The invention relates to loudspeakers suitable for home entertainment or professional sound reproduction applications. More specifically, it relates to a device including an array of electro-acoustic transducers capable of receiving a multi-channel audio input signal and producing independently steerable and focusable beams of audible sound.
Digital phased-array loudspeakers (or more correctly, Digital Delay Array Loudspeakers), hereinafter DDALs, are known in the art (for example, international Applications published as WO01/23104 and WO02/078388.) These patent applications teach how to use DDALs to produce full surround sound, in for example its common 5.1 channel form, using just one DDAL, and in this manner replacing a multitude of separate loudspeakers, dispersed around a listening room or space, and also dispensing with all the necessary connecting wires required for conventional multiple-discrete-loudspeaker surround sound systems.
The key to successful operation elaborated in these documents is twofold: first, producing multiple, simultaneous, independently steered, independently delayed beams of sound each containing independent acoustic signals, from one and the same DDAL; and second, using features of the listening space including walls, floors ceilings and possibly furniture and even deliberately positioned reflectors, to guide these multiple separate beams of independent sound towards the listening area from several different directions, so that the listener hears sound coming from a host of directions (because it really is), and thus experiences the full effects of surround sound.
The DDALs known in the art are area extensive, that is they fill a region of 2-D space. It is described in the prior art to cover a DDAL transducer array with an acoustically transparent optically reflective or diffusive screen, for the presentation of front-projected images onto the surface of the DDAL, thus combining (surround) sound generation and visual display into one compact unit. However, it has not been previously possible to so compactly combine DDALs with other conventional visual displays (i.e. non-front-projection) because the presence of the DDAL would obscure or otherwise limit the visibility of the visual display. In practice, DDALs have been used next to (e.g. above, below or beside), visual display screens resulting in bigger and less practical systems than is desirable. Additionally, for the all-important speech centre channel, there is a significant offset between the acoustic centre of the DDAL and the visual centre of the display, and this can be disconcerting to listeners, especially when close to the screen.
One aim of the present invention is to provide an audio-visual system capable of surround sound that is more compact, while maintaining good sound quality.
In the present invention, a practical effect is achieved somewhat similar to that produced by the abovementioned DDALs, using in some cases simpler physical hardware, which is therefore capable of manufacture at lower cost and with less complexity. Furthermore, there are practical advantages in the designs and methods of the present invention, which make the integration of a practical and useful DDAL into and around a conventional video display device possible, eliminating the requirement for an additional piece of equipment, adjacent to or separate from the video display itself.
A problem arises when a set of transducers in a non-contiguous group is used to direct sound beams in a direction spanning the non-contiguous part (i.e. the “hole” separating distant transducers of the same group).
Experiments and analysis of DDALs with substantial “holes” in them show that such holes in the array produce “alias” beam. These alias beams have similar amplitude to the intended beam and radiate in unintended directions. This problem of alias beams arises when the hole, that is, the area within the array devoid of transducers, has one or both dimensions (horizontal or vertical) greater than half a wavelength of sound at a given frequency. For example, when one of the dimensions of the hole is of the order of half a meter (a typical dimension for a television screen for example), the frequency above which alias beams occur is of the order of 1300 Hz, which is well within the speech band.
Due to the problem of alias beams, it has heretofore not been thought possible to provide adequate beam steering using a DDAL that is not contiguous and area extensive.
Thus it is one of the aims of the present invention to minimise or avoid production of unwanted alias beams despite the transducer array as a whole containing a very substantial hole or gap.
By partitioning the transducers into groups and using each group as a separate DDAL for a specific input signal (channel), such aliases can be avoided. One or more groups (for one or more respective channels) may comprise all the transducers of the array, but it is an important aspect of the invention that at least one group comprises transducers from part of the array only. Preferably, such a partial group comprises contiguous transducers only; that is, each transducer is adjacent to one or more other transducers in the group and there are no significant gaps in the group. More preferably, the group does not surround the ‘hole’, that is, it comprises transducers from one side of the hole but not transducers from the opposite side of the hole.
An example of transducer grouping to avoid alias beams is as follows. A digital loudspeaker for reproduction of 5-channel surround sound comprises transducers arranged along the left edge, the bottom edge and the right edge of a display screen. The centre channel is reproduced by all the transducers. The right channel is reproduced by a partial group comprising the transducers to the right of the screen, while the left channel is reproduced by the partial group comprising the transducers to the left of the screen. The Rear Right and Rear Left channels are reproduced by groups comprising transducers at the bottom edge of the screen and optionally some or all of the transducers on the respective right and left sides. Further details of this and other arrangements are given below.
The present invention provides a loudspeaker comprising:
Preferably, the groups of transducers are each contiguous. This, however, depends on the beam steering ability that is required and groups can be non-contiguous in a particular direction if beam steering ability in that direction is not necessary. For example, if beam steering in a left-right direction only is required, the group need only be contiguous in the left-right direction and can be non-contiguous in the up-down direction.
