SE545072C2

SE545072C2 - An acoustic system and method for controlling acoustic energy emitted from two parametric acoustic transducer arrays

Info

Publication number: SE545072C2
Application number: SE2151203A
Authority: SE
Inventors: Josef Hansson
Original assignee: Myvox Ab
Priority date: 2021-09-30
Filing date: 2021-09-30
Publication date: 2023-03-21
Also published as: EP4409929A1; WO2023055270A1; SE2151203A1

Abstract

An acoustic system contains a first and a second parametric acoustic transducer array (110a, 110b, 210a, 210b), emitting acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal (200a) and second modulated acoustic signal (200b), respectively. The first modulated acoustic signal (200a) comprises a first carrier wave (202a) and an audible sound signal (204) modulated onto the carrier wave (202a). The second modulated acoustic signal (200b) comprises a second carrier wave (202b) and the audible sound signal (204) modulated onto the carrier wave (202b) in counter phase compared to in the first modulated acoustic signal (200a). The transducer elements (ei) of the first parametric acoustic transducer array (110a, 210a) are controllable in response to a control signal (C1, C11) so as to emit the acoustic energy at a wavelength and phase determined by the control signal (C1, C11). The transducer elements (ej) of the second parametric acoustic transducer array (110b, 210b) are controllable in response to a control signal (C2, C12) so as to emit the acoustic energy at a wavelength and phase determined by the control signal (C2, C12). A controller (120) generates the control signals (C1, C2, C11, C12) such that the emitted acoustic energy forms a first directional beam of sound (B) having a first pressure maximum region (PMAX1) and a second directional beam of sound (B’) having a second pressure maximum region (PMAX2).

Description

AN ACOUSTIC SYSTEM AND METHOD FOR CONTROLLING ACOUSTIC ENERGY EMITTED FROM TWO PARAMETRIC ACOUSTIC TRANSDUCER ARRAYS TECHNICAL FIELD The present invention relates generally to an acoustic system and method for controlling acoustic energy emitted from a first and second parametric acoustic transducer arrays. Especially, the invention relates to a system and a corresponding computer-implemented method for controlling the acoustic energy from the first and second parametric acoustic transducer array to be emitted as two beams of modulated acoustic energy. The invention also relates to a computer program and a non-volatile data carrier storing such a computer program.

BACKGROUND A parametric array, in the field of acoustics, is a nonlinear transduction mechanism that generates narrow, nearly side lobe-free beams of low frequency sound, through the mixing and interaction of high frequency sound waves, effectively overcoming the diffraction limit associated with linear acoustics. The main beam of low frequency sound is created as a result of nonlinear mixing of two high frequency sound beams at their difference frequency. Parametric arrays can be formed in water, air, and earth materials/rock. Using the principle of parametric arrays, an audible sound signal modulated onto an ultrasonic carrier wave will, during propagation in air, spontaneously demodulate, creating a virtual end-fire array of audible sources. ln effect, this creates a highly directional beam of sound. By modulating audio onto a carrier wave, for example an ultrasonics carrier wave, an end-fire virtual array of audible sources is created due to demodulation of the combined signal in the air due to nonlinear effects. lf the primary source consists of an array of transducers, it is possible to steer the beam by adjusting the phase delay of individual transducers. The audio envelope signal is typically amplitude modulated onto the carrier signal. This technology is for example described in the article "A review of parametric acoustic array in air", in Applied Acoustics, 73 (2012), by Gan, W-S., Yang, J., Kamakura, T.

The applications for parametric arrays, creating a highly directional beam of sound, are numerous and include among others delivery of directional audible sound that is only audible to one person located in the correct position for receiving the directional beam of sound, but cannot be heard in the surroundings. A few non-limiting examples of when this is of interest are hands-free applications for vehicles, listening to music or talking over the phone in an open office environment or in public transport, information to museum visitors, presentation at fairs, etc.

There exist many solutions for how to apply directional, parametric, arrays to achieve audible sound in a specific location for applications such as the once mentioned herein. However, there are problems involved with the existing solutions. For ease of understanding, the problems are now described in connection with the specific application of controlling directional, parametric, arrays to achieve audible sound at the locations of two ears or a person. However, as described herein and as is apparent to a person skilled in the art, parametric arrays controlled in the manner of the present invention are useful in numerous other applications. ln prior art solutions wherein acoustic energy is emitted at frequencies around e.g. 40 kHz, a single beam from a parametric array is wide enough to reach both ears of the person. ln other words, this is a possible solution to the problem of how to achieve audible sound at the locations of two ears or a person. ln this case, there will be a one- to-one relationship between the parametric array and the person listening to the audio produced by the parametric array. lf the carrier frequency is high and the array footprint is low, the emitted beam of sound can be narrow enough that two different beams are required for audio to properly reach both ears of a person. ln this case, in order to achieve audible sound at both ears, either two arrays may be used, and the beam of each array be controlled to reach a respective ear of the person, or a single array may be used, and beamforming applied to split one beam into two beams that are controlled to reach a respective ear of the person. ln all of the above examples, even though parametric arrays are capable of generating highly directional sound, there is always some amount of sound outside the main lobe, both from sound generation in the sidelobes as well as diffracted and reflected sound.

Sound "leaking" from the directional beam(s) in this manner may cause unwantedaudible sound e.g. in areas around the main lobe of an acoustic parametric array, where no sound is intended to be heard. This may be especially problematic when two or more parametric arrays are generating sound in such a close vicinity of each other that the audible sound of the side lobes are at risk of interfering with each other. For example, the same audible sound signal may be generated by two parametric acoustic transducer arrays, and the emitted sound beam, or main lobe, of each parametric acoustic transducer array is intended to reach a respective user's ear or ears. lf the generated main lobes are in close proximity to each other, unwanted pressure maximum regions with audible sound may be created between the main lobes due to constructive interference of side lobes from the two main lobes.

There is thus a need to provide a solution for improved directivity of sound, and for reducing the generation of unwanted sound outside the main lobe, or main beam of sound.

SUMMARY The object of the present invention is to offer a solution that mitigates the above problem and renders it possible to improve the directivity of sound emitted by parametric acoustic transducer arrays and reducing the generation of unwanted sound outside the respective main beam of sound, particularly reducing the generation of unwanted sound that is generated by the side lobes from two main lobes, in close proximity to each other, interfering constructively.

The inventor has realized that the problem can be solved by using one or more pair of parametric acoustic transducer arrays, wherein the first parametric acoustic transducer array in each pair emits a first carrier wave with an audible sound signal modulated onto the first carrier wave and the second parametric acoustic transducer array in the pair emits a second carrier wave with the same audible sound signal modulated onto the second carrier wave in counter phase compared to in the first modulated acoustic signal. For example, if the first carrier wave is modulated with the audio signal g(t), or mg(t), the second carrier wave is modulated with the audio signal -g(t), or mg(t). Thereby, audible sound can be produced in a first and second location, in close proximity to each other, and any interference of side lobes between the main lobes will be destructive since the audible sound information of the two audible sound signals are in counterphase. ln other words, since the unwanted sound that escapes the main sound beam into side lobes will escape to a similar extent from each of the first and second audible sound signal, the unwanted sound of the side lobes will at least partially eliminate each other due to their opposing phase. Meanwhile, the sound produced at each of the main lobes will sound the same to a user listening to it, since it does not matter to the human ear if the sound signal is delivered in phase or in counterphase. ln a non-limiting example, two parametric acoustic transducer array loudspeakers may be mounted on each side of a screen, allowing audio in phase and counterphase, respectively, at the ears of a person sitting in front of the screen, while minimizing disturbance towards nearby people. ln another non-limiting example, one or more pair of parametric acoustic transducer arrays may be arranged to deliver sound in more or less parallel directions, for example towards visitors ofa museum orfair, allowing audio to reach persons standing in certain locations, while again minimizing disturbance Thereby, advantageously allow for a simple, non-complex, parametric array speaker setup towards nearby people. embodiments of the present invention providing high directivity of sound and a reduction in unwanted noise compared to prior solutions.

