Low-profile loudspeaker

Abstract

An acoustic enclosure (7) comprising an acoustic box (10), two first loudspeakers (21b, 21c) arranged to reproduce medium and high frequencies, and a second loudspeaker (22) arranged to reproduce low frequencies, the first two loudspeakers being positioned at the front, on each side of the box, being oriented outwards, so that for each first loudspeaker, an angle between an axis of a membrane (23b, 23c) of said first loudspeaker and a front-rear axis of the box is between 30° and 50°, a ratio between a distance between centers of the membranes of the first loudspeakers, and a height (h) of the box, being greater than 5, and a ratio between a diameter of the membrane of each first loudspeaker and the height of the box being greater than 0.4. FIGURE OF THE ABSTRACT: Fig.1

Description

Title of the invention: Low-height acoustic enclosure

[0001] The invention relates to the field of loudspeakers and, in particular, loudspeakers integrated into decoder boxes.

[0002] BACKGROUND OF THE INVENTION

[0003] A decoder box (or STB, for Set-Top Box) is, very traditionally, intended to be connected to a television via an HDMI cable (for High Definition Multimedia Interface).

[0004] The decoder box acquires an incoming stream, which is for example an audiovisual stream. The incoming stream may be an external incoming stream coming from an external source: local network, satellite, cable, DVB-T (for Digital Video Broadcasting-Terrestrial), xDSL (for Digital Subscriber Line), etc. The incoming stream may also be an internal incoming stream coming from a source internal to the decoder box, for example from a hard disk of the HDD type (for Hard Disk Drive).

[0005] The decoder box extracts an audio stream and a video stream from the audiovisual stream, and transmits the video stream and the audio stream to the television. The television plays the video stream via its screen, and plays the audio stream via its speakers.

[0006] The audio stream can also be transmitted to external equipment: sound bar, connected speaker, etc.

[0007] It is envisaged to equip a decoder box with an acoustic enclosure comprising an acoustic box and loudspeakers integrated into the acoustic box. The decoder box is thus capable of reproducing the audio stream and implementing sound spatialization effects.

[0008] The decoder box is generally positioned close to the television, for example next to it or in a piece of furniture on which the television is placed. The precise position of the decoder box relative to the user is therefore not known a priori.

[0009] Furthermore, the size of the decoder box must be limited so that it can be installed without difficulty by the user.

[0010] The random positioning of the decoder box relative to the user, as well as the limitation of its volume, clearly limit the acoustic performance of the decoder box as well as the good rendering of the spatialization effects of the sound.

[0011] SUBJECT OF THE INVENTION

[0012] The object of the invention is to improve the sound reproduction of an acoustic enclosure, and to improve the sound spatialization implemented via the acoustic enclosure, said enclosure being able to be integrated into a decoder box. Summary of the invention

[0013] In order to achieve this aim, an acoustic enclosure is proposed, comprising an acoustic box in which are integrated at least two first loudspeakers arranged to reproduce medium and high frequencies, and a second loudspeaker arranged to reproduce low frequencies, the first two loudspeakers being positioned at the front and on each side of the acoustic box, and each being oriented towards the outside of the acoustic box, so that for each first loudspeaker, an angle between a central axis of a membrane of said first loudspeaker and a front-rear axis of the acoustic box is between 30° and 50°, a central axis of a membrane of the second loudspeaker being a vertical axis, a ratio between a distance between centers of the membranes of the first loudspeakers, and a height of the acoustic box, being greater than 5,and a ratio between a diameter of the membrane of each first loudspeaker and the height of the acoustic box being greater than 0.4.,

[0014] The reduced height of the box allows, when the acoustic enclosure is integrated into a decoder box, to reduce the height of the decoder box. The decoder box can thus be positioned in front of the television and therefore in front of the user.

[0015] Furthermore, the relatively large dimensions of the first loudspeakers improve their low frequency reproduction capacity. It is therefore possible to increase the frequency range over which the spatialization effects are applied, without risking degrading the audio reproduction when mixing the low frequency components of the spatialized channels.

[0016] These characteristics, to which are added the significant spacing between the first loudspeakers, as well as their orientation, make it possible to significantly improve the sound spatialization effects.

[0017] In addition, the large spacing between the first loudspeakers makes it possible to maintain a large internal volume of the acoustic enclosure, despite its reduced height, which, again, improves the acoustic performance of the acoustic enclosure.

[0018] We further propose an acoustic enclosure as previously described, in which:

[0019] - for each first loudspeaker, the angle between the central axis of the membrane of said first loudspeaker and the front-rear axis of the acoustic box is included in the interval [38°; 42°];

[0020] - the distance between the centers of the membranes of the first loudspeakers is included in the interval [320 mm; 380 mm];

[0021] - the height of the acoustic box is within the interval [50 mm; 60 mm];

[0022] - the diameter of the membrane of each first loudspeaker is included in the interval [24 mm; 30 mm].

