Loudspeaker comprising a magnetic circuit defining at least one conduit for fluidly connecting an air gap and a loading volume

Abstract

Loudspeaker comprising a magnetic circuit defining at least one conduit for fluidly connecting an air gap and a loading volume. Loudspeaker (12), in particular intended to emit in the high frequencies, defining a central axis (X) and comprising: - a magnetic circuit (20) defining a housing (22), - an assembly (26) movable axially relative to the magnetic circuit, comprising a diaphragm (28) adapted to emit sound waves and defining a front side of the loudspeaker, - a suspension (34) mechanically connecting the diaphragm to a chassis (36) of the loudspeaker, and - a cover (38) extending axially from the rear side relative to the magnetic circuit and delimiting a loading volume (40).The magnetic circuit defines: - a radially internal surface (44) delimiting a central passage (46) axially connecting an air volume (48) located behind the membrane and the charge volume, and - a conduit (50A) fluidly connecting, on the one hand, the housing and, on the other hand, the charge volume or the central passage. Figure for the abbreviation: Figure 2.

Description

Title of the invention: Loudspeaker comprising a magnetic circuit defining at least one conduit for fluidly connecting an air gap and a loading volume

[0001] DOMAIN

[0002] The present invention relates to a loudspeaker, in particular intended for emitting high frequencies, the loudspeaker defining a central axis and comprising:

[0003] - a magnetic circuit comprising at least one magnet and defining a housing forming an air gap, and

[0004] - a movable assembly comprising a membrane adapted to emit waves sound, a coil holder fixed to the diaphragm, and a coil fixed to the coil holder and adapted to vibrate axially in the air gap, the diaphragm defining one front side of the loudspeaker along the central axis.

[0005] The invention also relates to an acoustic enclosure comprising at least one such loudspeaker. EARLIER ART

[0006] High-frequency speakers, known in English as tweeters, are adapted to emit high-frequency sound waves.

[0007] According to a known technology, the membrane is for example made up of a rigid dome.

[0008] However, loudspeakers, particularly high-efficiency, compact tweeters (thus requiring a small enclosure volume), can exhibit some harmonic distortion that may impair the sound quality of the loudspeaker. Harmonic distortion is measured, for example, as a percentage at 1 meter for a given emission level, such as 108 dB SPL.

[0009] An object of the invention is to provide a loudspeaker, in particular adapted to emit in the high range, exhibiting reduced harmonic distortion. Summary of the invention

[0010] To this end, the invention relates to a loudspeaker, in particular intended to emit high-frequency sound, the loudspeaker defining a central axis and comprising:

[0011] - a magnetic circuit defining at least one housing forming an air gap,

[0012] - a crew that moves axially with respect to the magnetic circuit, comprising a diaphragm adapted to emit sound waves, a voice coil holder fixed to the diaphragm, and a voice coil fixed to the voice coil holder and located in the air gap, the diaphragm defining one front side of the loudspeaker along the central axis,

[0013] - at least one suspension mechanically linking the membrane to an upper frame- speaker, and

[0014] - a hood mechanically attached to the magnetic circuit and extending axially on the rear side relative to the magnetic circuit, the hood delimits a charging volume,

[0015] the magnetic circuit defining a radially inner surface with respect to the central axis, the radially inner surface radially delimiting a central passage axially connecting an air volume located behind the membrane and the charge volume,

[0016] the magnetic circuit defining at least one conduit fluidly connecting, on the one hand, the housing and, on the other hand, the charge volume or the central passage.

[0017] According to other advantageous aspects of the invention, the loudspeaker comprises one or more of the following features, taken individually or in any technically possible combination: - the magnetic circuit defines a plurality of conduits fluidly connecting the housing and the charge volume or the central passage, the conduits of said plurality being distributed around the central axis and preferably being axially oriented; - the membrane defines an external diameter, the radially internal surface defining a minimum diameter of the central passage, the ratio defined by the minimum diameter of the central passage divided by the external diameter of the membrane being greater than 60%; - the radially inner surface comprises successively along the central axis: • a front section that flares axially towards the front, • a central section defining a pass in the central passage, and • a rear section flared axially towards the rear; - the magnetic circuit has an axial extension, and the middle part, defined as forming at every point with the central axis an angle of less than 10° with the central axis, has an axial extension, the ratio of the axial extension of the middle part divided by the axial extension of the magnetic circuit being less than 30%, preferably less than 20%; - the loudspeaker comprising a porous system containing one or more acoustic foam(s), and extending across the ducts and / or the central passage, the porous system adapted to reduce the speed and / or intensity of standing acoustic waves intended to form in the duct and / or the central passage when the loudspeaker is in operation; - the porous system expands: • straddling the central passage and the loading volume, across an outlet opening from the central passage to the loading volume, and / Or • against the magnetic circuit, across an outlet orifice of the conduit towards the charge volume; - the porous system comprises at least two layers of foam, one of the two layers being adapted to reduce the velocity of standing acoustic waves intended to form in the duct and / or the center passage when the loudspeaker is in operation, and the other of the two layers being adapted to attenuate said standing acoustic waves; and - the porous system is axially wedged between the magnetic circuit and the hood, and the hood includes an envelope defining an internal space, and supports extending into the internal space, the porous system extending against or being fixed to the supports.

