Acoustic deflector shielding
A shielding cover with a curved surface diffuses acoustic waves to reduce vibrations and resonance, improving sound quality in compact audio equipment with integrated loudspeakers and electronic components.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- SAGEMCOM BROADBAND SAS
- Filing Date
- 2024-12-16
- Publication Date
- 2026-06-19
AI Technical Summary
Compact audio equipment with integrated loudspeakers and electronic components face issues of parasitic vibrations and acoustic resonance due to the proximity of the loudspeaker diaphragm and shielding cover, leading to sound distortion and vibrations.
A shielding cover with a specifically designed curved surface to diffract acoustic waves and dissipate airflow, reducing unwanted vibrations and acoustic resonance by diffusing sound effectively.
The solution effectively reduces parasitic vibrations and improves sound quality by minimizing sound distortion and resonance, enhancing the acoustic performance of compact audio equipment.
Smart Images
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Abstract
Description
Title of the invention: Acoustic deflecting shield
[0001] The invention relates to the field of audio equipment integrating both one or more electronic components requiring electromagnetic shielding, and one or more loudspeakers.
[0002] BACKGROUND OF THE INVENTION
[0003] Some equipment integrates both electronic components enabling the implementation of complex functions, and an audio device comprising one or more loudspeakers.
[0004] This is for example the case of certain set-top boxes (or STBs) which integrate speakers and which, in addition to performing their "classic" functions (acquisition of an audio-video stream, decoding, broadcasting of the stream, etc.), reproduce at least partially the audio stream.
[0005] Such an "advanced" decoder box includes electronic processing components that must be protected against electromagnetic interference and therefore require electromagnetic shielding. However, this type of equipment is relatively compact, and the integration of the electronic components, shielding devices, and loudspeakers proves to be relatively complicated.
[0006] Such a decoder box 1 is shown in figures 1 to 4.
[0007] The outer casing of the decoder box 1 includes a top cover 2 defining The upper face of the decoder box 1. The decoder box 1 includes an electronic board 3, here the motherboard, which comprises a printed circuit board 4 on which electronic components are mounted. The printed circuit board 4 is attached to the upper cover 2 by screws at its four corners. Among the electronic components are electronic components 5 which are protected by an electromagnetic shielding device 6.
[0008] The shielding device 6 is formed for example of a shielding belt 7 mounted on the electronic board 3, and a shielding cover 8 inserted by force around the belt 7. These shielding elements are for example made of sheet metal folded all around, embossed and cut, 0.2 mm thick.
[0009] The decoder box 1 also includes a loudspeaker 10 integrated into an acoustic enclosure 11, itself integrated into the decoder box 1. This loudspeaker 10 is a woofer which, due to the very limited space available, is located close to the shielding device 6. The shielding cover 8 has a flat outer face located opposite and very close to the diaphragm 12 of the loudspeaker 10, and therefore parallel to the sound wave generated by the loudspeaker 10. The air then escapes mainly through the sides and rear of the decoder box 1, as indicated by the arrows in figures 1 and 2.
[0010] This configuration poses the following problems.
[0011] The energy generated by the movement of the diaphragm 12 of the loudspeaker 10 produces undesirable vibrations of the subassembly comprising the electronic board 3 and the shielding cover 8. In addition, as the shielding cover 8 is located just above the loudspeaker 10, the latter can also vibrate independently against the shielding belt 7.
[0012] Furthermore, the mechanical architecture of the decoder box 1 results in the presence of a cavity around the loudspeaker 10 with many parallel planes between the acoustic box 11 and the upper cover 2. This particular configuration therefore generates a phenomenon of acoustic resonance and creation of standing waves between the loudspeaker 10 and the electronic board 3.
[0013] This phenomenon is clearly visible in the graph in [Fig. 5]. The frequency response C1 of the loudspeaker 10, when it is integrated into its acoustic enclosure 11 and the enclosure 11 is assembled with the upper cover 2, has a pronounced peak 14 at approximately 1 kHz. Conversely, it can be seen that the frequency response C2 of the loudspeaker 10 does not include this peak at 1 kHz when the enclosure 11 is not assembled with the upper cover 2.
