Device with helmholtz resonator

Abstract

A device, such as a fan, an air conditioner, a space heater, an air cleaning or filtering device or an air freshener, includes an airflow generator and an elongated plenum configured to receive an airflow generated by the airflow generator. The apparatus includes a gas chamber having an outlet extending along at least a portion of the gas chamber such that a gas flow through the gas chamber flows out of the outlet, the apparatus including at least one Helmholtz resonator having an inlet port in fluid communication with the gas chamber at a location on the other side of the outlet relative to the gas flow generator and a cavity. The air chamber and the Helmholtz resonator are arranged and configured to reduce noise generated by the device near at least one frequency.

Description

BACKGROUND

[0001] Devices for moving air are known. For example, fans can be used to move air for the purposes of creating an air flow, air filtration, heating, cooling, etc. SUMMARY

[0002] According to the present invention, there is provided a device comprising:

[0003] an air flow generator;

[0004] an air chamber configured to receive an air flow generated by the air flow generator, the air chamber being elongate;

[0005] an outlet extending along at least a portion of the air chamber such that air flow passing through the air chamber exits the outlet; and

[0006] at least one Helmholtz resonator having an inlet port and a cavity, the inlet port being in fluid communication with the air chamber at a location on the other side of the outlet relative to the air flow generator;

[0007] the air chamber and Helmholtz resonator are arranged and configured to reduce noise generated by the device around at least one frequency.

[0008] By arranging the inlet port of the Helmholtz resonator on the other side of the outlet relative to the air flow generator, the effect of the air flow on the operation of the Helmholtz resonator can be reduced, and conversely, the effect of the Helmholtz resonator on the air flow can be reduced.

[0009] The device can comprise a plurality of Helmholtz resonators, each tuned to a different frequency.

[0010] The Helmholtz resonators tuned to different frequencies can provide the ability to reduce noise at corresponding frequencies.

[0011] The device can comprise a coupling region arranged between the air chamber and the inlet port of the Helmholtz resonator, the coupling region being configured to improve impedance matching between the air chamber and the Helmholtz resonator.

[0012] The improved impedance matching improves the operational efficiency of the Helmholtz resonator.

[0013] The coupling region can comprise a coupling volume for the or each Helmholtz resonator, each coupling volume being provided adjacent to the inlet port of its corresponding Helmholtz resonator.

[0014] The use of a coupling volume for each inlet port can allow for impedance matching of each Helmholtz resonator.

[0015] The inlet port of a Helmholtz resonator can be configured to face the wall of the gas chamber, and the connection volume of each Helmholtz resonator is defined between the inlet port of the Helmholtz resonator and a portion of the wall.

[0016] This arrangement can provide a compact and / or convenient manufacturing of Helmholtz resonators and connection volumes.

[0017] The cavity of a Helmholtz resonator can be cylindrical or prismatic, and / or can have a constant cross-section along at least one axis.

[0018] This arrangement can provide a compact and / or convenient way to manufacture Helmholtz resonators.

[0019] The cavities of a Helmholtz resonator can have different relative volumes, but they share a common linear dimension along at least one axis.

[0020] This arrangement can provide a compact and / or convenient way to manufacture Helmholtz resonators.

[0021] The cavity and / or inlet port of a Helmholtz resonator can be spaced apart in a direction away from the gas chamber.

[0022] This allows for a relatively compact layout and also simplifies modeling and / or design.

[0023] The volume of a Helmholtz cavity can decrease monotonically with the distance of its corresponding inlet port from the gas chamber.

[0024] The inlet port can be fluidly connected to the air chamber at a point where the airflow is essentially zero without a resonator.

[0025] This can reduce the impact of moving air on the operation of the Helmholtz resonator, and also allow the Helmholtz resonator to be positioned to minimize its influence on the airflow.

[0026] The device may include at least two gas chambers, each having at least one Helmholtz resonator.

[0027] The at least two air chambers can be supplied with airflow from a common airflow generator.

