Acoustic Transducer Arrangement and Method for Operating an Acoustic Transducer Arrangement

Abstract

The invention relates to a sound transducer arrangement (1) according to the principle of wave field synthesis, characterised in that at least one first sound transducer (11) is coupled to a respective acoustic low-pass filter device (5). The invention also relates to a method for operating a two-dimensional sound transducer arrangement.

Claims

1.-31. (canceled)

32. A sound transducer arrangement according to the principle of wave field synthesis or a beamforming method, in particular for the alignment of at least one sound wave front, wherein at least one first sound transducer is designed as a mid-frequency sound transducer, as a low-mid-frequency sound transducer and/or as a low-frequency sound transducer and is coupled in each case to an acoustic low-pass filter device, the at least one acoustic low-pass filter device having a vibrating air mass in a neck or a comparable constriction of the air outlet, and the acoustic centres of the first sound transducers and the respective low-pass acoustic filter devices coupled thereto, and the acoustic centres of second sound transducers of the sound transducer arrangement, the second sound transducers being designed as high-frequency sound transducers, are arranged in a surface, in particular a plane, in the region of the transmission frequencies of their transmission ranges.

33. The sound transducer arrangement according to claim 32, wherein the at least one acoustic low-pass filter device comprises a mechanical device.

34. The sound transducer arrangement according to claim 32, wherein the at least one acoustic low-pass filter device comprises a resilient air volume in an air chamber in front of the respective first sound transducer.

35. The sound transducer arrangement according to claim 34, wherein a cone volume of the at least one first sound transducer is part of or corresponds to the air chamber.

36. The sound transducer arrangement according to claim 32, wherein an opening in a plate in front of the respective at least one first sound transducer is formed as an opening of the neck of the at least one acoustic low-pass filter device or as the neck itself.

37. The sound transducer arrangement according to claim 32, wherein the neck of the at least one acoustic low-pass filter device has a circular cross-section.

38. The sound transducer arrangement according to claim 32, wherein the neck of the at least one acoustic low-pass filter device has a polygonal cross-section or corresponds to an opening in the sound transducer arrangement which is arranged in front of the at least one first sound transducer.

39. The sound transducer arrangement according to claim 32, wherein a plurality of first sound transducers of the same or different design are arranged in a first pattern relative to one another, in particular in a grid pattern.

40. The sound transducer arrangement according to claim 39, wherein further sound transducers, in particular high-frequency sound transducers, are arranged in a second pattern relative to one another, in particular in a grid pattern.

41. The sound transducer arrangement according to claim 39, wherein the first pattern and the second pattern represent a superposition of two grid patterns.

42. The sound transducer arrangement according to claim 32, wherein the at least one acoustic low-pass filter device comprises a Helmholtz resonator.

43. The sound transducer arrangement according to claim 42, wherein said at least one Helmholtz resonator has the property that the numerical value of the ratio of the area of the outlet opening to the product of the volume of its air chamber and the length of its neck is $\frac{S}{V.Math.L}$ is between 100 and 5000, the area and volume being expressed in square metres and cubic metres respectively, and the length of the neck being expressed in metres.

44. The sound transducer arrangement according to claim 32, wherein the first acoustic centre of the respective first sound transducer can be displaced by the at least one acoustic low-pass filter device, in particular for setting the spatial radiation characteristic of the sound transducer arrangement for a homogeneous structure of the elementary waves of the sound transducer arrangement.

45. The sound transducer arrangement according to claim 44, wherein the direction of displacement of the first acoustic centre of the at least one first sound transducer is collinear with the direction of propagation of an elementary wave generated by the at least one first sound transducer.

46. The sound transducer arrangement according to claim 44, wherein the displaced acoustic centre of the at least one first sound transducer lies in the plane of the height of a second sound transducer of the sound transducer arrangement and/or that the acoustic centre of a second sound transducer of the sound transducer arrangement lies in the plane of the height of the displaced acoustic centre.

47. The sound transducer arrangement according to claim 32, wherein a drive of at least one second sound transducer of the sound transducer arrangement is set up in order to compensate for an additional phase rotation of a signal of the at least one first sound transducer, which occurs by coupling with the acoustic low-pass filter device, so that the elementary waves are superimposed to form a common wave front.

48. The sound transducer arrangement according to claim 32, wherein the cut-off frequency of the at least one acoustic low-pass filter device can be tuned above a crossover frequency of a transmission range of the respective at least one first sound transducer.

49. The sound transducer arrangement according to claim 32, wherein the outlet of an air channel with its oscillating air mass, which as an acoustic centre is the starting point of the elementary wave of the at least one first sound transducer together with a loudspeaker chassis and the acoustic low-pass filter, ends in the plane of the acoustic centres of second sound transducers, in particular of high-frequency sound transducers.

50. The sound transducer arrangement according to claim 32, wherein the acoustic low-pass filter device is formed in dependence on at least one second sound transducer influencing the cut-off frequency of the at least one first sound transducer and that of the upstream acoustic low-pass filter device when it is mounted wholly or partially in the region of the air outlet of the acoustic low-pass filter device.

