EP4082222A1

EP4082222A1 - Enclosure for diffusing sound by reverberation

Info

Publication number: EP4082222A1
Application number: EP20851218.6A
Authority: EP
Inventors: Arnaud Cazes Bouchet
Original assignee: Focal JMLab SAS
Current assignee: Focal JMLab SAS
Priority date: 2019-12-24
Filing date: 2020-12-21
Publication date: 2022-11-02
Also published as: FR3105692B1; WO2021130441A1; FR3105692A1; US11627411B2; CN114930872B; CN114930872A; US20230044069A1

Abstract

The invention relates to an enclosure for diffusing sound by reverberation (10) comprising: - a loudspeaker (11) comprising a fixed frame (12), a cylindrical support (13) and a membrane (14) connected to an upper bearing surface (16) of the frame (12); and - a wave guide (20) mounted on the upper bearing surface (16), the wave guide being substantially in the form of a truncated pyramid with a long wall (21) forming a front face (Fa), a short wall (22) and lateral uprights (23); the wave guide (20) comprising at least one acoustic wall (25) fastened to the lateral uprights (23), the acoustic wall (25) extending tangentially relative to the generatrix line (Dg) of the cylindrical support (13) closest to the front face (Fa).

Description

DESCRIPTION

TITLE: REVERBERATION SOUND DIFFUSION SPEAKER

TECHNICAL AREA

The invention relates to a reverberating sound diffusion enclosure, that is, an enclosure for projecting sound waves onto a reflecting surface, typically a ceiling or wall of a room.

The invention relates more particularly to an enclosure in which the crosstalk is high between the sound waves obtained by reverberation and those projected in front of the enclosure.

The invention finds a particularly advantageous application for home cinema installations, cinemas, or music listening rooms for which it is desired to spatialize the sound waves in a room.

PRIOR ART

To spatialize the sound waves in a room, it is known to integrate several speakers in different places of the room in order to provide the audience with sounds coming from several directions. This solution is used in particular to improve immersion in a film or improve the listening quality of a musical work.

The scientific publication “Poletti et al .: Sound reproduction with fixed-directivity speakers; J. Acoust. Soc. Am., Vol. 127, No. 6, June 2010 ”describes the implantation constraints to form sound waves correctly spatialized in a room according to the position of the audience. As indicated in this publication, a major obstacle to the generalization of this technology lies in the complexity of integrating the speakers necessary to form the spatialized sound waves. For example, it is often complex to integrate speakers in a ceiling or in a wall of an individual wishing to create a home cinema room. To respond to this problem, speakers are known which make it possible to project sound waves onto a reflecting surface, typically a ceiling or a wall in a room, acting as an acoustic mirror.

This solution makes it possible to simulate the positioning of a speaker on a wall or a ceiling. Thus, instead of receiving the sound waves coming directly from a speaker oriented towards the audience, the audience can also receive one or more sound waves obtained by reverberation on a reflection surface by means of a speaker distant from this surface. reflection.

In the example of Figure 1, a reverberation sound diffusion speaker 100 is placed on the floor 40 in front of a screen, not shown, of a home cinema room. The enclosure 100 includes a speaker 110 oriented towards the ceiling 41 so as to transmit the sound waves by reverberation on the ceiling 41 of the home cinema room.

This type of enclosure nevertheless poses a problem of crosstalk. For the purposes of the invention, crosstalk corresponds to the ratio between the sound Sr picked up by the audience by reverberation and the sound Sd picked up coming directly from the speaker. For example, this crosstalk can be measured by a microphone 42, as shown in Figure 1.

Of course, the propagation time of sound waves obtained by reverberation is greater than the propagation time of sound waves transmitted directly from the loudspeaker of the enclosure. The presence of sound waves transmitted directly therefore disturbs the listening quality of sound waves obtained by reverberation and it is sought to limit the direct transmission of sound to improve crosstalk.

In addition, the acoustic energy radiated by the loudspeaker weakens in proportion to the square of the distance traveled. Thus, by using a loudspeaker operating by reverberation, the loudspeaker must provide much greater acoustic energy than to obtain direct propagation. To meet these requirements, it is possible to use a loudspeaker with a large diameter, that is to say with a diameter greater than 20 cm.

However, with this type of loudspeaker, it is not possible to obtain a low-profile enclosure, that is to say with dimensions less than 14 cm high by 28 cm long and 18 cm high. width.

To obtain a small footprint speaker, it is necessary to use a smaller speaker. However, the smaller sized loudspeakers are less directional and they pose diffraction and acoustic breakdown problems which deteriorate the acoustic performance.

