Sound absorbers

Abstract

An assembly for a sound absorber for a ventilation system, the assembly comprising a plurality of parts. The plurality of parts can from an unassembled condition be put into an assembled condition. In the assembled condition the parts form a sound absorber, comprising a ventilation duct defined by one or more walls of respectively one or more of the parts, and one or more of Helmholtz resonators extending from the ventilation duct. Each of the interiors of the one or more Helmholtz resonators communicate with the ventilation duct via one or more air passages in respectively the one or more walls. In the unassembled condition, the plurality of parts comprises one or more of a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent, and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators.

Description

[0001] SOUND ABSORBERS

[0002] FIELD

[0003] The present disclosure relates to for sound absorbers, and in particular sound absorbers for ventilation systems, parts for said sound absorbers and methods of manufacturing and assembling said sound absorbers and parts.

[0004] BACKGROUND

[0005] Noise is a common problem in ventilation systems such as those used in conjunction with HVACs, and more generally residential and commercial ventilation systems and heat recovery systems. In particular, noise from various parts of the ventilation system can propagate along ventilation ducts and be a nuisance to users.

[0006] Sound absorbers for ventilation systems can comprise one or more Helmholtz resonators connected to a ventilation duct. The cavities of the Helmholtz resonators have resonant frequencies such that when a sound wave propagates along the ventilation duct, pressure waves propagate into, and resonate within, the Helmholtz resonators, which dissipates the sound. Sound absorbers formed around a ventilation duct form a complex structure which can increase the complexity of manufacturing methods. Presently, the viability of sound absorbers for ventilation systems can be tested by 3D printing the prototype but such 3D-printed models are not suitable for mass production. There is a need to provide sound absorbing structures for ventilation systems comprising Helmholtz resonators which are easier to manufacture, ideally using methods of mass production.

[0007] There is also a need to improve the overall performance of sound absorbers comprising a ventilation duct and one or more Helmholtz resonators. For example, sound waves propagating through the sound absorber may cause distortion in the shape of the sound absorber itself, due to expansion and contraction of the structure caused the pressure waves of the propagating sound impacting on the structure. Similar distortions can be causes by forces exerted onto the sound absorber by other components, such as compressive forces exerted onto the sound absorber by neighbouring components, forces exerted onto the sound absorber by components resting on the sound absorber, or even distortions of the sound absorber caused by its own weight. Distortion of the shape of the sound absorber in turn changes the absorption properties of the sound absorber as the dimensions of the sound absorber vary dynamically. Distortion of the structure of the sound absorber by magnitudes as small as millimetres can cause a significant change in absorption spectrum of the sound absorber. Accordingly, there is a need for sound absorbers that are structurally reliable such that distortions in the structure caused by sound or other exerting forces are reduced. SUMMARY

[0008] According to a first aspect of the disclosure, there is provided an assembly for a sound absorber for a ventilation system, the assembly comprising a plurality of parts, wherein: the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more of Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein in the unassembled condition, the plurality of parts comprises one or more of: a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators.

[0009] According to a second aspect of the disclosure, there is provided a method of manufacturing an assembly of parts for a sound absorber for a ventilation system, the method comprising: providing a plurality of parts, the plurality of parts comprising one or more of: a segmental portion of a perimeter of a ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators; wherein the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls.

[0010] According to a third aspect of the disclosure, there is provided a method of assembling a sound absorber for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts comprises one or more of: a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators. According to a fourth aspect of the disclosure, there is provided an apparatus comprising one or more parts for a sound absorber for a ventilation system, at least one part of the one or more parts comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, the said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0011] According to a fifth aspect of the disclosure, there is provided a sound absorber comprising: a ventilation duct defined by one or more walls; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in the one or more walls; wherein one or more of the one or more air passages comprise one or more slits extending circumferentially and / or axially about the ventilation duct; wherein the wall further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0012] According to a sixth aspect of the disclosure, there is provided a method of manufacturing one or more parts for a sound absorber for a ventilation system, the method comprising: providing one or more parts comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, the said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0013] According to a seventh aspect of the disclosure, there is provided a method of assembling a sound absorber for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts include a set of parts each comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0014] According to a eighth aspect of the disclosure, there is provided a method of assembling a sound absorber, for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts comprise a plurality of hollow toroidal bodies each defining a Helmholtz resonator, each toroidal body extending around a respective inner lumen, wherein the one or more inner lumens collectively define the ventilation duct; and wherein one or more of the one or more air passages comprise one or more slits extending circumferentially and / or axially about the ventilation duct; wherein the wall further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0015] According to a ninth aspect of the disclosure, there is provided a method of manufacturing a sound absorber for a ventilation system, comprising: providing one or more hollow toroidal bodies each defining an interior chamber, each toroidal body extending around a respective inner lumen; and for each toroidal body, removing material from the toroidal body to form one or more air passages through a surface of the hollow toroidal body, the one or more air passages communicating the interior chamber with the inner lumen to form a Helmholtz resonator communicating with the inner lumen.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] To enable better understanding of the present disclosure, and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying schematic drawings, in which:Fig. 1A shows a schematic side view of a part for a sound absorber for a ventilation system according to one or more embodiments as shown and described herein. Fig. IB shows a schematic cutaway side view of the part shown in Fig. 1 A.

[0018] Fig. 1C shows a schematic front cross-sectional view of the part of Fig. IB, taken along the line C-C.

[0019] Fig. 2A shows a schematic front cross-sectional view of an assembled set of parts forming a sound absorber according to one or more embodiments as shown and described herein.

[0020] Fig. 2B shows a schematic cross-sectional side view of the sound absorber of Fig. 2A.

[0021] Fig. 3 A shows a schematic cutaway side view of a part for a sound absorber for a ventilation system according to one or more embodiments as shown and described herein.

[0022] Fig. 3B shows a schematic front cross-sectional view of the part of Fig. 3 A, taken along the line B-B.

[0023] Fig. 4 shows a schematic front cross-sectional view of an assembled set of parts forming a sound absorber according to one or more embodiments as shown and described herein.

[0024] Fig. 5 shows a side view of a part for a sound absorber for a ventilation system according to one or more embodiments as shown and described herein.

[0025] Fig. 6 shows a front view of a sound absorber for a ventilation system according to one or more embodiments as shown and described herein.

[0026] Fig. 7A shows a schematic cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0027] Fig. 7B shows an unravelled schematic view of a wall comprising two slits and of identical size, for use in a part or sound absorber according to one or more embodiments as shown and described herein.

[0028] Fig. 8A shows a schematic partial cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0029] Fig. 8B shows a schematic partial cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0030] Fig. 8C shows a schematic partial cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0031] Fig. 8D shows a schematic partial cross-sectional side view of a slit for a sound absorber according to one or more embodiments as shown and described herein.

[0032] Fig. 9 shows a transmission loss spectrum for different slit types. Fig. 10A shows a schematic cross-sectional side view of an assembly for a sound absorber for a ventilation system according to one or more embodiments as shown and described herein.

[0033] Fig. 10B shows a perspective view of the first set of parts shown in Fig. 10A.

[0034] Fig. 10C shows a perspective view of the first set of parts shown in Fig. 10A.

[0035] Fig. 10D shows a schematic view of a flash fit for use in a sound absorber according to one or more embodiments as shown and described herein.

[0036] Fig. 10E shows a schematic view of a compressible seal for use in a sound absorber according to one or more embodiments as shown and described herein.

[0037] Fig. 11 shows a schematic cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0038] Fig. 12A shows a schematic cross-sectional side view of an assembly for a sound absorber for a ventilation system according to one or more embodiments as shown and described herein.

[0039] Fig. 12B shows a schematic cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0040] Fig. 13 A shows a front perspective view of a part for a sound absorber according to one or more embodiments as shown and described herein.

[0041] Fig. 13B shows a schematic back view of the part shown in Fig. 13 A.

[0042] Fig. 13C shows a perspective view of a second set of parts for a sound absorber according to one or more embodiments as shown and described herein.

[0043] Fig. 13D shows a schematic perspective view of a sound absorber according to one or more embodiments as shown and described herein.

[0044] Fig. 14 shows a schematic perspective view of a sound absorber according to one or more embodiments as shown and described herein.

[0045] Fig. 15 shows a schematic partial cross-sectional side view of a sound absorber according to one or more embodiments as shown and described herein.

[0046] Fig. 16A shows a schematic perspective side view of a first set of parts for a sound absorber according to one or more embodiments as shown and described herein.

[0047] Fig. 16B shows a schematic perspective side view of a first set of parts for a sound absorber according to one or more embodiments as shown and described herein.

[0048] Fig. 17A shows a schematic top view of a hollow toroidal body. Fig. 17B shows a top view of the hollow toroidal body shown in Fig. 17A.

[0049] Fig. 17C shows a cross-sectional side view of the hollow toroidal body of Fig. 17A taken along line A-A.

[0050] Fig. 17D shows a cross-sectional top view of the hollow toroidal body taken along the line D- D of Fig. 17B.

[0051] Fig. 18A shows a schematic top view of a hollow toroidal body for a sound absorber according to one or more embodiments as shown and described herein.

[0052] Fig. 18B shows a top view of the hollow toroidal body shown in Fig. 17A.

[0053] Fig. 18C shows a cross-sectional side view of the hollow toroidal body of Fig. 17A taken along line A-A.

[0054] Fig. 18D shows a cross-sectional top view of the hollow toroidal body taken along the line D- D of Fig. 17B.

[0055] Fig. 19 shows a sound absorber according to one or more embodiments as shown and described herein.

[0056] DETAILED DESCRIPTION

[0057] As used herein, the term “ventilation duct” may refer to an element which comprises one or more inlets and one or more outlets, and a ventilation route extending between the one or more inlets and the one or more outlets. A ventilation duct may be defined by one or a plurality of walls and may take any suitable cross-sectional shape, e.g. circular, oval, square rectangular or any other regular or irregular polygon. The cross-sectional shape and / or size may vary along the length of the ventilation duct. The ventilation duct may be tapered or non-tapered and may have any size as suitable for its application.

[0058] As used herein, the term “communicate” or “communicatively connect”, when referring to communication between two volumes or spaces, refers to fluid communication between those two volumes or spaces such that sound waves are able to travel between the communicating volumes or spaces. For example, a ventilation duct communicates with an interior space such as that of a Helmholtz resonator when there is a fluid connection between them.

[0059] As used herein, the term “Helmholtz resonator” or “HHR” may refer to a resonant cavity defined by one or more resonator walls. The resonant cavity communicates with its exterior via one or more air passages. HHRs may take any suitable shape and size depending on the desired properties. Similarly, the one or more air passages may take any suitable shape and may have any suitable length, width and depth. As used herein, the term “slit” may refer to a shape which has a length which is longer than it is wide. In some embodiments, the slit may be defined by two opposing edges which run parallel to one another. In some embodiments, the two opposing edges may not be parallel to one another.

[0060] As used herein, the term “critically coupled” may refer to when the amount of sound energy that escapes from the HHR (known in the art as the leakage rate) substantially matches the inherent losses of the HHR, for example absorptive losses and frictional losses or viscothermal losses within the HHR that convert the sound energy to heat (known in the art as the inherent loss rate). In resonator systems, when the leakage rate matches the inherent loss rate, a critical coupling condition is observed in which optimal destructive interference between the incoming and outgoing sound waves of the HHR is achieved (see, for example, Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators, Romero-Garcia el al, Scientific Reports 6, article 19519, published on 19 January 2016). Methods of designing one or more critically coupled HHRs are disclosed in: Perfect and broadband acoustic absorption by critically coupled sub-wavelength resonators,' Use of complex frequency plane to design broadband and sub-wavelength absorbers (Romero-Garcia et al., J. Acoust. Soc. Am. 139, 3395-3403, published 30 June 2016); and Rainbow -trapping absorbers: Broadband, perfect and asymmetric sound absorption by subwavelength panels for transmission problems (Jimenez et al., Scientific Reports 7, article 13595, published 19 October 2017). It will be appreciated that slight deviations from the perfect critical coupling condition are acceptable without deviating from the scope of the present disclosure. For the purposes of this disclosure, an HHR is considered to be critically coupled when experimentally, the HHR exhibits an absorption of above about 90% at its resonant frequency. This can be measured using, for example, Kundt’s tube.

[0061] The term “incomplete HHR” may refer to an HHR in a sound absorber which communicates with a space exterior to the sound absorber by one or more routes which are not via the ventilation duct (i.e., not via the air passages communicatively connecting the ventilation duct and HHR).

[0062] The term “slit stiffening element” may refer to an element which inhibits relative movement of opposing edges defining a slit. This term may include elements such as struts, wires, brackets or any material connecting the opposite edges of the slit. The slit stiffening element may be unitary with the material through which the slit extends. For example, the slit stiffening element may be formed with, and unitary with, the wall material through which the slit extends. Alternatively, the slit stiffening element may be a separate element which is mounted to opposing sides of the slit (for example by adhesive or welding) after the slit is formed. Fig. 1 A shows a schematic side view of a part 10 for a sound absorber for a ventilation system according to one or more embodiments, the part optionally comprised in an assembly. Fig IB shows a cutaway side view of the part 10 shown in Fig. 1 A. Fig 1C shows a front cross-sectional view of the part of Fig. IB, taken along the line C-C (equivalently, Fig. IB is a cross-sectional side view of the part 10 shown in Fig. 1C taken along the line B-B).

