EP4211903A1

EP4211903A1 - System for reproducing sounds with virtualization of the reverberated field

Info

Publication number: EP4211903A1
Application number: EP21773783.2A
Authority: EP
Inventors: Jean-Marc SIOU
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-09-11
Filing date: 2021-09-09
Publication date: 2023-07-19
Also published as: FR3114209B1; FR3114210A1; FR3114209A1; WO2022053588A1; US20230362578A1

Abstract

The system (100) for reproducing sounds comprises at least four electroacoustic transducers, which each receive one audio signal and convert it into an audio 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 in the direction of 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 an audio wave in the direction of 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 themself such that they face the front transducers (105) and have their back to the rear transducers (107).

Description

SOUND REPRODUCTION SYSTEM WITH VIRTUALIZATION OF THE REVERBERE FIELD

FIELD OF THE INVENTION

[1] The present invention relates to sound reproduction systems.

[2] More specifically, the invention relates to a sound reproduction system simulating the phenomenon of reverberation, for example fitted to a seat.

TECHNOLOGICAL BACKGROUND

[3] In a closed environment, such as a concert hall or cinema, sound waves not only propagate in a straight line from their source, but also undergo multiple reflections on the walls, the ceiling and the various objects in between. located in the closed environment. The sound perceived by the listener is therefore the superposition of direct waves, called free field, and reverberated waves, constituting the diffuse field. The listener then has the sensation of being "enveloped" by the sound, which comes to him from multiple directions.

[4] The phenomenon of reverberation is essential in the perception of sound. In particular, it allows the listener to locate the sound scene with good precision. The reverberation on the walls of an interior space thus gives indications on the distance source - listener, but also the distances source-walls or walls-listener.

[5] However, this phenomenon is intimately dependent on the place of listening and can be the source of undesirable acoustic defects and notable differences between the sound as perceived in the room (or place) of recording and the sound as reproduced. It is therefore both desirable and inconvenient because it is difficult to control.

[6] The sounds that are perceived as participating in the reverberation are those that arrive with a sufficient delay on the direct sound, allowing the brain to separate the direct sounds from the reverberant sounds as shown in Figure 5. The delay necessary for the sound is in the reverberation zone depends on the frequency and it is all the more weak as the frequency is high.

[7] For example, a sound with a frequency of the order of 500 Hz resulting from a reflection on an obstacle placed so that its path is elongated by less than 1.8 m compared to the sound coming in a straight line at the The listener will be confused with the latter, whereas he will be perceived as participating in the reverberation phenomenon if his path is extended by a distance greater than 1.8 m. At 60 Hz, up to an elongation of the path of approximately 18 meters, the direct sound and the reflected sound will be confused by the listener, causing significant deformation. The different components of a sound are therefore significantly modified between the emission and the listener by the listening room due to the different obstacles found there, the low frequencies being impacted by obstacles located in a radius around of the source greater than the high frequencies.

[8] In the low frequencies, the waves thus easily find obstacles leading to the creation of stationary waves and an unpleasant comb filtering for the listener, except if one has a listening room of very large volume , with in particular a very high ceiling.

[9] It is possible to overcome the acoustic defects of a room of more common dimensions, but this requires an acoustic study specific to this room and the implementation of expensive acoustic treatments that are too expensive for private use.

[10] In the field of sound reproduction, for example the broadcasting of a stereophonic recording, it is known to use two electroacoustic transducers, such as loudspeakers, placed on either side of the user, facing him or at his side.

[11] The most common loudspeakers have three channels, dedicated respectively to the low, medium and high audible frequencies. The frequency ranges emitted by these three channels overlap two by two, which makes listening at short distance unpleasant due to the phase difference between two signals of the same frequency emitted by two different channels. The perception of this phase shift decreases with the distance from the loudspeakers. Loudspeakers are therefore generally used at a distance of one to several meters and their use at a listening distance of less than one meter is not common practice for those skilled in the art.

[12] The sound perceived by the listener results from the direct emission by the loudspeakers and multiple reflections in the room in which the listening of a recording is made.

[13] If one chooses to limit the phenomenon of reverberation in the listening room as much as possible, for example by means of appropriate acoustic insulation, in the case of such stereophonic listening, the time lag between the sound coming from the left loudspeaker and that of the right loudspeaker can only roughly reconstruct the original spatial scene. [14] Even with multi-channel recording and sound reproduction by a plurality of loudspeakers, the reconstruction of the original soundstage remains imprecise.

[15] The phenomenon of reverberation is necessary for an accurate reconstruction and for the listener to perceive the sound as natural.

[16] However, the phenomenon of reverberation in the listening room is specific to the listening room and is not always controlled or controllable. The sound perceived by the listener is therefore not faithful to the situation that the sound engineer in charge of the mixing would have liked to recreate, and/or the quality of the perceived sound is not controlled.

[17] Finally, the direct and/or reflected waves emitted by the two loudspeakers can interfere with each other. Certain frequencies are therefore significantly amplified or attenuated in the sound received by the listener compared to the original sound, as if a comb filter were applied to the original sound signal.

[18] Such a situation therefore does not allow for high-quality listening. It is therefore necessary for quality listening both to have a reverberation phenomenon and to exercise as precise control as possible of this phenomenon.

[19] If one wishes to overcome the specificities of the listening room, it is possible to carry out binaural listening by means of earphones. The disadvantage of such a simple stereophonic reproduction of sound is that the perceived sound lacks naturalness, spatial depth, since the phenomenon of reverberation is absent and in pure binaural listening, the sounds summed in phase are perceived by the listener as coming from a virtual source above his head.