Aspects and embodiments of the invention, and advantages obtained, are described in further detail herein.

According to one aspect of the invention, the object is achieved by an acoustic system comprising a first parametric acoustic transducer array, a second parametric acoustic transducer array and a controller communicably connected to the first and second acoustic transducer arrays. The first parametric acoustic transducer array is configured to emit acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal comprising a first carrier wave and an audible sound signal modulated onto the first carrier wave. The first parametric acoustic transducer array comprises a plurality of transducer elements each being controllable in response to a first control signal so as to emit the acoustic energy at a wavelength and phase determined by the first control signal. The second parametric acoustic transducer array is configured to emit acoustic energy of periodically varying intensity in the form of a second modulated acoustic signal comprising a second carrier wave and the audible sound signal, wherein the audible sound signal is modulated onto the second carrier wave in counter phase compared to in the first modulated acoustic signal. The second parametric acoustic transducer array also comprises a plurality of transducer elements each being controllable in response to a second control signal so as to emit the acoustic energy at a wavelength and phase determined by the second control signal. The controller is configured to generate the first control signal such that the emitted acoustic energy of the first parametric acoustic transducer array forms a first directional beam of sound having a first pressure maximum region and to generate the second control signal such that the emitted acoustic energy of the second parametric acoustic transducer array forms a second directional beam of sound having a second pressure maximum region.

Suitably, an acoustic system providing high directivity of sound towards two selected locations, the pressure maximum regions, and a reduction in unwanted noise around the two selected locations is thereby achieved. Another advantage is that the acoustic system according to the invention is a low complexity system, that can be manufactured at a low cost, compared to many other high directivity sound systems.

For each pair of a first and second parametric acoustic transducer arrays being controlled to emit the two modulated acoustic signals, one modulated in phase and one in counterphase, the advantageous effect of minimizing disturbance in the form of unwanted sound from the side lobes will increase the more parallel the first and second beams of sound are and/or the closer the pressure maximum regions of the two modulated acoustic signals are to each other. How close the pressure maximum regions of the two modulated acoustic signals need to be for the side lobes to interfere is also partially dependent on the width and distribution of the side lobes.

According to one or more embodiment of this aspect of the invention, the first and second parametric acoustic transducer arrays are micromachined ultrasonic transducers, MUTs, comprising micromachined ultrasonic transducer, MUT, elements configured to emit acoustic energy in the form of ultrasonic energy, wherein each of the first and second modulated acoustic signals is a modulated ultrasonic signal and wherein each of the first and second carrier waves is an ultrasonic carrier wave. Thereby, the acoustic system may advantageously be miniaturized. This enables application in for example handheld devices, such as mobile phones, and other applications which require small sized components.

According to one or more embodiment of this aspect of the invention, the first and second parametric acoustic transducer arrays are phased arrays. Suitably, a direct and simple generation and control of the acoustic-potential field is thereby enabled.

The controller may be configured to generate the control signals such that the first pressure maximum region and the second pressure maximum region are formed at a preset distance, d1, from each other. Thereby, the distance between the first pressure maximum region and the second pressure maximum region can be controlled to be generated at a preset distance selected according to the application to which they are intended. ln other words, the distance between the two modulated acoustic signals with human perceivable sound can be controlled. Advantageously, the preset distance, d1, may be set to any suitable value, depending on the application. ln some embodiments, the preset distance, d1, is set to 10 cm s d'| s 20 cm, and more preferably to 13 cm s d1 s 17 cm. ln a non-limiting example the distance d1 is preset to 15 cm. Advantageously, the exemplified distances and distance intervals correspond to the typical ear-to-ear distance of a human, thereby being suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. ln other embodiment, the preset distance, d1, may be set to a distance corresponding to the intended distance of two persons receiving audio, wherein anyone being near the two persons in the intended locations will suitably not be affected by any noise disturbance due to interference of side lobes. The preset distance also may be set dependent on the frequency of the carrier waves, such that the main lobes of the first and second directional beams of sound are not so close that they risk overlapping and at least partially cancel each other out.

According to one or more embodiments of this aspect of the invention, the controller is configured to generate the control signals such that the acoustic energy is emitted at a frequency of 100-300 kHz, preferably 150-200 kHz. ln a non-limiting example, the controller is configured to generate the control signal such that the acoustic energy is emitted at a frequency of 160 kHz. Advantageously, the exemplified frequencies are suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. ln applications wherein the sound is intended to be delivered to two different users, also referred to as a first and second user, the controller may instead be configured to generate the control signals such thatthe acoustic energy is emitted at another frequency selected based on to the distance, or intended distance, between the persons, and/or such that the width of the first and second directional beams of sound is suitable to reach both ears of the first user and the second user, respectively.

The transducer elements in at least one of the first and second parametric acoustic transducer array may be arranged in a first number of rows and a second number of columns. ln other words, the at least one acoustic transducer array has a general rectangular outline. Alternatively, or in combination, the transducer elements in at least one of the first and second parametric acoustic transducer array may be hexagonal in shape and be arranged in a hexagonal grid pattern. Thereby, an optimal packing/surface optimization of the acoustic transducer array elements in the acoustic transducer array is achieved.

The surface of one or more of the first and second parametric acoustic transducer array may be flat. Thus, a simple and compact design is accomplished. Alternatively, the transducer elements in at least one of the first and second parametric acoustic transducer array may be arranged on a concave side of a spherical surface segment. This configuration facilitates concentrating high acoustic energies to each focal point.

According to another aspect of the invention, the object is achieved by a computer- implemented method for controlling the emission of audible sound from an acoustic system. The system includes a first parametric acoustic transducer array configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal comprising a carrier wave and an audible sound signal modulated onto the carrier wave, wherein the parametric acoustic transducer array comprises a plurality of transducer elements. The transducer elements of the first parametric acoustic transducer array are controllable in response to a first control signal, which is configured to cause the first parametric acoustic transducer array to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the first control signal. The system further includes a second parametric acoustic transducer array configured to emit acoustic energy of periodically varying intensity in the form of a modulated acoustic signal comprising a carrier wave and an audible sound signal modulated onto the carrierwave, wherein the second parametric acoustic transducer array comprises a plurality of transducer elements. The transducerelements of the second parametric acoustic transducer array are controllable in response to a second control signal, which is configured to cause the second parametric acoustic transducer array to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the second control signal. The system also includes a controller communicably connected to the first and second parametric acoustic transducer array.

The method comprises generating, by the controller, the first control signal such that the audible sound signal is modulated onto the first acoustic carrier wave to form the first modulated acoustic signal acoustic signal and such that the emitted acoustic energy forms a first directional beam of sound having a first pressure maximum region. The method further comprises generating, by the controller, the second control signal such that the audible sound signal is modulated onto the second acoustic carrier wave in counter phase compared to in the first modulated acoustic signal to form the second modulated acoustic signal acoustic signal and such that the emitted acoustic energy forms a second directional beam of sound having a second pressure maximum region.

The method involves generating first and second control signals which are configured to cause the first and second parametric acoustic transducer array, respectively, to emit acoustic energy of periodically varying intensity. lt is presumed that each of the first and second parametric acoustic transducer arrays contains a set of transducer elements arranged on a surface extending in two or three dimensions. l.e. transducer elements are located on a flat or a curved surface. lt is further presumed that the transducer elements are controllable in response to the respective first or second control signal so as to emit the acoustic energy at a wave- length and a phase determined by the control signal. The control signals are generated such that the emitted acoustic energy of each of the first and second parametric acoustic transducer arrays forms an acoustic-potential field of acoustic waves. ln some embodiments of this aspect of the invention the first and second parametric acoustic transducer arrays are micromachined ultrasonic transducers, MUTs, wherein emitting acoustic energy by the first and second parametric acoustic transducer arrays comprises emitting ultrasonic energy, wherein each of the first and second modulated acoustic signals is a modulated ultrasonic signal and wherein each of the first and second carrier waves is an ultrasonic carrier wave.The method step of generating the first and second control signals, by the controller, may comprise generating the control signals such that the first pressure maximum region and the second pressure maximum region are formed at a preset distance, d1, from each other. The preset distance d1 is in some non-limiting embodiments set to 10 cm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm, but any suitable distance value may be set depending on the application.

