216] Example 10. A point within at least one audience region (3) is represented by a position vector s i Each position vector r corresponding to i The method according to at least one of the preceding embodiments, characterized in that the association associating with can be determined by a connecting line from at least one sound transducer assembly (1) to the audience area (3).

[0217] Example 11. The method according to at least one of the preceding examples, characterized in that the level at which the acoustic transducers (9) of the at least one acoustic transducer assembly (1) operate is adapted to uniform the sound pressure within the at least one audience area (3).

[0218] Example 12. The level at which the acoustic transducer (9) of at least one acoustic transducer assembly (1) operates is determined by the regulation

number

[0219] Example 13. The method according to at least one of the preceding examples, characterized in that at least one audience area (3) has at least two sub-areas that are sonicated with different signal contents.

[0220] Example 14. A method according to at least one of the preceding examples, characterized in that the common wavefront (4) is shaped to fit the geometry of at least one audience area (3) to which the grid points are associated, and the common wavefront (4) is shaped such that equally sized sub-areas (106) of the at least one audience area (3) are associated with substantially the same number of acoustic transducers (9) of the acoustic transducer assembly (1).

[0221] Example 15. A method according to at least one of the preceding examples, characterized in that sub-areas of the at least one audience area (3) are assigned sub-areas of the acoustic transducer assembly (1), each of which can be simultaneously associated with different audio content, and the directivity of the acoustic transducer device (1) is used to align the signal content to a predetermined portion of the at least one audience area (3), and in each sub-area (701, 702, 703) the number of intersections (6) corresponds to the number of intersections (5) of the auxiliary grid of the acoustic transducer assembly (1).

[0222] Example 16. A delay time τ is used to sonicate at least one audience area (3). j A delay time τ for operating the acoustic transducers (9) of at least one acoustic transducer assembly (1) having a plurality of acoustic transducers (9) j to generate elementary waves (8) according to j 1. A method for determining - determining a coordinate system (2), by which: o at least one acoustic transducer assembly (1) is approximately described as a two-dimensional reference surface (30) S of the at least one acoustic transducer assembly (1); o at least one audience region (3) is approximately described; - determining a position vector s of at least one acoustic transducer assembly (1) on a reference plane (30) S, from which the position of the acoustic transducer (9) of the at least one acoustic transducer assembly (1) can be determined; - determining an association that associates each position vector s on the reference plane (30) S of at least one acoustic transducer assembly (1) with a position vector r corresponding to a point in at least one audience region (3); -Position Vector

number

number

number

[0223] Example 17: For at least a part of the position vector s, the clause

number

number

number

[0224] Example 18. The method of example 16 or 17, wherein the position vector s describes the position of the transducer (9).

[0225] Example 19. Each position vector s on a reference plane (30) S of at least one acoustic transducer assembly (1) is associated with a position vector r on a reference plane R of at least one audience area (3), and a direction vector, in particular a normalized direction vector (61) for at least one position vector s is calculated.

number

number

[0226] Example 20. Normalized direction vector (61)

number

[0227] Example 21. The method according to at least one of Examples 16 to 20, characterized in that the association between the position vector s and the position vector r is performed automatically, in particular based on a 3D CAD file of at least one audience area (3).

[0228] Example 22. The method according to at least one of Examples 19 to 21, characterized in that the position vectors r are evenly distributed on the reference plane R of the at least one audience area (3) and therefore correspond to evenly distributed points within the at least one audience area (3).

[0229] Example 23. A method according to at least one of Examples 16 to 22, characterized in that the reference plane R of at least one audience area (3) is described by an auxiliary grid (6) on which the position vector r is at least partially intersected.

[0230] Example 24. The method according to at least one of Examples 16 to 23, characterized in that the reference plane (30) S of at least one acoustic transducer assembly (1) is described by an auxiliary grid (5) on which the position vector s is at least partially intersected.

[0231] Example 25. The method according to at least one of Examples 16 to 24, characterized in that the reference surface (30) S of at least one acoustic transducer assembly (1) is parameterized by coordinates s(u,v) = [x(u,v) y(u,v) z(u,v)], where u and v are real numbers, continuous variables or discrete variables, and therefore, in particular, the position vector s can be written in the form s = s(u,v).

