A Sound System for Emulating Spatial Sound

Abstract

A sound system 100 comprising a receiver (Fig.5 110) to receive inputs representative of a virtual sound source to be output in such a manner as to be perceived at a respective physical position relative to an intended listener. The system further comprises a transducer or loudspeaker body 110 with side-firing outputs 103 / 104 which are placed to direct sound in opposite directions perpendicular to the listener along a line at least partially in antiphase. A further loudspeaker 102 directs sound either non-parallel or otherwise displaced from the side-firing line. A gain unit is present to provide gain to the side or further speakers, resulting in a modulated signal wherein the side and further gain differs, with a control unit capable of driving the respective speakers from the modulated input. The system may comprise a dipole loudspeaker or a pair of opposed speakers in antiphase.

Description

Technical Field of the Invention The present invention relates to a sound system for emulating spatial sound. Background to the Invention Current top of the line spatial sound systems can have a variety of different loudspeaker setups, the position of each loudspeaker within a room or other area carefully chosen based on the system. One popular setup is shown in figure 1, a 7.1.4 setup 1. This comprises seven main loudspeakers: a centre loudspeaker 2, right loudspeaker 3, right surround loudspeaker 4, rear light loudspeaker 5, rear left loudspeaker 6, left surround loudspeaker 7, a left loudspeaker 8, one subwoofer (not shown) and four high loudspeakers: a high right 9, a high rear right 10, a high rear left 11, and a high left 12. In use each loudspeaker is typically driven with a separate dedicated input. The main loudspeakers are traditional loudspeakers approximately level with a listener’s ears in use. The main loudspeakers are placed on the circumference of an outer circle, and a listener will ideally be at the centre of the circle when the spatial sound system is in use. The centre loudspeaker 2 will be at 0° angular position on the outer circle, this being the position the listener will ideally face when the system is in use. The other main loudspeakers are placed as follows, moving clockwise around the outer circle when viewed from above: the right loudspeaker 3 at 30°, the right surround loudspeaker 4 at 100°, the rear right loudspeaker 5 at 135°, the rear left loudspeaker 6 at 225°, the left surround loudspeaker 7 at 260°, and the left loudspeaker 8 at 330°. All the main loudspeakers are placed generally in the same, lower, horizontal plane. The high loudspeakers are overhead loudspeakers which direct their output such that it comes, or appears to come, from above the user. The high loudspeakers are placed on the circumference of an inner circle, with a smaller diameter but the same centre as the outer circle. The high loudspeakers are placed as follows, again working clockwise from above: the high right loudspeaker 9 at 45°, the high rear right loudspeaker 10 at 135°, the high rear left loudspeaker 11 at 225°, and the high left loudspeaker 12 at 315°. The high loudspeakers can either be placed in a plane above the user (and the lower horizontal plane) and direct sound towards where the user would ideally be positioned when the system is in use (at the listener position), or on the same level as the main loudspeakers and direct their sound upwards. This setup provides an immersive experience for the listener and is one of several recommended setups to listen to spatial audio systems such as Dolby Atmos™. However, such spatial sound systems are difficult and expensive to set up, given the number of loudspeakers involved, and the specific positions on which they must be located. Further to this, in some situations (such as, for example, within a car) such a spatial sound system cannot be easily set up. Audio systems can adjust for fewer loudspeakers and / or loudspeakers in compromised positions (and can even work for headphones) but this is not ideal, and the user experience is impaired in the adjustment. Embodiments of the present invention seek to overcome these or other disadvantages. Summary of the Invention According to an aspect of the present invention there is provided a sound system for reproducing spatial sound in a space, the sound system comprising: a receiving unit operable to receive one or more inputs, the or each input representing a virtual sound source intended to be at a respective position within the space relative to an intended listening position; a side loudspeaker unit, the side loudspeaker unit being operable, in use, to output a sound signal from one side directed along a first line in one direction and the same sound signal from an opposite side directed along the first line in the opposite direction, the two outputs being in antiphase over at least part of their frequency range, and the first line extending substantially perpendicularly to a second line extending from the side loudspeaker to the listening position; at least one further loudspeaker being operable, in use, to direct sound along a third line, the third line extending in a direction which is non-parallel to, or is displaced from, the first line; a gain application unit operable to apply a respective side gain to the, or each, input to result in a modulated side input and a respective further gain to the, or each, same input to result in a modulated further input, where the absolute value of the respective side gain is different to the absolute value of the respective further gain for the or each input; and a control unit operable to drive the side loudspeaker unit with a side output being the, or sum of each, modulated side input, and the further loudspeaker with a further output being the, or sum of each, modulated further input. According to another aspect of the present invention there is provided a method for reproducing spatial sound in a space, the method comprising the steps of: receiving one or more inputs, the or each input representing a virtual sound source intended to be at a respective position within the space relative to an intended listening position; positioning a side loudspeaker unit to output a sound signal from one side directed along a first line in one direction and the same sound signal from an opposite side directed along the first line in the opposite direction, the two outputs being in antiphase over at least part of their frequency range, and the first line extending substantially perpendicularly to a second line extending from the side loudspeaker unit to the listening position; positioning at least one further loudspeaker to direct sound along a third line, the third line extending in a direction which is non-parallel to, or displaced from, the first line; applying a respective side gain to the, or each, input to produce a modulated side input and a respective further gain to the, or each, same input to produce a respective modulated further input, the absolute value of the respective side gain being different to the absolute value of the respective further gain; and driving the side loudspeaker unit with a side output being the, or sum of each, modulated side input, and the further loudspeaker with a further output being the, or sum of each, further modulated input. The side and further outputs created and outputted in this way result in the audio output of the further loudspeaker being steered to the position of the virtual sound source, and so for it to appear that audio is coming from this position to a listener in the listening position. The system can thereby emulate a spatial sound system with fewer and / or differently positioned loudspeaker units than intended. This makes the system easier and cheaper to implement. The absolute values of the respective side and further gains may differ by a factor of 0.9 or less, and in some cases by factors of less than 0.7, 0.6 and 0.5. The side loudspeaker unit may be a single dipole loudspeaker. This may be positioned in a baffle or duct to reduce interference between sound generated by opposite sides of the loudspeaker. The baffle may be annular with an outside diameter of at least 30cm or 40cm. The side loudspeaker unit may comprise a pair of opposed loudspeakers connected in antiphase. They may be arranged in a dual driver shared volume arrangement or an independent driver arrangement. In either arrangement, the