GB2408404A - Fabrication of enclosures for sonic devices, e.g. speakers - Google Patents

Abstract

The technique comprises the steps of providing a plurality of laminar substrates 10-110, at least one of which is configured to constitute part at least of a sonic cavity 50 and/or a conduit for sound energy 22, 72; and of stacking the substrates in juxtaposed relationship to form the sonic device. By this means, sonic devices which are reliable and rugged in operation can be produced accurately and economically, and can exhibit audio performance of good quality. Multi-speaker or multi-channel arrangements are also disclosed (figs 7 and 9). The invention provides a technique facilitating the fabrication of miniature sonic devices for audio applications and is particularly applicable to the fabrication of relatively complex component structures for sonic devices, particularly microspeakers 40, which structures can conveniently be regarded as "sonic integrated circuits", and which have controlled and pre-determined properties.

Description

1 2408404

FABRICATION OF SONIC DEVICES

The present invention relates to the fabrication of miniature sonic devices for audio applications and to products incorporating such devices. It relates especially, though not exclusively, to the fabrication of relatively complex component structures for sonic devices, which structures can conveniently be regarded as "sonic integrated circuits", and which have controlled and pre- determined properties.

The invention aims, as a principal object, to enable the fabrication of more sophisticated sonic devices for consumer products than has hitherto been possible.

As described in a co-pending patent application entitled "Sonic Emitter Devices" filed contemporaneously herewith by the same applicant (agent's reference SPQ002) and referred to hereinafter as "the said co-pending application", there is currently a trend towards the development of quite sophisticated hand-held electronic consumer products, such as mobile phones, portable games consoles and hand-held computers. Indeed, some of the individual technologies used in such products are converging to create hybrid products, such as cell-phones combined with gaming consoles, and it is already commonplace, for example, for cell-phones to incorporate music players using the MP3 format.

Audio is a feature vital to many of these new hand-held electronic consumer products, in which communications, music listening and interactive game-play have a significant role. It is expected that in future such products will include sophisticated noise-cancelling technologies, voice-activated interactive-menu systems and speechsynthesis capabilities, and these will all benefit from the ability to create sonic devices more sophisticated than those which are currently available.

It is therefore an object of this invention to provide a fabrication technique permitting the creation of sonic devices capable of meeting, at least in part, current and future demands for audio performance and functionality, particularly in the field of hand-held electronic consumer products.

Such products usually provide audio by way of personal earphones or headphones, partly because they are often used in public places, and partly because, hitherto, it has not been possible or worthwhile to incorporate into their structures small loudspeakers which provide more than a very basic listening experience. However, the said co-pending application describes and claims an invention capable of providing highfidelity sound using only very small "micro-speakers", typically less than 20 mm in diameter, and capable (inter alla) of reproducing 3D-positional audio.

It is another object of the present invention to facilitate the manufacture of miniature sonic devices capable of delivering relatively sophisticated audio performance.

According to the invention from one aspect there is provided a method of fabricating a sonic device comprising the steps of: (a) providing a plurality of laminar substrates; (b) configuring at least one of said substrates to constitute part at least of a sonic cavity and/or a conduit for sound energy; and (c) stacking said substrates in juxtaposed relationship to form said device.

By this means, sonic devices can be produced accurately and economically.

Moreover, the devices so produced are reliable and rugged in operation and, even when utilised in conjunction with miniaturized active components, such as micro-speakers, can exhibit audio performance of good quality.

Any or all of the laminar substrates may be of metallic material, such as aluminium, or plastics material, or resilient materials, such as rubber.

Moreover, laminar substrates of different materials may be used together in fabricating a single sonic device.

In one preferred embodiment, said at least one laminar substrate comprises a plate formed with an aperture therethrough. Such a plate may comprise part of a resonator cavity and/or an acoustic conduit linking two or more components. Preferably, the aperture is substantially central of the plate.

In another preferred embodiment, the aperture opens into a channel through which it communicates with an open edge of the plate to constitute a sonic emitter.

Preferably the channel flares in width as it progresses from the aperture to the edge of the plate.

Further preferably, the plate is mounted in direct communication with a loudspeaker. The loudspeaker preferably comprises, in some embodiments, a micro-speaker.