[0232] Example 26. The normal n to the reference surface (30) S of the acoustic transducer assembly (1) at the point represented by s = s (u, v) is su and s v By cross product of n=s u ×s v where s u and s v is the partial differential

number

[0233] Example 27. Each delay time τ j To determine this, first a scalar function of the delay time τ(u,v) for a finite number of position vectors of the form =s(u,v) is determined, and the position vector s i The delay time τ for an acoustic transducer (9) with j 27. The method of embodiment 26, wherein determining {overscore (u), v} is performed at least in part by interpolation of at least two respective values ​​of the form τ(u,v).

[0234] Example 28: A scalar function of the delay time τ(u,v) is calculated as a discrete 2D vector field [Δ u τΔ v is determined by the numerical integration of Here, the delay difference in the u direction Δ u τ or v Directional delay difference Δ v τ is given as follows:

number

number

number

number

number

number

[0235] Example 29. The method of example 27 or 28, wherein the numerical integration method comprises a complex trapezoidal method, a Simpson method, a Romberg method, or a more advanced inverse gradient method.

[0236] Example 30. Delay time τ for sonication of audience area (5) i A delay time τ for operating the acoustic transducer (2) i of at least one acoustic transducer assembly (1) having a plurality of acoustic transducers (2) i to generate an elementary wave (3) according to j 29。 A computer program product for determining a delay time τ for an acoustic transducer j according to at least any of Examples 1 to 15 or 16 to 29. j The method includes or is characterized by the use of means for executing at least one instruction for determining

[0237] Example 31. A device for sonicating at least one public area (3), comprising at least one acoustic transducer assembly (1) having a plurality of acoustic transducers (9), wherein the at least one acoustic transducer assembly (1) is operated according to the method described in at least one of Examples 1 to 15.

[0238] Example 32. At least one acoustic transducer assembly (1) and at least one audience region (3) are geometrically linked to one another by a coordinate system (2) that defines a position vector s for determining the physical location of individual acoustic transducers (9) within the at least one acoustic transducer assembly (1) and their coordinates within the region of the at least one acoustic transducer assembly (1). i and further, a point in the coordinate system (2) and a point in at least one audience region (5) are related by a position vector r i and the direction vector, specifically the normalized direction vector (61),

number

number

number

[0239] The local direction (50) of the common wavefront (4) is expressed as a normalized direction vector (61)

number

[0240] Example 33. A device according to example 31 or 32, characterized in that the different execution times of the acoustic transducers (9) of the acoustic transducer assembly (1) are realized using mechanical or geometric positioning of the acoustic transducers (9) controlled with a coherent signal, in particular the signal level for each acoustic transducer (9) can correspond to a value determined for the original intersection point of the grid.

[0241] Further exemplary embodiments are described below.

[0242] Concealing an acoustic system behind an acoustically semi-transparent panel leads to the absorption or reflection of sound energy, which in turn leads to an amplification change in the audio spectrum. The transfer function (TF) is the frequency-dependent reduction or amplification of the sound level of a sound source as it passes through the panel used to conceal the sound system.

[0243] Traditionally, compensation for the TF of a hidden speaker is achieved by equalizing the average TF over several angles, or simply by taking the on-axis TF and applying the inverse curve as the equalization stage profile. A preliminary evaluation of the TF in an anechoic chamber concluded that the evaluated panels introduced very different amplitude variations at different angles for the same frequency.

[0244] As a result, the spectral balance within the audience area deviates significantly at different angles and distances from the hidden audio module, reducing spectral uniformity. TF compensation as described above is not sufficient, but an angle-dependent spatial transfer function is required.

[0245] Wavefield synthesis and 3D audio beamforming technology is based on the high-resolution sensitivity and 3D directional balloon of the transducers integrated into the audio module. Utilizing 3D audio beamforming algorithms, level and phase manipulations can be used to define individually shaped wavefronts that perfectly fit the audience area. Furthermore, the resulting wavefronts are optimized for spatial and spectral uniformity based on a reference target curve.

[0246] If compensation of the spatial transfer function becomes an issue, solutions can be adopted to improve the spectral balance in the 3D space of the hidden audio module, as described herein.

[0247] If the algorithm knows the spatial transfer function introduced by the acoustic panel in front of the acoustic transducer, the optimization and equalization equipment will compensate for the effect of the panel in each direction, not just on-axis, to deliver power similar to that without the panel. Changes in the acoustic transducer's radiating balloon caused by panel resonance, reflections at specific angles, or sound absorption will be known in advance and partially compensated to achieve the desired spectral profile across the audible range.

[0248] The objective is to detect a directional balloon of transducers attached to the backside of, for example, a carbon fiber substrate.

