Patent Publication Number: US-2021162936-A1

Title: Partition member, vehicle, and electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2019/027693 filed on Jul. 12, 2019, which claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-153445 filed on Aug. 17, 2018. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a partition member including a soundproof structure, and a vehicle and an electronic device provided with the partition member, and more particularly to a partition member including a soundproof structure that absorbs a sound by a resonance structure formed by a membrane-like member and a rear surface space, and a vehicle and an electronic device provided with the partition member. 
     2. Description of the Related Art 
     In building materials, vehicles, and the like, a sound that shakes and comes through (is transmitted by) a wall becomes a problem as noise in many cases. In particular, noise of a single frequency sound is uncomfortable (harsh) to humans, and it is necessary to take measures. However, in a silencing method in the related art using a porous sound absorbing body, there are cases where the single frequency sound is not sufficiently reduced. 
     Another silencing method is to use a soundproof structure that adopts a resonance structure formed of a vibrating body. The resonance structure includes the vibrating body, a support body that supports the vibrating body in a vibrating manner, and a rear surface plate fixed to the support body on the side opposite to the vibrating body. In the above resonance structure, a sound absorbing mechanism is formed in which the vibrating body is a mass spring component and a rear surface space surrounded by the vibrating body, the support body, and the rear surface plate is an air spring component. The soundproof structure adopting this resonance structure is provided, for example, on a partition member such as a wall, and is used with a resonance frequency that matches the frequency of noise emitted from a sound source provided on one side of two spaces partitioned by the partition member. Accordingly, it is possible to selectively absorb a sound having a specific frequency (that is, the same frequency as the resonance frequency). 
     An example of the resonance structure described above is a resonance structure described in JP2016-170194A. JP2016-170194A discloses a sound absorbing body including a diaphragm that receives a sound wave from an external sound source and resonates, and a frame body that supports an end portion of the diaphragm and surrounds an air layer. According to the resonance structure described in JP2016-170194A, it is possible to selectively absorb a sound having a frequency that matches a resonance frequency. 
     In addition, a resonance structure that achieves soundproofing at a frequency different from a resonance frequency is already known, and examples thereof include a resonance structure disclosed in JP1998-205351A (JP-H10-205351A). JP1998-205351A (JP-H10-205351A) discloses a resonator having a diaphragm connected to a noise generating vibrating body (corresponding to a sound source of noise) via a connecting mechanism or the like. According to this resonator, in a case where the noise generating vibrating body vibrates and generates noise, the diaphragm vibrates and the volume inside the resonator changes. Here, at a frequency higher than the resonance frequency of the resonator, the sound radiated from the resonator and the noise emitted from the noise generating vibrating body are in antiphase, so that these sounds cancel each other out and silenced. 
     SUMMARY OF THE INVENTION 
     However, regarding the performance of a soundproof structure, there are cases where the soundproofing performance by sound insulation is required rather than the soundproofing performance by sound absorption. On the other hand, the resonance structure described in JP2016-170194A mainly reduces noise by sound absorption, and the sound insulation effect thereof is unknown. 
     In addition, in the resonance structure in which the membrane-like member is supported by the support body and the rear surface plate is fixed to the support body on the side opposite to the membrane-like member, as described above, the rear surface space surrounded by the membrane-like member, the support body, and the rear surface plate contributes to resonance. On the other hand, according to the examination by the present inventors, it became clear that in a case where the resonance frequency is matched to the frequency of noise in the above resonance structure, a sound is more likely to pass through the rear surface plate, and the sound insulation properties thereof are lower than that of a simple plate member. 
     In order to improve the sound insulation properties in the above resonance structure, for example, it is considered that the resonance frequency of the resonance structure is set in an appropriate range according to the frequency of noise. In a resonance structure body disclosed in JP1998-205351A (JP-H10-205351A) described above, the noise emitted from the noise generating vibrating body is canceled at a frequency higher than the resonance frequency of the resonator. However, in the resonance structure body of JP1998-205351A (JP-H10-205351A), it is necessary to provide a rigid body (connecting mechanism or the like) for connecting the diaphragm to the noise generating vibrating body, but regarding noise such as road noise or wind noise of a car, it is difficult to achieve connection to a source thereof. In the resonance structure body disclosed in JP1998-205351A (JP-H10-205351A), in a case where the resonance frequency is largely deviated from the frequency of the sound to be silenced, the silencing effect tends to be reduced. Therefore, the resonance frequency also needs to be set to a high frequency. However, in a case where high frequency resonance is to be generated, the resonance efficiency may decrease depending on the vibration mode of the vibrating body (for example, in fundamental vibration). 
     Further, as a method of improving the sound insulation properties of the soundproof structure, it is common to increase the weight of the entire structure. However, as the soundproof structure becomes heavier, it is difficult to handle the soundproof structure or a partition member to which the soundproof structure is attached, such as a wall. Therefore, it is required to improve the sound insulation properties of a resonance structure with a lightweight configuration. 
     Furthermore, in sound insulation according to the mass law by weight, the effect of sound insulation is obtained as the frequency becomes higher over the entire frequency range. However, in a case where a sound having a specific frequency or a sound of a narrow band of frequencies is noise, in a case where the noise is to be insulated according to the mass law, the sound pressure is reduced as a whole while a state where the noise is significantly higher than sounds of surrounding frequencies remains unchanged from the original state. For this reason, the state where the specific frequency that is heard is stronger than the surrounding frequencies remains unchanged. 
     The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the following purposes. 
     That is, the present invention solves the above-mentioned problems of the related art, and an object thereof is to provide a partition member provided with a soundproof structure capable of efficiently insulating noise with a lightweight configuration, and an electronic device and a vehicle using the partition member. 
     In order to achieve the above object, a partition member of the present invention is a partition member that includes a soundproof structure that reduces noise emitted from a sound source on one side of two spaces, and partitions the two spaces, in which the soundproof structure includes a support body having an opening, a membrane-like member that is fixed to an opening surface of the support body in which the opening is formed and that vibrates in a case where noise is incident, a rear surface plate fixed to the support body on a side opposite to the membrane-like member, the soundproof structure absorbs a sound by a resonance structure formed by a rear surface space surrounded by the rear surface plate, the membrane-like member, and the support body and the membrane-like member, and insulates a sound having a frequency higher than a relative maximum resonance frequency at which a sound absorption coefficient becomes a relative maximum among resonance frequencies of the resonance structure, the relative maximum resonance frequency is set to be lower than a sound insulation target frequency set for noise, and in a case where the sound insulation target frequency is indicated as fn and the relative maximum resonance frequency is indicated as fr, fn/fr is 1.05 to 1.50. 
     In the partition member, it is suitable that at least a part of each of the membrane-like member and the rear surface plate is fixed to the support body, and the vibration of the membrane-like member propagates from a part of the support body to which the membrane-like member is fixed to a part of the support body to which the rear surface plate is fixed. 
     In the partition member, it is suitable that the soundproof structure is formed by a plurality of membrane type resonators, the membrane-like member includes a fixed portion fixed to the opening surface, and a vibratable part located inside the fixed portion, each of the plurality of membrane type resonators absorbs a sound by the resonance structure in a case where the vibratable part of the membrane-like member vibrates, in each of the plurality of membrane type resonators, a sound absorption coefficient at a resonance frequency of at least one higher-order vibration mode present at 1 kHz or higher of the vibration of the vibratable part of the membrane-like member is higher than a sound absorption coefficient at a resonance frequency of a fundamental vibration mode, and the resonance frequency of the at least one higher-order vibration mode is set to be lower than the sound insulation target frequency. 
     In the partition member, it is suitable that in a case where a Young&#39;s modulus of the membrane-like member is indicated as E (Pa), a thickness of the membrane-like member is indicated as t (m), a thickness of the rear surface space is indicated as d (m), and a diameter or equivalent circle diameter of the vibratable part of the membrane-like member is indicated as Φ(m), a hardness E×t 3  (Pa·m 3 ) of the membrane-like member is 21.6×d −1.25 ×Φ 4.15  or less. 
     Furthermore, it is more suitable that the hardness E×t 3  (Pa·m 3 ) of the membrane-like member is 2.49×10 −7  or less. 
     In the partition member, it is suitable that the soundproof structure is formed by a plurality of membrane type resonators, and at least two membrane type resonators among the plurality of membrane type resonators are different from each other in kind. 
     In the partition member, the membrane-like member includes a fixed portion fixed to the opening surface, and a vibratable part located inside the fixed portion for each of the membrane type resonators, the fixed portion and the vibratable part provided for each of the membrane type resonators are disposed in the same membrane-like member, and a volume of the rear surface space is different between the at least two membrane type resonators that are different from each other in kind. 
     In the partition member, it is suitable that the soundproof structure is formed by a plurality of membrane type resonators, the membrane-like member includes a fixed portion fixed to the opening surface, and a vibratable part located inside the fixed portion, each of the plurality of membrane type resonators absorbs a sound by the resonance structure in a case where the vibratable part of the membrane-like member vibrates, and a through-hole is formed in the vibratable part of the membrane-like member in at least one of the plurality of membrane type resonators. 
     In the partition member, it is suitable that the soundproof structure further has a porous sound absorbing body provided in the rear surface space or at a position in contact with the membrane-like member. 
     In the partition member, it is suitable that the soundproof structure is disposed in a state where the membrane-like member faces the sound source side. 
     In the partition member, it is suitable that the soundproof structure is disposed on at least a part of a surface of the partition member. 
     In the partition member, it is suitable that a thickness of the membrane-like member is 10 μM to 200 μm. 
     In the partition member, it is suitable that a thickness of the rear surface space is 0.5 mm to 10 mm. 
     In the partition member, it is suitable that fn/fr is 1.10 to 1.35. 
     In addition, in order to solve the above-described problems, a vehicle of the present invention includes any one of the above-described partition members, in which the partition member is disposed between a space in which at least one of a motor, an inverter, an engine, or a tire is disposed, and a space in which an occupant rides. 
     Furthermore, in order to solve the above-described problems, an electronic device of the present invention includes the sound source in a housing; and any one of the above-described partition members is disposed in at least a part of the housing or in the housing. 
     According to the present invention, it is possible to provide a partition member including a soundproof structure capable of efficiently insulating noise with a lightweight configuration, and an electronic device and a vehicle using the partition member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic front view of a partition member according to an example of the present invention. 
         FIG. 2  is a schematic view illustrating a I-I cross section of  FIG. 1 . 
         FIG. 3  is an exploded view of a soundproof structure included in the partition member of the present invention. 
         FIG. 4  is a view illustrating a modification example of the soundproof structure, and is a cross-sectional view of a configuration in which the sizes of frames are different. 
         FIG. 5  is a view illustrating a modification example of the soundproof structure, and is a cross-sectional view illustrating a configuration in which a plate body is fitted into an opening of the frame. 
