EP3632132A1

EP3632132A1 - Acoustic chamber with reduced hiss

Info

Publication number: EP3632132A1
Application number: EP18727311.5A
Authority: EP
Inventors: Max RAINER
Original assignee: Devialet SA
Current assignee: Devialet SA
Priority date: 2017-05-30
Filing date: 2018-05-30
Publication date: 2020-04-08
Also published as: FR3067200A1; FR3067200B1; WO2018220054A1

Abstract

The invention relates to an acoustic chamber having: - a box structure (3) forming a first edge (24) defining an opening (26), - at least one loudspeaker having at least one diaphragm (50) that is configured to emit sound waves and extends through the opening, the diaphragm being movable in translation with respect to the box structure along an axis (D) of the loudspeaker about an equilibrium position that is taken up when the loudspeaker is at rest, the diaphragm being configured to oscillated in normal operation between a maximum outward position and a maximum inward position that define between one another a maximum axial displacement (E) of the diaphragm, the diaphragm defining a second peripheral edge (64) situated radially opposite the first edge at least in the rest position, the first edge and the second edge being separated radially by a distance (J), the first edge and the second edge having a first thickness (E1) and a second thickness (E2), respectively, along the axis (D), the first thickness and the second thickness defining a sum (E1+E2). The sum (E1+E2) divided by the maximum axial displacement (E) is less than 1/5^th, preferably less than 1/8^th, and even more preferably less than 1/12^th.

Description

Sound enclosure with reduced whistling

The present invention relates to an acoustic chamber comprising a box forming a first edge defining an opening, at least one loudspeaker comprising at least one membrane configured to emit sound waves and extending across the opening, the membrane being movable in translation relative to the box along an axis of the loudspeaker around an occupied equilibrium position when the loudspeaker is at rest, the diaphragm being configured to oscillate in normal operation between a maximum output position and a maximum retracted position defining between them a maximum axial displacement of the membrane, the membrane defining a second peripheral edge located radially opposite the first edge at least in the rest position, the first edge and the second edge being separated radially by a distance , the first edge and the second edge respectively having a first thickness and a second thickness the axis, the first thickness and the second thickness defining a sum.

The acoustic enclosure is for example configured to take place in the passenger compartment of a motor vehicle.

It is known that the maximum axial displacement of the membrane is sometimes important, especially for the bass speakers, that is to say having a bandwidth extending, for example, from 15 hertz to 500 hertz. The axial displacements of the membrane cause reciprocating air flows flow between the first edge of the box and the second peripheral edge of the membrane. The air movements can in turn generate whistles that affect the sound quality of the speaker.

To remedy this, it is known to increase the distance separating the peripheral edge of the membrane and the edge of the box. However, this sometimes impairs the aesthetics of the speaker and creates a gap through which dust or other bodies can enter the speaker.

An object of the invention is therefore to provide an acoustic enclosure of the type described above, in which the aforementioned whistle is eliminated or reduced, the acoustic enclosure having a more aesthetic structure.

For this purpose, the invention relates to an acoustic enclosure of the type described above, in which the sum divided by the maximum axial displacement is less than 1/5 ^e , preferably less than 1/8 ^e , and even more preferred less than 1/12 ^e . According to particular embodiments, the acoustic enclosure comprises one or more of the following characteristics taken separately or in any technically possible combination:

the membrane comprises at least one convex part whose convexity is turned towards the outside of the acoustic enclosure;

the convex part is spherical;

the membrane comprises a peripheral skirt extending substantially parallel to the axis and determining the second thickness;

the skirt is formed by a fold of the membrane and extends towards the inside of the loudspeaker;

the casing forms a reentrant collar around the membrane, the collar having an axial thickness being reduced towards the membrane, the collar having a radially inner end determining the first thickness;

- The collar has a flat outer face facing outwardly of the acoustic chamber, and a planar inner face facing the interior of the acoustic chamber;

the outer face is substantially orthogonal to the axis and the inner face forms an angle with the outer face, the angle being less than or equal to 45 degrees;

the loudspeaker further comprises a magnetic circuit forming at least one gap, and at least one coil located at least partly in the gap and configured to be traversed by an electric current, the air gap and the coil defining a game radial, said distance between the first edge and the second edge being substantially equal to the radial clearance; and

the loudspeaker further comprises at least one suspension seal of the membrane with respect to the casing, the seal having, in cross section, two ends located radially on either side of the first edge and the second edge, the joint forming a gutter axially located on the inner side of the acoustic chamber with respect to the first edge and the second edge in the equilibrium position.

