SOUND ABSORBING DEVICE AND VEHICLE

Abstract

For example, a sound-absorbing device capable of handling noise in various frequency bands is provided, as well as a vehicle to which the sound-absorbing device is mounted. A sound-absorbing device comprises a plurality of acoustic metamaterials, each of the plurality of acoustic metamaterials having a plurality of sound-absorbing parts, and at least a first acoustic metamaterial and a second acoustic metamaterial of the plurality of acoustic metamaterials differ in target frequencies, which are sound frequencies to be absorbed.

Description

Sound absorbing device and vehicle

[0001] The present disclosure relates to a sound absorbing device and a vehicle.

[0002] Various noises propagate within the cabin of an automobile, such as engine noise, road noise, booming noise, and wind noise. Measures have been taken to combat these noises, taking into account the frequencies specific to the noises. For example, measures have been taken to combat relatively low-frequency noise such as engine noise by placing damping material around the engine. Furthermore, measures have been taken to combat noise propagated through the air within the cabin (noise with a mid- to wide-range frequency) by placing nonwoven fabric in appropriate locations within the cabin. Furthermore, Patent Document 1 listed below describes a technology for combating noise within the cabin, in which a sound-absorbing structure that absorbs standing waves is placed within the cabin.

[0003] Japanese Patent Application Laid-Open No. 2021-15207

[0004] The sound-absorbing structure described in Patent Document 1 has a problem in that it can only absorb noise in a specific frequency band. Generally, the frequency band of noise propagating within a vehicle cabin varies depending on the type of noise, the direction from which it is coming, etc. Therefore, a sound-absorbing device that can absorb noise in various frequency bands is desired.

[0005] An object of the present disclosure is to provide a sound absorbing device that can deal with noise in various frequency bands and a vehicle to which the sound absorbing device is applied.

[0006] The present disclosure relates to a sound absorbing device, for example, having a plurality of acoustic metallurgies, each of which has a plurality of sound absorbing sections, and at least a first acoustic metallurgies and a second acoustic metallurgies among the plurality of acoustic metallurgies have different target frequencies, which are the frequencies of the sounds to be absorbed.

[0007] The present disclosure relates to a vehicle, for example, having a plurality of acoustic metallurgies, each of which has a plurality of sound-absorbing sections, and at least a first acoustic metallurgies and a second acoustic metallurgies among the plurality of acoustic metallurgies have different target frequencies, which are the frequencies of the sounds to be absorbed.

[0008] FIG. 1 is a diagram schematically illustrating an example of the configuration of a sound absorbing device according to a first embodiment. FIG. 2 is a diagram for explaining an example of the configuration of an acoustic metallization according to the first embodiment. FIG. 3 is a diagram for explaining an example of the configuration of an acoustic metallization according to the first embodiment. FIG. 4 is a diagram for explaining an example of the components of a sound absorbing section according to the first embodiment. FIGS. 1A and 1B are diagrams for explaining an example of the cross-sectional shape of a sound absorbing section according to the first embodiment. FIG. 5 is a graph showing an example of the resonance frequency of each sound absorbing section. FIG. 6 is a graph based on a theoretical formula for explaining that a high sound absorption coefficient can be obtained in a desired frequency band. FIG. 7 is a graph based on a simulation for explaining that a high sound absorption coefficient can be obtained in a desired frequency band. FIG. 7 is a graph showing the sound absorption coefficient by simulation of an acoustic metallization used in a sound absorption experiment. FIG. 8 is a graph showing the sound absorption coefficient (actually measured value) of an acoustic metallization used in a sound absorption experiment. FIG. 9 is a diagram for explaining an example of the arrangement of a sound absorbing device according to a second embodiment. FIG. 10 is a diagram referred to when explaining how interior noise changes depending on the presence or absence of a sound absorbing device according to the second embodiment. FIG. 11 is a diagram showing an example of the installation of a group of acoustic metallizations in a vehicle according to a third embodiment. 10A is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 1, and FIG. 10B is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 2. FIG. 10A is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 3, and FIG. 10B is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 4. FIG. 10A is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 5, and FIG. 10B is a diagram illustrating an example of a sound pressure distribution corresponding to acoustic mode 6. FIG. 10B is a diagram illustrating an example of a frequency characteristic of a sound near a driver's seat obtained by a predetermined simulation. FIG. 10C is a diagram illustrating a method for measuring noise propagating inside a vehicle according to a fourth embodiment. FIG. 10D is a diagram illustrating reference data for noise measured in a vehicle according to a fourth embodiment. FIG. 10A and FIG. 10B are diagrams illustrating an example of a frequency characteristic of noise arriving from the roof side of a vehicle according to a fourth embodiment. FIG. 10C is a diagram illustrating an example of a frequency characteristic of noise arriving from the seat cushion side of a vehicle according to a fourth embodiment. FIG. 10D is a diagram illustrating an example of a frequency characteristic of noise arriving from the front window side of a vehicle according to a fourth embodiment.10A and 10B are diagrams for explaining an example of frequency characteristics of noise arriving from a front door window on the right side of a vehicle according to a fourth embodiment. 10A and 10B are diagrams for explaining an example of frequency characteristics of noise arriving from a front door window on the left side of a vehicle according to a fourth embodiment. 10B are diagrams for explaining an example of frequency characteristics of noise arriving from an A-pillar side on the left side of a vehicle according to a fourth embodiment. 10C are diagrams for explaining an example of frequency characteristics of noise arriving from an A-pillar side on the right side of a vehicle according to a fourth embodiment. 10D are diagrams for explaining an example of frequency characteristics of noise arriving from an A-pillar side on the right side of a vehicle according to a fourth embodiment. 10E are diagrams for explaining an example of frequency characteristics of noise arriving from a B-pillar side on the left side of a vehicle according to a fourth embodiment. 10F are diagrams for explaining an example of frequency characteristics of noise arriving from an upper side of an A-pillar on the left side of a vehicle according to a fourth embodiment. 10F are diagrams for explaining an example of frequency characteristics of noise arriving from a floor portion side on the left side of a vehicle according to a fourth embodiment. 10F are diagrams for explaining an example of frequency characteristics of noise arriving from a center console side of a vehicle according to a fourth embodiment. FIG. 10 is a diagram illustrating an example of frequency characteristics of noise coming from the headrest side of a vehicle according to the fourth embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The description will be made in the following order: <First Embodiment> <Second Embodiment> <Third Embodiment> <Fourth Embodiment> <Modification> The embodiments described below are preferred specific examples of the present disclosure, and the contents of the present disclosure are not limited to these embodiments. Note that the size and positional relationship of components shown in the drawings may be exaggerated for clarity. Furthermore, to prevent the illustrations from becoming too complicated, only some reference symbols may be shown, some parts may be simplified, or cross-sectional hatching may be omitted. Furthermore, in the following description, the same names and symbols indicate the same or similar components, and redundant description will be omitted as appropriate. Furthermore, for convenience of description, directions such as up, down, left, and right are defined, but the present disclosure is not limited to the directions in the description.