[0023] We further propose an acoustic enclosure as previously described, the acoustic box comprising an upper piece and a lower piece defined according to the height of the acoustic box.

[0024] We further propose an acoustic enclosure as previously described, the membrane of the second loudspeaker being fixed to a lower face of the lower part of the acoustic box and opening into an opening formed in said lower face.

[0025] There is further provided an acoustic enclosure as previously described, in which the lower part of the acoustic box comprises an inclined lateral portion, which extends from said opening, so that a width of the lower face of the lower part of the acoustic box is less, at the level of the inclined lateral portion, than a width of an upper edge of the lower part which is opposite said lower face, the inclined lateral portion making it possible to facilitate a flow of air set in motion by the membrane of the second loudspeaker.

[0026] There is further provided an acoustic enclosure as previously described, in which an inner wall of an upper face of the upper part comprises first ribs forming a first pattern, and in which an inner wall of the lower face of the lower part comprises second ribs forming a second pattern, which is different from the first pattern.

[0027] There is further provided an acoustic enclosure as previously described, in which, when the acoustic box is assembled, a minimum distance between a top of the first ribs and a top of the second ribs is between 3 mm and 5 mm.

[0028] There is further provided an acoustic enclosure as previously described, in which one of the lower edges of the upper part or upper edge of the lower part comprises a rib extending around a circumference of said edge, and the other of the lower edges of the upper part or upper edge of the lower part comprises a groove extending around a circumference of said edge, a seal being positioned in the groove and being compressed by the rib when the acoustic enclosure is assembled.

[0029] We also propose a decoder box, integrating an acoustic enclosure as previously described.

[0030] A decoder box is further proposed as previously described, comprising a main electronic card comprising a decoding module and an audio module, the second loudspeaker and the main electronic card being positioned next to each other and extending successively along a length of the decoder box which is perpendicular to the front-rear axis.

[0031] We further propose a decoder box as previously described, in which the main electronic card is positioned, outside the acoustic box, in a receiving cavity defined in a recess formed in an external wall of a lower face of the lower part of the acoustic box.

[0032] A decoder box as previously described is further provided, comprising an acoustic enclosure as previously described, further comprising a lower cover which comprises a lower face and a rear lateral face, the lower face comprising first holes facing the membrane of the second loudspeaker, the rear lateral face comprising second holes facing the inclined lateral portion.

[0033] A decoder box as previously described is further provided, in which the first holes and the second holes form a honeycomb structure.

[0034] A decoder box is further provided as previously described, comprising a vertical wall, which is formed in an external wall of the lower face of the lower part of the acoustic box, which extends along a width of the lower part, and which thus physically separates the membrane of the second loudspeaker from the main electronic card.

[0035] The invention will be better understood in light of the following description of a particular non-limiting embodiment of the invention. Brief description of the drawings

[0036] Reference will be made to the accompanying drawings, among which:

[0037] [Fig-1] [Fig. 1] is an exploded and perspective view of the decoder box;

[0038] [Fig.2] [Fig.2] is a top view of the acoustic enclosure;

[0039] [Fig.3] [Fig.3] is a graph comprising loudspeaker reproduction level curves as a function of frequency;

[0040] [Fig.4] [Fig.4] is a perspective view of a first loudspeaker;

[0041] [Fig.5] [Fig.5] represents two front views of the decoder box, in which only some components are represented;

[0042] [Fig.6] [Fig.6] is a bottom and perspective view of the acoustic enclosure;

[0043] [Fig.7] [Fig.7] is a graph comprising frequency response curves of a loudspeaker depending on the acoustic volume of the enclosure;

[0044] [Fig.8] [Fig.8] represents a partial view of the lower cover, from below and in perspective, as well as an enlargement of the honeycomb structure;

[0045] [Fig.9] [Fig.9] represents a view of the internal wall of the lower face of the lower part of the box, and a view of the internal wall of the upper face of the upper part of the box;

[0046] [Fig. 10] [Fig. 10] is a sectional view of a groove and a rib formed on the edges of the upper and lower pieces of the box. DETAILED DESCRIPTION OF THE INVENTION

[0047] With reference to figures 1 and 2, the decoder box 1 is designed to implement the “classic” functions of a decoder box, which notably include the extraction, decoding and processing of the components of an audio-video input stream, and the transmission of said components to a television and possibly to other equipment (speakers for example).

[0048] The decoder box 1 is also designed to shape and restore audio signals, and to implement sound spatialization effects. The decoder box 1 can also implement a voice assistance method.

[0049] The decoder box 1 is intended to be placed on a support, so that its lower face 2 rests on said support.

[0050] The nominal operating position of the decoder box 1, allowing sound reproduction to be optimized, is a position in which the decoder box 1 is located in front of the television, so that its front face 3 is positioned in front of the user when the user is installed to watch a program on the television.

[0051] Here, all position terms, such as front, rear, top, bottom, left, right, etc., are interpreted by considering that the decoder box 1 is in its nominal operating position, and is seen from the front (as if seen by the user).

