Sound absorbing device and a method for sound absorption

Abstract

A sound absorbing device functioning as a Helmholtz resonator comprises a cavity, a neck, and a movable structure arranged within the neck, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator to achieve effective sound absorption.

Description

[0001] Sony Group Corporation

[0002] SOUND ABSORBING DEVICE AND A METHOD FOR SOUND

[0003] ABSORPTION

[0004] TECHNICAL FIELD

[0005] The present disclosure generally pertains to the field of acoustic engineering, in particular to a sound absorbing device and a method for sound absorption.

[0006] TECHNICAL BACKGROUND

[0007] Reducing noise is a significant challenge in acoustical engineering, especially when dealing with low-frequency sounds, which have long wavelengths and dissipate more slowly. For example, porous materials used as sound absorbers work well for high frequencies but need to be very thick to effectively absorb low-frequency sounds. Similarly, resonance-based absorbers only work well within a narrow range of frequencies, making them less effective when the noise frequency changes. This is particularly problematic in environments like air-conditioning systems or aircraft, where conditions frequently change. Additionally, addressing sound quality issues in spaces such as auditoriums and listening studios is challenging because it depends on factors like room dimensions, the location of sound sources and receivers, and changes in occupancy.

[0008] Although there exist techniques for sound absorption, it is generally desirable to improve on existing techniques.

[0009] SUMMARY

[0010] According to a first aspect the present disclosure provides a sound absorbing device functioning as a Helmholtz resonator comprising a cavity, a neck, and a movable structure arranged within the neck, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator to achieve effective sound absorption. According to a second aspect the present disclosure provides a method for sound absorption with a sound absorbing device functioning as a Helmholtz resonator, including the step of adjusting the resonance frequency of the Helmholtz resonator to achieve effective sound absorption by moving the movable structure.

[0011] Further aspects are set forth in the dependent claims, the drawings and the following description.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments are explained by way of example with respect to the accompanying drawings, in which: Sony Group Corporation

[0014] Fig. la shows a perspective view of a Helmholtz resonator with movable plug;

[0015] Fig. lb shows a cross-sectional perspective view of the Helmholtz resonator of Fig. la;

[0016] Fig. 2 shows a cross-sectional view of the Helmholtz resonator of Figs, la and lb;

[0017] Fig. 3 shows a detailed view of the neck of the Helmholtz resonator of Fig. 2;

[0018] Fig. 4 shows a detailed view of the plug head of the plug of the Helmholtz resonator of Fig. 2;

[0019] Fig. 5 shows a cross-sectional view of the Helmholtz resonator of Figs, la and lb including fluid domains;

[0020] Fig. 6 shows a plot of absorption curves depending on the position of the plug of the Helmholtz resonator of Fig. 3;

[0021] Fig. 7 shows a plot of absorption curves for the Helmholtz resonator of Fig. 3, with varying plug rod radii;

[0022] Fig. 8a shows a Helmholtz resonator where the surface profile of the plug and the surface profile of the lid are converging;

[0023] Fig. 8b shows a Helmholtz resonator where the surface profile of the plug and the surface profile of the lid are parallel;

[0024] Fig. 8c shows a Helmholtz resonator where the surface profile of the plug and the surface profile of the lid are diverging;

[0025] Fig. 8d shows a Helmholtz resonator where the surface profile of the plug and the surface profile of the lid are diverging maximally;

[0026] Fig. 9 shows a plot of absorption curves for the Helmholtz resonator of Fig. 2, with varying Rpiate,2 and constant a .

[0027] Fig. 10 shows a plot of absorption curves for the Helmholtz resonator of Figs. 3,4, with varying lid and plug truncation edges;

[0028] Fig. 11 shows a plot of absorption curves for the Helmholtz resonator of Fig. 2, with varying h.

[0029] Fig. 12 shows a plot of absorption curves for the Helmholtz resonator of Fig. 2 with parallel plug and lid surface profiles, with varying ai.'

[0030] Fig. 13 shows a plot of absorption curves for the Helmholtz resonator of Fig. 2, with varying Hi,

[0031] Fig. 14 shows a Helmholtz resonator with a movable plug that includes a threaded rod;

[0032] Fig. 15a shows a Helmholtz resonator with a movable plug and a movable cavity base; Sony Group Corporation

[0033] Fig. 15b shows a Helmholtz resonator with a movable plug and a movable elastic cavity base;

[0034] Fig. 16a shows a detailed view of a Helmholtz resonator with movable plug and a straight alternative pathway for sound waves to travel through the Helmholtz resonator;

[0035] Fig. 16b shows a detailed view of a Helmholtz resonator with movable plug and a coiled alternative pathway for sound waves to travel through the Helmholtz resonator;

[0036] Fig. 16c shows a detailed view of a Helmholtz resonator with movable plug and a coiled surface profile for lid and plug;

[0037] Fig. 17 shows a method for sound absorption with a Helmholtz resonator with movable plug; and

[0038] Fig. 18 shows a block diagram depicting an electronic device that can implement the process of tuning the Helmholtz resonator with the movable plug.

[0039] DETAILED DESCRIPTION OF EMBODIMENTS

[0040] Before a detailed description of the embodiments under reference of Fig. la is given, general explanations are made.

[0041] Room modes and sound absorption

[0042] In room acoustics, controlling room modes is essential for achieving a balanced and clear sound. A room mode refers to a natural resonance of a room, where specific frequencies of sound wave build-up are amplified due to the room's dimensions and geometry. In the context of sound absorption and room acoustics, room modes create areas within a room where certain frequencies become disproportionately louder or quieter, leading to uneven sound distribution, especially in small or medium-sized rooms.

[0043] This uneven distribution of sound can result in "hot spots" where certain frequencies are overly pronounced, and "dead spots" where they are barely audible.

[0044] Addressing these inconsistencies requires targeted sound absorption treatments that can mitigate these resonances and create a more uniform listening environment.

[0045] To address the challenges of changing acoustic environments, expanding the frequency range of a sound absorber, particularly for low frequencies, is important for achieving effective noise reduction in various settings.

[0046] Acoustic metamaterials

[0047] For example, the use of acoustic metamaterials, which are engineered structures designed to control, direct, and manipulate sound waves in ways that traditional materials cannot, may be Sony Group Corporation used to address the above challenge. That is, acoustic metamaterials can be tailored to target specific frequency ranges. An example of a resonance-based metamaterial is the Helmholtz resonator.

[0048] Helmholtz resonator

[0049] The embodiments described below relate to a Helmholtz resonator (HR). A Helmholtz resonator may function as a sound absorber or as a sound amplifier. It typically comprises a neck (taking the function of an acoustic mass) and a cavity (taking the function of an acoustic compliance). The cavity is connected to the outside through the neck which may be narrower than the cavity.

[0050] The Helmholtz resonator as a sound absorber works by using the interaction between the mass of air in the neck and the compressibility of the air inside the cavity. When sound enters the neck, the air inside the neck starts to oscillate. The oscillating air particles in the neck cause the air in the cavity to be compressed. That is, as the air oscillates in the neck, it causes a corresponding movement of the air in the cavity. When the air in the neck moves inward (into the cavity), it compresses the air inside the cavity, increasing the pressure. When the air in the neck moves outward (away from the cavity), it reduces the pressure inside the cavity due to rarefaction as the air expands.

[0051] Furthermore, as the air oscillates, friction occurs within a thin layer of air, the thermoviscous boundary layer, along the neck’s walls. This friction opposes the oscillation of the air, causing the air particles to lose kinetic energy. The energy lost through friction is converted into heat, which means sound energy is effectively absorbed and reduced.

[0052] In this way, the Helmholtz resonator can be modeled as a mass-spring-damper system. That is, the air in the cavity acts like a spring that stores and releases energy, the air in the neck acts as a mass that moves back and forth and the friction in the neck acts as a damper that dissipates energy and slows the movement.

[0053] Thus, a Helmholtz resonator may absorb sound by converting sound energy into heat through thermoviscous losses in the neck, and its effectiveness at different frequencies may be adjusted by changing its physical dimensions.

