LOUDSPEAKER ASSEMBLIES AND ASSOCIATED METHODS

Abstract

A loudspeaker assembly comprising: a first loudspeaker configured to receive a first electrical signal, and to produce sound along a first principal radiating axis based on the first electrical signal; a second loudspeaker configured to receive a second electrical signal, and to produce sound along a second principal radiating axis based on the second electrical signal; a third loudspeaker configured to receive a third electrical signal, and to produce sound along a third principal radiating axis based on the third electrical signal; and a control unit configured to produce each of the first, second and third electrical signals based on an input signal representative of audio. There is a first angular offset between the first and second principal radiating axes and a second angular offset between the first and third principal radiating axes.

Claims

1.-15. (canceled)

16. A loudspeaker assembly comprising: a first loudspeaker configured to receive a first electrical signal, and to produce sound along a first principal radiating axis based on the first electrical signal; a second loudspeaker configured to receive a second electrical signal, and to produce sound along a second principal radiating axis based on the second electrical signal; a third loudspeaker configured to receive a third electrical signal, and to produce sound along a third principal radiating axis based on the third electrical signal; and a control unit configured to produce each of the first, second and third electrical signals based on an input signal representative of audio; wherein there is a first angular offset between the first and second principal radiating axes and a second angular offset between the first and third principal radiating axes; wherein the control unit is configured to filter at least two of the first, second and third electrical signals so that there is a first gain and phase difference between the first and second electrical signals and a second gain and phase difference between the first and third electrical signals; wherein the first and second angular offsets and the first and second gain and phase differences are configured so that, when the loudspeaker assembly is in use, direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at each of a first listening position and a second listening position.

17. A loudspeaker assembly according to claim 16, wherein the loudspeaker assembly includes: a fourth loudspeaker configured to receive a fourth electrical signal, and to produce sound along a fourth principal radiating axis based on the fourth electrical signal; and wherein the control unit is configured to produce the fourth electrical signal based on the input signal representative of audio; wherein there is an third angular offset between the first and fourth principal radiating axes; wherein the control unit is configured to filter the fourth electrical signal so that there is a third gain and phase difference between the first and fourth electrical signals; wherein the first, second and third angular offsets and the first, second and third gain and phase differences are configured so that, when the loudspeaker assembly is in use, direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at each of a first listening position, a second listening position and a third listening position.

18. A loudspeaker assembly according to claim 16, wherein each loudspeaker in the loudspeaker assembly has a directivity index that is at least 6 dB at a frequency of 3 kHz.

19. A loudspeaker assembly according to claim 16, wherein each gain and phase difference is zero below 150 Hz.

20. A loudspeaker assembly according to claim 16, wherein the predetermined cancelling condition at each listening position requires that, over a frequency range of 200 Hz-3 kHz, the sound pressure level of direct sound produced by multiple loudspeakers in the loudspeaker assembly at the listening position is at least 12 dB lower than the sound pressure level of direct sound produced by a subset of the loudspeakers in the loudspeaker assembly at the listening position.

21. A loudspeaker assembly according to claim 16, wherein there is an angular offset between the principal axes of each pair of loudspeakers in the loudspeaker assembly that is at least 30.

22. A loudspeaker assembly according to claim 16, wherein the loudspeakers in the loudspeaker assembly are arranged so that between each pair of loudspeakers in the loudspeaker assembly there is a distance that is no more than 50 cm.

23. A loudspeaker assembly according to claim 16, wherein the loudspeakers in the loudspeaker assembly are mounted within a single loudspeaker assembly enclosure, with the listening positions located outside the loudspeaker assembly enclosure.

24. A loudspeaker assembly according to claim 23, wherein the loudspeaker assembly includes four loudspeakers arranged in a linear array mounted within a single loudspeaker assembly enclosure, wherein the two loudspeakers on the ends of the linear array have principal radiation axes that point out from opposing side faces of the single loudspeaker assembly enclosure, with the two loudspeakers interior of the two loudspeakers on the ends of the linear array having principal radiation axes that point out of a front face of the single loudspeaker assembly enclosure, wherein the front face of the single loudspeaker assembly enclosure faces the listening positions.