51. The sound transducer arrangement according to claim 32, wherein second transducers can be oriented differently from the main axis of the system with the aim of linearising the reproduction for distant listeners located far away from the main axis in the radiation direction of the array.

52. The sound transducer arrangement according to claim 32, wherein the sound transducer arrangement comprises at least one three-way module, which comprises dome high-frequency transducers which can be used for audio transmission of the upper frequency spectrum and which are mounted in groups on printed circuit boards in such a way that their distance from one another is smaller than the distance of the mid-frequency loudspeakers from one another, in order to ensure a reproduction which is largely free of aliassing effects, and which has at least one bass transducer which is arranged behind the high-frequency sound transducers and mid-frequency sound transducers and whose generated sound pressure can be implemented as a double-valved bandpass.

53. A modular sound transducer system, comprising at least two sound transducer arrangements according to claim 32 as modules.

54. The modular sound transducer system according to claim 53, wherein the at least two sound transducer arrangements are arranged such that the radiating surfaces of the respective sound transducer arrangements are arranged in a plane, are part of a curved surface or approximate a curved surface.

55. A method for operating a sound transducer arrangement according to the principle of wave field synthesis, wherein the signal of the at least one first sound transducer system of the sound transducer arrangement is filtered with an acoustic low-pass filter device each, wherein the at least one acoustic low-pass filter device comprises an oscillating air mass in a neck or a comparable constriction of the air outlet, and the acoustic centres of the first sound transducers, which are formed as mid-frequency sound transducers, as low-mid-frequency sound transducers and/or low-frequency sound transducers, and the respective low-pass acoustic filter devices coupled thereto, and the acoustic centres of second sound transducers, of the sound transducer arrangement, wherein the second sound transducers are designed as high-frequency sound transducers, lie in the range of the transmission frequencies of their transmission ranges in a surface, in particular a plane.

56. The method according to 55, wherein the actuation of at least one second sound transducer of the sound transducer arrangement is adapted, in particular delayed, in order to compensate for an additional phase rotation of a signal of the at least one first sound transducer which is produced by coupling the at least one first sound transducer to the at least one acoustic low-pass filter device, so that the elementary waves are superimposed to form a common wave front.

57. The method according to claim 55, wherein at least a second sound transducer of the sound transducer arrangement is coupled in the range of its free-air resonance, and not as usual one octave above its natural resonance, wherein the improved matching of the sound transducers in the sound transducer arrangement to the load resistance of the air in a sound transducer arrangement is utilised according to the principle of wave field synthesis.

58. The method according to 55, wherein a time correction is made in the low bass range between the low frequency range and the low-mid frequency range in order to improve the phase response, whereby different setups may prefer either the most linear phase response possible or the lowest possible latency of the system or a compromise between both.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Furthermore, the module may comprise at least one bass sound transducer, which is arranged behind the high-frequency sound transducers and mid-frequency sound transducers and whose generated sound pressure is executable as a double-vented bandpass.

[0052] In the following, the interrelationships and embodiments are explained with reference to the drawings:

[0053] FIG. 1 a sectional view of a sound transducer arrangement according to the prior art;

[0054] FIG. 2 a schematic sectional view of a sound transducer arrangement in which first sound transducers are each coupled to a low-pass acoustic filter device;

[0055] FIG. 3 a sectional view of a sound transducer arrangement in which first sound transducers are each coupled with an acoustic low-pass filter device and the generated elementary waves of the first and second sound transducers are superimposed to form a common, homogeneous wave front;

[0056] FIG. 4 a first sound transducer of a sound transducer arrangement coupled to a low-pass acoustic filter device;

[0057] FIG. 5 schematically shows a grid pattern in which first and second sound transducers of a transducer arrangement are arranged relative to each other;

[0058] FIG. 6 a sectional view of a sound transducer arrangement in which first sound transducers are each coupled to a low-pass acoustic filter device, resulting in a homogeneous wavefront.

[0059] FIG. 7 a sectional view of a sound transducer arrangement in which first sound transducers are each coupled to a low-pass acoustic filter device, and second sound transducers are coupled in a matched orientation;

[0060] FIG. 8 a perspective view of an exemplary embodiment of a sound transducer module;

[0061] FIG. 9 a perspective view of an embodiment of a modular sound transducer system;

[0062] FIG. 10 a further embodiment of a sound transducer arrangement.

DESCRIPTION OF THE INVENTION

[0063] FIG. 2 schematically shows a sectional view of a sound transducer arrangement 1 or a sound transducer module 7 (as exemplarily shown in FIG. 8). This and all following embodiments show embodiments for sound transducer arrangements and methods for operating sound transducer arrangements.

[0064] Shown are first sound transducers 11, to each of which an acoustic low-pass filter device 5 is coupled. The detail shows four first sound transducers 11, but the number is only to be understood as an example.

[0065] The acoustic low-pass filter device 5 is shown here in each case directly in front of the first sound transducers 11, i.e. in particular in the positive direction of propagation 3111 of the elementary wave 311 generated by the respective first sound transducers 11. This positioning is to be understood as exemplary only; a different, e.g. offset or lateral positioning of the acoustic low-pass filter device 5 with respect to the coupled first sound transducer 11 is also possible.