The method step of generating the first and second control signals, by the controller, may comprise generating each of the first and second the control signals (C1, C2, C11, C12) such that the acoustic energy is emitted at a frequency of 160 kHz.

According to a further aspect of the invention, the object is achieved by a computer program loadable into a non-volatile data carrier communicatively connected to a processor, or processing unit. The computer program includes software for executing the above method, according to any of the embodiments presented, when the program is run on the processing unit.

According to another aspect of the invention, the object is achieved by a non-volatile data carrier containing the above computer program.

Any advantages described herein for an embodiment of one aspects of the invention are equally applicable to the corresponding embodiments of the other aspects of the invenﬁon.

Further advantages, beneficial features and applications of the present invention will be apparent from the following description and the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention is now to be explained more closely by means of preferred embodiments, which are disclosed as examples, and with reference to the attached drawings.

Figure 1A illustrates an example of controlling a parametric array to achieve audible sound in a specific location; Figure 1B illustrates an example of controlling a parametric array to achieve audible sound in a specific location; Figure 1C illustrates an example of contro||ing two parametric arrays to achieve audible sound in two specific Iocations; Figure 1D illustrates an example of contro||ing a parametric array to achieve audible sound in two specific Iocations; Figure 2A illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2B illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2C illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2D illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2E illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2F illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2G illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2H illustrates controlling a first and a second parametric array to achieve audible sound in two specific Iocations according to one or more embodiment of the invention; Figure 2l illustrates controlling a first and a second parametric array to achieve audible sound in two specific locations according to one or more embodiment of the invention; Figure 3 schematically shows an acoustic system according to a first embodiment of the invention; Figure4 schematically shows an acoustic system according to a second embodiment of the invention; and Figure 5 illustrates, by means of a flow diagram, a method according to one or more embodiment of the invention.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated. DETAILED DESCRIPTION Introduction Audio signals are herein defined as signals having frequencies in the audio frequency range of roughly 20 to 20,000 Hz, which corresponds to the lower and upper limits of human hearing.

All embodiments herein relating to audio signals refer to monaural or monophonic sound reproduction. Embodiments herein may be applied to stereophonic sound reproduction, but this would require further alterations of the presented solution to provide a satisfactory result.

A distance is herein defined as a three-dimensional distance in space (x, y, z), unless otherwise specified.

The strength of the modulated signal herein typically refers to the amplitude of the modulated signal.Although the present disclosure is mainly focused on the control of generation and emission of modulated audio signals, it is evident to a person skilled in the technical field of signal modulation that embodiments presented herein may with slight modifications be applied to any amplitude modulated signal, for example radio signals, to achieve two separate beams conveying the same signal information with an improved directivity of energy emitted by the parametric acoustic transducer arrays and having a reduced generation of unwanted sound outside the respective main beam.

Turning first to Figs. 1A to 1D, there is shown examples of prior art solutions of controlling parametric arrays to achieve audible sound in one or more specific location, having related problems as further described herein. All the illustrating examples are in the context of the application wherein acoustic sound is intended to be delivered to two ears of a user of an acoustic system, or to one ear of a first user to the system and to one second ear of a second user of the system. This example application is used because it is easy to illustrate, and a relevant application. However, as is evident to a person skilled in the art, the problems as well as the solutions presented herein are transferable to numerous other applications of controlling one or more pair of parametric arrays to each achieve two separately directed beams conveying the same signal information with an improved directivity of energy emitted by the parametric acoustic transducer arrays and having a reduced generation of unwanted sound outside the respective main beam. ln Fig. 1A, a single parametric acoustic transducer array 1 is configured to emit acoustic energy that forms a directional beam of sound B1 having a pressure maximum region P1. As is illustrated in the figure, the solution of directing one highly directional beam of sound B1 emitted from the single parametric acoustic transducer array 1 towards the center of the user's 10 head, at a relatively high frequency, e.g. around 160 kHz, will lead to very little sound reaching either one of the user's 10 ears, since the beam B1 would be very narrow. ln this example, side lobes generated around the main lobe will also cause unwanted sound outside the main beam. ln likeness with Fig. 1A, Fig. 1B shows a single parametric acoustic transducer array 1 configured to emit acoustic energy that forms a directional beam of sound B2 having a pressure maximum region P2. ln this example the parametric acoustic transducerarray 1 is controlled to emit the beam B2 such that the pressure maximum region P2 is formed at one of the user's 10 ears. Also in this example the energy consumption is low, since only a single parametric acoustic transducer array is used. The acoustic energy in the pressure maximum region P2 is also in this case high since the parametric acoustic transducer array 1 is configured to emit the energy only at the region P2, but only one ear is in focus of the sound beam and hence the main lobe. This means that the user 10 will be able to hear the audio well at one ear, but no sound will reach the other ear, or the other ear may even receive unwanted sound generated by one or more side lobes, thereby deteriorating the acoustic experience of the user. ln Fig. 1C, two parametric acoustic transducer arrays 1, 2 are configured to each emit acoustic energy that forms a respective directional beam of sound B3, B4, which comprise the same signal information, having a respective pressure maximum region P3, P4 at a respective one of the user's 10 ears. ln this example, unwanted sound generated by one or more side lobe around the main lobe of the beam B3 risk reaching the ear to which the beam B4 is directed, and vice versa, causing deteriorated directionality and noise pollution that impairs the acoustic experience of the user. The side lobes of the respective beams B3, B4 may also interfere constructively, thereby causing even more, higher amplitude, unwanted noise that impairs the acoustic experience of the user. ln Fig. 1D, a single parametric acoustic transducer array 1 is configured to use beamforming to divide or split the emitted acoustic energy into two directional beams of sound B5, B6 having a respective pressure maximum region P5, P6 at a respective one of the user's 10 ears. ln this example, the same audio signal will reach, and can be heard at, each of the user's ears. However, the audio signal at each ear is emitted with only half the acoustic energy capacity of the parametric acoustic transducer array 1, whereby the volume/effect will be lower compared to e.g. the solution of Fig. 1C. Alternatively, the same volume of sound/effect may be conveyed from the single parametric acoustic transducer array 1 as from the two parametric acoustic transducer arrays 1, 2 of Fig. 1C in combination if the single array 1 is configured to emit the double amount of energy, but in that case the energy consumption for driving the single array 1 will also double. ln any of these alternatives, the same issues appear as in the example of Fig. 1C, namely that unwanted sound generated by one or more side lobe around the main lobe of the beam B3 risk reaching the ear to which the beam B4 isdirected, and vice versa, causing deteriorated directionality and noise pollution that impairs the acoustic experience of the user. The side lobes of the respective beams B3, B4 may also interfere constructively, thereby causing even more, higher amplitude, unwanted noise that impairs the acoustic experience of the user.

As described herein, the object of the present invention is to offer a solution that renders it possible to improve the directivity of sound emitted by parametric acoustic transducer arrays and reducing the generation of unwanted sound outside the respective main beam of sound, particularly reducing the generation of unwanted sound that is generated by the side lobes from two main lobes, in close proximity to each other, interfering constructively. System architecture Firstly, a system 100 according to embodiments of the invention will be described in connection with Figs. 2A to 2l, 3 and ln Figs. 2A to 2l, solutions according to different embodiments of the present invention for controlling two, or one or more pair of, parametric arrays to achieve audible sound in two specific locations are illustrated, which render it possible to improve the directivity of sound emitted by parametric acoustic transducer arrays and reducing the generation of unwanted sound outside the respective main beam of sound.

Fig. 3 shows an acoustic system 100 according to a first embodiment of the invention.

