CAVITIES AND ACTIVE REGIONS

Abstract

The present invention relates to a method and apparatus for providing and/or receiving audible sound. In particular, the invention relates to apparatus, such as a micro speaker, which includes an active region which comprises a particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or a membrane. The particulate adsorbent material is either in the form of loose or semi-loose granules, or it is supported by or impregnated into a woven, knitted or non-woven felt material. The apparatus of the present invention is suitable for use in an electronic device, for example a mobile or portable electronic device, to provide improved audible sound.

Claims

1. Apparatus for providing and/or receiving audible sound, comprising: a housing that provides at least one cavity region; a vibratable element in or proximate to the cavity region; and an active region that comprises a particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or a membrane.

2. The apparatus according to claim 1 wherein the adsorbent material is porous and has pores in the region of 1 nm to 10 nm in diameter.

3. The apparatus according to claim 1 or 2 wherein the adsorbent material is microporous.

4. The apparatus according to any of claims 1 to 3 wherein the adsorbent material has a cage-like structure.

5. The apparatus according to any of claims 1 to 4 wherein the adsorbent material provides a surface area of at least 500 m.sup.2/g.

6. The apparatus according to any of claims 1 to 5 wherein the adsorbent material is a material that does not have an ordered structure.

7. The apparatus according to any of claims 1 to 6 wherein at least 80% by weight of the adsorbent material particles have a maximum diameter of 120 microns.

8. The apparatus according to claim 1 wherein microporous organic polymer (MOP) material comprises poly-dichloroxylene (P-DCX).

9. The apparatus according to claim 1 wherein the metal organic framework (MOF) material is aluminium fumarate.

10. The apparatus according to any of claims 1 to 9 wherein the adsorbent material comprises one or more secondary adsorbent materials.

11. The apparatus according to any preceding claim wherein the adsorbent material is in loose/semi-loose particulate form.

12. The apparatus according to claim 11 wherein the adsorbent material is retained in position within the apparatus by a support element.

13. The apparatus according to any of claims 1-10 and 12 wherein the adsorbent material is coated on an outer surface of the support element.

14. The apparatus according to any of claims 1-10 and 12 wherein the adsorbent material is embedded throughout a supporting material that provides the support element.

15. The apparatus as claimed in claim 12 wherein the adsorbent material is impregnated in a supporting material that provides the support element.

16. The apparatus as claimed in claim 15 wherein the adsorbent material is impregnated in the support element with a fill factor of at least 60%.

17. The apparatus as claimed in claim 12 wherein the support element comprises a woven structure provided by interwoven threads of a support material, or a knitted structure provided by interlocking looped threads of a support material, or a non-woven structure provided by randomly oriented or pseudo randomly orientated strands of support material.

18. The apparatus according to claim 12 wherein the support element is sealed between one or more sheets of a sealing material.

19. The apparatus according to claim 18 wherein the sealing material is a flexible membrane.

20. The apparatus according to claim 19 wherein the flexible membrane is moisture impermeable.

21. The apparatus according to claim 12 wherein the support element is sealed via a thermal process.

22. The apparatus as claimed in claim 1 wherein the active region comprises a flexible bag including adsorbent material in the cavity region or the active region comprises at least one wall member of the housing and a panel or panels in the cavity region or the active region comprises at least one wall member of the housing and at least one flexible bag including adsorbent material in the cavity region.

23. A speaker or microphone comprising the apparatus according to any preceding claim.

24. A mobile electronic device, comprising: a case body; and at least one speaker unit or microphone unit in the case body; wherein each speaker unit or microphone unit comprises a housing that defines at least one cavity region, a vibratable element in or proximate to the cavity region and an active region that comprises a particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or a membrane.

25. The mobile electronic device according to claim 24 selected from a mobile phone, a smart phone, a laptop, a tablet or personal assistant, an electronic device for displaying images such as a television, a monitor, an audio visual projector or the like, a speaker such as a portable speaker, a smart speaker or a Bluetooth speaker, a vehicular speaker, a wearable electronic device such as a watch, hearing aid, a wearable computer, an earphone, a wearable smart device, a wearable navigation aid and a headphone.

26. A volume-enhancing material for use in a micro speaker or loudspeaker configuration, wherein the volume-enhancing material comprises particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or membrane.