To partially remedy these problems, it is possible to use a waveguide 120 on the loudspeaker 110 in order to limit the propagation of the sounds Sd, as illustrated in FIG. 1. However, even with a guide wave 120, it is necessary to limit the tilt angle α between the loudspeaker and the length of the enclosure box in order to obtain an acceptable level of crosstalk with a small loudspeaker. Typically, the tilt angle al of a small footprint enclosure is close to 70 °, which limits the possible distance between enclosure 100 and the audience. Thus, a small enclosure is conventionally placed less than 2m from the audience so that the sound waves obtained by reverberating on a ceiling reach the audience correctly.

The same problems arise for a reverb sound diffusion speaker configured to project sound waves onto a wall in a room.

Thus, the technical problem of the invention is to find how to improve the crosstalk of a sound diffusion speaker by reverberation, in particular for speakers of small dimensions.

DISCLOSURE OF THE INVENTION

To respond to this problem, the invention proposes to use at least one acoustic wall integrated in the waveguide to improve the performance of the waveguide. The invention is the result of a discovery resulting from the observation that the highest frequencies are not correctly picked up by the waveguide in the context of a sound diffusion enclosure by reverberation.

To remedy this problem, the invention has required extensive studies to determine how to modify the directivity of the high frequencies generated by the loudspeaker of a reverb sound diffusion enclosure. In particular, acoustic walls of very different shapes and positions were tested. It emerges from these studies that the crosstalk is improved in a very surprising way when at least one acoustic wall is fixed on the lateral uprights of the waveguide and that this acoustic wall extends tangentially with respect to the generating line of the cylindrical support. speaker closest to a front panel of the speaker.

To this end, according to a first aspect, the invention relates to a sound diffusion enclosure by reverberation comprising:

- a loudspeaker comprising:

. a fixed frame,

. a cylindrical support movable in translation, and

. a membrane, an annular outer edge of which is connected to an upper bearing surface of said frame by means of a suspension and an annular inner edge which is fixed to said cylindrical support; and

a waveguide mounted on said upper bearing surface of said frame, said waveguide having substantially the shape of a truncated pyramid with a wall of great length, a wall of short length and lateral uprights connecting said walls ; said long wall forming a front face of said enclosure so that said long wall blocks the propagation of sound in front of said enclosure so that most of the sound is directed towards a reflecting surface.

The invention is characterized in that said waveguide also comprises at least one acoustic wall fixed to said lateral uprights, said acoustic wall extending tangentially with respect to the line generating said cylindrical support closest to said front face. The modification carried out on the waveguide makes it possible to improve the crosstalk of a sound diffusion enclosure by reverberation by channeling the high frequencies generated by the enclosure.

This improvement in crosstalk makes it possible to use loudspeakers with small diameters, typically diameters between 5 and 15 cm, so as to obtain a cabinet with reduced dimensions. For example, the enclosure can be made in a box on which said speaker and said waveguide are fixed, said box having a height of less than 14cm, a length of less than 28cm and a width of less than 18cm.

These small dimensions make it possible to meet the space requirements of individuals.

The improved crosstalk also reduces the tilt angle of the speaker relative to the length of the cabinet. Thus, it is now possible to tilt the speaker at an angle of between 30 and 50 ° relative to the height of the cabinet.

According to the invention, the inclination of the loudspeaker relative to a length of the box means that the axis of the loudspeaker passing through the center of the cylindrical support is offset relative to an axis extending along the length of the box. , for example an axis directed towards a predetermined point of listening.

Increasing the tilt angle of the speaker increases the distance between the speaker and the audience. Indeed, while a small enclosure is necessarily placed less than 2m from the audience so that the sound waves obtained by reverberation on a ceiling reach the audience correctly, the invention makes it possible to place the enclosure at a distance of between 3 and 4.5m. As a result, the speaker can be less close to the audience, which also limits the installation constraints. The same principle applies for a speaker projecting sound onto a wall. To achieve the power performance required to maintain an acceptable sound level at this distance, the upper surface of the cylindrical support is preferably provided with a dome, for example an inverted dome.

For the purposes of the invention, an inverted dome corresponds to a dome whose curvature is oriented towards an interior part of the fixed frame.

By increasing the power of a small enclosure, diffraction and acoustic breakdown problems are however increased. To solve these problems, it is possible to further limit the crosstalk by using a second acoustic wall.

According to one embodiment, said waveguide also comprises a second acoustic wall fixed between said lateral uprights and between said first acoustic wall extending tangentially with respect to the generating line and said front face, said second acoustic wall extending substantially parallel to said first acoustic wall with a distance between said acoustic walls substantially equal to the radius of said cylindrical support.