[0249] One possibility is to determine the directivity of a loudspeaker using a holographic measurement approach. This method uses a special solution of the wave equation (spherical harmonics, Hankel functions) to determine the 3D sound pressure of an audio device. Compared to traditional measurement methods, this provides more comprehensive and accurate measurement data while minimizing costs (e.g., expensive measurement space) and measurement time.

[0250] The instrument to be checked remains in a fixed position in the center of the scanner. This simplifies handling of heavy instruments and ensures constant spatial excitation and therefore constant spatial reflection during the scanning process. A robotic arm moves the microphone around the instrument to be tested and detects sound pressure in the near field.

[0251] By scanning along the double layer, for example, direct sound separation can be used, which uses additional phase information to detect the direction of the sound waves and removes all spatial reflections from the direct sound of the loudspeaker. Thus, the measurement system provides accurate free-field data in any environment (such as a workroom or office).

[0252] Therefore, the effectiveness of acoustic panels used to cover audio modules can be evaluated based on an exemplary boofer-tweeter pair. Because near-field measurements do not involve signal processing, spectral power outside the operating range of the acoustic transducer is also shown. The frequency response of an individual acoustic transducer with and without an acoustic panel is shown in Figure 12.

[0253] A comparison of the acoustic results of both measurements shows a transmission loss in the frequency response near the axis. In a conventional approach, these frequency responses serve as the basis for calculating the transmission gain, compensating for this energy loss in the DSP. However, when the off-axis frequency response is also taken into account, the acoustically semi-transparent panel introduces additional disturbances. At certain frequencies, particularly in the range of 2 kHz to 5 Hz, there are additional resonances that affect the radiation pattern. Above f > 7 kHz, the measurements show a higher transmission loss on-axis than off-axis, resulting in a lower directivity index and slightly larger beam angles when the panel is installed.

[0254] The spatial transfer function of the acoustic panel in Figure 13 shows the angular dependence of the amplitude change across the complete spectrum. The spatial transfer function is the absolute spectral amplitude difference between a bare transducer and the same transducer behind an acoustic panel after applying one octave of frequency smoothing and 15 degrees of spatial smoothing. Spatial smoothing is applied to prevent isolated artifacts created by the panel used in the measurement from being included in the general compensation for other panels with different characteristics, i.e., bracing, differences in panel stiffness, and slight differences in manufacturing or panel positioning.

[0255] To illustrate the advantages of the 3D audio beamforming approach described here compared to traditional audio solutions, a 3 kHz frequency was used as an example in Figure 13. The level difference between 0° (on-axis) and 45° is approximately 2 dB, so any global spectral correction at 2 kHz will work effectively for one angle but will either overcompensate or undercompensate for other angles.

[0256] Differences in spatial transfer functions are difficult to resolve with a single global equalizer, but with 3D spectral compensation as part of the optimization engine, the acoustic transducers used to reproduce the beams can be individually spatially balanced, resulting in optimal spectral balance as the listener moves through the audience area.

[0257] Once the transducer balloon data is corrected using the spatial transfer function of the panel and incorporated into the algorithm as an audio module variant, the hidden audio module can be optimized, simulated and benchmarked.

[0258] Figure 14 shows, with 1 / 3 octave resolution, exemplary transfer functions of an optimized beam with an aperture angle of 120° under different scenarios at different angles (0°, 30°, and 60°): a simple audio module (black), the same module and beam configuration covered on the front with an MDI panel (red), and finally an audio module covered with an MDI panel and spatially compensated with an algorithm.

[0259] Figure 14 shows the different spectral variations at different angles that can only be resolved with individual equalization. Spatial compensation of the acoustic panels was implemented to restore the overall spectral balance of the desired frequency response. Isolated local artifacts or spectral discoloration due to panel resonances or reflections were not part of the compensation, as their compensation has been shown to be ineffective.

[0260] Audio systems can be concealed in several ways: Acoustically transparent materials such as cloth or perforated screens allow sound to pass through with minimal loss of sound power and can be effective in certain environments.

[0261] When projecting video content, a problem may exist if there is visible distortion. To solve this problem, a high-resolution video projection solution using a micro-perforated carbon fiber substrate can be used. This has proven very effective as it provides a seamless projection surface, but the underlying acoustic system has some drawbacks, namely, angle-dependent variations in the transfer function.

[0262] The near-field scanner system has proven to be an effective and robust method for detecting the directional characteristics of loudspeakers, including those hidden behind panels. The detection of the three-dimensional behavior of drivers fitted to audio modules and inserted behind panels was used to implement the necessary data for spatial-spectral balance correction.