outside air-path distance (between the opposed speakers) may be between 25-90cm; 35-80cm or about 40cm. The, or one of the, further loudspeakers may be between the two side opposed loudspeakers. The opposed speakers of a side speaker unit may be out of phase with each other at least for frequencies between 200Hz and 4000Hz. There may be more than one side loudspeaker unit, each arranged to direct its output along a line extending substantially perpendicularly to a second line extending from the respective side loudspeaker unit to the listening position. Each side loudspeaker unit may direct its output along a different line. Where there is more than one side loudspeaker unit arranged to direct its output along a different line at least one further loudspeaker may be provided for each side loudspeaker unit, the or each further loudspeaker being arranged to direct its output along a line extending in a direction which is non-parallel to, or displaced from, the line along which the side loudspeaker unit directs its output. The first line may be a tangent to a circle centred on the listening position. The circle may be in a horizontal plane, “the listening plane”. The third line may be a radius of the circle. The third line may be the second line. Alternatively, the third line may be parallel or substantially parallel to, but displaced from, the second line. The third line may extend towards the listening position. The third line may extend through the listening position. Where the first line is a tangent to a circle centred on the listening position the side loudspeaker unit and the further loudspeaker may be located in the plane of the circle, and may be on the circle. Any additional side loudspeaker units and further loudspeakers may also be located on the circle. In some arrangements all loudspeakers of the sound system are located on the circle. In others one or more loudspeakers are displaced from the circle either within or displaced from the plane of the circle. In one arrangement the side loudspeaker unit is in the plane of the circle and may be on the circle, and the further loudspeaker is displaced from the plane of the circle. There may be at least two further loudspeakers. One further loudspeaker may be a main loudspeaker arranged to direct sound so that it will be perceived at the listening position to come from within the listening plane. The main loudspeaker may face the listening position and may be at least partially in the listening plane. There may be two or more main loudspeakers. They may face the same direction and be driven in phase. The other further loudspeaker may be a height loudspeaker arranged to direct sound so that it will be perceived at the listening position to come from a location above the perceived source of sound from the main loudspeaker, or from above the listening plane. The height loudspeaker may lie in and arranged to direct its output upwards from the listening plane. Or, it may be displaced above and directed towards the listening plane. There may be two or more height loudspeakers. They may face the same direction and be driven in phase. The or each height loudspeaker may be operable to output audio predominately in a direction with a substantial component in the vertical direction. The or each height loudspeaker may be operable to output audio predominately in the vertical direction. The or each height loudspeaker may be arranged to output audio in an upwards direction. The or each height loudspeaker may be arranged to output audio in a downwards direction. The side loudspeaker unit and further loudspeaker may disposed together in a loudspeaker body with the or each speaker of the side loudspeaker unit and the further loudspeaker directed in mutually perpendicular directions. The further loudspeaker may be a main loudspeaker or a height loudspeaker. Where there are a main loudspeaker and a height loudspeaker both may be disposed in the loudspeaker body and directed in substantially perpendicular directions to each other and the side loudspeaker unit. The loudspeaker body may be elongate and may be cuboidal. In this case a pair of side loudspeakers may be disposed in an opposed fashion at respective ends of the body, or a single side loudspeaker disposed mid-way along the long axis of the body. A main loudspeaker may be disposed on a long side of the body, to direct its output substantially perpendicularly to that of the side loudspeaker or loudspeakers. A height loudspeaker or pair of height loudspeakers connect in phase may be disposed on another long side of the body to direct their output substantially perpendicularly to both the side and main loudspeakers. The sound system may comprise two or more loudspeaker bodies. Each body may be positioned on a circle centred on the listening position with the further, or main, loudspeaker directed towards the listening position, and the side loudspeaker unit arranged to direct its output along a tangent to the circle. In an embodiment a loudspeaker body comprising a side loudspeaker unit, main loudspeaker and height loudspeaker is placed at the 0° position on a circle centred on the intended listening position, being the position the listener is intended to face when the sound system is in use. In other embodiments one or more additional loudspeaker bodies are placed at some or all of the following positions on the circumference of the circle (positive angles representing a rightward (clockwise from above) displacement from the 0° position, and negative angles a leftward displacement): ±30°, ±135° and 180°. Many other arrangements using multiple loudspeaker bodies are possible and those bodies may be arranged symmetrically or asymmetrically on the circumference of the circle. Generally, for good sound reproduction, two or three loudspeaker units are sufficient. Such a sound system could comprise one or more additional further loudspeakers separate from the loudspeaker body or bodies. In embodiments single loudspeakers are used in addition to a side loudspeaker unit placed at the 0° position (and which may also comprise a main and / or height loudspeaker). A respective main loudspeaker may be positioned at ±30° and or ±135° positions. A height loudspeaker may be positioned at the 0° and or 180° positions. The side gain applied to an input may be dependent on the relative positions of the virtual sound source represented by the input, and the (or a particular) side loudspeaker unit, to the listening position. The side gain may be a function of the angular displacement in, or projected on to, a (typically horizontal) plane, between the positions of the virtual sound source represented by the input and the side loudspeaker unit to be driven, measured from the listening position. The side gain may be zero where the angular displacement is zero (i.e. the virtual sound source and driven loudspeaker are in the same angular position), an increasing positive side gain for angular displacement in a first direction and an increasing negative side gain for angular displacement in the opposite direction, reaching a maximum positive value in the first direction and a maximum negative value in the second direction before reducing to zero side gain with further angular displacement in the respective direction. The maximum value may be 100% gain, or a lower value. 100% positive gain is where the input is unchanged. 