[0063] The part 10 comprises a wall 12 having an outer surface 121 and an inner surface 122, and one or more Helmholtz resonators (HHRs) 14 extending from the wall 12, each HHR 14 comprising an interior 141 defined by one or more resonator walls 142 and part of wall 12. It will be appreciated that although the part 10 illustrates only one HHR 14, in any of the embodiments disclosed herein each of the parts may comprise any number of HHRs 14, which may be identical in shape and / or resonant frequency to one another or may have different dimensions and / or resonant frequencies to one another, or a mix of identical and non-identical resonators. Each HHR 14 may be located at the same axial position along the part 10 but displaced circumferentially from one another about the wall 12, or at the same circumferential position about the wall 12 but axially displaced from one another along part 10, or both axially and circumferentially displaced from one another.

[0064] The wall 12 comprises a segmental portion of a perimeter of the ventilation duct, and the part has a partial circumferential extent (i.e., as opposed to a complete circumferential extent). In other words, the part 10 does not itself form a ventilation duct, owing to the partial circumferential extent of the wall 12 and the part 10. This may simplify the manufacturing procedure of the part 10, for example, in the case of manufacture by injection molding, by simplifying the injection mold required for the part 10.

[0065] The part 10 further comprises one or more air passages 16 extending through the wall 12 and communicating with the interior 141. In the illustrated embodiment of Figs. 1A-1C, the air passage 16 is a circular cross-sectional shape whereas in other embodiments, the air passage 16 (or air passages) may take any suitable shape, such as oval, rectangular, or any suitable regular or irregular polygonal shape. Where the part 10 comprises a plurality of air passages 16, each air passage 16 may take any suitable shape and the respective shapes may be identical or different to one another. In some embodiments, one or more air passages 16 of the part 10 may comprise one or more slits having a circumferential and / or axial extent about the wall 12, as described herein with reference to later drawings. In any such embodiments, there may be provided one or more slit stiffening elements extending across one or more of the said slits.

[0066] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Figs. 8A and 8C), in some embodiments the wall 12 has a segmental inner wall surface 122, and the air passage 16 may comprise one or more slits defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface (i.e. one or both edges defining the slit are “square” edges).

[0067] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Figs. 3 A, 3B and 8A to 8D), in some embodiments the segmental wall 12 tapers towards the one or more slits on one or both sides of the one or more slits.

[0068] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Fig. 8C), the one or more slits have a tortuous shape along their length.

[0069] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Figs. 8A and 8B), in some embodiments the one or more slits each extend in a respective single direction about the wall 12.

[0070] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Fig. 8D), in some embodiments the wall 12 comprises a chamfered edge on one or both sides of the one or more slits.

[0071] Further, in alternative embodiments where one or more air passages 16 of part 10 comprises a slit, as described in further detail with reference to later drawings (see e.g. the embodiments described with reference to Fig. 8B), in some embodiments the wall 12 comprises a filleted edge on one or both sides of the one or more slits.

[0072] The part 10 may be made of any suitable material. In some embodiments, the part 10 is made of a material suitable for injection molding, such as a thermoplastic or thermosetting material or a metal.

[0073] In other embodiments, part 10 may be made of other materials not suitable for injection molding, for example materials which are millable or suitable for 3D printing.

[0074] According to an aspect of the invention, the part 10 is one of a plurality of parts forming an assembly, wherein the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber. In such embodiments, the sound absorber comprises a ventilation duct defined by one or more walls of respectively one or more of the parts. The sound absorber further comprises a plurality of HHRs extending from the ventilation duct, each of the interiors of the HHRs communicating with the ventilation duct via one or more air passages in respectively the one or more walls.

[0075] The assembly of parts including the part 10 may be provided in an unassembled condition (e.g. as shown in Figs 1 A to 1C) or an assembled condition.

[0076] One such assembled condition is illustrated in Fig. 2A, which shows a front cross-sectional view of an assembled set of parts 10a, 10b, 10c, lOd which together form a sound absorber 100 according to one or more embodiments. One or more, or all, of the parts 10a- lOd may be identical in shape to one another (for example identical to any embodiment of part 10 described above). In embodiments where at least some of the parts are identical to one another, this enables the same manufacturing process to be used for at least some of the constituent parts.

[0077] Fig 2B shows a cross-sectional side view of the sound absorber 100 of Fig. 2A, taken along the line B-B (equivalently, Fig. 2A is a cross-sectional side view of the sound absorber 100 shown in Fig. 2B taken along the line A- A). The sound absorber 100 comprises a ventilation duct 25 defined by the respective interior surfaces 122a, 122b, 122c, 122d of the respective walls 12a, 12b, 12c, 12d of the respective parts 10a, 10b, 10c, lOd. The sound absorber 100 comprises a plurality of HHRs 14a, 14b, 14c, 14d extending from the ventilation duct 25 via respective one or more air passages 16a, 16b, 16c, 16d. It is noted that although one air passage 16 illustrated for each HHR 14, each HHR 14 may alternatively have a plurality of air passages 16 communicatively connecting the respective interior 141 of the HRR 14 to the ventilation duct 25.

[0078] The HHRs 14a-14d may be identical or different in size, shape or natural resonant frequency. In some embodiments, only some of the HHRs 14a-14d may be present. For example, one or more of the parts lOa-lOd may comprise only wall 12 forming part of the ventilation duct, and may be free from HHRs and air passages extending through the respective wall(s) 12.

[0079] One or more or all of HHRs 14a-14d may be critically coupled , and preferably all of the HHRs in the sound absorber 100 are critically coupled.

[0080] The sound absorber 100 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 100 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 100 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less. Frequencies of 250 Hz or less (and 100 Hz or less) are commonly encountered in HVAC systems so that in such embodiments, the sound absorber is well-suited to ventilation systems connected to an HVAC system. The attenuation properties of the sound absorbers disclosed herein at each frequency can be measured experimentally by inputting sound at a given frequency and amplitude (i.e. at a first end of the ventilation duct) and measuring the amplitude emitted by the sound absorber (i.e. at a second end of the ventilation duct).

[0081] Although in the embodiment illustrated in Figs. 2A and 2B, the sound absorber 100 comprises four HHRs 14 situated radially about the same axial position along the ventilation duct 25, in other embodiments the sound absorber 100 may comprise at least two HHRs 14 which are displaced from one another in an axial direction of the ventilation duct 25. In some embodiments, one or more, or all, HHRs 14 which are axially displaced from one another in an axial direction of the ventilation duct 25 may be critically coupled.

[0082] Although in the embodiment illustrated in Figs. 2A and 2B, the sound absorber 100 comprises four parts lOa-lOd, it will be appreciated that the sound absorber 100 may be formed of any number of parts 10 (for example a higher numbers of parts 10, wherein each part 10 has a smaller circumferential extent than the parts 10a- lOd so that they collectively form the sound absorber 100).

[0083] In the assembled condition shown in Figs. 2A and 2B, the plurality of parts lOa-lOd may be assembled together by any suitable means. For example, the plurality of parts 10a- lOd may be assembled together by one or more of welding (such as ultrasonic welding) or adhesive. Alternatively, or additionally, each part 10 may comprise one or more interconnecting elements configured to connect with a corresponding interconnecting element on another part, such that in the assembled condition shown in Figs. 2A and 2B, the interconnecting elements are connected to one another. Examples of interconnecting mechanisms include a snap-fit mechanism, comprising a protrusion (first interconnecting element) configured to snap-fit inside a corresponding recess (second interconnecting element). Other examples include latches or hooks, although it will be appreciated that any interconnecting mechanism known in the art may be used. One example of an interconnecting mechanism is shown and described herein with reference to Fig. 13B. Alternatively or additionally, the parts lOa-d may be assembled in place within a heat-shrinkable tubing made of any suitable heat-shrinkable material (e.g. a heat-shrinkable polymer), and heat may be applied to the tubing to shrink onto the parts lOa-d to hold them in the assembled condition. Alternatively or additionally, another set of parts may be provided comprising a plurality of outer segmental portions configured to form an outer wall surrounding the outer surfaces 121 of the respective parts 10. The outer segmental portions may be assembled together (for example by adhesive, welding and / or interconnecting mechanisms) with the parts lOa-d held in place within the outer segmental portions.

[0084] Fig. 3 A shows a cutaway side view of a part 20 for a sound absorber for a ventilation system according to one or more embodiments, the part optionally comprised in an assembly. Part 20 is similar to part 10 described with reference to Figs. 1 A to 1C and like numerals are used for the same elements. Fig 3B shows a front cross-sectional view of the part 20 of Fig. 3 A, taken along the line B-B (equivalently, Fig. IB is a cross-sectional side view of the part 10 shown in Fig. 1C taken along the line B-B). Part 20 is similar to part 10 shown in Fig. 1 A except for the following features. Firstly, HHR 14 of part 20 comprises an air passage 160 which is a slit having a circumferential extent about the wall 12. As shown in Figs. 3A and 3B, the slit 160 extends in a direction perpendicular to the axial direction of the part 12, whereas in other embodiments the slit 160 may additionally have an axial (i.e., both an axial and a circumferential extent), or may only have an axial extent (such as shown in Fig. 16A). Secondly, part 20 differs from part 10 in that the part 20 does not itself form an HHR, but rather an incomplete HHR 140. The incomplete HHR 140 is incomplete because the interior 141 is not fully enclosed such that there are other passages for air which do not pass through the one or more air passages 160 in the wall 12 (i.e., such that the Helmholtz resonance phenomenon is not observed). For example, one or both of lateral ends 143a, 143b are open and form other air passages out of interior 143.

[0085] It will be appreciated that although the part 20 illustrates only one incomplete HHR 140, in any of the embodiments disclosed herein each of the parts may comprise any number of incomplete HHRs 140, which may be identical in shape to one another or may have different dimensions and / or to one another, or a mix of identical and non-identical incomplete HHRs 140. One such embodiment is shown in Fig. 5. Each incomplete HHR 140 may be located at the same axial position along the part 20 but displaced circumferentially from one another about the wall 12, or at the same circumferential position about the wall 12 but axially displaced from one another along part 20, or both axially and circumferentially displaced from one another.

[0086] The wall 12 comprises a segmental portion of a perimeter of the ventilation duct, and the part has a partial circumferential extent (i.e., as opposed to a complete circumferential extent). In other words, the part 20 does not itself form a ventilation duct, owing to the partial circumferential extent of the wall 12 and the part 20. This may simplify the manufacturing procedure of the part 20, for example, in the case of manufacture by injection molding, by simplifying the injection mold required for the part 20. Similarly, the incomplete HHR 140 simplifies manufacture of the part 20, for example simplifying the injection mold required in the case of manufacture by injection molding.

[0087] Where the part 20 comprises a plurality of air passages 160, each air passage 16 may take any suitable shape and the respective shapes may be identical or different to one another. In some embodiments, there may be provided one or more slit stiffening elements extending across one or more of the said slits 160. In the illustrated embodiment, the wall 12 of part 20 has a segmental inner wall surface 122, and the one or more slits 160 are defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface (i.e. one or both edges defining the slit are “square” edges, as illustrated in Fig. 3 A).

[0088] In other embodiments (see e.g. the embodiments described with reference to Figs. 8A to 8D), the segmental wall 12 of part 20 tapers towards the one or more slits 160 on one or both sides of the one or more slits.

[0089] Further, in some embodiments (see e.g. the embodiments described with reference to Fig. 8C), the one or more slits 160 of part 20 have a tortuous shape along their length.

[0090] Further, in some embodiments (see e.g. the embodiments described with reference to Fig. 8D), in some embodiments the wall 12 of part 20 comprises a chamfered edge on one or both sides of the one or more slits.

[0091] Further, in some embodiments (see e.g. the embodiments described with reference to Fig. 8B), the wall 12 of part 20 comprises a filleted edge on one or both sides of the one or more slits.

[0092] The part 20 may be made of any suitable material. In some embodiments, the part 20 is made of a material suitable for injection molding, such as a thermoplastic or thermosetting material or a metal.

[0093] In other embodiments, part 20 may be made of other materials not suitable for injection molding, for example materials which are millable or suitable for 3D printing.

[0094] According to an aspect of the invention, part 20, is one of a plurality of parts forming an assembly, wherein the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber. In such embodiments, the sound absorber comprises a ventilation duct defined by one or more walls of respectively one or more of the parts. The sound absorber further comprises a plurality of HHRs extending from the ventilation duct, each of the interiors of the HHRs communicating with the ventilation duct via one or more air passages in respectively the one or more walls. The part 20 comprises a segmental portion of a perimeter of the ventilation duct (i.e., wall 12) and has a partial circumferential extent. The part 20 further has one or more resonator walls forming one or more incomplete HHRs (i.e., resonator walls 142).

[0095] The assembly of parts including the part 20 may be provided in an unassembled condition (e.g. as shown in Figs. 3 A and 3B) or an assembled condition. One such assembled condition is illustrated in Fig. 4, which shows a front cross-sectional view of an assembled set of parts 20a, 20b, 20c, 20d which together form a sound absorber 200 according to one or more embodiments. One or more, or all, of the parts 20a-20d may be identical in shape to one another (for example identical to any embodiment of part 20 described above). In embodiments where at least some of the parts are identical to one another, this enables the same manufacturing process to be used for at least some of the constituent parts.

[0096] The sound absorber 200 comprises a ventilation duct 25 defined by the respective interior surfaces 122a, 122b, 122c, 122d of the respective walls 12a, 12b, 12c, 12d of the respective parts 20a, 20b, 20c, 20d. The sound absorber 200 comprises an HHR 14 extending from, and about, the ventilation duct 25 via respective one or more air passages 160a, 160b, 160c, 160d. The HHR 14 is formed collectively by interior spaces 143a, 143b, 143c and 143d and form an annular HHR 14 around the ventilation duct 25. It is noted that although four air passages 160 are illustrated for the HHR 14, the HHR 14 may alternatively have any number of air passages 160 communicatively connecting the interior 141 of the HRR 14 to the ventilation duct 25.