[20] It is known to use more than two loudspeakers so that the sound reproduced, actually perceived by the listener, is closer to the sound that he would have perceived directly.

[21] Document EP0036337B1 is an example in which at least two pairs of loudspeakers are placed around the listener's head, in the half-space facing the listener and/or in the half-space behind the listener. the listener. The sound emitted by the second pair of electro-acoustic transducers is controlled by an electronic system and the superposition of the sounds emitted by the two pairs of loudspeakers allows the listener to locate the source of the sound at a point in the half-space in front of it or behind it which depends on the values of the input parameters of the electronic system. The device provides the possibility of superimposing waves that simulate natural reverberation, with a delay of 10 to 50 ms with respect to the initial wave, to make the sound thus recreated as realistic as possible. However, the reverberation is simulated by superimposing the signal emitted by the loudspeakers a delayed signal, so that the direct field and the simulated reverberant field are emitted by the same loudspeaker. The perceived sound therefore always lacks naturalness insofar as it is not perceived as enveloping by the listener.

[22] Moreover, in this device, all the loudspeakers are located in the same horizontal plane, which does not make it possible to overcome the comb filtering effect mentioned above.

[23] In addition, the front speakers partially obscure the listener's field of vision. Such a device is therefore not necessarily suitable for equipping a seat in a cinema-type room or for broadcasting a recording for a person observing a visual scene, for example a painting in a museum.

[24] Finally, this system is designed to choose the localization perceived by the listener of the sound source, that is to say so that the listener positions, on the basis of the reproduced sound, the different sound objects of the scene. sound as faithful as possible to the original scene. The reproduction of the spatial aspect of the original sound is therefore optimized, but on the other hand, this system is not optimized so that the reproduced sound is as faithful as possible in all its other aspects to the sound recorded in a room. given recording or to the sound as it would have been perceived in an acoustic room precisely adapted to the sound stage to be reproduced.

[25] Patent application WO 2018/194501 A1 describes a sound reproduction system making it possible to overcome the limitations of conventional stereophonic reproduction - in particular to recreate the depth of the sound scene - by the use of sound processors. digital signal.

[26] The system has at least two loudspeakers, placed respectively to the left and to the right of the listener. A plurality of complementary loudspeakers can be provided and arranged at will in the room, around the listener. The signals supplying the various loudspeakers are calculated by a digital signal processing system from the left and right sound signals (L and R) recorded in stereo. In order to reproduce the acoustics of a room of the listener's choice, for example that of the recording room, different combinations of the L and R signals can be envisaged: sum, difference, application of a gain on the one or the other, of a delay in one or the other, etc.

[27] The frequency spectrum of the delayed signals is controlled to take into account the damping of certain frequencies during reflection on an obstacle and on the path of the wave. In this way, the listener's brain analyzes the superposition of signals emitted by each of the loudspeakers as coming from a single source and with reverberation.

[28] Each loudspeaker simultaneously emits a direct field and a simulated reverberant field. In a device containing two front speakers, the sound is therefore not perceived as enveloping.

[29] In this device, the impact of the position of the listener in relation to the loudspeakers is not taken into account. Typically, the device can be implemented in an audio headset version as well as to equip a room accommodating several listeners. It is therefore clear that such a device does not make it possible to overcome the reverberation of sound by the listening room, nor to obtain identical listening at all points of the room.

[30] Devices of the helmet type, such as the device described by patent US8442244 B1 can be envisaged to overcome this defect. In the latter case, the helmet is acoustically transparent, which does not allow good acoustic insulation of the listener. Headphones can also be a source of discomfort for the listener, especially for prolonged listening.

[31] Seats equipped with sound reproduction systems are also known. Document WO9930532A1 thus discloses a seat equipped with a multi-channel audio system that can be used with a screen to create a “virtual reality” environment, for example for video games. At least one loudspeaker is placed on each side of the user. In addition to these two loudspeakers, a loudspeaker emitting at frequencies below 10 kHz is placed facing the user in the median plane of the seat and an additional high-frequency loudspeaker (> 4 kHz) can be placed behind the listener or above their head to create a reverb effect. The distribution of the electrical signals between the various loudspeakers can be managed by a digital signal processor (Digital Signal Processing or DSP).

[32] However, in the seat described by WO9930532A1, the two front loudspeakers are placed in the seat cushion, so that the ears of the listener are not in the axis or close to the axis output from these speakers. The listener is therefore not in an optimal listening position in relation to the latter. In particular, the sound wave does not reach the listener's frontal lobe before his ears, a necessary condition for a monophonic sound to be perceived as coming from a source in front of the listener's head. [33] In addition, the emission being in the direction of the ceiling, the wave is reflected on it, which gives rise to an unwanted and uncontrolled reverberation phenomenon.

[34] Lastly, the seat does not make it possible to limit the perception by the user of unwanted sound waves coming from the left or the right of the latter, or even of the reflections of the sound waves emitted by the various loudspeakers of the device on obstacles to the left or right of the user. Such a seat is therefore not suitable for equipping a cinema-type room or for sound reproduction that is slightly disturbed by external noise.

[35] The invention thus aims to propose a sound reproduction system making it possible to overcome the acoustic characteristics of the listening room, so as to obtain in particular a sound perceived by the listener as faithful as possible to the scene. sound to be reproduced, the coloring of which depends for example on the recording room in the case of a recording in a concert situation.