27. A speaker system, comprising: a speaker unit; and a cabinet forming a chamber at a back region or side region of the speaker unit largely filled with a volume-enhancing fine particle Metal Organic Framework material, or an amorphous microporous organic polymer (MOP) such as Poly-dichloroxylene (P-DCX) wherein optionally the particles may be saturated with Methanol to cause a stabilised crust to form before the material is covered by a fine poro-elastic gauze material, or silk.

28. A speaker system, comprising: a speaker unit; and a cabinet forming a chamber at a back region or side region of the speaker unit largely filled with a felt comprising of a gas permeable upper layer, ultra-fine particles of gas adsorbing material dispersed at high concentrations within a fibrous matrix without using binder, and a permeable or impermeable back layer; wherein the gas-adsorbing material may be a Metal Organic Framework material treated with a hydrophobic coating, or an amorphous microporous organic polymer (MOP), featuring component materials with innate hydrophobicity, such as Poly-dichloroxylene (P-DCX).

29. A microphone system, comprising: at least one transducer element for converting sound to an electrical signal; optionally a preamplifier that receives an output from the transducer element; a housing or cabinet at a back region or side region of the transducer element; and an active region that comprises at least one support element and adsorbent material comprising a particulate adsorbent material comprising i) microporous organic polymer (MOP) material, and/or ii) metal organic framework (MOF) material treated with a hydrophobic coating or a membrane.

30. A mobile electronic device comprising the microphone system according to claim 29.

31. The mobile electronic device as claimed in claim 30 wherein the mobile electronic device is a mobile phone or hearing aid.

Description

[0116] Certain embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which:

[0117] FIG. 1 illustrates an exploded view of an ear speaker;

[0118] FIG. 2 illustrates a cross section through the ear speaker;

[0119] FIG. 3 illustrates an exploded view of an alternative speaker;

[0120] FIG. 4 illustrates an alternative speaker with side chambers filled with active region but with a remaining central region empty;

[0121] FIG. 5 illustrates a cross section through a speaker;

[0122] FIG. 6 illustrates a cross section through a speaker;

[0123] FIG. 7 illustrates low frequency response of empty and selected partially filled micro speakers according to the present invention;

[0124] FIG. 8 illustrates higher range frequency response of empty and selected partially filled micro speakers according to the present invention;

[0125] FIG. 9 illustrates differential frequency response (SR filled-SR empty) of selected partially filled micro speakers according to the present invention;

[0126] FIG. 10 illustrates electric impedance of micro speakers according to the present invention with an empty case and selected fillings;

[0127] FIG. 11 illustrates particle size effects;

[0128] FIGS. 12a to 12f illustrate frequency response with different fillings;

[0129] FIG. 13 illustrates electric impedance response; and

[0130] FIG. 14 illustrates differential frequency response.

[0131] In the drawings like reference numerals refer to like parts.

[0132] Certain embodiments of the present invention relate to a mobile electronic device and to apparatus in a mobile electronic device for generating audible sound. As mentioned above, a mobile electronic device can be a mobile phone such as a smartphone or laptop or earphone or earbud or headphones or navigation device or TV or monitor or smart speaker or Bluetooth speaker or vehicular speaker, or can be a wearable electronic device such as a smartwatch or smart clothing. The apparatus for providing audible sound can be a speaker or the like. The speaker can be small in which situation the speaker may be referred to as a mini speaker or micro speaker. An example of a micro speaker is an ear speaker or main external speaker of a smartphone.

[0133] A typical smartphone (for example a Samsung Galaxy S8 smartphone) includes a rear casing that has a grill for an ear speaker. In operation, the ear speaker generates sound pressure waves which provide sound audible to a human ear when it exits from an internal region within the housing where an ear speaker is located via multiple through apertures in the grill to the listener. In addition to the ear speaker, a smart phone may also include one or more further speaker units and generally one of these further speaker units is designated a main external speaker designed to provide audible sound through an exit aperture in a side panel of the smartphone. The side panel can be part of the overall smart phone casing, which forms a housing for the smartphone and supports a touchscreen.