One of the groups may comprise all of the transducers in the array. Some of these transducers are then shared with other groups and there is no limitation on groups overlapping or being otherwise related to one another. The first and second group of transducers must, however, be different, that is to say one of the groups must contain at least one transducer that is not contained in the other group.
In a preferred aspect of the invention the region is a 2D region and the set of transducers are disposed about the region so as to partially fill an extent of more than 2/7th (˜0.29) of the perimeter of the region.
In a preferred aspect of the invention, the region is nominally planar of rectangular shape, and in other preferred aspects region shapes such as planar square, circular or elliptical, and non-planar polygons, spheres and ellipsoids are used.
In another preferred aspect of the invention, a nominally rectangular visual display screen [VDS] (e.g. a CRT, plasma panel display, LCD display, or one of the more recent display developments such as LEP, field emission display, or even static or quasi-static visual display devices or posters as used e.g. in advertising or other information display devices) forms the region about which the set of electroacoustic transducers are located, close to or adjacent to its outer edge, so as not to overlap the visually-important portion of the visual display device, but possibly overlapping its other (non-visually important) structure. The array of electroacoustic transducers is used wholly, or partially, in one or more discrete groups, each group preferably forming a DDAL, so as to produce in total one or more different and simultaneous sound fields, each representative of different audio programmes related to the visual presentation on the VDS, or instead a totally unrelated set of audio programme material such as for example the soundtrack on a CD or DVD music disk, or e.g. an advertising message, or sounds and sound effects for a video game. The invention is not limited to such an array surrounding a rectangular VDS, as other shapes of VDS (or displayable portion of VDS screen), such as e.g. circular or elliptical, can equally be accommodated within the invention.
In a preferred form of the invention, all or some of the set of electroacoustic transducers to the left of the centre of the region, e.g. a VDS screen, are used to form a DDAL to reproduce that part of the audio programme normally assigned to the left channel of a surround sound system (the L channel), whilst some or all of the set of electroacoustic transducers to the right of the centre of the region, e.g. a VDS screen, are used to form a DDAL to reproduce that part of the audio programme normally assigned to the right channel of a surround sound system (the R channel). Some or all of the whole set of electroacoustic transducers are used to form a DDAL to reproduce that part of the audio programme normally assigned to the centre channel of a surround sound system (the C channel). Some or all of the whole set of electroacoustic transducers are used to form a DDAL to reproduce that part of the audio programme normally assigned to the left rear (effects) channel of a surround sound system (the LR channel), and some or all of the whole set of electroacoustic transducers are used to form a DDAL to reproduce that part of the audio programme normally assigned to the right rear (effects) channel of a surround sound system (the RR channel). Additional audio channels (such as exist in for example DTS 7.1channel sound, can be similarly assigned to a DDAL composed of some or all of the whole set of transducers and the invention is not limited to 2, 3, 4, 5, 6, 7, or other numbers of discrete channels of sound.
In another preferred form of the present invention, some of these DDALs will be composed of an identical group of transducers as other DDALs in the array. For example, in another variant, the whole set of transducers are used to form a DDAL used to reproduce both the LR, the RR and the C channels. In this case one, two or three separate sound beams may be formed by this particular DDAL group within the array of DDAL transducers comprising the whole device.
In the simplest case just one beam reproduces all three of these channels. In an enhanced version of this form, this particular DDAL uses one sound beam directed directly at the listening position to project the C channel audio, and a second sound beam directed over the heads of the listeners (in the listening position) which then bounces off for example the ceiling and rear wall(s) of the listening room, to return towards the listening position from behind the listeners, this beam carrying a mixture of the LR and RR audio channels. In a third preferred form of this aspect of the invention, this DDAL directs the C channel beam as before, and two additional sound beams (instead of one additional) are used to direct the LR channel over and to the left of the listening position, and the RR channel over and to the right of the listening position, so that the rear channels are heard by the listeners to come not just from behind the listeners, but also from behind and to the left and right respectively.
In another aspect of the invention the region-surrounding DDALs previously described are augmented by one or more woofers (loudspeakers especially good at the reproduction of low frequencies, say from 300 Hz downwards, or from 200 Hz downwards, to at least 100 Hz, or to 50 Hz or even to 20 Hz). These woofers may be disposed about the region (e.g. a VDS) in any way compatible with the desired disposition of the transducers forming the DDALs, and not obscuring the region, in which cases they are used to reproduce the low frequencies directly without any attempt at forming these low frequencies into steered sound beams, or alternatively, the woofers may instead be part of one or more of the totality of DDALs and incorporated into the digital delay sound beam-forming array(s) so as to extend downwards the frequency at which the apparatus is able to usefully direct and steer sound beams. In either case the low frequency sound signals applied to the woofers may be delayed to ensure that the sounds emitted by them reach the listeners in time synchronisation with the higher frequencies from the rest of the DDAL(s) which travel by potentially much longer acoustic paths involving one or more bounces.
