EP3510790B1

EP3510790B1 - Directional acoustic device

Info

Publication number: EP3510790B1
Application number: EP16767500.8A
Authority: EP
Inventors: Joseph A. COFFEY; Peter C. Santoro
Original assignee: Bose Corp
Current assignee: Bose Corp
Priority date: 2016-09-12
Filing date: 2016-09-12
Publication date: 2021-11-10
Anticipated expiration: 2036-09-12
Also published as: JP6878576B2; CN109863759A; JP2019526998A; EP3510790A1; CN109863759B; WO2018048438A1

Description

BACKGROUND

This disclosure relates to a directional acoustic device and methods for manufacturing a directional acoustic device.
Acoustic devices include loudspeakers and microphones. Loudspeakers generally include a diaphragm and a linear motor. When driven by an electrical input signal, the linear motor moves the diaphragm to cause vibrations in air, thereby generating sound. Various techniques have been used to control the directivity and radiation pattern of a loudspeaker, including acoustic horns, pipes, slots, waveguides, and other structures that redirect or guide the generated sound waves. In some of these loudspeaker structures, an opening in the horn, pipe, slot or waveguide is covered with an acoustically resistive material to improve the performance of the loudspeaker over a wider range of frequencies, e.g., to increase the directionality of the loudspeaker. Microphones can have one or more microphone elements that receive sound instead of a diaphragm and linear motor that generate sound. DE 197 03 311 shows a directional microphone consisting of a large acoustically guiding structure having apertures.

SUMMARY

The present invention relates to a directional acoustic device according to claim 1. Advantageous embodiments are recited in dependent claims of the appended set of claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For purposes of illustration some elements are omitted and some dimensions are exaggerated. For ease of reference, like reference numbers indicate like features throughout the referenced drawings.

Figure 1A is perspective view of a loudspeaker.
Figure 1B is front view of the loudspeaker of Figure 1A.
Figure 1C is a back view of the loudspeaker of Figure 1A.
Figure 2 shows a flow chart of a method for manufacturing the loudspeaker of Figures 1A through 1C.
Figure 3 shows a flow chart of an alternative method for manufacturing the loudspeaker of Figures 1A through 1C.
Figure 4 shows a flow chart of an alternative method for manufacturing the loudspeaker of Figures 1A through 1C.
Figure 5 shows a flow chart of an alternative method for manufacturing the loudspeaker of Figures 1A through 1C
Figure 6 shows a flow chart of a step that may be used in the methods for manufacturing shown in Figures 2 and 3.
Figure 7A is a plan view of a directionally radiating acoustic device and figure 7B is a cross-section taken along line 7B-7B.
Figures 8A and 8B are top and rear perspective views, respectively, of a housing for a directional receiving device.
Figure 9A is a top view of a thin sheet for a radiating surface;
Figure 9B is a top view of a radiating surface that includes the thin sheet of figure 9A;
Figure 9C is an exaggerated schematic side view of the radiating surface of figure 9B.

