WO2023284963A1

WO2023284963A1 - Audio device and method for producing a sound field using beamforming

Info

Publication number: WO2023284963A1
Application number: PCT/EP2021/069739
Authority: WO
Inventors: Peter GROSCHE; Andrew Watson
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2021-07-15
Filing date: 2021-07-15
Publication date: 2023-01-19

Abstract

An audio device (10) for producing a sound field is disclosed, comprising a plurality of loudspeakers (20, 21a-g, 22a-g) arranged along a longitudinal axis of the audio device (10), wherein each loudspeaker is configured to emit sound waves in a main radiation direction perpendicular to the longitudinal axis. The audio device (10) further comprises a processing circuitry configured to process input signals to obtain output signals for driving the loudspeakers (20, 21a-g, 22a-g). The processing circuitry is configured to implement one or more beamformers for obtaining, based on a desired beamforming direction, the output signals. The output signals for the loudspeakers comprise a respective first output signal component for generating a surround sound wave in the desired beamforming direction and a respective second output signal component for generating a compensation sound wave, wherein the compensation sound wave destructively interferes with the surround sound wave in the main radiation direction.

Description

AUDIO DEVICE AND METHOD FOR PRODUCING A SOUND FIELD USING BEAMFORMING

TECHNICAL FIELD

The present disclosure relates to audio processing and sound generation in general. More specifically, the disclosure relates to an audio device and method for producing a sound field using beamforming. BACKGROUND

In "virtual" surround-sound systems the surround channel signals are not reproduced by discrete loudspeakers positioned around or above the listener. Instead, the listener is tricked into thinking that by one of several possible approaches. One of these approaches based on beamforming involves the radiation of beams of sound from a single loudspeaker assembly, such as a soundbar, positioned at front centre, which are directed towards the walls and ceiling of a room to be subsequently reflected towards the listener, thereby giving the impression that the sound has come from those directions. In this way it is possible to mimic the performance of discrete surround speakers and achieve some measure of the spacious and immersive qualities of a full surround sound system. For the surround channel to clearly appear to come from the side (or above for a ceiling reflection), the level of the reflected signal needs to be significantly higher, approximately 20dB, than that of any sound that is travelling directly from the soundbar to the listener. This is related to the Precedence or Haas effect.

SUMMARY

An improved audio device and method for producing a sound field using beamforming are provided by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

More specifically, according to a first aspect, an audio device for producing a sound field is provided. The audio device comprises a plurality of loudspeakers (also referred to as transducers or acoustic drivers) arranged at a plurality of locations along a longitudinal axis of the audio device, wherein each loudspeaker is configured to emit sound waves in a main radiation direction substantially perpendicular to the longitudinal axis. The audio device further comprises a processing circuitry configured to process a plurality of input signals to obtain a plurality of output signals and output the plurality of output signals to the plurality of loudspeakers for driving the plurality of loudspeakers. The processing circuitry is configured to implement one or more beamformers for processing, based on a desired beamforming direction at a horizontal angle with the main radiation direction, the plurality of input signals to obtain the plurality of output signals. The one or more beamformers may comprise one or more delay and add beamformers.

The output signals for the plurality of loudspeakers comprise a respective first output signal component for generating a surround sound wave primarily directed in the desired beamforming direction and a respective second output signal component for generating a compensation sound wave, wherein the compensation sound wave destructively interferes with the surround sound wave in the main radiation direction. By the destructive interference between the surround sound wave and the compensation sound wave in the main radiation direction the reflected to direct sound ratio may be increased in the main radiation direction. This results in the surround channel being more clearly identified as coming from the side with a corresponding improvement in the perceived spaciousness of the reproduction. In addition, with less unwanted surround channel signal travelling directly from speaker to listener, the audibility and clarity of the left, centre, right, left height and right height channels may also be improved.

In a further possible implementation form, the audio device comprises a housing, wherein the plurality of loudspeakers are mounted in a side wall of the housing. The audio device may be a soundbarwith a correspondingly shaped housing. Thus, the audio device can be conveniently used in home entertainment scenarios.

In a further possible implementation form, the audio device comprises a further plurality of loudspeakers mounted in a top wall of the housing, wherein the further plurality of loudspeakers are each configured to emit sound waves in a further radiation direction at an vertical angle substantially perpendicular to a plane defined by the longitudinal axis and the horizontal main radiation direction. In addition to the further plurality of loudspeakers configured to emit primarily in a vertical direction the audio device may comprise further loudspeakers configured to emit primarily in the horizontal direction, such as additional bass drivers. By emitting sound in the vertical direction the radiation of sound beams towards the ceiling of a room can enhance the spacious and immersive qualities. In a further possible implementation form, the processing circuitry is configured to generate the respective second output signal component for generating the compensation sound wave using a plurality of equalization filter parameters based on a plurality of measurements of the surround sound wave. Thus, the compensation sound wave can be generated efficiently.