0% gain is where the volume of the input is reduced to zero. Intermediate gain values may represent a linear decrease in volume. For negative gains the polarity of the input is reversed. In one embodiment the side gain comprises or consists of a component derived from the following function: For angular displacements x = - 90° to 0 0 Side gain = (1-m) x |sin(x)|* Where m is a constant less than 1, and ¢=---- 2 For angular displacements x = 0° to +900 gain = (m-1) x |sin(x)|* For angular displacement x >±90° gain = 1-m The value for $ above is found to provide favourable acoustic properties but in other embodiments it may have a different value in the range 0.5 to 2.5 or the range I to 2. In another embodiment the change of side gain with displacement from zero gain is linear until it reaches 100% or -100% where it remains substantially constant for further displacement before returning to zero in a linear fashion. This forms a trapezoidal gain curve. The trapezoid may be isosceles. In another embodiment the change of the side gain as displacement increases in the first side direction forms an approximately bell-shaped curve, and an inverted bellshaped curve as displacement increases in the opposite direction. In this other embodiment the gain may rise or fall logarithmically from zero gain, at zero displacement, as displacement increases, to a plateau and then fall or rise logarithmically back to zero gain as the displacement in the respective side direction increases further. The logarithmic rises and falls may miiTor each other. The further gain applied to an input may be dependent on the relative positions of the virtual sound source represented by the input and the further loudspeaker to the listening position. The further gain may be a function of the angular displacement in, or projected onto, a plane, between the positions of the virtual sound source represented by the input and the further loudspeaker unit, measured from the listening position. The plane may be horizontal. The further gain may be 100% where the displacement is zero (i.e. the virtual sound source and driven loudspeaker are in the same angular position), reducing with (positive or negative) angular displacement at a first rate up to a predetermined angular displacement beyond which it is zero, or a constant non zero minimum value, or reduces at a second rate, greater than the first rate, and reaches to zero at a further predetermined angular displacement. In one embodiment the further gain comprises or consists of a component derived from the following function: For angular displacements x = 0 to ± 90° Further gain = 1 - (1-m) x |sin(x)| $ Where $ and m are the constants used in the function above for determining side gain. For angular displacement x >±90° Further gain = m As for the side gain in other embodiments $ may have a different value in the range 0.5 to 2.5 or the range 1 to 2. For any given angular displacement the side gain plus the further gain may always equal 1. In another embodiment the change of the further gain with respect to increasing displacement in opposite directions may be an approximately bell-shaped curve. The maximum further gain at zero displacement may be 100% positive gain. In another embodiment the further gain falls linearly or substantially linearly at the first rate from the maximum with increasing displacement in either direction. At a predetermined displacement in either direction the gain may immediately fall to zero (i.e. a sudden cut-off). Or it may fall at the second rate either linearly or logarithmically with further increasing displacement, ultimately to zero gain where the virtual sound source is considered too distant to reproduce from this audio input. The linear- and / or logarithmic falls may mirror each other. The linear falls may mirror each other. The further gain may cut off or transition from the first rate to the second rate at a displacement of ±30-90° and typically at about ±60° displacement. The sound system may comprise at least two further loudspeakers, which may be a main loudspeaker and a height loudspeaker. In this case the further gains applied to the inputs to produce outputs for driving those loudspeakers are respective main and height gains. The respective gains are dependent on the relative positions of the virtual sound source represented by the input and the main and height loudspeakers to the listening position in a plane, typically a horizontal plane and usually the listening plane. In some embodiments the modified input obtained by applying the further gain, may be split to provide components for driving both main and height loudspeakers, the level of each component being dependent of the height of the virtual sound source to be reproduced relative to the listening plane and / or the heights of the main and height loudspeakers. The sound system may comprise a memory for storing gain values for use by the gain application unit. The memory may be an electronic memory. The sound system may comprise an input device to enable a user to select a set of gain values to be applied by the gain application unit from a range of stored sets of values. A method of use of the system may therefore involve selecting a first set of gain values and arranging loudspeakers or loudspeaker bodies of the system in a first corresponding arrangement, and selecting a second set of gain values and arranging loudspeakers or loudspeaker bodies of the system in a second corresponding arrangement. The sound system may comprise an input device to enable a user to enter one or more gain values for application by the gain application unit, which may be stored in the memory of the device. The sound system may comprise a gain determination unit operable to determine, and the method may comprise the step of determining, the or each side gain and the or each further gain to be applied to each input based on the position of the or each virtual sound source represented by the or each inputs and positions of the or each side loudspeaker unit and the or each further loudspeaker, and provide the determined gains to the gain application unit. Gain may be determined by reference to a look-up table or by applying a function to the difference in displacement between the position of the virtual source associated with an input and the loudspeaker driven by the input, after modulation by applying the gain. The gain determination unit may determine the position of the or each virtual sound source from the or each input. The sound system may comprise an input device to enable a user to input the positions of the or each side loudspeaker unit and the or each further loudspeaker. The sound system may comprise a filtering unit operable to filter the side output to frequencies in the range 200Hz to 7kHz, or any of the following ranges: 350Hz-7000Hz; 200Hz-4000Hz; 250Hz-4500Hz; 350Hz-4000Hz; 250Hz-4000Hz; 350Hz-4500Hz; 200Hz or above; 250Hz or above; 350Hz or above. The filtering unit may also be operable to limit, or reduce the sensitivity of, the or each further output in the frequency region to which the or each side output is restricted to maintain the overall acoustic balance of the audio. The sound system may comprise a delay unit operable to delay one or selected inputs in dependence on the distance of the virtual sound source represented by that input from the listening position. The sound system may, for example, be used to emulate a spatial sound system with a centre loudspeaker positioned at 0° on the circumference of a first circle centred on a listening position, a right loudspeaker positioned at 30°, a surround right loudspeaker at 100°, a rear right loudspeaker at 135° a rear left loudspeaker at -135°’ a surround left loudspeaker at -100° and a left loudspeaker at -30°. The spatial sound system could additionally comprise high right and left, and high rear right and left loudspeakers positioned ±45° and + 135° on the circumference of a second smaller circle also centred on the listening position, which may be spaced above the first circle. Detailed Description of the Invention In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic plan view of a conventional 7.1.4 spatial sound system; Figure 2 shows a loudspeaker placement for a sound system for emulating spatial sound; Figure 3 shows the operation of a main loudspeaker and height loudspeakers; Figure 4 shows the operation of a main loudspeaker and height loudspeakers in combination with side loudspeakers; Figure 5 shows an arrangement for driving loudspeakers to emulate spatial sound; Figure 6 shows a gain unit of a sound system for emulating spatial sound; Figure 7 is a graph of further and side gains versus displacement for the sound system for emulating spatial sound; Figure 8a is a graph of main gain and height gains versus height above the listening plane for the sound system for emulating spatial sound; Figure 8b is a graph showing gain modifying ratios applied to the inputs of adjacent loudspeaker bodies when a virtual sound source is located in a crossover zone between the two bodies; Figure 8c is a graph showing further and side gains for the two speaker bodies of the arrangement shown in figure 10; Figures 9-15 show respective second to eighth loudspeaker placements for a sound system for emulating spatial sound; Figure 16 is a loudspeaker body for a sound system for emulating spatial sound, emulating an object; Figure 17a is a graph of side gain versus displacement for a sound system for emulating spatial sound; Figure 