SYSTEM FOR REPRODUCING SOUNDS WITH VIRTUALIZATION OF THE REVERBERATED FIELD

Abstract

The system for reproducing sounds (100) comprises at least four electroacoustic transducers, which each receive an audio signal and convert it into a sound signal, and a listening area for a single listener. Two of the four transducers, called front transducers (105), are placed mutually symmetrically with respect to a median vertical plane, and are oriented so as to each emit an audio wave towards the listening area, and two of the four transducers, called rear transducers (107), are placed mutually symmetrically with respect to said median vertical plane and are oriented so as to each emit a sound wave towards said listening area, so as thus to form two pairs of transducers that are mutually symmetric with respect to said median vertical plane. The single listener positions themselves such that they face the front transducers (105) and have their back to the rear transducers (107).

Claims

1-27. (canceled)

28. Sound reproduction system wherein the sound reproduction system comprises at least four electroacoustic transducers each receiving an audio signal and converting it into a sound signal, and comprising a listening area for a single listener, characterized in that: two of said four transducers, called front transducers, are placed symmetrically to each other with respect to a median vertical plane, and oriented so as to each emit a sound wave towards the listening area, two of said four transducers, called rear transducers, are placed symmetrically to each other with respect to said median vertical plane and oriented so as to each emit a sound wave towards the listening area, the four transducers, front and rear, thus form two pairs of transducers symmetrical to each other with respect to the median vertical plane, each pair of transducers comprising a front transducer and a rear transducer, the single listener being to be placed facing the front transducers and back to the rear transducers.

29. Sound reproduction system according to claim 28, characterized in that: each of the four transducers is a directional sound source characterized by a main axis of emission that is secant with said median vertical plane, for each of said pairs of transducers, the sound signal emitted by said rear transducer simulates a reverberant field corresponding to said sound signal emitted by the front transducer, the four transducers are included in a parallelepiped volume having a width of less than 200 cm, a length of less than 200 cm and height less than 200 cm, and the distance measured horizontally between the pairs of transducers is greater than the distance measured horizontally between the two ears of the single listener.

30. Sound reproduction system according to claim 29, characterized in that said emission axes of the front loudspeakers intersect at a point of intersection of the emission axes of the front loudspeakers, in that the front loudspeakers are each delimited by a flat front face on the emission side and in that the point of intersection of the emission axes of the front loudspeakers forms with the points of intersection of each of the emission axes of each front loudspeaker with the flat front face of this front loudspeaker an isosceles triangle which equal angles are between 50° and 70°.

31. Sound reproduction system according to claim 29, characterized in that each of the said pairs of transducers is integrated in a housing comprising one or more recesses in which the front and rear transducers of the pair of transducers are placed, and of which at least a part of the walls is covered with an acoustically insulating material.

32. Sound reproduction system according to claim 31, characterized in that each of the said housings is mounted on at least one support stand, optionally adjustable in height.

33. Sound reproduction system according to claim 28, characterized in that it further comprises: a rear wall, and two side walls, extending in depth in front of the rear wall and in height to a height lower than that of the upper edge of the rear wall and each comprising at least one recess so that the walls each form a housing in which one of the pairs of transducers is placed, the rear wall and the side walls constituting a symmetrical assembly with respect to said median vertical plane, the listening area corresponding to the empty volume being between the side walls at a height higher than that of the upper edges of the side walls and lower than that of the upper edge of the rear wall, the front transducers each emitting a sound wave towards the listening area in a emission cone entirely intercepted by the listener's head placed in the listening area and/or by the rear wall and/or by the side walls, and the rear transducers each emitting a sound wave towards the listening area in an emission cone entirely intercepted by the listener's head placed in the listening area and/or by the side walls.

34. Sound reproduction system according to claim 32, characterized in that the front transducers are placed at a distance from the listener enabling the listening of the direct field of these frontal transducers, i.e. a distance less than the critical distance for which the intensities of the direct field and the diffuse field are equal.

35. Sound reproduction system according to claim 31, characterized in that at least one of the housings (7) comprises a device for constraining in a fixed or adjustable manner the orientation of the axis of emission from at least one of said four transducers.

36. Sound reproduction system (100) according to any claim 31, characterized in that it comprises a seat (101) comprising at least one seat base (102), optionally covered at least partially with a sound-insulating material, so that the listening area is above said seat (102) and each of the housings (7) is linked to said seat (101).

37. Sound reproduction system (100) according to claim 36, characterized in that the seat (101) further comprises armrests to which the housings (7) are attached, optionally in a removable manner.

38. Sound reproduction system according to claim 31, characterized in that the housings are linked, optionally in a removable manner, to a wall of a building forming a rear wall, optionally covered with a material acoustically insulating, the housings being optionally foldable down against the rear wall when they are not used for the reproduction of sounds.