[0052] The decoder box 1 comprises an upper cover 4, a lower cover 5, a side support 6, an acoustic enclosure 7, a main electronic card 8 and a secondary electronic card 9 comprising microphones.

[0053] The main electronic card 8 comprises in particular a decoding module, which implements the decoding function, a communication module, arranged in particular to transmit audio and video streams to the equipment to which the decoder box 1 is connected, an audio module, and a power supply module, which provides power supply voltages and currents to these modules. The audio module is connected to the loudspeakers of the acoustic enclosure 7 of the decoder box 1 and comprises in particular amplifiers.

[0054] As will be seen below, the main electronic card 8 is mounted parallel to and close to the lower cover 5, and the secondary electronic card 9 is mounted parallel to and close to the upper cover 4 of the decoder box 1.

[0055] A fabric (not shown) covers the lateral support 6 by being fixed to it.

[0056] The acoustic enclosure 7 comprises an acoustic box 10 and loudspeakers integrated into the acoustic box.

[0057] The acoustic box 10 comprises two parts: an upper part 10a and a lower part 10b, which are defined in the height of the acoustic box 10. These two parts are assembled together during the manufacture of the acoustic enclosure 7.

[0058] The acoustic box 10 comprises an upper face 11 (which is the upper face of the upper part 10a), a lower face 12 (which is the lower face of the lower part 10b), a front face 14, a rear face 15, and side faces. The side faces comprise a left front side face 16, a left rear side face 17, a right front side face 18, and a right rear side face 19.

[0059] The loudspeakers comprise first loudspeakers 21, here three first loudspeakers 21a, 21b, 21c, and a second loudspeaker 22.

[0060] Each first loudspeaker 21 is a “midrange” loudspeaker, also called medium or medial. The design of the first loudspeakers 21 is therefore optimized for the reproduction of medium frequencies and high frequencies (frequencies between, for example, 500 Hz and 5 kHz).

[0061] The second loudspeaker 22 is a bass loudspeaker, also called a “boomer” or “woofer”. The design of the second loudspeaker 22 is therefore optimized for the reproduction of low frequencies (frequencies between, for example, 50 Hz and 500 Hz).

[0062] The first loudspeaker 21a is fixed to a central portion of the front face 14 of the box 10. Its membrane 23a opens into an opening made in said front face 14.

[0063] The first loudspeaker 21b is fixed to the front left side face 16 of the box 10. Its membrane 23b opens into an opening made in said front left side face 16.

[0064] The first loudspeaker 21c is fixed to the right front lateral face 18 of the box 10. Its membrane 23c opens into an opening made in said right front lateral face 18.

[0065] The second loudspeaker 22 is fixed to the lower face 12 of the box 10. Its membrane 24 opens into an opening made in said lower face 12.

[0066] The first two loudspeakers 21b and 21c are therefore positioned at the front and on each side of the box 10, and are each oriented towards the outside of the box 10, so that for each first loudspeaker 21b, 21c, an angle 0 between a central axis XI of a membrane of said first loudspeaker and a front-rear axis Y of the box 10 is between 30° and 50°.

[0067] Here, for each first loudspeaker 21b, 21c, the angle 0 between the central axis XI of the membrane of said first loudspeaker and the front-rear axis Y of the box 10 is preferably included in the interval [38°; 42°], and is advantageously equal to 40°.

[0068] It is noted that here, the membranes of the loudspeakers 21, 22 are pieces of revolution which each extend around an axis of revolution. The central axis of each membrane is its axis of revolution.

[0069] However, the membranes are not necessarily parts of revolution and can have, for example, when viewed in section along a plane P, an elliptical shape or a rounded rectangular shape. In this case, the central axis is the axis which passes through the center of said shape while being perpendicular to said plane P.

[0070] By “front-rear axis” is meant here an axis perpendicular to the front face 14 and to the rear face 15 of the box 10 and passing through the center of these faces.

[0071] The central axis XI of the membrane 23a of the first loudspeaker 21a is parallel to the front-rear axis Y (here coincident).

[0072] The central axes of the membranes of the first loudspeakers 21 are horizontal axes. The central axis X2 of the membrane 24 of the second loudspeaker 22 is a vertical axis.

[0073] The length L of the box 10 is clearly greater than its height h. The ratio between the distance d between the centers of the membranes 23b, 23c of the first loudspeakers 21b, 21c, and the height h of the box 10, is greater than 5 (by greater, we mean greater or equal).

[0074] By "center of a membrane" is meant the center of the membrane at its greatest circumference.

[0075] Here, the distance d between the centers of the membranes 23b, 23c of the first loudspeakers 21b, 21c is included in the interval [320 mm; 380 mm], and is advantageously equal to 350 mm.

[0076] The total length L of the acoustic box 10 is within the range [350 mm; 410 mm], and is advantageously equal to 380 mm.

[0077] The height h of the acoustic box 10 is included in the interval [50 mm; 60 mm], and is advantageously equal to 55 mm.