[0134] FIG. 1 illustrates an exploded view of the ear speaker. A speaker 200 includes a cabinet housing 410 which encompasses a “back-volume” which can be occupied (partially or fully) by a volume-enhancing active region. In the embodiment illustrated in FIG. 1 the cabinet housing 410 encompasses a back volume which is occupied by a volume enhancing material 420 which comprises adsorbent material comprising microporous organic polymer material and/or metal organic framework material which may optionally be treated with a hydrophobic coating. The volume enhancing material 420 comprises adsorbent material in the form of granules or powder which may be loose/semi-loose or in conjunction with a support element. As shown, the adsorbent material is covered by a thin membrane 430 which helps prevent material escaping and which can help protect the active region from moisture ingress. The thin membrane is located between the active region and an upward (in FIG. 1) facing loudspeaker driver 440 comprising a vibratable element 470 which is the element which provides soundwaves audible as sound. Aptly the thickness of the flexible membrane is less than 0.5 mm. The housing for the speaker has a front plate 450 which helps complete the composite enclosure. In an alternative embodiment, the ear speaker 200 illustrated in FIG. 1 may instead be a microphone unit for receiving sound. In this embodiment, the loudspeaker driver 440 may be replaced with a sound receiving unit such as a transducer element comprising a vibratable element which is the element which receives soundwaves and converts the air pressure variations associated with the soundwaves into an electrical signal. Optionally a preamplifier receives an output from the transducer element. It will be appreciated that according to certain aspects of the present invention, the microphone unit may be provided in proximity to or in a different location to a speaker unit. For example, the smartphone casing may comprise a further aperture which may enable audible sound to pass into the smartphone for reception by a microphone unit. It will also be appreciated that according to certain embodiments of the present invention one, two, three or more microphone units may be provided in a mobile device. In a further embodiment, at least one speaker unit and at least one microphone unit may be provided as a composite unit.

[0135] FIG. 2 illustrates a cross section through the ear speaker shown in FIG. 1 in more detail.

[0136] FIG. 3 illustrates an exploded view of an alternative speaker 600 which can, for example, be utilised as an external speaker. This includes a horn-like acoustic neck 610 that includes a channel for sound to feed out through the exit aperture in a casing of a smartphone. As shown in FIG. 3 the speaker 600 includes a speaker housing 710 which sits in an outer cavity 715 provided by an outer housing 717 in which an active region of volume enhancing material 718 is provided. In the embodiment shown in FIG. 3 the active region is a generally C-shaped region. A loudspeaker driver 740 which comprises a vibratable element 790 sits within the smaller internal speaker housing 710 and that smaller speaker housing 710 is partially closed by a cover 750. An outer cavity defined by the main outer housing 717 is closed by a cover plate 760. The speaker thus includes an inward facing loudspeaker 710, 740, 750 that sits within a larger volume defined by an outer housing 717, 760 augmented by a volume enhancing material 718. The driver 740 faces downwards (in FIG. 3) acting to generate pressure fluctuations within the cavity 770 within the inner housing 710. This horn like cavity 770 feeds sound to the outside of the device via an acoustic channel 780. The outer cavity defined by the lower housing 717 and the plate or cover 760 is acted upon by the rear of the driver. The volume enhancing material of the active region within this cavity acts to increase the acoustic compliance of the air inside the cavity thereby improving low frequency response.

[0137] FIG. 4 illustrates a speaker similar to that shown in FIG. 3, but with a cover plate 960 removed to reveal an active region with a basic rectangular design augmented with one or more (three shown) side chambers 910, 920, 930. In the embodiment illustrated in FIG. 4, the side chambers are full of volume enhancing material (an active region), whereas the back volume (the cabinet housing 840) is clear of fill material

[0138] In a similar but alternative embodiment of FIG. 4 (alternative embodiment not shown), all of the side chambers and the main chamber are filled with a volume-enhancing material (the active region).

[0139] FIG. 5 illustrates a cross section of a speaker featuring a horn like internal acoustic cavity similar to that shown in FIG. 4. FIG. 5 helps illustrate how a side chamber 930 includes an active region that is covered by a membrane 1025. The active region comprises adsorbent material which comprises microporous organic polymer material and/or metal framework material treated with a hydrophobic coating. The adsorbent material is in particulate form either provided as loose/semi-loose granules, or in conjunction with a support element. FIG. 5 also helps to illustrate how the active region 930 can be in fluid communication with an outer region of the loudspeaker driver 740 to thereby increase acoustic compliance of the air inside the cavity and thereby improve low frequency response.