[0066] The first sound transducers 11 shown in FIG. 2 are arranged equidistantly on a straight line. In further embodiments, first sound transducers 11 of an area of a sound transducer arrangement 1, of a sound transducer module 7 or also of the entire sound transducer arrangement 1 are arranged relative to each other in a first pattern 611, in particular a grid pattern. This pattern can be a one-, two- or three-dimensional pattern, in particular also such a grid pattern (see e.g. FIG. 5).

[0067] Furthermore, FIG. 2 shows second sound transducers 12 whose positions alternate with those of the first sound transducers 11 along the straight line. This particular arrangement is also to be provided by way of example only. The second sound transducers 12 could be arranged in a second pattern 612, in particular a grid pattern. Also, further sound transducers of the sound transducer arrangement shown in an excerpt could be arranged in a second pattern. In one embodiment, the first pattern 611 and the second pattern 612 can overlap to form a common pattern 6, as shown by way of example in FIG. 5.

[0068] Second sound transducers 12 referred to in the following may be second sound transducers 12 of the sectional view shown, but also second sound transducers 12 at another position of the sound transducer arrangement 1 shown in detail in FIG. 2. In particular, the second sound transducers 12 do not have to be in direct spatial proximity in the sound transducer arrangement to the first sound transducers 11.

[0069] The elementary waves 311 generated by the first sound transducers 11 have their apparent origin in an acoustic centre 211, which is shown as a point in FIG. 2 as an example. The acoustic centre 211 of a first sound transducer 11 may be determined, for example, by the design of the first sound transducer 11. For example, the acoustic centre of a cone transducer is located in the rear part of the cone, approximately at the front of the dust dome.

[0070] The acoustic centres 211 of the first sound transducers 11 can be positionable by means of the coupled acoustic low-pass filter device 5, in particular along an axis. This is explained by way of example with reference to FIGS. 3 and 4. The location of the displaced acoustic centre 211 is adjustable and determinable, for example, by the type or construction of the acoustic low-pass filter device 5 and/or by the placement of the acoustic low-pass filter device 5 with respect to the coupled first sound transducer 11.

[0071] In particular, the acoustic centre 211 of a first sound transducer 11 can be shifted collinearly to the propagation direction 3111 of the elementary wave 311 generated by the first sound transducer 11 by means of the coupled acoustic low-pass filter device 5.

[0072] By coupling with the acoustic low-pass filter device 5, the acoustic centre 211 of the first sound transducers 11 can be positioned such that the radii of curvature of the elementary waves 312, 311 generated by coupled first sound transducers 11 and by second sound transducers 12 are matched or correspond to each other, thus enabling the generation of a homogeneous wavefront 4 by the sound transducer arrangement 1 or the sound transducer module 7.

[0073] For example, the acoustic centres 212 of second sound transducers 12 and the acoustic centres 211 of first sound transducers 11 with coupled low-pass acoustic filter device 5 may be positioned on a common surface, in particular on a convex or concave plane.

[0074] The acoustic centre 211 of a first sound transducer 11 can be shifted by means of the coupled acoustic low-pass filter device 5 in such a way that the shifted acoustic centre 211 lies on the plane of the height of the acoustic centre 212 of a second sound transducer 12, wherein the plane of the height of the acoustic centre of a sound transducer is described by the plane which passes through the acoustic centre of the sound transducer and is perpendicular to the vector of the direction of propagation of the elementary waves generated by the sound transducer.

[0075] The cut-off frequency of an acoustic low-pass filter device 5 determines the frequency range that is attenuated by the filter device, specifically, sound is attenuated above the cut-off frequency and transmitted almost unhindered below the cut-off frequency.

[0076] In one embodiment, the cut-off frequency of the acoustic low-pass filter device 5 is tuned above the operating range or above, in particular one to two octaves above, the crossover frequency of a transmission range of the first sound transducer 11 coupled to the acoustic low-pass filter device 5.

[0077] In particular, the cut-off frequency can be tuned in such a way that the reproduction frequency range of the first sound transducer 11 is not significantly changed by coupling with an acoustic low-pass filter device 5, in particular the acoustic low-pass filter device 5 has no undesirable audible effect on the transmission range of the coupled first sound transducer 11.

[0078] Furthermore, if the cut-off frequency of the acoustic low-pass filter 5 is close to the upper limit of the transmission range of the respective first sound transducer 11 for the lower transmission range, harmonics of the first sound transducer 11 cannot reach the listeners, whereby the distortion factor of the first sound transducer 11 can be reduced.

[0079] The first sound transducers 11 can be, for example, mid-frequency sound transducers, low-mid-frequency sound transducers and/or low-frequency sound transducers. These can be realised, for example, as dynamic loudspeakers, in particular as cone sound transducers, as shown in FIGS. 3 and 4. The second sound transducers 12 can be high-frequency sound transducers which are realised as dome sound transducers (FIG. 3). The acoustic low-pass filter devices 5 may in particular comprise resonators (i.e. an air system consisting of a mass and a resilient air volume), as shown in FIGS. 3 and 4.