17b is a graph of main and height gain versus displacement for a sound system for emulating spatial sound; Figure 18a is another graph of side gain versus displacement for a sound system for emulating spatial sound; Figure 18b is another graph of main and height gain versus displacement for a sound system for emulating spatial sound; Figure 19a is a front view of a side loudspeaker and baffle configuration; Figure 19b is a side section view of the loudspeaker and baffle configuration of figure 19a; Figure 20a is a front view of a side loudspeaker and tube configuration; Figure 20b is a side section view of the loudspeaker and tube configuration of figure 20a; Figure 21a is a front view of a side loudspeaker and duct configuration; Figure 21b is a side section view of the loudspeaker and duct configuration of figure 21a; Figure 22 is a gain matrix for the embodiment of figure 10 Figure 23 is a side section view of a pair of side loudspeakers; Figure 24 is a side section view of an alternative pair of side loudspeakers; and Figure 25 is a side section view of a second alternative pair of side loudspeakers. Figure 2 shows a loudspeaker arrangement for a sound system 100. The system comprises a loudspeaker body 101, shown as a schematic part cut-away front elevation. The loudspeaker body is of an elongate rectangular shape and houses a forward facing (as shown) further, in this case main, loudspeaker 102 in the centre of a front face. Two side loudspeakers are 103, 104 mounted in the opposed end faces of the housing, facing in opposite directions to each other (together forming one side loudspeaker unit) and connected to be driven by a single input arranged to drive the two loudspeakers in antiphase Two height loudspeakers are 105 mounted in the top face of the housing at respective symmetrical positions at opposite sides of the centre of the top face of the housing and connected to be driven by a single input arranged to drive the two loudspeakers in phase. The main, side and height loudspeakers face in mutually perpendicular directions. As used herein, a main loudspeaker is a loudspeaker which is arranged so that in use it outputs audio which, to a listener, will appear to come from within a horizontal plane in which an intended listening position is located “the listening plane”. Ideally that plane is located at about the level of a listener’s ears. Typically, a main loudspeaker will be in that plane and directed towards the listening position. A height loudspeaker is a loudspeaker which is arranged so that, in use, it outputs audio which, to a listener, will appear to come from above any audio output by a main loudspeaker of the same audio system. In use, the loudspeaker body is intended to be placed in front of an intended listening position with the main loudspeaker facing the listening position, and at a height over a surface, e.g. a floor of a room, which is approximately the height of the intended listener’s ears over the surface, or slightly above that height. In figure 2 the loudspeaker body 101 is shown on a notional circle. The intended listening position is the centre of the circle, with the listener facing the loudspeaker body. The illustrated position of the loudspeaker body on the circle, i.e. the position on the circle that the intended listener faces, is referred to as the 0° position. The main loudspeaker 102, in use, directs its audio output predominately towards the listening position. The first side loudspeaker 103 of the side loudspeaker unit is on the left end face of the body viewed from the intended listening position facing left away from the loudspeaker body and the second side loudspeaker 104 is on the right end face of the body facing right away from the loudspeaker body. In use the first side loudspeaker 103 directs its audio predominately to the left and the second side loudspeaker 104 directs its audio predominately to the right, each along the same horizontal axis, as viewed from the listening position. There is a gap within the loudspeaker body 101 between the two side loudspeakers 103, 104, called an outside air-path distance. The main loudspeaker 102 and the height loudspeakers 105 sit in this gap. The height loudspeakers 105 are on the top face of the body and, in use, direct audio predominately upwards perpendicular to the direction of outputs of the main loudspeaker 102 and the side loudspeakers 103, 104. Figures 3 a, 3b, 4a and 4b show how the loudspeaker arrangement of figure 2 can be used to emulate virtual sound sources (e.g. virtual loudspeakers) located in different positions relative to a listener at the listening position. In figure 3a the sound system 100 is used to emulate a virtual loudspeaker 106 which is approximately level with the listener’s ears, facing the listening position, from the same position around the circle as the loudspeaker body 101. In this case all the audio input intended for that virtual loudspeaker is output from the main loudspeaker 102 (and none from the side loudspeakers 103, 104 or the height loudspeakers 105). This successfully emulates the virtual loudspeaker 106, since the main loudspeaker 102 is directing audio in the same direction (and from the same position) as the virtual loudspeaker 106. In contrast, and as shown in figure 3b, when emulating a height virtual loudspeaker 107 at a position spaced above the loudspeaker body but at the same position around the circle, all the audio input intended for the height virtual loudspeaker 107 is output by the height loudspeakers 105 (and none by the main loudspeaker 102 or the side loudspeakers 103, 104). This results in the audio being directed upwards, towards the position of the virtual height loudspeakers 107. This successfully mimics the virtual height loudspeaker 107 at the listening position. Were the virtual loudspeaker positioned at a lower height, as shown at 107a, the audio intended to drive that virtual loudspeaker is output by both the main 102 and height 105 loudspeakers such that sound appears to come from the virtual loudspeaker 107a. Figures 4a and 4b show the situation for virtual loudspeakers 108, 109 located at different positions around the circle to the loudspeaker- body 101. As shown in figure 4a, to emulate a virtual loudspeaker 108 at the same height as the loudspeaker body but displaced around the circle from it, the audio intended for that virtual loudspeaker 108 is output by both the main loudspeaker 102 and the side loudspeakers. An audio signal in phase with that driving the main loudspeaker 103 drives the side loudspeaker 103 which faces towards the position of the virtual loudspeaker, in the example shown the left loudspeaker 103, with the opposite, right, loudspeaker 104 outputting the audio in antiphase, i.e. with reverse polarity to the left loudspeaker. The magnitude of the respective audio driving the main and side loudspeakers is adjusted based on the position of the virtual loudspeaker relative to the loudspeaker body by applying different gains to the loudspeaker inputs, as discussed below. The output of the side loudspeaker “steers” that of the main loudspeaker from the point of view of a listener at the listening position, such that it appears to come from the position of the virtual loudspeaker 108. As shown in figure 4b, to emulate a height virtual loudspeaker 109 at a position displaced around the circle from and spaced above the loudspeaker body, the audio intended for the loudspeaker 109 is emitted from the height loudspeakers 105 and the side loudspeaker 104 facing the position of the virtual loudspeaker 109, in this example, the right side loudspeaker 104 (with the left loudspeaker outputting the same output but in antiphase). Again, different gains are applied to the audio input driving the two loudspeakers based on the position of the virtual loudspeaker relative to the loudspeaker body. In this example the output of the side loudspeaker ‘steers’ that of the height loudspeaker such that, from the point of view of the listener, the audio is coming from the position of the virtual loudspeaker 109. The loudspeakers of the loudspeaker body may be driven with a sum of inputs intended to reproduce the output of multiple virtual loudspeakers or other sound sources at the same time, so as to simultaneously reproduce all of the virtual sound sources. Figure 5 is a schematic diagram of an arrangement for driving one or more loudspeaker arrangements with one or more inputs. The