[0078] The height h' of the decoder box 1 is included in the interval [55 mm; 65 mm], and is advantageously equal to 60 mm.

[0079] The low height of the box 10, and therefore of the decoder box 1, proves advantageous for the following reason.

[0080] It has been found that a very large majority of televisions are designed so that, when a decoder box 1 of this height is positioned in front of the television, the decoder box 1 does not mask the image being reproduced at all. The decoder box 1 can therefore be positioned in front of the television and therefore in front of the user, which makes it possible to optimize the rendering of the spatialization effects of the sound.

[0081] The relatively large distance between the first loudspeakers 21b, 21c is also very advantageous.

[0082] Sound spatialization is the ability of an audio system to produce a three-dimensional sound field that gives the impression that sounds are coming from different positions in space. When the speakers are spaced a specific distance apart, this allows for a more realistic and accurate sound field to be reproduced, while that an unsuitable spacing can alter this spatialization.

[0083] When we listen to music or any other audio content, our brain uses the differences in arrival time and sound intensity between our two ears to locate sound sources in space. If the speakers are too close, these differences are insufficient and our brain cannot process spatial information correctly, resulting in a loss of precision and realism.

[0084] Conversely, if the speakers are too far apart, the spatialization may seem artificial or confusing, because the sound will take longer to reach the listener from each speaker, which can affect the perception of the direction of the sound sources. In addition, inappropriate spacing can also cause interference between the signals emitted by the speakers, producing unwanted distortion and coloration effects.

[0085] Thus, the spacing of the loudspeakers has an impact on the quality of the sound spatialization, because it can alter the precision, realism and clarity of the three-dimensional sound field, as well as the perception of the sound sources in space. To obtain optimal spatialization, it is therefore important to choose a spacing adapted to the listening room and the configuration of the loudspeakers: an example of an optimal configuration can be side loudspeakers spaced less than twice the average spacing of our ears, and placed more than two meters from the side walls of the room.

[0086] The dimensions of the acoustic box 10 and the spacing between the first loudspeakers 21b, 21c are therefore defined to optimize the sound reproduction.

[0087] The orientation of the first loudspeakers 21b, 21c, relative to the front-rear axis Y of the box 10, is very advantageous compared to a more conventional orientation of 90°.

[0088] If the loudspeakers are positioned so as to project the sound directly towards the listener's ears, this can improve spatialization at the central focus point, because the sound arrives directly at the place where it is supposed to be heard. On the other hand, when the listener deviates from this ideal listening zone, the spatialization is significantly degraded, making the multi-loudspeaker sound source equivalent to a monophonic point source.

[0089] The projection angle is the angle between the axis of the loudspeaker and the place where the sound is directed. This is an important factor that can affect the quality of sound spatialization. Indeed, the perception of the position of sound sources in space depends on how the sound is projected in the listening room, as well as on the location of the loudspeakers. If the loudspeakers are oriented in such a way as to project the sound towards walls or ceilings with reverberant characteristics (average absorption coefficient a < 0.5), this will produce reflections and echoes. Common spatialization algorithms (notably those of Dolby or DTS, or others audio software development companies) use these effects to widen the soundstage.

[0090] Furthermore, if the speakers are placed too close to the listener and aimed directly at them, the soundstage may appear narrow and confined. On the other hand, if the speakers are placed further away and aimed to create a wider angle, the soundstage may appear more spacious and immersive.

[0091] The sound projection angle is therefore a key element that has a significant impact on the quality of sound spatialization. The chosen orientation, 40° relative to the front-rear Y axis, is appropriate and optimal for obtaining precise and realistic spatialization, as well as a wide and immersive sound scene.

[0092] In the box 10, the second loudspeaker 22 is dedicated to the reproduction of the low-frequency components of the audio. The second loudspeaker 22 is connected to a dedicated audio output of the audio module implemented on the main electronic card 8.

[0093] The low frequency audio signal on this dedicated audio output is defined as follows.

[0094] In the case where the audio module receives a stereo input signal as input, this low-frequency audio signal is defined by the resultant of the extraction of the low frequencies from the other channels up to a frequency defined by the acoustic capabilities of the loudspeakers. This frequency is called: extraction frequency of the low-frequency components.

[0095] In the case of a multichannel input signal comprising an LFE channel (for Low Frequency Effects; this is a signal with frequencies typically lower than 120 Hz), the low-frequency audio signal is defined by mixing the LFE channel and the resultant of the extraction of the low frequencies from the other channels up to a frequency defined by the acoustic capabilities of the loudspeakers. This frequency is called: maximum extraction frequency of the low-frequency components.

[0096] Sound spatialization processes require applying delays and phase shifts to the different audio channels (essentially Left and Right) in our case. However, mixing together the low-frequency components of spatialized channels to a dedicated audio output (connected to the second loudspeaker 22) will significantly degrade the audio reproduction. Thus, in the worst case scenario of Left and Right channels in phase opposition, the resulting signal would be zero.