[0080] FIG. 3 shows a sectional view of a sound transducer arrangement 1 or a sound transducer module 7, which is to be understood as a special embodiment of the object of FIG. 2. In particular, descriptions of FIG. 2 can also be applied to FIG. 3. FIG. 3 is also to be understood as an embodiment applied to the object of FIG. 1.

[0081] The first sound transducers 11 are exemplarily shown in FIG. 3 as cone loudspeakers, which are usually used for the mid- to low-frequency range.

[0082] An acoustic low-pass filter device 5 is coupled to each of the first sound transducers 11. In FIG. 3, this is placed directly in front of each of the first sound transducers 11 and is shown as a mechanical device, which is described in more detail with reference to FIG. 4.

[0083] The illustrated mechanical acoustic low-pass filter device 5 each have a resilient air volume 53 in an air chamber 51. In the exemplary embodiment shown in FIG. 3, the air chamber 51 each comprises the cone 511 of the cone sound transducer 11 and a further air chamber 512. Therefore, the resilient air volume 53 each comprises the cone volume 531 and possibly a further air volume 532. However, the air chamber 51 could also correspond to the cone 511 or comprise or include another air chamber of the first sound transducer 11. A part, in particular a wall, of the first sound transducer 11 could be part of the boundary of the air chamber 51. However, the air chamber 51 could also be built independently of the first sound transducer 11, in particular the air chamber 51 could have no common boundaries with the first sound transducer 11.

[0084] In the embodiment shown in FIG. 3, the air chambers 51 of the acoustic low-pass filter devices 5 are partly delimited by a plate 55 which is placed in front of the first sound transducers 11.

[0085] The embodiment of the acoustic low-pass filter device shown in FIG. 3 further has a neck 52 comprising a vibrating air volume 54. In FIG. 3, the necks 52 of the three low-pass acoustic filter devices 5 are aligned so that their openings 521 into the environment lie in a plane. As shown, openings 551 in the plate 55 partially bounding the air chambers 51 are part of the boundary of the necks 52. This design is merely exemplary.

[0086] By coupling with the acoustic low-pass filter devices 5, the acoustic centre of the first sound transducers 11 is shifted approximately at the level of the openings of the necks 52. A comparison of the acoustic centres 211 of the first sound transducers 11 in FIG. 1 with the acoustic centres 211 of the first sound transducers 11 with the coupled acoustic low-pass filter devices 5 in FIG. 3 shows that the acoustic centres of the first sound transducers 11 have been shifted by the coupling with the acoustic low-pass filter devices 5. In particular, the acoustic centres were shifted along the propagation directions of the elementary waves 311 generated by the respective first sound transducers 11. The shifted acoustic centres 211 of the first sound transducers 11 lie on a surface.

[0087] FIG. 3 further shows second sound transducers 12, which are exemplarily shown as dome sound transducers, which are usually used for the high frequency range. The dome sound transducers are here exemplarily mounted on the plate 55, which represents the boundary of the air chambers 51 of the acoustic low-pass filter device 5. The plate can also be the carrier board of the second sound transducers.

[0088] The first sound transducers 11 and second sound transducers 12 are arranged in a common grid pattern 6, in particular, in the arrangement shown in FIG. 3, a first sound transducer 11 is followed by three second sound transducers 12 in a repetitive manner. This arrangement is to be understood as merely exemplary. The second sound transducers 12 can also be mounted in the area of the opening of the air channel if their influence on the vibrating air mass is taken into account accordingly when dimensioning the acoustic low-pass filter.

[0089] In the embodiment shown in FIG. 3, the openings 521 of the necks 52 of the low-pass acoustic filter devices 5 and the domes 721 of the dome sound transducers lie approximately on one surface. Since the displaced acoustic centres (displaced by the acoustic low-pass filter devices 5) lie approximately at the level of the opening of the necks 52 and the acoustic centres 212 of the dome sound transducers lie on their domes 721, the acoustic centres 211 of the first sound transducers 11 with coupled low-pass filter devices 5 and the acoustic centres 212 of the second sound transducers 12 lie approximately on one surface.

[0090] In particular, by coupling with the low-pass acoustic filter devices 5, the acoustic centres 211 of the first sound transducers 11, have been shifted to the plane in which the second sound transducers 12 have their acoustic centres 212.

[0091] The radii of curvature of the elementary waves 311, 312 of the first sound transducer 11 and the second sound transducer 12 are aligned with each other due to the displacement of the acoustic centres, as shown by a comparison with the radii of curvature of the elementary waves 311, 312 in FIG. 1.

[0092] Within the scope of a coupling with an acoustic low-pass filter device 5, a phase shift of the signals of the first sound transducers 11 is effected. This additional phase shift of the signal of the first sound transducers 11 can be compensated by an adapted control of second sound transducers 12, in particular by a delay of the control of the second sound transducers 12, so that the elementary waves 311, 312 superimpose to a common, homogeneous synthesised wave front 4. This is illustrated by a comparison of the wavefront in FIG. 3 with the wavefront in FIG. 1.