The invention also relates to a motor vehicle comprising at least one acoustic enclosure as described above.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

FIGS. 1 and 2 are two perspective views of an acoustic enclosure according to the invention, FIG. 3 is a sectional view of the acoustic chamber shown in FIGS. 1 and 2, in a plane passing through the axis of two bass speakers,

FIG. 4 is a detail of FIG. 3 centered on two suspension joints of one of the bass speakers,

FIG. 5 is a detail of FIG. 3 centered on an air gap of one of the subwoofers shown in FIGS. 1 to 3, and

FIG. 6 is a diagram illustrating a method for determining the first thickness (box edge) and the second thickness (peripheral edge of the membrane).

With reference to FIGS. 1 to 3, an acoustic enclosure 1 according to the invention is described. The acoustic enclosure 1 is for example integrated into the passenger compartment (not shown) of a motor vehicle (not shown).

According to particular embodiments (not shown), the acoustic enclosure 1 is located, for example, in the middle feet, in a rear seat, or in a front table of the vehicle.

In the example shown, the acoustic enclosure 1 comprises a caisson 3, two speakers 5,10 arranged head to tail along an axis D common to the two speakers, and two other speakers 15, 20.

The casing 3 advantageously has a generally spherical shape. In the example shown, the box 3 further comprises a substantially flat face 22 on which is mounted the speaker 20 (Figures 2 and 3).

The box 3 forms a first edge 24, for example circular, defining an opening 26.

For example, the first edge 24 is defined by a reentrant flange 28 (FIG. 4) of the casing 3.

The collar 28 has an axial thickness which decreases as one approaches the axis D. The flange 28 has a radially inner end defining a first thickness E1 of the first edge 24 along the axis D.

The flange 28 has an outer plane face 32 facing outwardly of the acoustic chamber 1, and an inner plane face 34 facing the interior of the acoustic chamber.

The outer face 32 is for example substantially orthogonal to the axis D.

The inner face 34 forms an angle α with the outer face 32.

The angle a is advantageously less than or equal to 45 degrees.

The first thickness E1 is for example between 0.5 and 1.5 millimeters, preferably between 0.5 and 0.8 millimeters. The loudspeaker 5 comprises a chassis 36 (FIG. 3) which is rather small in the example shown, a magnetic circuit 38, a mobile assembly 40, and two suspension joints 42, 44 connecting the mobile assembly to the chassis.

The frame 36 is mechanically secured to the casing 3.

The magnetic circuit 38 defines a gap 48.

The moving assembly 40 comprises a membrane 50, a spool holder 52 fixed on the membrane, a spool 54 fixed on the spool holder, and a holding member 56 also fixed to the membrane.

The spool holder 52 and the holding member 56 are, for example cylindrical axis

D.

The membrane 50 is for example convex, with a convexity turned towards the outside of the acoustic enclosure 1.

The membrane 50 is movable in translation relative to the casing 3 along the axis D about an equilibrium position (FIG. 1) occupied when the loudspeaker 5 is at rest. The membrane 50 is configured to oscillate in normal operation between a maximum output position and a maximum retracted position (not shown, but being deduced from the equilibrium position by translations along the axis D in opposite directions) defining between them a displacement axial maximum E of the membrane.

The maximum retracted position of the membrane 50 is for example defined by the fact that the moving assembly 40 comes into axial abutment. In the example shown, the holding member 56 could abut against the frame 36.

The maximum position output is in all cases symmetrical with the maximum position retracted relative to the equilibrium position of the membrane 50.

According to a particular embodiment, the maximum retracted position and the maximum membrane outlet position 50 are defined by an electronic control system (not shown) of the acoustic enclosure 1. In this case, the electronic control system is configured to limit the movements of the membrane 50.

The maximum retracted position and the maximum output position are for example determined by a simple test consisting of sending to the acoustic enclosure 1 a sinusoidal signal at 30 Hz, and to make it play more and more loudly by the acoustic enclosure, until the amplitude of the vibrations of the membrane 50 is limited by a mechanical stop (against which the membrane abuts) or by the electronic control system. The maximum axial displacement E is then measured between the two positions Extreme axial axis of the membrane 50. The input signal at 30Hz must be of sufficient amplitude not to affect the result.