The system 100 includes a first parametric acoustic transducer array 110a, a second parametric acoustic transducer array 110b and a controller 120. The first parametric acoustic transducer array 110a is configured to emit acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal 200a comprising a first carrier wave 202a and an audible sound signal 204 modulated onto the first carrier wave 202a. The first parametric acoustic transducer array 110a comprises a plurality of transducer elements el, the transducer elements e; being controllable in response to a control signal C1 so as to emit the acoustic energy at a wavelength and phase determined by the control signal C1. The second parametric acoustic transducer array 110b is configured to emit acoustic energy of periodically varying intensity in the form of a second modulated acoustic signal 200b comprising a second carrier wave 202b and the audible sound signal 204 modulated onto the second carrier wave 202b incounter phase compared to in the first modulated acoustic signal 200a. The second parametric acoustic transducer array 110b comprises a plurality of transducer elements ej, the transducer elements e,- being controllable in response to a control signal C2 so as to emit the acoustic energy at a wavelength and phase determined by the control signal C The first and second pressure maximum regions PiviAx1, PiviA><2 may also be referred to as first and second acoustic lobes, consisting of a respective central main lobe and surrounding side lobes having a lower amplitude than the main lobes.

The controller 120 is communicably connected to the first and second parametric acoustic transducer arrays 110a, 110b and is configured to the first control signal C1 such that the emitted acoustic energy of the first parametric acoustic transducer array 110a forms a first directional beam of sound B having a first pressure maximum region PiviA><1 and to generate the second control signal C2 such that the emitted acoustic energy of the second parametric acoustic transducer array 110b forms a second directional beam of sound B' having a second pressure maximum region PiviAx ln other words, audio generated at first pressure maximum region PMA><1 and the second pressure maximum region PMAXZ, respectively, will have opposite phase. The audible sound signal being modulated onto the second carrier wave in counter phase, or having opposite phase, compared to in the first modulated acoustic signal may also be described as the first pressure maximum region having a first strength envelope signal, mg(t') and the second pressure maximum region having a second strength envelope signal, -mg(t'), that is in counter phase to the first envelope signal, mg(t'), where g(t') contains the audio information and m is the modulation index. The envelope function g(t') can be an audio signal to be broadcasted, or a processed signal such that the reproduced audible sound has reduced distortion. ln other words, this will cause the first directional beam to be effectively amplitude modulated with the envelope signal mg(t') and the second directional beam to be effectively amplitude modulated with the inverse of the envelope signal -mg(t'). To the human ear these two modulated acoustic signals will sound identical. Thereby, if the first directional beam is directed to a first ear of a user and the second directional beam is directed to the second ear of the user, the user will perceive the same audio information at both ears, while the unwanted sound that escapes the first and second directional beams of sound B, B' into side lobes will escape to a similar extent from both directional beams of sound B, B', and partially eliminate each other due to their opposing phase. Hence, an improved directionality and reduction of unwanted noise is obtained.

Each of the first and second parametric acoustic transducer array 110a, 110b include a set of transducer elements el, el arranged on a surface. ln the embodiment of Fig. 3, the respective surface is flat and the transducer elements el, el may be arranged in a first number of rows and a second number of columns. Alternatively, the transducer elements in each of the parametric acoustic transducer arrays 110a, 110b may be hexagonal in shape and be arranged in a hexagonal grid pattern. Thereby, an optimal packing/surface optimization of the acoustic transducer array elements el, el in each acoustic transducer array 110a, 110b is achieved. Of course, the transducer elements el, el of one ofthe first and second parametric acoustic transducer array 110a, 110b may be arranged in a first number of rows and a second number of columns while the transducer elements of the other parametric acoustic transducer array are hexagonal in shape and arranged in a hexagonal grid pattern, if this is suitable for a specific application. All these alternatives render it comparatively straightfon/vard to control the transducer elements el, el to emit the acoustic energy. Namely, the transducer elements el, el are controllable in response to the first and second control signal C1, C2, respectively, so as to emit the acoustic energy at a wa- velength and a phase determined by the respective first or second control signal C1, C Fig. 4 shows an acoustic system 100 according to a second embodiment of the invention. Here, the transducer elements el, el of each of the first and second parametric acoustic transducer arrays 210a, 210b are arranged on a concave side of a spherical surface segment, i.e. a surface extending in three dimensions. The three- dimensional configuration on the concave side of a spherical surface segment is advantageous because it enables a higher concentration of acoustic energy towards first and second pressure maximum regions, PlvlAxt, PlvlA><2 than if the acoustic transducer array had extended along a flat, tvvo-dimensional, surface. ' The transducer elements el, el may be arranged in any suitable way on the respective spherical surface, for example but not limited to hexagonal transducer elements el, el arranged in a respective hexagonal grid pattern leading to an optimal packing/surfaceoptimization of the acoustic transducer array elements ei, e,- in each acoustic transducer array 210a, 210b. ln an alternative embodiment, a combination of arranging the transducer elements ei, e,- of one of the first and second parametric acoustic transducer array on a flat surface and the transducer elements of the other parametric acoustic transducer array on a surface extending in three dimensions may be used if this is suitable for a specific application. ln any of the embodiments of the system 100, each of the first and second parametric acoustic transducer array 110a, 110b, 210a, 210b may be a micromachined ultrasonic transducer, MUT, configured to emit acoustic energy in the form of ultrasonic energy, wherein each of the first and second modulated acoustic signals 200a, 200b is a modulated ultrasonic signal and wherein each of the first and second carrier waves 202a, 202b is an ultrasonic carrier wave. Thereby, the acoustic system may advantageously be miniaturized. This enables application in for example handheld devices, such as mobile phones, and other applications which require small sized components. ln some of these embodiments, the parametric acoustic transducer arrays may comprise piezoelectric micromachined ultrasonic transducer, pMUT, elements configured to emit acoustic energy in the form of ultrasonic energy. Thereby, the acoustic system may advantageously be miniaturized, and the power consumption may further be reduced, which even further enables use of the acoustic system in for example handheld devices, such as mobile phones, and other applications which require both low power consumption and small sized components.

The first and second parametric acoustic transducer arrays 110a, ,110b, 210a, 210b may be phased arrays, enabling direct and simple generation and control of the generated acoustic-potential field. ln any embodiment of the system 100, the controller 120 may be configured to generate the first and second control signals C1, C2, C11, C12 such that the first pressure maximum region PiviA><1 and the second pressure maximum region PiviAx2 are formed at a preset distance, d1, from each other. Thereby, the distance between the first pressure maximum region and the second pressure maximum region can be controlled to be generated at a preset distance selected according to the application to which they are intended. ln a non-limiting embodiment, the preset distance, d1, isset to 10 cm s d1 S 20 cm, preferably 13 cm s d1 S 17 cm. ln a non-limiting example the distance d1 is preset to 15 cm. Advantageously, the exemplified distances and distance intervals correspond to the typical ear-to-ear distance of a human, thereby being suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound.

Examples of generating the first and second pressure maximum regions PiviA><1, PiviA><2 at ears of a user 10, at a distance d1 approximating the ear-to-ear distance of a user 10 and emitting the carrier waves at a frequency of around 100-300 kHz, are shown in Figs. 2A, 2B and 2C. ln Fig. 2A, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane adjacent to each other, for example mounted side by side on a common, flat, surface. ln Fig. 2B, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are adjacent and mounted at an angle oi to each other, for example mounted side by side on two planes that are that may be represented by on a common, angled, surface, or two adjacent surfaces angled in relation to each other. The angle oi is typically less than 45 degrees, preferably less than 30 degrees, more preferably less than 15 degrees, but this may of course depend on the application. ln Fig. 2C, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane at a distance from each other, for example mounted at a distance from each other on a common, plane, surface.