25. A loudspeaker assembly according to claim 23, wherein the loudspeaker assembly enclosure has a bar shape.

26. A loudspeaker assembly according to claim 16, wherein each loudspeaker is an electro-dynamic loudspeaker that includes: a permanent magnet assembly comprising metal components and a permanent magnet; a voice coil assembly comprising a wire referred to as a voice coil wound/wrapped around a thin tube referred to as a voice coil former; a diaphragm; a chassis; a suspension system which suspends the diaphragm from the chassis; wherein the voice coil is configured to interact with a static magnetic field of the permanent magnet when an electric current is passed through the voice coil such that an interaction between the voice coil and the static magnetic field of the permanent magnet results in movement of the voice coil along a predetermined axis.

27. A loudspeaker assembly according to claim 16, wherein each loudspeaker in the loudspeaker assembly is mounted within its own individual loudspeaker enclosure so that back radiation from each loudspeaker does not have a significant influence on other loudspeakers in the loudspeaker assembly.

28. A method of configuring a loudspeaker assembly comprising: a first loudspeaker configured to receive a first electrical signal, and to produce sound along a first principal radiating axis based on the first electrical signal; a second loudspeaker configured to receive a second electrical signal, and to produce sound along a second principal radiating axis based on the second electrical signal; a third loudspeaker configured to receive a third electrical signal, and to produce sound along a third principal radiating axis based on the third electrical signal; and a control unit configured to produce each of the first, second and third electrical signals based on an input signal representative of audio; wherein there is a first angular offset between the first and second principal radiating axes and a second angular offset between the first and third principal radiating axes; wherein the control unit is configured to filter at least two of the first, second and third electrical signals so that there is a first gain and phase difference between the first and second electrical signals and a second gain and phase difference between the first and third electrical signals; wherein the method includes adjusting the first and second angular offsets and the first and second gain and phase differences so that, when the loudspeaker assembly is in use, direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at each of a first listening position and a second listening position.

29. A method according to claim 28, wherein the method includes: (i) at a first one of the listening positions, measuring direct sound produced by a first subset of the loudspeakers in the loudspeaker assembly and, based on the measured direct sound, adjusting one or more of the gain and phase differences so that direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at the first listening position; (ii) at a second one of the listening positions, measuring direct sound produced by multiple loudspeakers in the loudspeaker assembly and evaluating whether the direct sound produced by the multiple loudspeakers is cancelled in accordance with the predetermined cancelling condition at the second listening position; (iii) if the direct sound produced by the multiple loudspeakers is not cancelled in accordance with the predetermined cancelling condition at the second listening position, adjusting one or more of the angular offsets and returning to step (i).

30. A method according to claim 29, wherein the loudspeaker assembly includes: a fourth loudspeaker configured to receive a fourth electrical signal, and to produce sound along a fourth principal radiating axis based on the fourth electrical signal; and wherein the control unit is configured to produce the fourth electrical signal based on the input signal representative of audio; wherein there is an third angular offset between the first and fourth principal radiating axes; wherein the control unit is configured to filter the fourth electrical signal so that there is a third gain and phase difference between the first and fourth electrical signals; wherein the method includes adjusting the first, second and third angular offsets and the first, second and third gain and phase differences so that, when the loudspeaker assembly is in use, direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at each of a first listening position, a second listening position and a third listening position; wherein the method further includes: (iv) at a third one of the listening positions, measuring direct sound produced by a second subset of the loudspeakers in the loudspeaker assembly and, based on the measured direct sound, adjusting the third gain and phase difference so that direct sound produced by multiple loudspeakers in the loudspeaker assembly is cancelled in accordance with a predetermined cancelling condition at the third listening position; (v) at the second listening position, measuring direct sound produced by multiple loudspeakers in the loudspeaker assembly and evaluating whether the direct sound produced by the multiple loudspeakers is cancelled in accordance with the predetermined cancelling condition at the second listening position; (v) if the direct sound produced by the multiple loudspeakers is not cancelled in accordance with the predetermined cancelling condition at the second listening position, adjusting one or more of the angular offsets and returning to step (i).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0105] Examples of these proposals are discussed below, with reference to the accompanying drawings in which:

[0106] FIG. 1(a) shows a cardioid loudspeaker assembly.