[0097] The interiors 143a-143d may be identical or different in size or shape. Similarly, the air passages may be identical or different in shape or dimension. Although the sound absorber comprises only one HHR 14, in some embodiments, more than one HHR may be present. For example, one or more resonator walls may be provided with one or more of the parts 20 which divide the annular HHR 14 into a plurality of segmental HHRs at the same axial position of the ventilation duct 25, but distributed circumferentially about the ventilation duct. Alternatively or additionally, the sound absorber 200 may comprise a plurality of annular or segmental HHRs axially displaced from one another along the length of the ventilation duct 25.

[0098] One or more, or all, HHRs may be critically coupled. In some embodiments, at least two HHRs 14 which are axially displaced from one another in an axial direction of the ventilation duct 25 may be critically coupled. Preferably, all of the HHRs in the sound absorber 200 are critically coupled.

[0099] The sound absorber 200 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 200 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 200 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less. Frequencies of 250 Hz or less (and 100 Hz or less) are commonly encountered in HVAC systems so that in such embodiments, the sound absorber is well-suited to ventilation systems connected to an HVAC system. Although in the embodiment illustrated in Fig. 4, the sound absorber 200 comprises four parts 20a-20d, it will be appreciated that the sound absorber 200 may be formed of any number of parts 20 (for example a higher numbers of parts 20, wherein each part 20 has a smaller circumferential extent than the parts 20a-20d so that they may be assembled to form the sound absorber 200).

[0100] In the assembled condition shown in Fig. 4, the plurality of parts 20a-20d may be assembled together by any suitable means. For example, the plurality of parts 20a-20d may be assembled together by one or more of welding (such as ultrasonic welding) or adhesive. Alternatively, or additionally, each part 20 may comprise one or more interconnecting elements configured to connect with a corresponding interconnecting element on another part, such that in the assembled condition shown in Fig. 4, the interconnecting elements are connected to one another. Examples of interconnecting mechanisms include a snap-fit mechanism, comprising a protrusion (first interconnecting element) configured to snap-fit inside a corresponding recess (second interconnecting element). Other examples include latches or hooks, although it will be appreciated that any interconnecting mechanism known in the art may be used. One example of an interconnecting mechanism is shown and described herein with reference to Fig. 13B. Alternatively or additionally, the parts 20a-d may be assembled in place within a heat- shrinkable tubing, and heat may be applied to the tubing to shrink onto the parts 20a-d to hold them in the assembled condition. Alternatively or additionally, another set of parts may be provided comprising a plurality of outer segmental portions configured to form an outer wall surrounding the outer surfaces 121 of the respective parts 20. The outer segmental portions may be assembled together (for example by adhesive, welding and / or interconnecting mechanisms) with the parts 20a-d held in place within the outer segmental portions.

[0101] Fig. 5 shows a side view of a part 30 for a sound absorber for a ventilation system according to one or more embodiments, the part optionally comprised in an assembly. Part 30 is similar to part 20 described with reference to Figs. 3 A and 3B and like numerals are used for the same elements. Part 30 is similar to part 20, except that part 30 comprises a plurality of incomplete HHRs 140i- 140xii displaced from one another in an axial direction of the part 30, and further that the circumferential extent of part 30 is reduced (as it is configured to be assembled into a sound absorber formed of six parts as opposed to four). All of the possible variations of part 20 and its constituent element in various embodiments described above also apply to the part 30 and its corresponding constituent elements (e.g., size, shape and number of the various elements). The various different embodiments described above for air passage 160 of part 20 also apply to one or more, or all, of the air passages 160i-160xii. The various different embodiments described above for incomplete HHR 140 also apply to one or more, or all, of the incomplete HHRs 140i- 140xii . As in the case of part 20, The part 30 may be made of any suitable material. In some embodiments, the part 30 is made of a material suitable for injection molding, such as a thermoplastic or thermosetting material or a metal.

[0102] In other embodiments, part 30 may be made of other materials not suitable for injection molding, for example materials which are millable or suitable for 3D printing.

[0103] According to an aspect of the invention, part 30, is one of a plurality of parts forming an assembly, wherein the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber. In such embodiments, the sound absorber comprises a ventilation duct defined by one or more walls of respectively one or more of the parts. The sound absorber further comprises a plurality of HHRs extending from the ventilation duct, each of the interiors of the HHRs communicating with the ventilation duct via one or more air passages in respectively the one or more walls. The part 30 comprises a segmental portion of a perimeter of the ventilation duct (i.e., wall 12) and has a partial circumferential extent. The part 30 further has one or more resonator walls forming one or more incomplete HHRs (i.e., resonator walls which can be seen extending radially from wall 12 in Fig. 5).

[0104] The assembly of parts including the part 30 may be provided in an unassembled condition (e.g. as shown in Fig. 5) or an assembled condition.

[0105] One such assembled condition is illustrated in Fig. 6, which shows a front view of an assembled set of parts 30a-30f which together form a sound absorber 300 according to one or more embodiments. One or more, or all, of the parts 30a-30d may be identical in shape to one another (for example identical to any embodiment of part 30 described above). In embodiments where at least some of the parts are identical to one another, this enables the same manufacturing process to be used for at least some of the constituent parts.

[0106] The sound absorber 300 comprises a ventilation duct 25 defined by the respective interior surfaces of the respective walls 12a-12f of the respective parts 30a-30f. The sound absorber 300 comprises a plurality of HHRs extending from, and about, the ventilation duct 25 via respective one or more air passages. The HHRs are formed collectively by interior spaces of parts 30a-30f and form an annular HHR 14 around the ventilation duct 25.

[0107] The interiors of each part 30a-30f forming each HHR in sound absorber 300 may be identical or different in size or shape. Similarly, the air passages may be identical or different in shape or dimension. Although in the illustrated embodiment the sound absorber 300 comprises 12 HHRs, in some embodiments, other numbers of HHRs may be present. For example, one or more resonator walls may be provided on one or more of the parts 20 which divide an annular HHR into a plurality of segmental HHRs at the same axial position of the ventilation duct 25, but distributed circumferentially about the ventilation duct. Alternatively or additionally, the sound absorber 200 may comprise any number of annular or segmental HHRs axially displaced from one another along the length of the ventilation duct 25.

[0108] In sound absorber 300, one or more, or all, HHRs may be critically coupled. In some embodiments, at least two HHRs which are axially displaced from one another in an axial direction of the ventilation duct 25 may be critically coupled. Preferably, each of the HHRs in the sound absorber 300 are critically coupled.

[0109] The sound absorber 300 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 300 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 300 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less. Frequencies of 250 Hz or less (and 100 Hz or less) are commonly encountered in HVAC systems so that in such embodiments, the sound absorber is well-suited to ventilation systems connected to an HVAC system.

[0110] Although in the embodiment illustrated in Fig. 6, the sound absorber 300 comprises six parts 30a-30f, it will be appreciated that the sound absorber 300 may be formed of any number of parts 30 (for example a higher numbers of parts 30, wherein each part 30 has a smaller circumferential extent than the parts 30a-30f so that they may be assembled to form the sound absorber 300).

[0111] In the assembled condition shown in Fig. 6, the plurality of parts 30a-30f may be assembled together by any suitable means. For example, the plurality of parts 30a-30f may be assembled together by one or more of welding (such as ultrasonic welding) or adhesive. Alternatively, or additionally, each part 30 may comprise one or more interconnecting elements configured to connect with a corresponding interconnecting element on another part, such that in the assembled condition shown in Fig. 6, the interconnecting elements are connected to one another. Examples of interconnecting mechanisms include a snap-fit mechanism, comprising a protrusion (first interconnecting element) configured to snap-fit inside a corresponding recess (second interconnecting element). Other examples include latches or hooks, although it will be appreciated that any interconnecting mechanism known in the art may be used. One example of an interconnecting mechanism is shown and described herein with reference to Fig. 13B. Alternatively or additionally, the parts 30a-f may be assembled in place within a heat- shrinkable tubing, and heat may be applied to the tubing to shrink onto the parts 30a-f to hold them in the assembled condition. Alternatively or additionally, another set of parts may be providedcomprising a plurality of outer segmental portions configured to form an outer wall surrounding the outer surfaces of the respective parts 30. The outer segmental portions may be assembled together (for example by adhesive, welding and / or interconnecting mechanisms) with the parts 30a-f held in place within the outer segmental portions.

[0112] Fig. 7A shows a cross-sectional side view of a sound absorber 300A. The sound absorber 300A comprises a ventilation duct 25 defined by one or more walls 12, and a plurality of HHRs 14i- 14xii extending from the ventilation duct 25, each of the interiors of the HHRs 14 communicating with the ventilation duct 25 via one or more air passages 160 in the one or more walls 12 (for brevity, only air passage 160x is labelled but each HHR 14 comprises a corresponding air passage 160). The one or more air passages 160 are slits extending at least circumferentially about the ventilation duct 25. In addition, the wall further comprises one or more respective slit stiffening elements 165 extending across the respective one or more slits 160. As the resonant frequency of each HHR is dependent on the width of the slit 160, distortion of the sound absorber from bending, or axial compression or expansion, distorts the width of the slits and therefore dynamically changes the resonant frequency of the HHRs. The provision of one or more slit stiffening elements 165 extending across the slits assists in maintaining the width of the slits 160, and inhibits distortions of the widths by bending, compression or expansion of the sound absorber 300A.

[0113] The sound absorber 300A may be identical to any of the embodiments described for sound absorber 300 and it will be appreciated that any of the variations of the constituent elements described above for sound absorber 300 also apply to sound absorber 300A. It will also be appreciated that for any of the sound absorbers (or parts) disclosed herein which comprise one or more air passages, the one or more air passages of said sound absorber (or part) may comprise one or more slits 160 with one or more slit stiffening elements 165 extending across the one or more slits 160.

[0114] Fig. 7B shows an unravelled schematic view of a wall 12 comprising two slits 160a and 160b of identical size. Slit 160a is free from any slit stiffening elements 165 whereas slit 160b is interrupted by one or more slit stiffening elements 165. Slit 160a occupies a total surface area A of the wall 12, slit 160b occupies a total surface area B of the wall 12, and the slit stiffening elements 165 occupy a total surface area C of the wall 12. The surface area B of slit 160b is smaller than the surface area A of slit 160a by an amount equal to the total surface area C of the slit stiffening elements 165. The reduction in area of a slit caused by one or more slit stiffening elements can therefore be considered as the surface area A in the wall of an equivalent slit not comprising the slit stiffening elements, less the total surface area in the wall of the slit stiffening elements. In preferred embodiments of any of the sound absorbers or parts disclosed herein which comprise one or more slit stiffening elements, the reduction in surface area of the slit comprising the slit stiffening elements is less than 10%, and preferably less than 5%, and more preferably less than 3%. This ensures structural integrity of the slit, whilst maximising the size of the air passages, which allows for more sound energy to enter the sound absorber (as opposed to, e.g., a series of circular air passages) and thus increases the attenuation properties of the sound absorber.

[0115] Fig. 8A shows a partial cross-sectional side view of a sound absorber according to one or more embodiments. The sound absorber comprises a ventilation duct 25 defined by one or more walls 12 and a plurality of HHRs 14 extending from the ventilation duct 25, each of the interiors of the HHRs 14 communicating with the ventilation duct via one or more air passages 160 in the one or more walls 12. The one or more air passages 160 are slits having a circumferential extent in the ventilation duct 25. In the embodiment of Fig. 8A, the one or more air passages 160 are defined by opposing edges, wherein one or both of the opposing edges comprises a surface 161a, 161b traversing through the ventilation duct wall 12 in a direction perpendicular to the inner surface 122 of the ventilation duct wall 12 (also referred to in the art as a square edge). In any of the sound absorber or parts disclosed herein which comprise one or more slits, one or both edges defining the slit may be a square edge. Although the slits 160 are shown as extending in a single direction, the slits 160 may instead have a tortuous shape along the wall 12.

[0116] Fig. 8B shows a partial cross-sectional side view of a sound absorber according to one or more embodiments. The sound absorber comprises a ventilation duct 25 defined by one or more walls 12 and a plurality of HHRs 14 extending from the ventilation duct 25, each of the interiors of the HHRs 14 communicating with the ventilation duct via one or more air passages 160 in the one or more walls 12. The one or more air passages 160 are slits having a circumferential extent in the ventilation duct 25. In the embodiment of Fig. 8B, the one or more air passages 160 are defined by opposing edges, wherein one or both of the opposing edges comprises a filleted edge. In any of the sound absorber or parts disclosed herein which comprise one or more slits, one or both edges defining the slit may be a filleted edge. Although the slits 160 are shown as extending in a single direction, the slits 160 may instead have a tortuous shape along the wall 12.

[0117] Fig. 8C shows a partial cross-sectional side view of a sound absorber according to one or more embodiments. The sound absorber comprises a ventilation duct 25 defined by one or more walls 12 and a plurality of HHRs 14 extending from the ventilation duct 25, each of the interiors of the HHRs 14 communicating with the ventilation duct via one or more air passages 160 in the one or more walls 12. The one or more air passages 160 are slits having a circumferential extent in the ventilation duct 25. In the embodiment of Fig. 8C, the slits 160 have a tortuous shape along the wall 12. Although the slits 160 are shown as having square edges as in the case of Fig. 8 A, it will be appreciated that in other embodiments one or both edges may be filleted, tapered or chamfered. In any of the sound absorber or parts disclosed herein which comprise one or more slits, the one or more slits may have a tortuous shape.