The present invention relates to mono audio, i.e. that the same audio signal is emitted to form the first directional beam of sound B as well as the second directional beam of sound B". ln the intended main application the preset distance d1 is as explained above set to correspond to the ear- to-ear distance of a human, so that the first and second pressure maximum regions PiviA><1, PMAXZ, where audible sound is produced, are formed at the respective first and second ear ofa person, or user, 10 using the acoustic system 100 to listen to the audible sound produced by the system 100. For other applications, wherein the distance d1 is more suitably set to a greater value, a lower frequency may be considered.lf the distance d1 is too small, i.e. if the first and second pressure maximum regions are formed to close to each other in relation to the frequency at which they are emitted, they could constructively combine, which would lead to the audible signals cancelling each other out due to the inverted envelope functions. ln any of the first and second embodiment of the system 100, the controller 120 may be configured to set the value of the preset distance d1 based on the frequency of the first and second carrier wave 202a, 202b and/or input received from one or more measuring device and/or input received from an input device 130, as described herein. The controller 120 may be configured to set the value of the preset distance d1 once, as an initial calibration for a system 100 wherein the location for the audible sound is static and any user of the system 100 is intended to remain in this location to receive the audio. Alternatively, the controller 120 may be configured to set the value of the preset distance d1 iteratively using any available method for finding the three dimensional positions of a person, an ear, or another feature that defines a location at which the audible sound is to be directed. Such an iterative setting of the distance d1 may e.g. be performed at set time intervals, or in response to a detected change, such as movement of a user, ear, etc., detected using any suitable device being communicatively connected to the system 100. ln any of these embodiments the controller 120 may be configured to determine the three-dimensional location at which the audible sound of each of the first and second parametric transducer arrays 110a, 110b, 210a, 210b is to be directed independently, and further to control the emission of acoustic energy by the first and second parametric transducer arrays 110a, 110b, 210a, 210b independently, based on the respective control signals C1, C2, C11, C ln any of the first and second embodiment of the system 100, the controller 120 may be configured to generate the control signals C1, C2, C11, C12 such that the acoustic energy is emitted at a lower frequency than the ones exemplified above, for example but not limited to 40 kHz or thereabout, thereby generating wider first and second directional beams of sound B, B". ln these embodiments, the locations of the first and second pressure maximum regions PiviA><1, PiviA><2 to which the first and second directional beams of sound B, B', respectively, are directed at locations further apart than the two ears of a person. For example, the first and second directional beams of sound B, B' may be controlled to be directed at a first and second person being located a suitable distance apart from each other, such that the first person hears the acousticsignal having the first strength envelope signal, mg(t'), via the first beam of sound B and the second person hears the acoustic signal having the second strength envelope signal, -mg(t'), via the second beam of sound B'. The distance d1 is in this case suitably selected based on the frequency of the first and second carrier wave 202a, 202b such that the side lobes generated will destructively interfere and at least partially cancel each other out. Both persons will then perceive that the same, in phase, sound is delivered to them and the advantages of improving the directivity of sound emitted by the parametric acoustic transducer arrays 110a, 110b, 210a, 210b and reducing the generation of unwanted sound outside the respective main beam of sound, or main lobe, is achieved also by these embodiments. ln one or more embodiment, the controller 120 may be configured to generate the first and second control signals C1, C2, C11, C12 such that the acoustic energy is emitted at a frequency in the interval of 100-300 kHz, preferably in the interval of 150-200 kHz, including the end points of each interval. ln a non-limiting example, the controller 120 is configured to generate the control signal such that the acoustic energy is emitted at a frequency of 160 kHz. Advantageously, the exemplified frequencies are suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. For another application, wherein the distance d1 is set to a greater value, a lower frequency may be used, some non-limiting as exemplified of which are disclosed herein.

Examples of generating the first and second pressure maximum regions Piwm, PiviA><2 to be directed at a first and second user 10', 10" being located a suitable distance d1 apart from each other, such that the first user 10 hears the acoustic signal having the first strength envelope signal, mg(t'), via the first beam of sound B and the second user 10 hears the acoustic signal having the second strength envelope signal, -mg(t') via the second beam of sound B' are shown in Figs. 2D, 2E, 2F, 2G, 2H and 2l.

Turning to Figs. 2D, 2E and 2F, the examples show generation of the first pressure maximum region PMA><1 at a first ear of a first user 10' and generation of the second pressure maximum region PMA><2 at a first ear of a second user 10" by emitting the carrier waves at a frequency of around 100-300 kHz, the pressure maximum regions PiviA><1, PiviA><2 being separated by a distance d1 selected based on the frequency of the carrier waves such that side lobes of the beams of sound B, B' will at least partially cancel each other out. ln Fig. 2D, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane at a distance from each other, for example on a common, flat, surface. ln this example, the first pressure maximum region PMA><1 is located at or near a first ear of a first user 10' and the second pressure maximum region PMAXZ is located at or near a first ear of a second user 10". ln Fig. 2E, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane adjacent to each other, for example on a common, flat, surface. ln this example, the first pressure maximum region PiviA><1 is located at or near a first ear of a first user 10' and the second pressure maximum region PMAXZ is located at or near a first ear of a second user 10". ln Fig. 2F, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are adjacent and mounted at an angle d to each other, for example mounted side by side on two planes that are that may be represented by on a common, angled, surface, or two adjacent surfaces angled in relation to each other. The angle oi is typically less than 45 degrees, preferably less than 30 degrees, more preferably less than 15 degrees, but this may of course depend on the application. ln this example, the first pressure maximum region PiviA><1 is located at or near a first ear of a first user 10' and the second pressure maximum region PMAXZ is located at or near a first ear of a second user 10".

Turning now to Figs. 2G, 2H and 2l, the examples show generation of the first pressure maximum region PMA><1 at the head of a first user 10' and generation of the second pressure maximum region PMAXZ at the head of a second user 10" by emitting the carrier waves at a frequency that generates a beam of sound wide enough to reach both ears of the respective user 10', 10". ln a non-limiting example, the frequency is 40 kHz or close to 40 kHz. The pressure maximum regions PMA><1, PiviA><2 are in these examples separated by a distance d1 selected based on the frequency of the carrier waves such that side lobes of the beams of sound B, B' will at least partially cancel each other out. ln Fig. 2G, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane at a distance from each other, for example mounted at a distance from each other on a common, plane, surface. ln Fig. 2H, thereis shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are mounted in the same plane adjacent to each other, for example on a common, flat, surface. ln Fig. 2l, there is shown a system 100 wherein the first acoustic transducer array 110a, 210a and the second parametric acoustic transducer array 110b, 210b are adjacent and mounted at an angle oi to each other, for example mounted side by side on two planes that are that may be represented by on a common, angled, surface, or two adjacent surfaces angled in relation to each other. The angle oi is typically less than 45 degrees, preferably less than 30 degrees, more preferably less than 15 degrees, but this may of course depend on the application.

The controller 120 is in any of the examples of any of Figs. 2A to 2l configured to generate the first control signal C1, C11 such that the emitted acoustic energy of the first parametric acoustic transducer array 110a, 210a forms a first directional beam of sound B having a first pressure maximum region PiviA><1 and to generate the second control signal C2, C12 such that the emitted acoustic energy of the second parametric acoustic transducer array 110b, 210b forms a second directional beam of sound B' having a second pressure maximum region PiviA>< To determine the location of the persons at which the first and second directional beams of sound B, B' should be directed, any suitable method for detection or tracking of a human face, feature recognition, motion tracking, or the like may be used, for example but not limited to those detection and tracking methods mentioned herein in connection with determining the location or position of one or more ear or the head, or face, of a user.

The first and second pressure maximum regions PiviA><1, PiviA><2 are created around a first and second focal point, respectively, in which the emitted acoustic energy of each of the first and second parametric acoustic transducer array 110a, 110b, 210a, 210b is constructively combined, in response to the respective control signals C1, C2, C11, C12. The distance d1 may be defined as the distance between the center of the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2, the distance between the focal points around which the first pressure maximum region PiviA><1 and the second pressure maximum region PiviA><2 are formed, or any other selected point on each of the first pressure maximum region PiviA><1 and the secondpressure maximum region PiviA><2 are formed, e.g. the points on their periphery that provides the shortest or longest distance between the first pressure maximum region PiviA><1 and the second pressure maximum region PMAXZ. ln some embodiments, the distance d1 may be dependent on the distance between the center of the first pressure maximum region PiviA><1 and the second pressure maximum region PiviAx2 or the position of the foca| points and the frequency of the carrier wave and be set to a value that reduces the risk of interference between the main |obes of the first and second directiona| beams of sound B, B'.