SUMMARY OF THE INVENTION

[36] Thus, the invention relates to a sound reproduction system 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 :

- 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,

- 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,

- the four transducers, front and rear, thus form two pairs of transducers symmetrical to each other with respect to said median vertical plane, each pair of transducers comprising a front transducer and a rear transducer,

- the single listener is to be placed face towards the front transducers and back towards the rear transducers. [37] Thanks to this arrangement, the single listener receives signals from the four transducers which can be controlled, the front transducers allowing stereophonic listening and the rear transducers being able to be dedicated to the reproduction of a simulated reverberant field, possibly without fault.

[38] Depending on various aspects, it is possible to provide for one and/or the other of the provisions below.

[39] In a particular embodiment, each of the four transducers is a directive sound source characterized by a main axis of emission secant with the median vertical plane. Moreover, for each of the pairs of transducers, the sound signal emitted by said rear transducer simulates a reverberated field corresponding to the sound signal emitted by said front transducer. In addition, the four transducers are included in a parallelepiped volume with a width of less than 200 cm, a length of less than 200 cm and a height of 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.

[40] Thanks to this arrangement, the listener is placed in a listening position close to the four transducers, making it possible to exploit the psychoacoustic effects so that the perceived sound scene is as faithful as possible to the sound scene which gave rise at check-in. In particular, as the intensity of any existing reverberant field is generally naturally weak, this particular positioning of the rear loudspeakers in a precise area close to the listener makes it possible to ensure that the intensity of the reverberant field in the listening room is lower than that of the reverberant field simulated by the rear loudspeakers in the listening area and that listening to the rear loudspeakers takes place in the near field. Thanks to this choice of positioning the rear loudspeakers, the reverberant field simulated by these loudspeakers masks the reverberant field due to the elements surrounding the audio system. It is then essentially the audio signals from the two rear loudspeakers that will allow the listener to reconstruct the reverberation phenomenon corresponding to the sound scene reproduced by the front loudspeakers relatively independently of the listening room. .

[41] Furthermore, the flawless emission of the direct field and the simulated reverberant field by separate loudspeakers, in front of and behind the listener, provides the listener with a perception of a natural and enveloping sound, although listening is done in the near field. [42] The sound reproduction system is placed so that the ears of the listener in the listening area are not in contact with the sound reproduction system, which is therefore not a traditional headset and allows quality listening, little impacted by parasitic sound sources but without the discomfort associated with wearing headphones.

[43] According to one embodiment, in the sound reproduction system, the greater of the two distances among the distance measured horizontally between the two front transducers and the median plane and the distance measured horizontally between the two rear transducers and the plane mediator, and the distance measured in the front-to-rear direction between the front transducer and the rear transducer of each of said pairs of transducers are in a ratio in a ratio of the order of 0.7.

[44] Thanks to this arrangement, the listening area, corresponding to the area of overlap between the four beams of sound waves from the four transducers occupies a volume in space of the order of that of the head of the 'listener. The inventor has observed that this particular range of spatial configuration of the sound reproduction system gives the listener a particularly natural and enveloping sensation of sound.

[45] According to one embodiment, in the sound reproduction system, the emission axes of the front loudspeakers are secant at a point of intersection of the emission axes of the front loudspeakers, the loudspeakers 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 each of the emission axes of each loudspeaker frontal with the flat front face of this front loudspeaker an isosceles triangle whose equal angles are between 50° and 70°.

[46] The inventor has observed that this particular range of orientations of the loudspeakers of the sound reproduction system gives the listener a particularly natural and enveloping sensation of sound.

[47] In one embodiment, each of the pairs of transducers of the sound reproduction system is integrated in a box comprising one or more recesses in which said front and rear transducers of said pair of transducers are placed, and of which at least part of the walls is covered with an acoustically insulating material. [48] Thanks to this arrangement, the positioning of the two transducers of a pair of transducers relative to each other can be adjusted and the transducers and their positioning are protected from shocks.

[49] In addition, the insulation of at least part of the walls of the compartment makes it possible to partially isolate the listening area from parasitic sound sources and any uncontrolled reverberation phenomena on these walls.

[50] According to one embodiment, each of the boxes of the sound reproduction system is mounted on at least one foot, optionally adjustable in height.

[51] Thanks to this arrangement, a range of possible heights for the positioning of the listening area can be accessed, which depends on the height (heights in the adjustable case) of the stand and the footprint of the system of sound reproduction is reduced.

[52] Thanks to this arrangement, the sound reproduction system can also be linked to a seat, for example on the armrests, a backrest or any other suitable element of the seat. It can also be simply moved on the ground from place to place.

[53] According to one embodiment, the reproduction system 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 box in which one of said pairs of transducers is placed. The rear wall and the side walls constitute a symmetrical assembly with respect to the median vertical plane. The listening area is the empty volume between the side walls at a height higher than the upper edges of the side walls and lower than the upper edge of the rear wall. The front transducers each emit a sound wave in the direction of the listening area in an emission cone entirely intercepted by the head of the listener placed in the listening area and/or by the rear wall and/or by the side walls, and the rear transducers each emit a sound wave in the direction of 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.

[54] Thanks to these arrangements, the listener is placed in a near-field listening situation in relation to the various loudspeakers and the uncontrolled reverberation phenomenon associated with the listening room in which the sound system is located sound reproduction is limited thanks to the different rear and side walls. The listener perceives the direct sound from the various loudspeakers and the reverberant field real is masked by this direct field. It is then possible to recreate using part of the loudspeakers a virtual reverberated field, which will constitute the reverberated field perceived by the listener.