[0018] The invention also relates to an acoustic enclosure comprising:

[0019] - at least one first loudspeaker as described above, and

[0020] - preferably, a second loudspeaker, in particular intended to emit into the medium, preferably coaxial with the first speaker around the central axis. Brief description of the drawings

[0021] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings, in which:

[0022] [Fig-1] [Fig.1] is a schematic view of an acoustic enclosure according to the invention,

[0023] [Fig.2] [Fig.2] is a schematic view of a tweeter shown on the [Fig. 1], in cross-section along a plane passing through the central axis,

[0024] [Fig.3] [Fig.3] is a schematic, top view of part of the magnetic circuit of the loudspeaker shown in [Fig.2], and

[0025] [Fig.4] [Fig.4] is a schematic, exploded, perspective view showing the part of the magnetic circuit shown in [Fig.3], as well as a porous system and a speaker cover shown in [Fig.2]. DETAILED DESCRIPTION Acoustic enclosure

[0026] With reference to [Fig. 1], an acoustic enclosure 10 according to the invention is described.

[0027] The acoustic enclosure 10 comprises at least one first loudspeaker 12, for example intended to emit in the high frequencies, defining a central axis X.

[0028] In the example, the acoustic enclosure 10 advantageously includes a second loudspeaker 14, in particular intended to emit in the midrange, preferably coaxial with the first loudspeaker 12 around the central axis X, and for example two bass loudspeakers 16, 18.

[0029] By "designed to emit in the high range," it is meant, for example, that the loudspeaker 12 is adapted to reproduce high sound frequencies, i.e., high-pitched sounds. Generally, the frequencies reproduced are above 2,000 Hz and can extend into the ultrasonic range, for example, at least between 2,000 Hz and 20 kHz. Such a loudspeaker is often called a "tweeter."

[0030] By "intended to emit in the midrange", it is meant for example that the loudspeaker 14 is adapted to the reproduction of sounds located in the mid-range of audible frequencies, that is to say between bass and treble, generally in a frequency range between 150 Hz and 10 kHz, often between 500 Hz and 5 kHz.

[0031] By "bass speaker", it is understood for example that the speakers 16, 18 are adapted for the reproduction of bass sounds, that is to say in the low area of ​​audible frequencies, generally in a frequency range between 20 Hz and a few hundred Hz, for example 300 Hz.

[0032] The invention relates in the example to the first loudspeaker 12. Therefore, only the latter will be described below, the others being known in themselves to the person skilled in the art. Speaker

[0033] As can be seen in [Fig.2], the loudspeaker 12 includes a magnetic circuit 20 defining at least one housing 22 forming an air gap 24.

[0034] In an alternative (not shown), the loudspeaker 12 defines several air gaps.

[0035] According to a particular embodiment, the magnetic circuit 20 is common with another loudspeaker, for example with the second loudspeaker 14, which makes it possible to obtain a more intense magnetic field in the air gap 24. However, this explains why the loudspeaker 12 has dimensions, in particular radial dimensions, possibly smaller than those of a tweeter in the prior art.

[0036] The loudspeaker 12 includes a movable assembly 26 relative to the magnetic circuit 20, and comprising a diaphragm 28 adapted to emit sound waves (not shown), a coil holder 30 fixed on the diaphragm 28, and a coil 32 fixed on the coil holder and located in the air gap 24, the diaphragm 28 defining a front side of the loudspeaker along the central axis X.

[0037] The loudspeaker 12 includes a suspension 34 mechanically connecting the diaphragm 28 to a chassis 36 of the loudspeaker.

[0038] The loudspeaker 12 includes a hood 38 mechanically attached to the magnetic circuit 20 and extending axially from the rear side relative to the magnetic circuit, the hood delimiting a load volume 40.

[0039] Advantageously, the loudspeaker 12 comprises a porous system 42 containing one or more acoustic foam(s).