The controller 120 may apply any algorithm that allows for generating a first and second control signal C1, C2, C11, C12 causing the first and second parametric acoustic transducer arrays 110a, 110b, 210a, 210b, respectively, to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the respective first and second control signal C1, C2, C11, C12 such that the emitted acoustic energy forms a first directiona| beam of sound B having a first pressure maximum region PiviA><1 and a second directiona| beam of sound B' having a second pressure maximum region PiviA>< ln any embodiment, the system 100 may further comprise an input device 130 communicatively connected to the controller 120. The controller 120 may in these embodiments be configured to receive an input signal indicative of a distance value from the input device 130, and in response to receiving the input signal be configured to set or adjust the distance d1 based on the received distance value. Suitably, the preset distance, d1, may thereby be adjusted to optimize it to a changed position of one or both optimal positions for generation of the first and second pressure maximum regions PiviA><1, PMAXZ, respectively, such as e.g. a changed position of one or both ears of a user of the acoustic system, or a changed position of one or both of two persons, or users 10, at which the first and second beams of sound B, B' are directed. ln embodiments wherein sound is to be delivered to the two ears of one user 10, the distance d1 may, in the same application of the system, advantageously be adjusted based on differences in ear-to-ear distance, or a measurement from which this information can be derived, between different users of the system 100, thereby optimizing the acoustic experience for the current user of the system 100. ln some embodiments, the input device 130 may be configured to receive manual input whereby a user of the system 100 is enabled to interact with the input device 130 tomanually input a selected value for the distance d1, a distance change parameter indicating to the controller how the distance d1 should be adjusted, or the like. Alternatively, or additionally, the input device 130 may be configured to receive input from one or more distance measure device configured to identify in three dimensions one or both optimal positions for the first and second pressure maximum regions, PiviA><1, PiviA><2, respectively, such as e.g. one or both ears of a user. Such a distance measure device may use ultrasound, laser, imaging and/or any other suitable technique known in the art. ln some embodiments, the three-dimensional position of the user's ears, e.g. the distance and angle at which each of the user's ear is located in relation to the first or second parametric acoustic transducer array 110a, 110b, 21 Oa, 210b, may be determined using any suitable technique known in the art, for example a head tracking technique. ln these embodiments, the controller 120 may be configured to generate the first and second control signal C1, C2, C11, C12 such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PMA><1 at the first determined location, e.g. at or close to the first ear of a first user 10, and a second directional beam of sound B' having a second pressure maximum region PiviA><2, at the second determined location, e.g. at or close to the second ear of the first user 10, alternatively at or close to the first ear of a second user 10. The controller 120 may be configured to generate the control signals C1, C2, C11, C12 based on the determination of the three dimensional locations of the ears (or other points in space at which the audible sound is to be generated depending on the application), based on the preset distance d1, based on a detected distance change, or any combination of these parameters. lt is generally advantageous if the controller 120 is configured to effect the above- described procedure in an automatic manner by executing a computer program 127. Therefore, the controller 120 may include a memory unit 125, i.e. non-volatile data carrier, storing the computer program 127, which, in turn, contains software for making processing circuitry in the form of at least one processor 123 in the controller 120 exe- cute the actions mentioned in this disclosure when the computer program 127 is run on the at least one processor 123. ln one or more embodiment, the invention may therefore comprise a computer program 127 loadable into a non-volatile data carrier 125 communicatively connected to a processor 123, the computer program 127 comprising software for executing the method according any of the methodembodiments presented in connection with Fig. 5 when the computer program 127 is run on the processor 123. Furthermore, the invention may comprise a non-volatile data carrier 125 containing the computer program Method embodiments With reference to the flow diagram in Fig. 5, and also with reference to Figs. 2A-l, 3 and 4 as described above, we will now describe a computer-implemented method for controlling the emission of audible sound from an acoustic system 100 comprising a first parametric acoustic transducer array 110a, 210a, a second parametric acoustic transducer array 110b, 210b and a controller 120 communicably connected to the first and second parametric acoustic transducer arrays 110a, 110b, 210a, 210b, according to one or more embodiment of the invention. The method comprises: ln step 510: generating, by the controller 120, a first control signal C1, C11 which is configured to cause the first parametric acoustic array 110a, 210a to emit acoustic energy of periodically varying intensity. lt is presumed that the first parametric acoustic transducer array 110a, 210a is configured to emit acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal 200a comprising a first carrier wave 202a and an audible sound signal 204 modulated onto the first carrier wave 202a. lt is also presumed that the first acoustic transducer array 110a, 210a contains a set of transducer elements ei arranged on a surface extending in two or three dimensions. l.e. transducer elements ei are located on a flat or a curved surface. lt is further assumed that the first parametric acoustic transducer array 110a, 210a comprises a plurality of transducer elements e; that are controllable in response to the first control signal C1, C11 to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the first control signal C1, C The first control signal C1, C11 is generated such that the audible sound signal 204 is modulated onto the first acoustic carrier wave 202a to form the first modulated acoustic signal acoustic signal 200a and such that the emitted acoustic energy forms a first directional beam of sound B having a first pressure maximum region PMA>< ln step 520: generating, by the controller 120, a second control signal C2, C12 which is configured to cause the second parametric acoustic array 110b, 210b to emit acoustic energy of periodically varying intensity. lt is presumed that the second parametric acoustic transducer array 110b, 210b is configured to emit acoustic energy of periodically varying intensity in the form of a second modulated acoustic signal 200b comprising a second carrier wave 202b and the audible sound signal 204 modulated onto the second carrier wave 202b. lt is also presumed that the second acoustic transducer array 110b, 210b contains a set of transducer elements e,- arranged on a surface extending in two or three dimensions. l.e. transducer elements e,- are located on a flat or a curved surface. lt is further assumed that the second parametric acoustic transducer array 110b, 210b comprises a plurality of transducer elements e,- that are controllable in response to the second control signal C2, C12 to emit acoustic energy of periodically varying intensity at a wavelength and phase determined by the second control signal C2, C The second control signal C2, C12 is generated such that the audible sound signal 204 is modulated onto the second acoustic carrier wave 202b in counter phase compared to in the first modulated acoustic signal 200a to form the second modulated acoustic signal acoustic signal 200b and such that the emitted acoustic energy forms a second directional beam of sound B' having a second pressure maximum region PiviAx Generating the first and second control signals C1, C2, C11, C12, by the controller 120, may comprise generating the first and second control signals C1, C2, C11, C12 such that the first pressure maximum region PMA><1 and the second pressure maximum region PMA><2 are formed at a preset distance, d1, from each other. The distance dmay be set in any of the manners described herein. ln some embodiments, the preset distance d1 is set to 10 cm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm, but any suitable distance value may be set depending on the application.

Generating each of the first and second control signals C1, C2, C11, C12, by the controller 120, may comprise generating each of the first and second control signals C1, C2, C11, C12 such that the acoustic energy is emitted at a frequency of 100-300 kHz, preferably 150-200 kHz. ln a non-limiting example, generating each of the firstand second control signals C1, C2, C11, C12, by the controller 120, may comprise generating each of the first and second control signals C1, C2, C11, C12 such that the acoustic energy is emitted at a frequency of 160 kHz. Advantageously, the exemplified frequencies are suitable for the application of delivering acoustic sound to two ears of a user, by the first and second directional beams of sound. ln applications wherein the sound is intended to be delivered to a first and a second user 10', 10", generating each of the first and second control signals C1, C2, C11, C12, by the controller 120, may comprise generating the control signals such that the acoustic energy is emitted at the frequencies mentioned above, as illustrated in the examples of Figs. 2D, 2E and 2F. Alternatively, in other applications wherein the sound is intended to be delivered to a first and a second user 10', 10", generating each of the first and second control signals C1, C2, C11, C12, by the controller 120, may comprise generating the control signals such that the acoustic energy is emitted at other, lower, frequency selected based on the distance, or intended distance, between the first and second users 10', 10", and/or such that the width of the first and second directional beams of sound B, B' is suitable to reach both ears of the first user 10' and the second user 10", respectively. Examples of this are illustrated in Figs. 2G, 2H and 2l.