[55] In a particular embodiment, the front transducers of the sound reproduction system are placed at a distance from the listener allowing listening to the direct field of these front transducers, that is to say a distance less than the critical distance for which the intensities of the direct field and the diffuse field are equal.

[56] According to one embodiment, the distance between the listener and said front transducers is less than 1 m.

[57] Such a distance is unusual for positioning loudspeakers in a room when enveloping sound is desired, but it generally allows for the near-field listening which is precisely necessary to obtain the quality reproduction of sounds covered by the invention.

[58] According to one embodiment, at least one of the compartments of a box of the sound reproduction system comprises a device for constraining in a fixed or adjustable manner the orientation of the emission axis of at least one of said transducers.

[59] Thanks to this arrangement, the user or an operator can adjust the orientation of the two transducers of a pair of transducers relative to each other and/or relative to another pair of transducers, in particular for a given listener or to choose the height of the listening area relative to the ground, for example.

[60] According to one embodiment, the sound reproduction system comprises a seat comprising at least one seat, optionally covered at least partially with an acoustic insulating material, so that the listening area is above the seat and that each of the boxes is linked to the seat.

[61] Thanks to this arrangement, the optimal placement of the listener in relation to the listening area is facilitated and listening can be done over long periods of time without excessive fatigue for the listener.

[62] The at least partial acoustic insulation of the seat cushion makes it possible to limit unwanted reverberation phenomena on this seat and to further improve the precision of the reproduction of the sound scene.

[63] According to one embodiment, the seat that comprises the sound reproduction system further comprises armrests, to which the boxes of the sound reproduction system are connected, optionally in a removable manner. [64] Thanks to this arrangement, any seat provided with armrests can be transformed in a reversible manner into a quality audio listening seat according to the invention, without it being necessary to purchase a specific seat for the sound reproduction, the positioning of the boxes on the armrests being naturally optimal for the listener and the armrests participating in the acoustic insulation with respect to parasitic sound sources.

[65] In particular, optional box support installation inserts, placed on the armrests, can allow stable, simple and quick installation on any type of seat and offer height adjustment around the seat. 'listener

[66] According to one embodiment, the seat that includes the sound reproduction system includes at least one additional infrabass transducer placed in the seat cushion.

[67] Thanks to this arrangement, the reproduction of sub-bass frequencies, for which the position of the precise source around the listener does not matter for the localization of the sound stage, can be of good quality.

[68] According to one embodiment, a seat that includes the sound reproduction system includes a backrest forming a rear wall optionally covered with an acoustically insulating material.

[69] Thanks to this arrangement, the listener is better isolated from uncontrolled reverberation phenomena that would reach him from behind.

[70] According to one embodiment, the inclination of the backrest is adjustable and/or the position of the seat is adjustable in depth and/or in height.

[71] Thanks to this arrangement, the placement of the listener in relation to the listening area can be adjusted according to the size of the listener.

[72] According to one embodiment, the boxes of the sound reproduction system are linked, optionally in a removable manner, to a wall of a building forming a rear wall, optionally covered with an acoustic insulating material.

[73] Thanks to this layout, it is possible to form a listening area without the system taking hold of the ground. For example, a listening zone can be formed for a listener placed upright in a museum or elsewhere, or for a listener lying in bed.

[74] Moreover, if the rear wall is insulating, listening is not disturbed by uncontrolled reverberation phenomena towards the rear of the listener or by Interfering sound sources emitting sound waves could propagate and reach the listener directly from behind.

[75] According to one embodiment, the boxes of the sound reproduction system can be folded against a rear wall to which the reproduction system is linked, when these boxes are not used for the reproduction of sounds.

[76] Thanks to this arrangement, the size of the sound reproduction system is reduced when it is not in use.

[77] According to one embodiment, the sound reproduction system further comprises two additional low-frequency transducers placed symmetrically to each other in the boxes.

[78] This arrangement makes it possible to bring the source of the low frequencies as close as possible to the single listener, so that they are perceived as quickly as possible to better mask the reverberated field, which is particularly intense in the low frequencies, since they correspond at high wavelengths.

[79] According to one embodiment, the sound reproduction system comprises an upper wall integral with the boxes extending in a horizontal plane above the head of the user and covered with an acoustic insulating material.

[80] Thanks to this arrangement, listening is not disturbed by uncontrolled reverberation phenomena on the ceiling of the room or by parasitic sound sources emitting sound waves which could propagate and reach the listener through the top of his head.

[81] According to one embodiment, the sound reproduction system comprises at least one signal processing device, such that the audio signal received by the rear transducer of each of said pairs of transducers is generated by means of the processing device signal (DSP, "digital signal processor") from the same audio signal as that from which the audio signal received by said front transducer of said pair of transducers is formed.

[82] Thanks to this arrangement, the sound signals emitted by a front transducer and the rear transducer are linked, which makes it possible to simulate the reverberated field in a controlled manner, that is to say independently of the room in which the sound reproduction system is placed, but dependent on the settings chosen at the DSP level.

[83] According to one embodiment, in the sound reproduction system, the audio signal at the input of the rear transducer of each of the pairs of transducers is behind the audio signal from which the audio signal received by the front transducer of said pair of transducers is formed.