         FIG. 6  is a view illustrating a modification example of the soundproof structure, and is a cross-sectional view illustrating a configuration in which a through-hole is formed in a membrane-like member. 
         FIG. 7  is a view illustrating a modification example of the soundproof structure, and is a cross-sectional view illustrating a configuration in which a porous sound absorbing body is disposed in a rear surface space. 
         FIG. 8  is a diagram showing a sound absorption coefficient and a transmission loss difference of a membrane type resonating body according to the present invention. 
         FIG. 9  is a diagram showing a transmission loss of the membrane type resonating body according to the present invention. 
         FIG. 10  is a diagram showing a simulation result of a transmission loss difference in a case where the thickness of a membrane is 250 μm. 
         FIG. 11  is a diagram showing a simulation result of a transmission loss difference in a case where the thickness of the membrane is 180 μm. 
         FIG. 12  is a diagram showing a frequency ratio (fn/fr) in a case where the thickness of a rear surface plate is 2 mm. 
         FIG. 13  is a diagram showing a frequency ratio (fn/fr) in a case where the thickness of the rear surface plate is 1 mm. 
         FIG. 14  is a diagram showing a simulation result of a transmission loss difference in a case where the thickness of the membrane-like member is 100 μm. 
         FIG. 15  is a diagram showing a frequency ratio (fn/fr) in a case where the thickness of the membrane-like member is 100 μm. 
         FIG. 16  is a diagram showing a frequency ratio (fn/fr) in a case where the thickness of the membrane-like member is 50 mm. 
         FIG. 17  is a diagram showing a calculation result in a case where a sound absorption coefficient in a case where a sound is incident in a plane wave form from a membrane surface side of a resonance structure is simulated. 
         FIG. 18  is a diagram showing a calculation result in a case where a transmission loss in a case where a sound is incident in a plane wave form from the membrane surface side of the resonance structure is simulated (first). 
         FIG. 19  is a diagram showing a calculation result in a case where a transmission loss in a case where a sound is incident in a plane wave form from the membrane surface side of the resonance structure is simulated (second). 
         FIG. 20  is a diagram showing a sound absorption coefficient obtained for a soundproof structure produced in Example 1. 
         FIG. 21  is a diagram showing a difference in transmission loss obtained for each of the soundproof structure produced in Example 1 and a single acrylic plate. 
         FIG. 22  is a diagram showing a measurement result of the amount of transmitted sound pressure in a case where a soundproof structure produced in Example 2 is used and in a case where a single acrylic plate is used. 
         FIG. 23  is a diagram showing a difference in the amount of transmitted sound pressure between the case where the soundproof structure produced in Example 2 is used and the case where the single acrylic plate is used. 
         FIG. 24  is a diagram showing a calculation result in a case where a transmission loss is simulated by changing the thickness of a rear surface space from 1 mm to 6 mm in increments of 1 mm. 
         FIG. 25  is a diagram showing a calculation result in a case where the transmission loss is simulated by changing the thickness of the membrane-like member from 10 μm to 50 μm in increments of 10 μm. 
         FIG. 26  is a diagram showing a calculation result in a case where the transmission loss is simulated by changing the thickness of the membrane-like member from 60 μm to 100 μm in increments of 10 μm. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the present invention will be described in detail. Descriptions of the configuration requirements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments. 
     In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit and an upper limit. 
     Furthermore, in the present specification, for example, angles such as “45°”, “parallel”, “perpendicular”, or “orthogonal” are within a range in which the difference from a strict angle is less than 5 degrees unless otherwise specified. The difference from a strict angle is preferably less than 4 degrees, and more preferably less than 3 degrees. 
     In the present specification, “same”, “similar” and “identical” include an error range generally accepted in the technical field. In addition, in the present specification, in a case of referring to “all”, “any”, “entire surface”, and the like, in addition to the case of 100%, an error range generally accepted in the technical field is included, for example, a case of 99% or more, 95% or more, or 90% or more is included. 
     [Partition Member] 
     A partition member of the present invention is a member that partitions two spaces, and includes a soundproof structure that reduces noise emitted from a sound source on one side of the two spaces. The soundproof structure includes a support body having an opening, a membrane-like member fixed to an opening surface of the support body in which the opening is formed, and a rear surface plate fixed to the support body on the side opposite to the membrane-like member. The soundproof structure provides soundproofing by vibrating the membrane-like member as noise is incident on the membrane-like member. More specifically, the soundproof structure absorbs a sound a resonance structure formed by a rear surface space surrounded by the rear surface plate, the membrane-like member, and the support body and the membrane-like member. In addition, the soundproof structure insulates a sound having a frequency higher than a relative maximum resonance frequency at which a sound absorption coefficient becomes a relative maximum among resonance frequencies of the resonance structure. Here, the relative maximum resonance frequency is set to be lower than a sound insulation target frequency set for noise. Furthermore, in a case where the sound insulation target frequency is indicated as fn and the relative maximum resonance frequency is indicated as fr, fn/fr is 1.05 to 1.50. 
     In the partition member of the present invention configured as described above, the soundproof structure provided in the partition member can efficiently insulate noise with a lightweight configuration. As a result, it is possible to preferably perform soundproofing in an environment where sound insulation properties are particularly required as a soundproofing effect. 
     Here, “soundproofing” is a concept that includes both “sound insulation” and “sound absorption” as acoustic characteristics. “Sound insulation” means “sound is insulated”, that is, “sound is not transmitted”, and in easy terms, is “sound is reflected” (acoustic reflection), and “sound is canceled” (acoustic cancellation). “Sound absorption” means “sound is not reflected”, that is, “the reflection of sound is reduced”, and in easy terms, is “sound is absorbed” (acoustic absorption). (refer to Daijirin Japanese Dictionary of Sanseido (3rd edition) and http://www.onzai.or.jp/question/soundproof.html and http://www.onzai.or.jp/pdf/new/gijutsu201312_3.pdf of web pages of Acoustic Materials Association of Japan. 
     In addition, “sound insulation target frequency” corresponds to, for example, a frequency band in which the sound pressure of noise is a peak sound having a narrow frequency width, and more specifically, a specific frequency of noise. 
     Hereinafter, an example of the partition member of the present invention (hereinafter, partition member  10 ) will be described with reference to  FIGS. 1 and 2 .  FIG. 1  is a schematic front view of the partition member  10 .  FIG. 2  is a schematic cross-sectional view of a soundproof structure  20  included in the partition member  10 , and is a view illustrating a I-I cross section of  FIG. 1 . 
     The partition member  10  is a member that partitions two spaces as described above, and is a substantially plate-shaped member (for example, panel or board) used as a wall, a ceiling, a floor, a door, a partition, a partition material disposed inside a device or an apparatus, a housing, a case cover, and the like. The partition member  10  partitions the two spaces together with its peripheral member (for example, an adjacent wall member) without any gap (strictly speaking, a case where a slight air gap remains is included). 
     A sound source is disposed on one side of the two spaces partitioned by the partition member  10 . Examples of the sound source include rotating components such as a motor and a fan; electronic components such as an inverter, a power supply, a booster, a power control unit (PCU) including a boost converter and an inverter, a large-capacity capacitor, a ceramic capacitor, an inductor, a coil, and an electric control device such as a switching power supply and a transformer; and mechanical components such as a moving mechanism by a gear or an actuator. 
     A sound (noise) is generated from the sound source, and the noise propagates through the air. More specifically, in a case where the sound source is an electronic component such as an inverter, a sound (switching noise) corresponding to a carrier frequency is generated. In a case where the sound source is a rotating device such as a motor or a fan, a sound (electromagnetic noise) having a frequency corresponding to the rotation speed thereof is generated. At this time, the frequency of the sound to be generated is not necessarily limited to the rotation speed or a multiple thereof, but there is a strong relationship that a higher frequency sound is generated by increasing the rotation speed. That is, each sound source generates a sound having a frequency unique to the sound source. Many sound sources that generate sound at a natural frequency have a physical or electrical mechanism that generates vibration at a specific frequency. For example, a rotating system such as a fan emits a sound having a frequency determined by a value obtained by multiplying the rotation speed thereof by the number of blades, or a sound having a frequency that is a multiple thereof. In addition, a part of an inverter or the like that receives an AC electric signal generates a sound corresponding to the AC frequency thereof. 
     Whether or not a sound source has a natural frequency can be determined by the following experiment. 
     The sound source is disposed in an anechoic chamber, a semi-anechoic chamber, or a space surrounded by a sound absorbing body such as urethane. By disposing the sound absorbing body around the sound source as described above, it is possible to eliminate the influence of the reflection interference of the chamber and a measurement system. Then, a sound is generated from the sound source, the sound is collected by a microphone from a position distant from the sound source and measured, and the frequency information thereof is acquired. The distance between the sound source and the microphone can be appropriately selected according to the size of the sound source and the measurement system, but it is desirable that the distance is about 30 cm or more. 
     The partition member  10  includes the soundproof structure  20  illustrated in  FIGS. 1 and 2 . The soundproof structure  20  reduces noise emitted from the sound source. As a result, of the two spaces partitioned by the partition member  10 , the propagation of noise from the space where the sound source is installed to the space where the sound source is not installed is suppressed. 
     The soundproof structure  20  forms at least a part of the surface of the partition member  10 , and in the configuration illustrated in  FIG. 1 , forms substantially the entire surface of the partition member  10  except for the edge portion. However, the soundproof structure  20  is not limited thereto, and a part (for example, the central part) of the surface of the partition member  10  may be formed by the soundproof structure  20 . In addition, the soundproof structure  20  may be attached to the outer surface of the partition member  10 , or the soundproof structure  20  may be disposed inside the partition member  10 . 
     The partition member  10  can be suitably used as a partition in a building. In a case where the partition member  10  is used as a partition for a building, for example, in a chamber (room) partitioned by the partition member  10 , it is possible to suppress the propagation of a sound (strictly speaking, insulate a sound) generated from a sound source in another room. 
     As the partition for a building, there are walls, doors, partitions and screens, shutters, floors, and ceilings. 
     Moreover, the partition member  10  can be suitably used in an electronic device that includes a sound source in a space surrounded by an outer wall. Specifically, the partition member  10  may be disposed in at least a portion of the housing or in the housing of the electronic device. With such a configuration, it is possible to suppress the propagation of noise (specifically, insulate a sound) emitted from the sound source inside the electronic device to the outside of the electronic device. In particular, in a case where the partition member  10  is used as a cover for a sound source (for example, a motor, an inverter, or a power control unit) provided in a space surrounded by an outer wall, a characteristic noise emitted from the sound source, for example, a single frequency sound is suppressed (a sound is insulated). 