[0054] That is, the resonance frequency of a Helmholtz resonator determines the specific frequency at which it can absorb sound most effectively, if it is well-matched with the characteristic field impedance of the incident sound field, as it maximizes the transfer of acoustic energy into oscillatory motion of the air in the neck and cavity. Sony Group Corporation

[0055] The resonance frequency frof Helmholtz resonator 1 can be approximated by the following Eq. 1 : where c denotes the speed of sound; Aneckdenotes the (effective) neck cross-sectional area; lneck denotes the (effective) neck length and Vcavitydenotes the cavity volume.

[0056] Some embodiments described in more detail below pertain to a sound absorbing device functioning as a Helmholtz resonator comprising a cavity, a neck and a movable structure arranged within the neck, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator to achieve effective sound absorption.

[0057] This has the advantage that the resonance frequency of the sound absorbing device functioning as a Helmholtz resonator (in the following: Helmholtz resonator) is optimally configurable, which allows improved adaptation of sound absorption towards different and changing environments, as well as noises.

[0058] Effective sound absorption may refer to sound absorption above a predefined threshold. For example, effective sound absorption may refer to a sound transmission loss above a predefined threshold, such as a transmission loss greater than 10 dB, 20 dB, or 30 dB. It may refer to transmission loss above a predefined threshold at specific points, such as peaks, within a sound transmission loss (STL) spectrum. A STL spectrum is a graph that shows how effectively a material or assembly (such as a wall, floor, or window) prevents sound from passing through it across a range of frequencies. The STL spectrum indicates the amount of sound energy, measured in decibels (dB), that is reduced or "lost" as sound passes through a barrier. Typically, effective sound absorption occurs in a narrow frequency range (peak) around the resonance frequency of the Helmholtz resonator.

[0059] Effective sound absorption may refer to sound absorption above a predefined threshold of a sound absorption coefficient. The sound absorption coefficient is a measure of how effectively a material absorbs sound energy, rather than reflecting it. The value of the absorption coefficient ranges from 0 to 1, where a value of 1 indicates perfect absorption.

[0060] The minimum sound absorption coefficient for effective sound absorption may be 0.9 or 0.8 or 0.7. Sony Group Corporation

[0061] The sound absorption coefficient may be determined by measuring the amount of sound energy incident on the material and the amount of sound energy reflected by the material. If there is no sound transmission, the coefficient may be calculated using the formula: where a is the sound absorption coefficient, Iincident is the intensity of the incident sound, and {reflected is the intensity of the reflected sound.

[0062] Alternatively, if there is some sound transmission, the coefficient may also be calculated using the following formula: a = 1 — |r|2— 1121 , where r is the reflection coefficient and t is the absorption coefficient.

[0063] Alternatively, if there is some sound transmission, the coefficient may also be calculated using the following formula: a = 1 — R - T , where R is the reflected intensity and T is the transmitted intensity.

[0064] The movable structure may be a plug. The plug may include a rod, which may be inserted into the cavity and / or neck, and a plug head. The plug head may be arranged at least partly outside the cavity and / or the neck.

[0065] The cavity may include cavity walls that surround the cavity. The cavity walls may include a cavity base at the bottom, a lid at the top and side walls.

[0066] The cavity walls may form a cylindrical shape or a spherical shape, or a rectangular or cuboidal box. The cavity may be shaped triangular. The cavity may be axisymmetric but may also be shaped non-axisymmetric.

[0067] The plug may be axisymmetric, for example by the same axis as the cavity, but may also be shaped rectangular, triangular etc.

[0068] The neck may be arranged, at least partly, in the lid of the cavity, such that it may include an aperture structure within the lid. The neck may also include a space between the surface profile of the plug (e.g., underside of the plug head) and the surface profile of the lid.

[0069] In some embodiments the movable structure (e.g., plug) may be adjustable in height relative to the neck to alter the effective cross-sectional area (e.g., Aneck, Eq.l) of the neck thereby Sony Group Corporation reconfiguring the resonance frequency of the Helmholtz resonator. That is, Aneckof Eq.l may refer to the effective cross-sectional area instead of an actual cross-sectional area.

[0070] An actual cross-sectional area of the neck may not be constant, because in a conical lid geometry the wave is propagating along the rotationally symmetric axis of the cone. That is, because the shape of the cone inherently means that the diameter of the neck changes along its length. As you move along the axis of the cone (the rotationally symmetric axis), the radius of the cone varies, which in turn changes the actual cross-sectional area of the neck.

[0071] The effective cross-sectional area may refer to an averaged area rather than a true geometrical cross-sectional area (actual cross-sectional area). Thus, depending on the plug height the effective cross-sectional area may change.

[0072] Furthermore, the effective cross-sectional area may be determined based on an annulus, because the plug is inserted into the neck. Thus, at the smallest point the cross-sectional area of the neck may be: n * ((radius of the plug + neck width)2— radius of the plug2), where the radius of the plug may refer to the radius of the plug rod located in the smallest part of the neck and the neck width may refer to the free space between the rod and the lid edge surrounding the smallest part of the neck. This may be taken into consideration when determining the effective cross-sectional area.

[0073] Similarly, lneckmay refer to the effective neck length instead of an actual neck length (geometric parameter), but may instead be based on the actual neck length. That is , inecfcmay be representative of the equivalent neck length, but it may not directly correspond to a geometric parameter, but may instead be influenced by multiple geometric parameters.

[0074] For example, the Helmholtz resonator may be tuned by raising and lowering the plug arranged within the neck. For example, the effective cross-sectional area (e.g., Aneck, Eq.l) may be increased as the plug moves upwards. The movement of raising and lowering the plug may be based on a continuous range, such that the plug may be adjustable to any height or position between a range of predefined heights or positions.

[0075] Part of the plug, e.g., part of the plug rod, may also be inserted into the cavity through the neck.

[0076] The neck may be designed to optimize sound absorption performance over a frequency reconfigurability range. Sony Group Corporation

[0077] The frequency reconfigurability range may be defined as the range of frequencies over which the resonance frequency of the Helmholtz resonator can be adjusted by varying the position of the moveable plug within the neck, such that the sound absorption coefficient remains above a predefined threshold.

[0078] The frequency reconfigurability range may be defined by the minimum and maximum resonance frequencies achievable by adjusting the position of the moveable plug within the neck, such that the resonance frequency can be varied from a lower limit frequency (base frequency) to an upper limit frequency, with the neck dimensions and the position of the moveable plug being configured to provide an adjustment (e.g., a continuous adjustment) between these frequencies.

[0079] This may allow the sound absorbing device to be adjusted to cover a wide range of frequencies, ensuring that the sound absorption performance is optimized across this range.

[0080] The frequency reconfigurability range may be predefined.

[0081] The frequency reconfigurability range may be considered the effective bandwidth which may be defined as the difference between the minimum and maximum resonance frequency within which a predefined amount of sound absorption is achieved if not exceeded.

[0082] The movable plug may be configured to adjust, e.g., vary, the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range.

[0083] In some embodiments the neck may be configured such that the neck width depends on the predefined frequency reconfigurability range.

[0084] Hence, the optimized neck may include an optimized neck width. As the plug is inserted into the neck the cross-sectional area of the neck is decreased. The neck width may refer to the width of the remaining empty space, that is the distance from the plug, e.g. the rod inserted into the neck, to the inner surface of the neck. The inner surface of the neck may refer to the edge of the lid forming part of the neck. In a conical lid geometry, this may refer to the area of the neck where the neck’s actual cross-section is smallest. Thus, in a geometry where the actual cross-sectional area of the neck differs, the neck width may refer to the minimum neck width, i.e., the neck width where the neck is smallest.

[0085] An optimal neck width may be required to provide sufficiently large but not excessive resistance (hence large sound absorption) when the plug is lowered, thus retaining the desired sound absorption capability of the resonator, even when the plug is raised. Sony Group Corporation

[0086] For example, if an excessively large neck width is used, the resistance of the resonator decreases too quickly when raising the plug, consequently reducing the effective bandwidth of the resonator as this limits the maximum change in plug height.

[0087] Therefore, the neck width may be configured such that it is adapted to the desired or targeted frequency reconfigurability range.