[84] Thanks to this arrangement, the sound signals emitted by the rear transducers simulate a field actually perceived as a reverberated field associated with the free field emitted by the front transducers, and the control of the delay makes it possible to simulate a particular acoustic environment.

[85] According to one embodiment, in the sound reproduction system, the amplitude spectrum and/or the phase spectrum of said audio signal at the input of the rear transducer of each of the pairs of transducers is modified with respect to the corresponding spectrum of the audio signal from which the audio signal received by the front transducer of the same pair of transducers is formed.

[86] Thanks to this arrangement, it is possible to give a particular coloring to the reverberant field simulated by the rear transducers and, for example, to faithfully reproduce the acoustics of a particular recording room.

[87] According to one embodiment, the sound reproduction system comprises a memory storing predefined parameters chosen according to the acoustics of a given room, the parameters being used by the signal processing device for the modification the amplitude spectrum and/or the phase spectrum of the audio signal at the input of the rear transducer of each of the pairs of transducers.

[88] Thanks to this arrangement, acoustic ambiances can be memorized and selected by the user when listening or by an operator when adjusting the system.

[89] According to one embodiment, the sound reproduction system further comprises a second digital signal processing device and the audio signal received by a front loudspeaker is received at the output of the second digital signal processing device.

[90] Thanks to this provision, it is in particular possible to correct any intrinsic defects of the front loudspeakers so that the sound emitted by these loudspeakers is as faithful as possible to the sound that was recorded.

[91] According to one embodiment, the second digital signal processing device is adapted to correct the non-linearity of at least one of the front transducers. [92] According to one embodiment, the front transducers of the sound reproduction system are coaxial with mechanically aligned phase.

[93] The invention also relates to a room equipped with a plurality of sound reproduction systems.

[94] Finally, the invention relates to a box comprising one or more compartments suitable for receiving at least one front transducer and one rear transducer for a sound reproduction system.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[97] [Fig. 2] shows a top view of the sound reproduction system of Figure 1.

[98] [Fig. 3] shows a front view of the sound reproduction system of Figure 1.

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

[100] [Fig. 5] represents in the plane (frequency of a sound signal; delay of the sound reflected on the direct sound) 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. This graph was obtained following studies carried out in an anechoic chamber at the National Audiovisual Institute (INA, France, work by Patrick Thévenot.)

[101] [Fig. 6] represents the measurement of RT60 of a seat equipped with the invention. 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 shows the RT60 reverberation time as a function of the frequency of a study room. 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. [102] [Fig. 7] shows a box comprising compartments in which are placed a set of electro-acoustic transducers.

[103] In the drawings, identical references denote identical or similar objects.

DETAILED DESCRIPTION

[104] The invention therefore relates to a 100 n sound reproduction system 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: 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, 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.

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

[106] The single listener sits facing towards the front transducers and back towards the rear transducers.

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

[108] In addition, for each of the pairs of transducers, the sound signal emitted by said rear transducer 107 simulates a reverberated field corresponding to the sound signal emitted by the front transducer 105.

[109] In addition, the single listener is placed in a listening position close to the four transducers, without the reproduction system directly touching the listener's ears as in usual headphones: at. the four transducers are included in a parallelepipedic volume with a width of less than 200 cm, a length of less than 200 cm and a height of less than 200 cm. 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.

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

[111] 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 area of Listening, it is essentially the audio signals from the two rear loudspeakers that will allow the listener to reconstruct the reverberation phenomenon corresponding to the sound scene reproduced by the front loudspeakers. The simulated reverberant field masks any reverberant field due to elements surrounding the audio system.

[112] The transducers form an approximately symmetrical assembly with respect to a mediating 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 towards the front transducers 105, his back towards 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.

[113] The concept of symmetry here means the precision of adjustment and placement. 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 mediating plane.

[114] 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: at. the placement is done naturally close to the ideal position without being constrained by rigid positioning elements which would make use of the device uncomfortable. b. The head of the ideally placed listener intercepts most of the beams emitted by the four transducers, so that listening is not degraded by reflections of these undesirable 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.

[115] Depending on the directivity of the beams, it is possible that some of the sound beams are not intercepted by the listener's head. But it is understood 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.

[116] 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 planar front face on the emission side and the intersection point of the emission axes of the front loudspeakers forms with the intersection points of the emission axes with the planar front faces of the two front loudspeakers a isosceles triangle whose equal angles are between 50° and 70°.

[117] 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 .

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

[119] 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.

[120] The box 7 further comprises all the electrical and electronic components necessary for the operation of the electroacoustic transducers. [121] One of the boxes 7 (or both boxes 7) may include a technical area 110 allowing the mechanical and/or acoustic adjustments of the sound reproduction system 100 to be made.

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

[123] 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 at the place where the reproduction system is placed.

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

[125] A system for blocking the orientation of the loudspeakers after adjustment can be provided. Thanks to this arrangement, a preset can be made by an operator, for example when mounting the loudspeakers on the box, or even during the installation of the sound reproduction system 100 in a given place, and this adjustment cannot be modified only by voluntary release of the blocking system.

[126] 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 plane mediator, 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.

[127] The distances d1, d2, d3 are defined in relation to the center(s) of the membrane(s) of the loudspeaker(s) concerned.

[128] 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.

[129] In this way, the listening area is placed in an ideal manner with respect to the front loudspeakers to obtain listening that is little disturbed by the environment of the sound reproduction device 100. [130] The position of the listener's 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 transaurality.