39. Sound reproduction system (100) according to claim 28, characterized in that the distance between the single listener and the front transducers (105) is less than 1 m.

40. Sound reproduction system (100) according to claim 28, characterized in that it comprises at least one signal processing device, so that an audio signal received by the rear transducer of each pairs of transducers is generated by means of the at least one signal processing device from the same audio signal as that from which an audio signal received by the front transducer of the pair of transducers is formed, said audio signal received by the rear transducer of each of the pairs of transducers being delayed relative to said audio signal from which said audio signal received by the front transducer of the pair of transducers is formed.

41. Room equipped with a plurality of sound reproduction systems according to claim 28.

42. Housing comprising one or more compartments suitable for receiving at least the front transducer and the rear transducer of one of the pairs of transducers of a sound reproduction system according to claim 31.

43. Sound reproduction system according to claim 33, characterized in that the front transducers are placed at a distance from the listener enabling the listening of the direct field of these frontal transducers, i.e. a distance less than the critical distance for which the intensities of the direct field and the diffuse field are equal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Embodiments of the invention will be described below with reference to the drawings, briefly described below:

[0100] FIG. 1 shows a side view of the sound reproduction system according to one embodiment.

[0101] FIG. 2 shows a top view of the sound reproduction system of FIG. 1.

[0102] FIG. 3 shows a front view of the sound reproduction system of FIG. 1.

[0103] FIG. 4 is a block diagram of the audio signal processing chain in a particular embodiment.

[0104] FIG. 5 represents the zones for which the direct sound and the sound reflected on an obstacle are perceived as merged or on the contrary separated, so that the listener perceives a phenomenon of reverberation, in the plane (frequency of a sound signal; delay of the sound reflected on the direct sound). This graph was obtained following studies carried out in an anechoic chamber at the National Audiovisual Institute (INA, France, work by Patrick Thévenot.)

[0105] FIG. 6 represents the measurement of RT60 of a seat equipped with the invention. 6 RT60 is the time it takes for the sound pressure level to decrease by 60 dB, measured after the sound source has been turned off abruptly. The black and thicker curve indicates the RT60 reverberation time as a function of the frequency of a study room. 0 The thick gray curve indicates the RT60 reverberation time at the sound reproduction device in this same study room, without activation of the digital control of the reverberation zone (B). The thin gray curve corresponds to the reverberation time RT60 measured under the same conditions but with reverberation recreated virtually and set to 0.56 seconds.

[0106] FIG. 7 shows a housing comprising compartments in which are placed a set of electroacoustic transducers.

[0107] In the drawings, identical references designate identical or similar objects.

DETAILED DESCRIPTION

[0108] The invention therefore relates to a sound reproduction system 100 comprising at least four electroacoustic transducers each receiving an audio signal and converting it into a sound signal, and comprising a listening area for a single listener, in which: [0109] a. two of the four transducers, called front transducers, are placed symmetrically to each other with respect to a median vertical plane, and oriented so as to each emit a sound wave in the direction of the listening area, [0110] b. two of the four transducers, called rear transducers, are placed symmetrically to each other with respect to the median vertical plane and oriented so as to each emit a sound wave in the direction of the listening area.

[0111] The four transducers, front and rear, thus form two pairs of transducers symmetrical to one another with respect to the median (or equivalently mediating) vertical plane, each pair of transducers comprising a front transducer 105 and a rear transducer 107.

[0112] The single listener is placed facing the front transducers and back to the rear transducers.

[0113] In a particular embodiment, each of the four transducers is a directional sound source characterized by a main emission axis secant with the median vertical plane.

[0114] Moreover, for each of the pairs of transducers, the sound signal emitted by said rear transducer 107 simulates a reverberant field corresponding to the sound signal emitted by the front transducer 105.

[0115] In addition, the single listener is placed in a listening position close to the four transducers, without the reproduction system directly touching the listeners ears as in conventional headphones: [0116] a. the four transducers are included in a parallelepipedal volume with a width of less than 200 cm, a length of less than 200 cm and a height of less than 200 cm, [0117] b. the distance measured horizontally between the pairs of transducers is greater than the distance measured horizontally between the two ears of the single listener.

[0118] The distance measured horizontally between the pairs of transducers is defined as the shortest distance between a point of one pair of transducers and a point of the second pair of transducers lying in the same horizontal plane.

[0119] This particular listening position makes it possible to exploit the psychoacoustic effects: in particular, as the intensity of the possibly existing reverberant field is naturally much lower than that of the reverberant field simulated by the rear loudspeakers in the listening area, the listener is enabled to reconstruct the reverberation phenomenon corresponding to the sound scene reproduced by the front loudspeakers essentially based on the audio signals coming from the two rear loudspeakers.