     As the electronic device, there are household appliances such as air conditioners, outdoor units of air conditioners, water heaters, ventilation fans, refrigerators, vacuum cleaners, air purifiers, electric fans, dishwashers, microwave ovens, washing machines, televisions, mobile phones, smartphones, and printers; office equipment such as copiers, projectors, desktop personal computers (PCs), notebook PCs, monitors, and shredders; computer equipment that uses high power such as servers and supercomputers; and scientific experiment equipment such as thermostatic chambers, environmental testers, dryers, ultrasonic cleaners, centrifuges, washers, spin coaters, bar coaters, and carriers. 
     Moreover, the partition member  10  can be suitably used in a vehicle in which an occupant rides. Specifically, the partition member  10  may be disposed between a space in which at least one of the motor, the inverter, the engine, or the tire is disposed, and a space in which an occupant rides. More specifically, the partition member  10  including the soundproof structure  20  may be disposed between the seat on which the occupant sits and the sound source. For example, in a hybrid car or an electric car, in a case where the motor is disposed on the lower surface of the car, the axle, or the tire portion, it is desirable to dispose a vehicle cabin floor including the partition member  10  between the motor and the vehicle cabin. In a case where the motor and the inverter are accommodated in the front part (the part corresponding to the engine compartment of a gasoline vehicle) of the hybrid car or the electric car, it is desirable to dispose a dash insulator including the partition member  10  between the motor and the inverter, and the vehicle cabin. According to the above configuration, it is possible to suppress the propagation of noise emitted from the sound source in the vehicle to the place of the occupant (the space where the occupant is present) and to insulate the noise. 
     As the vehicle, there are electric cars (including buses or taxis), trains, aviation equipment (airplanes, fighters, helicopters, or the like), ships, aerospace equipment (rockets and the like), and personal mobility devices. In particular, in a hybrid car, an electric car, and a plug-in hybrid vehicle (PHV), a peculiar noise caused by a motor and a power control unit (including an inverter and a battery voltage boosting unit) installed inside the car and heard in the vehicle cabin becomes a problem. 
     &lt;Soundproof Structure&gt; 
     The soundproof structure (hereinafter, soundproof structure  20 ) included in the partition member  10  of the present invention will be described with reference to  FIGS. 2 and 3 .  FIG. 3  is an exploded view of the soundproof structure  20 . In  FIG. 3 , a frame  26  that forms a support body  24 , a membrane  32  that forms a membrane-like member  30 , and a plate body  44  that forms a rear surface plate  40  are each illustrated singly by broken lines. 
     The soundproof structure  20  reduces noise that propagates through the air from one of the two spaces partitioned by the partition member  10  in a state where there is no gap (or a slight gap is formed) to the other. The configuration of the soundproof structure  20  is briefly described. As illustrated in  FIGS. 2 and 3 , the soundproof structure  20  includes the support body  24 , the membrane-like member  30 , and the rear surface plate  40  as primary constituent elements. 
     The support body  24  is a member having openings  28 , and supports the membrane-like member  30  in a vibratable state. The membrane-like member  30  is formed of a sheet, a film, or a thin plate, and is fixed to an opening surface  24   s  of the support body  24  where the openings  28  are formed at a position where the openings  28  are closed. The membrane-like member  30  vibrates as noise is incident on a part of the surface thereof facing the opening  28 . That is, the membrane-like member  30  is fixed to the support body  24  in a state of covering the opening surface  24   s  of the support body  24 , and is thus vibratably supported by the support body  24 . 
     The rear surface plate  40  is a plate body having a sufficient thickness and a plane size, and, for example, in a case where the partition member  10  is a wall body, the rear surface plate  40  forms a main body part of the wall body. The rear surface plate  40  is fixed to the support body  24  on the side opposite to the membrane-like member  30 . More specifically, the rear surface plate  40  is fixed to the support body  24  so as to close the openings  28  on the side opposite to the membrane-like member  30 . Accordingly, in the soundproof structure  20 , a space surrounded by the rear surface plate  40 , the membrane-like member  30 , and the support body  24  (hereinafter, rear surface space  42 ) is formed. In the configuration illustrated in  FIG. 2 , the rear surface space  42  is a closed space. 
     Each of the membrane-like member  30  and the rear surface plate  40  is fixed to the support body  24  by at least a part of each thereof, as described above. Therefore, in a case where the membrane-like member  30  vibrates, the vibration propagates from the part of the support body  24  to which the membrane-like member  30  is fixed to the part to which the rear surface plate  40  is fixed. 
     The soundproof structure  20  configured as described above absorbs sound by the resonance structure (strictly, a membrane type resonance structure) configured by the membrane-like member  30  and the rear surface space  42 . That is, the soundproof mechanism of the soundproof structure  20  is formed by using the membrane-like member  30  as a mass spring component and the rear surface space  42  as an air spring component. In a case where noise is incident on the membrane-like member  30 , the membrane-like member  30  vibrates at a resonance frequency, and in conjunction with this, the air in the rear surface space  42  repeats adiabatic compression and adiabatic expansion. Accordingly, the energy of the noise is converted by heat energy and the noise is absorbed. 
     Here, among the resonance frequencies of the above resonance structure, there is a resonance frequency at which the sound absorption coefficient reaches a relative maximum value (hereinafter, also referred to as a peak). This peak frequency (that is, relative maximum resonance frequency, which will be simply referred to as “resonance frequency” for convenience hereinafter) can be easily adjusted by changing the density and weight of the membrane-like member  30 , the thickness of the rear surface space  42 , and the like. 
     For the purpose of more effective soundproofing of noise, in the partition member  10 , the soundproof structure  20  is preferably disposed with the membrane-like member  30  facing the sound source side. However, the direction of the soundproof structure  20  in a case where the partition member  10  is disposed (specifically, the direction in which the membrane-like member  30  is directed) is not particularly limited, and may be appropriately set according to the application and the like. 
     Next, a detailed configuration of the soundproof structure  20  will be described. As illustrated in  FIG. 1 , the soundproof structure  20  is formed by a plurality of (in the configuration illustrated in  FIG. 1 , 4 vertical×3 horizontal, a total of 12) membrane type resonating bodies  22  arranged on a plane. In other words, the soundproof structure  20  of the present invention is formed by, with one membrane type resonating body  22  as one unit (cell), integrating a plurality of cells continuously arranged as one unit. The number of membrane type resonating bodies  22  forming the soundproof structure  20  is not particularly limited, and may be only one or may be two or more. 
     Each of the plurality of membrane type resonating bodies  22  is formed by the membrane-like member  30 , the support body  24 , and the rear surface plate  40 . In the configuration illustrated in  FIG. 3 , the plurality of membrane type resonating bodies  22  are simultaneously created by overlapping (stacking) one membrane-like member  30 , one support body  24 , and one rear surface plate  40 . Hereinafter, each of the membrane-like member  30 , the support body  24 , and the rear surface plate  40  will be described in detail. 
     As illustrated in  FIG. 3 , the support body  24  is formed by disposing a plurality of rectangular frames  26 . More specifically, one or more the plurality of frames  26  arranged in a raw (frame row) are provided in a direction orthogonal to the frame row. In each frame  26 , the opening  28  having a substantially square opening shape as viewed in a plan view is formed. 
     Each frame  26  forms the membrane type resonating body  22 . A corresponding membrane  32  in the membrane-like member  30  is fixed to one end surface of each frame  26  (an end surface of the frame  26  in a thickness direction) so as to close the opening  28 . Accordingly, each frame  26  supports the corresponding membrane  32  in a vibratable state. The rear surface space  42  corresponding to the size and shape of the frame  26  is formed on the back side of the membrane  32 . 
     In the configuration illustrated in  FIG. 2 , the size and shape of the frames  26  (strictly speaking, the size and shape in the plan view) are uniform between the membrane type resonating bodies  22 . However, the size and shape of the frame  26  are not limited thereto and may be different between at least two membrane type resonating bodies  22 , as illustrated in  FIG. 4 .  FIG. 4  is a view illustrating a modification example of the soundproof structure  20 , and is a cross-sectional view of a configuration in which the sizes of the frames  26  are different. 
     In the configuration illustrated in  FIG. 4 , in a case where the sizes and shapes of the frames  26  are different, the areas of the vibrating parts of the membranes  32  and the volumes of the rear surface spaces  42  are different. The difference in these conditions means that the kinds of the membrane type resonating body  22  in which the vibrating parts of the membranes  32  and the rear surface spaces  42  are formed are different. That is, the plurality of membrane type resonating bodies  22  may all be of the same type, or the kinds of at least two membrane type resonating bodies  22  may be different from each other. In other words, the volumes of the rear surface spaces  42  may be different between at least two membrane type resonating bodies  22 . 
     The opening shape of the opening  28  is not particularly limited, and may be, for example, another quadrangle such as a rectangle, a rhombus, a parallelogram, and a trapezoid, a triangle including an equilateral triangle, a right triangle, and an isosceles triangle, a polygon including a regular polygon such as a regular hexagon and a regular pentagon, a circle, an ellipse, or the like, or may be an irregular shape. The frame  26  preferably has a closed cross-sectional structure that surrounds the entire periphery of the opening  28 , but is not limited thereto. The frame  26  may also have a discontinuous structure in which a part around the opening  28  is absent. 
     The material of each frame  26 , that is, the material of the support body  24  is not particularly limited as long as the material can support the membrane  32 , has a strength suitable for application to a sound source of noise, and is resistant to a soundproof environment, and can be selected according to the sound source, the soundproof environment, and the like. Examples of the material of the support body  24  include a metal material, a resin material, a reinforced plastic material, and a carbon fiber. Examples of the metal material include metal materials such as aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium molybdenum, nichrome molybdenum, copper, and alloys thereof Examples of the resin material include resin materials such as an acrylic resin, polymethylmethacrylate, polycarbonate, polyamidimide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, an acrylonitrile butadiene styrene copolymer synthetic resin (ABS resin), polypropylene, and triacetyl cellulose. As the reinforced plastic material, there are carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP). Furthermore, natural rubber, chloroprene rubber, butyl rubber, ethylene propylene diene rubber (EPDM), silicone rubber, and the like, and rubbers containing crosslinked structures thereof can also be used. Among the above-mentioned materials, some kinds of materials may be used in combination. 
     As the material of the support body  24 , a honeycomb core material can also be used. Since the honeycomb core material is used as a lightweight and highly rigid material, it is easy to obtain a ready-made product. As an example, a honeycomb core material formed of various materials such as an aluminum honeycomb core, an FRP honeycomb core, a paper honeycomb core (manufactured by Shin Nippon Feather Core Co., Ltd., manufactured by Showa Aircraft Industry Co., Ltd., or the like), and a honeycomb core (TECCELL manufactured by Gifu Plastic Industry Co., Ltd., or the like) made of a thermoplastic resin (specifically, polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), polycarbonate (PC) or the like) can be used as the support body  24 . 