It is further preferred that the plate is juxtaposed with a further plate formed with an aperture dimensioned to constitute a resonator cavity; an intermediate plate disposed between the first-mentioned plate and the further plate being formed with a relatively small aperture to form a conduit linking said cavity to said sonic emitter.

In further preferred embodiments, a further cavity-defining plate is disposed in underlying relationship to said loudspeaker.

Preferably, the resonator cavities are closed by means of substantially laminar end-plates.

In some embodiments it is preferred that the plate comprising the sonic emitter is also formed with an aperture constituting said resonator cavity, and with a passage of relatively small dimensions linking said resonant cavity to said emitter.

In further embodiments, dual cavities and/or conduits are formed in one or more of said laminar substrates to provide corresponding configurations for left-and right-audio channels.

According to the invention from another aspect there is provided a sonic device fabricated as described in any of the preceding paragraphs and/or an electronic consumer product containing at least one such sonic device.

The present invention is based upon the surprising realisation that useful sonic functions can be carried out within devices which are substantially smaller than the wavelengths of sound required for consumer audio s applications. This is illustrated in the said co-pending application, which describes efficient resonant cavities with dimensions which are measured in millimetres, but which resonate in the kHz region, where the wavelengths are hundreds of millimetres in size.

In order that the invention may be clearly understood and readily carried into effect, certain embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 shows, in block diagrammatic form, a "triplex" sonic device (comprising three cavities) which can be fabricated by means of an embodiment of the invention; Figure 2 shows, in exploded perspective view, a method in accordance with I S one embodiment of the invention of fabricating a sonic device of the kind shown in Figure 1; Figures 3(a) to 3 (e) show, in plan view, certain components used in the fabrication method described with reference to Figure 2; Figures 4(a) and 4(b) show respectively, for comparison, a plan view of the component shown in Figure 3(d) and a plan view of a modified form thereof; Figure 5 shows comparative performance curves for a sonic device fabricated as described with reference to Figures 1 to 4 and for a commercially available cellphone; Figure 6 shows in exploded perspective view a further embodiment of the invention; Figures 7(a) to (e) show, in plan view, certain components used in S accordance with another embodiment of the invention for fabricating a handset emulator comprising dual sonic emitters for leftand right-audio channels; Figure 8 shows the handset emulator; and Figures 9(a), 9(b) and 9(c) illustrate how sonic emitter arrays, such as loudspeaker columns, can be constructed from sonic emitter modules manufactured in accordance with examples of the invention.

Referring now to the drawings, Figures 1 and 2 show one embodiment of an efficient sonic emitter device as described in the said co-pending application.

Reference will also be made to Figure 3 in this connection.

A 16 mm diameter micro-speaker unit 40 is coupled to first and second resonant cavities, 10, 20 and a third resonant cavity 30 is linked to the second cavity 20. The second cavity 20, shown directly above the loudspeaker 40, acts as a sonic emitter, having a power-efficient output and smooth frequency response by virtue of the associated cavities, and in particular the third, linked cavity 30, which compensates for a large spectral peak which would otherwise be present at about 5 kHz for the dimensions in question. This third cavity 30 is relatively small, being only 0.1 ml in volume, and comprising an 8 mm diameter aperture 50 in a 2 mm thick aluminium plate 60. A neck like conduit 70 of the third resonant cavity 30, linking it to the second cavity 20, is also relatively small; having a cross sectional area of about 1.75 mm2, and a length of 2 mm.

As shown in Figure 2, the structure shown schematically in Figure 1 is S constructed, in accordance with one example of the invention, by providing a plurality of laminar substrates, in the form of aluminium plates, configuring some at least of the plates so as to form acoustic resonator cavities and/or conduits for sound energy, and juxtaposing the plates in a predetermined order of assembly; incorporating a micro- speaker as the sound generator.

Thus, in the example shown, the conduit 70 is formed by drilling a 1.5 mm diameter hole 71 in a 2 mm thick aluminium plate 72. An efficient emission cavity 20 comprises a further 2 mm thick aluminium plate 21 which is formed with a central aperture 22 of diameter 10 mm which communicates tangentially with a sonic emission conduit comprising a slot 23 that opens outwardly, via one edge 24 of the plate 21, and has a length of 12 mm. The width of the slot 23 thus flares from 10mm to 12 mm as it proceeds towards the edge 24 of the plate 21.