[0118] In any of the sound absorber or parts disclosed herein which comprise one or more slits, one or both edges of the one or more slits 160 may be chamfered as shown in Fig. 8D.

[0119] It will be appreciated that in embodiments where the slits 160 extend axially, such as shown in Fig. 16A, the slits 160 may take any of the forms described above with reference to Figs. 8A- 8D, and their variants described above.

[0120] Fig. 9 shows a transmission loss spectrum across the ventilation duct 25 of the sound absorbers in Figs. 8 A to 8C. Line 171 shows the transmission loss spectrum for the sound absorber of Fig. 8A. Line 172 shows the transmission loss spectrum for the sound absorber of Fig. 8B. Line 173 shows the transmission loss spectrum for the sound absorber of Fig. 8C.

[0121] For a slit comprises square edges, sharp, right-angled edges can create turbulent flow at the entrance of the air passage, impacting the resonator's effectiveness. By introducing fillet edges as in Fig. 8B, the airflow into the cavity becomes smoother, which may improve the efficiency of the HHR. This change can reduce noise and improve the acoustic filtering characteristics of the HHR, as can be seen by comparing the relatively narrower absorption spectrum of line 171 compared to line 173.

[0122] Providing a tortuous slit (e.g. Fig. 8C) instead of a slit extending in a single direction (e.g. Figs, 8A and 8B) also modifies the acoustic properties of the HHR. For a given HHR shape and size, this provides a wider range of absorption spectrums depending on the shape of the tortuous path of the slit.

[0123] Fig. 10A shows a cross-sectional side view of an assembly for a sound absorber for a ventilation system according to one or more embodiments. The assembly comprises a plurality of parts. The plurality of parts comprises a first set of parts 50 and a second set of parts 60. Fig. 10B shows a perspective view of the first set of parts 50 and Fig. 10C shows a perspective view of the second set of parts 60.

[0124] In the illustrated embodiment of Figs. 10A to 10C, the first set of parts 50 comprises a single part (i.e., a unitary part formed of one piece). The part 50 comprises a wall 12, the inner surface of which defines a ventilation duct 25. The part 50 further comprises a plurality of resonator walls 142a-142e. The resonator walls 142a-142e form a plurality of incomplete HHRs which are open chambers 144i-144iv. It will be appreciated that although the part 50 illustrates four open chambers 144, in other embodiments disclosed herein the part 50 may comprise any number of open chambers 144, including a single open chamber 144. The open chambers 144 may be identical in shape and size to one another or may have different dimensions shapes to one another, or a mix of identical and non-identical open chambers. Each open chamber 144 may be located at the same axial position along the part 50 but displaced circumferentially from one another about the wall 12, or at the same circumferential position about the wall 12 but axially displaced from one another along part 50, or both axially and circumferentially displaced from one another. The provision of parts comprising open chambers as opposed to enclosed HHRs improves the manufacturability of the parts.

[0125] The part 50 further comprises a plurality of air passages 160i-160iv extending through the wall 12 and communicating with the respective open chambers 144i-144iv. In the illustrated embodiment of Figs. 10A and 10B, the air passages 160 for each open chamber 144 comprises a slit having a complete circumferential extent about the wall 12, and one or more slit stiffening elements 165i-165iv extending across each air passage 160. In other embodiments, the air passages may alternatively have a circular cross-sectional shape. The air passages 160 may take any suitable shape, such as oval, rectangular, or any suitable regular or irregular polygonal shape. Each open chamber 144 may have any number of air passages communicatively connected to it, including a plurality of air passages. Where the part 50 comprises a plurality of air passages 160, each air passage 160 may take any suitable shape and the respective shapes may be identical or different to one another. The air passages may be any of those described with respect to any other embodiment herein. In embodiments where a given air passage 160 is a slit, the slit may be provided with or without the slit stiffening elements(s) 165.

[0126] In some embodiments the first set of parts 50 may comprise a plurality of parts configured to be assembled to form a similar structure to the part 50 described with reference to Figs. 10A- 10B. In particular, the first set of parts may comprise a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers. For example the first set of parts 50 may comprise segmental portions of the part shown in Fig. 10A which are identical and which have a circumferential extent of 360° / N, where N is the number of parts in the set 50. In such embodiments, the N parts can be assembled to form the shape shown in Figs. 10A and 10B.

[0127] In the illustrated embodiment of Figs. 10A to 10C, the second set of parts 60 comprises a single part (i.e. a unitary part formed of one piece). The part 60 comprises a tubular outer wall 180 which is configured to surround the first set of parts 50 such that the outer wall 180 encloses each of the open chambers 144i to 144iv to form respectively a plurality of HHRs. It will be appreciated that the number of HHRs in the assembled condition corresponds to the number of open chambers provided in the first set of parts 50. Fig. 11 shows the first and second set of parts 50, 60 in an assembled condition, forming a sound absorber 400 having a plurality of HHRs 14i-14iv. Accordingly, the first and second set of parts 50, 60, form an assembly of a plurality of parts which, can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber 400.

[0128] The inner surface of outer wall 180 comprises a plurality of stopping elements, for example shoulders, 182a-182d configured to abut with respective resonator walls 142a-142d of the first part 50 in an assembled condition. As the size of the resonator walls 142a-142e tapers from a first end to a second end of the part 50, the part 50 can be inserted into the outer wall 180, illustrated by the arrow D, until the respective resonator walls 142a-142d abut the respective stopping elements 182a-182d, as illustrated in Fig. 11. Further axial movement of the resonator walls 142a-142d is prevented by the stopping elements 182a-182d. Abutment of the respective shoulders 182a-182d with the respective resonator walls 142a-142d seals closed the open chambers so that the Helmholtz resonators are formed, as shown in Fig. 11. It is noted that although the stopping elements 182a-182d are depicted as annular shoulders, any stopping element configured to abut with the resonator walls in the axial direction may be used (for example, protrusions or recesses of any suitable shape). The stopping elements may have a partial or complete circumferential extent. As depicted in Fig. 10A, in some embodiments, the inner surface may be step-wise tapered.

[0129] In some embodiments, the second set of parts 60 may comprise a plurality of parts configured to be assembled to form a similar structure to the part 60 described with reference to Fig. 10C (for example segmental portions configured to form the outer wall 180).

[0130] In embodiments where the first set of parts 50 comprises a plurality of parts, the first set of parts 50 may be assembled to one another by any suitable means. For example, the first set of parts 50 may be assembled together by one or more of welding (such as ultrasonic welding) or adhesive. Alternatively, or additionally, each part of the set 50 may comprise one or more interconnecting elements configured to connect with a corresponding interconnecting element on another part, such that in the assembled condition similar to that shown in Figs. 10A and 10B, the interconnecting elements are connected to one another. Examples of interconnecting mechanisms include a snap-fit mechanism, comprising a protrusion (first interconnecting element) configured to snap-fit inside a corresponding recess (second interconnecting element). Other examples include latches or hooks, although it will be appreciated that any interconnecting mechanism known in the art may be used. One example of an interconnecting mechanism is shown and described herein with reference to Fig. 13B. Alternatively, the first set of parts 50 may be held together only indirectly by the second set of parts 60.

[0131] In embodiments where the second set of parts 60 comprises a plurality of parts, the second set of parts 60 may be assembled to one another by any suitable means. For example, the second set of parts 60 may be assembled together by one or more of welding (such as ultrasonic welding), adhesive, and / or one or more interconnecting mechanisms. Alternatively, or additionally, each part of the set 60 may comprise one or more interconnecting elements configured to connect with a corresponding interconnecting element on another part, such that in the assembled condition similar to that shown in Figs. 10A and 10C, the interconnecting elements are connected to one another. Examples of interconnecting mechanisms include a snap-fit mechanism, comprising a protrusion (first interconnecting element) configured to snap-fit inside a corresponding recess (second interconnecting element). Other examples include latches or hooks, although it will be appreciated that any interconnecting mechanism known in the art may be used. One example of an interconnecting mechanism is shown and described herein with reference to Fig. 13B. Alternatively or additionally, the parts in the second set 60 may be assembled in place within a heat-shrinkable tubing, and heat may be applied to the tubing to shrink onto the second set of parts 60 to hold them in the assembled condition.

[0132] The first set of parts may be assembled to the second set of parts 60 by any suitable means, for example, by one or more of a frictional fit, welding (e.g. ultrasonic welding), one or more interconnecting mechanisms and / or adhesive. A schematic of a frictional fit, known as a flash fit, is shown in Fig. 10D. In the example, the size of the resonator wall 142 closely matches the diameter inside the outer wall 180 above the stopping element 182. The outer edge 142 therefore closely abuts the inner surface of the outer wall 180 so that a flash or burr 185 is pressed against the inner surface of the outer wall, thereby increasing the amount of friction between the parts. The flash or burr 185 may be an artefact of the molding process. Advantageously, designing the mold so that the flash or burr is located on a surface of the first set of parts 50 which abuts with the second set of parts 60 assists in obtaining a frictional fit. Alternatively, or additionally, a frictional fit may be achieved by the use a compressible seal 186 made of a compressible material such as an elastomeric material, configured to be compressed between the resonator wall 142 and the outer wall 180, as shown in Fig. 10E. The compressible seal 186 may be mounted, attached or otherwise formed on either component. It will be appreciated that the flash / burr and / or compressible seal may be used between any two suitable components requiring a frictional fit as disclosed herein.

[0133] The assembly of parts including the first set 50 and the second set 60 may be provided in an unassembled condition (e.g. as shown in Figs 10A to 10C) or an assembled condition (e.g. as shown in Fig. 11).

[0134] In the illustrated embodiment, the sound absorber 400 comprises a plurality of annular HHRs

[0135] 14 which are different in size, shape or natural resonant frequency. In other embodiments, at least some of the HHRs 14 of the sound absorber may be identical in size, shape or natural resonant frequency.

[0136] One or more HHRs 14 in the sound absorber 400 may be critically coupled, and preferably all of the HHRs in the sound absorber 400 are critically coupled.

[0137] The first and second set of parts 50 and 60 and may be made of any suitable material. In some embodiments, the part 50 is made of a material suitable for injection molding, such as a thermoplastic or thermosetting material or a metal. In other embodiments, the first and second set of parts 50 and 60 may be made of other materials not suitable for injection molding, for example materials which are millable or suitable for 3D printing. The first and second set of parts 50 and 60 may be made of the same or different material.

[0138] The sound absorber 400 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 400 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 400 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less.

[0139] Although in the embodiment illustrated in Fig. 11, the sound absorber 400 comprises a plurality of annular HHRs 14 situated axially along the ventilation duct 25, in other embodiments the sound absorber 400 may comprise at least two HHRs 14 which are displaced radially about the same axial position along the ventilation duct 25 (for example as described in embodiments with reference to Figs. 13A-13D). In some embodiments, one or more HHRs 14 which are axially displaced from one another in an axial direction of the ventilation duct 25 may be critically coupled. Preferably each HHR 14 is critically coupled.

[0140] Fig 12A shows a cross-sectional side view of an assembly for a sound absorber for a ventilation system according to one or more embodiments. The assembly comprises a plurality of parts, the plurality of parts comprises a first set of parts 50 and a second set of parts 60. The first set of parts 50 may be the same as described with reference to Figs. 10A and 10B, and all of the alternative embodiments of the set of parts 50 described with reference to Figs. 10A and 10B also apply to the first set of parts 50 of Fig. 12A.

[0141] The second set of parts 60 comprises a tubular outer wall 190 which is made of a heat- shrinkable material. The first set of parts 50 is configured to be inserted into the tubular outer wall 190 as shown in Fig. 12A. Heat can then be applied to the heat-shrinkable material, causing the tubular outer wall 190 to shrink towards the first set of parts 50. A cross-sectional side view of the resulting device is shown in Fig. 12B. The tubular outer wall 190 surrounds and secures to the first set of parts 50 to form a sound absorber 500 comprising a ventilation duct, and a plurality of HHRs 14i- 14iv extending from the ventilation duct, each of the interiors of the Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls defining the ventilation duct.

[0142] In the illustrated embodiment, the sound absorber 500 comprises a plurality of annular HHRs 14 which are different in size, shape or natural resonant frequency. In other embodiments, at least some of the HHRs 14 of the sound absorber may be identical in size, shape or natural resonant frequency.

[0143] One or more HHRs 14 in the sound absorber 500 may be critically coupled, and preferably all of the HHRs in the sound absorber 500 are critically coupled.

[0144] The sound absorber 500 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 500 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 500 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less.

[0145] Although in the embodiment illustrated in Fig. 12B, the sound absorber 500 comprises a plurality of annular HHRs 14 situated axially along the ventilation duct 25, in other embodiments the sound absorber 500 may comprise at least two HHRs 14 which are displaced radially about the same axial position along the ventilation duct 25 (for example as described in embodiments with reference to Figs. 13A-13D). In some embodiments, at least two HHRs 14 which are axially displaced from one another in an axial direction of the ventilation duct 25 may be critically coupled. Preferably each HHR 14 is critically coupled.