[0140] FIG. 6 also illustrates a cross section through a speaker which includes a horn-like internal acoustic cavity and is similar to that shown in FIG. 5. In this embodiment, a back volume is augmented by volume enhancing material, optionally provided by loose/semi-loose granules of adsorbent material optionally covered by a membrane. Alternatively, the volume enhancing material may be provided in combination with a support element, for example a felt material which is coated or impregnated with microporous organic polymer (MOP) material and/or metal organic framework (MOF) material treated with a hydrophobic coating or a membrane.

[0141] The cabinet forming the horn cavity is formed from a conventional plastic wall. An acoustic enclosure around the back volume is formed from a high-density impermeable shell component 1110. The impermeable shell is bonded to the plastic walls of the horn component using glue (or binder or other such element) with a suitable overlapping tab to ensure that the back-volume enclosure is acoustically sealed.

[0142] Certain embodiments of the present invention relate to a smartphone micro speaker.

[0143] It has been determined that there is an acoustic benefit of providing an active region on the low frequency response (sub 900 Hz) behaviour of a mobile phone without causing electromagnetic masking of the behaviour of the phone antenna. Around a 3 dB improvement may be achieved. In one embodiment, the active region can be incorporated into the back volume of a micro speaker enclosure, either in loose/semi-loose form or in conjunction with a support element.

[0144] According to certain embodiments of the present invention an average gain of 3.49 dB is achieved with a silk-mesh-supported insertion of loose/semi-loose powder into an empty micro speaker.

[0145] Electric impedance and near-field frequency response of a micro speaker can be measured within a Bruel and Kjaer soundproof BOX, mounted within a structure that allows position fixing and a microphone distance of 10 mm from the speaker outcome. Audiomatica SRL—CLIO equipment and software, release 1.4, pocket version was used to perform the measurements.

[0146] The equipment consists of a CP-01 audio interface box and a condenser electret microphone (with accuracy of 1 dB from 20 Hz to 10 kHz). The audio interface with analog RCA connections and sampling frequencies of 96 and 48 kHz, containing: [0147] A signal generator of 1 Hz-45 kHz, with a frequency accuracy of 0.01% and resolution of 0.01 Hz. [0148] An AC analyser of 24 bit sigma delta A/D converter and an input range of +40 dBV down to −40 dBV [0149] A DC analyser of 12 bit A/D Converter with an input range of +6.5V to −6.5V

[0150] The performance enhancement of a micro speaker was measured after filling approximately 85-90% of its cavity with adsorbent material in the form of loose/semi-loose MOP powder sealed with a silk fabric. Other fill factors can of course be utilised. Empty and partially filled micro speakers were measured by these means, obtaining the electric impedance and frequency response. The improvement in performance was calculated afterwards as the difference between the frequency response of the partially filled and the empty micro speaker. In order to take account for the errors associated with the position of the microphone and speaker, several measurements were taken, and a correlation was established through standard deviation. As a non-limiting example, the MOP material may be polymerised dichloroxylene (P-DCX).

[0151] Test Results

[0152] A total of 28 micro speakers have been tested with an active region.

[0153] After the selection of an adequate glue and filling procedure (appropriate sealing mesh), 11 micro speakers were successfully enhanced but at different rates.

TABLE-US-00001 TABLE 1 Example filling characteristics for micro speakers Type of (partial, Speaker Trace notation 85-90%) Mean ΔfR [dB] Name in FIG. 7-10 filling f.sub.0 [Hz] 100 Hz < f < 900 Hz Empty Empty closed 897.6 ≈ micro speaker V.sub.0 speaker Speaker B Loose MOP powder 760.5 ≈ 3.4966 contained behind a 1.18 V.sub.0 silk fabric. Speaker D Methanol-hardened 804.7 ≈ 2.8749 loose MOP powder 1.12 V.sub.0 contained with a silk fabric.