[0014] The configuration of the loudspeaker 10 and the shielding cover 8 which has just been described can therefore lead to a diffusion of sound which is not homogeneous and which can be polluted by phenomena of distortion (Total Harmony Distortion) and vibrations (Rub&Buzz).
[0015] OBJECT
[0016] The invention aims to limit parasitic vibration phenomena in audio equipment integrating at least one loudspeaker and at least one electronic component protected by a shielding cover.
[0017] SUMMARY
[0018] For the purpose of achieving this goal, an audio equipment is proposed comprising:
[0019] - a printed circuit board on which at least one electronic component is mounted;
[0020] - a loudspeaker comprising a diaphragm;
[0021] - a shielding cover arranged to protect at least one electronic component electromagnetic interference, the shielding cover having an external face positioned opposite the speaker diaphragm;
[0022] the outer face comprising at least one curved surface extending from a central part of the outer face towards a contour of the outer face, the shielding cover being thus arranged to diffract acoustic waves produced by the upper membrane speaker in operation in such a way as to reduce unwanted vibrations of the printed circuit board and the shielding cover.
[0023] The specific shape of the shielding cover allows the incident acoustic energy produced by the movement of the loudspeaker diaphragm to be diffused, and thus the airflow generated by the loudspeaker to be dissipated more effectively. The shielding cover therefore fulfills a dual function. On the one hand, it protects the electronic components from electromagnetic interference, and on the other hand, it limits, or even eliminates, unwanted vibrations, thereby improving the sound quality of the audio equipment. The invention is particularly advantageous in compact audio equipment where the loudspeaker is positioned very close to the shielding cover.
[0024] We further propose an audio equipment as previously described, in which a central axis of the shielding cover, passing through a center of the external face, coincides with a central axis of the loudspeaker.
[0025] We further propose an audio equipment as previously described, in which a free space extending between, on the one hand, the diaphragm and a dust cap of the loudspeaker, and on the other hand, the shielding cover, has a substantially constant height h.
[0026] We further propose an audio device as previously described, in which the diaphragm is a circular diaphragm and in which the height h is such that:
[0027] h=D,
[0028] where is a diameter of the membrane.
[0029] An audio system as previously described is also proposed, in which the outer face of the shielding cover comprises:
[0030] - a frustoconical surface, comprising a concavity extending into the interior of the frustoconical surface;
[0031] - a ridge that extends at least over a certain length of the contour of the face external ;
[0032] and in which the speaker diaphragm extends opposite the frustoconical surface, a speaker dust cap extends opposite the concavity, and a speaker suspension extends at least partially into a channel defined between the rim and the frustoconical surface.
[0033] Audio equipment as previously described is further proposed, in which the bead extends over only part of the length of the contour of the external face, so that said channel comprises two ends and allows an airflow displaced by the speaker diaphragm to flow through these two ends.
[0034] Audio equipment as previously described is further proposed, wherein the outer face of the shielding cover, when viewed in cross-section along a plane passing through the central axis of the armored hood, a parabolic shape at the level of the bulge.
[0035] Audio equipment as previously described is further proposed, wherein the shielding cover includes, at at least one end of the channel, an extension which prolongs the bead and which at least partially covers another component mounted on the printed circuit board.
[0036] An audio equipment as previously described is further proposed, in which the shielding cover is fixed to a shielding belt mounted on the printed circuit board and surrounding at least one electronic component, the shielding cover having an inner face in which an internal cavity is formed, the shielding cover extending on either side of the shielding belt which is positioned in the internal cavity.
[0037] Audio equipment is also proposed as previously described, the audio equipment being a decoder box.