[0010] First Embodiment [Configuration Example of Sound-Absorbing Device] (Overview) First, the first embodiment will be described. The first embodiment relates to a sound-absorbing device having a plurality of acoustic metamaterials. Here, metamaterial means an artificially designed substance with properties that do not exist in nature, and acoustic metamaterial means a metamaterial for sound. A sound-absorbing device having acoustic metamaterials has high sound-absorbing performance and can be made lighter than steel, glass, rubber, etc.

[0011] Generally, interior noise propagating within a vehicle cabin (e.g., interior noise in a frequency band ranging from 20 to 10,000 Hz) tends to peak around 20 Hz and then decrease downward. Low-frequency interior noise (e.g., from 40 to 400 Hz) can be canceled by known active noise cancellation, which outputs a cancellation signal from a speaker. On the other hand, interior noise in the 200 to 1,000 Hz band may not be sufficiently canceled by active noise cancellation. As described below, the acoustic metallics of a sound-absorbing device can be appropriately adjusted to adjust the target frequency, which is the frequency of the sound to be absorbed. For example, by setting the target frequency near a frequency band where active noise cancellation is less effective (e.g., from 100 to 1,000 Hz), interior noise can be effectively reduced. An example of the configuration of a sound-absorbing device is described in detail below.

[0012] As shown in FIG. 1 , the sound absorbing device 1 has a plurality of acoustic metallurgies (acoustic metallurgies 10). In this embodiment, among the plurality of acoustic metallurgies 10, the target frequency of a predetermined first acoustic metallurgies 10 is different from the target frequency of a second acoustic metallurgies 10 that is different from the first acoustic metallurgies 10. Note that "the target frequencies of the acoustic metallurgies 10 are different" means that the target frequency ranges are different, and the target frequency ranges may be entirely different or may partially overlap. Furthermore, among the plurality of acoustic metallurgies 10, there may be acoustic metallurgies 10 that have the same target frequency.

[0013] (Configuration example of acoustic metallization) A configuration example of the acoustic metallization 10 of the sound absorbing device 1 will be described with reference to Figures 2 and 3. Figure 2 is a perspective view for explaining a configuration example of the acoustic metallization 10 of the sound absorbing device 1. Figure 3 is a cross-sectional view showing a cross section of the acoustic metallization 10 taken along the cutting line AA-AA in Figure 2.

[0014] The acoustic metallizer 10 has a box-shaped housing 11. The acoustic metallizer 10 has a plurality of sound absorbing sections formed inside the housing 11. The acoustic metallizer 10 shown in FIG. 2 has, for example, nine sound absorbing sections 21A, 21B, 21C, ... 21I. Note that when there is no need to distinguish between the individual sound absorbing sections, they may be simply referred to as sound absorbing sections 21. The nine sound absorbing sections 21 are arranged, for example, in a matrix pattern inside the housing 11. Note that this is just an example, and the number of sound absorbing sections 21 may be other than nine.

[0015] The sound absorbing section 21 is configured as, for example, a Helmholtz resonator. Specifically, the sound absorbing section 21 has a tubular neck with both open ends and a closed cavity communicating with the neck. Generally, the volume of the cavity is set to be larger than the volume of the neck. When sound is taken in through the opening of the neck, air in the neck is forced into the cavity, and the air forced into the cavity increases the pressure inside the cavity, which then tries to push the air back out again. This action is repeated alternately, causing the Helmholtz resonator to vibrate and produce sound. A Helmholtz resonator has the effect of absorbing the kinetic energy of sound, mainly of the sound it is resonating with (sound at the resonant frequency), and this effect produces a sound absorption effect.