[0088] In some embodiments the movable structure radius (e.g., plug radius) may be configured such that it depends on the predefined frequency reconfigurability range.

[0089] The plug’s rod may have an axisymmetric shape, for example, a cylindrical shape, and the plug radius may refer to the radius of the rod inserted into the neck.

[0090] Therefore, depending on the plug radius the neck width may be decreased or increased. For example, a plug with a larger radius decreases the neck width (e.g., distance from the outside surface of the rod to the inner surface of the neck (e.g., the inner surface of the neck may refer to an edge of the lid)).

[0091] Adapting the plug radius to the desired or targeted frequency reconfigurability range may adapt the neck width to the frequency reconfigurability range, thereby optimizing the sound absorption capabilities of the Helmholtz resonator to a wider frequency reconfigurability range.

[0092] In some embodiments the surface profile of the movable structure (e.g., plug) may be configured such that it depends on the predefined frequency reconfigurability range.

[0093] The surface profile of the plug may refer to the surface facing the cavity, e.g., the bottom side surface of the plug head.

[0094] In some embodiments the surface profile of the lid of the cavity may be configured such that it depends on the predefined frequency reconfigurability range.

[0095] The surface profile of the lid may refer to the surface facing the surface profile of the plug, e.g., the outside surface of the lid.

[0096] The surface profile of the lid of the cavity and the surface profile of the movable structure (e.g., plug), which may be facing each other, may be parallel to each other. That is the surface profile of the movable structure (e.g., plug) may be parallel to the surface profile of the lid of the cavity.

[0097] Alternatively, the surface profiles of the movable structure (e.g., plug) and lid may be converging or diverging. Sony Group Corporation

[0098] In some embodiments the edge of a lid of the cavity may be truncated. The edge of the lid may refer to an inner edge of the lid. The truncation of the lid may depend on the predefined frequency reconfigurability range.

[0099] In some embodiments the edge of the movable structure (e.g., plug) may be truncated. The edge of the plug may refer to the edge of the plug head. The truncation of the plug may depend on the predefined frequency reconfigurability range.

[0100] The truncation of the lid edge and the plug edge may be the same, e.g., same truncation length.

[0101] The lid may be conical, therefore the inner edge of the lid forming part of the aperture of the neck may be lower in the vertical direction than an outer edge of the lid.

[0102] In some embodiments the vertical distance between the inner edge of the lid to the outer edge of the lid may depend on the predefined reconfigurability range.

[0103] In some embodiments the horizontal distance between the center of the cavity and an outer edge of a lid of the cavity may depend on the predefined reconfigurability range.

[0104] In some embodiments the cavity base may be movable. Thereby the cavity volume (e.g., Vcavity, Eq. 1) and therefore also the resonance frequency (e.g., fr) may be adjustable.

[0105] The cavity base may be configured such that the movement depends on the frequency reconfigurability range.

[0106] In some embodiments the sound absorbing device may further include an actuation mechanism configured to raise and lower the movable structure (e.g., plug) within the neck, allowing for adjustment of the resonance frequency.

[0107] The actuation mechanism may be based on an electronic actuator. This may include a linear motor or a stack of piezoelectric ceramics which extends under an applied voltage. Further possible actuation mechanisms may include non-electrical means, for example, pneumatically using pressurized air to move the plug up and down or with the use of hydraulics. The actuation mechanism may include a piston or an elastic membrane.

[0108] The actuation mechanism for moving the plug or an alternative actuation mechanism may also raise and lower the cavity base in case of a Helmholtz resonator with a movable cavity base.

[0109] Some embodiments pertain to a method for sound absorption with the sound absorbing device functioning as a Helmholtz resonator described in this specification. The method may include the step of adjusting the resonance frequency of the Helmholtz resonator to achieve effective sound absorption by moving the movable structure (e.g., plug). Sony Group Corporation

[0110] The method may include any feature described with regard to the sound absorbing device.

[0111] For example, moving the movable structure (e.g., plug) may include adjusting the plug in height relative to the neck to alter the effective cross-sectional area of the neck, thereby reconfiguring the resonance frequency of the Helmholtz Resonator.

[0112] Also, the resonance frequency may be adjusted within a predefined frequency reconfigurability range.

[0113] Furthermore, the movable structure (e.g., plug) may be moved by an actuation mechanism.

[0114] If the cavity base is movable, adjusting the resonance frequency of the Helmholtz resonator may include moving the cavity base.

[0115] Methods of controlling the movement of the movable structure (e.g., plug) and / or cavity base, e.g., through an actuation mechanism, and thereby adjusting the resonance frequency of the Helmholtz resonator, as described in this specification, may also be implemented in some embodiments as a computer program causing a computer and / or a processor to perform the method, when being carried out on the computer and / or processor. In some embodiments, also a non-transitory computer-readable recording medium is provided that stores therein a computer program product, which, when executed by a processor, such as the processor described above, causes the methods described herein to be performed.

[0116] Application examples

[0117] In the context of reducing room modes, the sound absorbing device according to some embodiments may be attached vertically to a room’s ceiling or horizontally to a room’s wall. Similarly, in the context of duct noise reduction, the sound absorbing device may be attached along the duct’s length or at the duct’s end, depending on the target of the sound absorption.

[0118] Returning now to the figures:

[0119] Fig. la schematically illustrates a Helmholtz resonator with a plug according to an embodiment and Fig. lb illustrates a cross-sectional perspective view of the Helmholtz resonator of Fig. la.

[0120] Helmholtz resonator 1 (e.g., a sound absorbing device functioning as a Helmholtz resonator) includes cylindrical hollow cavity 2 and neck 4 which connects cavity 2 with the outside. Cavity 2 is enclosed by cavity walls 2a which include a lid 2b at the top side.

[0121] Plug 3 is movably inserted through the neck 4 into cavity 2 of Helmholtz resonator 1. Plug 3 is an example of a movable structure. Plug 3 includes a head 3a and a rod 3b that is inserted within Sony Group Corporation neck 4 and cavity 2. The bottom side of the plug head 3a has a convex surface profile 3c. The surface profile of lid 5 is concave.

[0122] Neck 4 includes a small round aperture structure within lid 2b. Furthermore, neck 4 includes the area between the surface profile 3 c of the plug head 3 a and the surface profile 5 of the lid 2b and extends to the area beyond the edge of the plug head 3 a, but within the edge of the lid 2b.

[0123] By fitting moveable plug 3 into neck 4 of Helmholtz resonator 1, the resonance frequency of Helmholtz resonator 1 can be varied by raising and lowering the plug 3. In effect, also the frequency band for effective sound absorption which occurs around the resonance frequency of Helmholtz resonator 1 can be varied. Thus, raising and lowering the plug increases and decreases the resonance frequency of Helmholtz resonator 1, thereby allowing a configurable target frequency according to a frequency reconfigurability range inherent to Helmholtz resonator 1.

[0124] Fig. 2 illustrates a cross-sectional view of the Helmholtz resonator 1 of Figs, la and lb. In the following the geometric properties of Helmholtz resonator 1 illustrated in Fig. 2 are discussed.

[0125] The geometry of the Helmholtz resonator 1 including plug 3 is axisymmetric about axis a. Therefore, Fig. 2 illustrates only half of the geometry of Helmholtz resonator 1.

[0126] The surface profile 5 of lid 2b is parallel to the surface profile 3c of the plug 3, i.e., surface profile 3 c of the bottom side of the plug head 3 a.

[0127] Cavity 2 of Helmholtz resonator 1 has a height Hi . Plug rod 3b has a radius Rpiate, i. Plug head 3a has a radius Rpiate, 2. The distance from axis a to the outer edge of the cavity lid 2b is a.2. The vertical distance from the upper surface of the inner edge of lid 2b to the upper surface of the outer edge of the lid 2b is h.

[0128] Fig. 2 also includes two boundary boxes with dashed and dotted lines, which denote the detailed section illustrated in Figs. 3 and 4 respectively.

[0129] Fig. 3 illustrates a detailed view of the neck of Fig. 2. There is a vertical gap between lid 2b and the plug head 3a, denoted as H<,ap, which indicates that plug 3 is raised by a small distance of Hgap.