In a further possible implementation form, the plurality of equalization filter parameters are based on a weighted average of the plurality of measurements of the surround sound wave at a plurality of locations within the horizontal plane defined by the longitudinal axis of the audio device and the main radiation direction. For instance, the measurements may be taken at angles of -10, -5, 0, 5 and 10 degrees within the horizontal plane. This can ensure a robust generation of equalization filters resulting in a large cancellation area where the listening position is not too critical.

In a further possible implementation form, the plurality of loudspeakers comprises a central group of loudspeakers, wherein the central group of loudspeakers comprises a central loudspeaker and a first pair of loudspeakers and a second pair of loudspeakers. The loudspeakers of the first pair of loudspeakers are arranged at a first distance from the central loudspeaker on opposites sides of the central loudspeaker and the loudspeakers of the second pair of loudspeakers are arranged at a second distance from the central loudspeaker on opposites sides of the central loudspeaker. Thus, different frequencies can be processed using different pairs of loudspeakers which enables a broad frequency range with a continuous and controlled horizontal response which approximates constant directivity.

In a further possible implementation form, a membrane of the central loudspeaker has a diameter in a range from about 20 to about 60 mm.

In a further possible implementation form, a respective membrane of the loudspeakers of the first and/or second pair of loudspeakers has a diameter in a range from about 20 to about 60 mm.

In a further possible implementation form, the first distance is in a range from about 40 to 60 mm. In a further possible implementation form, the second distance is in a range from about 80 to 100 mm.

In a further possible implementation form, the plurality of loudspeakers further comprises a left group of loudspeakers arranged on a left side of the central group of loudspeakers and a right group of loudspeakers arranged on a right side of the central group of loudspeakers. The left group of loudspeakers and the right group of loudspeakers define a third pair of loudspeakers, a fourth pair of loudspeakers and a fifth pair of loudspeakers arranged at a third distance, a fourth distance and a fifth distance from the central loudspeaker on opposites sides of the central loudspeaker. The inclusion of these further pairs of loudspeakers allows the directivity control to be extended to progressively lower frequencies.

In a further possible implementation form, the third distance is in a range from about 160 to about 200 mm, the fourth distance is in a range from about 340 to about 380 mm and the fifth distance is in a range from about 460 to 540 mm.

In a further possible implementation form, a respective membrane of the loudspeakers of the third, fourth and/or fifth pair of loudspeakers has a diameter in a range from about 20 to about 60 mm.

In a further possible implementation form, the processing circuitry is configured to apply a respective first order low-pass filter with a cut-off frequency in a respective range of about 3150 to 4750, 1800 to 2200, 850 to 1050, 450 to 660, and 320 to 660 Hz for generating the output signals for the first, second, third, fourth and/or fifth pair of loudspeakers, respectively.

According to a second aspect a method for producing a sound field with an audio device is provided. The method comprises the steps of: providing a plurality of loudspeakers at a plurality of locations along a longitudinal axis of the audio device, wherein each loudspeaker is configured to emit sound waves in a main horizontal radiation direction substantially perpendicular to the longitudinal axis; and processing a plurality of input signals by a processing circuitry of the audio device to obtain a plurality of output signals and outputting the plurality of output signals to the plurality of loudspeakers for driving the plurality of loudspeakers, wherein the processing circuitry is configured to implement one or more beamformers for processing, based on a desired beamforming direction at a horizontal angle with the main radiation direction, the plurality of input signals to obtain the plurality of output signals, wherein the output signals for the plurality of loudspeakers comprise a respective first output signal component for generating a surround sound wave primarily in the desired beamforming direction and a respective second output signal component for generating a compensation sound wave, wherein the compensation sound wave destructively interferes with the surround sound wave in the main radiation direction for increasing the reflected to direct sound ratio.

The method according to the second aspect of the present disclosure can be performed by the audio device according to the first aspect of the present disclosure. Thus, further features of the method according to the second aspect result directly from the functionality of the audio device according to the first aspect as well as its different implementation forms described above and below. In other words, further features and implementation forms of the method according to the second aspect correspond to the features and implementation forms of the audio device according to the first aspect.