DETAILED DESCRIPTION

A loudspeaker 10, which does not fall under the scope of the claims, shown in Figures 1A through 1C, includes an electro-acoustic driver 12 coupled to an acoustic waveguide 14. The acoustic waveguide 14 is coupled to a resistive screen 16, on which an acoustically resistive pattern 20 is applied. The acoustically resistive pattern 20 may be a substantially opaque and impervious layer that is applied to or generated on the resistive screen 16. The electro-acoustic driver 12, acoustic waveguide 14, and resistive screen 16 together may be mounted onto a base section 18. The base section 18 may be formed integrally with the acoustic waveguide 14 or may be formed separately. The loudspeaker 10 may also include a plurality of mounting holes 22 for mounting the loudspeaker 10 in, for example, a ceiling, wall, or other structure. One such loudspeaker 10 is described in US 20160295318 .
The electro-acoustic driver 12 typically includes a motor structure mechanically coupled to a radiating component, such as a diaphragm, cone, dome, or other surface. Attached to the inner edge of the cone may be a dust cover or dust cap, which also may be dome-shaped. In operation, the motor structure operates as a linear motor, causing the radiating surface to vibrate along an axis of motion. This movement causes changes in air pressure, which results in the production of sound. The electro-acoustic driver 12 may be a mid-high or high frequency driver, typically having an operating range of 200 Hz to 16 kHz. The electro-acoustic driver 12 may be of numerous types, including but not limited to a compression driver, cone driver, mid-range driver, full-range driver, and tweeter. Although one electro-acoustic driver is shown in Figures 1A through 1C, any number of drivers could be used. In addition, the one or more electro-acoustic drivers 12 could be coupled to the acoustic waveguide 14 via an acoustic passage or manifold component, such as those described in US20110064247 .
The electro-acoustic driver 12 is coupled to an acoustic waveguide 14 which, in the example of Figures 1A through 1C, guides the generated sound waves in a radial direction away from the electro-acoustic driver 12. The loudspeaker 10 could be any number of shapes, including but not limited to circular, semi-circular, spherical, semi-spherical, conical, semi-conical, toroidal, semi-toroidal, rectangular, and a shape comprising a section of a circle, sphere, cone, or toroid. In examples where the loudspeaker 10 has a non-circular or non-spherical shape, the acoustic waveguide 14 guides the generated sound waves in a direction away from the electro-acoustic driver 12. The acoustic waveguide 14 may be constructed of a metal or plastic material, including but not limited to thermoset polymers and thermoplastic polymer resins such as polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE). Moreover, fibers of various materials, including fiberglass, may be added to the polymer material for increased strength and durability. The acoustic waveguide 14 could have a substantially solid structure, as shown in Figures 1A through 1C, or could have hollow portions, for example a honeycomb structure.
Before the generated sound waves reach the external environment, they pass through a resistive screen 16 coupled to an opening in the acoustic waveguide 14. The resistive screen 16 may include one or more layers of a mesh material or fabric. In some examples, the one or more layers of material or fabric may each be made of monofilament fabric (i.e., a fabric made of a fiber that has only one filament, so that the filament and fiber coincide). The fabric may be made of polyester, though other materials could be used, including but not limited to metal, cotton, nylon, acrylic, rayon, polymers, aramids, fiber composites, and/or natural and synthetic materials having the same, similar, or related properties, or a combination thereof. In other examples, a multifilament fabric may be used for one or more of the layers of fabric.
In one example, the resistive screen 16 is made of two layers of fabric, one layer being made of a fabric having a relatively high acoustic resistance compared to the second layer. For example, the first fabric may have an acoustic resistance ranging from 200 to 2,000 Rayls, while the second fabric may have an acoustic resistance ranging from 1 to 90Rayls. The second layer may be a fabric made of a coarse mesh to provide structural integrity to the resistive screen 16, and to prevent movement of the screen at high sound pressure levels. In one example, the first fabric is a polyester-based fabric having an acoustic resistance of approximately 1,000 Rayls (e.g., Saatifil® Polyester PES 10/3 supplied by Saati of Milan, Italy) and the second fabric is a polyester-based fabric made of a coarse mesh (e.g., Saatifil® Polyester PES 42/10 also supplied by Saati of Milan, Italy). In other examples, however, other materials may be used. In addition, the resistive screen 16 may be made of a single layer of fabric or material, such as a metal-based mesh or a polyester-based fabric. And in still other examples, the resistive screen 16 may be made of more than two layers of material or fabric. The resistive screen 16 may also include a hydrophobic coating to make the screen water-resistant.