[0028] The device may take the form of one or more of the following: fan, air conditioner, space heater, air cleaner or filter, or air purifier. Attached Figure Description

[0029] Figure 1 It is the vertical cross-section passing through the fan-shaped device;

[0030] Figure 2 yes Figure 1 Front view of the fan;

[0031] Figure 3 yes Figure 1 A perspective view of the fan;

[0032] Figure 4 It is a vertical cross-section passing through the upper region of another fan;

[0033] Figure 5 It is a vertical section through the operation of another fan;

[0034] Figure 6 It is the vertical cross-section passing through the Helmholtz resonator array;

[0035] Figure 7 It includes two Figure 6 A perspective view of another fan in the array;

[0036] Figure 8 yes Figure 7 Front view of the fan;

[0037] Figure 9 yes Figure 7 and 8 Side view of the fan;

[0038] Figure 10 Is it through Figure 9 A cross-sectional view of line XX;

[0039] Figure 11 It shows the target Figures 7 to 10 A graph showing the modeled sound pressure level of a fan chamber with and without a Helmholtz resonator, relating to acoustic resonances; and

[0040] Figure 12 It is shown that... Figures 7 to 10 A graph showing the total sound output of a fan chamber and the sound pressure level associated with it. Detailed Implementation

[0041] refer to Figures 1 to 3 This illustrates a device for moving air within a room. Figures 1 to 3 In one embodiment, the device takes the form of a fan 100, which, for example, can be used to move air within a room to cool the occupants of the room.

[0042] The fan 100 includes a housing 102, which includes a base 104 supporting the housing 102 on a surface such as a table or floor (not shown). The base 104 includes a compartment 106, within which an airflow generator 108 is disposed. The airflow generator 108 includes, for example, a motor, an impeller driven by the motor, and control circuitry for driving the motor in response to user input via a user interface. The various components of the airflow generator 108 and the user interface, etc., are known and therefore will not be described in detail.

[0043] The housing 102 defines a plenum 110 extending upward from the compartment 106. The plenum 110 is elongated in a generally vertical direction. An outlet 112 in the form of an elongated slot extends along the front surface of the plenum 110.

[0044] The housing 102 defines a Helmholtz resonator 114 having an inlet port 116 in fluid communication with a gas chamber 110 and a cavity 118 in fluid communication with the inlet port 116. The inlet port 116 is in fluid communication with the gas chamber 110 at a location opposite the outlet 112 relative to the airflow generator 108.

[0045] Throughout this specification, terms such as "the other side of the outlet" will be interpreted according to the understanding of those skilled in the art. One such definition is that the distance from the airflow generator to the inlet port of the Helmholtz resonator (or the starting point of the connection region, as described below) is greater than or equal to the distance from the airflow generator to the furthest point from the outlet. For example, such a distance can be measured along the airflow path. Figures 1 to 3 In one embodiment, the inlet port 116 is in fluid communication with the gas chamber 110 at a position above the upper end 120 of the outlet 112.

[0046] In use, the airflow generator 108 generates an airflow by drawing air into compartment 106, as indicated by arrow 122, optionally passing it through one or more filters (not shown), and then driving the air into the lower region 124 of air chamber 110, as indicated by arrow 126. The increased air pressure within air chamber 110 causes the air to exit outlet 112 along its length, as indicated by arrow 128. As the air exits outlet 112, the movement of the air entrains ambient air, multiplying the mass of air moved by fan 100, thereby providing a breeze in the area in front of fan 100.

[0047] The operation of a fan (such as fan 100) can generate several different types of noise. These include, for example, mechanical noise from the airflow generator 108, airflow noise as air is drawn into compartment 106, airflow noise as air leaves outlet 112, and various resonances within the path taken by the air through the fan. For user comfort, noise reduction is generally desirable. The many different noise sources and their varying characteristics mean that a wide range of frequencies can generate noise.

[0048] The air chamber 110 and the Helmholtz resonator 114 are arranged and configured to reduce the noise generated by the fan 100 near at least one frequency.

[0049] Typically, a Helmholtz resonator consists of a cavity of a specific volume and an inlet port through which air can pass. An increase in air pressure at the inlet port causes some air to enter the cavity through the inlet port, resulting in an increase in pressure within the cavity. A subsequent decrease in air pressure at the inlet port allows some air to exit the cavity through the inlet port. The air moving into and out of the enclosed cavity through the inlet port causes resonance, the frequency of which is based on the cavity volume. The length and cross-sectional area of ​​the inlet port can also be chosen to achieve specific resonant frequencies and Q factors.

[0050] Back Figures 1 to 3 Placing the inlet 116 of the Helmholtz resonator 114 on the opposite side of the outlet 112 relative to the airflow generator 108 means that the inlet 116 is positioned relative to still or static air, at least from the perspective of airflow. This is because all the air entering the air chamber 110 exits the outlet 112. The only air movement experienced at the inlet 116 will be the tiny eddies caused by the non-laminar airflow within the air chamber 110, as well as sound waves including undesirable noise caused by air chamber resonance. This arrangement allows for the reduction or avoidance of the effects of continuous airflow (unlike pressure changes caused by sound waves) on the Helmholtz resonator.