[0038] The invention will be better understood in the light of the following description of particular, non-limiting embodiments of the invention. Brief description of the drawings
[0039] Reference will be made to the attached drawings, among which:
[0040] [Fig-1] [Fig.1] represents a perspective and top view of a subset of a decoder box from the prior art;
[0041] [Fig.2] [Fig.2] represents a perspective, side and cross-sectional view along a transverse plane of the decoder housing subassembly;
[0042] [Fig.3] [Fig.3] shows a view from below of the upper cover and the electronic board, when the shielding cover is not mounted on the shielding belt;
[0043] [Fig.4] [Fig.4] is a similar view to [Fig.3], while the hood is mounted on the armor belt;
[0044] [Fig.5] [Fig.5] is a graph representing frequency response curves of the loudspeaker in the acoustic enclosure, assembled and unassembled with the top cover;
[0045] [Fig.6] [Fig.6] represents a schematic, cross-sectional view of a sub-assembly of a decoder box comprising a top cover, an electronic board, a shielding cover according to a first embodiment, and an acoustic box integrating a loudspeaker;
[0046] [Fig.7] [Fig.7] is a figure similar to [Fig.4], with an armored hood according to a second embodiment;
[0047] [Fig.8] [Fig.8] is a figure similar to [Fig.7], but with a side view;
[0048] [Fig.9] [Fig.9] is a perspective and cross-sectional view along a transverse plane, of the "Returned" subset of the decoder box;
[0049] [Fig. 10] the [Fig. 10] represents a Helmholtz resonator;
[0050] [Fig. 11] [Fig. 11] is a graph representing displacement curves of the subassembly comprising the upper cover and the electronic board, with a conventional shielding cover and with the shielding cover according to the second embodiment;
[0051] [Fig. 12] [Fig. 12] is a graph representing frequency response curves 10 cm behind the acoustic box, the latter being integrated with a conventional shielding cover and with the shielding cover according to the second embodiment. DETAILED DESCRIPTION
[0052] With reference to [Fig.6], the decoder box 20 comprises a top cover 21, an electronic board 22 including a printed circuit board 23 and at least one electronic component 24 mounted on the printed circuit board 23, a shielding device 25, and an acoustic enclosure 26 incorporating a loudspeaker 27.
[0053] The printed circuit board 23 is fixed to an inner face 28 of the upper cover 21 by screwing, and extends parallel to it.
[0054] The electronic component 24 is mounted on an inner face 29 of the printed circuit board 23.
[0055] The shielding device 25 protects the electronic component 24 from electromagnetic interference generated by other components of the decoder box 20.
[0056] The shielding device 25 comprises a shielding belt 30 and a shielding cover 31 according to a first embodiment. The shielding belt 30 is attached to the printed circuit board 23 and extends around the electronic component 24. The shielding belt 30 is in direct contact with a ground plane of the electronic board 22 over its entire circumference.
[0057] The armored cover 31 is formed from a single piece of folded sheet metal. The armored cover 31 comprises an outer face 32, an inner face 33, and a peripheral portion 34.
[0058] The outer face 32 and the inner face 33 are surfaces of revolution around a central axis XI of the armored cover 31. The peripheral portion 34, cylindrical in shape having the central axis XI as its axis, extends from the contour of the inner face 33 of the armored cover 31.
[0059] The peripheral portion 34 is pressed around the armor belt 30 to fix the armor cover 31 to the armor belt 30 and thus to the electronic board 22. The peripheral portion 34 is then positioned against the belt of shielding 30 and outside the surface 36 of the electronic card 22 delimited by the belt 30, in which the component 24 is located.
[0060] The outer face 32 of the shielding cover 31 includes at least one curved surface 37 extending from a central part 38 of the outer face 32 towards the contour 39 of the outer face 32, the shielding cover 31 being thus arranged to diffract acoustic waves produced by the loudspeaker 27 in operation so as to reduce unwanted vibrations of the printed circuit 23 and the shielding cover 31.
[0061] Here, the central part 38 of the outer face 32 forms a peak whose apex is at the center 41 of the outer face 32. The outer face 32 comprises a first curved surface 37a and a second curved surface 37b which extend successively in a radial direction from the peak towards the contour 39 of the outer face 32. The first curved surface 37a and the second curved surface 37b are also surfaces of revolution about the central axis XI of the armored cover 31.