[0093] FIG. 4 shows a single first sound transducer 11 from a sound transducer arrangement 1, which is coupled to an acoustic low-pass filter device 5. The first sound transducer 11 is exemplarily shown here as a cone sound transducer.

[0094] An acoustic low-pass filter device 5 is coupled to the first sound transducer 11. This is shown here in the mechanical embodiment of an acoustic low-pass filter device, which is placed directly in front of the first sound transducer 11.

[0095] In the acoustic low-pass filter device 5, a resilient air volume 53 is coupled to a vibrating air volume 54; the former corresponds to a spring. The resilient 53 and the vibrating air volume 54 form a mass-spring system. The resilient air volume 53 is enclosed by an air chamber 51 and the oscillating air volume 52 is enclosed by a short neck 52. This corresponds to a Helmholtz resonator.

[0096] In FIG. 4, the air chamber 51 comprising the resilient air volume 53 comprises the cone 511 of the cone sound transducer 11 and a further air chamber 512. Thus, the resilient air volume 53 comprises the cone volume 531 and a further air volume 532.

[0097] Part of the boundary of the neck 52 of the low-pass acoustic filter device 5 shown in FIG. 4 is an opening 551 in a plate 55 in front of the first sound transducer 11, i.e. the opening 551 in a plate 55 is integrated into the neck 52. The opening 551 in the plate 55 could also correspond to the opening 521 of the neck 52 into the environment. However, the opening in the plate 551 could also correspond entirely to the neck 52. However, the neck 52 could also have been formed in another way.

[0098] If several, e.g. all mid frequency sound transducers, all low frequency sound transducers and/or all low-frequency sound transducers, in a sound transducer arrangement 1 are coupled to an acoustic low-pass filter device 5, a plate 55 in front of the sound transducer arrangement 1 may comprise several openings 551, which respectively serve as openings 521 of the necks 52 of the different acoustic low-pass filter devices 5 or are integrated into the necks 52 of the acoustic low-pass filter devices 5.

[0099] In the embodiment shown, the neck 52 is designed as a tube, in particular the neck 52 has a circular cross-section. However, it could also have another cross-section, e.g. a polygonal cross-section. The opening of the neck can also have a different shape, which can be determined in particular by the design of the sound transducer arrangement as a whole or results from the design.

[0100] The acoustic centre of the first sound transducer 11 migrates by coupling with the acoustic low-pass filter device 5 to the end of the neck 52 of the acoustic low-pass filter device 5, in which the vibrating air volume 54 determines the upper cut-off frequency of the acoustic low-pass filter device 5.

[0101] In the example shown in FIG. 4, the acoustic centre of the first sound transducer 11 is shifted by means of the coupled acoustic low-pass filter device 5 in the propagation direction 3111 or elementary wave 311 generated by the first sound transducer 11.

[0102] The calculation of the cut-off frequency of the acoustic low-pass filter device can be done analogously to the calculation of the resonance frequency of a Helmholz resonator. The value of the cut-off frequency of the acoustic low-pass filter device shall be at least one third to one octave higher than the electrical crossover frequency of an electronic crossover of the corresponding sound transducer.

[0103] The resonance frequency is calculated according to the following formula

[00002]$f=\frac{c}{2\pi }\sqrt{\frac{S}{V.Math.L}}$

where c is the speed of sound, S the cross-section of the opening of the neck, L the length of the neck and V the volume of the springy air mass. In addition, the orifice opening correction must be taken into account because part of the upstream air must be counted as part of the vibrating mass.

[0104] The calculation of the cut-off frequency of this acoustic low-pass filter device can be done analogously to the calculation of the resonance frequency of a Helmholtz resonator. This is calculated according to the formula

[00003]$f=\frac{c}{2\pi }\sqrt{\frac{S}{V.Math.L}}$

where c the speed of sound in m/s, S the area of the exit opening of the neck in m.sup.2, L the length of the neck in m and V the volume of the springy air mass in m.sup.3.

[0105] In addition, the muzzle opening correction must be taken into account, because part of the upstream air must be counted towards the oscillating mass. The formula then changes to

[00004]$f=\frac{c}{2\pi }\sqrt{\frac{S}{V.Math.\left(L+2d\right)}}$

because twice the diameter of the opening of the neck multiplied by the length of the neck is added to the moving air mass. This results in somewhat lower values for the cut-off frequency.

[0106] The upper end of the working range of a mid frequency sound transducer is typically between 1 and 4 kHz. With the cut-off frequency of the coupled acoustic low-pass above the transmission range of the mid-frequency loudspeaker, the ratio of the area of the exit port to the product of the volume and length of the neck, for example,

[00005]$\frac{S}{V.Math.L}$

between 100 and 5000.

[0107] FIG. 5 schematically shows a pattern 6 in which sound transducers of a sound transducer arrangement are arranged. A plurality of first sound transducers 11 arranged in a first grid pattern 611 and further sound transducers arranged in a second grid pattern 612 are shown.

[0108] In the form shown, the first grid pattern 611 and the second grid pattern 612 overlap to form a common grid pattern 6.