[0051] Technicians will understand that any required number of Helmholtz resonators can be supplied. For example, Figure 4 The upper end of an alternative embodiment of fan 500 is shown. Fan 500 shares several features with fan 100, and these features are indicated by the same reference numerals in both embodiments.

[0052] The fan 500 includes a first Helmholtz resonator 136 having a first inlet port 138 in fluid communication with the air chamber 110 and a first cavity 140 in fluid communication with the first inlet port 138. The fan 500 also includes a second Helmholtz resonator 142 having a second inlet port 144 in fluid communication with the air chamber 110 and a second cavity 146 in fluid communication with the second inlet port 144. The first inlet 138 and the second inlet 144 are each in fluid communication with the air chamber 110 at a location opposite to the outlet 112 relative to the airflow generator 108. Specifically, in this embodiment, both the first inlet port 138 and the second inlet port 144 are in fluid communication with the air chamber 110 at a location above the upper end 120 of the outlet 112.

[0053] Figure 5 The upper end of an alternative embodiment of fan 600 is shown. Fan 600 shares several features with fans 100 and 500, and these features are indicated by the same reference numerals in all three embodiments.

[0054] Fan 600 includes a connection region 130 (defined by dashed lines) disposed between air chamber 110 and inlet port 116. Connection region 130 includes a connection volume 132 for Helmholtz resonator 114, the connection volume 132 being disposed adjacent to inlet port 116. In fan 600, inlet port 116 of Helmholtz resonator 114 is configured opposite wall 134 of air chamber 110. Figure 4 In this embodiment, wall 134 forms part of housing 102. Connection volume 132 is defined between the inlet port 116 of Helmholtz resonator 114 and part of wall 134.

[0055] Connection region 130 is configured to improve impedance matching between chamber 110 and Helmholtz resonator 114. The configuration of connection region 130 typically includes its volume. While impedance matching between the Helmholtz resonator and chamber can be achieved in some cases by directly connecting the Helmholtz resonator and chamber, this can be challenging, especially when the cross-sectional area of ​​the inlet port is small compared to the cross-sectional area of ​​the chamber. The use of connection region allows for a transition from the cross-sectional area of ​​the chamber to the cross-sectional area of ​​the inlet port, which facilitates impedance matching.

[0056] Impedance matching can be achieved by utilizing an open Helmholtz resonator. A resonator is considered "open" when it is connected to another system (such as the air chamber described herein) and acoustic energy in both systems can interact across the interface between them (which, when used, includes the junction region). Therefore, acoustic energy can enter the resonator without using any mechanism to trap energy into it, but it can also leave the resonator through the interface.

[0057] The amount of energy entering and leaving a resonator is generally referred to as energy leakage. The resonator's loss characteristics arise from the friction between the air and the resonator's inner walls. This friction is primarily driven by the viscosity of the air and converts acoustic energy into heat. The amount of energy converted is also known as the resonator's inherent losses.

[0058] Impedance matching involves configuring the components of a system such that the losses within a resonator equal the energy leakage. In this case, impedance matching is also known as the critical connection condition. This occurs at the resonant frequency of the resonator and results in perfect absorption of wave energy by the resonator at that specific frequency.

[0059] Perfect absorption at broadband frequencies can also be achieved by using a set of resonators critically connected at different frequencies. It should be understood that "complete absorption" in this paper does not mean that energy is completely dissipated by the absorber, but rather that energy is completely captured within the absorber. The dissipation mechanism is part of the capture effect, but does not constitute the primary phenomenon observed.

[0060] Figure 6 An array of Helmholtz resonators 700 is shown, which can be attached to a device (such as any device described herein) or form part of a device. The array 700 shares several features with fans 100, 500 and 600, and these features are indicated by the same reference numerals in all four embodiments.

[0061] Array 700 comprises ten Helmholtz resonators 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168. Each Helmholtz resonator includes cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, and 188, and entrance ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208. Each Helmholtz resonator 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168 is tuned to different frequencies. As mentioned above, the resonant frequency of a Helmholtz resonator is related to the volume of its cavity and the length and cross-sectional area of ​​its entrance ports.