[0120] The transducers form an approximately symmetrical assembly with respect to a median vertical plane, which is also a mediating plane of the listening area for the listener. The listener is placed in an optimal manner when he is facing the front transducers 105, back to the rear transducers 107, his head in the listening area and the mediating plane of the sound reproduction system is also a mediating plane for the user.

[0121] The notion of symmetry is understood here relative to the precision of the adjustment and the implementation. Furthermore, by approximately symmetrical, it is meant that elements of decoration, wiring or other, not essential for the reproduction of sounds, can be non-symmetrical with respect to the median plane. For example, the position of the power supply of the sound reproduction system 100 is irrelevant for the quality of the reproduction of the sounds and may be outside the median plane.

[0122] The volume of the listening area is in this particular embodiment limited by the limitation of the horizontal distances between the various transducers. The listening area is thus of a limited volume but sufficient for a single listener, so that: [0123] a. the position is naturally close to the ideal position without being constrained by rigid positioning elements which would make the use of the device uncomfortable. [0124] b. the head of the ideally placed listener intercepts most of the beams emitted by the four transducers, so that listening is not impaired by undesirable reflections of these beams on the various elements of the sound reproduction system or of the room in which it is located, or by interference between these beams within the listening area itself.

[0125] 4 Depending on the directivity of the beams, some of the sound beams may not be intercepted by the listeners head. But one understands that the quality of listening in the sound reproduction system 100 is all the better as the opening of these beams is well controlled. We can also consider adapting waveguides on one or more of the four transducers for this purpose.

[0126] According to one embodiment, the emission axes of the front loudspeakers 107 intersect at a point of intersection of the emission axes of the front loudspeakers 107. The front loudspeakers 107 are each delimited by a flat front face on the emission side and the point of intersection of the emission axes of the front loudspeakers forms with the points of intersection of the emission axes with the flat front faces of the two front loudspeakers an isosceles triangle whose equal angles are between 50° and 70°.

[0127] It has been observed that this range of configurations of the sound reproduction device 100 provides the listener with particular listening comfort, allowing him to be particularly well immersed in the sound emitted by the front loudspeakers 107.

[0128] In one embodiment, each of the pairs of transducers of the sound reproduction system 100 is integrated into a housing 7, in which compartments are made to accommodate the front transducer 105 and rear transducer 107 of the pair of transducers. A housing 7 provided with a set of transducers is shown seen from above in FIG. 7.

[0129] The housing protects the transducers and facilitates their relative positioning and the positioning of each pair of transducers relative to the other pair of transducers.

[0130] The housing 7 further comprises all the electrical and electronic components necessary for the operation of the electroacoustic transducers.

[0131] One of the housings 7 (or the two housings 7) can include a technical zone 110 allowing the mechanical and/or acoustic adjustments of the sound reproduction system 100 to be made.

[0132] One or more walls of a housing 7 can be covered with acoustic insulating material. This arrangement makes it possible to partially isolate the listening area from parasite sound sources and from any uncontrolled reverberation phenomena on these walls.

[0133] In a particular embodiment, the compartments are configured in such a way as to limit the degrees of freedom of movement of the loudspeakers they contain. In particular, it is possible to leave only degrees of freedom in rotation, so that the inclination of the main emission axis of each loudspeaker can be adjusted where the reproduction system is placed.

[0134] In this way, the position of the listening area, in particular its height from the floor, can be adjusted, possibly depending on the listener.

[0135] A system for blocking the orientation of the loudspeakers after adjustment can be provided. Thanks to this arrangement, a preselection can be made by an operator, for example when mounting the loudspeakers on the housing, or even during the installation of the sound reproduction system 100 in a given place, and this adjustment will be allowed to be modified only by voluntary release of the blocking system.

[0136] In a particular embodiment, the greater of the two distances d1 and d2, the distance d1 being measured horizontally between the two front transducers and the median plane and the distance d2 being measured horizontally between the two rear transducers and the median plane, and the distance d3 measured in the front-to-rear direction between the front transducer 105 and the rear transducer 107 of each of the pairs of transducers are in a ratio of the order of 0.7.

[0137] The distances d1, d2, d3 are defined with respect to the center(s) of the membrane(s) of the loudspeaker(s) concerned.

[0138] Thanks to this arrangement, the listening area, in which the sound beams emitted by the four front and rear transducers intersect, has an optimal volume so that the listener has a feeling of enveloping sound.

[0139] In this way, the listening area is placed in an ideal manner with respect to the front loudspeakers in order to obtain listening that is little disturbed by the environment of the sound reproduction device 100.

[0140] The position of the listeners head that provides the most natural sound sensation is in the center of the listening area. The position of this center relative to the intersection of the straight lines joining a front transducer 105 and the rear transducer 107 on the opposite side can be adjusted by adjusting the ratio of the sound powers emitted by the rear transducers 107 compared to those emitted by the front transducers 105, but also by adjusting the delay of the sounds emitted by the rear transducers 107 relative to those emitted by the front transducers 105 which will be described later, as well as by adjusting transaurality.