According to a third aspect, a computer program product is provided comprising a computer-readable storage medium for storing program code which causes a computer or a processor to perform the method according to the second aspect when the program code is executed by the computer or the processor.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Figs. 1a and 1b show a side and plan view illustrating an audio device according to an embodiment located in a room relative to a listening position;

Fig. 2 shows a perspective view of an audio device according to an embodiment; Fig. 3 shows a schematic plan view illustrating a surround sound wave and a compensation sound wave generated by an audio device according to an embodiment; Fig. 4 shows a front view and a plan view of an audio device according to an embodiment;

Fig. 5 shows a front view of an audio device according to an embodiment implemented as a TV; Fig. 6 shows graphs illustrating the acoustic output as a function of frequency for a plurality of loudspeaker pairs of an audio device according to an embodiment;

Fig. 7 shows graphs illustrating the acoustic output as a function of frequency for a horizontal beam generated by an audio device according to an embodiment for different horizontal angles;

Fig. 8 shows a schematic diagram illustrating in more detail the signal processing implemented by an audio device according to an embodiment; Fig. 9 shows schematic diagrams illustrating in more detail the signal processing implemented by an audio device according to an embodiment for generating a surround sound wave based on a left and right surround channel input;

Fig. 10 shows a schematic diagram illustrating in more detail the signal processing implemented by an audio device according to an embodiment for generating a compensation sound wave based on a left surround channel input;

Figs. 11a-d show graphs illustrating the acoustic output as a function of frequency for a horizontal beam generated by an audio device according to an embodiment for different horizontal angles;

Fig. 12 shows a graph illustrating a measured acoustic output in a listening area as a function of frequency generated by an audio device according to an embodiment; Fig. 13 shows graphs illustrating a simulated acoustic output in a listening area as a function of frequency generated by an audio device according to an embodiment for different angles;

Fig. 14 shows a graph illustrating the acoustic output as a function of frequency for a horizontal beam generated by an audio device according to an embodiment for different horizontal angles;

Figs. 15a-e show front views of an audio device according to further embodiments; and

Fig. 16 shows a flow diagram illustrating an audio method for producing a sound field according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figures 1a and 1b show a side and plan view illustrating an audio device 10 according to an embodiment located in a room 80 relative to a listening position (indicated by the chair). Generally, the audio device 10 is configured to generate based on beamforming a sound field in a listening area by means of sound waves (or sound beams), which are directed towards the walls 80b and the ceiling 80a of the room 80 to be subsequently reflected towards the listener, thereby giving the impression that the sound has come from those directions.

Figure 2 shows a perspective view of an audio device 10 according to an embodiment in more detail. The audio device 10 comprises a plurality of loudspeakers (also referred to as transducers or acoustic drivers) 20, 21a-e, 22a-e arranged at a plurality of locations along a longitudinal axis B of the audio device 10. In the embodiment shown in figure 2, the audio device 10 is implemented as a soundbar 10 comprises a housing, wherein the plurality of loudspeakers 20, 21a-e, 22a-e are mounted in a side wall 50a of the housing. Thus, each loudspeaker of the plurality of loudspeakers 20, 21a-e, 22a-e is configured to emit sound waves in a main radiation direction A substantially perpendicular to the longitudinal axis B. As will be appreciated, the main radiation direction A and the longitudinal axis B define a substantially horizontal plane.

As will be described in more detail below (for instance in the context of figure 8), the audio device 10 further comprises a processing circuitry 30 configured to process a plurality of input signals 31 to obtain a plurality of output signals and output the plurality of output signals to the plurality of loudspeakers 20, 21a-e, 22a-e for driving the plurality of loudspeakers 20, 21a-e, 22a-e. The processing circuitry 30 is configured to implement one or more beamformers 30d (as will be described in more detail below in the context of figure 9) for processing, based on a desired beamforming direction C (shown in figure 3) at a horizontal angle with the main radiation direction A, the plurality of input signals 31 to obtain the plurality of output signals. In an embodiment, the one or more beamformers 30d may comprise one or more delay and add beamformers 30d. As schematically illustrated in figure 3, the output signals for the plurality of loudspeakers comprise a respective first output signal component for generating a surround sound wave 60 primarily directed in the desired beamforming direction C (in the exemplary scenario shown in figure 3 the desired beamforming direction C is 45 degrees) and a respective second output signal component for generating a compensation sound wave 70. As will be described in more detail below, the processing circuitry 30 is configured to generate the respective second output signal component in such a way that the compensation sound wave 70 destructively interferes, i.e. cancels with the surround sound wave 60 in the main radiation direction A (as illustrated in figure 3 on the right-hand side). By the destructive interference between the surround sound wave 60 and the compensation sound wave 70 in the main radiation direction A the reflected to direct sound ratio may be increased in the main radiation direction A and, thus, in the area, where the listener is located.