[0130] The edge of lid 2b is truncated to be as sharp as possible, while keeping the structural integrity and durability of the lid 2b, with a truncation thickness tud.

[0131] As plug 3 is inserted into the neck 4, rod 3b of plug 3 reduces the cross-sectional area of neck 4.

[0132] The distance between rod 3b and the side wall of neck 4 is denoted as neck width w. Sony Group Corporation

[0133] Neck width w is configured based on the target frequencies (frequency reconfigurability range) for effective sound absorption above a predefined threshold. That is, regardless of Hgap, the acoustic energy dissipation mainly occurs at the region of the neck with width w. As such, it is essential to optimize neck width w, as it governs the overall resistance and inherently the sound absorption capability of the Helmholtz resonator 1.

[0134] The dimension perpendicular to the surface profiles 3c, 5 of both plug 3 and lid 2b is the dimension of actual neck area n. The dimension of the actual neck area n may change based on the plug movement (plug height), which may change the effective cross-sectional area of the neck. For example, increasing n (e.g., by raising the plug) will increase the effective cross- sectional area (e.g., Aneck).

[0135] Fig. 4 illustrates a detailed view of the area of plug head 3a of Fig. 2. The edge of plug head 3a is truncated to be as sharp as possible, while keeping the structural integrity and durability of the plug head 3a, with a truncation thickness tpiugwhich is the same truncation thickness as the truncation thickness tud of lid 2b of Fig. 3.

[0136] Fig. 5 illustrates a cross-sectional view of the Helmholtz resonator 1 of Figs, la, lb and 2 including the fluid domains. Fig. 5 corresponds to Fig. 2 regarding the Helmholtz resonator 1, but additionally includes the upstream fluid domain 6 outside the Helmholtz resonator 1 as well as the fluid domain 7 of the Helmholtz resonator 1 for both neck and cavity.

[0137] Furthermore, in Fig. 5 a non-reflecting boundary 8 is illustrated which may be used for determining the sound absorption coefficient oc as discussed in Figs. 6, 7 and 9 to 12. The nonreflecting boundary 8 represents the acoustical domain the Helmholtz resonator 1 is used in, e.g., a bounded room, a duct or a free field. The non-reflecting boundary may prevent reflections of waves or disturbances. In Fig. 5 the non-reflecting boundary 8 is shown close to the Helmholtz resonator for illustration purposes only, but may be located much farther away from the Helmholtz resonator.

[0138] Fig. 6 illustrates a plot of the sound absorption coefficient plotted against frequency where each absorption curve 10a to 10g corresponds to a value of Hgapof the Helmholtz resonator of Fig. 3 that changes from 0.3 mm to 10.5 mm.

[0139] The sound absorption coefficient oc is obtained with oc = 1 - 7?, where Sony Group Corporation is the reflection coefficient; Poutand Pin, is the reflected and incident sound power, respectively, evaluated at the non-reflecting boundary 8 of Fig. 5 at the upper end of the upstream fluid domain 6 of Fig. 5.

[0140] Alternatively, the sound absorption coefficient oc may be obtained based on oc = 1 - | / ?|2, where

[0141] Hgap of 0.3 mm corresponds to absorption curve 10a, Hgapof 0.5 mm corresponds to absorption curve 10b, Hgapof 1.0 mm corresponds to absorption curve 10c, Hgapof 1.5 mm corresponds to absorption curve lOd, Hgapof 2.0 mm corresponds to absorption curve lOe, Hgapof 4.0 mm corresponds to absorption curve lOf, and Hgapof 10.5 mm corresponds to absorption curve 10g.

[0142] As the plug (e.g., 3, Figs, la-5) is raised from Hgap= 0.5 mm to 10.5 mm, the resonance frequency of the Helmholtz resonator (e.g., 1, Figs, la-5) increases from 420 Hz to 740 Hz. This increase of the resonance frequency is due to the increasing neck cross-sectional area, as the plug moves upwards. Based on the abovementioned Eq. 1, a larger i4neckresults in a higher fr, hence, the reconfigurability through varying Hgap.

[0143] As Hgapincreases from 0.5 mm to 10.5 mm the peak of the absorption curve converges asymptotically towards a specific frequency 740 Hz, where increasing Hgap, further only yields negligible changes in frequency. In other words, the frequency increases at a slowing rate. A major contributing factor to this behaviour could be that as the plug is raised, the plug gets more decoupled from the lid, hence, its influence on the resonance frequency diminishes. Thus, Hgaphas a diminishing influence on the neck’s properties as it exceeds a certain value. This is because the neck properties (e.g., effective cross-sectional area Aneck, and effective neck length lneck) eventually become independent of Hgap.

[0144] Ultimately, at the largest Hgap= 10.5 mm indicated by absorption curve 10g, fr, is mainly dictated by the small opening at the lid of the Helmholtz resonator. Also, lowering the plug by reducing Hgapfrom 0.5 mm to 0.3 mm shifts the absorption peak down in frequency from 460 Hz to 380 Hz. That said, the maximum absorption coefficient now decreases significantly from 0.88 Sony Group Corporation to 0.57, as the Helmholtz resonator becomes overdamped by the excessive resistance in the neck region, due to the narrower gap between the plug and the lid of the Helmholtz resonator.

[0145] The effective bandwidth (frequency reconfigurability range) of the Helmholtz resonator may be defined as the peak-to-peak difference between the minimum and maximum resonance frequency where a predefined minimum amount of absorption is achieved or exceeded.

[0146] For example, the predefined minimum amount of absorption as defined by the absorption coefficient may be 0.88, which in the embodiment of Fig. 6 corresponds to Hgap= 0.5 mm. In this case, the absolute frequency reconfigurability range is defined by the lower bound of 460 Hz (corresponding to Hgap= 0.5 mm) and the upper bound of 740 Hz (corresponding to Hgap= 10.5 mm) with an absolute bandwidth (or absolute frequency reconfigurability range) of 280 Hz and a relative bandwidth (or relative frequency reconfigurability range) of 48%. The relative bandwidth, A / rc| , is determined according to: where / io.5mm corresponds to the resonance frequency atHgap= 10.5 mm and / o.5mm corresponds to the resonance frequency atHgap= 0.5 mm.

[0147] Alternatively, with a desired minimum absorption coefficient of 0.8, the optimal minimum Hgapmay be 0.4 mm (instead of 0.5 mm) which would slightly lower the base (or lower limit) resonance frequency, thus further extending the frequency reconfigurability range.

[0148] Fig. 7 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Fig. 3, with varying plug rod radii RPiate,i.

[0149] Rpiate.i is varied from 0.5 mm (absorption curves l id, 12d), 1.0 mm (absorption curves 11c, 12c), 1.5 mm (absorption curves 11b, 12b) to 1.8 mm (absorption curves I la, 12a). The solid lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0150] The variation of Rpiate,i effectively varies the neck width w (Fig. 3) of the narrow region between the plug rod (3b, Fig. 3) and the edge of the lid (2b, Fig. 3).

[0151] As Rpiate,i increases from 0.5 mm, 10 mm, 1.5 mm to 1.8 mm, the resonance peaks at both Hgapof 0.5 mm (solid lines) and 10.5 mm (dotted lines) shift down in frequency. This may correspond to a decreasing cross-sectional area Aneckof Eq. 1 Sony Group Corporation

[0152] Furthermore, \. Hgap= 0.5 mm, the absorption coefficient decreases significantly from 1, 0.97, 0.88 to 0.60. This may occur due to an increasingly excessive resistance (from the narrow region) that causes a greater impedance mismatch with the background fluid medium.

[0153] On the other hand, at Hgap= 10.5 mm where the Helmholtz resonator (1, Figs, la to 5) is underdamped, the absorption coefficient increases with increasing Rpiate.i up to 1.5 mm. Thus, in this case, a Rpiate.i = 1.5mm is the optimal parameter where the absorption coefficient at both Hgaplimits is greater than 0.85.

[0154] In essence, an optimal neck width w (Fig. 3) provides a sufficiently large but not excessive resistance (hence large sound absorption) when the plug is lowered, and also retains the sound absorption capability of the Helmholtz resonator, even when the plug is raised.

