Patent Application
20230135696
The disclosure relates to a sound transducer arrangement and to a method of operating a sound transducer arrangement.
For the reproduction of audio signals, the principle of wave field synthesis is well known (see e.g. Berkhout, A. J. (1988): A holographic approach to acoustic control. Journal of the Audio Engineering Society, Vol. 36, No. 12, December 1988, pp. 977-995).
According to the Huygens principle, sound wave fronts are reconstructed from a multitude of elementary waves. Each elementary wave originates from the acoustic centre of a sound transducer, which is driven by its associated amplifier. The superposition of elementary waves is also the basis of beamforming principles, with which sound waves can be emitted preferentially in a desired direction (see e.g. Schroder, Jaeckel, Evaluation of beamforming systems, 4th Berlin Beamforming Conference 2012.4th).
In principle, these elementary waves are to synthesise the wave fronts in the entire audible transmission range. In order that the sound wave fronts synthesised from the elementary waves can be radiated with the same amplitude in every direction, the functional principle requires an undirected half-space radiation of the individual sound transducers. In order to avoid undesired interference in the reproduction range, which manifests itself in aliasing effects, the individual sound transducers should theoretically—even for the upper transmission range (e.g. more than 4 kHz)—be arranged at a distance from each other of less than half a wavelength of the radiated signal.
For the reproduction area, i.e. an indoor and/or outdoor area, wave field synthesis requires a swell-free volume, i.e. all reflections should be avoided. However, because complete acoustic control of the reproduction space is hardly realisable in practice, the wave fronts must be aligned in both the azimuth and elevation planes. In this way, the generation of reflections can be largely avoided by ensuring that the reflection surfaces of the reproduction space are not unintentionally hit by the synthesised wave fronts.
This is not possible with horizontal rows of transducers around the audience, such as those realised in a system at the TU-Berlin (http://www.fouraudio.com/de/referenzen/wellenfeldsynthese-an-der-tu-berlin.html). Directed cylindrical waves are created in the elevation plane.
From WO 2015/036845 A1 it is known to construct larger, two-dimensional sound transducer surfaces in modules according to the principle of wave field synthesis. However, with a two-dimensional transducer array (e.g. DE 2005 10001395 A2) according to the principle of wave field synthesis, the requirement for an aliasing-free reproduction in the entire transmission range leads to a disproportionately high effort, because the total number of transducers quadruples with halving their distance to each other. In practice, such radiating surfaces are therefore constructed in such a way that a largely closed wavefront can be generated up to the forman range of speech reproduction, i.e. approximately up to 4 kHz. The audio frequencies above this are of less importance for the localisation of the sound source, so that direction-dependent aliasing effects are allowed here.
Dynamic loudspeakers are commonly used as sound transducers. However, with the corresponding diaphragm diameter, their natural resonances are several octaves above the lower cut-off frequency of the audio range to be reproduced, which is required for high-quality reproduction. The sensitivity and power handling of dynamic loudspeakers are also far below the values that are standard for larger sound transducers.
It is true that in such a two-dimensional arrangement the efficiency of the individual sound transducers improves with increasing wavelength of the signal, because they work increasingly synchronously with decreasing frequency. The air in front of the diaphragm can therefore no longer escape unhindered to all sides, which is why a larger mass of air is now in front of the diaphragm. Compared to a single sound transducer, the load of the air column that now has to move causes a significantly improved adaptation to the radiation resistance of the air, because the diaphragm now no longer works almost into nothing, but finds a working resistance. This leads to a significant level increase towards lower frequencies. However, this cannot compensate for the steeper drop in sound pressure of the driver below its natural resonance. Therefore, the use of different sound transducers with the corresponding division of the frequency ranges to be radiated is an advantageous solution.
Such a division of the reproduction range into individual frequency ranges leads to only minor irregularities in the vertical directivity of the system in the horizontal WFS transducer rows, such as in the TU Berlin lecture hall (see Anselm Goertz, Michael Makatsch, Christoph Moldrzyk, Stefan Weinzierl: Zur Entzerrung von Lautsprechersignalen für die Wellenfeldsynthese (Equalization of loudspeaker signals for wave field synthesis systems), 25th TONMEISTERTAGUNG—VDT INTERNATIONAL CONVENTION, November 2008).