[0062] The cavities of Helmholtz resonators 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168 are rectangular prisms, but the cavities can be defined by any suitable three-dimensional volume. The use of rectangular prisms helps simplify the design and / or fabrication of Helmholtz resonators 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168. For example, the walls of all Helmholtz resonators can be extruded in a single process, requiring only the formation of the inlet ports 176, 178, 180, 182, 184, 186, 188, 190, 192, and 194 and end walls (not shown) to close them.

[0063] Cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, and 188 have different relative volumes, but are given the same depth (e.g., perpendicular to...). Figure 6 (The page measurements are taken within the same unit) and they share a common linear dimension.

[0064] Alternatively, other types of prisms, cylinders, or other volumes can be used in the cavity design.

[0065] Connection areas 210, 212, 214, 216, 218, 220, 222, 224, 226, and 228 (defined by dashed lines) are located between air chamber 110 and inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208. The connection regions 210, 212, 214, 216, 218, 220, 222, 224, 226, and 228 include corresponding connection volumes for their respective Helmholtz resonators 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168, with each connection volume adjacent to the entry ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208 of its respective Helmholtz resonator 150, 152, 154, 156, 158, 160, 162, 164, 166, and 168.

[0066] In array 700, inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208 are positioned opposite to the wall 134 of air chamber 110. Figure 6 In one embodiment, wall 134 forms part of housing 102. The connection volume is defined between inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, 208 and part of wall 134.

[0067] In array 700, cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, 188 and inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, 208 are spaced apart from each other in a direction away from gas chamber 110. That is, Helmholtz resonators 150, 152, 154, 156, 158, 160, 162, 164, 166, 168 are arranged in a linear array.

[0068] Furthermore, the corresponding volumes of cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, and 188 decrease monotonically with the distances of their respective inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208 from the gas chamber 110. This arrangement simplifies design and / or modeling, especially when a large number of resonators are to be used. For example, if the intention is to attenuate from F... min To F max The frequency range can be found in F. min Tune a resonator cavity at F, and can be done at F max Tune another resonator cavity. The volume of the other cavity must be within the calculated F. min and F max Between the volumes of the two cavities. By calculating F min and F max Monotonically adjusting the volumes of other resonant cavities between F will cause the attenuation to cover the range from F min To F max The frequency. Furthermore, the geometry of the resonator can be improved or optimized using numerical optimization procedures. Making the cavity depth decrease as they move away from the gas chamber makes this optimization easier to plan.

[0069] Examples of the dimensions and volumes of cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, 188, inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, 208, and connecting regions 210, 212, 214, 216, 218, 220, 222, 224, 226, 228 will now be described. It should be understood that these values ​​are merely exemplary. All values ​​are based on the dimensions of the rectangular prism.

[0070] The dimensions and volumes of cavities 170, 172, 174, 176, 178, 180, 182, 184, 186, and 188 are as follows (note that the length of each cavity is the dimension extending away from the inlet, and widths 1 and 2 are orthogonal to each other and to the length dimension):

[0071] Cavity Volume (m 3 ) Width 1 Length Width 2 170 4.4265E-05 0.0185 0.0337 0.071 172 2.1570E-05 0.014 0.0217 0.071 174 1.2013E-05 0.009 0.0188 0.071 176 1.2177E-05 0.005 0.0343 0.071 178 7.5970E-06 0.005 0.0214 0.071 180 5.7936E-06 0.004 0.0204 0.071 182 4.4588E-06 0.004 0.0157 0.071 184 3.4364E-06 0.004 0.0121 0.071 186 2.6128E-06 0.004 0.0092 0.071 188 2.0448E-06 0.003 0.0096 0.071

[0072] The dimensions and volumes of inlet ports 190, 192, 194, 196, 198, 200, 202, 204, 206, and 208 are as follows (note that the length of each inlet port is parallel to the length dimension of its corresponding cavity, and width 1 and width 2 are orthogonal to each other and to the length dimension):

[0073] Inlet port Volume (m 3 ) Width 1 Length Width 2 190 4.860E-09 0.0018 0.0015 0.0018 192 3.375E-09 0.0015 0.0015 0.0015 194 3.375E-09 0.0015 0.0015 0.0015 196 4.950E-09 0.0015 0.0022 0.0015 198 4.500E-09 0.0015 0.002 0.0015 200 4.500E-09 0.0015 0.002 0.0015 202 4.500E-09 0.0015 0.002 0.0015 204 4.725E-09 0.0015 0.0021 0.0015 206 5.175E-09 0.0015 0.0023 0.0015 208 5.400E-09 0.0015 0.0024 0.0015