The resistive screen 16 also includes an acoustically resistive pattern 20 that is applied to or generated on the surface of the resistive screen 16. The acoustically resistive pattern 20 may be a substantially opaque and impervious layer. Thus, in the places where the acoustically resistive pattern 20 is applied, it substantially blocks the holes in the mesh material or fabric, thereby creating an acoustic resistance that varies as the generated sound waves move radially outward through the resistive screen 16 (or outward in a linear direction for non-circular and non-spherical shapes). For example, where the acoustic resistance of the resistive screen 16 without the acoustically resistive pattern 20 is approximately 1,000 Rayls over a prescribed area, the acoustic resistance of the resistive screen 16 with the acoustically resistive pattern 20 may be approximately 10,000 Rayls over an area closer to the electro-acoustic driver 12, and approximately 1,000 Rayls over an area closer to the edge of the loudspeaker 10 (e.g., in areas that do not include the acoustically resistive pattern 20). The size, shape, and thickness of the acoustically resistive pattern 20 may vary, and just one example is shown in Figures 1A through 1C.
The material used to generate the acoustically resistive pattern 20 may vary depending on the material or fabric used for the resistive screen 16. In the example where the resistive screen 16 comprises a polyester fabric, the material used to generate the acoustically resistive pattern 20 may be paint (e.g., vinyl paint), or some other coating material that is compatible with polyester fabric. In other examples, the material used to generate the acoustically resistive pattern 20 may be an adhesive or a polymer. In still other examples, rather than add a coating material to the resistive screen 16, the acoustically resistive pattern 20 may be generated by transforming the material comprising the resistive screen 16, for example by heating the resistive screen 16 to selectively fuse the intersections of the mesh material or fabric, thereby substantially blocking the holes in the material or fabric.
Figure 2 shows a flow chart of a method 100 not falling under the scope of the claims for manufacturing the loudspeaker 10 of Figures 1A through 1C in the example where the resistive screen 16 is made of two layers of fabric, and a coating material is applied to the resistive screen 16 to form the acoustically resistive pattern 20. Although steps 102-112 of Figure 2 are shown as occurring in a certain order, it should be readily understood that the steps 102-112 could occur in a different order than is shown. Moreover, although steps 102-112 of Figure 2 are shown as occurring separately, it should be readily understood that certain of the steps could be combined and occur at the same time. As shown in Figure 2, to begin formation of the resistive screen 16, a first fabric is attached to a second fabric in step 102. The two fabrics may be attached by, for example, using a layer of solvent, adhesive, or glue that joins the two layers of fabric. Alternatively, the fabrics may be heated to a temperature that permits the two fabrics to be joined to each other. For example, the fabrics may be placed in mold that heats the fabrics to a predetermined temperature for a predetermined length of time until the fabrics adhere to each other, or a laser (or other heat-applying apparatus) may be used to selectively apply heat to portions of the fabrics until those portions adhere to each other. Alternatively, the fabrics could be joined by thermoforming, pressure forming and/or vacuum forming the fabrics.
In step 104, a coating material (such as paint, an adhesive or a polymer) is applied to the resistive screen 16 to form the acoustically resistive pattern 20. In one example, as shown in Figure 6, the coating material could be applied using a mask. In that example, a portion of the fabric could be masked (in step 120), and the coating material could be applied to the unmasked portion of the fabric (in step 122), by, for example, spraying or otherwise depositing the coating material onto the unmasked portion of the fabric. In some examples, after the mask has been applied, a coating material (e.g., adhesive beads or polymer beads) could be deposited on the unmasked portion of the fabric, and then melted onto the fabric via the application of heat. The coating material could be applied to the resistive screen 16 using other methods besides a mask, however. For example, the coating material could be pre-cut (for example, using a laser cutter or die cutter), and could then be ironed-on to the fabric or attached using an adhesive. For example, the coating material could comprise a sheet of polymer plastic, metal, paper, or any substantially opaque material having the same, similar, or related properties (or any combination thereof) that is pre-cut into the desired acoustically resistive pattern 20. The sheet could then be attached to the fabric via the application of heat or an adhesive. In yet another example, the coating material could be deposited directly onto the fabric, using a machine that can draw out the desired pattern 20, thereby selectively applying the coating material only to the portion of the fabric that should have the acoustically resistive pattern 20. In addition, the coating material could be applied to the resistive screen 16 using other known methods, including but not limited to a silkscreen, spray paint, ink jet printing, etching, melting, electrostatic coating, or any combination thereof.