     As the material of the support body  24 , a foam material, a hollow material, or a porous material can also be used. In a case of using a large number of membrane type soundproof structures, in order to provide a configuration in which air does not pass between cells, the frame can be formed using, for example, a closed cell foam material. Specifically, for example, various materials such as closed cell polyurethane, closed cell polystyrene, closed cell polypropylene, closed cell polyethylene, and closed cell rubber sponge can be selected. Compared to open cells, closed cells are impermeable to sound, water, and gas, and have a high structural strength, so that the closed cells are suitable for use as the material of the support body  24 . In a case where a porous sound absorbing body  50 , which will be described later, has sufficient supportability, the support body  24  may be formed of only the porous sound absorbing body, and the materials mentioned as the materials of the porous sound absorbing body  50  and the support body  24  may be used in combination, for example, by mixing or kneading. By using a material system containing air therein as described above, a reduction in the weight of the device can be achieved, and furthermore heat insulating properties can be imparted. 
     In the configuration illustrated in  FIG. 3 , the support body  24  is formed as one assembly of the plurality of frames  26  integrated, specifically, is formed by a grid-shaped member having a plurality of parts extending in two directions orthogonal to each other. However, the support body  24  is not limited thereto, and a configuration in which the frames  26  are separated (that is, the support bodies  24  are separated for the respective membrane type resonating bodies  22 ) may be adopted. 
     The membrane-like member  30  is formed by arranging a plurality of rectangular membranes  32 . The membranes  32  are elements that form the membrane type resonating bodies  22 , and are provided in the same number as the membrane type resonating bodies  22 , that is, in the same number as the frames  26  in the membrane-like member  30 . The membranes  32  in the membrane-like member  30  and the frames  26  in the support body  24  respectively correspond to each other. For example, the membrane  32  located at the upper right corner of the membrane-like member  30  in a front view corresponds to the frame  26  located at the upper right corner of the support body  24 . Each membrane  32  is fixed to one end surface (opening surface  24   s ) of the corresponding frame  26  at a position where the opening  28  is closed. 
     As illustrated in  FIG. 2 , each membrane  32  (membrane-like member  30 ) has a fixed portion  34  fixed to the opening surface  24   s  of the corresponding frame  26  (support body  24 ) and a vibratable part  36  located inside the fixed portion  34 . The fixed portion  34  is located at the outer edge portion of the membrane  32 , and is fixed to a part (edge portion) of the corresponding frame  26  around the opening  28 . The vibratable part  36  has a substantially square shape and is a part facing the opening  28 . The shape of the vibratable part  36  is not particularly limited and is determined according to the opening shape of the frame  26 . Therefore, for example, in a case where the opening shape is circular, the vibratable part  36  of the membrane  32  is also circular. 
     In the configuration illustrated in  FIGS. 2 and 3 , the size and shape (size and shape in the plan view) of the vibratable parts  36  of the membranes  32  are uniform between the membrane type resonating bodies  22 . However, the size and shape of the vibratable part  36  of the membrane  32  are not limited thereto, and may be different between at least two membrane type resonating bodies  22 . Here, the size of the vibratable part  36  is represented by, in a case of a shape other than a circle, an equivalent circle diameter (the diameter of a circle having the same area as that of the shape), and is represented by, in a case of a circular shape, the diameter of the circle. 
     A method of fixing the membrane  32  to the frame  26  is not particularly limited, and any method can be used without limitation as long as the membrane  32  is fixed to the frame  26  in a vibratable state. For example, a method using a double-sided tape or an adhesive, or a method using a physical fixing tool can be adopted. In a case of using a double-sided tape, for example, ultra high temperature double coated tape 9077 manufactured by 3M can be adopted. In a case of using an adhesive, for example, the adhesive is applied onto one end surface (opening surface  24   s ) of the frame  26 , and the membrane  32  is placed on the applied adhesive and fixed to the frame  26 . Examples of the adhesive include an epoxy-based adhesive (ARALDITE (registered trademark) (manufactured by NICHIBAN Co., Ltd.), or the like), a cyanoacrylate-based adhesive (Aron Alpha (registered trademark) (manufactured by NICHIBAN Co., Ltd.), and an acrylic adhesive. In a case of using a physical fixing tool, for example, the membrane  32  disposed at a position that closes the opening  28  is sandwiched between the frame  26  and a fixing member (not illustrated) such as a rod, and the fixing member is fastened to the frame  26  using the fixing tool such as a screw to fix the membrane  32  to the frame  26 . 
     The material of each membrane  32 , that is, the material of the membrane-like member  30  is not particularly limited as long as the material has a strength suitable for application to a sound source of noise, is resistant to a soundproof environment, and can vibrate in a case where noise is incident, and can be selected according to the sound source, the soundproof environment, and the like. For example, as the material of the membrane-like member  30 , various metals such as aluminum, titanium, nickel, permalloy, 42 alloy, kovar, nichrome, copper, beryllium, phosphor bronze, brass, nickel silver, tin, zinc, iron, tantalum, niobium, molybdenum, zirconium, gold, silver, platinum, palladium, steel, tungsten, lead, and iridium; and resin materials such as polyethylene terephthalate (PET), triacetyl cellulose (TAC), polyvinylidene chloride (PVDC), polyethylene (PE), polyvinyl chloride (PVC), polymethylpentene (PMP), a cyclo olefin polymer (COP), ZEONOR, polycarbonate, polyethylene naphthalate (PEN), polypropylene (PP), polystyrene (PS), polyarylate (PAR), Aramid, polyphenylene sulfide (PPS), polyethersulfone (PES), Nylon, polyester (PEs), a cyclic olefin copolymer (COC), diacetyl cellulose, nitrocellulose, a ellulose derivative, polyamide, polyamideimide, polyoxymethylene (POM), polyetherimide (PEI), polyrotaxane (slide-ring material or the like), and polyimide can be used. Furthermore, glass materials such as thin film glass, and fiber reinforced plastic materials such as carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) can also be used. In addition, natural rubber, chloroprene rubber, butyl rubber, ethylene propylene diene methylene linkage (EPDM), silicone rubber, and the like, and rubbers containing a crosslinked structure thereof can be used. Alternatively, a combination of the materials listed above may be used. 
     In a case of using a metal material, the surface may be plated with metal from the viewpoint of suppressing rust or the like. 
     In a system in which the environmental temperature changes, it is desirable that the material of the frame  26  and the material of the membrane  32  are the same, or at least the thermal expansion coefficients (linear expansion coefficients) of both materials are close to each other. In a case where the thermal expansion coefficients of the frame  26  and the membrane  32  are greatly different from each other, the frame  26  and the membrane  32  are different in the amount of displacement in a case where the environmental temperature changes, and thus strain is likely to occur in the membrane  32 . Since the strain and the tension change affect the resonance frequency of the membrane  32 , the silencing frequency is likely to change with the temperature change, and even in a case where the temperature returns to the original temperature, there are cases where the strain does not relax and the silencing frequency remains changed. On the other hand, in a case where the thermal expansion coefficients are set to be close to each other, the frame  26  and the membrane  32  are similarly expanded and contracted, so that strain is less likely to occur, resulting in a system that is stable against changes in the environmental temperature. 
     Furthermore, in the configuration illustrated in  FIG. 3 , the membrane-like member  30  forms one wide plate body by connecting a plurality of membranes  32 . That is, in the configuration illustrated in  FIG. 3 , the membranes  32  (the fixed portions  34  and the vibratable parts  36 ) provided for the respective membrane type resonating bodies  22  are disposed in the same membrane-like member  30 . With such a configuration, by overlapping and fixing the membrane-like members  30  to the support body  24  so as to cover the entire opening surface  24   s  of the support body  24 , it is possible to collectively fix the membranes  32  to all the frames  26  in the support body  24 . Accordingly, in each of the plurality of membrane type resonating bodies  22 , the membranes  32  can be fixed to the frames  26  in a state where the membranes  32  are located on the same plane (without a step). 
     However, the configuration is not limited thereto, and a configuration in which the membranes  32  are separated (that is, the membrane-like members  30  are separated for the respective membrane type resonating bodies  22 ) may be adopted. In such a configuration, the respective membrane-like members  30  of the membrane type resonating bodies  22  are individually fixed to the frames  26  (support body  24 ). Alternatively, as an intermediate therebetween, the membrane-like member  30  having a strip shape (the membrane-like member  30  formed into a size corresponding to the plurality of membranes  32  connected) is fixed to two or more continuous frames  26  among the plurality of frames  26 , and the single-cut membrane-like members  30  (the membrane-like members  30  formed into a size of the single membrane  32 ) may be individually fixed to the remaining frames  26 . 
     In a case where the membrane-like members  30  are divided for the respective membrane type resonating bodies  22 , the thickness and material of each membrane-like member  30  (that is, the membrane  32 ) may be uniform between the membrane-like members  30 . Alternatively, at least two or more membrane-like members  30  may be different. 
     The rear surface plate  40  may be formed of a single plate body, or may be formed by arranging a plurality of rectangular plate bodies  44 . In the following, a configuration in which the rear surface plate  40  is formed by a plurality of plate bodies  44  will be described as an example. The plate bodies  44  are elements that form the membrane type resonating bodies  22 , and are provided in the same number as the membrane type resonating bodies  22 , that is, in the same number as the frames  26  in the rear surface plate  40 . The plate bodies  44  in the rear surface plate  40  and the frames  26  in the support body  24  respectively correspond to each other. For example, the plate body  44  located at the upper right corner of the rear surface plate  40  in the front view corresponds to the frame  26  located at the upper right corner of the support body  24 . Each plate body  44  is fixed to the corresponding frame  26  at a position where the opening  28  is closed on the side opposite to the membrane  32 . More specifically, as illustrated in  FIG. 2 , each plate body  44  has a surface of the same size as the end surface of the corresponding frame  26  on the side opposite to the membrane  32 , and is fixed by joining the outer edge portion of the surface to the outer edge portion of the end surface of the frame  26  (peripheral portion of the opening  28 ). 
     In the configuration illustrated in  FIGS. 2 and 3 , the size and shape of the plate bodies  44  (the size and shape in the plan view) are uniform between the membrane type resonating bodies  22 . However, the size and shape of the plate bodies  44  are not limited thereto. For example, in a case where the size and shape of the frames  26  are different between the membrane type resonating bodies  22 , the size and shape of the plate bodies  44  may also different between the membrane type resonating bodies  22  in a form corresponding thereto. 
     A method of fixing the plate body  44  to the frame  26  is not particularly limited, and any method can be used without limitation as long as the plate body  44  is fixed to the frame  26  so as to close the opening  28  on the opposite side of the membrane  32 . For example, a method using a double-sided tape or an adhesive, or a method using a physical fixing tool can be adopted. In a case of using a double-sided tape, the above-mentioned double-sided tape can be used. In a case of using an adhesive, for example, the adhesive is applied onto the end surface (the end surface opposite to the membrane  32 ) of the frame  26 , and the plate body  44  is placed on the applied adhesive and fixed to the frame  26 . As the adhesive, the adhesives listed above can be used. Alternatively, the frame  26  may be fixed by applying an adhesive to the rear surface plate  40  side formed by the plate body  44 . Even if the adhesive is applied to the entire rear surface plate  40 , acoustic characteristics can be obtained in a case where the rear surface space  42  is secured. In the case of using a physical fixing tool, for example, the outer edge portion of the plate body  44  is abutted against the outer edge portion of the end surface of the frame  26 , and the outer edge portions are fastened to each other by the fixing tool such as a screw to fix the plate body  44  to the frame  26 . 