[0154] Table 1 presents the filling characteristics of the micro speakers that presented best frequency response enhancement and a summary of their performance. The selection included two micro speakers partially filled with loose microporous organic polymer (MOP) material, as it was perceived that an extra step was needed in order to retain the powder within the speaker when it was functioning inside the phone. For this purpose, a micro speaker was filled with wet MOP that produced a hardened surface, stopping it from leaking outside the speaker during operation, causing a slight performance penalty.

[0155] FIGS. 7 to 10 show low frequency response, wider range frequency response, differential frequency response and electric impedance (resonant frequency) of an empty micro speaker (shown as ‘-’ in FIGS. 7-10), a micro speaker sample with loose MOP (silk protected) inclusion (speaker B, shown as ‘- - -’ in FIGS. 7-10), and a micro speaker sample with hardened loose MOP (silk protected) inclusion (speaker D, shown as ‘-. - . -.’ in FIGS. 7-10).

[0156] The highest performance was obtained by speaker B, with a mean gain of approximately 3.5 dB and a shift in the resonant frequency of about 140 Hz, establishing that the cavity is behaving as if it was ˜18% larger. Speaker D, with a hardened MOP skin achieved a main gain of about 3 dB with slightly less resonant frequency shifting, increasing the volume by ˜12%.

[0157] FIG. 7 shows that in the very low frequency end, loose filled micro speakers produced a significant enhancement.

[0158] FIG. 8 shows the frequency response of the selected partially filled micro speakers for a broader frequency range, reaching to 6000 Hz. It can be seen that loose MOP filled micro speakers cause a shift in the peak performance by about 250 Hz to the right, reaching maximum performance at a frequency of about 4000 Hz.

[0159] FIG. 9 shows the relative frequency response of the various filled speakers to the empty case across the lower frequency range. The improvement in the very low frequency range is much higher with the loose MOP filled micro speakers.

[0160] FIG. 10 shows the electric impedance of the filled micro speakers compared to the empty micro speaker. The biggest compliance enhancement is seen by the inclusion of loose MOP in Speaker B; the peak shifted by about 140 Hz corresponding to an increase of ˜18% of the initial cavity volume. It can be seen that the inclusion of the Methanol-hardened MOP in Speaker D, exhibits a more damped resonant response (the peak shifted by about 100 Hz, equating to an apparent increase of volume of ˜11.5%), which leads to the conclusion that this preparation method may not be allowing the MOP to reach its potential enhancement performance.

[0161] Notably, a mean differential frequency response below 900 Hz of about 3 dB has been achieved for a micro speaker by introducing MOP as a dry powder within a silk mesh, filling about 85-90% of the micro speaker cavity.

[0162] This encapsulation method was found to present a limited risk of material leaking from the speaker, so an additional method has been tested and found to achieve close to 3 dB gains: [0163] Saturating the powder with methanol (pre-treated) to leave a crust, then covered with the silk mesh

[0164] While loose MOP powder achieves the best performance, the pre-treated loose MOP loudspeaker achieves the highest improvement in the very low frequency end.

[0165] It has been found that reducing the grain size of materials has a significant effect on their performance within the target range, with PoIMOF materials (P-DCX) that had previously shown poor performance being transformed into lead candidates (see FIG. 11). Notably, sifted PoIMOF material (is sifted P-DCX, herein referred to as ‘PoIMOFg2’) which passes through a mesh in the range 1/10- 1/12 mm shows improvements in frequency response of about around 3-5 dB in the 400-700 Hz frequency range in 1 cm deep loudspeaker cavities with 75% material fill. The MOP materials out-performed zeolite, perlite and silica reference materials, and produced very similar performance to high-activation carbon powders.

[0166] For materials in a representative speaker box, of about 58 mL volume, it has been found that a 60%-80% filling of MOF and/or MOP materials may introduce a benefit of ˜1.5 dB at the low frequency spectrum, while reducing the performance around the resonant frequency of the speaker and above. Although the low frequency response of micro speakers with a MOP material (e.g. P-DCX) which may be referred to as ‘PoIMOF’ and/or a MOF material (e.g. an Aluminium Fumerate based MOF) which may be referred to as ‘NewMOF’ herein treated with a hydrophobic coating or a membrane, is slightly down on the results obtained for activated carbon powder, MOP/MOF materials nevertheless provide significant further benefits such as introducing less damping and therefore better performance is achieved by their inclusion. Performance is illustrated in FIGS. 12a to 12f, with the most favourable results being illustrated in FIGS. 12e and 12f for the PolMOFg2 material.