Optionally, in step 106, the coating material may be cured, by, for example, baking the assembly at a predetermined temperature, applying ultraviolet (UV) light to the coating material, exposing the coating material to the air, or any combination thereof. If a coating material is selected that does not need to be cured, step 106 would be omitted. In some examples, steps 102, 104 and 106 could be combined into a single step. For example, the first and second layers of fabric could be placed on top of each other, and a UV-curable adhesive could be deposited onto one layer of the fabric in the desired acoustically resistive pattern 20. The adhesive could then be cured via the application of UV light, which would also result in adhering the two layers of fabric.
In step 108, the fabric is formed into the desired shape for the loudspeaker 10. For example, the fabric may be formed to be a semi-circle, circle, sphere, semi-sphere, rectangle, cone, toroid, or a shape comprising a section of a circle, sphere, cone, toroid and/or rectangle. The loudspeaker 10 may also be bent and/or curved along its length, as described in US 8,351,630 . These various shapes may be created by thermoforming the fabric (i.e., heating it to a pliable forming temperature and then forming it to a specific shape in a mold) and/or vacuum or pressure forming the fabric. Although Figure 2 shows step 108 as occurring after the coating material has been applied to the resistive screen 16, in other examples, the fabric could be formed into the desired shape before the coating material is applied. Moreover, step 108 could be combined with step 102, so that the forming process also joins the two layers of fabric.
In step 110, the resistive screen 16 is attached to the acoustic waveguide 14 via an adhesive, double-sided tape, a fastener (e.g., a screw, bolt, clamp, clasp, clip, pin or rivet), or other known methods. And in step 112, the electro-acoustic driver 12 is attached to the acoustic waveguide 14. The electro-acoustic driver 12 could be secured to the acoustic waveguide 14 via a fastener or other known methods. Although Figure 2 shows step 112 as occurring after the fabric has been attached to the acoustic waveguide, in other examples, the electro-acoustic transducer could be attached to the waveguide before the fabric is attached. The acoustic waveguide 14 could be constructed via compression molding, injection molding, plastic machining, or other known methods.
Figure 3 shows a flow chart of an alternative method 200 not falling under the scope of the claims for manufacturing the loudspeaker 10 of Figures 1A through 1C in the example where the resistive screen 16 is made of a single layer of fabric, and a coating material is applied to the resistive screen 16 to form the acoustically resistive pattern 20. Although steps 201-212 of Figure 3 are shown as occurring in a certain order, it should be readily understood that the steps 201-212 could occur in a different order than is shown. Moreover, although steps 201-212 of Figure 2 are shown as occurring separately, it should be readily understood that certain of the steps could be combined and occur at the same time. As shown in Figure 3, to begin formation of the resistive screen 16, a fabric is provided in step 201. In step 204, a coating material (such as paint, an adhesive or a polymer) is applied to the fabric to form the acoustically resistive pattern 20. The coating material could be applied using the methods previously pattern 20. The coating material could be applied using the methods previously described in connection with Figure 2 (e.g., via a mask, a pre-cut sheet of material, by depositing the coating material directly onto the fabric in the desired pattern 20, or via a silkscreen, spray paint, ink jet printing, etching, melting, electrostatic coating, or any combination thereof).
Optionally, in step 206, the coating material may be cured, by, for example, the methods previously described in connection with Figure 2 (e.g., baking the assembly at a predetermined temperature, applying UV light to the coating material, exposing the coating material to the air, or any combination thereof). If a coating material is selected that does not need to be cured, step 206 would be omitted. As with the example shown in Figure 2, steps 201, 204 and 206 could be combined into a single step.
In step 208, the fabric is formed into the desired shape for the loudspeaker 10. As with the example of Figure 2, the fabric may be formed to be a semi-circle, circle, sphere, semi-sphere, rectangle, cone, toroid, or a shape comprising a section of a circle, sphere, cone, toroid and/or rectangle. The loudspeaker 10 may also be bent and/or curved along its length, as described, for example, in U.S. Patent No. 8,351,630 . These various shapes may be created by thermoforming the fabric (i.e., heating it to a pliable forming temperature and then forming it to a specific shape in a mold) and/or vacuum or pressure forming the fabric. Although Figure 3 shows step 208 as occurring after the coating material has been applied to the resistive screen 16, in other examples, the fabric could be formed into the desired shape before the coating material is applied.