     Regarding the position in the frame  26  to which the plate body  44  is fixed, the plate body  44  may be fixed to the end surface of the frame  26  as illustrated in  FIG. 3 . Alternatively, as illustrated in  FIG. 5 , the plate body  44  which is formed corresponding to the outer edge of the opening  28  is fitted into the opening  28  formed in the frame  26 , and the side end of the plate body  44  and the inner wall surface of the opening  28  are joined and fixed to each other.  FIG. 5  is a view illustrating a modification example of the soundproof structure  20 , and is a cross-sectional view illustrating a configuration in which the plate body  44  is fitted into the opening  28  of the frame  26 . 
     The material of each plate body  44 , that is, the material of the rear surface plate  40  is not particularly limited as long as the material has a strength suitable for application to a sound source of noise and is resistant to a soundproof environment, and can be selected according to the sound source, the soundproof environment, and the like. Specifically, as the material of the support body  24 , the above-mentioned materials can be adopted. In addition, among the materials listed as the material of the support body  24 , a plurality of kinds may be combined and used as the material of the rear surface plate  40 . Furthermore, as the material of the rear surface plate  40 , similar to the support body  24 , a honeycomb core material can be used. As the honeycomb core material used as the rear surface plate  40 , it is possible to use the same material as the above-mentioned honeycomb core material as the material of the support body  24 . 
     In the configuration illustrated in  FIG. 3 , the rear surface plate  40  forms one wide board body by connecting a plurality of plate bodies  44 . With such a configuration, by overlapping and fixing the rear surface plate  40  so as to cover the entire end surface of the support body  24  located on the side opposite to the membrane-like member  30 , it is possible to collectively fix the plate bodies  44  to all the frames  26  in the support body  24 . However, the configuration is not limited thereto, and a configuration in which the plate bodies  44  are separated (that is, the rear surface plates  40  are separated for the respective membrane type resonating bodies  22 ) may be adopted. In such a configuration, the respective rear surface plates  40  of the membrane type resonating bodies  22  are individually fixed to the frames  26  (support body  24 ). Alternatively, as an intermediate therebetween, the rear surface plate  40  formed into a size corresponding to the plurality of plate bodies  44  connected is fixed to two or more continuous frames  26  among the plurality of frames  26 , and the rear surface plates  40  formed into the size of the single plate body  44  are individually fixed to the remaining frames  26 . 
     According to the soundproof structure  20  configured as described above, each of the plurality of membrane type resonating bodies  22  absorbs a sound by its resonance structure (strictly speaking, a membrane type resonance structure) in a case where noise is incident on the vibratable part  36  of the membrane  32  (the membrane-like member  30 ) and the vibratable part  36  vibrates. At this time, each of the membrane type resonating bodies  22  may be designed such that the sound absorption coefficient at a resonance frequency of at least one higher-order vibration mode present at 1 kHz or higher of the vibration of the vibratable part  36  of the membrane  32  (membrane-like member  30 ) is higher than the sound absorption coefficient at a resonance frequency of a fundamental vibration mode (refer to, for example,  FIG. 8 ). Such a state can be realized by appropriately adjusting the thickness of the rear surface space  42  and the size, thickness, hardness, and the like of the membrane-like member  30  (strictly speaking, the vibratable part  36  of each membrane  32 ). 
     More specifically, the thickness (indicated by symbol d in  FIG. 2 ) of the rear surface space  42  is preferably 20 mm or less, more preferably 10 mm or less, and even more preferably 0.5 mm to 6 mm for miniaturization and sound absorption due to higher-order vibration, still more preferably 1 mm to 5 mm, still more preferably 1 mm to 3 mm, and particularly preferably 1 mm to 2 mm from the viewpoint of further miniaturization of the membrane type resonating body  22 . In a case where the thickness of the rear surface space  42  is not uniform, the average value may be within the above range. 
     The thickness of the membrane-like member  30  (indicated by symbol t in  FIG. 2 ) is preferably 10 μm to 200 μm, more preferably 20 μm to 150 μm, and even more preferably 30 μm to 100 μm. In a case where the thickness of the membrane-like member  30  is not uniform, the average value may be within the above range. 
     The Young&#39;s modulus indicating the hardness of the membrane-like member  30  is preferably 1000 Pa to 1000 GPa, more preferably 10000 Pa to 500 GPa, and particularly preferably 1 MPa to 300 GPa. In a case where the Young&#39;s modulus of the membrane-like member  30  is not uniform, the average value may be within the above range. 
     The density of the membrane-like member  30 , it is preferably 10 kg/m 3  to 30,000 kg/m 3 , more preferably 100 kg/m 3  to 20,000 kg/m 3 , and particularly preferably 500 kg/m 3  to 10,000 kg/m 3 . In addition, in a case where the density of the membrane-like member  30  is not uniform, the average value may be within the above range. 
     The size of the membrane-like member  30 , more specifically, the diameter or equivalent circle diameter (indicated by symbol La in  FIG. 2 ) of the vibratable part  36  of the membrane  32  is preferably 1 mm to 100 mm, more preferably 3 mm to 70 mm and particularly preferably 5 mm to 50 mm. 
     Here, the present inventors examined in more detail the mechanism by which the higher-order vibration modes are excited in the soundproof structure  20 . As a result, it was found that in a case where the Young&#39;s modulus of the membrane-like member  30  is indicated as E (Pa), the thickness of the membrane-like member  30  is indicated as t (m), the thickness (rear surface distance) of the rear surface space  42  is indicated as d (m), and the diameter or equivalent circle diameter of the vibratable part  36  of the membrane-like member  30  is indicated as Φ (m), the hardness E×t 3  (Pa·m 3 ) of the membrane-like member  30  is preferably 21.6×d −1.25 ×Φ 4.15  or less. 
     In a case where a×d −1.25 ×Φ 4.15  is expressed using a coefficient a regarding the condition of the hardness condition of the membrane-like member  30 , it was found that the coefficient a is 11.1 or less, 8.4 or less, 7.4 or less, 6.3 or less, 5.0 or less, 4.2 or less, 3.2 or less, and the smaller the coefficient a, the more preferable. 
     The hardness E×t 3  (Pa·m 3 ) of the membrane-like member  30  is preferably 2.49×10 −7  or more, more preferably 7.03×10 −7  or more, even more preferably 4.98×10 −6  or more, still more preferably 1.11×10 −5  or more, particularly preferably 3.52×10 −5  or more, and most preferably 1.40×10 −4  or more. 
     By causing the hardness E×t 3  (Pa·m 3 ) of the membrane-like member  30  to be within the above range, it is possible to suitably excite the higher-order vibration mode in the soundproof structure  20 . In this case, the sound absorption coefficient in the higher-order vibration mode can be made higher than that in the fundamental vibration mode. Here, the “hardness of the membrane-like member  30 ” is, for example, the hardness in a case where the membrane-like member  30  is attached to the support body  24  in a state of being simply placed on the support body  24 , in a case where zero tension is applied, that is, without being stretched. In a case where the membrane-like member  30  is attached to the support body  24  while a tension is applied to the membrane-like member  30 , the hardness of the membrane-like member  30  may be obtained by performing correction for tension on the Young&#39;s modulus E of the membrane-like member  30 . 
     In addition, although the rear surface space  42  is a closed space completely surrounded by the support body  24 , the membrane-like member  30 , and the rear surface plate  40 , the rear surface space  42  is not limited thereto, and the space is substantially partitioned so that the air flow is blocked. Alternatively, an opening such as a hole or a cutout may be provided in at least one of the membrane-like member  30  or other members. Such a configuration is preferable because it is possible to avoid a situation in which the volume of the air in the rear surface space  42  is increased due to a temperature change and the like, a tension is applied to the membrane-like member  30 , the hardness of the membrane-like member  30  is changed, and thus the sound absorption characteristics are changed. As a method of providing the opening, for example, a through-hole  38  is suitably formed in the vibratable part  36  of the membrane  32  (membrane-like member  30 ) in at least one of the plurality of membrane type resonating bodies  22 , as illustrated in  FIG. 6 .  FIG. 6  is a view illustrating a modification example of the soundproof structure  20 , and is a cross-sectional view illustrating a configuration in which the through-hole  38  is formed in the membrane-like member  30 . 
     By providing the through-hole  38 , the frequency of a sound absorption peak (resonance frequency) can be changed. It is considered that this is because by providing the through-hole  38  in the membrane-like member  30 , the acoustic impedance of the membrane-like member  30  changes, and the weight of the membrane-like member  30  decreases as the through-hole  38  is formed, resulting in a change in resonance frequency. The peak frequency can also be adjusted depending on the size of the through-hole  38 . 
     The position where the through-hole  38  is provided is not particularly limited, and the through-hole  38  may be provided at the center position of the vibratable part  36  of the membrane-like member  30 , or at a position in the vicinity of the fixed portion  34  fixed to the support body  24 . The frequency of the sound absorption peak (resonance frequency) and the sound absorption coefficient change according to the position of the through-hole  38 . The frequency of the sound absorption peak and the amount of change in the sound absorption coefficient are greater in a case where the through-hole  38  is provided at the center position of the vibratable part  36  of the membrane-like member  30  than in a case where the through-hole  38  is provided in the vicinity of the fixed portion  34 . 
     The soundproof structure  20  may further include the porous sound absorbing body  50  as illustrated in  FIG. 7 . The porous sound absorbing body  50  is disposed in the rear surface space  42  or at a position in contact with the membrane-like member  30 , and in the example illustrated in  FIG. 7 , the porous sound absorbing body  50  is disposed in the rear surface space  24 . By disposing the porous sound absorbing body  50  in the rear surface space  42  as described above, the peak sound absorption coefficient (sound absorption coefficient at a resonance frequency) is reduced, but the sound absorption range is widened on a low frequency side. 
       FIG. 7  is a view illustrating a modification example of the soundproof structure  20 , and is a cross-sectional view illustrating a configuration in which the porous sound absorbing body  50  is disposed in the rear surface space  42 . 
     In order to dispose the porous sound absorbing body  50  at a position in contact with the membrane-like member  30 , for example, the porous sound absorbing body  50  may be disposed on the upper surface of the membrane-like member  30  (the surface opposite to the support body  24 ). According to the above configuration, a wide band sound absorption effect of the porous sound absorbing body  50  can be obtained, and the sound absorption and sound insulation effects having the peak by the membrane type soundproof structure  20  present on the rear surface thereof are obtained in the vicinity of the resonance frequency, so that both the effects can be achieved. 