inputs are intended to drive respective loudspeakers located at respective pre-determined positions (virtual loudspeakers), for example loudspeakers of a conventional 7.1.4 spatial sound setup. The driven loudspeakers are not located in all the same pre-determined positions as the virtual loudspeakers and there may be a lesser or greater number of driven speakers than inputs. The arrangement produces outputs to drive the driven speakers to emulate the virtual loudspeakers. The arrangement comprises a receiving unit 110, a gain unit 111, a gain application unit 112, a filtering unit 113 and control units 114. The gain 111 unit is optional, as discussed further below. In use the receiving unit 110 receives spatial sound inputs, each input intended to drive a virtual loudspeaker in the arrangement to be emulated (in this example, each loudspeaker of a 7.1.4 arrangement so there are 12 inputs). These inputs are then passed to the gain unit 111, where present. The gain unit 111 is shown in more detail in figure 6 and operates to determine the level of gain to be applied to each input to provide modulated inputs for driving each driven loudspeaker. The gain unit 111 comprises a positional unit 115, and a gain determination unit 116. The positional unit 115 obtains the positions of the virtual loudspeakers each input is intended to drive and the positions of loudspeakers to be driven, which may comprise a loudspeaker body as shown in figure 2, multiple loudspeaker bodies and / or, in different embodiments, individual loudspeakers or loudspeaker units. The position associated with each input may be determined by the positional unit 115 from the input itself where the input comprises information on the type of virtual loudspeaker the input is for. Or it may be assumed from the nature of the input, for example where inputs relate to an established spatial sound system, such as 7.1.4, the intended position of each loudspeaker is known and so can be assumed. Or position information may be provided separately to the positional unit. In this case the sound system 100 comprises an input unit 118, which can take the form of a keyboard, mouse, touchscreen or any other suitable input device enabling a user to input positional information. The positional unit 115 includes a height determination unit 119. This unit determines the height of the virtual loudspeaker the input is intended to drive as an angle between 0° and 90° with 0° denoting that the virtual loudspeaker is in the listening plane and 90° denoting that the virtual loudspeaker at a maximum height i.e. directed downwards towards the listening plane, again from the input (which will indicate accordingly) or by assumption. The position of the loudspeakers or loudspeaker body(ies) in the loudspeaker arrangement to be driven may also be assumed or input by a user. The positional unit also determines the difference in position, as angular displacement in or projected onto the listening plane around a notional circle centred on the listening position, between each virtual loudspeaker and each loudspeaker or loudspeaker body in the loudspeaker arrangement to be driven. Where a loudspeaker body is provided the position of all of the loudspeakers in the body is taken as the position of a single point on the body. In the described example this is central position mid-way along the axis of, and between, the side loudspeakers. Direction of displacement may be specified by specifying the angular displacement as a positive or negative value from a point on the circle the listener is intended to face. From this positional information the positional unit 115 determines the difference in position between each virtual loudspeaker and each loudspeaker or loudspeaker body of the loudspeaker arrangement expressed as an angular displacement and a direction of displacement in the plane relative the loudspeaker body or loudspeaker of the loudspeaker' arrangement. Thus, for each loudspeaker, or loudspeaker body, both horizontal and height angular displacements are determined. The positional unit 115 can populate these into a matrix of virtual loudspeaker versus loudspeaker body or loudspeaker of the loudspeaker arrangement. The positional differences associated with each input and loudspeaker body or loudspeaker of the loudspeaker arrangement are then passed to the gain determination unit 116. For each input and loudspeaker of the loudspeaker arrangement the gain determination unit 116 determines a gain by applying a function. To determine the further gains to be applied to an input to produce modulated inputs for driving main and height loudspeakers, for an arrangement consisting of a single loudspeaker body as shown in figure 2 the gain determination unit 116 applies the following function: For angular displacements x = 0 to ± 90° Further gain = 1- (1-m) x |sin(x)| $ Where $ and m are the constants used in the function above for determining side gain. For angular displacement x >±90° Further gain - m or uses a look up table, to determine a combination gain which is represented by the solid line on the graph shown in figure 7. This shows gain on the y axis, running from 0% at the origin upwards to 100%, and angular displacement on the x axis, running on the right to greater positive angular displacement in the right hand direction and on the left to greater negative angular displacement in the left hand direction. The gain determination unit determines what the percentage gain is at the determined displacement for each input (in the determined direction). As the position of a virtual loudspeaker is displaced around the listening plane from the position of a main or height loudspeaker used to reproduce it, the output of the main or height loudspeaker gradually reduces, according to the function, to a constant minimum level Depending on a particular speaker arrangement and installation it may be desirable to scale the function so that x = 90° occupies a smaller or larger real world angular space. For driving a main loudspeaker, the further gain is multiplied by the main ratio determined by the following function, to yield the main gain: main ratio = l-si^h)* where h is the angular height position of the virtual speaker and for driving a height loudspeaker the determined gain is multiplied by the height ratio determined by the following function to yield the height gain: height ratio = s i n (h These functions are illustrated in the graph of figure 8a where the main ratio is shown by a solid line and the height ratio by a broken line. Gain ratio is shown on the y axis, running from 0 at the origin upwards to 1 and angular height position h is shown on the x axis. Thus, an input intended for a loudspeaker' located within the listening plane solely drives the main speaker. And an input intended for a loudspeaker located at the maximum height position, denoted by 90°, solely drives the height loudspeaker. For a virtual speaker at an intermediate position the input is proportioned between the two speakers. At all height positions, the sum of the main ratio and height ratio is 1. To determine the gain to be applied to an input driving a side loudspeaker, side gain, the gain determination unit applies the following function: For angular displacements x = - 90° to 0 0 Side gain - (1-m) x |sin(x)|* Where m is a constant less than 1, and $= -.....-.....