[0141] The advantage of the sound reproduction device is that it leaves a certain latitude of positioning to the listener while maintaining a pleasant listening experience.

[0142] In particular, we note that the listener can be a little too far forward or behind this center, a little above or below this center, while maintaining a satisfactory listening sensation.

[0143] It is possible to provide the housing 7 with one or more support stand. In this way, the sound reproduction system 100 can be easily moved from one place to another if the support stand is not attached to any other object than the housing. The sound reproduction system 100 can thus also be placed at a certain height from the ground. 1 It can for example be adapted for a standing listener, in the center of a room or at least at a distance from the walls of this room.

[0144] Furthermore, the floor space requirement of the sound reproduction system is reduced.

[0145] This arrangement makes it possible, for example, to create, with several sound reproduction systems 100, a sound path with several quality listening areas that are independent of each other in a room such as a museum room.

[0146] The choice of the height of the support stand(s) determines the range of accessible heights for the listening area. It will thus be possible to create a sound reproduction system for a seated or standing listener, and for listeners of various sizes by choosing a support stand of height adapted to the desired use.

[0147] In a particular embodiment, the support stand is adjustable in height. This arrangement increases the flexibility of the adjustment of the sound reproduction system 100.

[0148] If, on the contrary, the sound reproduction system 100 is intended for a specific location near a wall or a partition, the housings 7 can in another embodiment be linked to this wall or this partition.

[0149] This arrangement makes it possible to not totally or not partially prevent the movement or positioning of objects or people on the floor due to the floor space requirement of the sound reproduction system 100.

[0150] For example, the housings 7 of a sound reproduction system 100 can be placed on either side of a screen, or of a painting in a museum, for a standing listener.

[0151] The housings 7 can also be placed on a wall or a headboard at the back of a bed to allow listening while lying down or leaning against the wall.

[0152] The wall can optionally be covered with an acoustically insulating material.

[0153] Thanks to this arrangement, listening is little disturbed by uncontrolled reverberation phenomena towards the rear of the listener or by parasite sound sources whose sound wave could propagate and reach the listener directly from behind.

[0154] The connection of the housings 7 to the wall or to the partition can, in a first variant, be of the embedding type, by means of screws for example.

[0155] This connection can, in a second variant, allow certain degrees of freedom of movement of the housings 7 with respect to the wall or to the wall. In particular, the housing 7 can be fixed to the wall by means of an articulated arm, which allows the adjustment of the position of the housing in depth relative to the wall, and/or the folding down of the housing 7 along the wall when the system sound reproduction 100 is not used.

[0156] Means for temporarily blocking the adjustment of the articulated arm can be provided.

[0157] In a particular embodiment, the reproduction system 100 is adapted specifically to the seated position. In this case, it comprises, as shown in FIG. 1, a seat 101 comprising a seat base 102, optionally a backrest 103, optionally a rear wall 111 and optionally two side walls 104. All of these elements are approximately symmetrical with respect to a vertical plane, called the “median” plane of the sound reproduction system 100, or equivalently mediating plane.

[0158] In a particular embodiment, the two side walls 104 comprise the housings 7 or are formed by the housings 7.

[0159] Alternatively, the side walls 104 are armrests of a seat on which are placed two housings 7, optionally provided with support stands.

[0160] In this way, a seat that a listener already has can be equipped, at lower cost and possibly reversibly, with two housings 7 so as to constitute a reproduction system 100.

[0161] In particular, optional implantation inserts for supporting the housing, placed on the armrests, can allow stable, simple and quick installation on any type of seat and offer height adjustment around the listener.

[0162] Whatever the embodiment, the pairs of transducers are symmetrical to each other. As seen previously, the notion of symmetry is understood here relative to the precision of the adjustment and the positioning. Moreover, by approximately symmetrical, it is meant that elements of decoration of the seat, of wiring or other, not essential for the reproduction of sounds, can be asymmetrical with respect to the median plane. 3 For example, the position of the power supply of the sound reproduction system 100 is irrelevant for the quality of the reproduction of the sounds and may be outside the median plane.

[0163] The seat 101 is also equipped with a plurality of electroacoustic transducers receiving an electrical signal at the input and emitting a sound signal at the output.

[0164] The seat 101 further comprises all the electrical and electronic components necessary for the operation of the electroacoustic transducers.

[0165] The dimensions of the seat 102, of the backrest 103 and of the side walls 104 are fixed so that the head and neck of the majority of the users for whom the seat is intended are located in a so-called listening zone, above the highest edges of the side walls, the rest of the body being, at most up to shoulder height, framed by the backrest and the two side walls. The listening area is thus not framed by the side walls, which avoids the comb response at the level of the listeners head.