As shown in Figure 3 (a) to (e), the respective laminae constituted in this example by the various aluminium plates are shown for convenience in their assembly sequence. In practice, the aluminium plates are assembled by stacking them in juxtaposed relationship as shown in Figure 2, such that the sonic emitting cavity 20, formed by elements 22 and 23 in the plate 21, lies underneath the plate 72 formed with the aperture 71, which in turn lies underneath the cavity plate 60, which is capped by a blanking plate 80 to define the upper extent of the cavity. The entire stack is mounted upon a further aluminium plate 90 of thickness 2 mm which supports the micro- speaker 40, and is apertured accordingly.

It will be appreciated from inspection of Figures 1 and 2 that the second cavity is formed directly beneath the micro-speaker 40 as viewed, and that it is constructed by means of plates 100 and 110 forming further laminar substrates; plate 100 being apertured to define the cavity 10 and plate 110 being a simple planar bottom plate resembling the upper plate 80.

Thus, in the sonic device of this example, the micro-speaker 40 communicates directly with the lower resonator cavity 10 and the upper resonator and emission cavity 20 and indirectly, via the linking conduit 70, with the frontal compensation resonant cavity 30. The micro-speaker 40 is arranged with its acoustic emitting surface facing the cavity 20; the lower cavity 10 thus constituting a "rear" cavity. Sonic emission occurs through the emission conduit 22, 23 which opens through the edge 24 of the plate 21.

l S It will be appreciated that the resonator cavities 10, 20 and 30, together with their associated conduits where appropriate, can be regarded as Helmholtz resonators.

In order to simplify the structure of the sonic emitter, the structure of the components 50/60 and 71/72 of the third cavity 30 (Figures 3(b) and 3(c)) can be integrated into the plate 21 of the emitter cavity 20 by recutting the metal as shown in Figure 4 which depicts, at Figure 4(a), the plate 21 configured as already described above and, at Figure 4(b), a plate 201 comprising a new, integrated emitter.

It can be seen from Figure 4(b) that the second, new cavity structure in the 2 mm-thick plate 201 comprises a rectangular cut-out 205, which is 5 mm by mm in size, linked to the rear of the flared emitter cavity 202, 203 via a 2 mm wide, 2 mm long slot 206 which is 2 mm deep. Hence the dimensions of the integrated, third cavity are: Volume: approximately 0.1 ml Length of neck = 2 mm; Area of neck = 4 mm2.

Although the 2 mm by 2 mm area of the neck 206 is slightly greater than that of the 1.5 mm diameter hole 71 of Figure 2, the difference is insignificant for this particular arrangement. The integrated compensating cavity successfully compensated the 5 kHz emission peak.

In other embodiments, the rectangular cut-out 205 has been replaced by a circular cavity (not shown) of diameter 7.5 mm. Although representing a slightly smaller volume, this dimension provides, as shown by the comparative performance curves in Figure 5, excellent audio performance in comparison with a good quality proprietary cell-phone. Moreover, the circular shape allows the use of pre-cut cylindrical plugs of cotton fibre damping material to be used when appropriate within the cavity, making for easier manufacture.

Accordingly, this example of the invention enables a "triplex" sonic device (one having three cavities) to be formed using only five laminar substrates (including the plain end-plates) stacked together, as is shown in Figure 6, comprising the following layers (listed in sequence from the uppermost layer to the lowermost layer).

1. Uppermost blanking end plate 80; 2. Integrated sonic emitting cavity and compensating cavity substrate 201; 3. Microspeaker mounting substrate (not shown); 4. Rear cavity volume substrate 100; and 5. Lowermost blanking end plate 110.

Acoustic damping materials are, in this example, used in the rear and compensating cavities10 and 205 although, for clarity, it has been omitted from the Figures. However, it is noteworthy that can easily be built in to the relevant substrate simply by plugging a pre-cut circle of fibre into the aperture, where it is held in place by friction ready for final assembly.