Figure 4 shows a front view and a plan view of the audio device 10 according to a further embodiment. The audio device 10 is implemented as a soundbar 10 and comprises the plurality of loudspeakers 20, 21a-g, 22a-g arranged at a plurality of locations along the longitudinal axis B of the soundbar 10 and mounted in the side wall 50a of the housing of the soundbar 10. In addition to the plurality of loudspeakers 20, 21a-g, 22a-g mounted in the side wall 50a of its housing the soundbar 10 shown in figure 4 comprises a further pair of loudspeakers 25a, 26a mounted in the top wall 50b of the housing of the audio device 10. The further pair of loudspeakers 25a, 26a is configured to emit sound waves in a further radiation direction at a-vertical angle substantially perpendicular to the horizontal plane defined by the longitudinal axis B and the horizontal main radiation direction A.

Figure 5 illustrates a further variant of the audio device 10 of figure 4, where the audio device is a component of a TV, which may further include a display 11.

In the embodiments shown in figures 2, 4 and 5, the plurality of loudspeakers 20, 21a-g, 22a-g comprises a central group of loudspeakers 20, 21 a, b, 22a, b, including a central loudspeaker 20, a first pair of loudspeakers 21a, 22a and a second pair of loudspeakers 21b, 22b. As can be taken, for instance, from figure 5, the loudspeakers of the first pair of loudspeakers 21a, 22a are arranged at a first distance from the central loudspeaker 20 on opposites sides of the central loudspeaker 20, while the loudspeakers of the second pair of loudspeakers 21b, 22b are arranged at a second larger distance from the central loudspeaker 20 on opposites sides of the central loudspeaker 20. In an embodiment, the first distance between the central loudspeaker 20 and the loudspeakers of the first pair of loudspeakers 21a, 22a is in a range from about 40 to 60 mm. In an embodiment, the larger second distance between the central loudspeaker 20 and the loudspeakers of the second pair of loudspeakers 21 b, 22b is in a range from about 80 to 100 mm.

In an embodiment, the membrane of the central loudspeaker 20 has a diameter in a range from about 20 to about 60 mm, such as 2”. In an embodiment, the membrane size of the central loudspeaker 20 may be chosen to provide a desired high frequency directivity (such as for frequencies larger than 15 kHz) of a non-steered beam and, in the case of larger sizes such as 2”, to provide high power handling for the discrete centre channel.

In an embodiment, a respective membrane of the loudspeakers 21 a, b, 22a, b of the first and/or second pair of loudspeakers has a diameter in a range from about 20 to about 60 mm, such as 1.5”. In an embodiment, the membrane size(s) of the loudspeakers 21 a, b, 22a, b of the first and/or second pair of loudspeakers may be chosen to allow the separations of the pairs to be as close as possible to the ideal separations for generating the desired beam shape.

As illustrated in figures 2, 4 and 5, in addition to the central group of loudspeakers 20,

21 a, b, 22a, b the audio device 10 may further comprise a left group of loudspeakers 21c-g arranged on a left side of the central group of loudspeakers 20, 21 a, b, 22a, b and a right group of loudspeakers 22c-g arranged on a right side of the central group of loudspeakers 20, 21 a, b, 22a, b. In an embodiment, the left group of loudspeakers 21 c-g and the right group of loudspeakers 22c-g may define at least a third pair of loudspeakers 21c, 22c, a fourth pair of loudspeakers 21 d, 22d and a fifth pair of loudspeakers 21 e, 22e arranged at a third distance, a fourth distance and a fifth distance from the central loudspeaker 20 on opposites sides of the central loudspeaker 20. In the embodiment shown in figures 4 and 5, the left group of loudspeakers 21 c-g and the right group of loudspeakers 22c-g may further define a sixth pair of loudspeakers 21 f, 22f and a seventh pair of loudspeakers 21 g, 22g arranged on opposite sides of the central loudspeaker 20.

As illustrated, for instance, in figure 4, the loudspeakers of the third, fourth and fifth pair of loudspeakers may have membranes having the same or similar sizes. In an embodiment, the respective membrane of the loudspeakers of the third 21c, 22c, fourth 21 d, 22d and/or fifth pair 21 e, 22e of loudspeakers has a diameter in a range from about 20 to about 60 mm, such as 2". In an embodiment, the membrane size(s) of the loudspeakers of the third, fourth and/or fifth pair of loudspeakers may be selected for maximum output capability (as their directivity may not be important, and there be enough space on the housing for them to be placed in the optimum positions).