[0107] FIG. 1(b) is a series of 2D polar plots showing the direct sound (sound pressure level) produced by the cardioid loudspeaker assembly 1001 of FIG. 1(a) at different frequencies, along with the polarity of each lobe.

[0108] FIG. 2 shows a loudspeaker assembly according to the present invention.

[0109] FIG. 3 compares the operation of (a) the cardioid loudspeaker assembly of FIG. 1(a) with (b) the operation of the loudspeaker assembly of FIG. 2.

[0110] FIG. 4 shows an example method of configuring the loudspeaker assembly of FIG. 2.

[0111] FIG. 5 is a schematic diagram that provides a simplified visualisation of the cancellation that occurs at listening positions P1-P3 when filtering derived according to the method of FIG. 4 is applied to electrical signals E1-E4 received by loudspeakers L1-L4 from the loudspeaker assembly of FIG. 2.

[0112] FIG. 6 illustrates the similarity in effect on the sound pressure level of direct sound produced by a loudspeaker at a listening position caused by either (i) increasing the angle between the principal radiating axis of the loudspeaker relative to the position of the loudspeaker; or (ii) filtering the electrical signal received by the loudspeaker to cancel the direct sound produced by another loudspeaker in the same loudspeaker array.

DETAILED DESCRIPTION

[0113] In general, the following discussion describes examples of our proposals that provide a loudspeaker assembly enclosure including a number of loudspeakers at predefined angles, where every loudspeaker unit receives an appropriate signal. A preferred aim is to obtain a given directional sound radiating.

[0114] In general terms, the present examples may be viewed as building on the concept of the cardioid loudspeaker assembly 1001 described with reference to FIG. 1(a).

[0115] In the examples discussed below, a number of speakers mounted in an enclosure have a geometry (mounting angles) that is dictated by the directivity of each loudspeaker.

[0116] In some examples, four or more loudspeakers may be mounted in a loudspeaker assembly enclosure in such a way that sound produced by each loudspeaker is radiating out from the enclosure in a controlled manner in the horizontal plane. In these examples, sound may radiate out from the enclosure in an arbitrary manner in the vertical planeif control in this vertical plane were wanted, then this may be achieved by mounting additional loudspeakers in the vertical plane, e.g. with a second and third row (and possibly additional rows) of loudspeakers.

[0117] In some examples, the specific signal processing for each loudspeaker may be tuned or adapted, dictated by the directivity of each loudspeaker unit, by the mounting angle of the loudspeakers, and by the desired polar pattern of the complete enclosure.

[0118] In some examples, the loudspeakers may be mounted also with a certain angle relative to a z-direction where the z direction is defined as being an axis orthogonal to the upper plane of the enclosure.

[0119] In some examples, the signal processing for each loudspeaker may be a delay, a gain, and a filter, whose parameters have to be defined in function of the target directivity, directivity of the individual loudspeaker units and the mounting angles.

[0120] In some examples, the directivity of the loudspeaker assembly may change in function of frequency, e.g. for low frequencies (e.g. below 150 Hz), all loudspeaker units may have the same driving signal, so that low frequencies are reproduced by all loudspeakers in the loudspeaker assembly.

[0121] FIG. 2 shows an example loudspeaker assembly 1 that includes four loudspeakers L1, L2, L3, L4 mounted within a single loudspeaker assembly enclosure 12. For reasons discussed below, the loudspeaker may be referred to as providing a hyper directional loudspeaker enclosure.