As with the example of Figure 2, in step 210, the resistive screen 16 is attached to the acoustic waveguide 14 via an adhesive, double-sided tape, a fastener (e.g., a screw, bolt, clamp, clasp, clip, pin or rivet) or other known methods; and in step 212, the electro-acoustic driver 12 is attached to the acoustic waveguide 14 via a fastener or other known methods. Although Figure 3 shows step 212 as occurring after the fabric has been attached to the acoustic waveguide, in other examples, the electro-acoustic transducer could be attached to the waveguide before the fabric is attached. As with the example of Figure 2, the acoustic waveguide 14 could be constructed via compression molding, injection molding, plastic machining, or other known methods.
Figure 4 shows a flow chart of an alternative method 300 not falling under the scope of the claims for manufacturing the loudspeaker 10 of Figures 1A through 1C in the example where the resistive screen 16 is made of two layers of fabric, and the acoustically resistive pattern 20 is formed by fusing the intersections of the fabric, thereby substantially blocking the holes in the fabric. Although steps 302-312 of Figure 4 are shown as occurring in a certain order, it should be readily understood that the steps 302-312 could occur in a different order than is shown. Moreover, although steps 302-312 of Figure 4 are shown as occurring separately, it should be readily understood that certain of the steps could be combined and occur at the same time. As shown in Figure 4, to begin formation of the resistive screen 16, a first fabric is attached to a second fabric in step 302. The first fabric could be attached to the second fabric using the methods previously described in connection with Figure 2 (e.g., via a layer of solvent, adhesive or glue, or via heating, thermoforming, pressure forming, vacuum forming, or any combination thereof).
In step 303, the fabric is fused to form the acoustically resistive pattern 20, such that the holes in the fabric are substantially blocked, thereby creating a substantially opaque and impervious layer on the fabric. The fabric could be fused by, for example, applying heat to the portions of the fabric that should have the acoustically resistive pattern 20, or by selectively applying chemical bonding elements to the portions of the fabric that should have the acoustically resistive pattern 20.
As with the examples of Figures 2 and 3, in step 308, the fabric is formed into the desired shape for the loudspeaker 10 (e.g., via thermoforming, vacuum forming and/or pressure forming); in step 310, the resistive screen 16 is attached to the acoustic waveguide 14; and in step 312, the electro-acoustic driver 12 is attached to the acoustic waveguide 14. These steps could be completed using the methods previously described in connection with Figures 2 and 3.
Figure 5 shows a flow chart of an alternative method 400 not falling under the scope of the claims for manufacturing the loudspeaker 10 of Figures 1A through 1C in the example where the resistive screen 16 is made of a single layer of fabric, and the acoustically resistive pattern 20 is formed by fusing the intersections of the fabric, thereby substantially blocking the holes in the fabric. Although steps 401-412 of Figure 5 are shown as occurring in a certain order, it should be readily understood that the steps 401-412 could occur in a different order than is shown. Moreover, although steps 401-412 of Figure 5 are shown as occurring separately, it should be readily understood that certain of the steps could be combined and occur at the same time. As shown in Figure 5, to begin formation of the resistive screen 16, a fabric is provided in step 401 .
In step 403, the fabric is fused to form the acoustically resistive pattern 20, such that the holes in the fabric are substantially blocked, thereby creating a substantially opaque and impervious layer on the fabric. The fabric could be fused by, for example, applying heat to the portions of the fabric that should have the acoustically resistive pattern 20, or by selectively applying chemical bonding elements to the portions of the fabric that should have the acoustically resistive pattern 20.
As with the examples of Figures 2 through 4, in step 408, the fabric is formed into the desired shape for the loudspeaker 10 (e.g., via thermoforming, vacuum forming and/or pressure forming); in step 410, the resistive screen 16 is attached to the acoustic waveguide 14; and in step 412, the electro-acoustic driver 12 is attached to the acoustic waveguide 14. These steps could be completed using the methods previously described in connection with Figures 2 through 4.
One or more acoustic sources or acoustic receivers can be coupled to a hollow structure such as an arbitrarily shaped conduit that contains acoustic radiation from the source(s) and conducts it away from the source, or conducts acoustic energy from outside the structure through the structure and to the receiver. The structure has a perimeter wall that is constructed and arranged to allow acoustic energy to leak through it (out of it or into it) in a controlled manner. The perimeter wall forms a 3D surface in space. Much of the following discussion concerns a directionally radiating acoustic device. However, the discussion also applies to directionally receiving acoustic devices in which receivers (e.g., microphone elements) replace the acoustic sources. In a receiver, radiation enters the structure through the leaks and is conducted to the receiver.