In an embodiment, the third distance between the central loudspeaker 20 and the loudspeakers 21c, 22c of the third pair of loudspeakers is in a range from about 160 to about 200 mm. In an embodiment, the fourth distance between the central loudspeaker 20 and the loudspeakers 21 d, 22d of the fourth pair of loudspeakers is in a range from about 340 to about 380 mm. In an embodiment, the fifth distance between the central loudspeaker 20 and the loudspeakers 21 e, 22e of the fifth pair of loudspeakers is in a range from about 460 to 540 mm.

In an embodiment, the loudspeakers 21 g, 21 f and 21 e (also referred to as loudspeakers 1 , 2 and 3 in figure 4) may be configured to generate a left channel component, the central group of loudspeakers 20, 21 a, b, 22a, b (also referred to as loudspeakers 6 to 10 in figure 4) may define a centre channel component and the loudspeakers 22e, 22f and 22g (also referred to as loudspeakers 13, 14 and 15 in figure 4) may be configured to define a right channel component. As already described above, the further loudspeakers 25a, 26a (also referred to as loudspeakers 16 and 17 in figure 4) may be configured to define the left and right height surround channels. In an embodiment, the loudspeakers 21c-f and 22c-f may be configured to reproduce a mono bass channel.

As will be described in more detail in the context of figures 8, 9 and 10 further below, in an embodiment, the processing circuitry 30 of the audio device 10 may be configured to apply a respective first order low-pass filter 30b with a cut-off frequency in a respective range of about 3150 to 4750, 1800 to 2200, 850 to 1050, 450 to 660, and 320 to 660 Hz for generating the output signals for the first, second, third, fourth and/or fifth pair of loudspeakers, respectively. In an embodiment, the low pass filter cut-off frequencies may be chosen to be inversely proportional to the separations of the loudspeakers of each pair. The amplitudes of each loudspeaker/pair can also be adjusted to fine tune the beam shape.

Figures 6 and 7 illustrate the measured performance of the default beam-shape generated by the audio device 10 of figure 4. Figure 6 illustrates the progressive low-pass filtering of the loudspeaker pairs as their separation increases, while figure 7 provides information about the resulting beam-shape (relative to the on-axis response). In an embodiment, the way the beam output changes from on-axis to off-axis is adjustable by the audio device 10. For instance, the beam can be made narrower with higher off-axis rejection or wider with less off-axis rejection.

In an embodiment, such a beam-shape may be desired for a beam functioning in a "quiet" or "privacy" mode, where the on-axis listener hears a normal sound, but for other off-axis room users the level is significantly reduced. The level falls off by approximately 3 dB at 15 degrees horizontally off-axis. This means that the listening position is not critical and the listener can move from side to side a reasonable amount (+/- 0.5m) without the sound changing too much. Beyond 60 degrees horizontally off-axis, the level falls off by approximately 10dB above 500Hz, offering a significant level reduction for off-axis room users.

Figure 8 shows a schematic diagram illustrating in more detail the signal processing implemented by an audio device 10 according to an embodiment. More specifically, figure 8 illustrates schematically the operation of the left, centre, right, left height, right height and bass channels of the audio device 10. As illustrated in figure 8, based on a 5.1.2 input signal 31 the processing circuitry 30 of the audio device 10 may generate a plurality of output signals for defining the left, centre, right, left height, right height and bass channels of the audio device 10. These output signals may be further processed by a power amplifier 32 of each of the plurality of loudspeakers.

Figure 9 shows schematic diagrams illustrating in more detail the signal processing implemented by the audio device 10 according to an embodiment for generating a steered surround sound wave based on a left and right surround channel input 31a, 31b. A high pass filter and overall equalization 30a can be applied to the first output signal components for the loudspeakers 21a-e, 22a-e to adjust the frequency spectrum of the resulting beam. Moreover, as already described above, the first output signal components for these loudspeakers 21a-e, 22a-e may be low pass filtered 30b in accordance with their separations to generate the (non-steered) default beam. In a further stage the first output signal components for the loudspeakers 20, 21a-e, 22a-e may be equalized by a respective equalizer 30c implemented by the processing circuitry 30 to ensure their acoustic responses are all consistent with each other. In a final stage, the processing circuitry 30 of the audio device 10 may apply time delays 30d to the first output signal components for the loudspeakers 21a-e, 22a-e to steer the beam to the appropriate horizontally off-axis angle (for instance, between 40 to 60 degrees), as already described above.