     The porous sound absorbing body  50  is not particularly limited, and a known porous sound absorbing body can be appropriately used. For example, various known porous sound absorbing bodies including foam materials such as foamed urethane, soft urethane foam, wood, ceramic particle sintered materials, and phenolic foams, and materials containing fine air; fibers and non-woven fabric materials such as glass wool, rock wool, microfiber (Thinsulate manufactured by 3M or the like), floor mats, carpet, melt blown non-woven fabric, metal non-woven fabric, polyester non-woven fabric, metal wool, felt, insulation boards, and glass non-woven fabric; wood wool cement boards; nanofiber materials such as silica nanofiber; gypsum board; or laminated materials or composite materials thereof can be used. 
     The flow resistance σ 1  of the porous sound absorbing body  50  is not particularly limited, but is preferably 1000 to 100,000 (Pa·s/m 2 ), and more preferably 5000 to 80,000 (Pa·s/m 2 ), and even more preferably 10,000 to 50,000 (Pa·s/m 2 ). The flow resistance σ 1  of the porous sound absorbing body  50  can be evaluated by measuring a normal incidence sound absorption coefficient of a porous sound absorbing body having a thickness of 1 cm, and fitting the measured value by a Miki model (J. Acoust. Soc. Jpn., 11(1) pp. 19-24 (1990)). Alternatively, the flow resistance σ 1  of the porous sound absorbing body  50  may be evaluated according to “ISO 9053”. 
     Furthermore, in the soundproof structure  20  (specifically, each of the plurality of membrane type resonating bodies  22 ), the combination of the membrane-like member  30  and the support body  24  (that is, the membrane  32  and the layer of the frame  26 ) may be provided only in one set as illustrated in  FIG. 2 , or may be provided in a state of overlapping a plurality of sets (that is, a configuration in which the plurality of rear surface spaces  42  may be overlapped in the thickness direction of the soundproof structure  20  may be adopted). 
     In the present invention, the soundproof structure  20  can absorb a sound by the above resonance structure, and can insulate a sound having a frequency higher than a relative maximum resonance frequency at which the sound absorption coefficient becomes a relative maximum among the resonance frequencies of the resonance structure. Therefore, the relative maximum resonance frequency is set to be lower than a sound insulation target frequency set for noise. More specifically, the resonance frequency of at least the fundamental vibration mode or one higher-order vibration mode of the membrane  32  (membrane-like member  30 ) of each membrane type resonating body  22  is set to be lower than the sound insulation target frequency. Here, the “resonance frequency of the higher-order vibration mode” means a resonance frequency whose sound absorption coefficient is higher than that at the resonance frequency of the fundamental vibration mode. 
     Furthermore, regarding the soundproofing performance of the soundproof structure  20 , in a case where the sound insulation target frequency is indicated as fn and the relative maximum resonance frequency is indicated as fr, fn/fr is 1.05 to 1.50. Accordingly, the soundproof structure  20  can efficiently insulate noise with a lightweight configuration. That is, according to the present invention, it is possible to achieve a relatively large higher-order vibration frequency on the high frequency side by the membrane type resonance structure in which the thickness of the rear surface space  42  is small, and to directly insulate an air propagation sound (noise) using highly efficient high-frequency resonance characteristics. 
     More specifically, as described in “SUMMARY OF THE INVENTION”, there is a situation where sound insulation properties are required rather than sound absorption as the performance of a soundproof structure, and for example, sound insulation properties are important in a space that is insulated from a noise source by a partition member such as a wall or a partition material with no gap. In such a situation, there is concern that a sufficient soundproofing effect may not be obtained even if the resonance structure described in JP2016-170194A in which noise is reduced by sound absorption is used. 
     On the other hand, a soundproof structure adopting a general resonance structure is considered to be able to selectively silence a sound at its resonance frequency (strictly speaking, a relative maximum resonance frequency) and is used in a state where the resonance frequency is matched to a specific frequency of noise (hereinafter, also referred to as a specific frequency). Here, in a case where the membrane type resonating body  22  illustrated in  FIG. 2  is used, as illustrated in  FIG. 8 , the sound absorption coefficient becomes a relative maximum at each of the resonance frequency of the fundamental vibration mode (1300 Hz) and the resonance frequencies of the higher-order vibration mode (about 3 kHz and about 4 kHz). Further, in the higher-order vibration mode, the sound absorption coefficient becomes higher than in the fundamental vibration mode, and two large peaks appear in the case illustrated in  FIG. 8 .  FIG. 8  is a diagram showing a sound absorption coefficient and a transmission loss difference of the membrane type resonating body  22 . In addition, in the graphs shown in  FIG. 8 , the graph showing the transmission loss difference shows the difference between the transmission loss in a case where the membrane type resonating body  22  (that is, the configuration in which the membrane  32  and the plate body  44  are fixed to the frame  26 ) is used, and the transmission loss in a case where only the plate body  44  (an acrylic plate having a thickness of 2 mm) is used. 
     However, according to the examination by the present inventors, it was found that in a case where the resonance frequency is matched to a specific frequency in order to insulate noise using the above-mentioned membrane type resonating body  22 , as shown in  FIGS. 8 and 9 , the transmission loss was rather small in the vicinity of the resonance frequency. Specifically, as shown in  FIG. 9 , it was found that in the vicinity of the resonance frequency of the higher-order vibration mode (about 3 kHz and 4 kHz), the transmission loss in a case of using the above-mentioned membrane type resonating body  22  is smaller than the transmission loss in a case of using only the plate body  44 .  FIG. 9  is a diagram showing the transmission loss of the membrane type resonating body  22 . In the figure, as a comparative example, the transmission loss in a case of using a structure in which the membrane  32  is excluded from the membrane type resonating body  22  (that is, a structure in which only the plate body  44  is fixed to the frame  26 ) and the transmission loss in a case of using only the plate body  44  (an acrylic plate having a thickness of 2 mm) are also shown. 
     On the other hand, it was found that the transmission loss shows a large peak in a frequency band exceeding the resonance frequency, as shown in  FIGS. 8 and 9 . That is, it became clear that in the membrane type resonating body  22 , the transmission loss of the air propagation sound in the plate body  44  (the rear surface plate  40 ) becomes small in the vicinity of the resonance frequency, but in a frequency band on the higher frequency side (strictly speaking, a band close to the resonance frequency), the transmission loss rises to the peak (relative maximum value). That is, according to the configuration of the membrane type resonating body  22 , at a frequency higher than the resonance frequency, higher sound insulation properties than the sound insulation properties obtained by the weight of a normal plate (that is, the sound insulation effect according to the mass law) are obtained. Therefore, while sound insulation properties are usually improved by increasing the weight of the plate body  44 , in the soundproof structure  20  of the present invention (specifically, the membrane type resonating body  22  forming the soundproof structure  20 ), it is possible to obtain large sound insulation properties only by fixing the membrane  32  which is relatively thin to the frame  26  without particularly increasing the volume and the mass. 
     In addition, in a case where noise having a specific frequency or noise having a narrow frequency band is insulated according to the mass law that is the mechanism of a normal sound insulation material, the sound pressure decreases overall, but a state where the noise at the specific frequency is significantly higher than sounds of surrounding frequencies remains unchanged. For this reason, even if the sound insulation material is applied, the noise at the specific frequency is still stronger than the noise at the surrounding frequencies, and therefore the state where the noise at the specific frequency is heard remains unchanged. On the other hand, in the soundproof structure  20  of the present invention, as shown in  FIGS. 8 and 9 , since the transmission loss has a peak at a frequency higher than the resonance frequency, noise having a frequency in the vicinity of the peak can be selectively insulated. As a result, it is possible to eliminate the state where the noise to be insulated is relatively louder than the sounds of the surrounding frequencies, so that it is possible to effectively suppress the state where the noise having the specific frequency is harsh to the ear. 
       FIG. 8  and  FIG. 9  show simulation results in a case where a plane wave sound is incident on the membrane type resonating body  22  from the membrane  32  side. The simulation is performed using the finite element method calculation software COMSOL ver. 5.3a (COMSOL Inc.), and the calculation condition is the same as the condition of Simulation 1, which will be described later. As the membrane  32 , a polyethylene terephthalate (PET) film having a Young&#39;s modulus of 4.5 GPa and a density of 1.4 g/cm 3  was postulated, and the thickness thereof was set to 50 The frame  26  was an acrylic cylinder, and the diameter of the opening (in other words, the diameter of the vibratable part  36  of the membrane  32 ) thereof was set to 20 mm. The plate body  44  was an acrylic plate having a thickness of 2 mm, and the thickness of the rear surface space  42  was set to 3 mm. 
     The mechanism of the sound insulation behavior described above will be described. In a case where noise is incident on the membrane  32  (the membrane-like member  30 ) in the membrane type resonating body  22  and the membrane  32  vibrates, the air in the rear surface space  42  undergoes elastic deformation (adiabatic compression and adiabatic expansion) due to the vibration, and the sound pressure in the rear surface space  42  changes accordingly. In a case where the membrane  32  vibrates, the vibration propagates from a part of the frame  26  (support body  24 ) fixed to the membrane  32  to a part thereof fixed to the plate body  44  (rear surface plate  40 ), so that the frame  26  itself vibrates. At this time, at the resonance frequency, both the vibration of the frame  26  and the sound pressure in the rear surface space  42  become large, and as a result, the plate body  44  (rear surface plate  40 ) is shaken, which causes a sound to escape (be transmitted). On the contrary, in a frequency band higher than the resonance frequency, the phase of the vibration of the membrane  32  and the shaking phase of the plate body  44  are in antiphase, so that the sound shaking the plate body  44  (rear surface plate  40 ) is canceled out, resulting in an increase in the transmission loss. 
     On the basis of the sound insulation behavior as described above, in the present invention, the sound insulation properties can be enhanced by intentionally setting the resonance frequency (strictly speaking, the relative maximum resonance frequency) that is usually matched to the specific frequency of noise to a low frequency side. As a result, the partition member  10  provided with the soundproof structure  20  effectively insulate high frequency noise (particularly single frequency sounds such as motor operating noise or inverter switching noise) without particularly increasing the volume and weight thereof. 
     As a resonance structure that cancels out noise at a frequency higher than the resonance frequency, the resonance structure body of JP1998-205351A (JP-H10-205351A) can be adopted. In the resonance structure body, in order to resonate (vibrate) the vibrating body, the noise generating vibrating body is connected to the vibrating body via the rigid body such as the connecting mechanism. However, the resonance structure body is not suitable in a case where a sound source is far from the vibrating body and a case where it is difficult to provide connection to a source of noise such as road noise or wind noise of a car. 