— 2 For angular displacements x = 0° to +90 ° gain = (m-1) x |sin(x)|* For angular displacement x >+90° gain = 1-m or uses a look up table, to determine a side gain represented by the broken line on the graph shown in figure 7. At zero displacement, the gain is 0. With left hand displacement the gain rises to a constant value. With right hand displacement the gain is the inverse to that of left hand displacement. The shape of the side gain curve means that at 0° displacement there is no input to the side loudspeaker. With displacement an increasing input is generated up to a maximum value. A key point is that in one direction (the left in this case) the gain is positive, while in the opposite second direction (the right in this case) it is negative. This means in the right hand direction the audio output will be reverse polarity. This reverse polarity provides the steering of the audio in the correct direction. The system would also work with a mirrored gain curve, i.e. with a negative gain with left hand displacement and positive gain with right hand displacement. The sum of the sum of the main, height and side gains is always 100%. This avoids the perceived total volume of audio output varying depending on the position of a virtual speaker. In other embodiments there is no gain determination unit and, instead, the gains are preset based on an expected inputs and an expected loudspeaker setup. The apparatus may include a memory for storing one or more sets of preset gain values and an input device may enable a user to select a set of values to use. These may correspond to different input types and / or to different driven loudspeaker set-ups. The determined or pre-set gains for each input and output are passed to the gain application unit 112. The gain application unit 112 applies the gains associated with each loudspeaker or loudspeaker unit to be driven to the respective inputs to generate modulated inputs and these modulated inputs are added together to produce an output for driving each driven loudspeaker. For certain input signal types and driven loudspeaker setups the gain to be applied for certain input / loudspeaker combination will always be zero, or may for convenience be chosen to be zero. In some embodiments, the outputs are then passed to the filtering unit 113. Outputs for driving side loudspeakers are filtered to restrict them to between 200-350Hz and 4-7KHz, since sound in these ranges gives cues to spatial location. Outputs for driving main and height loudspeakers may be filtered to reduce their output in this range, to balance the overall sound. The outputs are then passed to the control unit 114. The control unit 114 applies volume control, specifically to boost the outputs for driving side loudspeakers relative to the other speakers to increase the overall sensation of space in the sound and amount of spatial steering. For example, the outputs driving the side loudspeakers may be +8dB over those for driving main loudspeakers. The preferred actual differential will depend on the set-up of a particular system and might typically be in the range +4 to +18dB. A user operable volume control may be provided to enable the user to control the output of the side loudspeakers relative to the other loudspeakers. In this example the outputs thus modified drive the loudspeakers to emulate 7.1.4 spatial sound. The subwoofer input passes through the sound system with relatively few changes, being output by the subwoofer of the sound system 100 (not shown). The arrangement of figure 5 may be implemented in any convenient way, as will be apparent to one of ordinary skill in the art, for example by one or more programmed microprocessors. Whilst the arrangement is described as having various different functional units, these functions may in practice be implemented by the same hardware. They need not by physically separate. Figure 10 shows an arrangement with a first loudspeaker body 101 at the 0° position relative to the intended listening position, the same as shown in figure 2, and a second identical loudspeaker body 101 at the 180° position with its main loudspeaker 102 directed towards the intended listening position. For an arrangement such as this with more than one loudspeaker body the functions applied by the gain determination unit 116 to determine the main, height and side gains are further modified to apportion the gain between that applied to the inputs to adjacent loudspeaker bodies where the virtual loudspeaker concerned is located in a defined angular crossover zone between the speakers. Typically, this is an angular region in or projected onto the listening plane centred at the midpoint between two loudspeaker bodies and extending over about 30% of the angular distance between the loudspeaker bodies. The inputs are apportioned according to the following functions: first loudspeaker body ratio = cos (z)2 second loudspeaker body ratio = sin (z)2 where z = [angular displacement from the centre of the crossover zone / 90°] x 90° These ratios are shown by the two lines on the graph of figure 8b. At all point the two ratios add up to 1. Figure 8c shows the combination gain (solid line) and side gain (broken line) curves for both speaker bodies. The crossover function effects hand-over of an input from one speaker body to the next as the position of the virtual speaker moves between the two bodies. At all points the sum of absolute gains applied to a given input is one. Figure 22 shows an example gain matrix determined by the gain determination unit 116. for the setup shown in figure 10. The left-hand column of the matrix lists the twelve inputs of a 7.1.4 spatial sound system. The bottom row of the matrix lists the loudspeakers (or side loudspeaker units) of the two loudspeaker bodies. Where a gain figure is present (shown here as a decimal rather than percentage) that gain is applied to the input and the resulting modulated inputs are summed to drive the loudspeakers of the loudspeaker bodies. Where there is no gain figure is shown, it is pre-set to zero. The front main loudspeaker 102 reproduces a combination of the inputs for the Left 8, Right 3, Centre 2, Sub, Surround Left 7, and Surround Right 4 loudspeakers of a 7.1.4 system. The gain applied to the input for the centre loudspeaker 2 is 1 since it is intended to be in the same position as the front main loudspeaker 102. The gain applied to the left, right and surround left and right inputs is lower, reducing with the displacement of those loudspeaker positions from that of the main front loudspeaker. The sub loudspeaker input is also applied to the main front loudspeaker, but the remaining inputs are not applied to the main loudspeaker (i.e. a zero gain is applied). This is because the displacement of the positions of the loudspeakers those inputs are intended for is sufficiently great not to require any reproduction of the inputs from the main front loudspeaker. The arrangement for driving the main rear loudspeaker is similar except that there is no corresponding input for a rear centre loudspeaker. The Front height loudspeakers 105 emulate the height left and hight right loudspeakers 12, 9 and are driven only by a combination of their inputs, and likewise for the Rear Height loudspeakers. In each case the gain for the inputs is lower than 1 since both the emulated loudspeaker positions are displaced to the respective sides of the front and rear height loudspeakers. The pair of front side loudspeakers 103, 104 emulate the left 8, right 2, surround left 7, surround right 4, height left 12, and height right 9 loudspeakers, being driven only by a combination of their inputs. The right-hand side loudspeaker has a negative gain, whereas the left-hand side loudspeaker has a positive gain. The left 8, right 2, height left 12, and height right 9 are at the apex of the gain curves and so have gains of 1 (or -1), while the surround loudspeakers have lower absolute gain values. The arrangement is similar for the rear side loudspeakers save that it is the left-side loudspeaker inputs which have a positive gain and the right-side loudspeaker inputs which have a negative gain, since the first side direction (the direction of positive gain) is anticlockwise around the notional circle and the second side direction (the direction of negative gain) is clockwise in this example. Figures 9-15 show different sound system 100 loudspeaker setups. Figures 9 and 11 show full 3D and reverse 3D setups, which provide better emulation of a 7.1.4 system than the singular loudspeaker body 101 setup shown in figure 2 and the basic 3D setup shown in figure 10 (although the basic 3D setup is better than the single loudspeaker body setup). In the figure 9 setup a first loudspeaker body is located at the 0° position with its main loudspeaker facing the intended listening position. Second and third loudspeaker bodies are positioned at the 135° and -135° positions with their main loudspeakers directed towards the intended listening position. The figure 11 setup is a mirrored version of the figure 9 setup with loudspeaker bodies at the 45° -45° and 180° positions. Figures 12 and 13 show irregular setups, which may be best for more irregular spaces which cannot accept the more regular 3D setups. Figures 14 and 15 show embodiments which do not employ the loudspeaker body of figure 2. These setups are useful for implementation in cars as an augmentation of an existing stereo system. In figure 14, the there are four main loudspeakers 102 arranged as opposed pairs, for example mounted