[0146] Fig. 13 A shows a front perspective view of a part 70a. The part 70a comprises a segmental wall 12a which is a segmental portion for a perimeter of a ventilation duct. The part 70a comprises a plurality of open chambers 144i-144v defined by resonator walls 142a-142f and 142L and 142R. Each of the open chambers 144i-144v is communicatively connected to at least one air passage 160i-160v. It will be appreciated that although the part 70a illustrates five open chambers 144, in other embodiments disclosed herein the part 70a may comprise any number of open chambers 144, including a single open chamber 144. The open chambers 144 may be identical in shape and size to one another or may have different dimensions shapes to one another, or a mix of identical and non-identical open chambers. Although a series of axially displaced open chambers 144 is illustrated, in other embodiments each open chamber 144 may be located at the same axial position along the part 70a but displaced circumferentially from one another about the wall 12, or both axially and circumferentially displaced from one another. 1

[0147] In the illustrated embodiment of Fig. 13A, the air passages 160 for each open chamber 144 comprises a slit having a partial circumferential extent about the wall 12, and further may one or more slit stiffening elements (not shown) extending across each air passage 160. In alternative embodiments, the slits may extend both circumferentially and axially, or only axially. In other embodiments, the air passages may alternatively have a circular cross-sectional shape. The air passages 160 may take any suitable shape, such as oval, rectangular, or any suitable regular or irregular polygonal shape. Each open chamber 144 may have any number of air passages communicatively connected to it, including a plurality of air passages. Where the part 70a comprises a plurality of air passages 160, each air passage 160 may take any suitable shape and the respective shapes may be identical or different to one another. The air passages may be any of those described with respect to any other embodiment herein. In embodiments where a given air passage 160 is a slit, the slit may be provided with or without the slit stiffening element(s) 165.

[0148] Fig. 13B shows a back view of the part 70a shown in Fig. 13 A. The part 70a comprises at least one interconnecting element 205a, 205b configured to connect with a corresponding interconnecting element on another part in the set of parts 70. In the illustrated embodiment, interconnecting element 205b is a snap-fit protrusion configured to snap-fit inside a corresponding recess of another part. Similarly, interconnecting element 205a is a recess configured to receive a snap-fit protrusion of another part.

[0149] Fig. 13C shows a perspective view of a second set of parts 80. In the illustrated embodiment, the second set of parts 60 comprises a single part (i.e. a unitary part formed of one piece). The part 60 comprises a tubular outer wall 180 which is configured to surround the first set of parts 70 such that the outer wall 180 encloses each of the open chambers 144 of the first set of parts 70 to form respectively a plurality of HHRs. It will be appreciated that the number of HHRs in the assembled condition corresponds to the number of open chambers provided in the first set of parts 70. Fig. 13D shows the first and second set of parts 70, 80 in an assembled condition, forming a sound absorber 600 having a plurality of HHRs (not shown). Accordingly, the first and second set of parts 70, 80, form an assembly of a plurality of parts which, can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber 500.

[0150] In the embodiment shown in Fig. 13D, the first set of parts comprise parts 70a-70d which are each identical to that described with reference to Figs. 13A and 13B. It will be appreciated that the parts 70a-70d need not be identical.

[0151] In some embodiments, one or mroe HHRs 14 of the sound absorber 600 are critically coupled.

[0152] Preferably each HHR 14 is critically coupled. Although in the illustrated embodiment of Figs. 13 A to 13D the first set of parts 70 are assembled together by snap-fit interconnecting mechanisms, it will be appreciated that the first set of parts 70 may be assembled together by any other suitable means as disclosed herein, for example by adhesive, welding, or indirectly by a frictional fit with the tubular body 180.

[0153] Similarly, the first set of parts 70 may be assembled to the tubular body 180 by any suitable means as disclosed herein, such as by a frictional fit, welding and / or adhesive. In some embodiments, the tubular body 180 may be replaced with the heat-shrinkable tube 190 described with reference to Fig. 12A and the first set of parts 70 may be assembled to the heat- shrinkable tube by heat-shrinking the tube 190 onto the first set of parts 70.

[0154] The first and / or second set of parts 70, 80 may be made of any suitable material. In some embodiments, the first and / or second set of parts 70, 80 are made of a material suitable for injection molding, such as a thermoplastic or thermosetting material or a metal.

[0155] In other embodiments, first and / or second set of parts 70, 80 may be made of other materials not suitable for injection molding, for example materials which are millable or suitable for 3D printing.

[0156] The sound absorber 600 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 600 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 600 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less.

[0157] Fig. 14 shows a perspective side view of a sound absorber 600A which is identical to that of Fig. 13D, except that the second set of parts 80 comprises a plurality outer segmental portions 180a, 180b, each segmental portion having a partial circumferential extent. The outer segmental portions form, in the assembled condition, an outer wall surrounding the first set of parts 70 and enclosing each of the one or more open chambers of those parts to form respectively one or more Helmholtz resonators. There may be any number of outer segmental portions and they may be assembled to one another by any suitable means disclosed herein, for example by one or more interconnecting mechanisms, or by adhesive and / or welding.

[0158] It will be appreciated that the alternative embodiments described with reference to Figs. 13A- 13D are also applicable to the sound absorber 600A of Fig. 14.

[0159] Fig. 15 shows a partial cross-sectional side view of a sound absorber having a plurality of critically coupled annular HHRs 14i to 14v. The labelled distances are all in millimetres. Any of the sound absorbers disclosed herein which comprise annular HHRs may, in some embodiments, comprise air passages and associated HHRs having the disclosed dimensions of Fig. 15.

[0160] Fig. 16A shows a schematic perspective side view of a first set of parts 90 for a sound absorber according to one or more embodiments. The first set of parts 90 comprises one or more ventilation duct walls 12 defining a ventilation duct 20, and a plurality of open chambers forming a plurality of incomplete Helmholtz resonators 140a- 1401 located about the one or more ventilation duct walls 12. The plurality of incomplete Helmholtz resonators 140a-1401 extend axially alongside the ventilation duct 20, distributed circumferentially about the ventilation duct 20, and are open at both axial ends 93 a and 93b. The interior of each incomplete Helmholtz resonator 140a- 1401 communicates with the ventilation duct 20 via one or more air passages, which in the illustrated embodiment are axially-extending slits 160a- 1601. The incomplete HHRs 140a- 1401 and ventilation duct 20 may have a fixed cross-sectional shape along their length, allowing them to be formed by extrusion of an extrudable material through a suitably shaped die. Additionally, in the illustrated embodiment, the slits 160a-1601 also have a fixed cross-sectional shape along their length, allowing them to be formed by extrusion with the incomplete HHRs 140a- 1401. However, in other embodiments, the air passages may be formed in the first set of parts 90 subsequent to the extrusion process, for example by removing material from the ventilation duct wall 20 by milling, drilling, by lathe or any other suitable method of removal.

[0161] It will be appreciated that although the first set of parts 90 comprises twelve incomplete HHRs 140, the first set of parts 90 may comprise any number of incomplete HHRs 140, which may be identical in shape and / or resonant frequency to one another or may have different dimensions and / or resonant frequencies to one another, or a mix of identical and non-identical resonators.

[0162] It will further be appreciated that although the respective air passages communicating the ventilation duct 20 to the interior of the respective incomplete chambers 140 are axially- extending slits, in other embodiments the air passages may take any other suitable shape, for example circular holes extending through the ventilation duct wall 12, or oval, rectangular, or any suitable regular or irregular polygonal shape. Where the first set or parts 90 comprises a plurality of air passages, each air passage may take any suitable shape and the respective shapes may be identical or different to one another. In some embodiments, one or more air passages of the part 90 may comprise one or more slits having a circumferential and / or axial extent about the wall 12, as described herein with reference to the other drawings. In any embodiments of the first set of parts 90 comprising at one or more slits, there may be provided one or more slit stiffening elements extending across one or more of the said slits. For example, when the slits are formed by extrusion, the one or more slit stiffening elements can be attached to the wall 12 after the extrusion process.

[0163] It will also be appreciated that for the first set of parts 90, any suitable slit shape disclosed herein, including the embodiments and variants disclosed with reference to Figs. 8A to 8C, may be used.

[0164] The first set of parts 90 may comprise a plurality of parts or a single unitary body. For example, the first set of parts 90 may be a plurality of axially-stacked parts forming the incomplete HHRs 140, wall 12, ventilation duct 20 and air passages. The first set of parts 90 may be made of any suitable material such as a thermoplastic or thermosetting material or a metal. When formed by extrusion, the first set of parts 90 may be formed of any suitable extrudable material such as metals or polymers.

[0165] Fig. 16B shows a schematic view of a second set of parts 95 for a sound absorber according to one or more embodiments. The second set of parts 95 comprise one or more end covers 92 configured to cover the incomplete HHRs 140 at their axial ends in order to form respective HHRs. In the illustrated embodiments, the one or more end covers 92 comprise two annular end covers with an inner hole 92a. When assembled to the first set of parts 90 at each axial end 93 a, 93b, the annular end covers close all of the incomplete HHRs 140 at both axial ends 93 a, 93b so form respective enclosed HHRs. The inner holes 92a align with the ventilation duct 20 to maintain the ventilation duct 20 open.

[0166] It will be appreciated that the shape of the end cover 92 shown in Fig. 16B is exemplary only, and other shapes may be used. For example, individual end caps may be provided for each open end of each incomplete HHR 140. Similarly, a single end cover 92 may be used to close both axial ends 93a and 93b (for example a horseshoe or U-shaped cover). The second set of parts 95 may be manufactured by any suitable method, for example by injection molding. They may be made of any suitable material, such as a thermoplastic or thermosetting material or a metal.

[0167] The first set of parts 90 and the second set of parts 95 may be assembled together by one or more of a frictional fit, welding, one or more interconnecting mechanisms, and / or adhesive.

[0168] When in the assembled condition, the first set of parts 90 and the second set of parts 95 collectively form a sound absorber having one or more HHRs whose interiors communicate with the ventilation duct 20 by one or more air passages.

[0169] As for the other embodiments disclosed herein, it will be appreciated that the sound absorber formed by the first set of parts 90 and the second set of parts 95 may comprise one or more critically coupled HHRs. Preferably all of the HHRs are critically coupled. The sound absorber may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less.

[0170] Fig. 17A shows a schematic top view of a hollow toroidal body 96 extending around a respective inner lumen 97. Fig. 17B shows a schematic top view of the hollow toroidal body 96 shown in Fig. 17A. Fig. 17C shows a cross-sectional side view of the hollow toroidal body taken along line A-A. Fig. 17D shows a cross-sectional top view of the hollow toroidal body 96 taken along the line D-D. The hollow toroidal body 96 defines an interior chamber 98 which extends around the inner lumen 97. In Figs. 17A to 17C, the interior chamber 98 is completely enclosed, that is, the interior chamber 98 is not communicatively connected to the inner lumen 97.

[0171] The hollow toroidal body 96 may be made of any suitable material. The hollow toroidal body 96 may be made of a rotomoldable material (such as rotomoldable polymers) or rotocastable material (such as rotocastable resins), and may be formed by, for example, rotational molding (also referred to herein as rotomolding) or rotational casting (also referred to herein as rotocasting).

[0172] Fig. 18A shows a schematic top view of the hollow toroidal body 96 after material has been removed from the toroidal body to form one or more air passages. Fig. 18B shows a schematic top view of the hollow toroidal body 96 shown in Fig. 18 A. Fig. 18C shows a cross-sectional side view of the hollow toroidal body taken along line A-A. Fig. 18D shows a cross-sectional top view of the hollow toroidal body 96 taken along the line D-D. After the hollow toroidal body 96 is formed as shown in Figs. 17A-17D, material may be removed from the hollow toroidal body 96, for example by milling, drilling, by lathe, or any suitable method of removal, to form one or more air passages (shown in Figs. 18C and 18D as one or more slits 160), thus communicating the interior chamber 98 with the inner lumen 98 to form an HHR 14 extending about the inner lumen 97. As such, the hollow toroidal body 96 acts as a sound absorber for a ventilation system, wherein the inner lumen 97 acts as the ventilation duct.

[0173] Fig. 19 shows a schematic perspective view of a sound absorber comprising a plurality of hollow toroidal bodies 96a-96f which are axially stacked. Each hollow toroidal body 96a-96f comprises an inner lumen as described with reference to Figs. 17A to 18D, which collectively form the ventilation duct 20 of the sound absorber 700. The hollow toroidal bodies 96a-96f have the same features as those described with reference to Figs. 18A to 18D and they are not repeated here for brevity. It will be appreciated that although the sound absorber 700 comprises six hollow toroidal bodies 96 each comprising an HHR, the sound absorber 700 may comprise any number of hollow toroidal bodies 96 (i.e., one or more bodies 96). The HHRs of each toroidal body 96 may be identical in shape and / or resonant frequency to one another or may have different dimensions and / or resonant frequencies to one another, or a mix of identical and non-identical resonators. The bodies 96 may be assembled together by one or more of welding, adhesive, a frictional fit and / or one or more interconnecting mechanisms. The adjacent hollow toroidal bodies may connected by a flash fit or a compressive seal between one or more adjacent surfaces of one or more adjacent hollow toroidal bodies.

[0174] It will further be appreciated that although the respective air passages communicating the ventilation duct 20 to the interior of the respective interior chambers 98 are circumferentially- extending slits 160, in other embodiments the air passages may take any other suitable shape, for example circular holes extending through the ventilation duct wall 12, or oval, rectangular, or any suitable regular or irregular polygonal shape. The air passages may differ in shape and size between the hollow toroidal bodies. Where the sound absorber 700 comprises a plurality of air passages, each air passage may take any suitable shape and the respective shapes may be identical or different to one another. Optionally, one or more air passages sound absorber 700 may comprise one or more slits 160 having a circumferential and / or axial extent about the wall defining the ventilation duct 20, as described herein with reference to the other drawings. In any embodiments of the sound absorber 700 comprising at one or more slits, there may be provided one or more slit stiffening elements 165 extending across one or more of the said slits 160, such as illustrated in Fig. 18C. For example, when the slits are formed by removing material from a hollow toroidal body 96, the one or more slit stiffening elements 165 can be attached to the hollow toroidal body 96 after the removal process. Alternatively, the removal process can leave a part of the material of the hollow toroidal body 96, to form a slit stiffening element 165 which is integral and unitary with the hollow toroidal body material.