[0263] Spectral balance correction compensates for level differences between different angles in 3D space for the same frequency across the entire audio spectrum. This function significantly increases the spectral uniformity of the audio beam when used, representing a clear advantage over traditional compensation methods that do not use it. [Explanation of symbols]

[0264] 1. Acoustic Transducer Assembly 2 Common coordinate system 3 Audience Area Wavefronts formed from four elementary waves 5. Auxiliary grid on the reference surface of the acoustic transducer assembly 6 Audience Area Sub-Grid 7-directional vector 8 element waves 9 acoustic transducers 10 Wavefront Supply Area 105 Wavefront Subregions 106 Audience Area Subarea 12 Virtual Sound Sources 30 curved acoustic transducer surfaces 31 normal 40 Vector Determination Cube 50 Local direction of the common wavefront Standard rectangular parallelepiped with 60 diagonals and 1 61 Standardized Direction Vector 701, 702, 703 Audience area subarea 801 used intersections 802 fixed audience area 90 Mechanically Curved Acoustic Transducer Assembly 91 Spatial Offset (Item 1) A method of operating and / or configuring a two-dimensional acoustic transducer assembly (1) comprising a plurality of individually controllable acoustic transducers (9), comprising: each of the acoustic transducers (9) of the acoustic transducer assembly (1) generates elementary waves that overlap to form at least one acoustic wavefront according to the principles of wavefield synthesis and / or according to a beamforming method; The method, wherein the local propagation direction of the at least one acoustic wavefront of at least one first acoustic transducer (9) of the acoustic transducer assembly (1) is known or can be determined, detecting at least one acoustic disturbance coefficient causing a frequency-dependent and / or direction-dependent variation in the sound pressure of the at least one first acoustic transducer (9) of the acoustic transducer assembly (1); an input signal of the at least one first acoustic transducer (9) of the acoustic transducer assembly (1) is coupled to at least one correction device, in particular a filter device, which influences the acoustic disturbance coefficient for the at least one first acoustic transducer (9) depending on the local propagation direction of the at least one acoustic wavefront, in particular minimizing it by forward correction; The method, characterized by: (Item 2) the frequency response of the at least one first acoustic transducer (9) of the acoustic transducer assembly (1) is determined for a plurality of radiation directions in a low-reflection space, which can be described in particular by spherical coordinates; the correction device includes an inverse filter that significantly compensates for nonlinearity of the frequency response of the at least one first acoustic transducer (9) based on a frequency response error of the at least one first acoustic transducer (9) in the local propagation direction of the at least one wavefront in the at least one first acoustic transducer (9); Item 1. The method according to item 1, (Item 3) the acoustic disturbance coefficients include acoustic obstacles in a direction of propagation of the at least one acoustic wavefront; The correction device includes a filter, the filter comprising: the frequency response of the at least one first acoustic transducer (9) when radiation is blocked by the acoustic obstacle; the frequency response of the at least one first acoustic transducer (9) in the case of unimpeded radiation along the local propagation direction of the at least one wavefront on the at least one first acoustic transducer (9); 3. The method according to claim 1 or 2, wherein the influence of the acoustic obstacle is minimized based on the difference between the acoustic obstacles. (Item 4) the acoustic disturbance coefficient comprises an airborne sound insulation within an audience area into which the at least one acoustic wavefront is emitted; and / or The correction device minimizes the effects of airborne sound insulation based on the current values ​​of relative humidity (%), air pressure (kPa) and temperature (K) in the audience area. 4. The method according to at least one of items 1 to 3, characterized in that: (Item 5) A two-dimensional acoustic transducer assembly (1) configured and configured to carry out at least one of the methods described in items 1 to 4. (Item 6) 5. A computer program product configured to be executed on a processor to perform at least one of the methods according to any one of items 1 to 4.

Claims

1. A method of operating and / or configuring a two-dimensional acoustic transducer assembly (1) comprising a plurality of discretely controllable acoustic transducers (4) arranged on a planar or curved surface and controlled according to a wave field synthesis or beamforming method, comprising: frequency-dependent and / or direction-dependent variations in the sound pressure of the wavefront (6) emanating from the acoustic transducers of the acoustic transducer assembly (1) are compensated for by each acoustic transducer of the acoustic transducer assembly (1) comprising at least one upstream inverse filter for each input signal, The inverse filter comprises in the signal path: a) the radiation characteristics of each said acoustic transducer, determined in spherical coordinates φ and θ and stored in the system, causing a variation in the frequency response or sound pressure level of the reproduction in the direction of propagation of the local wavefront (6) determined by the direction vector d; b) the insertion loss of said wavefront (6) through at least one partially sound-transparent obstacle in the acoustic path depending on the direction vector d of the associated local direction of said wavefront (6); c) a frequency-dependent sound insulation in the air between each acoustic transducer and the audience area, which depends on the path length of the wavefront (6) in the local direction to the audience area (2), the temperature, humidity and air pressure of the audience area; The method is characterized by correcting the above.