[0097] It is therefore necessary to spatialize the channels from a frequency higher than the extraction frequency of the low frequency components.

[0098] Nevertheless, in order to benefit from the best possible spatialization, it is necessary to allow the spatialization effects to be applied over the widest possible frequency range and therefore to use the lowest possible bass extraction frequency. low possible.

[0099] The value of this frequency of extraction of the low frequency components is determined by the characteristics of the loudspeakers associated with each of the channels. A thorough study of these is necessary.

[0100] In [Fig.3] we see curve C1 representing, as a function of frequency, the restitution level of a small left-hand loudspeaker (midrange). Curve C2 is an equivalent curve for a larger left-hand loudspeaker. Curve C3 is an equivalent curve for a small right-hand loudspeaker (midrange). Curve C4 is an equivalent curve for a larger right-hand loudspeaker. Curve C5 is an equivalent curve for a small central loudspeaker. Curve C6 is an equivalent curve for a larger central loudspeaker (midrange). Curve C7 is an equivalent curve for a small low-frequency loudspeaker. Curve C8 is an equivalent curve for a larger low-frequency loudspeaker.

[0101] In this example, the configuration with small loudspeakers (thick line curves) induces a low-frequency component extraction frequency of 475 Hz. The configuration with larger loudspeakers (thin line curves) induces a low-frequency component extraction frequency of 350 Hz. In the first case, the spatialization effects can be reproduced, without risk of loss, from 475 Hz. In the second case, the spatialization effects can be reproduced, without risk of loss, from 350 Hz. We can therefore see the advantage of having loudspeakers whose membranes have a relatively large size.

[0102] In the acoustic box 10, the ratio between the diameter D of the membrane 23 of each first loudspeaker 21 and the height h of the box 10 is greater than 0.4 (by greater, we mean greater than or equal).

[0103] It is noted that, if the membrane is not circular, the term "diameter" means the largest dimension of the shape of the membrane seen in section along the plane P perpendicular to the central axis (i.e. for example the length of the major axis of the ellipse or the length of the rounded rectangle).

[0104] Here, with reference to [Fig.4], the diameter D of the membrane 23 of each first loudspeaker 21 is included in the interval [24 mm; 30 mm], and is advantageously equal to 27 mm.

[0105] This relatively large diameter makes it possible to increase the extraction frequency of the low-frequency components. The Thiele & Small parameters are a set of electromechanical parameters that define the low-frequency performance of a loudspeaker. Among these quantities, the resonant frequency is the frequency at which the loudspeaker naturally resonates when it is in open circuit, that is, without being mounted in an enclosure. Since the loudspeaker can be considered a mass-spring system, the resonant frequency of a loudspeaker is determined by the moving mass (usually a cone or dome) and the stiffness of the suspension that holds the moving mass in place. According to the formula F = (1 / (2. ir)).'V(k / m), the larger the membrane, and therefore the larger the moving mass "m", the lower the resonant frequency will be. This means that the speaker is more efficient at reproducing low frequencies, because it can move a greater amount of air at lower frequencies.

[0106] However, it is important to note that the quality of low frequency reproduction does not depend solely on the size of the loudspeaker. Other factors, such as the enclosure design, the material of the loudspeaker membrane and the quality of the magnetic circuit can also have a significant impact on the low frequency performance. All these aspects have been taken into account in the design of the product considered in this description, in particular the use of full-range loudspeakers having a cut-off frequency around 250 Hz.

[0107] With reference to figures 5 and 6, the second loudspeaker 22 and the main electronic card 8 are positioned next to each other and extending successively along a length L' of the decoder box 1 which is perpendicular to the front-rear axis Y. The second loudspeaker 22 is located to the left of the main electronic card 8.

[0108] The second loudspeaker 22 and the main electronic card 8 are therefore not one above the other but one next to the other, which makes it possible to reduce the height of the decoder box 1.

[0109] The spacing between the first loudspeakers 21b, 21c makes this arrangement possible.

[0110] The main electronic card 8 is positioned in a receiving cavity 30, which is located in a recess formed in the external wall of the lower face 12 of the lower part 10b of the acoustic box 10. The main electronic card 8 is fixed to the lower part 10b of the acoustic box 10 while being positioned outside of the latter.

[0111] A vertical wall 31 is formed in the external wall of the lower face 12 of the lower part 10b of the acoustic box 10. This wall 31 extends along the width 1 of the acoustic box 10 and thus physically separates the membrane 24 from the second loudspeaker 22 and the main electronic card 8. The cables 34 which connect the main electronic card 8 to the loudspeakers are distinguished by passing through the wall 31 via a sealed connection.

[0112] The wall 31 makes it possible to isolate the second loudspeaker 22 from the receiving cavity 30 of the acoustic box 10 reserved for the main electronic card 8. This avoids the formation of standing waves, resulting from the movement of the membrane 24 of the second loudspeaker 22, in the receiving cavity 30.