[0175] It will also be appreciated that for the toroidal bodies 96, any suitable slit shape disclosed herein, including the embodiments and variants disclosed with reference to Figs. 8A to 8C, may be used.

[0176] It will be appreciated that the shape of the hollow toroidal bodies 96 is exemplary only, and other suitable shapes may be used (for example oval or polygonal).

[0177] As for the other embodiments disclosed herein, it will be appreciated that the sound absorber 700 formed by the toroidal bodies 96 may comprise one or more critically coupled HHRs. Preferably all of the HHRs are critically coupled. The sound absorber 700 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz. In preferred embodiments, the sound absorber 700 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies between 50 Hz and less than 3000 Hz. Preferably, the sound absorber 700 may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies of 250 Hz or less, and more preferably 100 Hz or less.

[0178] Also disclosed herein is a method of manufacturing an assembly of parts for a sound absorber for a ventilation system. The method may be performed to form any of the assembly of parts disclosed herein. The method comprises providing a plurality of parts, each part comprising one or more of: a segmental portion of a perimeter of a ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators. The plurality of parts can from a unassembled condition be put into an assembled condition. In the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and a plurality of Helmholtz resonators extending from the ventilation duct, each of the interiors of the Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls. The method may comprise forming the plurality of parts prior to providing the plurality of parts.

[0179] The step of forming the plurality of parts may comprise forming at least one of the plurality of parts by an injection molding process (where the said parts are made of an injection-moldable material). For example, the parts described with reference to Figs. 5, 6, 7A, 10A-10E, 11, 12A, 12B, 13A-13D, 14, 15, 16A and 16B, and their variants described with reference to those figures, may be formed at least partially by injection molding. It is noted that some features may be separate formed after injection molding (for example the air passages may be formed subsequently by milling or cutting or the slit stiffening element may be added subsequently).

[0180] The step of forming the plurality of parts may comprises forming at least one of the plurality of parts by an extrusion process. For example, the part described with reference to Fig. 16A, and its variants described with reference to that figure, may be formed at least partially by extrusion. It is noted that some features may be separate formed after extrusion (for example the air passages may be formed subsequently by milling or cutting or the slit stiffening element may be added subsequently).

[0181] Similarly, any of the sound absorbers disclosed herein which are comprised of a plurality of parts may be assembled by assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and a plurality of Helmholtz resonators extending from the ventilation duct, each of the interiors of the Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein each part comprises one or more of: a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators.

[0182] For the above method of assembly, the plurality of parts may comprise a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators; and the second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators (for example, any of the embodiments disclosed with reference to Figs. 10A to 15). Additionally, the step of assembling the plurality of parts into the assembled condition may comprise locating the first set of parts within the second set of parts.

[0183] The first set of parts may comprise a plurality of segments having a partial circumferential extent, and each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers (for example any of the embodiments described with reference to Figs. 10A to 15 in which the first set of parts 50 or 70 are a plurality of segments). The step of locating the first set of parts within the second set of parts may comprise locating the plurality of segments within the second set of parts.

[0184] The second set of parts may comprise one or more tubular parts for forming the outer wall (for example any of the embodiments described with reference to Figs. 10A to 15 in which the second set of parts 60 or 80 form a tubular part), and the step of locating the first set of parts within the second set of parts may comprise inserting the first set of parts into the tubular part(s). The step of assembling the plurality of parts into the assembled condition may comprise assembling the first set of parts to the tubular part(s) by one or more of a frictional fit, welding, and / or adhesive.

[0185] In embodiments where the first set of parts is assembled to the tubular part(s) by a frictional fit, the step of assembling the plurality of parts into the assembled condition may comprise pressing one or more flashes or burrs, extending from one or more parts of the first set of parts, against the tubular part(s). Alternatively or additionally, the step of assembling the plurality of parts into the assembled condition may comprise compressing a compressible seal between the first set of parts and the tubular part(s). In any embodiments where the tubular part(s) is made of a heat-shrinkable material (such as the embodiments described with reference to Figs. 12A and 12B), the step of assembling the plurality of parts may comprise: inserting the first set of parts into the tubular part(s) in a preshrink condition; and after inserting the first set of parts into the tubular part(s), applying heat to the tubular part(s) to cause the tubular part(s) to shrink onto the first set of parts to form the outer wall of the sound absorber.

[0186] In some embodiments, the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured to abut respectively against one or more resonator walls of the one or more open chambers to inhibit relative axial movement of the resonator walls and the at least one tubular part, and the inner surface may be tapered (such as the embodiment described with reference to Fig. 11). The one or more stopping elements may comprise one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers. The step of assembling the plurality of parts may comprise inserting the first set of parts into the at least one tubular part until the respective resonator walls abut against the respective stopping elements on the tapered inner surface.

[0187] In some embodiments, the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent (such as the embodiments described with reference to Fig. 14). The step of assembling the plurality of parts may comprise assembling the plurality of segmental portions together to form the outer wall. Assembling the plurality of segmental portions together to form the outer wall may comprise connecting the plurality of segmental portions together by one or more of adhesive, welding, and / or by connecting respective interconnecting mechanisms of respective segmental portions.

[0188] In some embodiments, the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; and the second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators (such as the embodiments described with reference to Figs. 16A and 16B). Assembling the plurality of parts may comprise connecting the one or more end covers to the axial ends of the open chambers to cover the open chambers and form respectively the one or more Helmholtz resonators.

[0189] In any of the embodiments comprises a first set of parts and a second set of parts (such as sets 50 and 60, or 70 and 80 described above), assembling the plurality of parts may comprise connecting the first set of parts to the second set of parts by one or more of a frictional fit, welding, adhesive, and / or by connecting respective interconnecting mechanisms of respective parts in the first and second sets.

[0190] In embodiments where at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprising a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting element configured to connect with the second interconnecting element in the assembled condition (for example the interconnecting mechanisms 205a and 205b), the step of assembling the plurality of parts into the assembled condition may comprise connecting the first and second interconnecting elements of said at least one pair of parts.

[0191] Any of the methods of assembly disclosed herein may further comprise connecting the sound absorber to a ventilation system. The ventilation system may be a ventilation system of an air conditioning unit.

[0192] Similarly, any of the parts disclosed herein comprising one or more slits having one or more slit stiffening elements, may be manufactured by the following method: providing one or more parts, each part comprising a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent, and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator is communicatively connected to at least one air passage; wherein the one or more air passages comprise one or more slits extending at least circumferentially and / or axially about the wall portion; wherein for at least one part,, said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits. The method may comprise forming the plurality of parts prior to providing the plurality of parts.

[0193] The step of forming the part may comprise forming the part by an injection molding process (when said part is made of an injection-moldable material). For example, the parts described with reference to Figs. 5, 6, 7A, 10A-10E, 11, 12A, 12B, 13A-13D, 14, 15, 16A and 16B, and their variants described with reference to those figures, may be formed at least partially by injection molding (in embodiments where said parts comprise a slit with a slit stiffening element). It is noted that some features may be separate formed after injection molding (for example the air passages may be formed subsequently by milling or cutting or the slit stiffening element may be added subsequently).

[0194] The step of forming the plurality of parts may comprises forming at least one of the plurality of parts by an extrusion process. For example, the part described with reference to Fig. 16A, and its variants described with reference to that figure, may be formed at least partially by extrusion (in embodiments where said parts comprise a slit with a slit stiffening element). It is noted that some features may be separate formed after extrusion (for example the air passages may be formed subsequently by milling or cutting or the slit stiffening element may be added subsequently).

[0195] Similarly, any of the sound absorbers disclosed herein, which are formed of a plurality of parts and which comprise one or more slits having one or more slit stiffening elements, may be assembled by the following method: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts, and a plurality of Helmholtz resonators extending from the ventilation duct, each of the interiors of the Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts include a set of parts each comprising: a segmental wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent, and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the segmental wall portion; wherein the segmental wall portion comprises one or more air passages extending through the segmental wall portion such that each at least partially formed Helmholtz resonator is communicatively connected to at least one air passage; wherein the one or more air passages comprise one or more slits extending at least circumferentially about the segmental wall portion; wherein the wall further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

[0196] For the above method of assembly, the plurality of parts may comprise a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators; and the second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators (for example, any of the embodiments disclosed with reference to Figs. 10A to 15). The step of assembling the plurality of parts into the assembled condition may comprise locating the first set of parts within the second set of parts.

[0197] The first set of parts may comprise a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers(for example any of the embodiments described with reference to Figs. 10A to 15 in which the first set of parts 50 or 70 are a plurality of segments). The step of locating the first set of parts within the second set of parts may comprise locating the plurality of segments within the second set of parts.

[0198] The second set of parts may comprise at least one tubular part forming the outer wall (for example any of the embodiments described with reference to Figs. 10A to 15 in which the second set of parts 60 or 80 form a tubular part). The step of locating the first set of parts within the second set of parts may comprise inserting the first set of parts into the at least one tubular part. The step of assembling the plurality of parts into the assembled condition may comprise assembling the first set of parts to the at least one tubular part by one or more of a frictional fit, welding, and / or adhesive.

[0199] In embodiments where the first set of parts is assembled to the at least one tubular part by a frictional fit, the step of assembling the plurality of parts into the assembled condition may comprise pressing one or more flashes or burrs, extending from one or more parts of the first set of parts, against the at least one tubular part. Alternatively or additionally, the step of assembling the plurality of parts into the assembled condition may comprise compressing a compressible seal between the first set of parts and the at least one tubular part.

[0200] In any embodiments where the at least one tubular part is made of a heat-shrinkable material (such as the embodiments described with reference to Figs. 12A and 12B), the step of assembling the plurality of parts may comprise: inserting the first set of parts into the at least one tubular part in a pre-shrink condition; and after inserting the first set of parts into the at least one tubular part, applying heat to the tubular part to cause the at least one tubular part to shrink onto the first set of parts to form the outer wall of the sound absorber.

[0201] In some embodiments, the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured to abut respectively against one or more resonator walls of the one or more open chambers to inhibit relative axial movement of the resonator walls and the at least one tubular part, and the inner surface may be tapered (such as the embodiment described with reference to Fig. 11). The one or more stopping elements may comprise one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers. The step of assembling the plurality of parts may comprise inserting the first set of parts into the at least one tubular part until the respective resonator walls abut against the respective stopping elements on the tapered inner surface. In some embodiments, the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent (such as the embodiments described with reference to Fig. 14). The step of assembling the plurality of parts may comprise assembling the plurality of segmental portions together to form the outer wall. Assembling the plurality of segmental portions together to form the outer wall may comprise connecting the plurality of segmental portions together by one or more of adhesive, welding, and / or by connecting respective interconnecting mechanisms of respective segmental portions.

[0202] In some embodiments, the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; and the second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators (such as the embodiments described with reference to Figs. 16A and 16B). Assembling the plurality of parts may comprise connecting the one or more end covers to the axial ends of the open chambers to cover the open chambers and form respectively the one or more Helmholtz resonators.

[0203] In any of the embodiments comprises a first set of parts and a second set of parts (such as sets 50 and 60, or 70 and 80 described above), assembling the plurality of parts may comprise connecting the first set of parts to the second set of parts by one or more of a frictional fit, welding, adhesive, and / or by connecting respective interconnecting mechanisms of respective parts in the first and second sets.

[0204] In embodiments where at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprising a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting element configured to connect with the second interconnecting element in the assembled condition (for example the interconnecting mechanisms 205a and 205b), the step of assembling the plurality of parts into the assembled condition may comprise connecting the first and second interconnecting elements of said at least one pair of parts.

[0205] A sound absorber such as the sound absorber 700 disclosed with reference to Fig. 19, in embodiments where the air passages comprise one or more slits 160 with one or more slit stiffening elements 165, can be assembled by assembling a plurality of parts together, the plurality of parts comprising the plurality of hollow toroidal bodies 96.

[0206] Assembling the plurality of parts may comprise stacking the plurality of hollow toroidal bodies such that the inner lumens collectively define a ventilation duct. Stacking the plurality of parts may comprise connecting the adjacent hollow toroidal bodies by one or more of welding, adhesive, frictional fit, and / or one or more interconnecting mechanisms. The adjacent hollow toroidal bodies may connected by a flash fit or a compressive seal between one or more adjacent surfaces of one or more adjacent hollow toroidal bodies.

[0207] The method may comprise connecting the sound absorber to a ventilation system. The ventilation system may be a ventilation system of an air conditioning unit.

[0208] A sound absorber comprising one or more toroidal bodies as disclosed with reference to Figs. 18A to 18D may be manufactured according to the following method: providing one or more hollow toroidal bodies each defining an interior chamber, each toroidal body extending around a respective inner lumen; and for each toroidal body, removing material from the toroidal body to form one or more air passages through a surface of the hollow toroidal body, the one or more air passages communicating the interior chamber with the inner lumen to form a Helmholtz resonator communicating with the inner lumen. A plurality of hollow toroidal bodies may be manufactured. The material may be removed by milling, drilling or by use of a lathe. The one or more air passages may comprise one or more slits having a circumferential and / or axial extent about the ventilation duct. The resulting sound absorber may further comprise one or more respective slit stiffening elements extending across the respective one or more slits. In some embodiments, the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall, wherein for at least one slit the ventilation duct wall tapers towards the slit on one or both sides of the slit; and / or at least one slit has a tortuous shape along their length; and / or at least one slit extends in a respective single direction about the ventilation duct; and / or the ventilation duct comprises a chamfered edge on one or both sides of at least one slit; and / or the ventilation duct comprises a filleted edge on one or both sides of at least one slit. The step of providing one or more hollow toroidal bodies may comprise forming the one or more hollow toroidal bodies, for example by rotomolding or rotocasting the one or more hollow bodies.