     On the other hand, in the resonance structure (that is, the structure of the membrane type resonating body  22 ) adopted by the soundproof structure  20  of the present invention, the noise propagating in the air is directly incident on the surface of the membrane-like member  30 , and the membrane-like member  30  resonates (vibrates). Therefore, it is not necessary to particularly provide connection between the membrane-like member  30  and the sound source. Therefore, in the soundproof structure  20  of the present invention, it is not necessary to provide a connecting mechanism or the like for transmitting vibration. 
     Furthermore, in the resonance structure body disclosed in JP1998-205351A (JP-H10-205351A), in a case where the resonance frequency largely deviates from the frequency of the sound to be silenced, the silencing effect tends to be reduced. Therefore, the resonance frequency also needs to be set to a high frequency. However, in a case where high frequency resonance is generated, the resonance efficiency may decrease depending on the vibration mode of the vibrating body (for example, in the fundamental vibration). 
     On the other hand, in the resonance structure adopted by the soundproof structure  20  of the present invention, by setting fn/fr, which is the ratio of the frequency of the sound absorption peak (relative maximum resonance frequency) to the sound insulation target frequency, to a suitable range, it is possible to effectively insulate noise. 
     More specifically, as shown in  FIGS. 10 and 11 , the transmission loss difference becomes a relative minimum at the resonance frequency, and the transmission loss difference becomes a relative maximum on the high frequency side of the resonance frequency. In  FIGS. 10 and 11 , the transmission loss difference is the difference between the transmission loss in a case of using the membrane type resonating body  22 , and the transmission loss in a case of using the structure in which only the plate body  44  is fixed to the frame  26  (the structure in which the membrane  32  is not attached).  FIGS. 10 and 11  are diagrams showing simulation results of the transmission loss difference in a case where the thickness of the membrane  32  is 250 μm and 180 μm. The simulations in which the results shown in  FIGS. 10 and 11  were obtained were performed under the same conditions as those in the case of  FIGS. 8 to 10  described above, except for the thickness of the membrane  32 . 
     Furthermore, as shown in  FIGS. 12 and 13 , in a case where the thicknesses of the membrane  32 , the plate body  44 , and the rear surface space  42  change, the resonance frequency itself changes, but the ratio of the frequency at which the transmission loss difference becomes a relative maximum to the frequency at which the transmission loss difference becomes a relative minimum (hereinafter referred to as the frequency ratio) is in a range of 1.1 to 1.4. Strictly speaking, the frequency ratio in a case where the thickness of the plate body  44  (rear surface plate  40 ) is 2 mm is in a range of 1.15 to 1.32 as shown in  FIG. 12 . The frequency ratio in a case where the thickness of the plate body  44  (rear surface plate  40 ) is 1 mm is in a range of 1.14 to 1.31 as shown in  FIG. 13 . 
       FIGS. 12 and 13  are diagrams showing frequency ratios in a case where the thickness of the membrane  32  is set to 125 μm, 180 μm, and 250 μm, and the thickness of the rear surface space  42  is changed in a range of 1 to 6 mm in increments of 1 mm.  FIG. 12  shows the frequency ratio in a case where the thickness of the plate body  44  is 2 mm, and  FIG. 13  shows the frequency ratio in a case where the thickness of the plate body  44  is 1 mm. Here, the frequency ratio is obtained from the following formula by performing the same simulation as in the case of  FIGS. 10 and 11  and calculating the frequency at which the transmission loss difference becomes a relative maximum and the frequency at which the transmission loss difference becomes a relative minimum. 
       Frequency ratio=(frequency at which transmission loss difference becomes relative maximum)/(frequency at which transmission loss difference becomes relative minimum) 
     Furthermore, as shown in  FIG. 14 , the frequency at which the transmission loss difference becomes a relative maximum and the frequency at which the transmission loss difference becomes a relative minimum are respectively present in a fundamental vibration mode and a higher-order vibration mode. That is, as shown in  FIG. 14 , from the low frequency side, the frequency at which the transmission loss difference becomes a relative minimum in the fundamental vibration mode, the frequency at which the transmission loss difference becomes a relative maximum in the fundamental vibration mode, the frequency at which the transmission loss difference becomes a relative minimum in the higher-order vibration mode, and the frequency at which the transmission loss difference becomes a relative maximum in the higher-order vibration mode appear in this order.  FIG. 14  is a diagram showing a simulation result of a transmission loss difference in a case where the thickness of the membrane  32  is 100 μm. The simulation in which the results shown in  FIG. 14  were obtained was performed under the same conditions as those in the case of  FIGS. 10 and 11  described above, except for the thickness of the membrane  32 . 
     Furthermore, as shown in  FIGS. 15 and 16 , the frequency ratio of each of the fundamental vibration mode and the higher-order vibration mode (the ratio of the frequency at which the transmission loss difference becomes a relative maximum and the frequency at which the transmission loss difference becomes a relative minimum) slightly changes in a case where the thickness of the membrane  32  is changed, but is in the range of 1.1 to 1.4. Strictly speaking, the frequency ratio of each vibration mode in a case where the thickness of the membrane  32  is 100 μm is in a range of 1.15 to 1.27 as shown in  FIG. 15 . The frequency ratio in a case where the thickness of the membrane  32  is 50 μm is in a range of 1.16 to 1.24 as shown in  FIG. 16 . 
       FIGS. 15 and 16  are diagrams showing the frequency ratio of each vibration mode in a case where the thickness of the rear surface space  42  is changed in a range of 2 to 6 mm (or 3 to 6 mm) in increments of 1 mm.  FIG. 15  shows the frequency ratio in a case where the thickness of the membrane  32  is 100 μm, and  FIG. 16  shows the frequency ratio in a case where the thickness of the membrane  32  is 50 mm. The frequency ratio of each vibration mode is obtained from the following formula by performing the same simulation as in the case of  FIGS. 10 and 11  and calculating the frequency at which the transmission loss difference becomes a relative maximum and the frequency at which the transmission loss difference becomes a relative minimum for each of the fundamental vibration mode and the higher-order vibration mode.
         Frequency ratio of fundamental vibration mode=(frequency at which transmission loss difference becomes relative maximum in fundamental vibration mode)/(frequency at which transmission loss difference becomes relative minimum in fundamental vibration mode)   Frequency ratio of higher-order vibration mode=(frequency at which transmission loss difference becomes relative maximum in higher-order vibration mode)/(frequency at which transmission loss difference becomes relative minimum in higher-order vibration mode)       

     From the above results, it was found that in a case where the frequency at which the transmission loss becomes a relative minimum, that is, the resonance frequency of the membrane type resonating body  22  is determined, the transmission loss becomes a relative maximum at a frequency in a range of 1.05 to 1.50 times the resonance frequency (in other words, sufficient sound insulation properties are obtained). Based on this, in the present invention, the resonance frequency of the membrane type resonating body  22  is set to an appropriate value with respect to the specific frequency of noise, that is, the sound insulation target frequency. Specifically, considering that fn/fr, which the ratio of the relative maximum resonance frequency to the sound insulation target frequency, is 1.05 to 1.50, the resonance frequency is set to a lower frequency side than the sound insulation target frequency. Accordingly, the frequency at which the transmission loss becomes a relative maximum matches the sound insulation target frequency, so that it is possible to effectively insulate the sound of the sound insulation target frequency. 
     In a case where the membrane  32  (the membrane-like member  30 ) vibrates in the higher-order vibration mode, the resonance frequency in the higher-order vibration mode is set to an appropriate value in a lower frequency band than the sound insulation target frequency. Accordingly, the frequency at which the transmission loss becomes a maximum in the higher-order vibration mode matches the sound insulation target frequency, so that it is possible to effectively insulate the sound of the sound insulation target frequency. 
     In addition, fn/fr is preferably in a range of 1.08 to 1.40, and more preferably in a range of 1.10 to 1.35. 
     EXAMPLES 
     [Simulation 1] 
     The soundproofing performance of the resonance structure of the soundproof structure of the present invention was examined by a simulation using the finite element method calculation software COMSOL ver. 5.3a (COMSOL Inc.). 
     A calculation model used for the simulation was a two-dimensional axisymmetric structure calculation model, and the simulation was performed on the resonance structure of the soundproof structure of the present invention, that is, a structure in which a membrane-like member was fixed to one end of a support body with an opening formed therein and a rear surface plate was fixed to the opposite side. As the membrane-like member, a polyethylene terephthalate (PET) film having a Young&#39;s modulus of 4.5 GPa and a density of 1.4 g/cm 3  was postulated, and the thickness thereof was set to 50 μm. The support body was an acrylic cylinder, and the diameter of the opening (in other words, the diameter of a vibratable part of the membrane-like member) thereof was set to 20 mm. The rear surface plate was an acrylic plate having a thickness of 2 mm, and thickness of the rear surface space was set to 3 mm. 
     In the simulation, the transmittance, the reflectance, and the sound absorption coefficient were calculated in a case where a plane wave sound was incident from the membrane surface (surface of the membrane-like member) side of the resonance structure. The sound absorption coefficient was calculated in a normal incidence sound absorption coefficient arrangement, and each relative maximum value and the frequency at that time were calculated. 
       FIG. 17  shows a calculation result in a case where the sound absorption coefficient in a case where a sound is incident in a plane wave form from the membrane surface side of the resonance structure is simulated. As shown in  FIG. 17 , the sound absorption coefficient becomes a relative maximum at each of a resonance frequency of the fundamental vibration mode (about 1300 Hz) and the resonance frequencies of a higher-order vibration mode (about 3 kHz and about 4 kHz). In the higher-order vibration mode, the sound absorption coefficient becomes higher than in the fundamental vibration mode, and two large peaks appear as shown in  FIG. 17 . 
       FIG. 18  shows a calculation result in a case where a transmission loss in a case where a sound is incident in a plane wave form from the membrane surface side of the resonance structure is simulated. The vertical axis of  FIG. 18  represents the difference between the transmission loss in a case of using the above resonance structure and the transmission loss in a case of using a single acrylic plate having a thickness of 2 mm. That is, it becomes clear from  FIG. 18  how much the transmission loss becomes larger in a case where the resonance structure (membrane type resonance structure) is attached to the rear surface plate than in a case where a single plate (acrylic plate) having the same thickness is used. 
     In a case where the above resonance structure is used, as can be seen from  FIG. 18 , it was found that even though the membrane type resonance structure is formed, the transmission loss becomes smaller than zero in the vicinity of the resonance frequency of the higher-order vibration mode (that is, the transmittance of a sound passing through the rear surface plate is increased). 