[0016] As shown in FIG. 3 , for example, the sound absorbing unit 21A has a cylindrical tubular neck portion 221A and a cavity portion 222A, which is a closed space formed within the housing 11 and communicates with the neck portion 221A. The neck portion 221A has a first opening 223A, which is an open end facing the outside of the housing 11, and a second opening 224A (located within the cavity portion 222A) on the opposite side. Sound captured through the first opening 223A is absorbed by the Helmholtz resonance principle described above. Note that, although the neck portion 221A has a cylindrical tubular shape in this embodiment, it may have other shapes, such as a triangular prism or a square prism. Furthermore, the shapes of the first opening 223A and the second opening 224A do not have to be circular, but may be triangular or square. Furthermore, although the cavity portion 222A has a box-like shape in this embodiment, it may also have other shapes, such as a spherical shape. However, from the viewpoint of arranging a plurality of sound absorbing parts 21, it is preferable that the shape of cavity 222A be a cube or a rectangular parallelepiped. The same applies to the neck parts, cavity parts, first openings, and second openings of the other sound absorbing parts 21.

[0017] Similarly, sound absorbing section 21B has a cylindrical tubular neck section 221B and a hollow section 222B that communicates with neck section 221B and is a closed space formed within housing 11. Neck section 221B has a first opening 223B that is an end that opens to the outside of housing 11, and a second opening 224B (located within hollow section 222B) on the opposite side. Sound absorbing section 21C has a cylindrical tubular neck section 221C and a hollow section 222C that communicates with neck section 221C and is a closed space formed within housing 11. Neck section 221C has a first opening 223C that is an end that opens to the outside of housing 11, and a second opening 224C (located within hollow section 222C) on the opposite side. In addition, when there is no need to distinguish between the neck portion, hollow portion, first opening, and second opening of each sound-absorbing portion 21, they will be collectively referred to as the neck portion 221, hollow portion 222, first opening 223, and second opening 224 as appropriate.

[0018] The acoustic metallizer 10 can be obtained, for example, by molding a resin material using a 3D printer or mold. However, the material of the acoustic metallizer 10 is not limited to resin. The material of the acoustic metallizer 10 may be metal, wood, foam material, etc. However, since the sound-absorbing device 1 including the acoustic metallizer 10 may be installed in a vehicle, etc., it is preferable that the material be lightweight. The applicant of the present application has previously filed European Patent Application No. 22164643.3 for a Helmholtz resonator and an acoustic metallizer having a Helmholtz resonator. The matters disclosed in that patent application are applicable to the present application.

[0019] (Sound-Absorbing Section Characteristics) In this embodiment, the nine sound-absorbing sections 21 that make up the acoustic metallic 10 have slightly different resonant frequencies. As shown in FIG. 4 , when the sound-absorbing section 21 is viewed in cross section, the length of the neck portion 221 is D1, the diameter of the first opening is W1, and the diameter of the second opening is W2. For example, by making at least one of D1, W1, and W2 of each sound-absorbing section 21 different, the resonant frequencies of each sound-absorbing section 21 can be made different. The cross-sectional shape of each sound-absorbing section 21 may also be changed. For example, as shown in FIG. 5A , when the sound-absorbing section 21 is viewed in cross section, the shape from the first opening 223 to the second opening 224 can be made convex tapered, slightly curved, rather than straight, or as shown in FIG. 5B , the resonant frequency can also be changed by making the shape slightly concave tapered, slightly curved, from the first opening 223 to the second opening 224.

[0020] The graph in Figure 6 shows an example of the resonant frequency of each sound absorbing section 21. The horizontal axis of the graph in Figure 6 is frequency, and the vertical axis is acoustic impedance, which indicates the ease of sound propagation. The dips in each line shown in Figure 6 correspond to the resonant frequency of each sound absorbing section 21. As such, the resonant frequencies of the sound absorbing sections 21A to 21I that make up the acoustic metallic 10 are slightly different.

[0021] Fig. 7 is a graph of the resonance frequencies obtained by applying the known theoretical formula of the Helmholtz resonator to each sound absorbing section 21. In the graph of Fig. 7, the horizontal axis represents frequency, and the vertical axis represents sound absorption coefficient. The relationship between resonance frequency and sound absorption coefficient obtained by acoustic simulation using a computer is shown in the graph of Fig. 8, which combines the sound absorption characteristics of each sound absorbing section 21. In the graph of Fig. 8, the horizontal axis represents frequency, and the vertical axis represents sound absorption coefficient. As shown in the graphs of Figs. 7 and 8, by slightly shifting the resonance frequencies of each sound absorbing section 21, it is possible to achieve a high sound absorption coefficient in the required frequency band.

[0022] For example, with the acoustic metallic 10 according to this example, a sound absorption coefficient of 0.5 or more can be obtained in the frequency band (220 to 320 Hz) enclosed by the frame AR shown in the graph of FIG. 8, and further, a high sound absorption coefficient of 0.8 or more can be obtained in the range of 260 Hz to 280 Hz.

[0023] [Sound Absorption Experiment Results] Next, the results of a sound absorption experiment using an actual acoustic metallization will be described. The acoustic metallization was configured with 8 sound absorbing sections (64 sections) arranged vertically and 8 sections horizontally within a housing (15 cm long, 15 cm wide, and 3 cm high). As described above, the resonant frequencies of the 64 sound absorbing sections were set to be slightly different. The sound absorption coefficient of the manufactured acoustic metallization was measured through the sound absorption experiment. A known sound absorption experiment can be used for the sound absorption experiment. In this example, a cylindrical sound conduit is prepared, and a speaker is placed at the end. The manufactured acoustic metallization is placed at a predetermined position within the sound conduit (on the propagation path of the sound reproduced from the speaker), and microphones are placed before and after the acoustic metallization. A test sound is then reproduced from the speaker, and the sound pressure of the test sound is measured with the microphones before and after the test sound passes through the location where the acoustic metallization is placed. The sound absorption coefficient (vertical sound absorption coefficient) is obtained by measuring the sound pressure loss. The target frequency of the acoustic metallization was set to the lowest frequency band (250 to 330 Hz) among the target frequencies at which efficient production of the acoustic metallization becomes difficult.