[0155] For example, if an excessively large (small) neck width w is used, the resistance of the Helmholtz resonator decreases (increases) too quickly when raising (lowering) the plug, consequently reducing its effective bandwidth as this limits the maximum value (minimum) of Hgapuntil the sound absorption value falls below the threshold value.

[0156] Therefore, it has been found that adapting the neck width w of the Helmholtz resonator to a desired frequency reconfigurability range allows for most effective tuning of the Helmholtz resonator to a target frequency of the frequency reconfigurability range by raising and lowering the plug.

[0157] Fig. 8a illustrates a Helmholtz resonator (e.g., 1, Figs, la, lb) where the surface profile 3c of the plug head 3 a and the surface profile 5 of the lid 2a are converging.

[0158] Fig. 8b illustrates a Helmholtz resonator (e.g., 1, Figs, la, lb) where the surface profile 3c of the plug head 3a and the surface profile 5 of the lid 2a are parallel as shown in Fig. 2.

[0159] Fig. 8c illustrates a Helmholtz resonator (e.g., 1, Figs, la, lb) where the surface profile 3c of the plug head 3 a and the surface profile 5 of the lid 2a diverging.

[0160] Fig. 8d illustrates a Helmholtz resonator where the surface profile 3 c of the plug head 3 a and the surface profile 5 of the lid 2a diverging maximally, such that the plug head 3a is minimized to the rod 3b.

[0161] In Figs. 8a to 8d the radius of the plug head 3a is denotated as Rpiate,2. RPiate,2 is maximal in Fig. 8a where the surface profiles 3c, 5 are diverging. Rpiate,2 is larger in Fig. 8b, where the surface profiles 3c, 5 are parallel, than in Fig. 8c where the surface profiles 3c, 5 are converging. As the plug head 3a is minimized to the rod 3b in Fig. 8d RPiate,2 is also minimized to Rpiate.i (see Fig. 2, e.g., RPiate,2 =RPiatei = 1.5 mm, see 11c, l id, Fig. 7). Sony Group Corporation

[0162] Fig. 9 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Fig. 2, with varying Rpiate,2 and constant a2.

[0163] As Rpiate, 2 varies while ct2 is constant, in Fig. 9 absorption curves of Helmholtz resonators (e.g., 1, Fig. la, lb) with either a converging (absorption curves 13b, 14b, Rpiate, 2 = 8.75 mm), parallel (absorption curves 13c, 14c, Rpiate, 2 = 17.50 mm) or diverging (absorption curves 13d, 14d, Rpiate, 2 = 19.25 mm) surface profiles 3a, 5 are plotted, as illustrated in Fig. 8a to 8c.

[0164] An extreme case of an entirely straight plug where Rpiate, 2 is equivalent to 1.55 mm (absorption curves 13a, 14a) is also included (Here Rpiate, 2 = RPiatei = 1.5 mm, see 11c, l id, Fig. 7). The solid lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0165] In Fig. 9 a larger plug head radius Rpiate, 2 (absorption curves 13d, 13c) results in a lower resonance frequency. As Rpiate, 2 increases, the reconfigurable frequency range (corresponding to the resonance frequency difference between Hgap= 0.5 mm and 10.5 mm (see Fig. 7 description for detailed explanation)) increases from 130 Hz, 280 Hz to 320 Hz which is equivalent to a relative bandwidth of 19%, 48% and 60%, respectively.

[0166] This is because for a converging surface profile (Fig. 8c), as the plug is raised, the portion of the plug that is closer to the neck entrance (or further away from the cavity entrance) is decoupled (from the rest of the structure) earlier than the portion of the plug further away from the neck entrance (or closer to the cavity entrance). When decoupling occurs, the portion of the plug that is decoupled no longer has a significant influence on the Helmholtz resonator, as if it was not present in the first place.

[0167] Specifically, the neck properties associated with the decoupled portion of the plug are no longer changeable upon further increment of Hgap, thus no longer contribute to the resonance frequency shift. As a result, the decoupled neck region decreases the ratio of reconfigurable neck region to total neck region (reconfigurable neck region / total neck region) which has been found to be a metric that determines the reconfigurability range (e.g., the larger the ratio, the larger the reconfigurability range).

[0168] The total neck region includes the region defined by the neck width w (Fig. 3), the region defined by the actual neck area n (Fig. 3, i.e., the chancel between surface profile 3c of the plug and surface profile 5 of the lid), and include the region beyond / next to the edge of plug head (3a, Fig. 2) up to the edge of the lid (with a dimension of a.2 - Rpiate, 2, Fig. 2).

[0169] The reconfigurable neck region is the region where either the entire surface profile (3c, Fig. 2) of the plug or a portion of the surface profile (3c, Fig. 2) of the plug is still closely coupled to Sony Group Corporation surface profile (5, Fig. 2) of the lid or a portion of the surface profile of the lid (5, Fig. 2). Closely coupled refers to the surface profile (3c, Fig. 2) of the plug being in close proximity to the surface profile (5, Fig. 2) of the lid from a sound wave's perspective, such that changing Hgapstill yields a change in the resonance frequency above a predefined threshold.

[0170] From the perspective of the resonance frequency equation (see Eq. 1), a smaller Rpiate, 2 increases the effective neck cross-sectional area, Aneck, as well as decreases the neck length, lneck, which results in a shift of the resonance peak to higher frequencies when Hgap= 0.5 mm. In essence, a larger Rpiate,2 has been found to be more beneficial in terms of achieving a larger frequency reconfigurability range.

[0171] However, the impedance mismatch between the Helmholtz resonator and the background fluid medium needs to be considered as well, as too large values for Rpiate,2 (e.g., 19.25 mm in this case) result in an excessively large resistance which, consequently, compromises the absorption coefficient. As such, a parallel gap profile between the plug and the lid has a minimal trade-off between frequency reconfigurability range and absorption coefficient.

[0172] The entirely straight plug (absorption curve 13a) imitates a situation where all portions of the plug are decoupled. In this configuration, raising the plug does not yield any appreciable resonance frequency shift.

[0173] Also, aHHgai>, = 10.5 mm, the other absorption curves 14b-d (dotted lines) converge towards absorption curve 14a (entirely straight plug) at its resonance frequency of 780 Hz.

[0174] In other words, regardless of the surface profile (e.g., diverging / parallel / converging), when the plug is fully decoupled, the resonance frequency of the Helmholtz resonator mainly depends on the lid and cavity and is largely independent of the plug.

[0175] That said, a larger Rpiate,2 results in a minimal but non-negligibly lower resonance frequency at Hgap= 10.5 mm. This is likely due to the larger radiation impedance associated with the smaller opening at the neck entrance of the Helmholtz resonator, hence the lower resonance frequency.

[0176] Thus, a parallel profile for the plug and lid surfaces results in a minimal trade-off between the frequency reconfigurability range and absorption coefficient.

[0177] Fig. 10 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Figs. 3,4, with varied tud and tpiug.

[0178] In Fig. 10 tud and tpiugvary from 0.1 mm (absorption curve 15a, 16a), 1.0 mm (absorption curve 15b, 16b), 2.0 mm (absorption curve 15c, 16c) to 3.0 mm (absorption curve 15d, 16d). The solid Sony Group Corporation lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0179] Both tud and tpiugare varied by the same magnitude.

[0180] Fig. 10 shows that when both tud and tpiugincrease, the resonance frequency decreases due to the longer extra neck that is formed.

[0181] Furthermore, as tud and tpiugincrease from 0.1 mm, 1.0 mm, 2.0 mm to 3.0 mm, the frequency reconfigurability range decreases from 280 Hz, 190 Hz, 140 Hz to 100 Hz, which is equivalent to a relative bandwidth of 48%, 37%, 29% and 22%, respectively.

[0182] Ideally, the edge of the lid and the plug have perfectly sharp edges at the exterior corners. This is because a perfectly sharp comer (that reduces to a zero-thickness point) will yield the greatest frequency reconfigurability range. However, with a finite wall thickness (e.g., filleted or truncated corner (see Figs. 3 and 4)), the frequency reconfigurability range will decrease.