       FIG. 19  shows a calculation result in a case where a transmission loss in a case where a sound is incident in a plane wave form from the membrane surface side of the resonance structure is simulated. The vertical axis of  FIG. 19  represents the difference between the transmission loss when using the above resonance structure and the transmission loss when using a structure excluding only the membrane-like member from the resonance structure (that is, a structure including only the rear surface plate and the support body). As shown in  FIG. 19 , the transmission loss becomes larger in a case where a frame (support body) is attached to the plate than in a case of using a single plate body. On the other hand, it was found that in a case where the membrane-like member is further attached, the transmission loss becomes small in the vicinity of the resonance frequency exhibiting a high sound absorption coefficient, and the transmission loss has a large peak on the high frequency side above the resonance frequency. That is, according to the resonance structure of the soundproof structure of the present invention, it became clear that the transmission loss of an air propagation sound becomes smaller in the vicinity of the resonance frequency, but in a frequency band on the higher frequency side (particularly, a band near the resonance frequency), the transmission loss increases and reaches the peak. That is, according to the resonance structure in which the membrane-like member and the rear surface plate are fixed to the support body, larger sound insulation properties can be obtained for noise having a higher frequency than the resonance frequency than sound insulation properties achieved by the weight of a normal plate (that is, sound insulation properties according to the mass law). Therefore, while sound insulation properties are usually enhanced by increasing the weight of a plate, in a case where the resonance configuration described above is used, large sound insulation properties can be obtained only by fixing the membrane-like member having a small thickness and a small mass (in Simulation 1, the membrane-like member having a thickness of 50 μm) to the support body without particularly increasing the volume and the mass of the structure. 
     Example 1 
     &lt;Production of Soundproof Structure&gt; 
     As a membrane-like member, a PET film (Lumirror manufactured by Toray Industries, Inc.) having a thickness of 50 μm was prepared and cut into a circular shape having a diameter of 60 mm. 
     An acrylic plate (manufactured by Hikari Co., Ltd.) having a thickness of 3 mm was prepared and cut into a disc having a diameter of 60 mm using a laser cutter, and an opening having a square shape of 20 mm on a side was formed in the center portion thereof to produce a ring-shaped plate (hereinafter, doughnut-shaped member). This doughnut-shaped member was used as a support body. Then, one surface of the produced doughnut-shaped member and the circular PET film were overlapped so that the outer edges of the two were coincident with each other, and the two were bonded using a double-sided tape (Genba no Chikara ASKUL Corporation). 
     A circular acrylic plate (rear surface plate) having a thickness of 2 mm and a diameter of 60 mm was attached to the other surface of the doughnut-shaped member with a double-sided tape. 
     By the above procedure, a soundproof structure having a drum-shaped vibrating membrane structure (membrane type resonance structure) was produced. The rear surface space of the soundproof structure is a closed space and has a thickness of 3 mm. 
     &lt;Evaluation&gt; 
     Acoustic tube measurement was performed with the produced soundproof structure disposed such that a sound was incident from the membrane surface (membrane-like member) side. Specifically, according to “ASTM E2611-09: Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method”, a transmittance and reflectance measurement system using a 4-terminal microphone (not illustrated) was prepared and evaluation was performed. The internal diameter of the acoustic tube was set to 40 mm. In addition, WinZacMTX manufactured by Nihon Onkyo Engineering Co., Ltd. can be used for the same measurement. 
     Furthermore, by the same acoustic tube measurement as described above, the transmittance and the reflectance were measured for a single acrylic plate having a thickness of 2 mm and a diameter of 60 mm. 
     Thereafter, the transmission loss was obtained from the transmittance obtained in each measurement, and the absorption coefficient (sound absorption coefficient) of the sound, which was (1-transmittance-reflectance), was obtained. 
     The sound absorption coefficient obtained for the produced soundproof structure is shown in  FIG. 20 . In addition, the difference between the transmission losses respectively obtained for the produced soundproof structure and the single acrylic plate is shown in  FIG. 21 .  FIG. 21  is a diagram showing how much the transmission loss is increased by fixing the membrane-like member and the rear surface plate to the support body. 
     As can be seen from  FIG. 20 , in the produced soundproof structure, the frequency of the fundamental vibration mode is present in the vicinity of 1.5 kHz, and the sound absorption peaks are present at the frequencies (3 kHz and 4 kHz) on the higher frequency side. That is, the produced soundproof structure is a structure that exhibits a large sound absorption effect in the higher-order vibration mode. 
     Furthermore, as can be seen by comparing  FIGS. 20 and 21 , at the resonance frequency of the higher-order vibration mode exhibiting a high sound absorption coefficient, the transmission loss of the soundproof structure produced by fixing the membrane-like member and the rear surface plate to the support body becomes smaller than the transmission loss of the single acrylic plate (in other words, the transmittance becomes higher). On the other hand, on the higher frequency side than the above resonance frequency, the transmission loss of the produced soundproof structure becomes larger than the transmission loss of the single acrylic plate. As described above, in a case where a sound is incident on the soundproof structure as a plane wave, a large insulation effect is obtained on the higher frequency side than the resonance frequency. 
     Example 2 
     &lt;Production of Box for Radiated Sound Experiment&gt; 
     In order to investigate a radiated sound of a sound source, which was radiated from the sound source, a radiated sound experiment in a box was examined. Therefore, a box was prepared by surrounding a square cubic space of 300 mm on a side with five acrylic plates (thickness 10 mm). One surface of this box was an opening surface, and had a square opening of 300 mm on a side. In addition, a porous sound absorbing body having a thickness of 10 mm (CALMFLEX manufactured by Inoac Corporation) was attached to the inner surface of each of the five acrylic plates surrounding the space. In addition, a speaker as a sound source was disposed inside the box so that the acoustic output surface (speaker surface) thereof faced the opening. In addition, a soundproof structure produced by the procedure described below was disposed at a position where the opening in the box was closed. Accordingly, an experiment system in which radiation of a sound spreading from the speaker was insulated by the soundproof structure disposed on the opening surface was set. 
     &lt;Production of Soundproof Structure&gt; 
     By the same procedure as in Example 1, a soundproof structure having a membrane type resonance structure was produced. Acrylic was used as the material of a frame. Regarding the frame, a structure having a thickness of 3 mm, a square opening of 20 mm on a side, and an edge width of 5 mm was a basic unit, and a structure in which a plurality of the basic structures were arranged to reach an overall size of 300 mm×300 mm was used as a frame structure (support body). Regarding a method of producing the frame structure, a square was cut out from an acrylic plate having a thickness of 3 mm using a laser cutter to produce the frame structure. Accordingly, the frame structure having a size of 300 mm×300 mm in which 20 mm squares were periodically arranged at a pitch of 25 mm could be obtained. A rear surface plate made of an acrylic plate having a thickness of 2 mm was attached to the frame structure with a double-sided tape. In addition, a PET film having a thickness of 50 μm was attached to the surface (one end surface) of the frame structure. Accordingly, a soundproof structure in which a plurality of the same vibrating membrane structures as in Example 1 were periodically arranged and attached to the rear surface plate was produced. 
     &lt;Evaluation&gt; 
     The produced soundproof structure was attached to the position where the opening of the above-mentioned box was closed, and the amount of sound pressure transmitted through the opening surface was measured. Specifically, the amount of sound pressure emitted from the opening was measured by disposing three microphones at a position 150 mm away from the opening surface on the outside of the opening surface, and obtaining the average value of the sound pressure energies in the microphones. 
     In addition, the amount of transmitted sound pressure was measured by the same procedure as above in a case where a single acrylic plate having a thickness of 2 mm and a diameter of 60 mm was disposed on the opening surface. 
     The measurement results of the transmitted sound energies in a case of using the produced soundproof structure and in a case of using the single acrylic plate are shown in  FIG. 22 . In addition, the difference in transmission loss between the case where the produced soundproof structure was used and the case where the single acrylic plate was used is shown in  FIG. 23 . 
     As is clear from  FIGS. 22 and 23 , while the amount of transmitted sound is higher in the vicinity of the resonance frequency in the case of using the produced soundproof structure than in the case of using the single acrylic plate, on the higher frequency side, the amount of transmitted sound is smaller in the case of using the produced soundproof structure than in the case of using the single acrylic plate (that is, the insulation is larger). It was found that even in the case of a radiation source having such a spread, as in the case of the plane wave incidence as in Example 1, a large insulation region is provided on the higher frequency side than the resonance frequency. 
     [Simulation 2] 
     A transmission loss in a case where the thickness of the rear surface space was changed from 1 mm to 6 mm in increments of 1 mm was simulated using the same model as the calculation model used in Simulation 1. Each setting value in the calculation model is the same as in the case of Simulation 1 except for the thickness of the rear surface space. 
     The transmission loss calculated for the thickness of each rear surface space is shown in  FIG. 24 . The vertical axis of  FIG. 24  represents the difference between the transmission loss calculated for the thickness of each rear surface space and the transmission loss in a case where a structure in which only the membrane-like member was excluded from the resonance structure of the soundproof structure of the present invention (that is, a structure with only the rear surface plate and the support body) was used. 
     In a case where the thickness of the rear surface space is in the above range, as can be seen from  FIG. 24 , with any thickness, a region in which the transmission loss becomes a relative minimum in the vicinity of the resonance frequency, and the transmission loss becomes a peak (a relative maximum) on the higher frequency side is present. That is, the soundproof structure of the present invention having the resonance structure (membrane type resonance structure) exhibits its effect regardless of the thickness of the rear surface space. 
     [Simulation 3] 
     A transmission loss in a case where the thickness of the membrane-like member was changed from 10 μm to 100 μm in increments of 10 μm was simulated using the same model as the calculation model used in the simulation 1. Each setting value in the calculation model is the same as in the case of Simulation 1 except for the thickness of the membrane-like member. 
     The transmission loss calculated for the thickness of each membrane-like member is shown in  FIGS. 25 and 26 . The vertical axis of each of  FIGS. 25 and 26  represents the difference between the transmission loss calculated for the thickness of each membrane-like member and the transmission loss in a case where the structure in which only the membrane-like member was excluded from the resonance structure of the soundproof structure of the present invention (that is, the structure with only the rear surface plate and the support body) was used. 
     In a case where the thickness of the membrane-like member is in the above range, as can be seen from  FIGS. 25 and 26 , with any thickness, a region in which the transmission loss becomes a relative minimum in the vicinity the resonance frequency, and the transmission loss becomes a peak (a relative maximum) on the higher frequency side is present. That is, the soundproof structure of the present invention having the resonance structure (membrane type resonance structure) exhibits its effect regardless of the thickness and hardness of the membrane-like member. 
     In each of Examples 1 and 2 of the present invention and Simulations 1 to 3 described above, the relative maximum resonance frequency fr is set to be lower than the sound insulation target frequency fn, and fn/fr is in the range of 1.05 to 1.50, so that both are within the ranges of the present invention. Therefore, the effect of the present invention is clear. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               10 : Partition member 
               20 : Soundproof structure 
               22 : Membrane type resonating body 
               24 : Support body 
               24   s : Opening surface 
               26 : Frame 
               28 : Opening 
               30 : Membrane-like member 
               32 : Membrane 
               34 : Fixed portion 
               36 : Vibratable part 
               38 : Through-hole 
               40 : Rear surface plate 
               42 : Rear surface space 
               44 : Plate body 
               50 : Porous sound absorbing body