[0122] The loudspeakers L1, L2, L3, L4 are arranged in a linear array, with each loudspeaker L1, L2, L3, L4 preferably being mounted within its own individual loudspeaker enclosure so that back radiation from each loudspeaker L1, L2, L3, L4 does not have a significant influence on other loudspeakers in the loudspeaker assembly 1.

[0123] As shown in FIG. 2, each loudspeaker L1, L2, L3, L4 has a respective principal radiating axis X1, X2, X3, X4 along which it produces sound.

[0124] As is also shown in FIG. 2, there is a first angular offset between the first and second principal radiating axes X1, X2, a second angular offset between the first and third principal radiating axes X1, X3, and a third angular offset between the first and fourth principal radiating axes X1, X4.

[0125] It can be seen from FIG. 2 that there is an angular offset between the principal axes of each pair of loudspeaker in the loudspeaker assembly that is at least a 30.

[0126] The distance between L1 and L4 is preferably no more than 50 cm.

[0127] Each loudspeaker L1, L2, L3, L4 is configured to receive a respective electrical signal E1, E2, E3, E4 from a control unit (not shown), based on an input signal representative of audio (not shown). The control unit may be a DSP, for example.

[0128] In this example, a first electrical signal E1 received by the first loudspeaker L1 is unfiltered, but the control unit is configured to filter second, third and fourth electrical signals E2, E3, E4 received (respectively) by the second, third and fourth loudspeakers L2, L3, L4 such that there is a first gain and phase difference between the first and second electrical signals E1, E2, a second gain and phase difference between the first and third electrical signals E1, E3, and a third gain and phase difference between the first and fourth electrical signals E1, E4.

[0129] FIG. 3 compares the operation of (a) the cardioid loudspeaker assembly 1001 of FIG. 1(a) with (b) the operation of the loudspeaker assembly 1 of FIG. 2.

[0130] As shown in FIG. 3(a), whilst direct sound produced by the loudspeakers in a cardioid loudspeaker assembly may cancel at a first listening position P1, the direct sound will in general not cancel in an adjacent listening position P2, at least not across a wide range of frequencies. Thus, only a listener positioned at the first listening position P1 will perceive sound produced by the cardioid loudspeaker assembly in a mainly reflective (indirect) way.

[0131] In contrast, FIG. 3(b) shows the loudspeaker assembly 1 of FIG. 2 which is preferably configured, e.g. according to the method described below, so that direct sound produced by the loudspeakers in the loudspeaker assembly cancel at first, second and third listening positions P1, P2, P3. Thus, a listener positioned at any of the first, second or third listening positions P1, P2, P3, or indeed between such positions, will perceive sound produced by the loudspeaker assembly 1 in a mainly reflective (indirect) way.

[0132] FIG. 4 shows an example method for configuring the loudspeaker assembly 1 of FIG. 2 to obtain the operation shown in FIG. 3(b).

[0133] Initial mounting angles of the loudspeakers L1, L2, L3, L4 may be chosen to provide a good starting point for obtaining cancellation of direct sound at each listening position, e.g. as shown in FIG. 2. The loudspeakers L1, L2, L3, L4 preferably have a directivity index (according to the above definition) that is at least 6 dB at a frequency of 3 kHz, preferably so that loudspeaker L4 can be deemed to have an insignificant effect at listening position P1 and so that loudspeaker L1 can be deemed to have an insignificant effect at listening position P3 (as described below).

[0134] In Step 1, a mounting angle is chosen for loudspeaker L1. Loudspeaker L4 may be mounted to have its principal radiating axis X4 symmetrically arranged in relation to the principal radiating axis X1 in relation to a plane of symmetry W, if stereophonic sound is wanted.

[0135] In Step 2, the direct sound produced by loudspeaker L1 at listening position P1 is measured.