[0209] The method may further comprise stacking the plurality of hollow toroidal bodies such that the inner lumens collectively form a ventilation duct. The method may also comprise connecting adjacent hollow toroidal bodies by one or more of welding, adhesive, and / or one or more interconnecting mechanisms.

[0210] In some embodiments of the method, at least one, and preferably all, of the Helmholtz resonators are critically coupled.

[0211] The sound absorber manufactured by the method may be configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz, more preferably one or more frequencies in the range of 50 to 3000 Hz, more preferably at least one frequency of 250 Hz or less, and more preferably at least one frequency of 100 Hz or less. wherein the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall having an inner surface, and for at least one slit, the slit is defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface.

[0212] It is noted that although the sound absorbers disclosed herein are made of an assembly of a plurality of parts, it will be appreciated that in the appended claims, unless expressly claimed as a plurality of parts, a sound assembly may be made of a singular unitary body (for example manufactured by 3D printing or any suitable manufacturing technique). Similarly, it will be appreciated that the shape of the sound absorbers illustrated in the drawings are schematic only. For example, where the illustrated embodiments show a tapered sound absorber, in other embodiments the sound absorber may have a non-tapered shape, and vice versa.

[0213] All of the above are fully within the scope of the present disclosure, and are considered to form the basis for alternative embodiments in which one or more combinations of the abovedescribed features are applied, without limitation to the specific combination disclosed above.

[0214] In light of this, there will be many alternatives which implement the teaching of the present disclosure. It is expected that one skilled in the art will be able to modify and adapt the above disclosure to suit its own circumstances and requirements within the scope of the present disclosure, while retaining some or all technical effects of the same, either disclosed or derivable from the above, in light of his common general knowledge in this art. All such equivalents, modifications or adaptations fall within the scope of the present disclosure.

Claims

CLAIMS1. An assembly for a sound absorber for a ventilation system, the assembly comprising a plurality of parts, wherein: the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein in the unassembled condition, the plurality of parts comprises one or more of: a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators.

2. The assembly of claim 1, wherein the assembly is in the assembled condition.

3. The assembly of claim 1, wherein the assembly is in the unassembled condition.

4. The assembly of any previous claim, wherein in the assembled condition at least one, and preferably all, of the Helmholtz resonators are critically coupled.

5. The assembly of claim 4, wherein in the assembled condition the parts form a sound absorber comprising a plurality of Helmholtz resonators, wherein at least two of the Helmholtz resonators of the plurality of critically coupled Helmholtz resonators are displaced from one another in an axial direction of the ventilation duct, and preferably all the Helmholtz resonators of the plurality of critically coupled Helmholtz resonators are displaced from one another in an axial direction of the ventilation duct.

6. The assembly of any preceding claim, wherein the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators; andthe second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators.

7. The assembly of claim 6, wherein the first set of parts comprises a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers.

8. The assembly of claim 6 or 7, wherein the second set of parts comprises at least one tubular part for forming the outer wall.

9. The assembly of claim 8, the assembly in the assembled condition, wherein the first set of parts is assembled to the at least one tubular part by one or more of a frictional fit, welding, and / or adhesive.

10. The assembly of claim 9, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, and for one or more parts of the first set, said part comprises one or more flashes or burrs extending from said part pressed against the at least one tubular part.

11. The assembly of claim 9 or 10, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, the assembly further comprising one or more compressible seals compressed between the first set of parts and the at least one tubular part.

12. The assembly of any of claims 8 to 11, wherein the at least one tubular part is made of a heat-shrinkable material and the first set of parts is assembled to the at least one tubular part by heat-shrinking the at least one tubular part onto the first set of parts.

13. The assembly of any of claims 8 to 11, wherein the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured to abut respectively against one or more resonator walls of the one or more open chambers to inhibit relative axialmovement of the resonator walls and the at least one tubular part, optionally wherein the inner surface is tapered, optionally wherein the one or more stopping elements comprises one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers.

14. The assembly of claim 6 or 7, wherein the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent.

15. The assembly of claim 14, wherein the assembly is in the assembled condition, wherein the second set of parts are assembled together by one or more of adhesive, welding, and / or one or more interconnecting mechanisms.

16. The assembly of any of claims 1 to 5, wherein the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; and the second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators; optionally wherein the first set of parts is a unitary body having a fixed cross-sectional shape along its axial length.

17. The assembly of any of claims 14 to 16, wherein the assembly is in the assembled condition, wherein the first set of parts are assembled to the second set of parts by one or more of a frictional fit, welding, one or more interconnecting mechanisms, and / or adhesive.

18. The assembly of any preceding claim, wherein at least some of the parts are identical in shape.

19. The assembly of any preceding claim, wherein at least some of the parts are made of a material for injection molding.

20. The assembly of any preceding claim, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz, more preferably one or more frequencies in the range of 50 to 3000 Hz.

21. The assembly of claim 20, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 250 Hz or less.

22. The assembly of claim 21, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 100 Hz or less.

23. The assembly of any preceding claim, wherein the one or more air passages comprise one or more slits having a circumferential and / or axial extent about the ventilation duct.

24. The assembly of claim 23, further comprising one or more respective slit stiffening elements extending across the respective one or more slits.

25. The assembly of claim 23 or 24, wherein the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall having an inner surface, and at least one of the one or more slits is defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface.

26. The assembly of any of claims 23 to 25, wherein the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall, wherein for at least one slit, the ventilation duct wall tapers towards the slit on one or both sides of the slit.

27. The assembly of any of claims 23 to 26, wherein at least one slit has a tortuous shape along their length.

28. The assembly of any of claims 23 to 27, wherein at least one slit extends in a single direction about the ventilation duct.

29. The assembly of any of claims 23 to 28, wherein the ventilation duct comprises a chamfered edge on one or both sides of at least one slit.

30. The assembly of any of claims 23 to 29, wherein the ventilation duct comprises a filleted edge on one or both sides of at least one slit.

31. The assembly of any preceding claim, wherein at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprises a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting element configured to connect with the second interconnecting element in the assembled condition.

32. A method of manufacturing an assembly of parts for a sound absorber for a ventilation system, the method comprising: providing a plurality of parts, the plurality of parts comprising one or more of: a segmental portion of a perimeter of a ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators; wherein the plurality of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more of Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls.

33. The method of claim 32, wherein the method comprises forming the plurality of parts prior to providing the plurality of parts.

34. The method of claim 33, wherein for at least one part, the step of forming the part comprises forming the part by an injection molding process.

35. The method of claim 34, wherein the injection molding process forming a first set of parts according to any of claims 6, 7, 10, 16, or 17, and / or injection molding a second set of parts according to any of claims 6, 8, 14, 15, 16 or 17 by an injection molding process.

36. The method of claim 33, wherein for at least one part, the step of forming the part comprises forming the part by an extrusion process.

37. The method of claim 36, wherein the extrusion process includes forming a first set of parts according to claim 16 by an extrusion process.

38. A method of assembling a sound absorber for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more of Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts comprises one or more of: a segmental portion of a perimeter of the ventilation duct, the part having a partial circumferential extent; and / or one or more resonator walls forming respectively one or more incomplete Helmholtz resonators, wherein the one or more resonator walls form in the assembled condition a part of respectively one or more Helmholtz resonators.

39. The method of claim 38, wherein: the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators; and the second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators; and the step of assembling the plurality of parts into the assembled condition comprises locating the first set of parts within the second set of parts.

40. The method of claim 39, wherein: the first set of parts comprises a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers; and the step of locating the first set of parts within the second set of parts comprises locating the plurality of segments within the second set of parts.

41. The method of claim 39 or 40, wherein the second set of parts comprises at least one tubular part for forming the outer wall and the step of locating the first set of parts within the second set of parts comprises inserting the first set of parts into the at least one tubular part.

42. The method of claim 41, wherein the step of assembling the plurality of parts into the assembled condition comprises assembling the first set of parts to the at least one tubular part by one or more of a frictional fit, welding, and / or adhesive.

43. The method of claim 42, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, wherein the step of assembling the plurality of parts into the assembled condition comprises pressing one or more flashes or burrs, extending from one or more parts of the first set of parts, against the at least one tubular part.

44. The assembly of claim 42 or 43, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, wherein the step of assembling the plurality of parts into the assembled condition comprises compressing a compressible seal between the first set of parts and the at least one tubular part.

45. The method of any of claims 41 to 44, wherein the at least one tubular part is made of a heat-shrinkable material and the step of assembling the plurality of parts comprises: inserting the first set of parts into the at least one tubular part in a pre-shrink condition; and after inserting the first set of parts into the at least one tubular part, applying heat to the at least one tubular part to cause the at least one tubular part to shrink onto the first set of parts to form the outer wall of the sound absorber.

46. The method of any of claims 41 to 44, wherein the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured to abut respectively against one or more resonator walls of the one or more open chambers to inhibit relative axial movement of the resonator walls and the at least one tubular part, optionally wherein the inner surface is tapered, optionally wherein the one or more stopping elements comprises one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers; andwherein the step of assembling the plurality of parts comprises inserting the first set of parts into the at least one tubular part until the respective resonator walls abut against the respective stopping elements on the tapered inner surface.

47. The method of claim 41 or 42, wherein the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent, wherein the step of assembling the plurality of parts comprises assembling the plurality of segmental portions together to form the outer wall.

48. The method of claim 47, wherein assembling the plurality of segmental portions together to form the outer wall comprises connecting the plurality of segmental portions together by one or more of adhesive, welding, and / or by connecting respective interconnecting mechanisms of respective segmental portions.

49. The method of claim 38, wherein the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; and the second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators; wherein assembling the plurality of parts comprises connecting the one or more end covers to the axial ends of the open chambers to cover the open chambers and form respectively the one or more Helmholtz resonators.

50. The method of any of claims 47 to 49, wherein assembling the plurality of parts comprises connecting the first set of parts to the second set of parts by one or more of a frictional fit, welding, adhesive, and / or by connecting respective interconnecting mechanisms of respective parts in the first and second sets.

51. The method of any of claims 38 to 50, wherein at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprising a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting elementconfigured to connect with the second interconnecting element in the assembled condition; and wherein the step of assembling the plurality of parts into the assembled condition comprises connecting the first and second interconnecting elements of said at least one pair of parts.

52. The method of any of claims 38 to 51, further comprising connecting the sound absorber to a ventilation system.

53. The method of any of claims 38 to 52, wherein the ventilation system is a ventilation system of an air conditioning unit.

54. An apparatus comprising one or more parts for a sound absorber for a ventilation system, at least one part of the one or more parts comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, the said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

55. The apparatus comprising an assembly of a plurality of parts according to claim 54, wherein the assembly of parts can from an unassembled condition be put into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and a plurality of Helmholtz resonators extending from the ventilation duct, each of the interiors of the Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls.

56. The apparatus of claim 55, wherein the assembly is in the assembled condition.

57. The apparatus of claim 55, wherein the assembly is in the unassembled condition.

58. The apparatus of any of claims 55 to 57, wherein the one or more parts are a first set of parts and the apparatus comprises a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators; and the second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators.

59. The assembly of claim 58, wherein the first set of parts comprises a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers.

60. The apparatus of claim 58 or 59, wherein the second set of parts comprises at least one tubular part for forming the outer wall.

61. The apparatus of claim 60, the assembly in the assembled condition, wherein the first set of parts is assembled to the at least one tubular part by one or more of a frictional fit, welding, and / or adhesive.

62. The apparatus of claim 61, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, and for one or more parts of the first set, said part comprises one or more flashes or burrs extending from said part and pressed against the at least one tubular part.

63. The apparatus of claim 61 or 62, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, the assembly further comprising one or more compressible seals compressed between the first set of parts and the at least one tubular part.

64. The apparatus of any of claims 60 to 63, wherein the at least one tubular part is made of a heat-shrinkable material and the first set of parts is assembled to the at least one tubular part by heat-shrinking the at least one tubular part onto the first set of parts.

65. The apparatus of any of claims 60 to 63, wherein the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured for abutting respectively against one or more resonator walls of the one or more open chambers to inhibit relative axial movement of the resonator walls and the at least one tubular part, optionally wherein the inner surface is tapered, optionally wherein the one or more stopping elements comprises one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers.

66. The apparatus of claim 58 or 59, wherein the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent.

67. The apparatus of claim 66, wherein the assembly is in the assembled condition, wherein the second set of parts are assembled together by one or more of adhesive, welding, and or one or more interconnecting mechanisms.

68. The apparatus of any of claims 55 to 57, wherein the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; and the second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators; optionally wherein the first set of parts is a unitary body having a fixed cross-sectional shape along its axial length.

69. The apparatus of any of claims 66 to 68, wherein the assembly is in the assembled condition, wherein the first set of parts are assembled to the second set of parts by one or more of a frictional fit, welding, one or more interconnecting mechanisms, and / or adhesive.

70. The apparatus of any of claims 54 to 69, wherein at least some of the parts are identical in shape.

71. A sound absorber comprising: a ventilation duct defined by one or more walls; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in the one or more walls; wherein one or more of the one or more air passages comprise one or more slits extending circumferentially and / or axially about the ventilation duct; wherein the wall further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

72. The sound absorber of claim 71, wherein the sound absorber comprises one or more hollow toroidal bodies each defining a Helmholtz resonator, each toroidal body extending around a respective inner lumen, wherein the inner lumens collectively define the ventilation duct.