This specific positioning of the second acoustic wall makes it possible to efficiently channel the intermediate frequencies between the high frequencies, picked up by the first acoustic wall, and the low frequencies, picked up by the waveguide.

According to one embodiment, said acoustic wall extending tangentially with respect to the generating line comprises a semicircular lip extending in the direction of said cylindrical support substantially at the center of said lateral uprights.

This embodiment further improves crosstalk by channeling the highest frequencies, generated as close as possible to the speaker, onto the first acoustic wall.

The invention thus makes it possible to obtain an enclosure for diffusing sound by reverberation, of small dimensions, and having significant crosstalk. According to a second aspect, the invention relates to a home cinema installation incorporating a speaker according to the first aspect of the invention.

BRIEF DESCRIPTION OF THE FIGURES

The manner of carrying out the invention as well as the advantages which result therefrom will emerge from the following embodiments, given as an indication but not limited to, in support of the appended figures in which:

[Fig 1] Figure 1 is a schematic sectional view of a state-of-the-art reverberation sound diffusion speaker implemented in a home cinema installation;

[Fig 2] Figure 2 is a schematic sectional view of a sound diffusion speaker by reverberation, according to a first embodiment of the invention, implemented in a home cinema installation;

[Fig 3] Figure 3 is a schematic sectional view of a speaker and a waveguide according to a second embodiment of the invention;

[Fig 4] Figure 4 is a schematic sectional view of the first acoustic wall of the waveguide of Figure 3;

[Fig 5] Figure 5 is a schematic sectional view of the second acoustic wall of the waveguide of Figure 3;

[Fig 6a] Figures 6a-6f are sectional views of the loudspeaker and waveguide of figure 3 for different frequencies generated by the loudspeaker: 100Hz (figure 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f). [Fig 6b] Figures 6a-6f are sectional views of the speaker and waveguide of Figure 3 for different frequencies generated by the speaker: 100Hz (Figure 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f). [Fig 6c] Figures 6a-6f are sectional views of the speaker and waveguide of Figure 3 for different frequencies generated by the speaker: 100Hz (Figure 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f). [Fig 6d] Figures 6a-6f are sectional views of the speaker and waveguide of Figure 3 for different frequencies generated by the speaker: 100Hz (Figure 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f). [Fig 6e] Figures 6a-6f are sectional views of the loudspeaker and waveguide of the FIG. 3 for different frequencies generated by the loudspeaker: 100Hz (FIG. 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f). [Fig 6f] Figures 6a-6f are sectional views of the speaker and waveguide of Figure 3 for different frequencies generated by the speaker: 100Hz (Figure 6a); 1 kHz (Figure 6b); 2kHz (figure 6c); 5kHz (Figure 6d); 10kHz (figure 6e) and 16kHz (figure 6f); [Fig 7a] Figure 7a is a first perspective view of the speaker and waveguide of Figure 3;

[Fig 7b] Figure 7b is a second perspective view of the speaker and waveguide of Figure 3;

[Fig 7c] Figure 7c is a third perspective view of the speaker and waveguide of Figure 3; and

[Fig 7d] Figure 7d is a fourth perspective view of the speaker and waveguide of Figure 3

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 illustrates a speaker for broadcasting sound by reverberation 10 integrated into a home cinema room. To do this, the enclosure 10 is placed on the floor 40 in front of a screen, not shown. The enclosure 10 comprises a loudspeaker 11 oriented towards the ceiling 41 of the cinema room so as to use the ceiling 41 as a reflecting surface for the sound waves emitted from the loudspeaker 11. The nature of the surface reflection can vary without changing the invention.

For example, the speaker 10 can be arranged on the ceiling 41 using the floor 40 as a reflecting surface or the speaker 10 can be turned up by a 90 ° angle to use a wall in the home theater room as a surface. reflection.

The loudspeaker 11 comprises a frame 12 fixed inside a box 30 forming the external dimensions of the enclosure 10. Preferably, the box 30 has a height of less than 14 cm, a length of less than 28 cm and a width less than 18 cm. Preferably, the power of the loudspeaker 11 is substantially 250 Watts. The orientation of the loudspeaker 11 with respect to the box 30 makes it possible to adjust the angle of inclination al and, thus, the distance traveled by the sound waves obtained by reverberation between the enclosure 10 and the audience. In the example of FIG. 2, the angle a1 between an axis of revolution Ar of the loudspeaker 11 and an axis extending along the length of the box 30 is between 40 and 60 degrees, and preferably between 50 and 52 degrees.