The magnitude of the acoustic energy leaked through a leak (i.e., out of the conduit through the leak or into the conduit through the leak) at an arbitrary point on the perimeter wall depends on the pressure difference between the acoustic pressure within the conduit at the arbitrary point and the ambient pressure present on the exterior of the conduit at the arbitrary point, and the acoustic impedance of the perimeter wall at the arbitrary point. The phase of the leaked energy at the arbitrary point relative to an arbitrary reference point located within the conduit depends on the time difference between the time it takes sound radiated from the source into the conduit to travel from the source through the conduit to the arbitrary reference point and the time it takes sound to travel through the conduit from the source to the selected arbitrary point. Though the reference point could be chosen to be anywhere within the conduit, for future discussions the reference point is chosen to be the location of the source such that the acoustic energy leaked through any point on the conduit perimeter wall will be delayed in time relative to the time the sound is emitted from the source. For a receiver configured to receive acoustic output from a source located external to the conduit, the phase of the sound received at any first point along the leak surface relative to any second point along the leak surface is a function of the relative difference in time it takes energy emitted from the external acoustic source to reach the first and second points. The relative phase at the receiver for sounds entering the conduit at the first and second points depends on the relative time delay above, and the relative distance within the conduit from each point to the receiver location.
The shape of the structure's perimeter wall surface through which acoustic energy leaks (also called a "radiating section" or "radiating portion" herein) is arbitrary. In some examples, the perimeter wall surface (radiating portion) may be generally planar. One example of an arbitrarily shaped generally planar wall surface 40 according to the invention is shown in Figs. 7A and 7B. The cross hatched surface 41 of wall 40 represents the radiating portion through which acoustic volume velocity is radiated.
Directionally radiating acoustic device 30 includes structure or conduit 32 to which loudspeaker (acoustic source) 34 is acoustically coupled at proximal end 36; the source couples to the conduit along an edge of the 2D projected shape of the conduit. There could be two or more acoustic sources rather than the one shown. Radiating portion 41 in this non-limiting example is the bottom surface of conduit 32, but the radiating surface could be on the top or on both the top and bottom surfaces of generally planar conduit 32. Arrows 42 depict a representation of acoustic volume velocity directed out of the conduit 32 through leak section 43 in bottom wall 40 into the environment. The length of the arrows is generally related to the amount of volume velocity emitted. The amount of volume velocity emitted to the external environment may vary as a function of distance from the source. For use as a receiver, source 34 would be replaced with one or more microphone elements, and the volume velocity would be received into rather than emitted from radiating portion 41.
Leak section 43 is a portion of the radiating portion 41 of wall 40, and is depicted extending along the direction of sound propagation from speaker 34 toward conduit periphery 38. The following discussion of leak section 43 is also applicable to other portions of the radiating portion 41 of wall 40. It is useful to only consider what is happening in section 43 for purposes of discussion, to better understand the nature of operation of the examples disclosed herein. Leak section 43 is depicted as continuous, but could be accomplished by a series of leaks aligned along the sound propagation direction (or sound reception direction for a receiver). Leak section 43 is shown in Fig. 7A as a rectangular strip extending in a straight line away from the location of speaker 34. This is a simplification to help illustrate the lengthwise extent of the radiating portion 41 of wall 40. In general, a significant or in some examples the entire portion of surface 40 may be radiating, as illustrated by the cross-hatching. In some examples, the portion of surface 40 incorporating a leak may vary as a function of distance or angle or both from the location of a source (or sources in examples with more than one source). The location, size, shape, acoustical resistance and other parameters of the leaks are variables that can be taken into account to achieve a desired result, including but not limited to a desired directionality of sound radiation or sound reception.
An exemplary end fire shell acoustic receiver is shown in Figs. 8A and 8B. Device 50 comprises housing 52 with openings 62 and 63 that each hold a microphone element (not shown). There can be one, two or more microphone elements. Device 50 has a generally ¼ circle (i.e., generally circular segment) shape or profile, subtending an angle of about 90 degrees. End/sidewalls 53 allow the device to be pitched downward, but this is not a necessary feature. Peripheral flange 56 provides rigidity. Ribs 57-59 that project above solid wall 54, along with interior shelf 60, define a surface on which a resistive screen (not shown, but such as the radiating surface 70 depicted in figures 9A-9C) is located. The screen accomplishes the leaks. The screen can be of any type, including but not limited to those described herein. The conduit is formed between this screen and wall 54. As can be seen, from peripheral wall 56 to the microphone location the depth of the conduit progressively increases, but the depth could be consistent or could progressively decrease, or could have a different profile.