[131] The advantage of the sound reproduction device is that it leaves the listener some latitude in positioning while maintaining a pleasant listening experience.

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

[133] It is possible to equip the box 7 with one or more feet. In this way, the sound reproduction system 100 can be easily moved from one place to another if the stand is not attached to any other object than the cabinet. The sound reproduction system 100 can thus also be placed at a certain height from the ground. 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.

[134] Furthermore, the footprint of the sound reproduction system 100 on the ground is reduced.

[135] This arrangement makes it possible, for example, to create, from 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.

[136] The choice of the height of the leg(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 stand of height adapted to the desired use.

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

[138] If, on the contrary, the sound reproduction system 100 is intended for a specific location near a wall or a wall, the boxes 7 can in another embodiment be linked to this wall or this wall, [139] This arrangement makes it possible not to totally or partially prevent the movement or positioning of objects or people at ground level due to the influence of the sound reproduction system 100.

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

[141] The 7 subwoofers 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.

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

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

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

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

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

[147] In a particular embodiment, the reproduction system 100 is adapted specifically to the seated position. It then comprises, as shown in Figure 1 a seat 101 comprising a seat 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 equivalent median plane.

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

[149] Alternatively, the side walls 104 are armrests of a seat on which are placed two boxes 7, optionally provided with feet. [150] In this way, a seat that a listener already has can be equipped, at lower cost and possibly reversibly, with two boxes 7 so as to constitute a reproduction system 100.

[151] In particular, optional box support installation inserts, placed on the armrests, can allow stable, simple and quick installation on any type of seat and offer height adjustment around the seat. 'listener.

[152] Whatever the embodiment, the pairs of transducers are symmetrical to each other. As seen previously, the notion of symmetry is understood here 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. 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.

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

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

[155] The dimensions of the seat 102, the backrest 103 and the side walls 104 are fixed so that the head and the neck of the majority of the users for whom the seat is intended are located in a so-called zone of listening, 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 listener's head.

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

[157] The distances d1, d2, d3 are defined from the center of the loudspeaker membrane. [158] 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.

[159] The foams that make up the seat 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.

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

[161] 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 reproduction of sounds 100.

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

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

[164] In the embodiment of Figure 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 boxes 7, in front of the rear wall 111.

[165] The shape of the recesses can help guide the sound wave emitted by the transducers in the desired direction.

[166] 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.

[167] Mechanically phase-aligned coaxial loudspeakers exhibit very high precision phase alignment between the two paths at the transmit level. Such loudspeakers are therefore close to a single point source.

[168] In the embodiment depicted in Figure 1, the listener is typically within one meter of the sources. This unusual listening position has the second advantage of allowing near-field listening, to mask the reverberated field.

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

[170] The front 105 and rear 107 transducers typically emit at least in the frequency range [100 Hz; 20kHz],

[171] 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 point of measurement and the source point. The proximity of the listener to the transducers makes it possible to obtain satisfactory listening with a lower sound intensity emitted than when the listener is at a more usual listening distance (a few meters) from the loudspeakers, since the The sound intensity decreases as the distance from the source increases.

[172] The placement of the front transducers 105 in the front part of the side walls 104 of the embodiment of FIG. 1, therefore under the user's head and in front of his trunk, allows the user to be out of the zone in which the waves emitted by the two frontal 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 that we are trying to reproduce. This modality can be implemented in other embodiments.

[173] 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 apex of the source point and containing at least part of the user's head. [174] In particular embodiments, the two front loudspeakers 105 are oriented so that their emission axes intersect at the level of the listener's frontal lobe, close to his vertical median plane.

[175] 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 included between about 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 it and not above it.

[176] The frequencies best analyzed by the human brain are those located 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 seat.

[177] When the front transducers 105 are placed in the side walls 104 of a seat or in boxes 7 placed so as to respect the constraints on the distances d1, d2 and d3 mentioned above, they are at a distance of l 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.

[178] Figure 6 shows the influence of the sound reproduction system 100 according to the embodiment of Figure 1 with activation of only the front transducers 105. It is noted that, with respect to the listener located at a given point of The room of measurement, the phenomenon of reverberation 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). In the absence of a 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 reverberation phenomenon exists but is not very dependent on the frequency, so it 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.

[179] Near-field listening has the additional 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.

[180] 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.

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

[182] 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.

[183] 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 seats. contiguous: the user of a given seat will practically 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.

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

[185] 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 whose purpose is to correct the non-linearity of the front transducers

[186] 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.

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

[188] At the level of the front transducers 105, the frequency response of which 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 direct field reproduced as faithfully as possible to the recorded sound signal.

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

[190] In the embodiment shown in Figure 1, at least two other rear electroacoustic transducers 107 are placed in or above the upper part of the rear wall 111, approximately at the height of the user's ears, either side of the user, so that they are symmetrical to each other with respect to the median plane of the seat.

[191] The rear transducers are oriented so that the emission axis of each of these transducers passes close to the ear of the user who is on the same side of the median plane of the seat as the transducer. [192] These two transducers 107 emit sound signals whose frequencies are typically included at least in the range [100 Hz; 20kHz],

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

[194] 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 as it of the median plane of the seat.

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

[196] 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 the front and rear transducers.

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

[198] 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 cushion 101.

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

[200] The electrical signal to be supplied at the input of the rear transducers 107 is calculated from the electrical signal supplied at the input of the front transducers 105, so as to create a virtual reverberation effect. [201] In particular, the electrical signal at the input of each rear transducer 107 lags behind the electrical signal at the input of the front transducer 105 from which it is calculated.