[0166] In a particular embodiment, the distance (d1) measured horizontally between the two front transducers and the middle plane and the distance (d2) measured horizontally between the two rear transducers and the middle plane and the distance (d3) measured along the direction front-to-rear between the front transducer and the rear transducer of each of said pairs of transducers are in particular in a ratio preferably of the order of 0.7.

[0167] The distances d1, d2, d3 are measured from the center of the loudspeaker membrane.

[0168] According to a particular embodiment, the height of the seat 102 and the inclination of the backrest 103 can be adjusted by the user or at least personalized according to the user of the seat.

[0169] The foams that make up the seat base 102, the side walls 104, the rear wall 111 and the backrest 103 preferably have a high alpha Sabine sound absorption coefficient in the range of audible frequencies, and more particularly in the range [500 Hz, 5000 Hz] in which the sensitivity of the ear is greatest.

[0170] The seat base 102, the side walls 104, the rear wall 111 and the backrest 103 are also preferably covered with acoustic fabrics, transparent to sound waves.

[0171] This arrangement makes it possible to limit the reflections of the sound waves emitted by the transducers on these various elements, so that the resulting sound wave perceived by the user is essentially made up of direct waves emitted by the transducers of the sound reproduction system 100.

[0172] In particular, in this embodiment, the waves emitted by the various transducers do almost not propagate outside the reproduction system 100, which limits the reverberation phenomenon linked to the listening room perceptible for the listener.

[0173] The vertical extension of the side walls 104 of the seat 101 approximately up to the users shoulder height also allows partial isolation of the listener from sound sources external to the sound reproduction system 100.

[0174] In the embodiment of FIG. 1, the sound reproduction system 100 comprises at least four electroacoustic transducers, including at least two front electroacoustic transducers 105, which are placed in recesses of the side walls 104 of the seat which constitute the housings 7, in front of the rear wall 111.

[0175] The shape of the recesses can participate in guiding the sound wave emitted by the transducers in the desired direction.

[0176] These transducers are in this embodiment, as well as possibly in the other embodiments, by way of non-limiting example, of the “source point” type, coaxial with mechanically aligned phase for the two channels corresponding to the different frequency ranges (bass/medium and treble), or broadband loudspeakers.

[0177] Mechanically phase-aligned coaxial speakers feature very high precision phase alignment between the two paths at the emitting end. Such loudspeakers are therefore close to a single point source.

[0178] In the embodiment described in FIG. 1, the listener is typically within one meter of the source. This unusual listening position has the second advantage of allowing near-field listening, so as to mask the reverberant field.

[0179] Comb filtering in the frequency ranges corresponding to the overlap between the different channels is very limited and the reproduced sound is of very good quality.

[0180] The front transducer 105 and the rear transducer 107 typically emit at least in the frequency range [100 Hz; 20 kHz].

[0181] In the case of “point source” transducers, the wave emitted from the loudspeaker is approximately spherical, so that the sound intensity is an inverse function of the square of the distance between the measurement point and the point source. The proximity of the listener to the transducers makes it possible to obtain satisfactory listening with a lower emitted sound intensity than when the listener is at a more usual listening distance (a few meters) from the loudspeakers, since the sound intensity decreases as the distance from the source increases.

[0182] The placement of the front transducers 105 in the front part of the side walls 104 of the embodiment of FIG. 1, consequently under the users head and in front of his trunk, allows the user to be outside the zone in which the waves emitted by the two front transducers as well as the waves reflected on the corresponding side walls significantly interfere. In other words, the user is outside the comb response zone, which allows for high-precision listening, faithful to the original sound to be reproduced. This modality can be implemented in other embodiments.

[0183] The placement of the two front transducers 105 in the side walls 104, so that they are oriented towards the head of the user also contributes to controlling the area of space in which the sound wave emitted by each of these transducers remains audible. Most of the sound intensity is distributed in a cone 106 with its apex at the source point and containing at least part of the users head.

[0184] In particular embodiments, the two front loudspeakers 105 are oriented so that their emission axes intersect at the level of the listeners frontal lobe, close to his vertical median plane.

[0185] The alpha angle then formed by these two emission axes may vary depending on the inclination of the backrest and/or the length of the side walls, but these parameters will be limited so that the alpha angle is between approximately 60° and 90°. In this case, the listener will perceive monophonic sounds (i.e., identical in phase and amplitude for two transducers symmetrical with respect to the median plane of the seat, for example sounds placed in the center during mixing operations) as emitted in the median plane of the seat, in front of him and not above him.

[0186] The frequencies best analysed by the human brain are between 500 Hz and 5 kHz. The ears of the listener must therefore be, if possible, in the axis of radiation of the loudspeakers emitting these frequencies. We therefore understand the interest, in order to obtain high listening precision, of constraining the positioning of the listener in relation to the various transducers, by linking the position of the latter and of the sea.