[0024] Figure 9 shows the sound absorption coefficient obtained by computer simulation for the manufactured acoustic metallic. In Figure 9, the horizontal axis represents frequency and the vertical axis represents sound absorption coefficient. The computer simulation shows that the acoustic metallic has a high sound absorption coefficient of 0.8 or more at the target frequency of 250 Hz to 350 Hz.

[0025] FIG. 10 shows the results (measured values) of a sound absorption experiment. The horizontal axis in FIG. 10 represents frequency, and the vertical axis represents sound absorption coefficient. Furthermore, line L1 in FIG. 10 represents the results of a sound absorption experiment in which acoustic metallization was provided, and line L2 represents the results of a sound absorption experiment in which acoustic metallization was not provided. As shown in FIG. 10 , comparing line L1 and line L2, it can be seen that line L1 has a higher sound absorption coefficient than line L2 in the target frequency range. In other words, it can be seen that a high sound absorption coefficient is achieved by the acoustic metallization of this embodiment. Furthermore, as shown by line L1, it can be seen that within the target frequency range, the results are substantially similar to the simulation results (sound absorption coefficient of approximately 0.8 or more).

[0026] In this way, the sound absorbing device having the acoustic metallization according to this embodiment can obtain a high sound absorption coefficient in a desired frequency band. By adjusting the shape of the sound absorbing part, the target frequency of the acoustic metallization can be appropriately set, making it possible to respond to noise in various frequency bands.

[0027] <Second Embodiment> Next, a second embodiment will be described. In the description of the second embodiment, the same or similar components as those in the above description will be denoted by the same reference numerals, and duplicated descriptions will be omitted as appropriate. Furthermore, unless otherwise specified, the matters described in the first embodiment can be applied to the second embodiment. The same applies to other embodiments such as the third embodiment.

[0028] The second embodiment is an embodiment in which a sound absorbing device is installed in a vehicle. The sound absorbing device (sound absorbing device 1A) according to the second embodiment has a configuration substantially similar to the sound absorbing device 1 described in the first embodiment. That is, the sound absorbing device 1A has a plurality of acoustic metallizers 10. Specifically, the sound absorbing device 1A according to this embodiment has a configuration in which approximately 40 to 50 acoustic metallizers 10 are arranged. The acoustic metallizer 10 according to this embodiment is configured, for example, with eight sound absorbing sections 21 arranged vertically and eight sound absorbing sections arranged horizontally within a housing measuring 15 cm in length, 15 cm in width, and 3 cm in height (64 sound absorbing sections 21). As with the first embodiment, the resonance frequencies of the sound absorbing sections 21 are slightly different. Specifically, the shape of each sound absorbing section 21 is adjusted so that the target frequency range of the acoustic metallizer 10 is 250 to 350 Hz.

[0029] In this embodiment, a sound-absorbing device 1A was arranged inside a vehicle cabin through a computer-based simulation. Specifically, as shown in Fig. 11 , a vehicle 30 having a predetermined shape was set up, and multiple acoustic metallics 10 of the sound-absorbing device 1A according to this embodiment were uniformly arranged on a roof portion 31 of the vehicle 30. In Fig. 11 , the sound-absorbing device 1A arranged in the vehicle 30 is indicated by diagonal lines. Then, interior noise propagating inside the vehicle 30 was set up on a computer, and a simulation was performed to determine how the interior noise changed depending on whether or not the sound-absorbing device 1A was present.

[0030] Figure 12 shows the simulation results. The horizontal axis of the graph in Figure 12 represents frequency, and the vertical axis represents the sound pressure of interior noise. Furthermore, line L3 in Figure 12 represents the simulation results for an example in which acoustic metallic 10 is present, i.e., the case in which sound-absorbing device 1A is installed in vehicle 30, and line L4 represents the simulation results for an example in which acoustic metallic 10 is not present, i.e., the case in which sound-absorbing device 1A is not installed in vehicle 30.

[0031] As shown in Figure 12, comparing line L3 and line L4 in the target frequency range of 250 to 350 Hz for sound-absorbing device 1A, it can be seen that line L3 provides a lower sound pressure for interior noise. Specifically, interior noise around 300 Hz is reduced by about 10 dB. In other words, by arranging sound-absorbing device 1A having multiple acoustic metallics 10 on roof portion 31 of vehicle 30, interior noise propagating within the cabin of vehicle 30 can be effectively reduced. Furthermore, interior noise in the 250 to 350 Hz frequency range is difficult to reduce using active noise cancellation, but sound-absorbing device 1A can effectively reduce interior noise in this frequency range.

[0032] <Third Embodiment> The third embodiment is an embodiment in which a sound absorbing device is installed in a vehicle, similar to the second embodiment. In this embodiment, the sound absorbing device has an acoustic metallurgical group consisting of a plurality of acoustic metallurgicals. The acoustic metallurgical 10 described in the first embodiment or an acoustic metallurgical having a similar configuration can be used as the acoustic metallurgical. In this embodiment, the plurality of acoustic metallurgical groups are not uniformly installed at predetermined locations on the vehicle, but are installed at separate locations on the vehicle 30. The acoustic metallurgical group is built into predetermined locations on a component (body) of the vehicle.

[0033] 13 is a diagram showing an example of the installation of an acoustic metallic group on a vehicle 30. For example, an acoustic metallic group 41A is installed on the roof portion 31 of the vehicle 30. The acoustic metallic group 41A is installed on the roof portion 31 so that the first openings of the acoustic metallic members constituting the acoustic metallic group 41A face downward. The acoustic metallic group 41A has a configuration in which a total of 48 acoustic metallic members are arranged in a matrix, for example, eight in the front-rear direction of the vehicle 30 and six in the left-right direction of the vehicle 30.