Complex challenges arise in a planar or spatial sound transducer arrangement based on the principle of wave field synthesis. The assembly of the different sound transducers is not possible in one plane, because the wave front must be reconstructed in all three spatial dimensions without large gaps in the spacing of the high-frequency sound transducers. Therefore, the acoustic centres of the elementary waves that make up the wavefront to be synthesised do not lie in a common plane.
The first sound transducer 11 and the second sound transducer 12 each emit elementary waves 311, 312 which have their point of origin in the acoustic centres 211, 212 of the first sound transducer 11 and the second sound transducer 12 respectively.
In dome transducers, such as the second transducers 12 shown here, the acoustic centres 212 are located approximately on the front side of the dome. With cone sound transducers, like the first transducers 11 shown here, the acoustic centres 211 of the elementary waves 311 are located in the rear part of the cone, slightly in front of the front of the dust dome (Sven Franz, Christina Imbery, Menno Wüller, Jörg Bitzer: “Bestimmung des frequenzabhängigen akustischen Zentrums eines Lautsprechers im Zeitbereich”; Institut für Hörtechnik and Audiologie Oldenburg). The exact position is frequency-dependent. Regarding the superposition of the elementary waves of the first and second sound transducers 11, 12 the position of the acoustic centres in the transition range of their working frequencies is decisive.
As can be seen from
This geometric offset cannot simply be compensated in time in the wave field synthesis and also leads to problems in the beamforming methods when superimposing the elementary waves. In the illustration of
The superimposition of inhomogeneous wave fronts inevitably leads to directional irregularities in the frequency response and to undesirable side loops, especially in the crossover range. However, it is precisely such side loops that should be avoided as far as possible if the reproduction room is to be avoided. They could create unwanted reflections that would counteract the principle of source freedom of the reproduction space that is inherent in wave field synthesis. Especially in the mid frequency range, where the crossover frequency is usually located, such reflections are easy to localise, which is why they would permanently distort the spatial reproduction.
It is an object underlying the proposed solution to improve the radiation characteristics of a sound transducer arrangement, in particular it should be possible to compensate for a geometric offset of sound transducers in a sound transducer arrangement.
This object is achieved by a sound transducer arrangement with features as described herein.
At least one first transducer in the transducer arrangement is coupled to a low-pass acoustic filter device.
For example, the acoustic centre of the first sound transducer may be located behind the acoustic centres of the high-frequency sound transducers with respect to the front of the sound transducer arrangement.
The acoustic centre of the first sound transducer and the low-pass filter device can, e.g. in one embodiment, be shifted into a plane with acoustic centres of high-frequency sound transducers as second sound transducers. This makes it possible to ensure a homogeneous superposition of elementary waves even in the transition range of the transmission frequencies, although the chassis of the sound transducers themselves are mounted in different planes. In such a “loudspeaker system”, the sound waves no longer emanate from the loudspeaker itself. It only builds up an air pressure in the chamber, not a wave. The sound wave originates at the exit of the air channel from the vibrating air column.
An acoustic low-pass filter device uses the spring effect of a volume of air in series with the mass of the air (1.293 g/l) in a channel. The volume can then be taken to be the chamber volume plus the volume of the membrane cone. Air can only come out of the channel, so the acoustic centre then lies at the outlet of this channel. The acoustic low-pass causes, among other things, a 90 degree phase shift at the outlet of the air channel, which is taken into account when driving high-frequency loudspeakers.
The at least one acoustic low-pass filter device can be placed in front of, i.e. in particular in the main propagation direction of the elementary wave that can be generated by the at least one first sound transducer. However, the filter device can also assume other positions relative to the coupled sound transducer, e.g. be offset or positioned laterally. However, in one embodiment, the outlet of the 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, can end in the plane of the acoustic centres of the sound transducers.
The acoustic low-pass filter device may be or comprise a mechanical device. As such, it may have a resilient air volume in an air chamber. The air chamber may be located in front of the coupled transducer.
Also, a cavity, in particular the volume of the diaphragm cone, of the coupled sound transducer may be part of the air chamber of the low-pass acoustic filter device and/or part of the sound transducer may be part of the boundary of the air chamber. In particular, a cone of the sound transducer may be part of the air chamber or make up the entire air chamber. However, the cone may also be in air-conducting communication with a further air chamber to the air chamber of the low-pass acoustic filter device. A cone volume of the at least one first sound transducer may be part of or correspond to the resilient air volume.