[0109] The first sound transducers 11 can be, for example, mid-frequency sound transducers, low-mid-frequency sound transducers and/or low-frequency sound transducers. These could, for example, have been realised as cone baffles. The first pattern can be a grid pattern, as shown in FIG. 5, but other regular arrangements of the sound transducers are also possible. Also, the pattern may be a one-, two- or three-dimensional pattern. For clarity, the low-pass filter devices 5 coupled to the first sound transducers 11 are shown here only with their mouth opening. A second sound transducer 12 may also be mounted within the mouth opening if its influence is included in the calculation of the low-pass.

[0110] In the first pattern 611, for example, sound transducers of a similar construction type or of a similar working range may occupy analogue positions.

[0111] The further sound transducers can be, for example, high-frequency sound transducers, low-frequency sound transducers and/or mid-frequency sound transducers. For example, further sound transducers may have been realised as dome sound transducers.

[0112] In the second pattern 612, further sound transducers of a similar construction type or a similar working range may occupy similar or repetitive positions. However, their position may also deviate from the regular grid if propagation times and levels for their control are interpolated accordingly to the coordinates of the regular grid. As described in DE 10 2009 006 762 A2, aliasing effects in the upper playback frequency range can be reduced in this way.

[0113] The first and second patterns may be a superposition of two grid patterns or may combine to form a common grid pattern. In this grid pattern, sound transducers of a similar type (e.g. cone or dome loudspeakers) or of a similar designated transmission range (e.g. high-frequency, mid-frequency and/or bass sound transducers) can occupy analogue positions.

[0114] The solution will be explained in the following by means of a further example of an embodiment. Other designs, also with a different division of the frequency ranges, are possible.

[0115] FIG. 6 shows a sectional view of a sound transducer arrangement 1 or a sound transducer module 7 similar to the embodiment according to FIG. 3. The descriptions from FIG. 3 can be transferred to the representation shown here.

[0116] In addition, FIG. 6 shows the directional characteristics 3121 of the second sound transducers, which are shown here as dome sound transducers as in FIG. 3. The directions of propagation of the elementary waves generated by the first and second sound transducers run parallel to each other.

[0117] High-frequency sound transducers can only radiate evenly in all directions if their membrane diameter is smaller than the wavelength of the sound to be produced. At 16 kHz, this is only 2.15 cm. With such a small diaphragm area, however, only little sound pressure can be generated at the lower end of its reproduction range. Here, a compromise must always be found between even spatial dispersion, maximum sound pressure and the lower cut-off frequency of the transmission range. A crossover frequency as low as possible to the mid frequency sound transducers allows a larger distance between the individual mid frequency sound transducers, because aliasing effects in the crossover area must be avoided. This larger distance then also allows for larger diaphragm diameters, which then allows for more efficient reproduction at the lower end of the reproduction frequency range of the mid frequency sound transducers.

[0118] The radiation pattern of high-frequency sound transducers is not constant in all directions; at certain frequencies, directional dips in the radiation are unavoidable. This is illustrated in FIG. 6 by the irregular shape of the directional patterns 3121. These problems increase with the diameter of the diaphragm. For listeners far away from the sound transducer arrangement, the solid angle of adjacent sound transducers is almost the same. This leads to a non-linearity in the frequency response of the reproduction at the relevant frequencies, depending on the position of the listener in the reproduction range.

[0119] This non-linearity cannot be compensated for by equalising the overall signal, because this would be associated with an overemphasis of the frequency in question at other places. With reference to FIG. 7, it is explained how the described effect can be reduced.

[0120] FIG. 7 shows a sectional view of a set-up comparable to FIG. 6. In contrast to the set-up in FIG. 6, the mounting directions of the second sound transducer 12 have been changed.

[0121] In particular, second sound transducers 12, which can be used for the high frequency range in the exemplary set-up, are oriented differently from the main axis 81 of the system. The aim of this is to linearise the reproduction for distant listeners who are located far away from the main axis in the direction of radiation of the sound transducer arrangement 1.

[0122] In the exemplary embodiment shown, the high-frequency sound transducers 12 are not mounted parallel on a plate but slightly inclined, as a result of which the angles of inclination of the high-frequency sound transducers are slightly different and deviate in particular from the main axis 81 of the system.

[0123] This randomly distributed slight variation in the mounting direction of the high-frequency sound transducers 12 can reduce the effect described with reference to FIG. 6. Although, as in the scenario illustrated by FIG. 6, the radiation pattern of high-frequency sound transducers 12 is not constant in all directions, as represented by the irregular shape of the directional patterns 3121, not all high-frequency loudspeakers are now aligned in the same way when viewed from a particular listening position. In this way, it can be avoided that an extended area of the sound transducer arrangement is mechanically located exactly in the direction towards the listener in which the radiation of a certain frequency is significantly reduced.

[0124] FIG. 8 shows an example of the construction of a sound transducer module, which is shown here as a three-way module, according to the principle of wave field synthesis.

[0125] The upper frequency spectrum of the audio transmission range is realised with dome sound transducers 72 in the exemplary set-up. For the middle frequency spectrum, cone sound transducers 71 are used and the bass range is implemented as a double-vented bandpass 731, 732.