[0034] Additionally, an acoustic metallic group 41B is installed above the front door 32 of the vehicle 30. The acoustic metallic group 41B is installed above the front door 32 so that the first openings of the acoustic metallic elements that make up the acoustic metallic group 41B face inward (toward the vehicle compartment). Note that an acoustic metallic group having a shape similar to that of the acoustic metallic group 41B is also installed above the front door on the opposite side, which is not shown in Fig. 13. The acoustic metallic group 41B has a configuration in which, for example, four acoustic metallic elements are arranged in the longitudinal direction of the vehicle 30 and two acoustic metallic elements are arranged in the vertical direction of the vehicle 30, for a total of eight acoustic metallic elements, in a matrix form.

[0035] Additionally, an acoustic metallic group 41C is installed on the underside of the front door 32 of the vehicle 30. The acoustic metallic group 41C is installed on the underside of the front door 32 so that the first openings of the acoustic metallic elements that make up the acoustic metallic group 41C face inward (toward the vehicle compartment). Note that an acoustic metallic group having a similar shape to the acoustic metallic group 41C is also installed on the underside of the opposite front door, which is not shown in Fig. 13. The acoustic metallic group 41C has a configuration in which a total of three acoustic metallic elements are arranged in a matrix, for example, three in the front-to-rear direction of the vehicle 30 and one in the up-to-down direction of the vehicle 30.

[0036] Additionally, an acoustic metallic group 41D is installed on the rear door 33 of the vehicle 30. The acoustic metallic group 41D is installed on the rear door 33 so that the first openings of the acoustic metallic elements that make up the acoustic metallic group 41D face inward (toward the passenger compartment). Note that an acoustic metallic group having a shape similar to that of the acoustic metallic group 41D is also installed on the rear door on the opposite side, which is not shown in Fig. 13. The acoustic metallic group 41D has a configuration in which, for example, four acoustic metallic elements are arranged in the front-to-rear direction of the vehicle 30 and three acoustic metallic elements are arranged in the up-to-down direction of the vehicle 30, for a total of 12 acoustic metallic elements, in a row.

[0037] Additionally, acoustic metallurgical group 41E is installed on hat tray 34, which is a flat area behind the rear seats of vehicle 30. Acoustic metallurgical group 41E is installed on hat tray 34 so that the first openings of the acoustic metallurgical members constituting acoustic metallurgical group 41E face upward (toward roof portion 31). Acoustic metallurgical group 41E has a configuration in which a total of 12 acoustic metallurgical members are arranged in a matrix, for example, two in the front-to-rear direction of vehicle 30 and six in the left-to-right direction of vehicle 30.

[0038] Generally, standing waves are generated in a vehicle interior due to the influence of acoustic modes specific to the vehicle shape, and these standing waves cause peaks (antinodes of the standing waves) and dips (nodes of the standing waves) in the frequency characteristics, for example, at the driver's seat. The frequencies at which these peaks and dips occur have a negative impact on the acoustic environment inside the vehicle, including sound reproduction and interior noise.

[0039] The magnitude and frequency of standing waves generated at predetermined locations within the vehicle cabin according to the acoustic mode can be measured by simulation. Figure 14A shows the results of a simulation of the sound pressure distribution of a specific acoustic mode 1, specifically, a first-order standing wave propagating from the front to the rear of the vehicle 30. Reference symbol WN indicates a location corresponding to a node of the standing wave. The simulation results shown in Figure 14A reveal that the areas indicated by the four black circles, such as the roof portion above the front seats, the hat tray, and areas near their bottom, are antinodes of the standing wave (areas where sound pressure is high). By placing the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by standing waves can be reduced.

[0040] Figure 14B shows the results of a simulation of the sound pressure distribution of a primary standing wave propagating in the left-right direction of the front seats of the vehicle 30, specifically, the inherent acoustic mode 2. As in Figure 14A, reference symbol WN indicates a location corresponding to a node of the standing wave. The simulation results shown in Figure 14B reveal that the locations indicated by the three black circles, namely the upper roof portion near the front seats (excluding the area near the center) and the area near the front doors, are antinodes of the standing wave (locations where sound pressure is high). By arranging the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by the standing wave can be reduced.

[0041] 15A shows the results of a simulation of the sound pressure distribution of a second-order standing wave propagating from the front to the rear of the vehicle 30, specifically, the inherent acoustic mode 3. As in FIG. 14A and other figures, the reference symbols WN (two locations) indicate the locations corresponding to the nodes of the standing wave. From the simulation results shown in FIG. 15A , it can be seen that the locations indicated by the four black circles, namely, the floor portion of the front seats, the roof portion above the rear seats, the vicinity of the lower sides of the rear doors, and the vicinity of the lower rear of the vehicle 30, are the antinodes of the standing wave (locations where sound pressure is high). By arranging the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by the standing wave can be reduced.

[0042] Figure 15B shows the results of a simulation of the sound pressure distribution of a primary standing wave propagating in the vertical direction of the front seat of the vehicle 30, specifically, the inherent acoustic mode 4. As in Figure 14A and other figures, the reference symbols WN (two locations) indicate the locations corresponding to the nodes of the standing wave. The simulation results shown in Figure 15B reveal that the locations indicated by the two black circles near the floor and roof of the front seat are antinodes of the standing wave (locations where sound pressure is high). By arranging the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by the standing wave can be reduced.