[0183] The reason for this is that the non-zero wall thickness acts like an extension to the Helmholtz resonator neck, that increases with the wall's thickness. At the same time, the controllable part of the neck length depends on the shape of the plug. Therefore, if the wall's thickness is increased (without changing the plug geometry), the adjustable portion of the neck becomes smaller in proportion to the total neck length. This extension to the Helmholtz resonator neck also leads to increased therm oviscous-induced resistance, which may lead to an impedance mismatch and thus lower absorption occurring more easily.

[0184] Using the controllable neck region to total neck region ratio (as explained with regard to Fig. 9), a larger wall thickness results in a smaller ratio, hence a smaller frequency reconfigurability range.

[0185] A lower resonance frequency may be achieved by increasing the value of tud and tpiug. However, minimal values may still be used in favour of a larger frequency reconfigurability range. For example, other geometrical parameters (e.g., cavity volume, see Fig.13) may achieve a lower base resonance frequency, while retaining the frequency reconfigurability range.

[0186] Fig. 11 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Fig.2, with varied h.

[0187] In Fig. 11 h varies from 0.1 mm (absorption curves 17a, 18a), 3.0 mm (absorption curves 17b, 18b), 6.0 mm (absorption curves 17c, 18c) to 9.0 mm (absorption curves 17d, 18d). The solid lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0188] When h increases, the circumference of the lid elongates in the vertical direction, essentially the lid conforms more towards a conical shape (see Fig. 2), which affects the effective neck length Sony Group Corporation

[0189] As li increases from 3.0 mm, 6.0 mm to 9.0 mm (excluding h = 0.1 mm), the resonance frequency at Hgap= 0.5 mm decreases by a very small margin and the resonance frequency remains approximately constant at 460 Hz.

[0190] This may be counter intuitive as it goes against the typical trend that a longer Helmholtz resonator neck results in a lower resonance frequency (see Eq.1). However, the actual neck area (dimension perpendicular to the surface profile of both plug and lid, see n, Fig. 2) becomes larger when h increases. Since the effective cross-sectional area of the neck is a more dominant factor for the resonance frequency than the effective neck length, the increase of the resonance frequency due to the slightly larger neck area ( / / , Fig. 3) cancels out the effect of a noticeably longer neck.

[0191] For Hgap = 10.5 mm, as h increases from 3.0 mm, 6.0 mm to 9.0 mm, the resonance frequency decreases from 740 Hz, 720 Hz to 700 Hz, respectively. This is because, similar to the effect of Rpiate,2 shown in Fig. 7 a larger radiation impedance is associated with the smaller opening of the Helmholtz resonator (when h increases), hence, the lower resonance frequency.

[0192] In essence, a smaller h may be used as it generally results in better performance in terms of achieving slightly lower base resonance frequency, as well as a larger frequency reconfigurability range (regardless of whether it may defined with absolute or relative bandwidth).

[0193] The extreme case of a very small h of 0.1 mm, represents an infinitely thin, flat plug and lid. h = 0.1 mm gives the largest frequency reconfigurability range among all other variations of h. For example, as h decreases from 3.0 mm to 0.1 mm, the absolute frequency reconfigurability range increases from 280 Hz to 320 Hz, which is equivalent to an increase of the relative frequency reconfigurability range from 48% to 56%, although the absorption coefficient at Hgap= 0.5 mm slightly decreases.

[0194] The extremely thin plug and lid may act as another dissipation mechanism, contributing positively to the absorption performance of the Helmholtz resonator.

[0195] However, instead of a flat plug and lid it may be easier to manufacture a Helmholtz resonator with a thicker h, which may also, depending on the material, prevent a cutting hazard, and provide a better structural integrity. Furthermore, a thicker h may prevent a resonance of plug and lid to oscillate with such a large displacement in the frequency range of interest, that it may change the actual value of Hgap, especially when Hgapis small (e.g., at 0.5 mm), where the resonance frequency is highly sensitive to the change in Hgap. Sony Group Corporation

[0196] Fig. 12 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Fig.2 with parallel plug and lid surface profiles, with varied a2.

[0197] In Fig. 12 ci2 is varied from 6.0 mm (absorption curve 19c, 20c), 12.0 mm (absorption curve 19b, 20b) to 18.0 mm (absorption curve 19a, 20a). The solid lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0198] As ci2 increases from 6.0 mm, 12.0 mm to 18.0 mm, \. Hgap= 0.5 mm, the resonance frequency decreases from 560 Hz, 500 Hz to 460 Hz, respectively.

[0199] The reason for this decrease is because the actual neck area (dimension perpendicular to the surface profile of both plug and lid) becomes smaller as ct2 increases. Also, a larger ct2 results in a longer neck, which as described by the resonance frequency equation of Eq. 1 reduces the resonance frequency as well.

[0200] Since the plug and lid surface profiles are parallel, having a larger ct2 inherently results in a larger Rpiate,2 (see Fig. 9) which delays the decoupling of the plug from the lid, as mentioned with regard to Fig. 2.

[0201] At Hgap= 10.5 mm, the resonance frequency increases with a larger ci2. This may be due to the smaller radiation impedance associated with the larger opening of the Helmholtz resonator (formed by the lid and cavity only).

[0202] In essence, a larger ct2 is advantageous, as it results in the best performance in terms of achieving a lower base resonance frequency, as well as a larger frequency reconfigurability range.

[0203] Fig. 13 illustrates a plot of absorption curves (sound absorption coefficient plotted against frequency) for the Helmholtz resonator of Fig. 2, with varying Hi.

[0204] Hi denotes the cavity height as illustrated in Fig. 2 and varies from 12.0 mm (absorption curves 21a, 22a), 24.0 mm (absorption curves 21b, 22b) to 36.0 mm (absorption curves 21c, 22c). The solid lines correspond to Hgap= 0.5 mm and the dotted lines correspond to Hgap= 10.5 mm.

[0205] As Hi increases from 12 mm, 24 mm to 36 mm, the resonance frequency at Hgap= 0.5 mm decreases from 460 Hz, 320 Hz to 260 Hz, respectively, due to the greater cavity volume as described by the resonance frequency Eq. 1 described above.

[0206] Also, the absolute frequency reconfigurability range increases with decreasing cavity volume.

[0207] For example, the absolute bandwidth for the cavity heights of 12 mm, 24 mm and 36 mm are 280 Hz, 200 Hz and 160 Hz, respectively. Sony Group Corporation

[0208] The relative bandwidth may be a better indicator of the frequency reconfigurability range, especially in the context of low frequency sound absorption.

[0209] The relative bandwidth remains fairly constant at approximately 49%. Therefore, the cavity height (or generally the cavity volume) can be used as a geometrical tuning parameter to shift the resonance absorption peaks up / down towards the target frequency range, without affecting the relative frequency reconfigurability range.

[0210] Also, the amplitude of the absorption peaks remains approximately constant when Hi is changed, as the compliance component of the cavity only affects the reactance of the Helmholtz resonator.

[0211] Instead of using Helmholtz resonators of different heights, as is the case for Fig. 13, to change Hi the cavity if the Helmholtz resonator may include a movable cavity base as explained in Fig. 15a and 15b.

[0212] Fig. 14 illustrates a Helmholtz resonator with a movable plug that includes a threaded rod.

[0213] The Helmholtz resonator 1 (e.g., 1, Figs, la-2) includes a movable plug 3 (e.g., 3, Figs. la-2).

[0214] The movable plug 2 includes a plug head 3a and a threaded rod 3b. The threaded rod 3b includes a threaded part 9. The threaded rod 3b is inserted through the neck 4 into the cavity 2 of the Helmholtz resonator 1. The threaded part 9 of the threaded rod 3b is inserted through the cavity base 2c of the cavity walls 2a.

[0215] The plug 3 is raised or lowered by rotating the threaded rod 3b clockwise or anti-clockwise. In this way the frequency of effective sound absorption is reconfigured based on the frequency reconfigurability range of the Helmholtz resonator 1.

[0216] For automation purposes, an electronic actuator may be used.

[0217] Fig. 15a illustrates a Helmholtz resonator with a movable plug and a movable cavity base.