[0126] The dome sound transducers shown in FIG. 8 have a very small overall depth. They are mounted in groups on printed circuit boards, which connect them to the amplifiers at the back of the modules via connectors. Their distance to each other is chosen in such a way that a reproduction largely free of aliasing effects is ensured up to the forman range of the vowels. In their working range, they guarantee a half-space radiation without deep dips in the directional directivity. In principle, however, the proposed solution is not limited to the use of dynamic sound transducers.

[0127] At the upper frequency limit of their working range, the diaphragm diameter of high-frequency sound transducers is in the range of the radiated wavelength. Here, therefore, they are relatively well matched to the working resistance of the air and the phase position of the signal can differ significantly between adjacent sound transducers. Therefore, an improvement in efficiency due to improved matching compared to each individual sound transducer is not to be expected here.

[0128] In contrast, the phase differences between adjacent sound transducers are small at the lower frequency limit of their operating range. The wavelength of the signal is several times greater than their diaphragm diameter. Here, therefore, the advantage of better matching of the arrangement to the load resistance of the transmission medium comes into play compared to the single sound transducer. The efficiency increases significantly compared to that of an identical single radiator and the weight of the air column now bearing down on the dome shifts its self-resonance significantly downwards. The otherwise necessary coupling of the sound transducer about an octave above its natural resonance can be shifted downwards into the range close to its free-air resonance.

[0129] The improved efficiency then contributes to the fact that the sound transducer arrangement 1 can produce higher maximum sound pressure levels than is possible with conventional PA loudspeakers. Because of the distributed arrangement of the sound transducers, the problem does not arise that the air in front of the small diaphragm area of a high-frequency sound transducer has to be compressed to the point of non-linearity in order to still produce the high sound pressure levels that are often common at live events, even in a large audience area. This limits the theoretically possible maximum sound pressure level of conventional loudspeaker systems.

[0130] In front of the larger total area of the generating drivers in the planar sound transducer arrangement 1 according to the principle of wave field synthesis, the sound pressure in front of each individual sound transducer remains much lower, so that with appropriate design of the amplifiers and drivers in the audience area, a significantly higher sound pressure can be generated without the non-linearity of the compression curve of the air leading to non-linearities in the perceived audio signal.

[0131] In addition, the improved efficiency in the planar sound transducer arrangement 1 makes it much easier to select the sound transducers for the adjacent frequency range. Their distance to each other should again be smaller than the wavelength at the upper limit of their transmission range. This can also be realised practically due to the relatively low coupling of the high-frequency sound transducers 72.

[0132] Here the diaphragm diameter of the cone loudspeakers used remains below the radiated wavelength throughout their frequency range. At the lower end of the band, the wavelength of the signal is more than a power of ten greater than each individual diaphragm, so that it would be completely mismatched here if it did not work in the group with the neighbouring sound transducers. In the bass range, the improved matching of the group therefore results in a very significant increase in efficiency, comparable to the better matching of the drivers in horn loudspeakers.

[0133] However, drivers with the diaphragm diameter resulting from their relatively small distance from each other are not sufficient to produce the extreme sound pressure in the low bass range that is considered indispensable in the PA area today. The self-resonance of dynamic loudspeakers with a corresponding diameter is usually well above 100 Hz, if they have the high sensitivity required in PA applications. Below the self-resonance, the sound pressure curve falls much steeper than the increase due to the efficiency of the group can compensate.

[0134] The two-way modules could be supplemented with external subwoofers as usual. However, integrating the sub-bass range into a wave-field synthesis sound transducer surface has significant advantages when a larger number of modules are combined into one sound transducer surface. In addition to better matching, a sufficiently large wall surface can also achieve a clear directional effect down to the low bass range.

[0135] The wavelengths of the signal are so large in the deep bass range that the membrane excursions in the wave field synthesis itself are largely synchronous across several modules. Despite its large diameter, each individual membrane is much smaller in its entire working range than the wavelength of the generated signal. Therefore, the efficiency in the bass range also benefits from the arrangement of the individual sound transducers in the module arrangement of a two-dimensional radiating surface.

[0136] Therefore, the exemplary construction is designed as a three-way module 7. The volume required for the bass sound transducer 73 can only be arranged behind the sound transducers for the mid-frequency and high-frequency range 71, 72. This creates the problem that the generated sound pressure must find its way to the front of the plane sound transducer arrangement 1. The continuity of the radiating surface in front of the sound transducer must be disturbed as little as possible, because this causes diffraction effects with corresponding side lobes in the directional characteristic.

[0137] As can be seen in FIG. 8, the exemplary solution is therefore designed as a double-vented acoustic bandpass filter device 731, 732. The two forward channel interrupt the structure of the high-frequency sound transducers 72 and mid-frequency sound transducers 71 only to a tolerable extent, but the operating principle of the double-vented allows an efficiency with which the bass range does not drop against the high sound pressure of the upstream sound transducer arrangement 1 for the mid- and high-frequency range. In principle, it would also be possible to arrange high-frequencies in the area of the openings of the double-vented bandpass system, if they were included in the calculation of the system. However, the air movement in the channels of the sketched example is so strong that audible swirling noises are to be expected then.