Figure 10 shows a schematic diagram illustrating in more detail the signal processing implemented by the audio device 10 according to an embodiment for generating a compensation sound wave (also referred to as "cancellation beam") based on a left surround channel input 31a. As will be appreciated, the signal processing for the right surround channel would be essentially identical. Also in this case, an overall equalization 30a can be applied to the second output signal components for the loudspeakers 21a-e, 22a-e to adjust the frequency spectrum of the compensation sound wave. Moreover, the second output signal components for these loudspeakers 21a-e, 22a-e may be low pass filtered 30b in accordance with their separations. In a further stage the second output signal components for the loudspeakers 20, 21a-e, 22a-e may be equalized by a respective equalizer 30c implemented by the processing circuitry 30 to ensure their acoustic responses are all consistent with each other. In addition to these processing stages already shown in figure 9, the processing stages shown in figure 10 further include an overall equalization stage 30e based on a spatial averaging of the left surround channel in the main radiation direction A and a phase inversion stage 30f. In an embodiment, the overall equalization stage 30e is based on measuring the output of the steered beam in the main radiation direction A (that constitutes the direct sound that would travel towards the listener) and averaged an angular range of, for instance, +/- 10 degrees with an appropriate weighting function. For instance, in an embodiment, the following weighting function may be used by the overall equalization stage 30e:

0.5 * 0 deg + 0.3 * (+5 deg. + -5 deg.) + 0.2 * (+10 deg. + -10 deg.)

Equalization is then applied to the second output signal components so that the compensation sound wave, i.e. the cancellation beam matches the spatial average. The thus processed second output signal components are then phase inverted (stage 30f).

Due to symmetry, this equalization may be the same for the opposite surround channel.

To optimise both left and right surround channel beams the cancellation beam may be fed by a signal comprising (left surround + right surround).

Figures 11 a and 11 b show the calculated acoustic response of a +45 degree (left) steered beam (from a boundary element simulation) for different angles. Figure 11 c shows just the +45, 0 and -45 degree curves for simplicity. As will be appreciated, the +45 degree curve shows the high frequency roll-off associated with the centre and close to central loudspeaker 20 natural directivities. This may be still improved by using a smaller loudspeaker 20 in the centre position as mentioned above. Figure 11 d shows the actual measured data for the steered beam, for comparison with Figure 11c, and to justify simulations being used further to demonstrate the cancellation principle.

To test and verify the cancellation technique implemented by the audio device 10, a simple monopole signal was radiated by the central loudspeaker 20 only, radiating equally in all directions. A cancellation beam was then constructed to cancel the radiation in the listening area. The corresponding data shown in figure 12 illustrates the expected 15- 20dB level reduction in the listening area, and listening tests verified the subjective effectiveness of this. The weighting function used in this case was relatively simple - 0.75 x on-axis + 0.25 x 15 deg. A greater attenuation in the on-axis region may be achieved by increasing the weighting on the on-axis data or by changing to the 0, +1-5 and +/-10 degree weighting function described above. For a steered beam a greater attenuation in the listening area may be expected, closer to 20dB up to 8kHz, due to the inherent off-axis attenuation of the beam.

Figure 13 shows software simulated cancellation of the +45 degree steered surround channel beam, for cancellation off and cancellation on. The data shows the beam output, with and without the cancellation beam operating, at 45 degrees (the beam direction), 0 degrees (the listening axis) and at +/- 15 degrees. As can be taken from these figures, the cancellation technique allows a level difference of up to 20 dB between the beam output at +45 degrees and on-axis. The useful operational range extends to around 8 kHz.

Figure 14, for comparison, shows the cancellation on based on the software summation of the measured data for the steered and phase inverted cancellation beams. Agreement is good apart from the +/- 15 degrees curves above 8kHz.

In an embodiment, the processing circuitry 30 of the audio device 10 is configured to adjust both the steered beams and the cancellation beam independently. The angle of the steered beam could be user adjustable to suit the listener’s room geometry with a number of pre-programmed steered/cancellation beam options. If the user’s setup is asymmetrical then the left and right surround channel beams could be set to different angles. The cancellation beam could be steered to account for off-axis listening positions. Figures 15a-e show front views of further variants of the audio device 10 shown in figure 4 (for the sake of clarity only those loudspeakers have been identified by a reference sign in figures 15a-e that differ from the embodiment shown in figure 4). Figures 15a,b show different choices of the membrane sizes for the central loudspeaker 20. Smaller and more closely spaced loudspeakers may offer improved high frequency extension of the steered beam at the expense of power handling and output capability.

Figure 15c shows a variant of the audio device 10, where the loudspeakers 21 a, b and 22a, b of the first and second pair of loudspeakers may have a membrane of the same or similar dimensions as the central loudspeaker 20. This variant of the audio device 10 may provide an improved power handling and output capability at the expense of a high frequency extension of the steered beam.

In the variant of the audio device 10 shown in figure 15d the loudspeakers 21 f and 21 g and the loudspeakers 22f and 22g have been interchanged. This allows the pair 21 g and 22g to be the outermost pair in the array at an increased separation, thus allowing improved directivity control of the beam at the lower frequencies.