[0043] Figure 16A shows the results of a simulation of the sound pressure distribution of a primary standing wave propagating in the left-right direction of the rear seat of a vehicle 30, specifically, a characteristic acoustic mode 5. As with Figure 14A and other figures, reference symbols WN indicate locations corresponding to nodes of the standing wave. The simulation results shown in Figure 16A reveal that the areas indicated by the three black circles, namely the rear seat and the roof portion above it (excluding the area near the center) and the area near the rear door, are antinodes of the standing wave (areas where sound pressure is high). By arranging the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by the standing wave can be reduced.

[0044] Figure 16B shows the results of a simulation of the sound pressure distribution of a tertiary standing wave propagating from the front to the rear of the vehicle 30, which is a characteristic acoustic mode 6. As with Figure 14A and other figures, the reference symbols WN (three locations) indicate the locations corresponding to the nodes of the standing wave. The simulation results shown in Figure 16B reveal that the locations indicated by the three black circles, namely the floor portion of the rear seat, the roof portion above the rear seat, and the areas below the same, are the antinodes of the standing wave (locations where sound pressure is high). By arranging the acoustic metallics of the sound-absorbing device in these locations, the adverse effects caused by the standing wave can be reduced.

[0045] The frequency of the standing wave can also be measured by simulation. The graph shown in Fig. 17 shows an example of the frequency characteristics of sound measured at the front seat (for example, the driver's seat side). The horizontal axis in Fig. 17 represents frequency, and the vertical axis represents sound pressure. The graph shown in Fig. 17 is a result of combining the frequency characteristics of the sound measured at the driver's seat during the simulation of the above-mentioned acoustic modes 1 to 6.

[0046] As described above, unlike general sound-absorbing materials, the acoustic metallurgy according to the present disclosure (for example, the acoustic metallurgy 10) can be set to have a target frequency within any frequency range. That is, instead of uniformly installing acoustic metallurgy with the same target frequency as in the second embodiment, efficient standing wave elimination can be achieved by installing acoustic metallurgy with a target frequency equal to the frequency of the standing wave at the antinode of the amplitude (the area surrounded by a black circle in FIGS. 14 to 16).

[0047] For example, in the case of the driver's seat, acoustic metallization with a target frequency of around 200 to 450 Hz is installed near the roof portion 31 above the driver's seat and the front door 32. Furthermore, for example, let us assume that a simulation shows that the sound pressure of sounds in the 150 to 300 Hz range is high near the roof portion 31 above the rear seat and the rear door 33, in other words, that these locations are the antinodes of the standing wave. In this case, acoustic metallization with a target frequency of around 150 to 300 Hz is installed on the roof portion 31 above the rear seat, and acoustic metallization with a target frequency of around 150 to 300 Hz is installed on the rear door 33. This effectively reduces the adverse effects of standing waves propagating within the cabin of the vehicle 30.

[0048] Fourth Embodiment In this embodiment, an acoustic metallization or a group of acoustic metallizations is provided at a position corresponding to the direction of noise arrival in a vehicle. For example, an acoustic metallization having a target frequency corresponding to the frequency of the noise and the sound pressure for each frequency, or a group of acoustic metallizations having a plurality of such acoustic metallizations, is provided at a position corresponding to the direction of noise arrival. Here, the direction of noise arrival, frequency, and sound pressure can be obtained by measurement. The measurement may be a computer-based simulation, or may be an actual measurement performed while the vehicle is traveling. In this embodiment, the description will be given assuming that the direction of noise arrival, frequency, and sound pressure are obtained by measurement performed while the vehicle is traveling.

[0049] For example, as shown in Fig. 18, a microphone 61 is installed at the passenger seat position in a vehicle 50. The microphone 61 has a configuration in which multiple microphones (for example, 19 channels) are arranged radially on the surface of a spherical housing. The direction from which noise comes can be distinguished depending on the position of each microphone.

[0050] In the measurements, the 1 / 3 octave band characteristics of noise NS0 in the seatback direction (the direction coming from the rear seat 51), which had the lowest noise level among the noises measured by all 19 microphone channels, were used as a reference. In FIG. 18, the noise NS0 is shown schematically with a diagonal line. FIG. 19 shows the frequency characteristics of noise NS0 set as the reference. The horizontal axis of FIG. 19 represents frequency, and the vertical axis represents sound pressure. The reference frequency characteristics peak between 80 and 250 Hz, with values ​​approximately 30 dB lower at 1 kHz and above. Note that the microphone used in this measurement has a reduced sensitivity below 80 Hz, making the characteristics less accurate, so data below 80 Hz was not used.

[0051] Fig. 20A is a diagram schematically showing noise NS1 arriving from the roof portion 52 side of vehicle 50. Fig. 20B shows the frequency characteristics of noise picked up by one of microphones 61 facing upward, i.e., noise NS1 arriving from the roof portion 52 side of vehicle 50. The solid line in Fig. 20B shows the frequency characteristics of noise NS1 arriving from the roof portion 52 side, and the dotted line shows the frequency characteristics of the reference. Fig. 20B shows that the sound pressure of noise NS1 arriving from the roof portion 52 side increases by 1 to 2 dB in the range of 100 to 400 Hz.

[0052] Fig. 21A is a diagram schematically showing noise NS2 arriving from the seat cushion 51A side of the rear seat 51 of the vehicle 50. Fig. 21B shows the frequency characteristics of noise picked up by one of the microphones 61 facing downward, i.e., noise NS2 arriving from the seat cushion 51A side of the rear seat 51. The solid line in Fig. 21B shows the frequency characteristics of noise NS2 arriving from the seat cushion 51A side, and the dotted line shows the frequency characteristics of the reference. Fig. 21B shows that the sound pressure of noise NS2 arriving from the seat cushion 51A side is increased by 1 to 2 dB in the range of 150 to 250 Hz relative to the reference.