The low-pass acoustic filter device may have a neck or similar constriction of the air outlet comprising a vibrating air mass.
The neck of the acoustic low-pass filter device does not have to be a tube. Rather, it can deviate from a straight line and have an approximately circular or polygonal cross-section or any other shape. A straight tube can also have a cross-section that deviates from a circular cross-section.
The opening of the neck into the environment may be integrated in a plate in front of the respective at least one first sound transducer; also, an opening in such a plate may be formed as an opening of the neck into the environment or may be formed as the neck itself.
It should be noted that part of the upstream air is relatively rigidly connected to the air in the channel and must therefore be added to the vibrating mass. The corresponding calculation basis for this is known from the orifice correction for bass reflex tubes.
The at least one first sound transducer can be designed as a mid-frequency sound transducer, a low-mid-frequency sound transducer and/or a low-frequency sound transducer. It can be a dynamic loudspeaker, in particular a cone sound transducer, but can also be realised by another transducer principle.
A plurality of first sound transducers may be arranged in a pattern in one embodiment. This pattern can in particular be a one-, two- or three-dimensional grid pattern in which the first sound transducers are arranged regularly or almost regularly (e.g. a slight offset due to aliasing is possible). The grid pattern does not necessarily have to be arranged in a plane, so that grid arrangements in a surface with curvatures are also conceivable. For example, sound transducers of a similar type or a similar transmission range (e.g. mid-frequency, low-mid-frequency or low-frequency sound transducers) can take up an analogue position.
Further sound transducers of the sound transducer arrangement can be arranged in a second pattern, in particular a grid pattern, relative to each other. Further sound transducers can be, for example, high-frequency sound transducers, in particular dome sound transducers. These further sound transducers do not necessarily have to be arranged in a planar pattern either.
The first and second patterns can overlap to form a common pattern or represent a superposition of two grid patterns. In one embodiment, the second sound transducers can also be mounted in the vibrating air mass, in which case their influence on the cut-off frequency of the acoustic low-pass filter must be taken into account.
The at least one acoustic low-pass filter device can be designed as a Helmholtz resonator or have a Helmholtz resonator. A Helmholtz resonator has an air volume of any shape that is connected to the environment via a comparatively small-volume neck. The air in the neck can be regarded as an inert mass. The entire air volume forms an elastic volume, so that a spring-mass system is present. Such a spring-mass system can, for example, be coupled to a sound transducer by being arranged in front of the sound transducer. Thus, the Helmholtz resonator serves as a low-pass filter device.
In a further embodiment, the acoustic low-pass device may be designed such 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
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.
If a plurality of first sound transducers of the sound transducer arrangement are coupled with acoustic low-pass filter devices, the acoustic centres of the first sound transducers with coupled low-pass filter devices can lie on a surface, in particular a plane.
Furthermore, the acoustic centre of the at least one first sound transducer with coupled low-pass filter device and of a second sound transducer of the sound transducer arrangement may lie on a surface, in particular a two-dimensional plane.
The surface can be spanned in particular by the acoustic centres of the first and second sound transducers—using the low-pass filter device. Accordingly, the acoustic centres of the first sound transducers and low-pass acoustic filter devices coupled thereto and the acoustic centres of second sound transducers of the sound transducer arrangement can be arranged in a surface, in particular a plane.
The acoustic centre of the at least one first sound transducer can be positionable by means of the coupled acoustic low-pass filter device, in particular displaceable along the direction of sound propagation. This can be used to adjust the spatial radiation characteristic of the sound transducer arrangement, in particular for a homogeneous structure of the elementary waves of the wave field synthesis or a related beamforming method.
The direction of the displacement of the first acoustic centre of the at least one first sound transducer can be collinear to the direction of propagation of an elementary wave generated by the at least one first sound transducer. In this case, the propagation direction of the elementary wave is determined by the vector that is perpendicular to the plane that delimits the half-space into which the sound transducer radiates.