in the doors of a four door car. A single height, and pair of side. loudspeakers 105, 103, 104 are provided in a loudspeaker body located at the 0° position. In figure 15 the setup is the same as that of figure 14 with additional side and height loudspeaker bodies at the 90° and -90° positions and further height loudspeaker at 180°. In the above discussed embodiments, the virtual loudspeakers to be reproduced by the system are all found in a 7.1.4 setup and height-wise are either main loudspeakers intended to produce an output at the level of the listener, a minimum height, or height loudspeakers intended to produce an output at a higher level, a maximum height, above the listener. Inputs intended to drive a main virtual loudspeaker of a system being emulated are typically employed, with the relevant calculated main gain applied, to drive one or more main loudspeakers of the system being driven. And inputs intended to drive a height virtual loudspeaker of a system being emulated are typically employed, with the relevant calculated height gain applied, to drive one or more height loudspeakers of the system being driven. In alternative embodiments the inputs may represent virtual loudspeakers or other virtual sound emitting objects, such as musical instruments, at various heights between the minimum and maximum heights. The latter case is shown in figure 16. In an alternative embodiment the height determination unit 119 determines the height of each virtual sound source, from information within its input or as otherwise provided and then determines the difference between that height and the maximum height, x, and the difference between the height and the minimum height, y. The height determination unit 119 then determines a main and height ratios using the following equations: x main ratio =---- x + y y height ratio = ——— Main and height components obtained from each input are combined to drive the main and height loudspeakers. In some embodiments the virtual sound source 120 can move within the space. The sound system 100 can account for this, the gains being calculated dynamically, and the outputs of the loudspeakers being dynamically changed as the sound source (or sources) move. In some embodiments different gain determination functions are employed to those illustrated in figures 7 and 8a to c. Figure 17a shows an alternative further gain function to that shown in figure 7. The gain falls linearly from 100% gain at zero displacement, in both directions of displacement. At 30-90° (typically 60 °) displacement in each direction the gain then falls logarithmically to 0% gain. The linear and logarithmic falls mirror each other in each direction of displacement. Alternatively, in a simpler arrangement, the gain cuts off (i.e. becomes zero) at 30-90° (typically 60 °) displacement in each direction. Figure 17b shows an alternative side gain function to that shown in figure 7. At zero displacement, the gain is 0. With left hand displacement the gain rises logarithmically to a plateau at 10-30° displacement, at which point the gain is 100%, and then falls logarithmically from the plateau at 30-60° displacement back to zero gain at approximately 100° displacement. The width of the plateau may be at least the width of the rise from zero, and typically it is about double the width of the rise. The result is an approximately bell-shaped curve. To the right hand side of the graph the gain is the inverse of that on the left hand side. Figure 18a shows another further gain function. In this embodiment the gain falls linearly from 100% with a first gradient in both directions of angular displacement from zero up to a given displacement at which point it falls linearly with a second gradient, steeper than the first, eventually to zero. The function has a similar overall shape and turning points to that shown in figure 17a, save that the logarithmic portions of the curve of figure 7 are replaced with linear portions. Alternatively, the gain may become zero where the function meets the horizontal cut-off line shown in figure 18. Figure 18b shows an alternative side gain function. In this embodiment the gain rises linearly from zero with negative (i.e. left hand) displacement to reach a plateau, from which it then falls linearly back to zero with further displacement. The function has a similar shape and turning points to that shown in figure 8 with the change that the logarithmic rise and fall of gain with displacement is replaced with a linear rise and fall. For positive angular displacement the function is the same shape, but inverted. The curve of the function thereby forms an isosceles trapezoid with the x-axis on each side of the y-axis. The embodiments above all include a pair of side loudspeakers forming a side loudspeaker unit. In alternative embodiments the side loudspeaker unit consists of a single dipole loudspeaker which will inherently emit out of phase versions of the driving input in opposite directions. If a dipole loudspeaker is in free space this can lead to unwanted cancellation between the out of phase signals. To avoid this some structure can be introduced. In the embodiment shown in figures 19a and 19b the single side loudspeaker 103 is mounted within the centre of a circular baffle 125 to reduce cancellation. In this example the baffle 125 has a 40cm radius. In the embodiment shown in figures 20a and 20b the loudspeaker 103 is instead mounted within a tube 126 forming a duct. The front of the loudspeaker 103 directly faces towards one end of the tube 126, while the back directly faces towards the other end. In the embodiment shown in figures 21a and 21b, the loudspeaker 103 is mounted within a duct 127. The loudspeaker 103 is in contact with the inner walls of the duct 127. The front of the loudspeaker 103 faces towards one end of the duct 127, while the back of the loudspeaker 103 faces towards the other end, although in neither case directly. The loudspeaker 103 is positioned at an oblique angle to the long axis of the duct 127. Figures 23-25 show embodiments of a pair of side loudspeakers 103, 104. Figure 23 shows an embodiment in which the side loudspeakers 103, 104 are in a dual driver, shared internal volume arrangement. The side loudspeakers 103, 104 are in the same duct 121, each at a respective opposite end of the duct. There is an outside air-path distance between the side loudspeakers 103, 104. Figures 24 and 25 show side loudspeakers in an independent driver arrangement. In figure 24 the side loudspeakers 103, 104 are in the same duct 121, but with a baffle 122 behind each side loudspeaker to separate the loudspeakers 103, 104. In figure 25 each side loudspeaker is in its own duct 123, the opposite end of the duct closed off by a respective baffle 124. It is to be noted that both the relative position and orientation of loudspeakers and loudspeaker bodies will affect a listener’s perception of the source of sound. So, a height loudspeaker may be positioned at the level of a listener but directed upwards, or at a level above the listener and directed downwards to achieve a similar result. Where a loudspeaker faces generally horizontally towards the listening position it should broadcast a main input when located at the level of a listener and a height input when located at a level above the listener. In the embodiments described above loudspeakers of the sound system and the virtual loudspeakers they seek to reproduce are all shown on or near to a notional circle centred on an intended listening position and therefore all approximately the same distance from the listening position. In other embodiments the position of the virtual loudspeakers or virtual objects may be outside the notional circle. In such cases, the sound system 100 comprises a time delay unit operable to determine the difference in distance between the virtual source and the listening position, and the loudspeaker or loudspeakers reproducing the input for the virtual source and the listening position, create a time delay based on the difference, and apply the time delay to the or each output component to the driven loudspeaker or loudspeakers derived from the input for the virtual source. This adjusts that component of the audio to appear to be coming from further away than the loudspeaker or loudspeakers (i.e. from the position of the virtual sound source). The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection defined by the appended claims.