[0062] The first curved surface 37a is a concave surface and the second curved surface 37b is a convex surface.
[0063] The loudspeaker 27, for its part, conventionally comprises a diaphragm 43, a core 44, a dust cap 45, a chassis 46, and a suspension 47 which allows the diaphragm 43 to be attached to the chassis 46. The loudspeaker 27 is here a woofer (W oofef). A woofer is a loudspeaker that reproduces low frequencies, for example between 100 Hz and 2 kHz. Here, the loudspeaker 27 has a crossover frequency of 300 Hz.
[0064] Membrane 43 is here a circular membrane.
[0065] Here, the central axis XI of the shielding cover 31, passing through the center 41 of the outer face 32, and the central axis X2 of the loudspeaker 27, coincide. By "concurred," it is meant that they are actually coincident, or that the distance separating them is very small.
[0066] We thus have, advantageously:
[0067] a <D,
[0068] where d is the distance between the two central axes XI, X2 and D is the diameter of the membrane 43.
[0069] The inner face 33 of the armored cover 31 is a flat surface. The armored cover 31 is thickened, that is to say that the thickness e of the armored cover 31, which is therefore the dimension along an axis parallel to the axis XI between the outer face 32 and the inner face 33, is greater than that of a traditional sheet metal cover.
[0070] Here, the thickness ec of the cover 31 at the center 41 of the cover 31 is such that:
[0071] ec>2xem,
[0072] where em is the minimum thickness of the hood 31.
[0073] This particular shape of the shielding cover 31, as well as its centered position relative to the loudspeaker 27, promotes the diffraction and subsequent diffusion of the incident sound wave, thus reducing the vibrational energy transmitted to the electronic board 22. This shape and position also limit, or even eliminate, the formation of standing waves by avoiding parallel planes. Furthermore, the thickening of the shielding cover 31 stiffens it to prevent any risk of vibration against the shielding belt 30.
[0074] A second embodiment of a shielding hood 50 is now described with reference to Figures 7 to 9.
[0075] Again, the shielding cover 50 is intended to protect one or more electronic components 51 of an electronic card 52 whose printed circuit board 53 is fixed to the upper cover 54 of the decoder box 55.
[0076] The shape of the armor cover 50 is this time different and adapted to a very small available space.
[0077] The loudspeaker 56, which is again a bass loudspeaker, comprises a diaphragm 57, a core 67, a dust cap 58 and a suspension 59.
[0078] A free space 60, extending between, on the one hand, the diaphragm 57 and the dust cap 58, and on the other hand, the shielding cover 50, has a substantially constant height h. This height h is defined here as a dimension parallel to the central axis XI of the shielding cover 50 and to the central axis X2 of the loudspeaker 56, which coincide.
[0079] By "substantially constant", we consider here that this height A is constant to ± 10%.
[0080] This free space 60 forms a passage for air.
[0081] The profile of the external surface of the loudspeaker 56 with respect to this passage 60, is identical to the profile of the external face 61 of the shielding cover 50 with respect to said passage 60.
[0082] The shape of the hood 50 therefore follows the profile of the diaphragm 57 of the loudspeaker 56, which makes it possible to maximize the non-planar surface in relation to the loudspeaker 56, while taking into account the maximum displacement of its diaphragm 57.
[0083] The outer face 61 of the armored cover 50 comprises: • a frustoconical surface 64 and a concavity 65 which extends inside the frustoconical surface 64; • a ridge 66 which extends at least over a certain length of the contour 68 of the external face 61.
[0084] The frustoconical surface 64 and the concavity 65 are surfaces of revolution around the central axis XI of the armored hood 50.
[0085] The diaphragm 57 of the loudspeaker 56 extends opposite the frustoconical surface 64, the dust cap 58 of the loudspeaker 56 extends opposite the concavity 65, and the suspension 59 of the loudspeaker 56 extends at least partially into a channel 70 defined between the bead 66 and the frustoconical surface 64.