[0187] When the front transducers 105 are placed in the side walls 104 of a seat or in housings 7 placed so as to respect the constraints on the distances d1, d2 and d3 mentioned above, they are at a distance from the listener less than the critical distance for which the intensity of the free field, corresponding to the wave coming directly from the source, becomes equal to that of the diffuse field, corresponding to the multiple reflections of the initial sound wave. Below the critical distance, the free field predominates: the listener essentially perceives the direct sounds coming from the front transducers. The phenomenon of natural reverberation (which results, despite the partial acoustic insulation of the seat, from the propagation of a fraction of the sound emitted by the loudspeakers towards the outside of the seat) is largely masked by these direct sounds, as indicated in FIG. 6, and an essentially virtual reverberation could be created thanks to transducers other than the front transducers, which will be introduced later in this description. In other words, the phenomenon of reverberation perceived by the listener is essentially virtual and controllable.

[0188] FIG. 6 shows the influence of the sound reproduction system 100 according to the embodiment of FIG. 1 with activation of only the front transducers 105. 4 It can be seen that, with respect to the listener located at a given point in the room measurement, the reverberation phenomenon is much less dependent on the frequency in the presence of the sound reproduction system (gray and thick curve) than in the absence of this system (black and thicker curve). Without the seat, the reverberation time RT60 depends on the frequency, which means that the spectrum of the signal perceived by the listener will not be identical to the spectrum of the emitted signal. Listening is impacted by the room in which it is performed. In the presence of the reproduction system, the phenomenon of reverberation exists but is not very dependent on the frequency; it thus modifies all the frequencies of the signal approximately in the same way: the sound is perceived by the listener with a spectrum that is not very distorted compared to the emission spectrum.

[0189] Near-field listening has the added benefit of reducing noise pollution. Typically a conventional sound reproduction system placed two meters from the listener would require a sound intensity 10 dB higher acoustically at the source for the same perception by the listener than when placed in the seat equipped with the system sound reproduction described in this document.

[0190] Concomitantly, the reduction of the sound intensity at the level of the sources compared to a conventional system for the same sound intensity perceived by the listener makes it possible to reduce the rate of harmonic distortion and therefore to increase the fidelity of the sound perceived by the user.

[0191] The sound reproduction system 100 described here makes it possible, for example, to obtain a sound restitution power of the order of 100 dB in terms of sound pressure level (dB SPL) with a harmonic distortion rate of less than 3% for the listener for frequencies above 60 Hz.

[0192] Specific waveguides can optionally be added to the output of each of the front transducers to better control the angle at the top of this cone.

[0193] Thanks to these provisions, an appropriate adjustment of the distance between two consecutive seats and of the maximum sound powers emitted by the transducers, as well as possibly of the shape of the waveguides, also allows a relative separation of two contiguous seats: the user of a given seat will almost only perceive the sound corresponding to the transducers fitted to his own seat. In particular, the sound power emitted in the low frequency range is adaptable to each seat so as to be able to control the overall intensity of the low frequencies in the room, for which the effect of physical coupling with the room is particularly sensitive, in the case where the different seats simultaneously reproduce the same sound.

[0194] The two front transducers 105 each receive an audio signal as input and emit a sound signal as output.

[0195] The audio signals at the input of the two front transducers 105 are the audio signals as recorded, or else having undergone, by means of a digital signal processor, a processing step in order to correct the non-linearity of the front transducers.

[0196] In a particular embodiment, the audio signal corresponding to the recording to be reproduced is not directly sent to the input of the front transducer considered, but it constitutes the input signal of a digital signal processing system (DSP) dedicated to the front transducers 105. The digital signal processor filters this input signal, in particular to correct the linearity defects of the front transducers. The audio signal at the output of the digital signal processing system constitutes the audio input signal for the front transducer 105 concerned.

[0197] The digital signal processing system can for example be placed in the housing 7 or in a side wall 104 or a technical area 110.

[0198] At the level of the front transducers 105, whose frequency response is not perfectly linear given the modification of acoustic impedance brought about by the recesses guiding the wave, this filtering step aims to obtain a reproduced direct field as faithful as possible to the recorded sound signal.

[0199] In one embodiment, for each of the channels of the front transducers 105, an amplification device can be inserted between the digital signal processing system and the front transducers 105.

[0200] In the embodiment shown in FIG. 1, at least two other rear electroacoustic transducers 107 are placed in or above the upper part of the rear wall 111, approximately at user ear height, on both sides of the user, so that they are symmetrical to each other with respect to the median plane of the seat.

[0201] The rear transducers are oriented so that the emission axis of each of these transducers passes close to the user's ear that is on the same side of the median plane of the seat as the transducer.

[0202] These two transducers 107 emit sound signals having frequencies typically included at least in the range [100 Hz; 20 kHz].