Another example of a radiating surface according to the invention is depicted in part, and as a whole, in figures 9A, 9B and 9C. Radiating surface 70 comprises thin acoustically-opaque (or highly acoustically resistant) sheet 72 (fig. 9A) with a number of openings (only openings 90, 116, 124 and 130 are numbered in figure 9A, simply for convenience of illustration). The openings are through the sheet thickness, between top surface 73 and lower surface 75. Sheet 72 generally has the same shape as the surface of the conduit that it covers so as to define the radiating portion of the conduit. In this non-limiting example sheet 72 has a generally one-half circular segment shape defined by outer perimeter walls 74, 76, 78 and 80. Arc-shaped support ribs 82, 84, 86, 88, 90, 92, 94, 96, 98 and 100 each extend from side 76 to side 78. Support ribs, if present in the thin sheet, do not need to be arc shaped and do not need to extend from side to side. Generally radial support ribs that generally lie along radii from center point 109 (only ribs 110, 112, 114, 120, 122, 126 and 128 are numbered in figure 9A, simply for convenience of illustration) are connected between the arc-shaped support ribs. The support ribs (or support structures that are not rib-shaped) in total define the openings while maintaining the necessary stiffness. In this non-limiting example the area of sheet 72 includes the outer perimeter walls, the inner support ribs, and the openings. To further illustrate the relationship of these elements, opening 116 is defined between outer wall 80, rib 100 and ribs 112 and 114. Opening 124 is defined between ribs 96, 98, 120 and 122. Opening 130 is defined between ribs 92, 94, 126 and 128. Opening 90 is defined between inner wall 74, peripheral wall 76, rib 82 and rib 110. More generally, since the openings are the features of the sheet that contribute to leaks, sheet material remaining after the openings have been created may comprise ribs or may have other shapes, such shapes not being critical to the operation of the radiating surface. According to the invention, the thin sheet has a generally circular segment shape, the openings are generally arc shaped and the ribs will generally but not necessarily be arc shaped and fully or partially radial.
Sheet 72 is typically made from a thin sheet of plastic, metal or other material that is sufficiently strong to span the radiating portion of the acoustic device without sagging in a way that detrimentally affects the function of the device, and that is also effectively acoustically opaque. In one non-limiting example sheet 72 is a 1 mm thick sheet of polycarbonate or polyethylene terephthalate (PET) or another plastic. The openings can be created in any desired fashion such as by die cutting, laser cutting, or machining as three non-limiting examples. The sheet should be sufficiently thin that it does not substantially affect the acoustic performance of the openings. For example, it should not be so thick that the openings act like ports.
At least parts of at least some of the openings in sheet 72 are partially or fully covered by a cover material that has a greater acoustic resistance than the acoustic resistance of the openings (which is typically very low or zero). In one non-limiting example cover material 120, shown in figures 9B and 9C, is a sheet of the approximately 1,000 Rayl Saatifil® Polyester PES 10/3 material described above. Other woven or non-woven materials can be used, some examples of which are described above. Other possibilities include very thin solid sheets with patterns of holes that accomplish the desired acoustic resistance or pattern of graded acoustic resistances. The cover material 120 can cover the entire bottom surface 75 of sheet 72 (as shown in fig. 9C), or can be arranged in other manners to cover some or all of some or all of the openings in sheet 72. If the radiating surface does not lay flat in use in the directional acoustic device but instead is bent, then the fabric (mainly for aesthetic reasons) is preferably on the side that is in tension so the fabric is in tension and thus is less likely to fold or bunch.
Radiating surface 70 can be fabricated as follows. A 1 mm thick sheet of polycarbonate is covered on one surface (side 75 in this case) with a pressure sensitive adhesive 122 (fig. 9C). The sheet is then die cut to create the openings. The Saatifil fabric is then adhered to the sheet via the adhesive. The fabric covers all of or substantially all of side 75 of sheet 72.
As described above, other materials could be used for the thin sheet. Also, other types of adhesives could be used such as an RTV or other. The cover material (e.g., the fabric) could optionally cover some or all of only some of the openings in the thin sheet. The cover material could comprise one sheet of material or two or more portions of material that were separately coupled to the thin sheet. The cover material could be coupled to the thin sheet in ways other than via an adhesive, such as with mechanical fasteners, for example.
A number of implementations have been described. Nevertheless, it will be understood that additional modifications may be made without departing from the scope of the following claims.