[0074] The dimensions and volumes of connection regions 210, 212, 214, 216, 218, 220, 222, 224, 226, and 228 are as follows (note that the length of each connection region is a dimension parallel to the length dimension of its corresponding cavity and inlet port, and width 1 and width 2 are orthogonal to each other and to the length dimension):

[0075] Coupling region Volume (m 3 ) Width 1 Length Width 2 210 1.9596E-05 0.0138 0.071 0.02 212 2.7477E-05 0.0258 0.071 0.015 214 2.0448E-05 0.0288 0.071 0.01 216 5.2824E-06 0.0124 0.071 0.006 218 1.0906E-05 0.0256 0.071 0.006 220 9.4430E-06 0.0266 0.071 0.005 222 1.1076E-05 0.0312 0.071 0.005 224 1.2354E-05 0.0348 0.071 0.005 226 1.3348E-05 0.0376 0.071 0.005 228 1.0508E-05 0.037 0.071 0.004

[0076] Go to Figures 7 to 10 An alternative embodiment in the form of fan 800 is shown. Fan 800 shares several features with fans 100, 500 and 600 and array 700, and these features are indicated by the same reference numerals in all embodiments.

[0077] The fan 800 includes a first air chamber 230 and a second air chamber 232. The two air chambers 230 and 232 are elongated in a generally vertical direction. A first array 234 of Helmholtz resonators is disposed at the upper end of the first air chamber 230, and a second array 236 of Helmholtz resonators is disposed at the upper end of the second air chamber 230. The first array 234 and the second array 236 are each internally configured similarly to array 700, and therefore will not be described separately.

[0078] In use, the airflow generator 108 generates an airflow by drawing air into compartment 106, as indicated by arrow 122, optionally through one or more filters (not shown), and then driving the air into a common area 238 at the entrances of the first air chamber 230 and the second air chamber 232. The air is split as indicated by arrow 240, with approximately half of the air entering each of the first air chamber 230 and the second air chamber 232.

[0079] The air pressure increases within the first chamber 230 and the second chamber 232, causing air to exit from outlet 112 along its length, as indicated by arrow 128. The movement of the air as it exits outlet 112 provides the breeze with respect to fan 100 as described above.

[0080] The first air chamber 230 and the second air chamber 232, along with the corresponding first array 234 and second array 236, are arranged and configured to reduce noise generated by the fan 100 near certain frequencies.

[0081] Go to Figure 11 The graphs illustrate the acoustic gain resulting from the air chambers of fan 800 with and without resonator arrays (for simplicity, only half are modeled). The first line 242 shows the acoustic output without any Helmholtz resonators, and the second line 244 shows the acoustic output with... Figures 7 to 11 The attached arrays 234 and 700 are shown for acoustic output.

[0082] The peaks of 246, 248, 250, and 252 at approximately 200 Hz, 486 Hz, 950 Hz, and 1400 Hz represent resonances within the air chamber due to reflections and the physical internal dimensions of the chamber. The 486 Hz and 950 Hz resonances are of particular interest because they fall within a relatively sensitive portion of the audible spectrum. While sound-absorbing materials can be used for sound absorption, such materials tend to be less effective at lower frequencies, such as 486 Hz and 950 Hz.

[0083] The second line, 244, illustrates the effects of arrays 234 and 700. The resonance at 486 Hz is essentially eliminated. The overall gain between approximately 400 Hz and 900 Hz is significantly flatter, which can be perceived as lower noise. The 950 Hz peak shifts upwards to approximately 1050 Hz and its amplitude is significantly reduced.

[0084] The first peak at 200 Hz remains largely unchanged, but it has not yet been corrected because this frequency is outside the most sensitive part of the audible spectrum and would require a relatively large resonator.

[0085] Go to Figure 12 The graph shows the self-noise (also known as flow-induced noise) generated by air chambers with and without resonators (line 260) for a flow rate of 50 L / s. This indicates that the airflow is not significantly affected by the Helmholtz resonators because they do not generate additional flow-induced noise in the air chambers. Furthermore, the use of resonators, particularly in the 300–700 Hz region, reduces flow-induced noise overall.