The membrane 50 comprises a convex portion 60, in the spherical example, and a peripheral skirt 62.

The convex portion 60 has for example center the center O of the box 3.

The membrane 50 defines a second peripheral edge 64 having a second thickness E2 along the axis D.

The thickness E2 is determined here by the extension of the skirt 62 along the axis D.

The second thickness E2 is for example between 0.20 and 1.0 millimeters, preferably between 0.20 and 0.50 millimeters.

Referring to Figure 6, defines a method for determining the first thickness E1 and the second thickness E2, useful in particular if the first edge 24 and the peripheral edge 64 have a rounded shape. Figure 6 is a section of the first edge 24 and the peripheral edge 64 in a plane passing through the axis D.

To determine the first thickness E1, a point A1 of the first edge 24 is determined at a minimum distance from the axis D. Then the first edge 24 is cut by a first plane P1 parallel to the axis D and perpendicular to the plane of the plane. FIG. 6, the first plane P1 being located radially at a distance d from the point A1. The first plane P1 intercepts the first edge 24 at two axially extreme points A1 'and A1 "The axial distance between the points A1' and A1" defines the first thickness E1.

Similarly, to determine the second thickness E2, a point A2 of the peripheral edge 64 located at a maximum distance from the axis D is determined. Then the peripheral edge 64 is cut by a second plane P2 parallel to the axis D and perpendicular in the plane of Figure 6, the second plane P2 being located radially at the distance d of the point A2. The second plane P2 intercepts the peripheral edge 64 at two axially extreme points A2 'and A2 "The axial distance between the points A2' and A2" defines the second thickness E2.

The distance d is, for example, 0.2 mm.

The skirt 62 is for example formed by a fold 63 in the membrane 50.

The sum E1 + E2 divided by the maximum axial displacement E is less than 1/5 ^e , preferably less than 1/8 ^e , and even more preferably less than 1/12 ^e .

The coil 54 is located at least partly in the gap 48. The coil 54 and the air gap 48 define a radial clearance J1.

The first edge 24 and the second edge 64 are separated radially by a distance J (FIG. 4), for example substantially equal to the radial clearance J1 (FIG. 5). The coil 54 is separated from the magnetic circuit 38 on the radially outer side by a distance J1 '. The spool holder 52 is separated from the magnetic circuit 38 on the radially inner side by a distance J1 ".

In the example shown, the sum of the distances J1 'and J1 "forms the radial clearance J1.

For example, the distance J1 "is smaller than the distance J1 ', advantageously from 10% to 20%, so that the coil 54 touches the radially inner part of the air gap more easily than the radially external part. particular embodiment, the distance J is between 1, 1 times the distance J1 "and 1/5 ^e (one fifth) of the maximum axial displacement E of the membrane 50.

The seal 42 is fixed on the frame 36 by gluing, and on a ring 66, also by gluing.

The seal 42 has for example a cradle shape, the bottom of the cradle being directed axially opposite the membrane 50.

The seal 42 has ends 68, 70 located radially on either side of the first edge 24 and the second edge 64 considered together. The seal 42 forms a groove 72 located axially on the inner side of the acoustic chamber 1 with respect to the first edge 24 and the second edge 64 in the equilibrium position.

The seal 44 is for example structurally similar to the seal 42. The seal 44 is distinguished only by its orientation, in which the bottom of the cradle is directed axially towards the membrane 50.

The loudspeaker 10 is advantageously structurally analogous to the loudspeaker 5 and will not be described in detail.

The loudspeaker 15 is for example adapted to emit in the medium and treble, that is to say with a bandwidth extending for example between 200 Hz and 25 kHz. The loudspeaker 15 comprises for example a grid 74, for example of spherical shape, and advantageously located in the continuity of the box 3.

The loudspeaker 15 is for example configured to transmit directly into the interior space of the motor vehicle.

The speaker 20 is for example also a loudspeaker medium and treble. In the example shown, the loudspeaker 20 is not configured to transmit directly into the interior of the vehicle, but into one or more conduits (not shown) defined by the passenger compartment of the vehicle.

The operation of the loudspeaker 1 will be briefly described below. The coil 54 is traversed by an electric current. This creates axial displacements of the mobile assembly 40, in particular of the membrane 50 which emits sound waves 76.

The axial displacements of the membrane 50 are of variable amplitude depending on the signals received by the coil 54 and the loudness. The axial displacements have an amplitude less than or equal to the maximum axial displacement E.