[0136] In Step 3, the direct sound produced by loudspeakers L2 and L3 at listening position P1 is measured, and a respective filter F2, F3 is defined for each of loudspeakers L2 and L3 so that the phase and amplitude of the direct sound produced by loudspeaker L1 and filtered loudspeakers L2, L3 at listening position P1 is cancelled in accordance with a predetermined cancelling condition (that requires the sound pressure level of direct sound produced by loudspeakers L1, L2, L3 at listening position P1 over 200 kHz-3 kHz to be at least 12 dB lower than the sound pressure level of direct sound produced by loudspeaker L1 at listening position P1). The effect of loudspeaker L4 at listening position P1 is ignored, since the angle of its principal radiating axis X4, its directivity index, and the subsequent filtering of this loudspeaker (see Step 5) mean that the effect of direct sound produced by loudspeaker L4 at listening position P1 is deemed to be insignificant.

[0137] In Step 4, the direct sound produced by loudspeaker L1 and the direct sound produced by filtered loudspeakers L2 and L3 is measured at listening position P2 to determine whether the direct sound produced by loudspeakers L1, L2, L3 at listening position P2 is cancelled in accordance with the predetermined cancelling condition (that requires the sound pressure level of direct sound produced by loudspeaker L1, L2, L3 at listening position P2 over 200 kHz-3 kHz to be at least 12 dB lower than the sound pressure level of direct sound produced by loudspeaker L1 at listening position P2).

[0138] If yes, the method proceeds to Step 5.

[0139] If no, then the mounting angle of loudspeakers L2 and L3 is adjusted (preferably with these loudspeakers having principal radiating axes that are symmetrical in relation to the plane of symmetry W) and the method returns to Step 3 until at Step 4 the direct sound produced by loudspeaker L1 and filtered loudspeakers L2 and L3 at listening position P2 is cancelled in accordance with the predetermined cancelling condition.

[0140] In Step 5, the direct sound produced by filtered loudspeakers L2 and L3 at listening position P3 is measured, and a filter F4 is defined for loudspeaker L4 so that the phase and amplitude of the filtered direct sound produced by loudspeakers L2, L3, L4 at listening position P3 is cancelled in accordance with the predetermined cancelling condition (that requires the sound pressure level of direct sound produced by loudspeakers L2, L3, L4 at listening position P3 over 200 kHz-3 kHz to be at least 12 dB lower than the sound pressure level of direct sound produced by loudspeakers L2, L3 at listening position P3). The effect of loudspeaker L1 at listening position P3 is ignored, since the angle of its principal radiating axis and its directivity index mean that the effect of direct sound produced by loudspeaker L1 at listening position P3 is deemed to be insignificant.

[0141] In Step 6, the direct sound produced by loudspeaker L1 and the filtered direct sound produced by loudspeakers L2, L3, L4 at listening position P2 is measured to determine whether the direct sound produced by loudspeakers L1, L2, L3, L4 at listening position P2 is cancelled in accordance with the predetermined cancelling condition (that requires the sound pressure level of direct sound produced by loudspeaker L1-L4 at listening position P2 over 200 kHz-3 kHz to be at least 12 dB lower than the sound pressure level of direct sound produced by loudspeaker L1 at listening position P2).

[0142] In the above method, direct sound is preferably measured in anechoic conditions, to avoid the influence of reflections.

[0143] FIG. 5 is a schematic diagram that provides a simplified visualisation of the cancellation that occurs at listening positions P1-P3 when filtering derived according to the method of FIG. 4 is applied to electrical signals E1-E4 received by loudspeakers L1-L4 from the loudspeaker assembly of FIG. 2.

[0144] Each chart in FIG. 5 shows sound pressure level (SPL) against frequency (f), with L1 being used as a reference (0 dB).

[0145] Only amplitude is depicted in FIG. 5. The effect of phase differences caused by applying filters is to cause the cancellation shown by dotted lines in FIG. 5(d)-(f).

[0146] In FIG. 5(a)-(c), the sound pressure level at listening positions P1-P3 is shown when no filtering is applied to the electrical signals received by loudspeakers L1-L4. The different amplitude characteristics of the different loudspeakers shown in these figures is therefore caused solely by the mounting angle and directivity indices.