It is also worthy of note that, as with electronic integrated circuits, the component and interconnection complexity may readily be increased without incurring a proportional additional manufacturing cost. For example, it was required to construct a sonic device pair according to the above description, in order to develop and demonstrate 3D-positional audio algorithms on a cell- phone handset-sized substrate. Consequently, a new design was created with a pair of sonic devices integrated into a common set of substrates, providing left- and right-channel emission on the lateral edges of a 50 mm wide unit.

The substrate layers for this arrangement are shown in Figure 7, as items (a) to (e), in top-downwards sequence, as follows.

1. Top cover plate 80; 2. Integrated sonic emitter-pair substrate 201 L and 201 R; 3. Micro-speaker mounting substrate (and main chassis) 90; 4. Rear cavity volume substrate 1 OOL, 1 OUR; and 5. Rear cover plate 110.

The layer structure is similar to the previously described example, but provides six integrated resonant cavities (three for the left (L) audio channel and three for the right (R) channel), implemented by only five layers, including the two blanking plates 80 and 110. These planar substrates are simple to manufacture, for example by moulding in rigid plastic, and can be arranged so as to possess snap-together lugs, around the periphery, for ease of manufacture.

The final handset simulator unit, featuring the two, triplex sonic emitters, is depicted in Figure 8, and represents a sonic integrated circuit featuring six resonant cavities and two active devices (the microspeakers) with respective edge-emitting apertures.

Metallic and/or plastics materials or, indeed any other materials having suitable acoustic properties and capable of being configured into the requisite forms can be used as any or all of the laminar substrates.

Moreover, it is advantageous in some circumstances to use differing materials for the different layers. For example, the inclusion of elastic or resilient layers, for example of rubber, can enhance hermetic sealing to the adjacent layers. Also, it might be required to have a strong, but light structure, in which case a combination of (say) metal layers and plastic layers can be used.

One or more of the substrates can be formed from a printed circuit board, so as to provide electrical connection means to active sonic devices, such as micro-speakers and microphone modules.

Another embodiment provides that the substrates be made from a flexible material, such that they can be bent so as to conform to a curved surface, for example, the inner surface of a cell-phone casing.

S The rear cavity 10 may if desired be vented by way of a separate tube or conduit opening externally of the device.

In a further embodiment, the substrates are made having differing edge profiles so as to conform to a host device's structure. For example, a series of circular substrates having differing diameters could be assembled so as to form a conical or spherical shape. This is useful for incorporating an integrated sonic circuit into an "in-ear" earphone housing.

A further embodiment of the invention relates to the use of the sonic edge IS emitter in arrays. Each emitter is a low-cost item and a moulded, snaptogether plastic housing featuring integrated sonic components, as described hereinbefore, does not add significantly to this cost. Consequently, it is practical to use a relatively large number of such sonic emitters as an array or matrix, where there are significant advantages over the prior art.

For example, an edge emitter, as shown in Figure 9(a), can readily be manufactured, utilising a 0.3 W. 16 mm diameter micro-speaker and having the following dimensions: height (h) = 25 mm; width (w) = 8 mm; depth (d) = 25 mm.

This can be manufactured in the form of a module, in which one of the integrating layers comprises a printed circuit board forming electrical connections to the micro-speaker, and having an edge connector enabling it to be plugged into a back-plane motherboard. A plurality of such modules can be stacked together, either as a linear array, or as a twodimensional matrix. Figure 9(b) shows a three-element vertically oriented array.

Such arrays are ideal for incorporation into consumer products, including computer peripherals, and the like. For example, a vertical array is ideal for adding to both lateral edges of a computer monitor for adding sound capability. An even larger array can usefully form an ultra-thin hi- fi loudspeaker for use in the home, as shown in Figure 9(c), which depicts a twelve-element stacked array. In practice, it is practical, by utilising this invention, to create even larger arrays for other applications. An array providing, say, a 1 metre tall unit, contains (based on the example of Figure 9) 40 sonic emitter modules, with a power-handling capability of 12 W. The resultant loudspeaker unit is thus 1 metre tall and only 8 mm wide.