[0040] The or at least one of these acoustic foams advantageously has an alpha absorption coefficient at 2500 Hz greater than or equal to 0.8. The alpha absorption coefficient is used to characterize the acoustic performance of a material. For example, ISO 10534-2:2023 of October 2023 defines a method for measuring the alpha absorption coefficient.

[0041] The membrane 28 is advantageously rigid, with a Young's modulus advantageously greater than 40 GPa. For example, the membrane 28 comprises mainly, in particular at least 90% by mass, a metal, such as aluminum, or an alloy.

[0042] The membrane 28 advantageously forms a dome whose convexity is facing forward. The membrane 28 is, for example, spherical in shape.

[0043] The membrane 28 defines an external diameter Dl, for example between 10 and 50 mm.

[0044] The suspension 34 is, for example, a seal made of elastomer or polymer material, or of fabric. The suspension 34 is, for example, fixed to a radially external edge of the membrane 28. The suspension 34 advantageously has a "Q" shape, the bulbous part of the "Q" being, for example, facing forward.

[0045] The spool holder 30, for example, has a general cylindrical shape.

[0046] The spool holder 30 is advantageously devoid of any opening in a radial direction relative to the central axis X. Indeed, such an opening would increase the harmonic distortion of the speaker 12.

[0047] The coil 32 is adapted to vibrate axially in the air gap 24 when a current (not shown) flows through it. Magnetic circuit - conduit(s)

[0048] The magnetic circuit 20 defines a radially internal surface 44 with respect to the central axis X, the radially internal surface radially delimiting a central passage 46 connecting axially, on the one hand, an air volume 48 located at the rear of (under) the membrane 28 and, on the other hand, the charge volume 40.

[0049] In the example, the magnetic circuit 20 defines a plurality of conduits 50A to 50E (see [Fig. 3]) fluidly connecting the housing 22 and the charge volume 40. The conduits 50A to 50E are distributed around the central axis X, advantageously regularly, and are preferably axially oriented. In the example, there are five conduits 50A to 50E.

[0050] According to variants not shown, the conduits are in different numbers, for example one, two, three, four, or more than five.

[0051] In the example, the conduits 50A to 50E are perforations, for example cylindrical (with a circular base), and define outlet orifices 52 opening into or towards the charge volume 40.

[0052] Conduits 50A to 50E are for example located under housing 22.

[0053] According to one variant (not shown), the conduits 50A to 50E are not axially oriented, or even the outlet ports 52 open into the central passage 46. In reality, the central passage 46, or at least a rear part of the latter, can be considered as constituting a load volume.

[0054] According to yet another variant (not shown), the 50A to 50E conduits are not cylindrical in shape.

[0055] The magnetic circuit 20 has an axial extension Ll, for example between 5 and 30 mm.

[0056] In the example, the magnetic circuit 20 includes, for example, a magnet 54, a core 56, and advantageously a pole piece 58.

[0057] The core 56 comprises a central part 60 delimiting the central passage 46, and a rear part 62 extending radially outwards from the central part 60.

[0058] In the example, it is the core 56, advantageously its rear part 60, which defines the conduits 50A to 50E. With the exception of the conduits 50A to 50E, the core 56 advantageously has a shape of revolution around the central axis X.

[0059] The magnet 54, for example, has a disc shape and is located axially between the pole piece 58, situated on the front side, and the rear part 60, situated on the rear side. The magnet 54 is, for example, made of neodymium and advantageously has a volume of less than 4.0 cm³.

[0060] In the example, the air gap 24 extends radially between the pole piece 58 and the central part 60 of the core 56.

[0061] According to unrepresented and less preferred variants, the magnet 54 is located in a different place in the magnetic circuit 20. In some cases (not shown), the magnet 54 can define, at least in part, the conduits 50A to 50E.

[0062] The conduits 50A to 50E are adapted to promote pressure balancing on either side of the coil holder 30 radially by allowing communication between the air volume 48 and an air volume 64 located under the suspension 34, via the housing 22, the conduits 50A to 50E, the charge volume 40 and the central passage 46. As explained above, the coil holder 30 does not allow a more direct, or sufficient, communication between the air volume 48 and the air volume 64. Central passage

[0063] The radially internal surface 44 defines a minimum diameter D2 of the central passage 46, perpendicular to the central axis X. The minimum diameter D2 is advantageously greater than 12 mm.

[0064] The ratio defined by the minimum diameter D2 divided by the external diameter DI of the membrane 28 is for example greater than 60%.