[0147] In FIG. 5(d)-(f), the sound pressure level at listening positions L1-L3 is shown when the filtering derived according to the method of FIG. 4 is applied to the electrical signals received by loudspeakers L1-L4 (note: according to the method of FIG. 4, no filtering is applied to loudspeaker L1). For the purpose of this figure, direct sound produced by a filtered loudspeaker is represented as L+F (e.g. so direct sound produced by L2 is represented as L2+F2).

[0148] As described above, the filtering, directivity index and mounting angle of the loudspeakers L1-L4 is chosen so as to achieve cancelling of direct sound at listening positions P1-P3.

[0149] Although there is some residual sound at listening positions P1-P3, the residual sound pressure level is adequately low, and the cancellation of direct sound at these positions has the effect of increasing the proportion of sound received at those positions indirectly from reflections of the audio signals off walls at the periphery of the enclosed space. Such reflections can acts as virtual sound sources, thereby improving the listening experience of audience member(s).

[0150] In more detail, at listening position P1 (see FIGS. 5(a) and 5(d)) the sound of loudspeaker L1 is cancelled by the direct sound produced by filtered loudspeakers L2, L3. The direct sound produced by filtered loudspeaker L4 at listening position P1 is adequately low, and doesn't contribute significantly to the observation at position P1. The directivity index of the loudspeakers, the mounting angle and the electrical filtering are chosen as described above, so that cancellation of direct sound occurs at P1.

[0151] At listening position P2 (see FIGS. 5(b) and 5(e)), filtered loudspeaker L2 is producing more direct sound at listening position P2 than at listening position P1, while loudspeaker L3 is producing less direct sound at listening position P2 than at listening position P1. Careful choice of mounting angle and directivity of the speakers as described according to the iterative process described above has the effect of direct sound from filtered loudspeakers L2, L3 cancelling direct sound produced by loudspeaker L1 at listening position P2, whilst maintaining the cancelling of direct sound produced by loudspeaker L1 at listening position P1. Direct sound produced by filtered loudspeaker L4 is deemed adequately low to be ignored at listening positions P1 and P2 (although the direct sound produced by filtered loudspeaker L4 is later taken into account at listening position P2, see Step 6 in FIG. 4).

[0152] At listening position P3 (see FIGS. 5(c) and 5(e)), direct sound produced by filtered loudspeaker L2 is dominant over direct sound produced by filtered loudspeaker L3 and is now cancelled by direct sound produced by filtered loudspeaker L4. This is possible by careful adjustment of filtering, mounting angle and directivity, as described previously.

[0153] FIG. 6 illustrates the similarity in effect on the sound pressure level of direct sound produced by a loudspeaker at a listening position caused by either (i) increasing the angle between the principal radiating axis of the loudspeaker relative to the position of the loudspeaker; or (ii) filtering the electrical signal received by the loudspeaker to cancel the direct sound produced by another loudspeaker in the same loudspeaker array.

[0154] In FIG. 6, filter 1 is a filter configured to cancel direct sound from L1 at sound at P3 and filter 2 is a filter configured to cancel sound at P2. Hence, the response curve of the direct sound produced by L1 at P1 when filter 1 is applied is the substantially same as the unfiltered (straight) direct sound produced by L1 at P3, and the response curve of the direct sound produced by L1 at P1 when filter 2 is applied is the substantially same as the unfiltered direct sound produced by L1 at P2.

[0155] This figure can help to explain the relationship between mounting angle and electrical filtering to create the desired radiation characteristics of each loudspeaker at the target positions, and also explains, for example, why the direct sound produced by loudspeaker L4 will have less of an effect at listening position P2 than the direct sound produced by loudspeaker L1.

[0156] When used in this specification and claims, the terms comprises and comprising, including and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the possibility of other features, steps or integers being present.

[0157] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0158] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0159] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0160] All references referred to above are hereby incorporated by reference.