[0113] The spacing of the first loudspeakers 21b, 21c makes it possible, despite the reduced height of the decoder box 1 and therefore of the acoustic box 10, to obtain a very substantial acoustic volume dedicated to the second loudspeaker.

[0114] This volume is here equal to 1 L.

[0115] An acoustic enclosure is essentially a box that contains one or more loudspeakers. Each loudspeaker produces a front sound wave that propagates outside the acoustic enclosure, and a rear sound wave that remains in the enclosure. Thus, the greater the volume of air at the rear of the loudspeaker, the lower the limitation of the deflection of the membrane of said loudspeaker. However, since the reproduction of low frequencies requires more air displacement than that of the midrange and treble, the internal volume of the enclosure and the level of reproduction of low frequencies are directly correlated. A large internal volume of the enclosure will make it possible to produce more powerful low frequencies.

[0116] What has just been said is illustrated with reference to [Fig.7].

[0117] The frequency response of the same loudspeaker was simulated in an enclosure with an internal volume equal to a quarter of a liter (curve C9), half a liter (curve CIO), one liter (curve Cl 1) and two liters (curve Cl2).

[0118] It is therefore clearly seen that the cut-off frequency in the bass is inversely proportional to the volume of the speaker 7.

[0119] It can be seen in [Fig.6] that the lower part 10b of the acoustic box 10 comprises an inclined lateral portion 32, which extends from the opening formed in the lower face 12 of the acoustic box 10, into which the membrane 24 of the second loudspeaker 22 opens. Due to this inclined lateral portion 32, the width of the lower face 12 of the lower part 10b of the acoustic box 10 is less, at the level of the inclined lateral portion 32, than the width of the upper edge 33 of the lower part 10b of the acoustic box 10 which is opposite said lower face 12.

[0120] The inclined lateral portion 32 facilitates a flow of air set in motion by the membrane 24 of the second loudspeaker 22. This maximizes the open surface by taking advantage not only of the lower face 2 of the decoder box 1, but also of its rear face.

[0121] It is noted that all the outer edges of the acoustic box 10 are radiated, again to facilitate the flow of air.

[0122] The arrangement of the second loudspeaker 22 and the main electronic card 8 makes it possible to position the secondary electronic card 9 so that the microphones 35 are offset, along the length of the housing 1, relative to the second loudspeaker 22. The microphones 35 are located outside a cylindrical “virtual” volume having as its longitudinal axis the central axis X2 of the membrane 24 of the second loudspeaker speaker 22, and for diameter the diameter of said membrane 24.

[0123] The sensitive cells of the microphones 35 are in acoustic communication with the exterior of the decoder box 1 via holes made in the upper cover 4 of the decoder box 1, while the membrane 24 of the second loudspeaker 22 opens into an opening formed in the lower face 12 of the acoustic box 10, and therefore at the level of the lower cover 5 of the decoder box 1.

[0124] The surface comprising the microphones 35 and the second loudspeaker 22 are therefore completely decorrelated: the elements are not in the same axis, and the output of the second loudspeaker 22 is on the opposite plane (lower surface of the decoder box 1). As a result, the noise pollution, captured by the microphones 35 and induced by the second loudspeaker 22, is greatly reduced.

[0125] Furthermore, the main electronic card 8 and the second loudspeaker 22 are each very little impacted by the thermal releases of the other. In addition, the two faces of the main electronic card 8 now face inert surfaces that can serve as heat sinks.

[0126] The lower cover 5 of the decoder box 1 is here made of a material which has high thermal conductivity. This material is for example a metallic material. The lower cover 5 is here made of cast aluminum.

[0127] If the lower cover 5 were made of plastic, it would be necessary to add a dissipation sheet under the main electronic card 8. Here, this sheet is not necessary: ​​the material used to manufacture the lower cover 5 therefore makes it possible to reduce the height of the decoder box 1.

[0128] In addition, the lower aluminum cover 5 is more rigid than a plastic cover, which makes it possible to reduce the overall flexibility of the assembled product and thus to limit the risks of rub&buzz, which are parasitic vibration noises created by two rigid parts colliding when the system is vibrated by the speakers.

[0129] With reference to [Fig.8], the lower face 2 of the lower cover 5 of the decoder box 1 is that of the decoder box 1. The lower cover 5 further comprises a rear lateral face 36. The lower face 2 comprises first holes 37 facing the membrane 24 of the second loudspeaker 22. The rear lateral face 36 comprises second holes 38 facing the inclined lateral portion.

[0130] The first holes 37 and the second holes 38 form a honeycomb structure.

[0131] This allows for optimal sound diffusion in the low frequencies and avoids any risk of whistling linked to an open surface that is too small in relation to the second loudspeaker 22. The structure of juxtaposition of hexagonal holes makes it possible to maximize the opening rate, compared to a repetition of round or square holes.

[0132] The first holes 37 and the second holes 38 are delimited by edges 39 (formed on the surface of the lower cover 5). Each edge 39 is beveled. The addition of these bevels helps to promote air flow.