[0065] In the example, the radially interior surface 44 comprises, successively along the central axis X, a front part 66 flared axially towards the front, a middle part 68 delimiting a neck of the central passage, and a rear part 70 flared axially towards the rear.

[0066] The median part 68 is for example defined as forming at every point with the central axis X, in any radial half-plane P, an angle a less than 10° with the central axis X. The median part 68 thus defined has an axial extension L2.

[0067] The ratio of the axial extension L2 divided by the axial extension L1 of the magnetic circuit 20 is advantageously less than 30%, preferably less than 20%. This makes it possible to limit the Helmholtz resonance effect that can appear in the central passage 46. Porous system

[0068] The porous system 42 extends for example across the ducts 50A to 50E and the central passage 46, and is adapted to reduce the speed and intensity of standing acoustic waves (resonance) destined to form in the ducts and in the central passage when the loudspeaker 12 is in operation.

[0069] The porous system 42 advantageously avoids reflection phenomena inside the charge volume 40 by acting directly on the standing acoustic waves.

[0070] According to variants (not shown), the porous system 42 extends only across the conduits 50A to 50E or the central passage 46, and is adapted to reduce only the speed or intensity of standing acoustic waves.

[0071] The porous system 42 advantageously extends across the central passage 46 and the charge volume 40, across an outlet orifice 72 from the central passage 46 to the charge volume 40.

[0072] In addition or alternatively, the porous system 42 advantageously extends against the magnetic circuit 20, across the outlet orifices 52 of the conduits 50A to 50E towards the charge volume 40.

[0073] The porous system 42 extends for example perpendicularly to the central axis X.

[0074] The porous system 42 comprises, for example, two layers of foam 42A, 42B advantageously superimposed one on top of the other (figures 2 and 4).

[0075] The foam layer 42A, advantageously located axially at the front, is, for example, resistive and suitable for reducing the speed of standing acoustic waves intended to form in conduits 50A to 50E and / or the central passage 46. The foam layer 42A is for example made of non-woven textile (forming a mesh, or "wiremesh" in English), advantageously made of polypropylene.

[0076] The foam layer 42B, advantageously located at the rear, is for example absorbent and suitable for attenuating said standing acoustic waves.

[0077] The foam layer 42B advantageously comprises polyester fibers, for example between 10% and 60% by mass. According to a particular embodiment, the foam layer 42B comprises staple polyester fibers, preferably recycled, for example at about 38% by mass, and polyethylene fibers, for example at about 62% by mass.

[0078] The foam layer 42B advantageously has an alpha absorption coefficient at 2500 Hz greater than or equal to 0.8.

[0079] According to an unrepresented variant, the porous system 42 comprises only one of the two foam layers 42A, 42B.

[0080] The porous system 42 is for example axially wedged between the magnetic circuit 20 and the hood 38.

[0081] The hood 38 includes for example an envelope 74 defining an internal space 76, and supports 78 ([Fig.4]) extending into the internal space, the porous system 42 extending against or being fixed on the supports 78.

[0082] The supports 78 are advantageously adapted to press the porous system 42 against the magnetic circuit 20.

[0083] The supports 78 form, for example, ribs extending radially from the envelope 74 towards the central axis X, preferably without joining each other so as not to divide the load volume 40 into disjoint sectors around the central axis X.

[0084] There are, for example, three supports 78. Benefits

[0085] Thanks to the characteristics described above, the loudspeaker 12 exhibits reduced harmonic distortion. The total harmonic distortion (THD), particularly at 4000 Hz, is advantageously less than 1.0%.

[0086] Furthermore, the speaker 12 is very compact and its power consumption is relatively low, all other things being equal. The magnet 54 advantageously has a small volume, which reduces the cost of the speaker 12.

[0087] Thanks to the conduits 50A to 50E, the possible pressure imbalance between the air volume 48 and the air volume 64 is reduced or non-existent, which reduces or prevents a phase shift between the membrane 28 and the suspension system 34.

[0088] The load volume 40 is advantageously as large as possible while respecting any space constraints, for example due to the coaxial mounting with the second loudspeaker 14, which surrounds the first loudspeaker 12.

[0089] In addition, the optional features concerning the shape of the radially inner surface 44 make it possible to reduce a Helmholtz type resonance in the central passage 46, which for example takes place at 2800 Hz, while maintaining the efficiency of the magnetic circuit 20 in terms of guiding the magnetic flux.

[0090] The optional presence and characteristics of the porous system 42 further reduce Helmholtz resonance in the central passage 46 and / or in the conduit(s) 50A to 50E. Tests have shown the optimal performance of one or more layers of foam 42A, 42B applied to the outlet 72 of the central passage 46 and the outlets of the conduits 50A to 50E.