[0086] The frustoconical surface 64 has a first end 71 (which delimits the concavity 65), here circular, located on the side of the center 72 of the outer face 61, and a second end 73, also circular, located on the side of the contour 68 of the outer face 61. The diameter of the second end 73 is greater than that of the first end 71, and the frustoconical surface 64 therefore flares out from its first end 71, forming a slope that extends to the second end 73 and to the bottom of the rim 66. The frustoconical surface 64 has a shape substantially complementary to that of the diaphragm 57 of the loudspeaker 56.
[0087] The concavity 65 forms a curved surface which extends from a central part 63 of the external face 61 (here from the center 72 of the external face 61) towards the contour 68 of the external face 61. The center 72 of the external face 61, through which the axis XI passes, is also the deepest point of the concavity 65.
[0088] The concavity 65 here has a parabolic or circular profile and presents a shape substantially complementary to that of the dust cap 58 of the loudspeaker 56.
[0089] The external face 61 of the hood 50 has, when viewed in section along a plane passing through the central axis XI of the hood, a parabolic shape at the level of the bead 66.
[0090] Thus, when the decoder housing 55 is assembled, the diaphragm 57 extends opposite and parallel to the frustoconical surface 64, and the dust cap 58 extends opposite the concavity 65. When the loudspeaker 56 is operating, the diaphragm 57 vibrates and moves, causing the diaphragm 57 and the dust cap 58 to move towards and away from the outer face 61 of the shielding cover 50. The dust cap 58 partially penetrates the concavity 65. The frustoconical surface 64 and the concavity 65 are dimensioned so that the diaphragm 57 and the dust cap 58 do not come into contact with the shielding cover 50.
[0091] The shape of the shielding cover 50 therefore optimizes the integration of the loudspeaker 56 and the shielding cover 50, which is extremely advantageous when the very small footprint does not allow the integration of a shielding cover such as the cover 8 according to the first embodiment.
[0092] The displacement of the membrane 57 generates an airflow.
[0093] Advantageously, to avoid acoustic disturbances and overpressures in front of the loudspeaker 56, the airflow velocity at the outlet of the decoder housing 55 should be as close as possible to the velocity of the diaphragm 57 of the loudspeaker speaker 56. For this to happen, the product of the height h of the free space 60 above the membrane 57 by its perimeter P must be equal to its surface area S:
[0094] h*P = S,
[0095] or in the particular case of a circular membrane of diameter:
[0096] h = ll.
[0097] It can be seen that the bead 66 extends over only part of the length of the contour 68 of the outer face 61 of the shielding cover 50, so that the channel 70 comprises two ends 76 and forms an air evacuation channel having as outlets said ends 76, which allows an airflow 77 displaced by the diaphragm 57 of the loudspeaker 56 to flow through these two ends. The airflow is therefore carried out in directions parallel to tangents, at the level of the ends 76, to the circle formed by the second end 73 of the frustoconical surface 64.
[0098] The air exhaust channel 70 allows air to be exhausted laterally to the outside of the decoder box 55, here via openings provided for this purpose in a lower part of the upper cover 54 which forms an upper part of the rear face 79 of the decoder box 55.
[0099] Here, we see that two other shielding devices are mounted on the printed circuit board 53, with "traditional" shielding covers 80. These shielding covers 80 are positioned so that the air exhaust channel 70 opens, at each of its ends 76, onto one of the shielding covers 80.
[0100] It is noted that the ridge 66 could be extended to extend over the armor covers 80, which would make it possible to obtain a surface with little or no discontinuity and thus promote airflow.
[0101] The shielding cover 50 can therefore include, at at least one end of the channel 70, an extension 81 which extends the bead 66 and which at least partially covers another component mounted on the printed circuit 53.
[0102] The shielding hood 50 can include two extensions 81, i.e. one extension 81 at each end of the channel 70. These are shown schematically, in dotted lines, on [Fig.8].
[0103] Each extension 81 then extends along the direction of the airflow 77 and covers at least partially one of the armored hoods 80.