2. The frequency response of the acoustic transducer (4) of the acoustic transducer assembly (1) associated with each correction element is determined in a low-reflection space and stored in a system for a plurality of radiation directions that can be described in particular using spherical coordinates φ and θ, and the reproduction side correction device is adapted to calculate the function G ｉｎｖ 2. The method of claim 1, further comprising: an inverse filter having a function (f) that, depending on the propagation direction d of the associated local wavefront, balances corresponding nonlinearities in the frequency response of the corresponding acoustic transducer based on a direction-dependent frequency response error of the corresponding acoustic transducer in the local propagation direction of the associated wavefront stored in the system, so that, during cooperation with the acoustic transducer of the acoustic transducer assembly, the frequency response of each radiated local wavefront becomes independent of its propagation direction d, and thus a complete wavefront of the acoustic transducer assembly is linearized for a corresponding channel independently of its propagation direction by applying the method separately for each individual acoustic transducer and each individual input channel of the acoustic transducer assembly.

3. The attenuation of the partially acoustically transparent acoustic obstacle in the propagation direction d of the associated acoustic wavefront is given by: the frequency response stored in the system of the unimpeded radiation local wavefront (6) emanating in the direction of the propagation direction d; the measured frequency response of the local wavefront (6) emitted by a partially acoustically transparent acoustic obstacle and emanating in the direction of the propagation direction d; for the discrete spherical coordinates φ and θ, so that for each individual acoustic transducer of the acoustic transducer assembly (1) and for each individual input channel, the amplitude and frequency response of the signal of the associated local wavefront (6) is calculated as a function of the function H ｉｎｖ 2. The method according to claim 1, characterized in that the frequency response of the radiation wavefront is independently corrected via the inverse filter with (f) and in this way, in cooperation with the surrounding acoustic transducers belonging to the acoustic transducer assembly (1), the frequency response of the radiation wavefront is made independent of its propagation direction d in the direction-dependent attenuation of the acoustic obstacles.

4. The acoustic disturbance coefficient determines the air sound insulation in the audience area (2) based on the current values ​​of relative humidity (%), air pressure (kPa) and temperature (K) in the audience area (2), and the path length to the audience area, which depends on the direction vector d(3) of the local wavefront (6), is calculated for each individual sound transducer and each individual input channel of the sound transducer assembly (1) by a function A ｉｎｖ 2. The method of claim 1, wherein the reproducing side correction device individually balances the reproducing side correction device using an inverse filter having (f).

5. 2. The method according to claim 1, wherein the order of the correction elements in the signal path can be freely selected and individual correction possibilities can be bridged or omitted.

6. 2. The method of claim 1, wherein if the direction of the wavefront in the system is fixed, a fixed correction value can be stored in the system.

7. 10. The method of claim 1, wherein the system with permanently programmed directivity and permanently programmed direction-dependent frequency response correction can operate autonomously as an individual module or can be combined with additional correspondingly programmed modules to form a permanently programmed acoustic transducer array.

8. 2. The method of claim 1, wherein targeted, directionally dependent frequency response variations are made possible by deliberate manipulation of the corrective inverse filter, e.g. to shape the specific preferences of individual audience groups, or to compensate for hearing loss in individuals, or to extend the artistic possibilities of sound field design.

9. 2. The method of claim 1, characterized in that the data of the compensation filters of each of the three filter blocks is preprocessed and normalized in a first step to vary the overall amplification in all directions by a fixed value, followed by frequency limiting and spatial and spectral smoothing of the data, the degree of which depends on the required quality of compensation and the available filter resolution, and finally the normalized and smoothed frequency response data is inverted for given angles φ and θ to obtain the final inverse filter.

10. data relating to the directional characteristics is stored in the individual modules and can be read from a central memory during the configuration process and overwritten via a data path; 2. The method of claim 1.

11. A two-dimensional acoustic transducer assembly (1) configured and shaped to carry out at least one of the methods according to claims 1 to 10.

12. A computer program product configured to be executed on a processor to perform at least one method according to claims 1 to 10.

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