[0086] Typically, placing the inlet ports of Helmholtz resonators in fluid communication with the gas chamber at a point where airflow would be essentially zero without the resonator can improve the overall system performance. This is especially true when this point is also a region of high acoustic reflection, for example, due to its proximity to the relatively rigid end walls of the gas chamber. This acoustic reflection generates acoustic resonance within the gas chamber, amplifying the acoustic sound emitted from the outlet slot. By placing the inlet ports at or near this region and matching their impedance to that of the gas chamber, reflections are reduced or eliminated, which in turn reduces or eliminates resonance, and thus reduces or eliminates the acoustic sound emitted from the outlet slot. For example, this reduction or elimination would be different if the resonator inlets were positioned adjacent to or opposite the outlet slot.

[0087] Optionally, at least a portion of the interior of any Helmholtz resonator may be filled with a sound-absorbing material, such as acoustic foam. This can alter the resonant characteristics of the Helmholtz resonator and further contribute to energy absorption. Similarly, at least some of the inner surfaces of any Helmholtz resonator may be covered with a sound-absorbing material.

[0088] Although all described embodiments use a single airflow generator, it should be understood that more than one airflow generator may be used. For example, in the case of using two or more air chambers, each air chamber may optionally have its own airflow generator.

[0089] The device can be manufactured in any suitable manner. For example, it can be assembled from parts manufactured by molding, machining, additive manufacturing, extrusion, or other methods. Any suitable material can be used, such as polymers, metals, ceramics, composite materials, or any combination thereof.

[0090] While various fans have been described, it should be understood that the present invention can be implemented in other types of air-moving devices. A non-exhaustive list of such devices includes air conditioners, space heaters, air cleaning or filtering devices, and air purifiers. The additional components required for such devices compared to fans are well known to those skilled in the art and will therefore not be described in detail.

[0091] Although various embodiments have been described, those skilled in the art will understand that the invention can be implemented in many other forms.

Claims

1. An apparatus comprising: Airflow generator; An air chamber configured to receive an airflow generated by the airflow generator, the air chamber being elongated; An outlet, which extends along at least a portion of the air chamber, such that airflow passing through the air chamber exits through the outlet; and At least one Helmholtz resonator, the at least one Helmholtz resonator having an inlet port and a cavity, the inlet port being in fluid communication with the gas chamber at a position opposite to the outlet of the airflow generator; The air chamber and Helmholtz resonator are arranged and configured to reduce noise generated by the device near at least one frequency.

2. The apparatus of claim 1, comprising a plurality of the Helmholtz resonators, each of the Helmholtz resonators being tuned to a different frequency.

3. The apparatus of claim 1 or 2, comprising a connection region disposed between the gas chamber and the inlet port of the Helmholtz resonator, the connection region being configured to improve impedance matching between the gas chamber and the Helmholtz resonator.

4. The apparatus according to claim 3, wherein, The connection region includes a connection volume for the Helmholtz resonator or each Helmholtz resonator, each connection volume being configured to be adjacent to the inlet port of its corresponding Helmholtz resonator.

5. The apparatus according to claim 4, wherein, The inlet port of the Helmholtz resonator is disposed opposite to the wall of the gas chamber, and the connection volume for each Helmholtz resonator is defined between the inlet port of the Helmholtz resonator and a portion of the wall.

6. The apparatus according to any one of the preceding claims, wherein, The cavity of the Helmholtz resonator, or each Helmholtz resonator, is cylindrical or prismatic, and / or has a constant cross-section along at least one axis.

7. The apparatus according to claim 2 or any one of claims 3 to 6 when dependent on claim 2, wherein, The cavities of the Helmholtz resonators have different relative volumes, but share a common linear dimension along at least one axis.

8. The apparatus according to claim 2 or any one of claims 3 to 7 when dependent on claim 2, wherein, The cavity and / or the inlet port of the Helmholtz resonator are spaced apart in a direction away from the gas chamber.

9. The apparatus according to claim 2 or any one of claims 3 to 8 dependent on claim 2, wherein, The volume of the Helmholtz cavity decreases monotonically with the distance of the corresponding inlet port of the Helmholtz cavity from the gas chamber.

10. The apparatus according to any one of the preceding claims, wherein, The inlet is in fluid communication with the air chamber at a point where the airflow is zero in the absence of the resonator.

11. The apparatus according to any one of the preceding claims, comprising at least two gas chambers, each of the gas chambers having at least one Helmholtz resonator.

12. The apparatus according to claim 11, wherein, The at least two air chambers are supplied with airflow from a common airflow generator.

13. The apparatus according to any one of the preceding claims, wherein, The device is one or more of a fan, air conditioner, space heater, air cleaning or filtering device, or air purifier.

Images