[0218] Helmholtz resonator 1 with movable plug 3 of Fig. 15a corresponds to any one of the Helmholtz resonators 1 of this specification, but it also includes a movable cavity base 2c. The movable cavity base 2c is sealed to the side walls of the cavity walls 2a with seals 9 to prevent leakage.

[0219] The cavity base 2c is movable in the vertical direction as indicated by the arrow. The cavity base 2c is rigidly attached to rod 3b of plug 3. Thus, the cavity base 2c is realized as a piston that can move up and down with the rigidly attached plug 3 as indicated by the dotted lines.

[0220] Moving the cavity base 2c changes the cavity volume (e.g., cavity height Hi, Fig. 2), thereby shifting the resonance frequency of the Helmholtz resonator 1, as described with regard to Fig. 13. Furthermore, moving the cavity base 2c also raises or lowers the plug 3 (i.e., changes Hgap, Sony Group Corporation

[0221] Figs. 3, 6), thereby also shifting the resonance frequency of the Helmholtz resonator 1 as described with regard to Fig. 6.

[0222] Fig. 15b illustrates a Helmholtz resonator with a movable plug and a movable elastic cavity base.

[0223] Helmholtz resonator 1 with movable plug 3 of Fig. 15b corresponds to any one of the Helmholtz resonators 1 of this specification, but it also includes a movable cavity base which is formed as an elastic membrane 23.

[0224] The elastic membrane 23 is movable in the vertical direction as indicated by the arrow. The elastic membrane 23 is attached to rod 3b of plug 3. A piston (not visible) moves the elastic membrane 23 together with the plug 3, which stretches the elastic membrane 23 as the piston moves up, simultaneously reducing cavity volume. Thus, the resonance frequency of the Helmholtz resonator 1 is changed due to the position change of plug 3 (i.e., changes in Hgap, Figs. 3, 6) and cavity volume.

[0225] Fig. 16a illustrates a detailed view of a Helmholtz resonator with movable plug and a straight alternative pathway for sound waves to travel through the Helmholtz resonator.

[0226] Here the movable plug (e.g., 3, Fig. la-4) is not raised, such that Hgap(Fig. 3) can be considered to be zero.

[0227] A highly narrow gap (e.g., Hgap« 0.5 mm) between the plug and surface profile (e.g., 5, Fig. 2) of the lid 2b would generate excessive resistance that, consequently, would reduce the absorption coefficient due to impedance mismatch.

[0228] However, plug head 3a of the Helmholtz resonator (e.g., 1, Fig. la-5) of Fig. 16a includes a straight alternative pathway 25 within the plug head 3a. Thus, lower resonance frequencies for effective sound absorption are achieved, because of the alternative pathway 25.

[0229] From the perspective of electroacoustics analogy, this could be interpreted as having two inertance components connected parallelly, where one of the components is mainly short- circuited.

[0230] Also, the alternative pathway 25 may not necessarily have to be straight but may also be coiled as illustrated in Fig. 16b.

[0231] Fig. 16b illustrates a detailed view of a Helmholtz resonator with movable plug and a coiled alternative pathway for sound waves to travel through the Helmholtz resonator.

[0232] Here the movable plug (e.g., 3, Fig. la-4) is also not raised, such that Hgap(Fig. 3) can be considered to be zero. Sony Group Corporation

[0233] However, there is a coiled alternative pathway 25 within the plug head 3a of the plug that is closed completely. The coiled alternative pathway 25 extends the sound wave propagation path. Thereby, the base resonance frequency is lowered and the frequency reconfigurability range is extended.

[0234] Fig. 16c illustrates a detailed view of a Helmholtz resonator with movable plug and a coiled surface profile for lid and plug.

[0235] The surface profile 5 of lid 5 includes convex extrusions and the surface profile 3c of the plug (e.g., 3, Fig. la-4) includes corresponding concave intrusions. This generates an alternative pathway 25, which extends the sound wave propagation path. Thereby, the base resonance frequency is lowered and the frequency reconfigurability range is extended.

[0236] In addition, the Helmholtz resonator may also be made as a part of a larger panel with other Helmholtz resonators, where each Helmholtz resonator element is tuned differently (e.g., with different base resonance frequency) to achieve more broadband absorption. By doing so, some Helmholtz resonator elements may also be fully “switched off’ by lowering the plug depending on the objectives, e.g., for better impedance matching.

[0237] Fig. 17 illustrates a method for sound absorption with a Helmholtz resonator with movable plug.

[0238] The method 40 of Fig. 17 includes steps 41, 42 and 43. At 41 a Helmholtz resonator (e.g., 1, Fig. la-4) with a movable plug is provided. At 42 the frequency of effective sound absorption is varied based on the frequency reconfigurability range. In this way the Helmholtz resonator is tuned to a frequency of effective sound absorption based on the frequency reconfigurability range of the Helmholtz resonator. At 43 sound absorption is performed with the Helmholtz resonator. Thus, effective sound absorption occurs at the tuned frequency.

[0239] The tuning of the frequency at 42 may be automated, for example via an actuator, which may be controlled by an electronic device, e.g. electronic device 100 of Fig. 18.

[0240] It should be recognized that the embodiment of Fig. 17 describes a method with an exemplary ordering of method steps. The specific ordering of method steps is however given for illustrative purposes only and should not be construed as binding. Changes of the ordering of method steps may be apparent to the skilled person.

[0241] Fig. 18 shows a block diagram depicting an electronic device that can implement the process of tuning the Helmholtz resonator with the movable plug. The electronic device 100 comprises a CPU 101 as processor. Sony Group Corporation

[0242] The electronic device 100 further comprises an actuator 109 of a Helmholtz resonator (e.g., 1, Fig. la-5, 14-15b) with movable plug, which is configured to move the plug and / or the cavity base of the Helmholtz resonator (see 2c, 23, Fig. 15a, 15b). The processor 101 may for example implement the tuning of the Helmholtz resonator 1 to a frequency for effective sound absorption, e.g., as described with regard to Fig. 17, by controlling the movement of the actuator.

[0243] The electronic device 100 further comprises a user interface 108 that is connected to the processor 101. This user interface 108 acts as a man-machine interface and enables a dialogue between a user and the electronic device. For example, a user may make configurations to the system using this user interface 108. The electronic device 100 further comprises a Bluetooth interface 104, and a WLAN interface 105. These units 104, 105 act as I / O interfaces for data communication with external devices. For example, additional actuators, or loudspeakers, microphones, and cameras, with WLAN or Bluetooth connection may be coupled to the processor 101 via these interfaces 104 and 105.

[0244] The electronic device 100 further comprises a data storage 102 and a data memory 103 (here a RAM). The data memory 103 is arranged to temporarily store or cache data or computer instructions for processing by the processor 101. The data storage 102 is arranged as a long-term storage.

[0245] The connection between the CPU 101 and the actuator 109 may include an interface through which control signals from the CPU 101 may be sent to the actuator 109. Thus, the control signals regarding moving the plug and / or moving the cavity base implemented by the CPU 101 are sent via the interface to the actuator 109 of the Helmholtz resonator.

[0246] It should be noted that the description above is only an example configuration. Alternative configurations may be implemented with additional or other sensors, storage devices, interfaces, or the like.

[0247] The electronic device 100 may be a personal computer, a laptop, a mobile device or any other kind of portable or wearable device, for example, a smartphone, a tablet, smart glasses, head mounted displays (HMDs) or other types of smart wearable devices, or the like.

[0248] Please note that the division of the control into unit 101 is only made for illustration purposes and that the present disclosure is not limited to any specific division of functions in specific units. For instance, the control could be implemented by a respective programmed processor, field programmable gate array (FPGA) and the like. Sony Group Corporation

[0249] A method for controlling an electronic device, such as electronic device 100 and / or actuator 109 discussed above, is described for example under reference of Fig. 17, step 42. The method can also be implemented as a computer program causing a computer and / or a processor, such as CPU 101 discussed above, to perform the method, when being carried out on the computer and / or processor. In some embodiments, also a non-transitory computer-readable recording medium is provided that stores therein a computer program product, which, when executed by a processor, such as the processor described above, causes the method described to be performed.

[0250] All units and entities described in this specification and claimed in the appended claims can, if not stated otherwise, be implemented as integrated circuit logic, for example on a chip, and functionality provided by such units and entities can, if not stated otherwise, be implemented by software.