[0203] In all the embodiments, the audio signal at the input of each rear transducer 107 is generated thanks to a digital signal processing system (Digital Signal Processor, DSP) dedicated to these two rear transducers. Depending on the embodiment, the digital signal processing system can for example be placed in the housing 7 or in a side wall 104 or a technical area 110.

[0204] Each transducer 107 receives an electrical input signal which is calculated with respect to the electrical input signal of the transducer 105 located on the same side of the median plane of the seat.

[0205] If a digital signal processing system has been dedicated to the front transducers 105, the audio signal at the input of this signal processing system constitutes the input signal for the signal processing system dedicated to the rear transducers 107.

[0206] In the two embodiments (with or without a digital signal processing system dedicated to the front transducers 105), the notion of stereophony is retained for all of the front and rear transducers.

[0207] In one embodiment, a broadband amplifier device can be inserted between the digital signal processing system dedicated to the rear transducers and the rear transducers 107.

[0208] In one embodiment, the digital signal processing system and the electronic components necessary to generate the electrical signal at the input of the rear transducers are placed in a technical area 110 under the seat base 101.

[0209] As a variant, in the case where a room is equipped with several sound reproduction systems 100, all the technical zones of the different sound reproduction systems 100 can be grouped together in a single technical zone distinct from the sound reproduction systems 100.

[0210] The electric signal to be supplied at the input of the rear transducers 107 is calculated from the electric signal supplied at the input of the front transducers 105, so as to create a virtual reverb effect.

[0211] In particular, the electric signal at the input of each rear transducer 107 is delayed compared to the electric signal at the input of the front transducer 105 from which it is calculated.

[0212] The delay is the sum of two terms: [0213] the first term is constant and determined according to the geometry of the seat. It takes into account the difference in positioning of the front transducer and the corresponding rear transducer with respect to the listening area. 6 In the presence of this term alone, the waves emitted by a given front transducer and the corresponding rear transducer are in phase at the center of the listening area; [0214] the second term can be adjusted by the user or an operator, for example by means a potentiometer. 3 The delay can for example be set in the range [0 s; 5 s], the range [0.3 s; 0.7 s] giving a satisfactory perception for most sound scenes.

[0215] We will understand the influence of the second term using FIG. 6. 3 In this figure, we have already seen above that, in the presence of the seat but without activation of the rear transducers 107, the RT60 is an almost constant function of the frequency for frequencies above 100 Hz. It is of the order of 0.3 s for the seat tested in the test room.

[0216] 2 The reverberant field generally depends on the geometric and acoustic characteristics of the listening room. On the contrary, the sound reproduction system 100 makes it possible to obtain a reverberant field which is virtually reconstituted and as constant as possible in frequency: as the listener is placed close to the various transducers, and thanks to the various elements of the sound reproduction system 100, there remains a real reverberant field which, as already seen in FIG. 6, was very little dependent on the frequency The delay, of the order of 300 ms, is sufficient for this real reverberant field not to be confused with the direct field by the listener, who therefore perceives an enveloping sound but little distorted compared to the direct sound. The rear transducers 107 will then make it possible to create a controlled virtual reverberant field thanks to the adjustable delay.

[0217] The effect of the delay can be seen on the thinner gray curve in FIG. 6 In the case presented here, a second term has been added to the first constant term, so as to obtain a delay of 0.56 s between the signal emitted by the rear transducers and the signal emitted by the corresponding front transducers. We can see that this delay is actually obtained with an entirely satisfactory precision in the range [500 Hz, 5 kHz] corresponding to the maximum sensitivity of the human ear.

[0218] A short delay will be more suitable for reproducing a sound produced by an instrument such as drums, while a long delay will be more suitable for reproducing a sound produced by an organ. A high delay will in particular give a sound that dies out more slowly, and therefore provide a more “enveloping” sound sensation than a low delay.

[0219] In one embodiment, as seen above, a second digital signal processing (DSP) system is dedicated to the rear transducers 107. This second DSP makes it possible to control the sound coloration of the reverberant field, so that it best reproduces that of the chosen room, for example the one where the recording was made.

[0220] For this purpose, various parameters can be adjusted by intervention on the DSP, for example on the technical area 110. The sound coloration can be chosen from the digital parameters supplied to the digital signal processing system. For example, the amplitude and/or the phase of the reverberated wave can be modulated according to the frequency to obtain the desired coloration.

[0221] It is for example possible to predefine one or more sound signatures associated with one or more given rooms at the level of the technical area. In this case, the technical zone contains a memory able to store the parameters characterizing these sound signatures and to transmit them to the DSP controlling the sound coloration of the reverberant field.

[0222] The sound intensity of the reverberant field can also be adjusted at the level of the technical area.

[0223] Adjusting all of these parameters makes it possible to obtain acoustics adapted to the type of sounds listened to by the listener, for example acoustics close to a concert hall for a symphony orchestra, or adapted to a rock music concert, etc.