[0133] As seen, almost all the electronics of the decoder box 1 are located on a single electronic board (the main electronic board 8), which is located outside the acoustic box 10. The acoustic box 10 is therefore simple to assemble and easy to test individually.

[0134] In addition, static interconnections between several cards, which are expensive and generate electromagnetic disturbances, are avoided. Static inter-module connections also constitute a sensitive point of mechanical reliability in the event of the product being dropped. This problem is not found in the decoder box 1.

[0135] The decoder box 1 further comprises capacitors (not shown), which are electrolytic capacitors which have a large volume.

[0136] These electrolytic capacitors are connected to the audio module of the main electronic card 8 and contribute to the power supply function of the audio electrical components of the decoder box 1.

[0137] These capacitors have been moved inside the acoustic box 10 in order to optimize the acoustic volume available for the second loudspeaker 22.

[0138] Indeed, if these capacitors had been mounted on the main electronic card 8, it would have been necessary to remove the acoustic enclosure 10 opposite these components to avoid interference. More volume would therefore have been lost because the plastic wall would have been added to the volume of the components themselves. The high internal volume of the acoustic enclosure, allowing the capacitors to be positioned there, also has the advantage of having a local energy reserve, reducing the complexity of the external power supply unit, and reducing large remote current draws, resulting in a reduction of electromagnetic emissions.

[0139] With reference to [Fig.9], the internal wall of the upper face 11 of the upper part 10a of the acoustic box 10 is provided with a network of first ribs 4L. Similarly, the internal wall of the lower face 12 of the lower part 10b of the acoustic box 10 is provided with a network of second ribs 42.

[0140] The ribs 41, 42 extend vertically from the internal walls, and connect the fixing points 43 of these two parts 10a, 10b.

[0141] The ribs 41, 42 make it possible to limit the deformations of the box linked to the variations in internal pressure created by the movement of the loudspeaker membranes and by the vibrations generated by the latter.

[0142] The first ribs 41 form a first pattern. The second ribs 42 form a second pattern, which is different from the first pattern. This makes it possible to avoid the formation of partitions, inside the box 10, which would hinder the air flows.

[0143] The height of the ribs is a very important parameter to prevent bending of the parts, because it counts to the power of 3.

[0144] The height of the ribs 41, 42 has therefore been maximized in both parts.

[0145] The ribs 41, 42 are however designed so as to maintain a certain minimum distance between the top of the first ribs 41 of the upper part 10a and the top of the ribs 42 of the lower part 10b of the acoustic box 10 when the latter is assembled.

[0146] This minimum distance is here between 3 mm and 5 mm, and is for example equal to 4 mm.

[0147] This space makes it possible to avoid the whistling effects which would have been created by the movement of air through the fine slits thus created.

[0148] With reference to [Fig. 10], the acoustic box 10 comprises a seal 44 between the two parts 10a, 10b. The seal 44 is positioned on the internal periphery of the box 10 (between the two parts 10a, 10b) making it possible to maintain a closed acoustic volume.

[0149] Given the large size of the parts constituting the acoustic box 10, the manufacturing tolerances using the plastic injection process are large, of the order of + / - 1 mm.

[0150] A seal 44 made of circular cross-section elastomer is used. This solution is easily industrializable and without loss of material during manufacturing (unlike, for example, a flat foam seal, the cutting of which generates a lot of material loss).

[0151] One of the lower edges 48 of the upper part 10a or upper edge 33 of the lower part 10b comprises a rib 46 extending along the entire circumference of said edge, and the other of the lower edges of the upper part or upper edge of the lower part comprises a groove 47 extending along the entire circumference of said edge.

[0152] Here, the rib 46 extends over the upper edge 33 of the lower part 10b and the groove 47 extends over the lower edge 48 of the upper part 10a.

[0153] It would be possible to reverse this configuration: the groove 47 would then be formed on the periphery of the lower part 10b, and the rib 46 on the periphery of the upper part 10a.

[0154] The groove 47, when viewed in section along a plane perpendicular to the periphery, comprises a semi-circular shaped bottom and two vertical walls which extend from the opening of the groove 47 to the bottom.

[0155] The seal 44 is placed in the groove 47. The rib 46 compresses the seal 44 during the assembly and fixing between them of the upper part 10a and the lower part 10b (by screwing via the fixing points 43 for example).

[0156] The maximum width of the groove 47, i.e. the distance between the walls vertical, is between 2 and 4 times the width of the rib 46.

[0157] A significant clearance is therefore left between the crushing rib 46 and the side walls of the groove 47 to absorb dimensional dispersions.

[0158] Returning to [Fig.l], we note that the front face 3 of the acoustic box 10 has a recess 50 allowing it to accommodate, in addition to the status LEDs and the infrared receiver, a camera module.