Generating any or both of the first and second control signal C1, C2, C11, C12 may in these embodiments comprise receiving, from an input device 130 communicatively connected to the controller 120, an input signal indicative of a distance value, and in response to receiving the input signal setting or adjusting the distance d1 based on the received distance value. Suitably, the preset distance, d1, may thereby be adjusted to optimize it to a changed position of one or both optimal positions for generation of the first and second pressure maximum regions PiviA><1, PMAXZ, respectively, such as e.g. a changed position of one or both ears of a user 10, a first user 10' and/or a second user 10" of the acoustic system 100. ln some embodiments, the method may comprise receiving, in the input device 130, manual input from a user or operator of the system 100 indicative of a selected value for the distance d1, or a distance change parameter indicating to the controller 120 how the distance d1 should be adjusted. Alternatively, or additionally, the method may comprise receiving, in the input device 130, input from one or more distance measure device configured to identify in three dimensions one or both optimal positions for the first and second pressure maximum regions, PiviA><1, PiviA><2, respectively, such as e.g. detecting one or both ears of a user. Such a distancemeasure device may use ultrasound, laser, imaging and/or any other suitable technique known in the art. ln some embodiments, the three-dimensional position of the user's ears, e.g. the distance and angle at which each of a user's 10. 10', 10" ear is located in relation to the first and/or second parametric acoustic transducer array 110a. 110b, 210a, 210b, may be determined using any suitable technique, for example a head tracking technique, known in the art. ln these embodiments, generating the first and second control signals C1, C2, C11, C12 in step 510 and 520, by the controller 120, may comprise generating each of the control signals C1, C2, C11, C12 such that the emitted acoustic energy of each of the first and second parametric acoustic transducer arrays 110a, 110b, 210a, 210b forms a first directional beam of sound B having a first pressure maximum region PMA><1 at the first determined location, and a second directional beam of sound B' having a second pressure maximum region PiviA><2, at the second determined location. Generating the first and second control signals C1, C2, C11, C12, by the controller 120, may in these embodiments be based on the determination of the three dimensional locations of the ears, faces, heads (or other points in space at which the audible sound is to be generated depending on the application), based on the preset distance d1, based on a detected distance change, or any combination of these parameters. ln embodiments wherein the first and second directional beams of sound B, B' are intended to be delivered to a first and second ear, respectively, of a single user, the method may further comprise adjusting, by the controller 120, the distance d1 based on differences in ear-to-ear distance, or a measurement from which this information can be derived, between different users of the system 100, thereby optimizing the acoustic experience for the current user of the system ln step 530: emitting, by the first parametric acoustic transducer array 110a, 210a, acoustic energy that has a wavelength and a phase delay determined by the first control signal, C1, C ln embodiments wherein the first parametric acoustic transducer array 110a, 210a is a micromachined ultrasonic transducer, MUT, the first modulated acoustic signal 200a is a modulated ultrasonic signal, and the first acoustic carrier wave 202a is an ultrasonic carrier wave. ln these embodiments, emitting acoustic energy by the first parametric acoustic transducer array 110a, 210a comprises emitting ultrasonic energy.ln step 540: emitting, by the second parametric acoustic transducer array 110b, 210b, acoustic energy that has a wavelength and a phase delay determined by the second control signal, C2, C ln embodiments wherein the second parametric acoustic transducer array 110b, 210b is a micromachined ultrasonic transducer, MUT, the second modulated acoustic signal 200b is a modulated ultrasonic signal, and the second acoustic carrier wave 202b is an ultrasonic carrier wave. ln these embodiments, emitting acoustic energy by the second parametric acoustic transducer array 110b, 210b comprises emitting ultrasonic energy.

The method steps 510 and 520 may be performed in any order, either in sequence or in parallel. Steps 530 and 540 are preferably performed simultaneously. lf this is suitable to the application of the invention, the computer-implemented method for controlling the emission of audible sound from an acoustic system 100, according to any embodiment described herein, may of course be applied to controlling an acoustic system comprising more than one pair of a respective first acoustic transducer array 110a, 210a and a second acoustic transducer array 110b, 210b.

Further embodiments All of the process steps, as well as any sub-sequence of steps, described with reference to Fig. 5 may be controlled by means of a programmed processor. Moreover, although the embodiments of the invention described above with reference to the drawings comprise processor and processes performed in at least one processor, the invention thus also extends to computer programs, particularly computer programs on or in a carrier, adapted for putting the invention into practice. The program may be in the form of source code, object code, a code intermediate source and object code such as in partially compiled form, or in any other form suitable for use in the implementation of the process according to the invention. The program may either be a part of an operating system or be a separate application. The carrier may be any entity or device capable of carrying the program. For example, the carrier may comprise a storage medium, such as a Flash memory, a ROM (Read Only Memory), for example a DVD (Digital VideoNersatile Disk), a CD (Compact Disc) or a semiconductor ROM, an EP- ROM (Erasable Programmable Read-Only Memory), an EEPROM (ElectricallyErasable Programmable Read-Only Memory), or a magnetic recording medium, for example a floppy disc or hard disc. Further, the carrier may be a transmissible carrier such as an electrical or optical signal which may be conveyed via electrical or optical cable or by radio or by other means. When the program is embodied in a signal, which may be conveyed, directly by a cable or other device or means, the carrier may be constituted by such cable or device or means. Alternatively, the carrier may be an integrated circuit in which the program is embedded, the integrated circuit being adapted for performing, or for use in the performance of, the relevant processes.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps, or components. The term does not preclude the presence or addition of one or more additional elements, features, inte- gers, steps or components or groups thereof. The indefinite article "a" or "an" does not exclude a plurality. ln the claims, the word "or" is not to be interpreted as an exclusive or (sometimes referred to as "XOR"). On the contrary, expressions such as "A or B" covers all the cases "A and not B", "B and not A" and "A and B", unless otherwise indicated. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. lt is also to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

The invention is not restricted to the described embodiments in the figures but may be varied freely within the scope of the claims.

Claims

1. An acoustic system (100) comprising: a first parametric acoustic transducer array (110a, 210a) configured to emit acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal (200a) comprising a first carrier wave (202a) and an audible sound signal (204) modulated onto the first carrier wave (202a), wherein the first parametric acoustic transducer array (110a, 21 comprises a plurality of transducer elements (ei), the transducer elements (ei) being controllable in response to a first control signal (C1, C11) so as to emit the acoustic energy at a wavelength and phase determined by the first control signal (C1, C11); a second parametric acoustic transducer array (110b, 210b) configured to emit acoustic energy of periodically varying intensity in the form of a second modulated acoustic signal (200b) comprising a second carrier wave (202b) and the audible sound signal (204), wherein the audible sound signal (204) is modulated onto the second carrier wave (202b) in counter phase compared to in the first modulated acoustic signal (200a), wherein the second parametric acoustic transducer array (110b, 210b) comprises a plurality of transducer elements (ej), the transducer elements (ej) being controllable in response to a second control signal (C2, C12) so as to emit the acoustic energy at a wavelength and phase determined by the second control signal (C2, C12); and a controller (120) communicably connected to the first and second acoustic transducer arrays (110a, 110b, 210a, 210b), the controller (120) being configured to generate the first control signal (C1, C11) such that the emitted acoustic energy of the first parametric acoustic transducer array (110a, 210a) forms a first directional beam of sound (B) having a first pressure maximum region (PMAX1) in the form of a first acoustic lobe created around a first focal point where the emitted acoustic energy of the first directional beam of sound (B) is constructively combined and to generate the second control signal (C2, C12) such that the emitted acoustic energy of the second parametric acoustic transducer array (110b, 210b) forms a second directional beam of sound (B')having a second pressure maximum region (PiviAx2) in the form of a second acoustic lobe created around a second focal point where the emitted acoustic energy of the second directional beam of sound (Bﬁ) is constructively combined.