[0224] The sound reproduction system 100 is thus suitable both for work in a recording studio—such as the editing or mixing of sound documents—and for recreational listening or even for cinemas or video games.

[0225] As a variant, the sound reproduction system 100 can be adapted to listening to sounds obtained by multi-channel mixing. The number of front 105 and rear 107 transducers is then adapted to the number of channels, the relationship between the signals emitted by each front transducer 105 and the corresponding rear transducer 107 being managed in the manner described in the preceding paragraphs.

[0226] In the case of cinema room equipment according to the embodiment represented in FIG. 1, this sound reproduction system 100 allows listening of the same quality regardless of the positioning of the seat in the room, whereas with the sound reproduction systems commonly used, only listeners located in the axis of the sound diffusion system perceive the sounds that were centred on this axis during the mixing as coming from a point on this axis.

[0227] In a particular embodiment, as seen above, the sound reproduction system 100 has neither a base nor a backrest but has side walls 104 and can for example be positioned so as to be used by a standing listener.

[0228] In a particular embodiment, in particular in a noisy environment, such as a public place or an exhibition hall, an upper wall covered with an acoustic insulating material forming a roof over the head of the user can be added to the sound reproduction system so as to further isolate the listener from sounds other than those emitted by the transducers fitted to the system. Depending on the embodiment, this wall can be fixed on the housings 7, a rear wall 111 or even a wall if necessary.

[0229] In a particular embodiment, two additional electroacoustic transducers 108 emitting in the low frequency range (for example between 20 Hz and 500 Hz, or even between 20 Hz and 150 Hz) are placed in the housings 7, approximately as close as possible to the users ears. This close proximity to the listeners ears allows to mask the reverberant field at low frequencies, which is particularly tricky due to the long wavelengths of the corresponding sound waves. It makes it possible to recover the nuances of the low frequencies present in the recording, which are lost if, on the contrary of what is proposed in the invention, the listener is moved away from the source, the loss being all the more important as the source-listener distance increases.

[0230] Since the 108 transducers are dedicated to low frequencies and therefore to long wavelengths, they can be placed closer to the listener than the 105 transducers. Moreover, the location of the source of the low frequencies being of low precision for the listener, the height of the transducers 108 in the boxes 7 is irrelevant for the quality of the listening.

[0231] A DSP is connected to the additional transducers 108, so that each additional transducer 108 receives as input the low frequency components of the audio signal at the input of the front transducer 105 which is located on the same side of the median plane, on which a delay has been applied so that the waves emitted by a given frontal transducer and the additional transducer 108 located on the same side of the listener are perceived in phase at the listening point.

[0232] The signal at the input of each additional transducer 108 is also low-pass filtered, freeing the front transducers of these low frequencies at the crossover frequency. The front transducers 105 then have high-pass filtering forming a symmetrical acoustic target, as defined by the general transfer functions of the Linkwitz-Riley, Bessel, Butterworth type, with acoustic orders which can vary from 2 to 12, for example an order 4.

[0233] Dedicating additional transducers 108 to low frequencies makes it possible to limit the electrical power to be supplied to the front loudspeakers 105 and thus the distortion at the level of the latter, by relegating the lowest frequencies to subwoofers whose Thieles/Small settings are suitable for this purpose.

[0234] The additional transducers 108 can finally have a phase adjustment (traditional stereophony) or a partially or totally inverted phase adjustment between them to benefit from the work of David Gresinger (acoustical society meeting in Vancouver, May 2005).

[0235] In a particular embodiment, an electroacoustic transducer 109 emitting in the infra-bass range, that is to say at frequencies below 20 Hz, is placed in the seat base to complete the sound environment created by the reproduction of sounds 100.

[0236] As with the front transducers, a digital signal processing device to correct the linearity defects of each of the additional 108 and/or sub-bass 109 transducers, as well as an amplification device at the output of the digital processing device can be implemented in a particular embodiment.

[0237] Last, in a particular embodiment, a video screen 201 can be placed facing the listener, through which the user can for example view video content, in particular films or audiovisual recordings of concerts, and/or adjust some of the parameters of the sound reproduction system 100.

REFERENCE SIGNS

[0238] 100: sound reproduction system [0239] 101: seat of a sound reproduction system 100 comprising a seat [0240] 102: seat base of a seat 101 [0241] 103: backrest of a seat 101 [0242] 104: side wall of a sound reproduction system 100 [0243] 105: front loudspeaker [0244] 106: main emission axis of a front loudspeaker 105 [0245] 107: rear loudspeaker [0246] 108: low frequency transducer [0247] 109: infra-bass transducer [0248] 110: technical area [0249] 111: rear wall of a reproduction system 100 [0250] 210: screen [0251] 7: housing [0252] 701: passive resonator