[202] The delay is the sum of two terms:

- the first term is constant and fixed by 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. 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;

- the second term can be adjusted by the user or an operator using a potentiometer, for example. The delay can for example be set between in the range ]0s, 5s], the range [0.3s; 0.7 s] giving a satisfactory perception for most sound scenes.

[203] The influence of the second term will be understood using figure 6. 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 a function almost frequency constant for frequencies above 100 Hz. It is of the order of 0.3 s for the seat tested in the test room.

[204] The reverberant field generally depends on the geometric and acoustic characteristics of the listening room. The sound reproduction system 100 on the contrary makes it possible to obtain a reverberated 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 reverberated field which, as we have already seen in FIG. 6, was very little dependent on the frequency. The time lag, of the order of 300 ms, is sufficient for this real reverberated 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.

[205] The effect of the delay can be visualized on the gray and thinner curve of figure 6. In the case presented here, a second term was summed 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. It can be seen 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.

[206] 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, therefore a more “enveloping” sound sensation than a low delay.

[207] 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 reverberated field, so that it reproduces the better that of the chosen room, for example the one where the recording was made.

[208] For this, various parameters are adjustable by intervention on the DSP, for example on the technical area 110. The sound coloring 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.

[209] 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 coloring of the reverberated field.

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

[211] Adjusting all of these parameters makes it possible to obtain an acoustic adapted to the type of sounds heard by the listener, for example an acoustic close to a hall for a symphony orchestra, or adapted to a rock music concert , ....

[212] 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 movie theaters or of video games.

[213] 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.

[214] In the case of equipment for movie theaters according to the embodiment shown in Figure 1, this sound reproduction system 100 allows listening of identical quality regardless of the positioning of the seat in the room, so that with currently used sound reproduction systems, only listeners located in the axis of the sound diffusion system perceive the sounds centered on this axis in the mix as coming from a point on this axis.

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

[216] 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 above 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. This wall can, depending on the chosen embodiment, be fixed on the boxes 7, a rear wall 111 or even a wall if necessary.

[217] 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 boxes 7, approximately at the closer to the user's ears. This close proximity to the listener's ears allows masking of 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 find 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, and loss all the more important as the source-listener distance increases.

[218] The transducers 108 being dedicated to low frequencies and therefore to long wavelengths, they can be placed closer to the listener than the transducers 105. Furthermore, the localization 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 listening. [219] A DSP is connected to the additional transducers 108, so that each additional transducer 108 each receives as input the low frequency components of the audio signal as input from the front transducer 105 which is located on the same side of the median plane as it, on which a delay has been applied so that the waves emitted by a given front transducer and the additional transducer 108 located on the same side of the listener are perceived in phase at the listening point.

[220] 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.

[221] 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 returning the lowest frequencies to subwoofers ("subwoofers"). ”) whose Thieles / Small settings are suitable for this purpose.

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

[223] In a particular embodiment, an electroacoustic transducer 109 emitting in the infrabass range, that is to say at frequencies below 20 Hz, is placed in the seat to complete the sound environment created by the sound reproduction device 100.

[224] As for the front transducers, a digital signal processing stage to correct the linearity defects of each of the additional 108 and/or sub-bass 109 transducers, as well as an amplification stage at the output of the stage digital signal processing can be implemented in a particular embodiment. These stages always have the purpose of obtaining a reproduced sound that is as faithful as possible to the sound that was used for the recording to be reproduced.

[225] Finally, 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.

[226] REFERENCES

100: sound reproduction system

101: seat of a sound reproduction system 100 comprising a seat

102: seat cushion 101

103: seat back 101

104: side wall of a reproductive system 100

105: front speaker

106: main emission axis of a front loudspeaker 105

107: rear speaker

108: low frequency transducer

109: sub-bass transducer

110: technical area

111: rear wall of a reproduction system 100

210: screen

7: box

701: passive resonator

Claims

33 CLAIMS

1. 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, characterized in that: two of the said four transducers , said front transducers (105), 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, two of said four transducers, said rear transducers (107), are placed symmetrically to each other with respect to said median vertical plane and oriented so as to each emit a sound wave in the direction of the listening area, the four front transducers (107) and (105) thus forming two pairs of transducers symmetrical to each other with respect to the median vertical plane, each pair of transducers comprising a front transducer (105) and a rear transducer e (107), the single listener being placed facing towards the front transducers (105) and back towards the rear transducers (107).

2. Sound reproduction system (100) according to claim 1, characterized in that: each of the four transducers is a directional sound source characterized by a main emission axis secant with said median vertical plane, for each of said pairs of transducers, the sound signal emitted by said rear transducer (107) simulates a reverberated field corresponding to said sound signal emitted by the front transducer (105), the four transducers are included in a parallelepipedic volume of width less than 200 cm, of length less than 200 cm and of 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.

3. Sound reproduction system (100) according to claim 2 characterized in that said emission axes of the front loudspeakers (107) intersect at a point of intersection of the emission axes of the front loudspeakers ( 107), in that the front loudspeakers (107) 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 loudspeakers 34 front loudspeakers form 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 whose equal angles are between 50° and 70°.

4. Sound reproduction system according to claim 2 or claim 3 characterized in that each of said pairs of transducers is integrated in a box (7) comprising one or more recesses in which the front (105) and rear ( 107) of the pair of transducers are placed, and of which at least part of the walls is covered with an acoustically insulating material.