[0138] The high efficiency of the double vented bandpass 731, 732 bass sound transducer is due to the limited bandwidth and the non-linearity of the phase response.

[0139] However, with the radiated wavelength of several metres, both openings in the front can almost be considered as a common acoustic centre. Thus, a temporal correction is possible without creating an inhomogeneous field in the transition area. However, a time correction increases the latency of the system considerably with the large wavelengths in this area. This becomes a problem with every live performance. Here, it must be weighed up whether a low latency of the system or a linear phase response has priority. Compromises or different setups are possible here.

[0140] The wavelengths of the signal are so large in the deep bass range that the membrane excursions in the wave field synthesis itself are largely synchronous across several modules. Despite its large diameter, each individual membrane is much smaller in its entire working range than the wavelength of the generated signal. Therefore, the efficiency in the bass range also benefits from the arrangement of the individual sound transducers in the module arrangement of a two-dimensional radiating surface.

[0141] Basically, one can speak of a two-dimensional sound transducer arrangement if the individual sound transducers are not only arranged in a row (linear). In this case, e.g. a slight offset of individual sound transducers perpendicular to the linear extension can usually be neglected.

[0142] When speaking of a three-dimensional sound transducer arrangement, the arrangement of individual sound transducers perpendicular to the surface is important in addition to the planar arrangement. The entire surface can also be curved or bent.

[0143] In this sense, the embodiments described above, e.g. according to FIG. 8, can be described as three-dimensional sound transducer arrangements. In these embodiments, the relative distance of the individual sound transducers to each other is quite important.

[0144] FIG. 9 shows an example of a modular sound transducer system in which a number of sound transducer arrangements—as described above—are used as modules. In principle, the transducer system can have more columns and/or more rows.

[0145] FIG. 10 shows an arrangement of several second sound transducers 12, which are also mounted in the air channel of the acoustic low-pass filter device of the first sound transducer 11. This divides the air channel with the vibrating air mass 54 into several sections. The total air mass in the air channel remains unchanged. However, there is no longer a single acoustic centre of the acoustic low-pass filter device, but several air outlets 56. Each of these air outlets 56 forms the starting point of an elementary wave 57 according to Huygens' principle.

[0146] These elementary waves 57 each have the same radius in the schematic representation, i.e. they have the same time delay as the elementary wave emanating from the acoustic centre of the first sound transducer 58. It is clearly visible that these elementary waves 57 diverge significantly from the elementary wave 59 of one of the second sound transducers 12 in the acoustic centre of the first sound transducer 11 with increasing deviation from the centre line. However, they remain symmetrically distributed around this elementary wave 59. This means that the pressure maximum of the wavefront of the elementary waves 57 emanating from the multiple acoustic centres (i.e. acoustic centres at the air outlets of the distributed channels of the low-pass acoustic filter device) is in phase with the one elementary wave 59. Thus, the jointly formed wave front remains homogeneous. A common synthesised wave front 4 is formed.

LIST OF REFERENCE SIGNS

[0147] 1 Sound transducer—Arrangement [0148] 11 First sound transducer [0149] 12 Second sound transducer [0150] 211 Acoustic centre of the first sound transducer [0151] 212 Acoustic centre of the second sound transducer [0152] 311 Elementary wave of the first sound transducer [0153] 312 Elementary wave of the second sound transducer [0154] 3111 Direction of propagation of the elementary wave of the first sound transducer [0155] 3121 Directional characteristic of the second sound transducer [0156] 4 Synthesised wavefront [0157] 5 acoustic low-pass filter device [0158] 51 Air chamber of the acoustic low-pass filter device [0159] 52 Neck/Narrowing of the acoustic low-pass filter device [0160] 521 Opening of the neck [0161] 53 resilient air volume [0162] 54 Oscillating air mass [0163] 511 Cone [0164] 512 more air chamber [0165] 531 Cone volume [0166] 532 further air volume [0167] 55 Plate [0168] 551 Opening in the plate [0169] 56 Air outlets [0170] 57 Elementary wave of the acoustic centres at the air outlets of the acoustic low-pass filter device [0171] 58 Common acoustic centre of the first and second sound transducer [0172] 59 Elementary wave of the second sound transducer in the acoustic centre of the acoustic low-pass of the first sound transducer [0173] 6 Patterns [0174] 611 first sample [0175] 612 second sample [0176] 7 Three-way module [0177] 71 Mid frequency sound transducer [0178] 711 Chamber volume of the mid frequency sound transducer [0179] 72 Dome sound transducer [0180] 721 Dome of the dome sound transducer [0181] 73 Bass sound transducer [0182] 731 front channel of the bandpass [0183] 7311 Front volume of the bandpass [0184] 732 rear channel of the bandpass [0185] 7321 Bandpass rear volume [0186] 8 Direction to a distant listener [0187] 81 Main axis of the sound transducer arrangement [0188] 9 Elementary waves of the second sound transducer