The frame 12 supports a motor for driving a membrane 14. To do this, the loudspeaker 11 comprises a cylindrical support 13 movable in translation by means of the magnetic field generated by the motor, not shown. This cylindrical support 13 is connected to the membrane 14 by an inner annular edge 18 of the membrane 14 fixed to an upper end of the cylindrical support 13.

In the description, the relative terms “upper” or “lower” refer to the conventional positioning of a loudspeaker as illustrated in FIG. 3 in which the motor is arranged in the lower part while the membrane 14 is arranged in the lower part. upper part of the loudspeaker 11. Of course, the loudspeaker 11 can be turned upside down without changing the invention.

The annular outer edge 15 of the membrane is for its part connected to an upper bearing surface 16 of the frame by means of a suspension 17. Thus, the frame 12 extends from the base of the loudspeaker 11 to its upper end by surrounding the cylindrical support 13 and the membrane 14.

In the lower part of the loudspeaker 11, the cylindrical support 13 preferably has an upper surface 28 provided with a dome, for example an inverted dome. In the upper part of the loudspeaker 11, the upper bearing surface 16 of the frame 12 preferably has a diameter of between 5 and 15 centimeters.

In addition to fixing the membrane 14, this upper bearing surface 16 also makes it possible to mount a waveguide 20 also fixed inside the box 30. This waveguide 20 has a substantially truncated pyramidal shape with a wall. front of great length 21 is a rear wall of short length 22. References to the relative terms "front" and "rear" are understood in relation to Figure 2 in which the front part of the enclosure 10 is the part intended to be positioned close to the audience while the rear part of the speaker. enclosure 10 is the part intended to be positioned farthest from the audience. Of course, the loudspeaker 11 can be arranged differently without changing the invention but, in all cases, the front wall of great length 21 forms a front face Fa of the enclosure 10 as regards the propagation of the sound waves. .

It is sought to limit the propagation of sound waves in the front part of the enclosure 10 in order to increase the crosstalk of the enclosure 10. The crosstalk is measured at the level of the audience, for example by a microphone 42, by means of the ratio Sr to Sd between the sound Sr picked up by the audience by reverberation and the sound Sd picked up by the audience coming directly from the speaker 10.

In the waveguide 20, the very long wall 21 limits the propagation of direct sound waves Sd to promote reception by the audience of sound waves Sr obtained by reverberation on the ceiling 41. The walls 21 and 22 of the guide d 'wave 20 are connected by lateral uprights 23. The opening angle of the waveguide 20, that is to say the angle of inclination a2 of the various walls 21 to 23 of the waveguide 20 from the upper bearing surface 16 of the frame 12, is preferably between 5 and 10 degrees.

For a loudspeaker 11 whose upper support surface 16 is between 5 and 15 cm, the long front wall 21 may have a length of between 12 and 20 cm, preferably between 14 and 15 cm.

The rear wall of short length 22 may have a length of between 0 and 5 cm. Around the terminal end of the walls 21 to 23, that is to say at the level of the end opposite to that fixed on the upper bearing surface 16 of the frame 12, the waveguide 20 may have a flap intended to allow the fixing of the waveguide 20 on the box 30. The invention proposes to improve the waveguide 20 by integrating at least one acoustic wall 25 fixed between the side uprights 23. Thus, in the embodiment of FIG. 2, the enclosure 10 comprises a single acoustic wall 25. while, in the second embodiment of Figure 3, the waveguide 20 incorporates a second acoustic wall 26. This embodiment of Figure 3 is also shown in perspective in Figures 7a to 7d.

The first acoustic wall 25 is fixed between the side uprights 23. It can extend over the entire height of these side uprights 23 to form a substantially trapezoidal plate. As a variant, the height of this acoustic wall 25 can extend over only part of the height of the vertical uprights 23.

In addition, this first acoustic wall 25 extends substantially tangentially to a generating line Dg of the cylindrical support 13. In fact, the cylindrical support 13 has an axis of revolution Ar around which a set of generating lines form the various points of the cylinder. Among all of these generating lines, the generating line Dg closest to the front face Fa constitutes the line on which the first acoustic wall is formed. Thus, as illustrated in Figure 4, the line Dg passes substantially through the center of the trapezoidal shape of the first acoustic wall 25.

Preferably, the lower part of the first acoustic wall 25 is provided with a semicircular lip 25 extending in the direction of the cylindrical support 13 and substantially in the center of the side uprights 23.

In the example of FIG. 3, a second acoustic wall 26 is also fixed between the two lateral uprights 23 over only part of the height of these lateral uprights 23, as illustrated in FIG. 5.