[0167] The following presents results obtained for 12 MOP-partially filled micro speakers, in loose powder form attached by a silk mesh.

[0168] Table 2 below presents filling characteristics and main measured obtained parameters for each partially filled micro speaker.

[0169] FIGS. 13 and 14 display impedance shifting (resonant frequency) of the enhanced micro speakers and the differential frequency response for each case. It should be noted, that while Speaker P showed high enhancement, it was outperformed by speaker B, with similar filling procedures.

[0170] Complete Improved Micro Speaker List

TABLE-US-00002 TABLE 2 Complete list of filling characteristics for micro speakers Type of Speaker Trace notation (partial, 85- Mean ΔfR [dB] Name in FIG. 13, 14 90%) filling f.sub.0 [Hz] 100 Hz < f < 900 Hz Empty micro Empty closed 897.6 ≈ — speaker speaker V.sub.0 spkB Loose MOP/silk 760.5 ≈ 3.4966 fabric. 1.18 V.sub.0 spkD Methanol- 804.7 ≈ 2.8749 hardened MOP/ 1.12 V.sub.0 silk fabric. spkP Loose MOP/silk 786.8 ≈ 2.825 fabric. 1.14 V.sub.0 spkX Not shown Loose MOP/silk 810.8 ≈ 2.0605 fabric. 1.11 V.sub.0 spkN Not shown Loose MOP/silk 801.7 ≈ 1.8227 fabric. 1.12 V.sub.0

[0171] The procedure for filling the micro speakers involved un-gluing the junctions of the speakers with heat and a scalpel. Once the device was open and divided into two parts, the material filling was introduced. [0172] Speaker B: about 80% of the volume of the speaker was filled with loose MOP and two silk pieces cut in the shape of the back-cavity parts were glued in the internal boundary of the back cavity, protecting the loose MOP from leaving the area. The back and front original parts of the speakers were then glued back with liquid fast operating glue and clamped during the curing process of the glue to create an air-tight seal. [0173] Speaker D: Methanol was poured into the MOP, in order to wet it until achieving a consistency that is loose enough to allow easier pouring in the back cavity of the speaker. The wet process allowed to pour more MOP than when it was dried filling about 80% of the volume. Again, the two silk pieces (cut in the shape of the back-cavity parts) were glued in the internal boundary of the back cavity. The back and front original parts of the speakers were then glued back with liquid fast operating glue and clamped during the curing process of the glue to create an airtight seal. The glued speaker was left at a temperature of around 70° C. for around 12 hours to evaporate the methanol from the MOP.

[0174] Metal-organic framework (MOF) materials are hybrid materials that take advantage of the properties of both organic and inorganic porous materials, and they form stable, ordered and high surface areas structures.

[0175] Metal organic framework (MOF) materials are known as porous coordination networks, porous coordination polymers (PCPs) etc.

[0176] Certain metal organic framework (MOF) materials possess one or more of the following characteristics: [0177] 1. multifunctional hybrid (inorganic-organic) materials [0178] 2. formed of metal ions (nodes or joint) to which organic ligands (linker or strut) attach and extend to other ligand molecules—components provide endless possibilities [0179] 3. 3D crystalline structure (although can also be 1D or 2D)5. [0180] 4. Have an “indefinite” extent [0181] 5. Nanoporous—have large pore sizes and ultrahigh porosity (up to 90% free volume) [0182] 6. Extremely large internal surface area typically» 1,000 m2/g (extending beyond 6,000 m2/g) [0183] 7. Selectively uptake small molecules [0184] 8. Can have optical or magnetic responses to the inclusion of guests [0185] 9. Synthesis from molecular building blocks holds the potential to tailor the properties of the resulting MOF [0186] 11. Behave akin to molecular sponges [0187] 12. Functionalist ion of the organic unit can provide predictably functionalised pores

[0188] Typically, MOFs are synthesised by combining organic ligands and metal salts in solvothermal reactions at relatively low temperatures (below 300 degrees Celsius).