In one variant of the invention, the transducers are disposed right around the periphery of the region, with substantially uniform a real density (but not necessarily with uniform or constant spacing) and substantially uniformly spaced from the edge of the region, and this is particularly preferred when the region is rectangular, and more particularly preferred when the region is a rectangular VDS. A first simplified version of this variant eliminates some or all of the transducers positioned along the top, or bottom, or both, of the region, while a second simplified version of these preferred aspects eliminates some or all of the transducers positioned along the left side, or right side, or both, of the region, again especially preferred when the region is a VDS. One preferred variant of these just-described forms has transducers of uniform size uniformly spaced around the region.
In another preferred aspect of the invention, any or all of the previously described DDAL forms when disposed around a VDS, may be augmented by one or more optically transparent loudspeaker forms covering some or all of the visually important areas of the VDS (i.e. exactly those areas of the VDS not otherwise populated by DDAL transducers), and these transparent loudspeaker forms may be either incorporated into one or more of the DDAL groups or instead used separately and independently, for example to reproduce low frequencies, or perhaps to reproduce centre-channel information in a surround sound system built around a VDS.
In all of the above aspects of the invention it is intended that the transducers forming the DDAL groups surrounding or partially surrounding the region devoid of transducers may be of any size at all consistent with the area aspects already defined, and consistent with the acoustic requirements of the beam forming DDAL as described in the prior art. Where the transducers are relatively small compared to the greatest linear dimension of the whole array of transducers, they may form concentric (not necessarily circular) rings around the region, or be otherwise disposed around the region so that some transducers are naturally closer to the edge of the region than others, and so that others are closer to other transducers than they are to the edge of the region. That is to say, there is no restriction to the transducers being in only one line (straight or curved) around the region, nor that they should necessarily as a group, enclose the region.
In another preferred aspect of the invention, a subset of the transducers forming one of the DDAL groups are arranged in multiple substantially parallel rows with substantially similar spacing within each and every row, although the row-to-row spacing may differ from this intra-row spacing, and where the substantially parallel rows are substantially parallel to at least one significant portion of an edge of the region (e.g. where the region is substantially rectangular, the transducer rows may be parallel to at least one edge of the region). In such a case, and where it is not necessary to be able to electronically steer this DDAL beam in a plane normal to the parallel rows of transducers, the complexity of the DDAL drive and control electronics may be simplified by driving adjacent transducers in adjacent parallel rows (i.e. transducers in the same ‘column’) with signals of the same identical delay (rather than different delays), whilst retaining the ability to vary the signal delay from transducer to transducer within each row. Such an arrangement provides one-dimensional (1D) beam forming and electronic steering in a plane parallel to the parallel rows of transducers. If the separation between the outer edges of transducers in the first and last rows is substantial, and specifically comparable to or greater than a wavelength of sound in air at a frequency of interest for directing the sound, then the parallel row array will be substantially directional if not electronically steerable in the plane orthogonal to the parallel rows of transducers, and in this case it may be advantageous to tilt the plane of the rows of transducers relative to the region so as to orientate the directional beam in a preferred direction relative to the region. A similar effect may be achieved by using just one (or a few) row(s) of transducers with high aspect ratio (e.g. elliptical transducers) with their short axis parallel to the row direction.
In a preferred embodiment of the invention, a digital loudspeaker comprises an array of electoacoustic transducers, used in two or more non-identical groups, each group forming a DDAL, so as to produce two or more different and simultaneous sound fields, each representative of different audio signals.
In a further embodiment of the invention, a closed region of a planar or non-planar surface has a set of more than four, preferably more than 8, electroacoustic transducers positioned close to or adjacent to its outer edge, so as not to overlap the region and not to substantially overlap each other, the surface area of the region being substantially greater than the acoustic-radiating surface area of any of the transducers and in a preferred aspect the region-surface-area being greater than half of the total acoustic-radiating surface area of all of the transducers, wherein the set of electroacoustic transducers is used wholly, or partially, in one or more discrete groups, each group forming a DDAL, so as to produce in total two or more different and simultaneous sound fields, each representative of different audio signals.
As already mentioned, one application for the invention is to provide surround sound with less cabling and no need for satellite speakers. Another application is to output two beams of audio signals, each signal representing a completely different programme, for example a television programme audio signal. If the beams are steered in different directions two users standing or sitting in different positions can receive different audio programmes. This can be combined with a split screen VDS to allow two users to watch different TV channels, with full sound, without disturbing each other.
This can be extended to 3, 4 or more separate programmes being shown simultaneously on the same device, the audio channel for each programme being directed towards a user in a different direction, with an optional corresponding video channel being shown on the VDS in split-screen mode.
The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:—
In
It will be noted that groups 72 and 73 each overlap somewhat with group 74. In this embodiment, three transducers of group 74 are also used in group 73 and three different transducers of group 74 are also used in group 72. There is no restriction on the amount of overlapping that can be allowed between groups.
The loudspeaker of the present invention is preferably provided as an integral unit having a casing in which each of the transducers of the array are disposed. When the region devoid of transducers comprises a screen, the screen is preferably integrated with the speaker casing so as to provide a single consumer unit.
Number | Date | Country | Kind |
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0321676.9 | Sep 2003 | GB | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/GB04/03980 | 9/16/2004 | WO | 12/27/2006 |