[0104] Advantageously, each extension 81 of the bead 66 has a parabolic shape when viewed in a plane through which passes the direction of the airflow 77 out of the channel 70.
[0105] Advantageously, at least one of the ends 76 of the channel 70, or at least one of the extensions 81, opens onto the electronic board 52 at a surface on which is mounted at least one component whose operation requires a Cooling. This component is, for example, an audio component that is activated when the speaker 56 is operating. The airflow generated by the speaker 56 and circulating in the channel 70 thus helps to cool this component.
[0106] The shielding cover 50 then fulfills three functions: electromagnetic shielding; acoustic deflector; cooling.
[0107] With reference to [Fig. 10], an analogy with a simple model allows us to consider the cavity between the loudspeaker 56 and the sound outputs of the decoder box 55 as a Helmholtz resonator:
[0108] f = J Helmholtz
[0109] where c is the speed of sound in air (c = 340 ms'), A is the cross-section of the neck, L its length, and V the volume of the cavity.
[0110] The use of the shielding cover 50 “deflector” makes it possible to reduce the volume V of the cavity. The use of the extensions 81 with a parabolic profile makes it possible not to reduce the cross-sectional dimensions.
[0111] Thus, by reducing the volume V, the deflector shielding cover 50 has the effect of increasing the associated acoustic resonance frequency so that it is outside the bandwidth of the loudspeaker (e.g., woofer). This advantage of the deflector shielding cover 50 is described below using the example of [Fig. 12].
[0112] It is also noted that the particular profile of the armor cover 50 makes it possible to stiffen the armor cover 50 more effectively by shifting the addition of material, and therefore mass, from the center of the sheet metal to distribute it around the perimeter of the armor cover 50 and therefore at the level of the bead 66.
[0113] Here, in addition, in order to limit as much as possible the presence of parallel planes and increase the efficiency of sound diffusion and diffraction, the shielding hood 50 extends on both sides of the shielding belt 85.
[0114] We have here:
[0115] dl> l,3z / 2,
[0116] where d1 is the diameter of the armored hood 50 and d2 is the diameter of the armored belt 85.
[0117] The hood 50 includes an inner face 86.
[0118] An internal cavity 87 is formed in the inner face 86. The internal cavity 87 is positioned at the center of the inner face 86 and is cylindrical in shape with a diameter substantially equal to that of the armor belt 85 (very slightly larger). When the armor cover 50 is attached to the armor belt 85, the latter is positioned in the internal cavity 87 and the lateral surface of the internal cavity 87 is pressed against the outer surface of the armor belt 85.
[0119] Generally, the diameter d of the shielding cover 50 is determined as a function of the available volume in the internal cavity 87, this volume being defined as a function of the diameter of the internal cavity.
[0120] With reference to [Fig. 11], measurements of the displacement of a subassembly comprising the upper cover 50 and the electronic board 52 were carried out using a laser measuring device when the loudspeaker 56 is in operation.
[0121] It is observed that, with a conventional shielding cover (without a deflecting effect), the frequency response C3 includes a resonance peak 90 corresponding to the maximum displacement of the upper cover. With the shielding cover 50, it is found that the amplitude of the resonance peak 91 of the frequency response C4 has decreased by 30%, and therefore that the maximum displacement of the upper cover 54 has also decreased by 30%. An increase in the resonance frequency of the peak of 12% is also noted.
[0122] This increase in the resonance frequency, and therefore in the frequency of the maximum measured displacement, is very interesting. Indeed, if it is made higher than the cutoff frequency of the loudspeaker 56 (e.g., 300 Hz in the case of the decoder box 55), it cannot be reached, and therefore the decoder box 55 will not be affected by this resonance.
[0123] With reference to [Fig. 12], the frequency response C5 of the loudspeaker 56 at 10cm, facing the rear of the acoustic enclosure, with a traditional cover, and the frequency response C6 with the shielding cover 50, were also measured.