73. The sound absorber of claim 72, wherein adjacent hollow toroidal bodies are connected by one or more of welding, adhesive, and / or one or more interconnecting mechanisms.

74. The sound absorber of any of claims 71 to 73, wherein the plurality of hollow toroidal bodies are made of a rotomoldable or rotocastable material.

75. The apparatus of any of claims 55 to 70 in the assembled condition, or the sound absorber of any of claims 71 to 74, wherein at least one, and preferably all, of the Helmholtz resonators are critically coupled.

76. The apparatus or sound absorber of claim 75, comprising a plurality of said Helmholtz resonators, wherein at least two of the Helmholtz resonators of the plurality of critically coupled Helmholtz resonators are displaced from one another in an axial direction of the ventilation duct, and preferably all the Helmholtz resonators of the plurality of critically coupled Helmholtz resonators are displaced from one another in an axial direction of the ventilation duct.

77. The apparatus of any of claims 54 to 70 or 75 to 76, wherein at least some of the parts are made of a material for injection molding; orthe sound absorber of any of claims 71 to 76, wherein the sound absorber is made of a material for injection molding.

78. The apparatus of any of claims 54 to 70 or 75 to 77, or the sound absorber of any of claims 43 to 46, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz, more preferably one or more frequencies in the range of 50 to 3000 Hz.

79. The apparatus or sound absorber of claim 78, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 250 Hz or less.

80. The apparatus or sound absorber of claim 79, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 100 Hz or less.

81. The apparatus of any of claims 54 to 70 or 75 to 80, wherein for at least one part, the wall portion has an inner surface and at least one slit in said at least one part is defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface; or the sound absorber of any of claims 71 to 80, wherein the one or more walls collectively define a ventilation duct wall having an inner surface, and at least one slit is defined by opposing surfaces traversing through the ventilation duct wall in a direction perpendicular to the inner surface.

82. The apparatus of any of claims 54 to 70 or 75 to 80, wherein for at least one part, the wall portion tapers towards at least one slit on one or both sides of the at least one slit; or the sound absorber of any of claims 71 to 81, wherein for at least one slit, the respective wall tapers towards the slit on one or both sides of the slit.

83. The apparatus of any of claims 54 to 70 or 75 to 82, or the sound absorber of any of claims 71 to 82, wherein at least one slit has a tortuous shape along their length.

84. The apparatus of any of claims 54 to 70 or 75 to 83, wherein at least one slit extends in a single direction about the wall portion; or the sound absorber of any of claims 71 to 83, wherein at least one slit extends in a single direction about the ventilation duct.

85. The apparatus of any of claims 54 to 70 or 75 to 84, wherein for at least one slit, the wall portion comprises a chamfered edge on one or both sides of the respective at least one slit; or the sound absorber of any of claims 71 to 84, wherein for at least one slit, the respective wall comprises a chamfered edge on one or both sides of the respective at least one slit.

86. The apparatus of any of claims 54 to 70 or 75 to 85, wherein for at least one slit, the wall portion comprises a filleted edge on one or both sides of the respective at least one slit; or the sound absorber of any of claims 71 to 85, wherein for at least one slit, the respective wall comprises a filleted edge on one or both sides of the respective at least one slit.

87. The apparatus of any of claims 54 to 70 or 75 to 86, wherein at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprising a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting element configured to connect with the second interconnecting element in the assembled condition.

88. A method of manufacturing one or more parts for a sound absorber for a ventilation system, the method comprising: providing one or more parts comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, the said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

89. The method of claim 88, wherein the method comprises forming the plurality of parts prior to providing the plurality of parts.

90. The method of claim 89, wherein for at least one part, the step of forming the part comprises forming the part by an injection molding process.

91. The method of claim 90, wherein the injection molding process includes injection molding a first set of parts according to any of claims 58, 59, 62, 68 or 69, and / or injection molding a second set of parts according to any of claims 58, 60, 66, 67, 68 or 69.

92. The method of claim 89, wherein for at least one part, the step of forming the part comprises forming the part by an extrusion process.

93. The method of claim 92, wherein the extrusion process includes forming a first set of parts according to claim 68 by an extrusion process.

94. A method of assembling a sound absorber for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts include a set of parts each comprising: a wall portion of a perimeter for a ventilation duct, the part having a partial or complete circumferential extent; and one or more resonator walls at least partially forming respectively one or more Helmholtz resonators extending from the wall portion; wherein the wall portion comprises one or more air passages extending through the wall portion such that each at least partially formed Helmholtz resonator communicates with at least one air passage; wherein the one or more air passages comprise one or more slits extending circumferentially and / or axially about the wall portion; wherein for at least one part, said part further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

95. The method of claim 94, wherein: the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, andone or more open chambers forming respectively one or more incomplete Helmholtz resonators; and the second set of parts forming, in the assembled condition, an outer wall surrounding the first set of parts and enclosing each of the one or more open chambers to form respectively one or more Helmholtz resonators; and the step of assembling the plurality of parts into the assembled condition comprises locating the first set of parts within the second set of parts.

96. The method of claim 95, wherein: the first set of parts comprises a plurality of segments having a partial circumferential extent, each segment in the unassembled condition comprising: a segmental portion of a perimeter of the ventilation duct, one or more open chambers forming respectively one or more incomplete Helmholtz resonators, and one or more air passages extending through the segmental portion respectively to the one or more open chambers; and the step of locating the first set of parts within the second set of parts comprises locating the plurality of segments within the second set of parts.

97. The method of claim 95 or 96, wherein the second set of parts comprises at least one tubular part for forming the outer wall and the step of locating the first set of parts within the second set of parts comprises inserting the first set of parts into the at least one tubular part.

98. The method of claim 97, wherein the step of assembling the plurality of parts into the assembled condition comprises assembling the first set of parts to the at least one tubular part by one or more of a frictional fit, welding, and / or adhesive.

99. The method of claim 98, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, wherein the step of assembling the plurality of parts into the assembled condition comprises pressing one or more flashes or burrs, extending from one or more parts of the first set of parts, against the at least one tubular part.

100. The method of claim 98 or 99, wherein the first set of parts is assembled to the at least one tubular part by a frictional fit, wherein the step of assembling the plurality of parts into the assembled condition comprises compressing a compressible seal between the first set of parts and the at least one tubular part.

101. The method of any of claims 97 to 100, wherein the at least one tubular part is made of a heat-shrinkable material and the step of assembling the plurality of parts comprises: inserting the first set of parts into the at least one tubular part in a pre-shrink condition; and after inserting the first set of parts into the at least one tubular part, applying heat to the at least one tubular part to cause the at least one tubular part to shrink onto the first set of parts to form the outer wall of the sound absorber.

102. The method of any of claims 97 to 100, wherein the at least one tubular part comprises an inner surface comprising one or more stopping elements, wherein in the assembled condition, the one or more stopping elements are configured to abut respectively against one or more resonator walls of the one or more open chambers to inhibit relative axial movement of the resonator walls and the at least one tubular part, optionally wherein the inner surface is tapered, optionally wherein the one or more stopping elements comprises one or more shoulders respectively matching with a respective resonator wall, wherein in the assembled condition the abutment of the respective shoulders and the matching resonator walls seals a portion of one or more of the open chambers; and wherein the step of assembling the plurality of parts comprises inserting the first set of parts into the at least one tubular part until the respective resonator walls abut against the respective stopping elements on the tapered inner surface103. The method of claim 95 or 96, wherein the second set of parts comprises a plurality of outer segmental portions, each segmental portion having a partial circumferential extent, wherein the step of assembling the plurality of parts comprises assembling the plurality of segmental portions together to form the outer wall.

104. The method of claim 103, wherein assembling the plurality of segmental portions together to form the outer wall comprises connecting the plurality of segmental portions together by one or more of adhesive, welding, and / or by connecting respective interconnecting mechanisms of respective segmental portions.

105. The method of claim 95, wherein the plurality of parts comprises a first set of parts and a second set of parts; the first set of parts forming, in the assembled condition, the one or more walls of the ventilation duct, the one or more air passages in respectively the one or more walls, and one or more open chambers forming respectively one or more incomplete Helmholtz resonators, wherein the one or more open chambers are open at their axial ends; andthe second set of parts forming, in the assembled condition, one or more end covers covering the open chambers at their axial ends to form respectively one or more Helmholtz resonators; wherein assembling the plurality of parts comprises connecting the one or more end covers to the axial ends of the open chambers to cover the open chambers and form respectively the one or more Helmholtz resonators106. The method of any of claims 103 to 105, wherein assembling the plurality of parts comprises connecting the first set of parts to the second set of parts by one or more of a frictional fit, welding, adhesive, and / or by connecting respective interconnecting mechanisms of respective parts in the first and second sets.

107. The method of any of claims 94 to 106, wherein at least one pair of parts are configured to be assembled together by an interconnecting mechanism, the interconnecting mechanism comprising a first interconnecting element on a first part of the pair, and second interconnecting element on the second part of the pair, the first interconnecting element configured to connect with the second interconnecting element in the assembled condition; and wherein the step of assembling the plurality of parts into the assembled condition comprises connecting the first and second interconnecting elements of said at least one pair of parts.

108. A method of assembling a sound absorber, for a ventilation system, the method comprising: assembling a plurality of parts into an assembled condition, wherein in the assembled condition the parts form a sound absorber comprising: a ventilation duct defined by one or more walls of respectively one or more of the parts; and one or more Helmholtz resonators extending from the ventilation duct, each of the interiors of the one or more Helmholtz resonators communicating with the ventilation duct via one or more air passages in respectively the one or more walls; wherein the plurality of parts comprise a plurality of hollow toroidal bodies each defining a Helmholtz resonator, each toroidal body extending around a respective inner lumen, wherein the one or more inner lumens collectively define the ventilation duct; and wherein one or more of the one or more air passages comprise one or more slits extending circumferentially and / or axially about the ventilation duct;wherein the wall further comprises one or more respective slit stiffening elements extending across the respective one or more slits.

109. The method of claim 108, wherein assembling the plurality of parts comprises stacking the plurality of hollow toroidal bodies such that the inner lumens collectively define a ventilation duct.

110. The method of claim 109, wherein stacking the plurality of parts comprises connecting the adjacent hollow toroidal bodies by one or more of welding, adhesive, a frictional fit and / or one or more interconnecting mechanisms; optionally wherein the adjacent hollow toroidal bodies are connected by a flash fit or a compressive seal between one or more adjacent surfaces of one or more adjacent hollow toroidal bodies.11 l.The method of any of claims 94 to 110, further comprising connecting the sound absorber to a ventilation system.

112. The method of claim 111, wherein the ventilation system is a ventilation system of an air conditioning unit.

113. A method of manufacturing a sound absorber for a ventilation system, comprising: providing one or more hollow toroidal bodies each defining an interior chamber, each toroidal body extending around a respective inner lumen; and for each toroidal body, removing material from the toroidal body to form one or more air passages through a surface of the hollow toroidal body, the one or more air passages communicating the interior chamber with the inner lumen to form a Helmholtz resonator communicating with the inner lumen.

114. The method of claim 113, wherein the step providing one or more hollow toroidal bodies comprises forming the one or more hollow toroidal bodies, optionally by rotomolding or rotocasting the one or more hollow toroidal bodies.

115. The method of claim 113 or 114, further comprising removing the material by drilling, milling or a lathe.

116. The method of any of claims 113 to 115, wherein a plurality of hollow toroidal bodies are manufactured.

117. The method of claim 116, further comprising stacking the plurality of hollow toroidal bodies such that the inner lumens collectively form a ventilation duct.

118. The method of any of claims 116 or 117, further comprising connecting adjacent hollow toroidal bodies by one or more of welding, adhesive, a frictional fit, and / or one or more interconnecting mechanisms; optionally wherein the adjacent hollow toroidal bodies are connected by a flash fit or a compressive seal between one or more adjacent surfaces of one or more adjacent hollow toroidal bodies.

119. The method of any of claims 113 to 118, wherein at least one, and preferably all, of the Helmholtz resonators are critically coupled.

120. The method of any of claims 113 to 119, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for one or more frequencies less than 3000 Hz, more preferably one or more frequencies in the range of 50 to 3000 Hz.

121. The method of claim 120, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 250 Hz or less.

122. The method of claim 121, wherein the sound absorber is configured to attenuate sound emitted through the ventilation duct for at least one frequency of 100 Hz or less.

123. The method of any of claims 113 to 122, wherein the one or more air passages comprise one or more slits having a circumferential and / or axial extent about the ventilation duct.

124. The method of claim 123, further comprising one or more respective slit stiffening elements extending across the respective one or more slits.

125. The method of any of claims 123 or 124, wherein the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall having an inner surface, and for at least one slit, the slit is defined by opposing edges, wherein one or both of the opposing edges comprises a surface traversing through the ventilation duct wall in a direction perpendicular to the inner surface.

126. The method of any of claims 123 to 125, wherein the one or more walls of respectively one or more of the parts collectively define a ventilation duct wall, wherein for at least one slit the ventilation duct wall tapers towards the slit on one or both sides of the slit.

127. The method of any of claims 123 to 126, wherein at least one slit has a tortuous shape along their length.

128. The method of any of claims 123 to 127, wherein at least one slit extends in a respective single direction about the ventilation duct.

129. The method of any of claims 123 to 128, wherein the ventilation duct comprises a chamfered edge on one or both sides of at least one slit.

130. The method of any of claims 123 to 129, wherein the ventilation duct comprises a filleted edge on one or both sides of at least one slit.

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