[0251] In so far as the embodiments of the disclosure described above are implemented, at least in part, using software-controlled data processing apparatus, it will be appreciated that a computer program providing such software control and a transmission, storage or other medium by which such a computer program is provided are envisaged as aspects of the present disclosure.

[0252] Note that the present technology can also be configured as described below.

[0253] [1] A sound absorbing device (1) functioning as a Helmholtz resonator comprising a cavity (2), a neck (4), and a movable structure (3) arranged within the neck (4), wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator to achieve effective sound absorption.

[0254] [2] The sound absorbing device (1) of [1], wherein the movable structure (3) is adjustable in height relative to the neck (4) to alter the effective cross-sectional area of the neck (4), thereby reconfiguring the resonance frequency of the Helmholtz resonator.

[0255] [3] The sound absorbing device (1) of [1] or [2], wherein the neck (4) is designed to optimize sound absorption performance over a frequency reconfigurable range.

[0256] [4] The sound absorbing device of any one of [1] to [3], wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the neck (4) is configured such that the neck width (w) depends on the predefined frequency reconfigurability range.

[0257] [5] The sound absorbing device (1) of any one of [1] to [4], wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined Sony Group Corporation frequency reconfigurability range, wherein the movable structure radius (Rpiatei) is configured such that it depends on the predefined frequency reconfigurability range.

[0258] [6] The sound absorbing device (1) of any one of [1] to [5], wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a surface profile (3c) of the movable structure (3) is configured such that it depends on the predefined frequency reconfigurability range.

[0259] [7] The sound absorption device (1) of any one of [1] to [6], wherein the movable structure (3) is configured to vary the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a surface profile (5) of a lid (2b) of the cavity (2) is configured such that it depends on the predefined frequency reconfigurability range.

[0260] [8] The sound absorption device of any one of [1] to [7], wherein a surface profile (3c) of the movable structure (3) is parallel to a surface profile (5) of a lid (2b) of the cavity (2).

[0261] [9] The sound absorption device (1) of any one of [1] to [8], wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, wherein an edge of a lid (2b) of the cavity (2) is truncated, and wherein the truncation of the lid (2b) depends on the predefined frequency reconfigurability range.

[0262]

[0010] The sound absorption device (1) of any one of [1] to [9], wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, wherein an edge of the movable structure (3) is truncated, and wherein the truncation of the movable structure (3) depends on the predefined frequency reconfigurability range.

[0263]

[0011] The sound absorption (1) device of any one of [1] to

[0010] , wherein a lid (2b) of the cavity (2) is conical.

[0264]

[0012] The sound absorption device (1) of

[0011] , wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the vertical distance ( / / ) between an inner edge of the lid (2b) to an outer edge of the lid (2b) is configured such that it depends on the predefined reconfigurability range

[0265]

[0013] The sound absorption device (1) of any one of [1] to

[0012] , wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the horizontal distance (a?) between the center Sony Group Corporation

[0266] (a) of the cavity (2) to an outer edge of a lid (2b) of the cavity (2) may depend on the predefined reconfigurability range.

[0267]

[0014] The sound absorption device (1) of any one of [1] to

[0013] , wherein the movable structure (3) is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a cavity base (2c, 23) of the cavity (2) is configured movable such that the movement depends on the frequency reconfigurability range.

[0268]

[0015] The sound absorption device (1) of

[0014] , wherein the cavity base (2c, 23) is an elastic membrane (23).

[0269]

[0016] The sound absorbing device (1) of any one of [1] to

[0015] , further includes an actuation mechanism configured to raise and lower the movable structure (3) within the neck (4), allowing for adjustment of the resonance frequency.

[0270]

[0017] A method for sound absorption with the sound absorbing device (1) functioning as a Helmholtz resonator of claim 1, including the step of adjusting the resonance frequency of the Helmholtz resonator to achieve effective sound absorption by moving the movable structure (3).

[0271]

[0018] The method of

[0017] , wherein moving the movable structure (3) includes adjusting the movable structure (3) in height relative to the neck (4) to alter the effective cross-sectional area of the neck (4), thereby reconfiguring the resonance frequency of the Helmholtz Resonator.

[0272]

[0019] The method of

[0017] or

[0018] , wherein the resonance frequency is adjusted within a predefined frequency reconfigurability range.

[0273]

[0020] The method of any one of

[0017] to

[0019] , wherein the movable structure (3) is moved by an actuation mechanism.

[0274]

[0021] The method of any one of

[0017] to

[0020] , wherein a cavity base (2c, 23) of the cavity (2) is movable, and wherein adjusting the resonance frequency of the Helmholtz resonator includes moving the cavity base (2c, 23).

[0275]

[0022] The method of

[0021] , wherein the cavity base (2c, 23) of the cavity (2) is an elastic membrane (23).

Claims

Sony Group CorporationCLAIMS1. A sound absorbing device functioning as a Helmholtz resonator comprising a cavity, a neck, and a movable structure arranged within the neck, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator to achieve effective sound absorption.

2. The sound absorbing device of claim 1, wherein the movable structure is adjustable in height relative to the neck to alter the effective cross-sectional area of the neck, thereby reconfiguring the resonance frequency of the Helmholtz resonator.

3. The sound absorbing device of claim 1, wherein the neck is designed to optimize sound absorption performance over a frequency reconfigurable range.

4. The sound absorbing device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the neck is configured such that the neck width (w) depends on the predefined frequency reconfigurability range.

5. The sound absorbing device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, wherein the movable structure radius is configured such that it depends on the predefined frequency reconfigurability range.

6. The sound absorbing device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a surface profile of the movable structure is configured such that it depends on the predefined frequency reconfigurability range.

7. The sound absorption device of claim 1, wherein the movable structure is configured to vary the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a surface profile of a lid of the cavity is configured such that it depends on the predefined frequency reconfigurability range.

8. The sound absorption device of claim 1, wherein a surface profile of the movable structure is parallel to a surface profile of a lid of the cavity.

9. The sound absorption device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequencySony Group Corporation reconfigurability range, wherein an edge of a lid of the cavity is truncated, and wherein the truncation of the lid depends on the predefined frequency reconfigurability range.

10. The sound absorption device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, wherein an edge of the movable structure is truncated, and wherein the truncation of the movable structure depends on the predefined frequency reconfigurability range.

11. The sound absorption device of claim 1, wherein a lid of the cavity is conical.

12. The sound absorption device of claim 11, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the vertical distance between an inner edge of the lid to an outer edge of the lid is configured such that it depends on the predefined reconfigurability range.

13. The sound absorption device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein the horizontal distance between the center of the cavity to an outer edge of a lid of the cavity may depend on the predefined reconfigurability range.

14. The sound absorption device of claim 1, wherein the movable structure is configured to adjust the resonance frequency of the Helmholtz resonator within a predefined frequency reconfigurability range, and wherein a cavity base of the cavity is configured movable such that the movement depends on the frequency reconfigurability range.

15. The sound absorption device of claim 14, wherein the cavity base is an elastic membrane.

16. The sound absorbing device of claim 1, further includes an actuation mechanism configured to raise and lower the movable structure within the neck, allowing for adjustment of the resonance frequency.

17. A method for sound absorption with the sound absorbing device functioning as a Helmholtz resonator of claim 1, including the step of adjusting the resonance frequency of the Helmholtz resonator to achieve effective sound absorption by moving the movable structure.

18. The method of claim 17, wherein moving the movable structure includes adjusting the movable structure in height relative to the neck to alter the effective cross-sectional area of the neck, thereby reconfiguring the resonance frequency of the Helmholtz Resonator.

19. The method of claim 17, wherein the resonance frequency is adjusted within a predefined frequency reconfigurability range.Sony Group Corporation20. The method of claim 17, wherein the movable structure is moved by an actuation mechanism.

21. The method of claim 17, wherein a cavity base of the cavity is movable, and wherein adjusting the resonance frequency of the Helmholtz resonator includes moving the cavity base (2c, 23).

22. The method of claim 21, wherein the cavity base of the cavity is an elastic membrane.

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