5. Sound reproduction system (100) according to claim 4 characterized in that each of said boxes (7) is mounted on at least one foot, optionally adjustable in height.

6. Sound reproduction system (100) according to claim 1 characterized in that it further comprises: a rear wall (111), and two side walls (104), extending in depth in front of the rear wall (111) and in height to a height lower than that of the upper edge of the rear wall (111), and each comprising at least one recess so that the walls (104) each form a box (7) in which a pairs of transducers is placed, the rear wall (111) and the side walls (104) constituting a symmetrical assembly with respect to said median vertical plane, the listening zone corresponding to the empty volume being between the side walls (104) at a height higher than that of the upper edges of the side walls (104) and lower than that of the upper edge of the rear wall (111), the front transducers (105) each emitting a sound wave in the direction of the listening area in a fully intercepted emission cone ted by the listener's head placed in the listening area and/or by the rear wall (111) and/or by the side walls (104), and the rear transducers (107) each emitting a sound wave in the direction of the listening area in an emission cone completely intercepted by the head of the listener placed in the listening area and/or by the side walls (104).

7. Sound reproduction system (100) according to any one of claims 5 or 6 characterized in that the front transducers (105) are placed at a distance from the listener allowing listening to the direct field of these frontal transducers (105), that is to say a distance less than the critical distance for which the intensities of the direct field and of the diffuse field are equal.

8. Sound reproduction system (100) according to any one of claims 4 to 7 characterized in that at least one of the boxes (7) comprises a device for constraining in a fixed or adjustable manner the orientation of the axis transmission of at least one of said four transducers.

9. Sound reproduction system (100) according to any one of claims 4 to 8 characterized in that it comprises a seat (101) comprising at least one seat (102), optionally covered at least partially with a material sound insulation, so that the listening area is above said seat (102) and each of the boxes (7) is linked to said seat (101).

10. Sound reproduction system (100) according to claim 9 characterized in that the seat (101) further comprises armrests to which the boxes (7) are connected, optionally in a removable manner.

11. Sound reproduction system (100) according to any one of claims 9 and 10 characterized in that it comprises at least one additional infra-bass transducer (109) placed in the seat (102) of the seat (101).

12. Sound reproduction system (100) according to one of claims 9 to 11 characterized in that the seat (101) further comprises a backrest (103) forming a rear wall optionally covered with an acoustically insulating material.

13. Sound reproduction system (100) according to claim 12 characterized in that the inclination of said backrest (103) is adjustable and/or in that the position of the seat (102) is adjustable in depth and/or in height.

14. Sound reproduction system (100) according to claim 4 characterized in that the boxes (7) are linked, optionally in a removable manner, to a wall of a building forming a rear wall (111), optionally covered with an acoustically insulating material.

15. Sound reproduction system (100) according to claim 14 characterized in that the boxes (7) can also be folded down against the rear wall (111) when they are not used for the reproduction of sounds.

16. Sound reproduction system (100) according to any one of claims 4 to 15 characterized in that it further comprises two additional low-frequency transducers (108) placed symmetrically to each other in the boxes ( 7).

17. Sound reproduction system according to any one of claims 4 to 16 characterized in that it comprises an upper wall integral boxes (7) extending in a horizontal plane above the head of the user and covered with an acoustic insulating material.

18. Sound reproduction system (100) according to any one of claims 1 to 17 characterized in that the distance between the single listener and the front transducers (105) is less than 1 m.

19. Sound reproduction system (100) according to any one of claims 1 to 18 characterized in that it comprises at least one signal processing device, so that the audio signal received by the rear transducer (107) of each of the pairs of transducers is generated by means of the at least one signal processing device from the same audio signal from which the audio signal received by the front transducer (105) of the pair of transducers is formed .

20. Sound reproduction system (100) according to claim 19 characterized in that the audio signal at the input of the rear transducer (107) of each of the pairs of transducers is late on the audio signal from which the audio signal is formed. received by the front transducer (105) of the pair of transducers.

21. Sound reproduction system (100) according to any one of claims 19 and 20 characterized in that the amplitude spectrum and/or the phase spectrum of the audio signal at the input of the rear transducer (107) of each of the pairs of transducers is modified with respect to the corresponding spectrum of the audio signal from which the audio signal received by the front transducer (105) of the pair of transducers is formed.

22. Sound reproduction system (100) according to claim 21 characterized in that it comprises a memory storing predefined parameters chosen according to the acoustics of a given room, said parameters being used by the at least a signal processing device for modifying the amplitude spectrum and/or the phase spectrum of said audio signal at the input of said rear transducer (107) of each of the pairs of transducers.

23. Sound reproduction system (100) according to any one of claims 19 to 22 characterized in that it further comprises a second digital signal processing device and that the audio signal received by a front loudspeaker ( 105) is received at the output of the second digital signal processing device.

24. Sound reproduction system (100) according to claim 23, characterized in that the second digital signal processing device is adapted to correct the non-linearity of at least one of the front transducers (105). 37

25. Sound reproduction system (100) according to any one of claims 1 to 24 characterized in that the front transducers (105) are coaxial with mechanically aligned phase.

26. Room equipped with a plurality of sound reproduction systems (100) according to any one of claims 1 to 25.

27. Box (7) comprising one or more compartments suitable for receiving at least the front transducer (105) and the rear transducer (107) of one of the pairs of transducers of a sound reproduction system according to any one of claims 4 to 25.