[0053] Noise NS1 arriving from the roof portion 52 side is reflected by the seat cushion 51A, etc., and reaches the acoustic metallurgy (actually, a group of acoustic metallurgy consisting of multiple acoustic metallurgy) installed on the roof portion 52. Furthermore, noise NS2 arriving from the seat cushion 51A side reaches the acoustic metallurgy installed on the roof portion 52. Therefore, the acoustic metallurgy to be installed on the roof portion 52 of the vehicle 50 is determined using the measurement results shown in Figures 20B and 21B. That is, based on the measurement results of Figures 20B and 21B, an acoustic metallurgy having a target frequency in a frequency band (for example, 150 to 250 Hz) that includes a frequency band that is significantly different from the reference is installed on the roof portion 52 of the vehicle 50.

[0054] Fig. 22A is a diagram schematically showing noise NS3 arriving from the windshield 53 side of vehicle 50. Fig. 22B shows the frequency characteristics of noise picked up by one of microphones 61 facing the windshield 53 side, i.e., noise NS3 arriving from the windshield 53 side. The solid line in Fig. 22B shows the frequency characteristics of noise NS3, and the dotted line shows the frequency characteristics of the reference. Fig. 22B shows that the sound pressure of noise NS3 is increased by 3 to 5 dB in the range of 150 Hz to 400 Hz compared to the reference.

[0055] Noise NS3 arriving from the front window 53 side reaches the acoustic metallic installed in the hat tray 54. Therefore, the measurement results shown in Fig. 22B are used to determine the acoustic metallic to be installed in the hat tray 54 of the vehicle 50. That is, based on the measurement results in Fig. 22B, an acoustic metallic with a target frequency in a frequency band (for example, 150 to 400 Hz) that includes a frequency band that is significantly different from the reference is installed in the hat tray 54.

[0056] Fig. 23A is a diagram schematically showing noise NS4 arriving from the front right window 56 side of vehicle 50. Fig. 23B also shows the frequency characteristics of noise picked up by one of microphones 61 facing right, i.e., noise NS4 arriving from the front right window 56 side of vehicle 50. The solid line in Fig. 23B shows the frequency characteristics of noise NS4 arriving from the right window 56 side, and the dotted line shows the frequency characteristics of the reference. Fig. 23B shows that the sound pressure of noise NS4 arriving from the front right window 56 side is increased by 1 to 2 dB in the range of 100 to 400 Hz compared to the reference.

[0057] Fig. 24A is a diagram schematically showing noise NS5 arriving from the front left window 57 side of vehicle 50. Fig. 24B also shows the frequency characteristics of noise picked up by one of microphones 61 facing left, i.e., noise NS5 arriving from the front left window 57 side of vehicle 50. The solid line in Fig. 24B shows the frequency characteristics of noise NS5 arriving from the front left window 57 side, and the dotted line shows the frequency characteristics of the reference. Fig. 25B shows that noise NS4 arriving from the front left window 57 side has a sound pressure that is 5 to 10 dB higher across almost the entire range compared to the reference.

[0058] The reflected components of noise NS4 and noise NS5 reach the acoustic metallic installed in the left front door 58A. Furthermore, the reflected components of noise NS4 and noise NS5 reach the acoustic metallic installed in the right front door 58B. Therefore, the acoustic metallic to be installed in each of front doors 58A and 58B is determined using the measurement results shown in FIGS. 23B and 24B. That is, based on the measurement results in FIGS. 23B and 24B, acoustic metallics with target frequencies in a frequency band (e.g., 200 to 500 Hz) that includes a frequency band where it is difficult to obtain the effect of active noise cancellation and where there is a large difference from the reference frequency are installed in each of front doors 58A and 58B.

[0059] In this way, by installing acoustic metallization having a target frequency suitable for absorbing noise at a position corresponding to the direction from which the noise propagates inside the vehicle cabin, specifically at the position to which the noise propagates, it is possible to reduce interior noise including components other than standing waves, and effectively improve the sound field environment inside the vehicle cabin.

[0060] Data other than the measurement data described above may be used when considering the target frequency of the acoustic metallic. FIG. 25 shows the frequency characteristics of noise arriving from the left A-pillar side. FIG. 26 shows the frequency characteristics of noise arriving from the right A-pillar side. FIG. 27 shows the frequency characteristics of noise arriving from the left B-pillar side. FIG. 28 shows the frequency characteristics of noise arriving from above the left A-pillar. FIG. 29 shows the frequency characteristics of noise arriving from the underside (door trim) of the left front door 58A. At least one of the frequency characteristics of noise shown in FIGS. 25 to 29 may be taken into consideration, and acoustic metallic having a target frequency that can effectively absorb noise having the considered frequency characteristics may be installed on the front door 58A, etc.

[0061] 30 shows the frequency characteristics of noise coming from the right rear window side. An acoustic metallic having a target frequency that can effectively absorb noise having this frequency characteristic may be installed in the rear door.

[0062] 31 shows the frequency characteristics of noise coming from the left floor section, and FIG. 32 shows the frequency characteristics of noise coming from the center console. Taking into consideration at least one of these frequency characteristics of noise, acoustic metallization having a target frequency that can effectively absorb noise having the considered frequency characteristics may be installed in the roof section 52.