In the variant of the audio device 10 shown in figure 15e, the loudspeakers 21 d and 22d of the embodiment shown in figure 4 have been omitted.

Figure 16 shows a flow diagram illustrating an audio method 1600 for producing a sound field according to an embodiment. In an embodiment, the audio method 1600 may be performed by the audio device 10 and its different embodiments described above.

The method 1600 comprises a step 1601 of providing the plurality of loudspeakers 20, 21a-g, 22a-g at a plurality of locations along the longitudinal axis B of the audio device 10, wherein each loudspeaker 20, 21a-g, 22a-g is configured to emit sound waves in a main horizontal radiation direction A substantially perpendicular to the longitudinal axis B.

The method 1600 comprises a further step 1603 of processing a plurality of input signals 31 by the processing circuitry 30 of the audio device 10 to obtain a plurality of output signals and outputting the plurality of output signals to the plurality of loudspeakers 20, 21a-g, 22a-g for driving the plurality of loudspeakers 20, 21a-g, 22a-g, wherein the processing circuitry 30 is configured to implement one or more beamformers 30d for processing, based on the desired beamforming direction C at a horizontal angle with the main radiation direction A, the plurality of input signals 31 to obtain the plurality of output signals, wherein the output signals for the plurality of loudspeakers 20, 21 a-g, 22a-g comprise a respective first output signal component for generating a surround sound wave 60 primarily in the desired beamforming direction C and a respective second output signal component for generating a compensation sound wave 70, wherein the compensation sound wave 70 destructively interferes with the surround sound wave 60 in the main radiation direction A for increasing the reflected to direct sound ratio.

Thus, embodiments disclosed herein allow the audio device 10 to function as a virtual- surround channel speaker by steering a beam, for instance, towards the side wall 80b of the room 80 (typically by 40-60 degrees). As described above, the reflection of this sound towards the listener then gives the impression that the sound is coming from the side, provided there is sufficient level difference between the reflected and direct signals.

As described above, by sampling and averaging the direct output in the listening area from the steered beam, embodiments of the audio device 10 disclosed herein may generate a (non-steered) cancellation beam for cancelling the steered beam in the listening area, thereby increasing the level difference and allowing a much stronger surround effect. The cancellation may be effective up to around 8kHz. This process may be applied to both the left and right surround channels.

As will be appreciated, both the surround and cancellation beams are radiated by the same group of loudspeakers. Hence the acoustic centres are at the same place (the position of the central loudspeaker 20) and the beams are time aligned in all directions. This, and the sampling and averaging of the steered beam, ensures that the cancellation is effective over a wide horizontal and vertical range allowing a comfortable listening experience with the precise listening position not being too critical.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

For the several embodiments disclosed herein, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely a logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms. The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments. In addition, functional units of the embodiments disclosed herein may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

1. An audio device (10) for producing a sound field, comprising: a plurality of loudspeakers (20, 21a-g, 22a-g) arranged at a plurality of locations along a longitudinal axis (B) of the audio device (10), each loudspeaker configured to emit sound waves in a main radiation direction (A) perpendicular to the longitudinal axis (B); and a processing circuitry (30) configured to process a plurality of input signals (31) to obtain a plurality of output signals and output the plurality of output signals to the plurality of loudspeakers (20, 21a-g, 22a-g) for driving the plurality of loudspeakers (20, 21a-g, 22a-g), wherein the processing circuitry (30) is configured to implement one or more beamformers (30d) for processing, based on a desired beamforming direction (C), the plurality of input signals (31) to obtain the plurality of output signals, wherein the output signals for the plurality of loudspeakers (20, 21a-g, 22a-g) comprise a respective first output signal component for generating a surround sound wave (60) in the desired beamforming direction (C) and a respective second output signal component for generating a compensation sound wave (70), wherein the compensation sound wave (70) destructively interferes with the surround sound wave (60) in the main radiation direction (A).

2. The audio device (10) of claim 1 , wherein the audio device (10) comprises a housing, wherein the plurality of loudspeakers are mounted in a side wall (50a) of the housing.

3. The audio device (10) of claim 2, wherein the audio device (10) comprises a further plurality of loudspeakers (25a, 26a) mounted in a top wall (50b) of the housing, wherein the further plurality of loudspeakers (25a, 26a) are each configured to emit sound waves in a further radiation direction at an angle perpendicular to a plane defined by the longitudinal axis (B) and the main radiation direction (A).

4. The audio device (10) of any one of the preceding claims, wherein the processing circuitry (30) is configured to generate the respective second output signal component for generating the compensation sound wave (70) using a plurality of equalization parameters (30e) based on a plurality of measurements of the surround sound wave (60).