[0189] Characteristics/structure of the resulting MOF is influenced by: [0190] 1. Characteristics of the ligand (bond angles, ligand length, bulkiness chirality etc.) [0191] 2. Metal ion used: tendency to adopt certain geometries

[0192] Reactants mixed in high boiling polar solvents e.g. water, dialkyl formamides, dimethyl sulfoxide or acetonitrile or the like.

[0193] Concentrations of both metal salt and organic ligand which can be varied across a large range, extent of solubility of reactants, pH of the solution.

[0194] There are also several other methods for treatment e.g. electrochemical, microwave irradiation et al.

[0195] Secondary building units (SBUs) dictate the final topology of the framework. Organic linkers seldom change structure during assembly. The SBUs are often metal clusters based and result from the initial bonding between the metal ions and bridging ligands. Can form several shapes e.g. trigonal planar, square planar tetrahedral. Shape of SBU depends on structure of ligand, type of metal, ratio of metal to ligand, solvent, and source of anions to balance metal ion charge.

[0196] Pores are the void spaces formed within MOFs upon the removal of guest molecules.

[0197] In general, large pores are advantageous for conducting host-guest chemistry such as catalysis therefore mesoporous (openings between 20 and 500 Å) or macroporous (greater than 500 Å) materials are attractive.

[0198] Microporous (less than 20 Å) materials have smaller pores which result in strong interactions between gas molecules and the pore walls making them good for gas storage or gas separation applications.

[0199] Measurements of openings is performed from atom to atom while subtracting the van der Waals radii to give the space available for access by guest molecules.

[0200] Pores are usually occupied by solvent molecules that must be removed for most applications. Structural collapse can occur, the larger the pore the more likely this is. Permanent porosity results when framework remains intact.

[0201] Frameworks can interpenetrate one another to maximize packing efficiency.

[0202] MOFs may participate in post-synthetic modification (PSM) where further chemical reactions can be used to decorate the frameworks. This may be applied to modify the surface property and pore geometry.

[0203] A range of MOF and amorphous microporous organic polymer (MOP) materials can be utilised to provide an active region according to certain embodiments of the present invention. They can achieve performance benefits of traditional loudspeaker-enhancing materials, but in a cost-effective, highly stable and hydrophobic form by virtue of the support material they may be impregnated within. In the case of MOP materials, the microporous impregnate material itself is highly hydrophobic which has benefits.

[0204] The MOP materials can be synthesized from component parts with innate hydrophobicity, resulting in a high degree of natural hydrophobicity if the resultant material. The material is preferably presented to the sound field in an uncompacted and binderless aerated suspension.

[0205] This can be achieved by impregnating the microporous organic polymer (MOP) material into a fine non-woven felt structure using ultrasonic or electrostatic entrainment. Preferably a fill factor of 80% is achieved.

[0206] The felt can then be thermally sealed to keep the powder in using a thin and flexible impermeable membrane, which further adds to the materials immunity to the effects of moisture. This encapsulated felt with high adsorbent material content can be held close to the loudspeaker element within the housing.

[0207] FIG. 7 illustrates a frequency response curve for a micro speaker (for example as per the speaker shown in FIG. 4).

[0208] The solid black line (A) represents the acoustic frequency response of an empty micro speaker, with no filling material.

[0209] The dashed line (B) shows the frequency response of the micro speaker when the side chambers are around 80% occupied by loose, dry MOP powder covered by a silk membrane. The improvement over the empty case is around 3.5 dB under 900 Hz.

[0210] The chain dashed line (C) shows the response curve of the micro speaker for the same volume of MOP powder, this time fixed through saturation by Methanol which is evaporated prior to being covered by the silk membrane. The improvement over the empty case is 2.87 dB below 900 Hz, but the shape of the curve is different, with more improvement now seen at very low frequencies (under 200 Hz), and with the resonant peak at 800-1000 Hz damped down by around 4 dB. The combination of these effects results in a broader, more refined (if slightly quieter) sound quality.

[0211] This range of outcomes represents an opportunity to tune the beneficial response according to the desire of the customer.

[0212] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to” and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0213] Features, integers, characteristics or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of the features and/or steps are mutually exclusive. The invention is not restricted to any details of any foregoing embodiments. The invention extends to any novel one, or novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0214] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.