The low- and mid-frequency performance is related to the rear-volume size of the integrated cavity. Thus, by increasing the depth of the emitter module somewhat, this feature can readily be designed to specifications similar to conventional loudspeaker systems. In addition, a sub-woofer arrangement can be incorporated into the pedestal base of the floorstanding unit shown in Figure 9(c).

By using a slightly larger micro-speaker, say a 28 mm diameter unit having 1 W power handling capability, then much more powerful sonic emitter loudspeakers can be made. The size of an edge-emitter module such as that shown in Figure 9(a) but dimensioned to incorporate a 28 mm micro-speaker is typically: height (h) = 33 mm; width (w) = 10 mm; depth (d) = 50 mm.

Thus, a 1 metre tall, floor-standing loudspeaker made with these units still exhibits an extremely small depth, and is moreover only 10 mm wide, whilst having a power rating of 30 W. The advantages of such an array are as follows.

1. The vertical array is extremely thin, and relatively unobtrusive when used, say, on either side of a television screen or panel.

2. The frequency response is substantially flat throughout spectrum, resulting in high fidelity performance.

3. There is no need for additional high-frequency "tweeter" units and associated crossover arrangements.

4. The small emitter area is substantially omni-directional in nature, unlike conventional loudspeakers. The "beam forming" characteristics are related to the size of the emitting surface in relation to the wavelengths which are being emitted. The emission area of the present invention (2 mm) is two orders of magnitude smaller than a typical conventional loudspeaker (20 cm).

5. The spatial imaging capability is good, because the sound is emitted from a line array rather than a large area. The emitted sonic wavefronts are spatially well defined, rather than being smeared out; this characteristic being especially beneficial for 3D-positional audio.

Whilst there have been previous proposals to use large arrays of small loudspeakers for sound reproduction, either to improve linearity or to create "phased arrays" for beam steering, such proposals have been envisaged only in conjunction with conventional enclosures. In contrast to this, the present invention affords that each micro-speaker has its own enclosure arrangements, which significantly improves acoustic performance.

Where references made herein imply directionality, in connection for example with plates being described as "upper" or "lower" plates or where any component or feature is described as lying above or below another, it is stressed that such description is used for convenience and ease of understanding only in relation to the layouts as shown in the drawings, and is not intended to place any limitation whatsoever upon the orientation in which the plates or components or features in question, or the devices as a whole, IS may be assembled or used in practice.

It will be appreciated that, in broad outline, the present invention provides a means whereby relatively complex sonic devices can be fabricated by creating or deploying one or more sonic components in a substantially planar substrate, and then combining a plurality of said substrates together in a stack to form an integrated sonic circuit.

Here, the term "sonic component" means an active or passive device which performs a useful sonic operation, in an analogous manner to active and passive electronic devices. Some examples of sonic components suitable for incorporation into sonic integrated circuits, and their nature, include (without limitation) the following.

1. Electro-acoustic transducer (such as a micro-speaker); 2. Acousto-electric transducer (such as a sub-miniature microphone element); 3. Passive filter (such as high-frequency cut; low-frequency cut; bandpass); 4. Wave-guide type transmitter (exponential horn); 5. Sonic receiver (a simple aperture); 6. Resonator (Helmholtz-type or related); 7. Transmission-line / wave-guide/ delay-line (linear or folded conduit); 8. Interconnection bus (linked conduits); to 9. Adder/weighted adder; 10. Attenuator (restriction in conduit).

In relation to the invention in general it will be appreciated that, whilst there are many examples of disclosures relating to the incorporation of miniature sonic devices into larger host devices, such as noise-cancelling headphones, for example, they are invariably connected, both electrically and acoustically, as discrete components, using tubing or conduits inset into the mouldings of the headset.

Moreover, sonic components have traditionally been treated and used as individual, discrete components, and have thus been employed in a similar way to that in which discrete electronic components used to be assembled together in order to form more complicated and useful electronic circuits prior to the advent of the electronic integrated circuit. In general, two classes of sonic components can be distinguished: active components, such as loudspeakers in portable radios and the sub-miniature microphones used in cell-phones, and passive components such as resonator cavities, which are used to reduce the noise emitted by vehicle-exhaust systems, and the fur type acoustic cladding for outdoor microphone shielding which provides a low- frequency filtering affect, thus reducing wind-noise artefacts.