2. The acoustic system (100) of c|aim 1, wherein the first and second parametric acoustic transducer arrays (110a, 110b, 210a, 210b) are micromachined u|trasonic transducers, MUTs, configured to emit acoustic energy in the form of u|trasonic energy, wherein each of the first and second modulated acoustic signals (200a, 200b) is a modulated u|trasonic signal and wherein each of the first and second carrier waves (202a, 202b) is an u|trasonic carrier wave. _ The acoustic system (100) of c|aim 1 or 2, wherein the first and second parametric acoustic transducer arrays (110a, 110b, 210a, 210b) are phased arrays. _ The acoustic system (100) according to any one of the preceding c|aims, wherein the controller (120) is configured to generate the control signals (C1, C2, C11, C12) such that the first pressure maximum region (PiviAx1) and the second pressure maximum region (PiviAx2) are formed at a preset distance (d1) from each other. _ The acoustic system (100) of c|aim 4, wherein the preset distance (d1) is set tocm s d1 s 20 cm, preferably 13 cm s d1 s 17 cm. _ The acoustic system (100) according to any one of the preceding c|aims, further comprising an input device (130) communicatively connected to the controller (120), wherein the input device (130) is configured to receive information from one or more distance measurement devices on a first three dimensional position at which the first directional beam of sound (B) should be directed and a second three dimensional position at which the second directional beam of sound (B') should be directed, and wherein the controller (120) is configured to generate the first control signal (C1, C11) based on the first three dimensional position at which the first directional beam of sound (B) should be directed such that the emitted acoustic energy forms the first directional beam of sound (B) to have the first pressure maximum region (PiviAx1 ) at the first determined position and to generate the second control signal (C2, C12) based on second three dimensional position at which the second directional beam of sound (B') should be directed such that the emitted .The acoustic system (100) according to any one of the acoustic energy forms the second directional beam of sound (B') to have the second pressure maximum region (PlvlAx2) at the second determined position. _ The acoustic system (100) according to any one of the preceding claims, wherein the controller (120) is configured to generate the control signals (C1, C2, C11, C12) such that the acoustic energy is emitted at a frequency of 160 kHz. _ The acoustic system (100) according to any one of the preceding claims, wherein the transducer elements (el, el) in at least one of the first and second parametric acoustic transducer array (110a, 110b, 210a, 210b) are arranged in a first number of rows and a second number of columns. _ The acoustic system (100) according to any one of the claims 1 to 7, wherein the transducer elements (el, el) in at least one of the first and second parametric acoustic transducer array (110a, 110b, 210a, 210b) are hexagonal in shape and are arranged in a hexagonal grid pattern. wherein the transducer elements (el, el) in at least one of the first and second parametric acoustic transducer array (110a, 110b, 210a, 210b) are arranged on a concave side of a spherical surface segment. .A computer-implemented method for controlling the emission ofaudible sound from an acoustic system (100), the system (100) comprising: a first parametric acoustic transducer array (110a, 210a) configured to emit acoustic energy of periodically varying intensity in the form of a first modulated acoustic signal (200a) comprising a first acoustic carrier wave (202a) and an audible sound signal (204) modulated onto the first acoustic carrier wave (202a), wherein the first parametric acoustic transducer array (110a, comprises a plurality of transducer elements (el), the transducer elements (el) being controllable in response to a first control signal (C1, C11) so as to emit the acoustic energy at a wavelength and phase determined by the first control signal (C1, C11); a second parametric acoustic transducer array (110b, 210b) configured to emit acoustic energy of periodically varying intensity in the form of a second modulated acoustic signal (200b) comprising a second acoustic carrier wave (202b) and the audible sound signal (204), wherein the audible sound signal (204) is modulated onto the second acoustic carrier wave (202b), wherein the second parametric acoustic transducer array (110b, 210b) comprises a plurality of transducer elements (ej), the transducer elements (ej) being controllable in response to a second control signal (C2, C12) so as to emit the acoustic energy at a wavelength and phase determined by the second control signal (C2, C12); and a controller (120) communicably connected to the first and second acoustic transducer arrays (110a, 110b, 210a, 210b), wherein the method comprises: generating, by the controller (120), the first control signal (C1, C11) such that the audible sound signal (204) is modulated onto the first acoustic carrier wave (202a) to form the first modulated acoustic signal acoustic signal (200a) and such that the emitted acoustic energy forms a first directional beam of sound (B) having a first pressure maximum region (PMAX1) in the form ofa first acoustic lobe created around a first focal point where the emitted acoustic energy of the first directional beam of sound (B) is constructively combined; and generating, by the controller (120), the second control signal (C2, C12) such that the audible sound signal (204) is modulated onto the second acoustic carrier wave (202b) in counter phase compared to in the first modulated acoustic signal (200a) to form the second modulated acoustic signal :»::»S¿~»(200b) and such that the emitted acoustic energy forms a second directional beam of sound (B') having a second pressure maximum region (PiviAx2) in the form of a second acoustic lobe created around a second focal point where the emitted acoustic energy of the second directional beam of sound (Bf) is constructively combined. 12.The method of claim 11, wherein the first and second parametric acoustic transducer arrays (110, 210) are micromachined ultrasonic transducers, MUTs, wherein emitting acoustic energy by the first and second parametric acoustictransducer arrays (110, 210) comprises emitting ultrasonic energy, wherein each of the first and second modulated acoustic signals (200a, 200b) is a modulated ultrasonic signal and wherein each of the first and second carrier waves (202a, 202b) is an ultrasonic carrier wave. 13.The method of any of the claims 11 or 12, wherein generating the first and second control signals (C1, C2, C11, C12), by the controller (120), comprises generating the control signals (C1, C2, C11, C12) such that the first pressure maximum region (PiviAx1) and the second pressure maximum region (PiviAx2) are formed at a preset distance (d1) from each other. 14.The method of claim 13, wherein the preset distance (d1) is set to 10 cm s d1 scm, preferably 13 cm s d1 s 17 cm. 15.The method of any of the claims 11 to 14, further comprising receiving, via an input device (130) communicatively connected to the controller (120), information from one or more distance measurement devices on a first three dimensional position at which the first directional beam of sound (B) should be directed and a second three dimensional position at which the second directional beam of sound (B') should be directed, wherein generating the first control signal (C1, C11), by the controller (120), comprises generating the first control signal (C1, C11) based on the first three dimensional position at which the first directional beam of sound (B) should be directed such that the emitted acoustic energy forms the first directional beam of sound (B) to have the first pressure maximum region (PiviAx1) at the first determined position, and wherein generating the second control signal (C2, C12), by the controller (120), comprises generating the second control signal (C2, C12) based on the second three dimensional position at which the second directional beam of sound (B') should be directed such that the emitted acoustic energy forms the second directional beam of sound (B') to have the second pressure maximum region (PiviAx2) at the second determined position. 16.The method of any one of the claims 11 to 15, wherein generating each of the first and second control signals (C1, C2, C11, C12), by the controller (120), comprises generating each of the first and second control signals (C1, C2, C11, C12) such that the acoustic energy is emitted at a frequency of 160 kHz. 17.A computer program (127) Ioadable into a non-volatile data carrier (125) communicatively connected to a processor (123), the computer program (127) comprising software for executing the method according any of the claims 11 to 16 when the computer program (127) is run on the processor (123). 18.A non-volatile data carrier (125) containing the computer program (1 27) of the c|aim 17.