In particular, the acoustic centre of the at least one first sound transducer can be shifted by means of the coupled acoustic low-pass filter device in such a way that it lies on the plane of a second sound transducer, in that the shifted acoustic centre lies on the plane of the height of the acoustic centre of a second sound transducer, the plane of the height of the acoustic centre of a sound transducer being 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.
Conversely, the acoustic centre of the first sound transducers can also be shifted by means of the coupled acoustic low-pass filter device so that the acoustic centre of a second sound transducer lies on the plane of the height of the shifted acoustic centre.
In a further embodiment, the additional phase rotation of a signal of the at least one first sound transducer resulting from coupling with an acoustic low-pass filter device can be compensated for by adapting the drive, in particular by delaying the drive of the at least one second sound transducer, so that the elementary waves of the sound transducers in the sound transducer arrangement are superimposed to form a common wavefront.
In one embodiment, the cut-off frequency of the at least one acoustic low-pass filter device can be tuned above, in particular one to two octaves above, a crossover frequency of a transmission range of the respective at least one first sound transducer. Accordingly, the transmission range of the at least one first sound transducer does not have to be substantially changed by coupling with one of the acoustic low-pass filter devices.
Furthermore, second sound transducers, especially for the high-frequency range, can be oriented differently from the main axis of the sound transducer arrangement, which is perpendicular to the two-dimensional sound transducer surface, with the aim of linearising the reproduction for distant listeners who are located far away from the main axis in the radiation direction of the sound transducer arrangement. The main axis of the sound transducer arrangement may be related to a local area in the case of curved surfaces.
The described embodiments also relate to a modular sound transducer system comprising, for example, at least two sound transducer arrangements 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. The described embodiments refer to a module in the modular sound transducer system or also to the modular sound transducer system as a whole.
A module in a sound transducer system can in particular be designed as a three-way module or have such a module. This can have first sound transducers, which are designed as cone sound transducers and can be used for the transmission of the medium frequency spectrum. These are each coupled with an acoustic low-pass filter device.
Furthermore, the module can have dome sound transducers that can be used for audio transmission of the upper frequency spectrum. These can be mounted in groups on printed circuit boards in such a way that their distance to each other is smaller than the distance of the mid-frequency loudspeakers to each other. In particular, their distance to each other is smaller than the shortest wavelength of the frequency range to be transmitted without perceptible aliasing effects. At the upper limit of the transmission range, wavelengths of approx. 2.15 cm result. In practice, a distance of 4-12 cm, especially 8 cm, between high-frequency sound transducers is usually sufficient to ensure transmission without perceptible aliasing effects.
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.
In the following, the interrelationships and embodiments are explained with reference to the drawings:
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.
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.
The first sound transducers 11 shown in
Furthermore,
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
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
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
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.
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.
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.
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.
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.
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.
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.
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.
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
The first sound transducers 11 are exemplarily shown in
An acoustic low-pass filter device 5 is coupled to each of the first sound transducers 11. In
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
In the embodiment shown in
The embodiment of the acoustic low-pass filter device shown in
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
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
In the embodiment shown in
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.
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
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
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.
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.
In
Part of the boundary of the neck 52 of the low-pass acoustic filter device 5 shown in
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.
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.
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.
In the example shown in
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.
The resonance frequency is calculated according to the following formula
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.
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
where c the speed of sound in m/s, S the area of the exit opening of the neck in m2, L the length of the neck in m and V the volume of the springy air mass in m3.
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
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.
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,
between 100 and 5000.
In the form shown, the first grid pattern 611 and the second grid pattern 612 overlap to form a common grid pattern 6.
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
In the first pattern 611, for example, sound transducers of a similar construction type or of a similar working range may occupy analogue positions.
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.
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.
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.
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.
In addition,
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.
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
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
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.
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.
This randomly distributed slight variation in the mounting direction of the high-frequency sound transducers 12 can reduce the effect described with reference to
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.
The dome sound transducers shown in
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
As can be seen in
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.
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.
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.
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.
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.
In this sense, the embodiments described above, e.g. according to
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 203 659.4 | Mar 2020 | DE | national |
This application is the United States national phase of International Application No. PCT/EP2021/057145 filed Mar. 19, 2021, and claims priority to German Patent Application No. 10 2020 203 659.4 filed Mar. 20, 2020, the disclosures of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/057145 | 3/19/2021 | WO |