For example, the distance DI between the first 25 and the second 26 acoustic wall is preferably substantially equal to the radius R of the cylindrical support 13. Thus, the second acoustic wall 26 extends along an axis A2 parallel to the axis of revolution Ar and on the generating line Dg. Figures 6a to 6f show sound wave propagation simulations of the embodiment of Figure 3. As illustrated in Figure 6a, for a 100 Hz sound wave, the entire surface of the membrane 14 is used to generate the sound waves and the front face Fa of the waveguide 20 is sufficient to guide the sound waves towards the ceiling 41.

When the frequency of the sound waves increases, as illustrated in FIG. 6b for a frequency of 1 kHz, the sound waves tend to escape from the waveguide 20 through the front face Fa and these sound waves risk creating disturbance to the audience.

From the frequency of 2 kHz, as illustrated in FIG. 6c, the second acoustic wall 26 captures part of the sound waves generated by the loudspeaker 11 to redirect them towards the ceiling 41.

For even higher frequencies, such as the 5 kHz frequency illustrated in FIG. 6d, the generation of the sound waves is very localized in the center of the membrane 14. In this simulation, the second acoustic wall 26 becomes inoperative and it is the first acoustic wall 25 which guides the acoustic waves towards the ceiling

41.

Then, for larger frequencies, such as the 10 kHz frequency shown in Figure 6e or the 16kHz frequency shown in Figure 6f, sound waves are generated from the level of the inverted dome of speaker 11. For these frequencies , the semicircular lip 27 of the first acoustic wall 25 makes it possible to channel the sound waves on the first acoustic wall 25 in order to transmit them towards the ceiling 41.

To conclude, the invention proposes to modify a waveguide 20 of a speaker 10 for diffusing sound by reverberation in order to improve crosstalk.

This improvement in crosstalk makes it possible to reduce the angle of inclination α1 of the loudspeaker 11 and, thus, to place the enclosure 10 further away from the audience in order to reduce the installation constraints of the enclosure 10. It follows that the invention makes it easier to form a home cinema or a musical listening room.

Claims

1. Sound diffusion enclosure by reverberation (10) comprising:

- a loudspeaker (11) comprising:

. a fixed frame (12),

. a cylindrical support (13) movable in translation, and

. a membrane (14) of which an annular outer edge (15) is connected to an upper bearing surface (16) of said frame (12) by means of a suspension (17) and an annular inner edge (18) which is fixed on said cylindrical support (13); and

- a waveguide (20) mounted on said upper bearing surface (16) of said frame (12), said waveguide having substantially the shape of a truncated pyramid with a very long wall (21), a short wall (22) and side posts (23) connecting said walls (21-22); said long wall (21) forming a front face (Fa) of said enclosure (10) so that said long wall (21) blocks the propagation of sound in front of said enclosure (10) so that the greater part of the its is directed towards a reflecting surface (41); characterized in that said waveguide (20) also comprises at least one acoustic wall (25) fixed to said lateral uprights (23), said acoustic wall (25) extending tangentially with respect to the generating line (Dg) of said cylindrical support (13) closest to said front face (Fa).

2. Reverberation sound diffusion enclosure according to claim 1, wherein said waveguide (20) also comprises a second acoustic wall (26) fixed between said side uprights (23) and between said first acoustic wall (25). extending tangentially with respect to the generating line (Dg) and said front face (Fa), said second acoustic wall (26) extending substantially parallel to said first acoustic wall (25) with a distance (Dl) between said acoustic walls (25-26) substantially equal to the radius (R) of said cylindrical support (13).

3. Reverberation sound diffusion enclosure according to claim 1 or 2, wherein said acoustic wall (25) extending tangentially with respect to the generating line (Dg) comprises a semicircular lip (27) extending in direction of said cylindrical support (13) substantially at the center of said lateral uprights (23).

4. Reverberation sound diffusion enclosure according to one of claims 1 to 3, wherein said enclosure (10) comprises a box (30) on which said speaker (11) and said waveguide (20) are integrated, said box (30) having a height (H) less than 14cm, a length less than 28cm and a width less than 18cm.

The reverberation sound diffusing enclosure according to claim 4, wherein said loudspeaker (11) is inclined at an angle (a1) of between 40 and 60 ° with respect to a length of said box (30).

6. A reverberation sound diffusion enclosure according to one of claims 1 to 5, wherein an upper surface (28) of said cylindrical support (13) is provided with a dome.

7. A reverberation sound diffusion enclosure according to claim 6, wherein said dome is inverted.

8. Reverberation sound diffusion enclosure according to one of claims 1 to 7, wherein said loudspeaker (11) has a membrane (14) whose diameter is between 5 and 15 cm.

9. home cinema installation comprising a speaker for broadcasting sound by reverberation according to one of claims 1 to 8.