[0159] The decoder box 1 further comprises a certain number of radiofrequency antennas, connected to radiofrequency modules of the communication module of the main electronic card 8. These antennas comprise an antenna 52 positioned on the upper cover 4 of the decoder box 1, and surrounds the control interface 53 (buttons) of the decoder box 1 and the microphones 35. These antennas also comprise antennas 54, 55 and 56, located respectively on the front face 14, the left rear side face 17, and the right rear side face 19 of the box 10. These antennas, due to the significant length of the box 10 and the decoder box 1, benefit from good physical separation even when they share the same frequencies.

[0160] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

Claims

Claims

1. An acoustic enclosure (7), comprising an acoustic box (10) in which are integrated at least two first loudspeakers (21b, 21c) arranged to reproduce medium and high frequencies, and a second loudspeaker (22) arranged to reproduce low frequencies, the two first loudspeakers (21b, 21c) being positioned at the front and on each side of the acoustic box, and each being oriented towards the outside of the acoustic box, so that for each first loudspeaker, an angle (0) between a central axis (X1) of a membrane (23b, 23c) of said first loudspeaker and a front-rear axis (Y) of the acoustic box is between 30° and 50°, a central axis (X2) of a membrane (24) of the second loudspeaker (22) being a vertical axis, a ratio between a distance (d) between centers of the membranes of the first speakers, and a height (h) of the acoustic box, being greater than 5,and a ratio between a diameter (D) of the membrane of each first loudspeaker and the height of the acoustic box being greater than 0.4.,

2. An acoustic enclosure according to claim 1, wherein: - for each first loudspeaker (21b, 21c), the angle (0) between the central axis (XI) of the membrane of said first loudspeaker and the front-rear axis (Y) of the acoustic box is within the interval [38°; 42°]; - the distance (d) between the centers of the membranes of the first loudspeakers is within the interval [320 mm; 380 mm]; - the height (h) of the acoustic box (10) is within the interval [50 mm; 60 mm]; - the diameter (D) of the membrane of each first loudspeaker is within the interval [24 mm; 30 mm].

3. Acoustic enclosure according to one of the preceding claims, the acoustic box (10) comprising an upper part (10a) and a lower part (10b) defined according to the height (h) of the acoustic box.

4. Acoustic enclosure according to claim 3, the membrane (24) of the second loudspeaker (22) being fixed to a lower face (12) of the lower part (10b) of the acoustic box and opening into an opening formed in said lower face.

5. An acoustic enclosure according to claim 4, wherein the in- lower (10b) of the acoustic box (10) comprises an inclined lateral portion (32), which extends from said opening, so that a width of the lower face (12) of the lower part of the acoustic box is less, at the level of the inclined lateral portion, than a width of an upper edge (33) of the lower part (10b) which is opposite said lower face, the inclined lateral portion making it possible to facilitate a flow of air set in motion by the membrane (24) of the second loudspeaker (22).

6. Acoustic enclosure according to one of claims 3 to 5, in which an internal wall of an upper face (11) of the upper part (10a) comprises first ribs (41) forming a first pattern, and in which an internal wall of the lower face (12) of the lower part (10b) comprises second ribs (42) forming a second pattern, which is different from the first pattern.

7. An acoustic enclosure according to claim 6, wherein, when the acoustic box is assembled, a minimum distance between a top of the first ribs (41) and a top of the second ribs (42) is between 3 mm and 5 mm.

8. An acoustic enclosure according to one of claims 3 to 7, wherein one of the lower edges (48) of the upper part (10a) or upper edge (33) of the lower part (10b) comprises a rib (46) extending around a circumference of said edge, and the other of the lower edges of the upper part or upper edge of the lower part comprises a groove (47) extending around a circumference of said edge, a sealing gasket (44) being positioned in the groove and being compressed by the rib (46) when the acoustic enclosure is assembled.

9. Decoder box (1), integrating an acoustic enclosure (7) according to one of the preceding claims.

10. Decoder box according to claim 9, comprising a main electronic card (8) comprising a decoding module and an audio module, the second speaker (22) and the main electronic card (8) being positioned next to each other and extending successively along a length (L') of the decoder box (1) which is perpendicular to the front-rear axis.

11. Decoder box according to claim 10, in which the main electronic card (8) is positioned, outside the acoustic box (10), in a reception cavity (30) defined in a recess formed in an external wall of a lower face (12) of the lower part (10b) of the acoustic box.

12. Decoder box according to one of claims 9 to 11, comprising an acoustic enclosure (7) according to claim 5, further comprising a lower cover (5) which comprises a lower face (12) and a rear lateral face (36), the lower face comprising first holes (37) facing the membrane (24) of the second loudspeaker (22), the rear lateral face (36) comprising second holes (38) facing the inclined lateral portion (32).

13. The set-top box of claim 12, wherein the first holes and the second holes form a honeycomb structure.

14. Decoder box according to one of claims 10 to 13, comprising a vertical wall (31), which is formed in an external wall of the lower face (12) of the lower part (10b) of the acoustic box (10), which extends along a width of the lower part, and which thus physically separates the membrane of the second loudspeaker (22) from the main electronic card (8).

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