[0063] 33 shows the frequency characteristics of noise coming from the headrest side. To effectively absorb noise having this frequency characteristic, an acoustic metallic may be installed on the dashboard, for example. Specifically, an acoustic metallic having a target frequency that can effectively absorb noise having the frequency characteristic shown in FIG. 33 may be installed on the dashboard.

[0064] <Modifications> Although the embodiments of the present disclosure have been specifically described above, the contents of the present disclosure are not limited to the above-described embodiments, and various modifications based on the technical ideas of the present disclosure are possible.

[0065] In the above-described embodiment, an example in which the sound absorbing device is mainly applied to a vehicle has been described, but the sound absorbing device according to the present disclosure can be applied not only to a vehicle but also to closed spaces such as listening rooms and movie theaters.

[0066] The configurations, methods, steps, shapes, materials, and values ​​described in the above-described embodiments are merely examples, and different configurations, methods, steps, shapes, materials, and values ​​may be used as needed. The above-described embodiments and modifications can be combined as appropriate.

[0067] The present disclosure may also adopt the following configurations. (1) A sound absorbing device comprising a plurality of acoustic metallurgies, each of which comprises a plurality of sound absorbing sections, wherein at least a first acoustic metallurgie and a second acoustic metallurgie among the plurality of acoustic metallurgies have different target frequencies, which are the frequencies of sounds to be absorbed. (2) The sound absorbing device described in (1), wherein the sound absorbing sections have different resonant frequencies. (3) The sound absorbing device described in (1) or (2), wherein the sound absorbing sections have a neck section and a cavity section communicating with the neck section. (4) The sound absorbing device described in (3), wherein the neck section has a first opening section that is an open end and a second opening section disposed on the cavity section side, and wherein the plurality of sound absorbing sections differ from each other in at least one of the diameter of the first opening section, the diameter of the second opening section, the length of the neck section, and the cross-sectional shape of the neck section. (5) The sound absorbing device described in any of (1) to (4), wherein the acoustic metallurgies have a plurality of the sound absorbing sections arranged in a matrix. (6) The sound absorbing device according to any one of (1) to (5), wherein the sound absorption coefficient of the acoustic metallurgy at the target frequency is 0.8 or more. (7) A vehicle comprising a plurality of acoustic metallurgy, wherein the acoustic metallurgy has a plurality of sound absorbing sections, and wherein at least a first acoustic metallurgy and a second acoustic metallurgy among the plurality of acoustic metallurgy have different target frequencies, which are the frequencies of sounds to be absorbed. (8) The vehicle according to (7), wherein the plurality of acoustic metallurgy are provided on a roof section. (9) The vehicle according to (7) or (8), wherein the acoustic metamaterial is provided at a position in the vehicle interior where the amplitude of a standing wave becomes large. (10) The vehicle according to (7) or (8), wherein the acoustic metallurgy is provided at a position corresponding to the direction from which noise propagating into the vehicle interior comes. (11) The vehicle according to (10), wherein the acoustic metallurgy is provided at a position in the vehicle interior to which the noise propagates. (12) The vehicle according to (11), further comprising an acoustic metallic element having a target frequency corresponding to the direction, frequency, and sound pressure of the noise.(12) The vehicle according to (11), wherein the noise arrival direction and the noise frequency are obtained by measurement.

[0068] REFERENCE SIGNS LIST 1... sound absorbing device 10... acoustic metallic 21... sound absorbing part 30, 50... vehicle 31... roof part 221... neck part 222... cavity part 223... first opening 224... second opening

Claims

1. A sound absorbing device comprising a plurality of acoustic metallurgies, each of which has a plurality of sound absorbing sections, and at least a first acoustic metallurgies and a second acoustic metallurgies among the plurality of acoustic metallurgies have different target frequencies, which are the frequencies of the sounds to be absorbed.

2. The sound absorbing device according to claim 1, wherein the resonance frequencies of the sound absorbing parts are different.

3. The sound absorbing device according to claim 1, wherein the sound absorbing portion has a neck portion and a cavity portion communicating with the neck portion.

4. The sound absorbing device according to claim 3, wherein the neck portion has a first opening which is an open end and a second opening which is disposed on the hollow portion side, and the plurality of sound absorbing portions are different from each other in at least one of the diameter of the first opening, the diameter of the second opening, the length of the neck portion, and the cross-sectional shape of the neck portion.

5. The sound absorbing device according to claim 1, wherein the acoustic metallization has a plurality of the sound absorbing portions arranged in a matrix.

6. The sound absorbing device according to claim 1, wherein the sound absorption coefficient of the acoustic metallization at the target frequency is 0.8 or more.

7. A vehicle having a plurality of acoustic metallurgies, each of the acoustic metallurgies having a plurality of sound absorbing sections, and at least a first acoustic metallurgies and a second acoustic metallurgies among the plurality of acoustic metallurgies have different target frequencies, which are the frequencies of the sounds to be absorbed.

8. The vehicle according to claim 7, wherein the plurality of acoustic metallics are provided on a roof portion.

9. The vehicle according to claim 7, wherein the acoustic metamaterial is provided in a position in the vehicle interior where the amplitude of standing waves is large.

10. The vehicle according to claim 7, wherein the acoustic metallic is provided at a position corresponding to the direction from which noise propagating within the vehicle compartment comes.

11. The vehicle according to claim 10, wherein the acoustic metallic is provided at a position in the vehicle interior to which the noise propagates.

12. The vehicle according to claim 11, further comprising an acoustic metallic device having a target frequency according to the direction, frequency and sound pressure of the noise.

13. The vehicle according to claim 12, wherein the direction of arrival of the noise and the frequency of the noise are the direction of arrival and frequency obtained by measurement.

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