[0091] Tuning the pressures between the air volume 48 and the air volume 64 also makes it possible to shift the standing waves towards higher frequencies, making the damping by the porous system 42 more efficient.

Claims

Demands

1. Loudspeaker (12), in particular intended for emitting high frequencies, the loudspeaker (12) defining a central axis (X) and comprising: - a magnetic circuit (20) defining at least one housing (22) forming an air gap (24), - an assembly (26) axially movable relative to the magnetic circuit (20), comprising a diaphragm (28) adapted for emitting sound waves, a voice coil holder (30) fixed to the diaphragm (28), and a voice coil (32) fixed to the voice coil holder (30) and located in the air gap (24), the diaphragm (28) defining a front side of the loudspeaker (12) along the central axis (X), - at least one suspension (34) mechanically connecting the diaphragm (28) to a chassis (36) of the loudspeaker (12), and - a cover (38) mechanically attached to the magnetic circuit (20) and extending axially from the rear side relative to the magnetic circuit (20), the hood (38) delimiting a charge volume (40),the magnetic circuit (20) defining a radially internal surface (44) with respect to the central axis (X), the radially internal surface (44) radially delimiting a central passage (46) axially connecting an air volume (48) located behind the membrane (28) and the charge volume (40), the magnetic circuit (20) defining at least one conduit (50A) fluidly connecting, on the one hand, the housing (22) and, on the other hand, the charge volume (40) or the central passage (46).

2. Loudspeaker (12) according to claim 1, wherein the magnetic circuit (20) defines a plurality of conduits (50A to 50E) fluidly connecting the housing (22) and the loading volume (40) or the central passage (46), the conduits (50A to 50E) of said plurality being distributed around the central axis (X) and preferably being axially oriented.

3. Loudspeaker (12) according to claim 1 or 2, wherein the diaphragm (28) defines an external diameter (Dl), the radially inner surface (44) defining a minimum diameter (D2) of the center passage (46), the ratio defined by the minimum diameter (D2) of the center passage (46) divided by the external diameter (Dl) of the diaphragm (28) being greater than 60%.

4. Loudspeaker (12) according to any one of claims 1 to 3, wherein the radially inner surface (44) comprises successively along the central axis (X): - a front part (66) flared axially towards the front, - a middle part (68) delimiting a neck of the central passage (46), and - a rear part (70) flared axially towards the rear.

5. Loudspeaker (12) according to claim 4, wherein: - the magnetic circuit (20) has an axial extension (L1), and - the middle part (68), defined as forming at every point with the central axis (X) an angle (a) less than 10° with the central axis (X), has an axial extension (L2), the ratio of the axial extension (L2) of the middle part (68) divided by the axial extension (L1) of the magnetic circuit (20) being less than 30%, preferably less than 20%.

6. Loudspeaker (12) according to any one of claims 1 to 5, comprising a porous system (42) containing one or more acoustic foam(s), and extending across the ducts (50A to 50E) and / or the center passage (46), the porous system (42) adapted to reduce the speed and / or intensity of standing acoustic waves intended to form in the duct (50A) and / or the center passage (46) when the loudspeaker (12) is in operation.

7. Loudspeaker (12) according to claim 6, wherein the porous system (42) extends: - across the central passage (46) and the loading volume (40), across an outlet orifice (72) from the central passage (46) to the loading volume (40), and / or - against the magnetic circuit (20), across an outlet orifice (52) from the conduit (50A) to the loading volume (40).

8. Loudspeaker according to claim 6 or 7, wherein the porous system (42) comprises at least two layers of foam (42A, 42B), one of the two layers (42A, 42B) being adapted to reduce the velocity of standing acoustic waves intended to form in the duct (50A) and / or the center passage (46) when the loudspeaker (12) is in operation, and the other of the two layers (42A, 42B) being adapted to attenuate said standing acoustic waves.

9. Loudspeaker (12) according to any one of claims 6 to 8, wherein - the porous system (42) is axially wedged between the magnetic circuit (20) and the hood (38), and - the hood (38) comprises an enclosure (74) defining an internal space (76), and supports (78) extending into the internal space (76), the porous system (42) extending against or being fixed to the supports (78).

10. Acoustic enclosure (10) comprising: - at least one first loudspeaker (12) according to any one of claims 1 to 9, and - preferably, a second loudspeaker (14), in particular intended to emit in the midrange, preferably coaxial with the first loudspeaker (12) around the central axis (X).