Claims

A directional acoustic device (30), comprising:
an acoustic source (34) or an acoustic receiver; and

a conduit (32) to which the acoustic source or acoustic receiver is acoustically coupled and within which acoustic energy travels in a propagation direction from the acoustic source or to the acoustic receiver, wherein the conduit has a radiating portion (41) that has a radiating surface with leak openings that define controlled leaks through which acoustic energy radiated from the source into the conduit can leak to the outside environment or through which acoustic energy in the outside environment can leak into the conduit;

wherein the radiating surface comprises a sheet (72) with a plurality of openings (62,63,90,116,124,130) through the sheet, and a cover material (120) with a greater acoustic resistance than an acoustic resistance of an opening, where the cover material covers at least parts of at least some of the openings, to define a plurality of controlled acoustic leaks into or out of the conduit;

characterized in that the sheet has a generally circular segment shape, and in that at least some of the openings through the sheet are generally arc-shaped.
The directional acoustic device of claim 1, wherein the cover material comprises an open weave material.
The directional acoustic device of claim 2, wherein the open weave material comprises a fabric material.
The directional acoustic device of claim 1, wherein the sheet is substantially acoustically opaque.
The directional acoustic device of claim 1, wherein the sheet comprises a plastic sheet.
The directional acoustic device of claim 5, wherein the plastic sheet comprises a polycarbonate material.
The directional acoustic device of claim 1, wherein the sheet comprises a plurality of generally arc-shaped support ribs.
The directional acoustic device of claim 7, wherein the sheet has a width and at least some of the support ribs extend across at least most of the width.
The directional acoustic device of claim 1, wherein the cover material is adhered to the sheet.
The directional acoustic device of claim 9, wherein the cover material is adhered to the sheet with a pressure-sensitive adhesive.
The directional acoustic device of claim 9, wherein the cover material fully covers all of the openings through the sheet.
The directional acoustic device of claim 1, wherein the cover material fully covers all of the openings through the sheet.
The directional acoustic device of claim 1, wherein the radiating surface is mounted to the conduit such that the radiating surface defines an outer surface of the directional acoustic device.
The directional acoustic device of claim 13, wherein the cover material is in tension.