Claims

1. A sound system for reproducing spatial sound in a space, the sound system comprising:a. a receiving unit operable to receive one or more inputs, the or each input representing a virtual sound source intended to be at a respective position within the space relative to an intended listening position;b. a side loudspeaker unit, the side loudspeaker unit being operable, in use, to output a sound signal from one side directed along a first line in one direction and the same sound signal from an opposite side directed along the first line in the opposite direction, the two outputs being in antiphase over at least part of their frequency range, and the first line extending substantially perpendicularly to a second line extending from the side loudspeaker to the listening position;c. at least one further loudspeaker being operable, in use, to direct sound along a third line, the third line extending in a direction which is nonparallel to, or is displaced from, the first line;d. a gain application unit operable to apply a respective side gain to the or each input to result in a modulated side input and a respective further gain to the or each same input to result in a modulated further input, where the absolute value of the respective side gain is different to the absolute value of the respective further gain; ande. a control unit operable to drive the side loudspeaker unit with a side output being the, or sum of each, modulated side input, and the further loudspeaker with a further output being the, or sum of each, modulated further input.

2. The sound system according to claim 1 wherein the side loudspeaker unit is a single dipole loudspeaker.

3. The sound system according to claim 1 wherein the side loudspeaker unit comprises a pair of opposed loudspeakers connected in antiphase.

4. The sound system according to any preceding claim wherein the first line is a tangent to a circle centred on the listening position.

5. The sound system according to claim 4 wherein the third line is a radius of the circle, and optionally the third line is the second line.

6. The sound system according to either claim 4 or 5 where the side loudspeaker unit and the further loudspeaker are in the plane of the circle, optionally on the circle.

7. The sound system according to either claim 4 or 5 wherein the side loudspeaker unit is in the plane of the circle, optionally on the circle, and the further loudspeaker is displaced from the plane of the circle.

8. The sound system according to any preceding claim wherein there are at least two further loudspeakers, a main loudspeaker arranged to direct sound so that it will be perceived at the listening position to come from within a horizontal plane in which a listening position is located, and a height loudspeaker arranged to direct sound so that it will be perceived at the listening position to come from a location above the perceived source of sound from the main loudspeaker.

9. The sound system according to any preceding claim wherein the side loudspeaker unit and further loudspeaker are disposed together in a loudspeaker body and directed in mutually substantially perpendicular directions.

10. The sound system according to claim 9 where there are at least two further loudspeakers, being a main loudspeaker and a height loudspeaker, both disposed in the loudspeaker body and directed in mutually substantially perpendicular directions.

11. The sound system according to either claim 9 or 10 comprising two or more loudspeaker bodies, wherein each body is positioned on a circle centred on the listening position with the further, or main, loudspeaker directed towards the listening position.

12. The sound system according to any of claims 9 to 11 comprising one or more additional further loudspeakers separate from the loudspeaker body.

13. The sound system according to any preceding claim wherein the side gain applied to an input is dependent on the relative positions of the virtual sound source represented by the input and the side loudspeaker unit to the listening position.

14. The sound system according to claim 13 wherein the side gain is a function of the angular displacement, in a plane, between the positions of the virtual sound source represented by the input and the side loudspeaker unit measured from the listening position.

15. The sound system according to claim 14 wherein the side gain is zero where the displacement is zero, an increasing positive side gain for angular displacement in a first direction and an increasing negative side gain for angular displacement in the opposite direction, reaching a maximum value in either direction. .

16. The sound system according to any preceding claim wherein the further gain applied to an input is dependent on the relative positions of the virtual sound source represented by the input and the further loudspeaker to the listening position.

17. The sound system according to claim 16 wherein the further gain is a function of the angular displacement, in a plane, between the positions of the virtual sound source represented by the input and the further loudspeaker unit measured from the listening position.

18. The sound system according to claim 17 wherein the further gain is 100% where the displacement is zero, reducing with angular displacement.

19. The sound system according to any of claims 16 to 18 wherein there are at least two further loudspeakers, a main loudspeaker and a height loudspeaker, and the further gains applied to the inputs to produce outputs for driving those loudspeakers are respective main gains and height gains, the main gain being dependent on the relative position of the virtual sound sources represented by the input and the main loudspeaker to the listening position and the height gain being dependent on the relative position of the virtual sound sources represented by the input and the height loudspeaker to the listening position, both theangular displacement within a horizontal plane containing the main loudspeaker and any displacement above that plane.

20. The sound system according to any preceding claim comprising a memory for storing gain values for use by the gain application unit.

21. The sound system according to claim 20 comprising an input device to enable a user to select a set of gain values to be applied by the gain application unit from a range of stored sets of values.

22. The sound system according to claim 21 or 22 comprising an input device to enable a user to enter one or more gain values for application by the gain application unit.

23. The sound system according to any preceding claim comprising a gain determination unit operable to determine the or each side gain and the or each further gain to be applied to each input based on the position of the or each virtual sound source represented by the inputs and positions of the side loudspeaker unit and the or each further loudspeaker, and provide the determined gains to the gain application unit.

24. The sound system according to claim 23 wherein the gain determination unit determines the position of the or each virtual sound source from the or each input.

25. The sound system according to either claim 23 or 24 comprising an input device to enable a user to input the positions of the side loudspeaker unit and the or each further loudspeaker.

26. The sound system according to any preceding claim comprising a filter unit operable to filter the side output to frequencies in the range 200Hz to 7kHz.

27. The sound system according the any preceding claim comprising a delay unit operable to delay one or selected inputs in dependence on the distance of the virtual sound source represented by that input from the listening position.

28. A method for reproducing spatial sound in a space, the method comprising the steps of:a. receiving one or more inputs, the or each input representing a virtual sound source intended to be at a respective position within the space relative to an intended listening position;b. positioning a side loudspeaker unit to output a sound signal from one side directed along a first line in one direction and the same sound signal from an opposite side directed along the first line in the opposite direction, the two outputs being in antiphase over at least part of their frequency range, and the first line extending substantially perpendicularly to a second line extending from the side loudspeaker unit to the listening position;c. positioning at least one further loudspeaker to direct sound along a third line, the third line extending in a direction which is non-parallel to, or displaced from, the first line.d. applying a respective side gain to the or each input to produce a modulated side input and a respective further gain to the same input to produce a respective modulated further input, the absolute value of the respective side gain being different to the absolute value of the respective primary gain; ande. driving the side loudspeaker unit with a side output being the or sum of each modulated side input, and the primary loudspeaker with a further output being the further modulated input or sum of each further modulated input.

29. The method according to claim 28 wherein the first line is a tangent to a circle centred on the listening position.

30. The method according to claim 29 wherein the third line is a radius of the circle, and optionally the third line is the second line.

31. The method according to any of claims 29 to 30 comprising determining the side gain applied to an input depending on the relative positions of the virtual sound source represented by the input and the side loudspeaker unit to the listening position.

32. The method according to any of claims 29 to 31 comprising determining the further gain applied to an input depending on the relative positions of the virtual sound source represented by the input and the further loudspeaker to the listening position.5 33. The method according to any of claims 29 to 32 comprising positioning at leasttwo further loudspeakers, one being a main loudspeaker and the other a height loudspeaker, and determining and applying further gains to the inputs to produce outputs for driving those loudspeakers, respectively main gains and height gains, where the main gain is determined dependent on the relative10 positions of the virtual sound source represented by the input and the mainloudspeaker to the listening position and the height gain being determined dependent on the relative positions of the virtual sound source represented by the input and the height loudspeaker to the listening position.

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