The axial movements of the membrane 50 create substantially axial air displacements 78 in the passage between the membrane and the casing 3.

When the membrane 50 is at rest, the first edge 24 and the second edge 64 are substantially vis-à-vis, that is to say located substantially at the same level axially.

In the equilibrium position, the width of the passage is equal to the distance J radially separating the first edge 24 and the second edge 64.

However, thanks to the property of the ratio (E1 + E2) / E, the width of the passage increases rapidly as soon as the membrane 50 deviates axially from the equilibrium position, either upwards or downwards. Figure 4. Thus, the hissing that could exist if the passage for the air remained equal to the distance J, does not occur, or is very attenuated.

As a result, the speaker 1 has a better sound quality.

According to a variant not shown, the speaker 1 comprises only the speaker 5, or the speaker 5 and any number of other speakers.

According to a particular embodiment not shown, the membrane 50 does not have a spherical portion, does not have a convexity turned towards the outside of the acoustic enclosure 1, or even is not convex.

Claims

1. - Acoustic speaker (1) comprising:

- a box (3) forming a first edge (24) defining an opening (26), - at least one speaker (5) having at least one membrane (50) configured to emit sound waves (76) and s' extending across the opening (26),

the membrane (50) being movable in translation relative to the casing (3) along an axis (D) of the loudspeaker (5) around an occupied equilibrium position when the loudspeaker (5) is at rest, the diaphragm (50) being configured to oscillate in normal operation between a maximum output position and a maximum retracted position defining between them a maximum axial displacement (E) of the diaphragm (50), the diaphragm (50) defining a second edge (64); ) located radially opposite the first edge (24) at least in the rest position, the first edge (24) and the second edge (64) being radially separated by a distance (J),

the first edge (24) and the second edge (64) respectively having a first thickness (E1) and a second thickness (E2) along the axis (D), the first thickness (E1) and the second thickness (E2) defining a sum (E1 + E2),

characterized in that the sum (E1 + E2) divided by the maximum axial displacement (E) is less than 1/5 ^e , preferably less than 1/8 ^e , and even more preferably less than 1/12 ^e .

2. - acoustic chamber (1) according to claim 1, wherein the membrane (50) comprises at least one convex portion (60) whose convexity is turned towards the outside of the acoustic enclosure.

3. - acoustic chamber (1) according to claim 2, wherein the convex portion (60) is spherical.

4. Acoustic speaker (1) according to any one of claims 1 to 3, wherein the membrane (50) comprises a skirt (62) peripheral extending substantially parallel to the axis (D) and determining the second thickness. (E2).

5. Acoustic speaker (1) according to claim 4, wherein the skirt (62) is formed by a fold (63) of the membrane (50) and extends inwardly of the speaker (5).

6. - acoustic chamber (1) according to any one of claims 1 to 5, wherein the box (3) forms a flange (28) reentrant around the membrane (50), the flange (28) having an axial thickness reducing to the membrane (50), the flange (28) having a radially inner end (30) determining the first thickness (E1).

7. - acoustic chamber (1) according to claim 6, wherein the flange (28) has a flat outer face (32) facing outwardly of the acoustic chamber (1), and a flat inner face (34). turned towards the inside of the loudspeaker (1).

8. - acoustic chamber (1) according to claim 7, wherein the outer face (32) is substantially orthogonal to the axis (D) and the inner face (34) forms an angle (a) with the outer face (32); ), the angle (a) being less than or equal to 45 degrees.

9. Acoustic speaker (1) according to any one of claims 1 to 8, wherein the speaker (5) further comprises a magnetic circuit (38) forming at least one air gap (40), and at least one coil (54) located at least partly in the gap (40) and configured to be traversed by an electric current, the gap (40) and the coil (54) defining a radial clearance (J1), said distance (J ) between the first edge (24) and the second edge (64) being substantially equal to the radial clearance (J1).

10. Acoustic speaker (1) according to any one of claims 1 to 9, wherein the speaker (5) further comprises at least one seal (42) for suspending the membrane (50) relative to the box (3), the seal (42) having, in cross section, two ends (68, 70) located radially on either side of the first edge (24) and the second edge (64), the seal (42) forming a gutter (72) located axially on the inner side of the acoustic chamber with respect to the first edge (24) and the second edge (64) in the equilibrium position.