A common aspect of designing sonic components into host products is that the engineer is used to thinking terms of the wavelengths of sound in question. For example, typical hi-fi loudspeaker cabinets have unwanted resonant modes which are dependent on their physical dimensions, such that a 0.3 x 0.3 x 0.5 metre high cabinet will have a fundamental resonance when the greatest internal distance (the diagonal here is about 0.66 m) is equal to one-half of a wavelength. In this case, the resonant frequency would be about 520 Hz, lying in a significant part of the spectrum for speech and music.

In terms of electronic products with smaller dimensions, such as portable radios, the associated resonances occur at higher frequencies which are less troublesome (and indeed might well complement the fall-off in highfrequency performance of the loudspeaker itself). It is common, therefore, to incorporate sonic components such as loudspeakers into host devices without much consideration about their potential interaction with adjacent components and accordingly they are used as discrete, stand- alone elements. flu

Claims (20)

1. Claims: 1. A method of fabricating a sonic device comprising the steps of:

   (a) providing a plurality of laminar substrates; (b) configuring at least one of said substrates to constitute part at least of a sonic cavity and/or a conduit for sound energy; and (c) stacking said substrates in juxtaposed relationship to form said device.
2. 2. A method according to claim 1 further including the steps of providing at least one of said laminar substrates in the form of a plate, and forming at least one aperture through said plate.
3. 3. A method according to claim 2 wherein an aperture is formed substantially centrally of said plate.
4. 4. A method according to any preceding claim including the step of configuring a sonic cavity to form part at least of a resonator cavity.
5. 5. A method according to any preceding claim comprising the step of configuring a conduit as a channel having an opening through which sound energy can emerge from the device.
6. 6. A method according to claim 5 wherein the channel is configured to flare in width as it approaches said opening.
7. 7. A method according to claim 5 or claim 6 comprising the steps of juxtaposing the laminar substrate bearing said channel with a further substrate formed with an aperture dimensioned to constitute a resonator S cavity; and of disposing an intermediate substrate between the firstmentioned and further substrates; and of forming said intermediate substrate with a relatively small aperture to form a conduit positioned to acoustically link said resonator cavity to said channel.
8. 8. A method according to claim 7 further comprising the steps of providing a plain laminar substrate and juxtaposing said plain laminar substrate with the substrate bearing said resonator cavity to close said resonator cavity.
9. 9. A method according to claim 5 or claim 6 comprising the steps of lS configuring, in a common substrate: (a) the said channel, (b) an aperture constituting said resonator cavity, and (c) a passage of relatively small dimensions linking said resonant cavity to said channel.
10. 10. A method according to any preceding claim including the steps of providing loudspeaker means and of mounting said loudspeaker means with an intended emission surface thereof in direct communication with a said cavity and/or conduit.
11. 11. A method according to claim 10 wherein said loudspeaker means comprises a micro-speaker.
12. 12. A method according to claim 10 or claim 11, in either case as dependent upon any of claims 7, 8 or 9' comprising the steps of providing a further cavity-defining plate, and disposing said further cavitydefining plate in direct communication with a surface of said loudspeaker means not intended as an emission surface thereof.
13. 13. A method according to claim 12 further comprising the steps of providing a plain laminar substrate and juxtaposing said plain laminar substrate with said further cavity-defining plate to close the cavity defined thereby.
14. 14. A method according to any preceding claim comprising the step of forming dual cavities and/or conduits in one or more of said laminar substrates to provide corresponding configurations for left-and rightaudio channels.
15. 15. A method according to any preceding claim wherein at least one of the laminar substrates comprise aluminium or other metallic material.
16. 16. A method according to any preceding claim wherein at least one of the laminar substrates comprise plastics material.
17. 17. A method according to any preceding claim wherein at least one of the laminar substrates comprise rubber or other resilient material.
18. 18. A method of fabricating a sonic device substantially as herein described with reference to and/or as shown in the accompanying drawings.
19. 19. A sonic device fabricated by a method according to any preceding claim.
20. 20. A consumer electronic product including at least one sonic device according to claim 19. s