[0124] It can be seen that reducing the cavity volume leads to an increase in the resonance peak frequency. Furthermore, the overall level of the C6 curve is higher, indicating that the amount of energy radiated from the rear is greater. In addition, the frequency response measured with the shielding cover 50 is more homogeneous and flat (e.g., + / -2dB in the loudspeaker's passband frequency range).
[0125] 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.
[0126] The electrical equipment in which the invention is implemented is not necessarily a decoder box. The invention applies to any audio equipment (i.e., any equipment capable of reproducing a sound signal) comprising at least one loudspeaker, electronic components and a shielding cover: connected speaker, television, etc.
[0127] The shielding device, including the shielding cover, does not necessarily include a shielding belt. The shielding cover could be attached to the circuit board (and connected to the ground plane) in a different way.
[0128] The speaker is not necessarily a bass speaker.
[0129] The speaker diaphragm does not necessarily have a circular diaphragm, it could have a square or rectangular cross-section.
Claims
Demands
1. Audio equipment (20; 55) comprising: - a printed circuit board (23; 53) on which is mounted at least one electronic component (24; 51); - a loudspeaker (27; 56) comprising a diaphragm (43; 57); - a shielding cover (31; 50) arranged to protect the at least one electronic component from electromagnetic interference, the shielding cover comprising an external face (32; 61) positioned opposite the diaphragm (43; 57) of the loudspeaker (27; 56); the outer face (32; 61) comprising at least one curved surface (37; 65) extending from a central part (38; 63) of the outer face (32; 61) to a contour (39; 68) of the outer face, the shielding cover (31; 50) being thus arranged to diffract acoustic waves produced by the speaker diaphragm in operation so as to reduce unwanted vibrations of the printed circuit board (23; 53) and the shielding cover (31; 50).
2. Audio equipment according to claim 1, wherein a central axis (XI) of the shielding cover (31; 50), passing through a center (41; 72) of the outer face (32; 61), coincides with a central axis (X2) of the loudspeaker (27; 56).
3. Audio equipment according to claim 2, wherein a free space (60) extending between, on the one hand, the diaphragm (57) and a dust cap (58) of the loudspeaker (56), and on the other hand, the shielding cover (50), has a substantially constant height h.
4. Audio equipment according to claim 3, wherein the diaphragm (57) is a circular diaphragm and wherein the height h is such that: h~~- where O is a diameter of the diaphragm (57).
5. Audio equipment according to claim 3 or 4, wherein the outer face (61) of the shielding cover (50) comprises: - a frustoconical surface (64), including a concavity (65) extending inside the frustoconical surface (64); - a bead (66) extending at least over a certain length of the contour (68) of the outer face (61); and wherein the diaphragm (57) of the loudspeaker (56) extends opposite the frustoconical surface, a dust cap (58) of the loudspeaker the speaker extends in relation to the concavity (65), and a suspension (59) of the speaker extends at least partially into a channel (70) defined between the rim and the frustoconical surface.
6. Audio equipment according to claim 5, wherein the bead (66) extends over only a part of the length of the contour (68) of the outer face (61), so that said channel (70) comprises two ends (76) and allows an airflow (77) displaced by the speaker diaphragm to flow through these two ends.
7. Audio equipment according to claim 5 or 6, wherein the outer face (61) of the shielding cover has, when viewed in section along a plane passing through the central axis (XI) of the shielding cover, a parabolic shape at the level of the bead (66).
8. Audio equipment according to claim 6 or 7, wherein the shielding cover (50) includes, at at least one end of the channel (70), an extension (81) which prolongs the bead (66) and which at least partially covers another component (80) mounted on the printed circuit board (53).
9. Audio equipment according to any one of the preceding claims, wherein the shielding cover is fixed to a shielding belt (85) mounted on the printed circuit board (53) and surrounding at least one electronic component (51), the shielding cover (50) having an inner face (86) in which an internal cavity (87) is formed, the shielding cover (50) extending on either side of the shielding belt (85) which is positioned in the internal cavity (87).
10. Audio equipment according to any one of the preceding claims, the audio equipment being a decoder box (20; 55).