5. The audio device (10) of claim 4, wherein the plurality of equalization parameters (30e) are based on a weighted average of the plurality of measurements of the surround sound wave (60) at a plurality of locations within a plane defined by the longitudinal axis (B) of the audio device (10) and the main radiation direction (A).

6. The audio device (10) of any one of the preceding claims, wherein the plurality of loudspeakers (20, 21a-g, 22a-g) comprises a central group of loudspeakers (20, 21 a, b, 22a, b), wherein the central group of loudspeakers comprises a central loudspeaker (20) and a first pair of loudspeakers (21a, 22a) and a second pair of loudspeakers (21b, 22b), wherein the loudspeakers of the first pair of loudspeakers (21a, 22a) are arranged at a first distance from the central loudspeaker (20) on opposites sides of the central loudspeaker (20) and wherein the loudspeakers of the second pair of loudspeakers (21b, 22b) are arranged at a second distance from the central loudspeaker (20) on opposites sides of the central loudspeaker (20).

7. The audio device (10) of claim 6, wherein a membrane of the central loudspeaker (20) has a diameter in a range from about 20 to about 60 mm.

8. The audio device (10) of claim 6 or 7, wherein a respective membrane of the loudspeakers of the first (21 , 22a) and/or second pair (21 , 22b) of loudspeakers has a diameter in a range from about 20 to about 60 mm.

9. The audio device (10) of any one of claims 6 to 8, wherein the first distance is in a range from about 40 to 60 mm.

10. The audio device (10) of any one of claims 6 to 9, wherein the second distance is in a range from about 80 to 100 mm.

11. The audio device (10) of any one of claims 6 to 10, wherein the plurality of loudspeakers (20, 21a-g, 22a-g) further comprises a left group of loudspeakers (21c-g) arranged on a first side of the central group of loudspeakers (20, 21 a, b, 22a, b) and a right group of loudspeakers (22c-g) arranged on a second opposite side of the central group of loudspeakers (20, 21a, b, 22a, b), wherein the left group of loudspeakers (21c-g) and the right group of loudspeakers (22c-g) define a third pair of loudspeakers (21c, 22c), a fourth pair of loudspeakers (21 d, 22d) and a fifth pair of loudspeakers (21 e, 22e) arranged at a third distance, a fourth distance and a fifth distance from the central loudspeaker (20) on opposites sides of the central loudspeaker (20).

12. The audio device (10) of claim 11 , wherein the third distance is in a range from about 160 to about 200 mm, the fourth distance is in a range from about 340 to about 380 mm and the fifth distance is in a range from about 460 to 540 mm.

13. The audio device (10) of claim 11 or 12, wherein a respective membrane of the loudspeakers of the third, fourth and/or fifth pair of loudspeakers (21c-e, 22c-e) has a diameter in a range from about 20 to about 60 mm.

14. The audio device (10) of claim 12 or 13, wherein the processing circuitry (30) is configured to apply a respective first order low-pass filter (30b) with a cut-off frequency in a respective range of about 3150 to 4750, 1800 to 2200, 850 to 1050, 450 to 660, and 320 to 660 Hz for generating the output signals for the first, second, third, fourth and/or fifth pair of loudspeakers (21a-e, 22a-e).

15. A method (1600) for producing a sound field with an audio device (10), wherein the method (1600) comprises: providing (1601) a plurality of loudspeakers (20, 21a-g, 22a-g) at a plurality of locations along a longitudinal axis (B) of the audio device (10), each loudspeaker configured to emit sound waves in a main radiation direction (A) perpendicular to the longitudinal axis (B); and processing (1603) a plurality of input signals (31) by a processing circuitry (30) to obtain a plurality of output signals and outputting the plurality of output signals to the plurality of loudspeakers (20, 21a-g, 22a-g) for driving the plurality of loudspeakers (20, 21a-g, 22a-g), wherein the processing circuitry (30) is configured to implement one or more beamformers (30d) for processing, based on a desired beamforming direction (C), the plurality of input signals (31) to obtain the plurality of output signals, wherein the output signals for the plurality of loudspeakers (20, 21a-g, 22a-g) comprise a respective first output signal component for generating a surround sound wave (60) in the desired beamforming direction (C) and a respective second output signal component for generating a compensation sound wave (70), wherein the compensation sound wave (70) destructively interferes with the surround sound wave (60) in the main radiation direction (A).

16. A computer program product comprising a computer-readable storage medium carrying program code which causes a computer or a processor to perform the method (1600) of claim 15 when the program code is executed by the computer or the processor.