Electroacoustic transducer

Abstract

[Problem] To provide an electroacoustic transducer applicable to all kinds of cabinets and capable of maintaining the expansion of the lowest reproducible frequency for a long period of time. [Solution] In an electroacoustic transducer 1 according to the present invention, a sealing body 4, which stores a gas, having a volume elastic modulus smaller than that of air under the conditions of 1 atm and 20ºC, in an airtight state, and has enough flexibility to propagate the vibration of air to internal gas, is provided in a cabinet 2 in which one or more speaker units 3 for emitting sound waves are attached to at least one surface.

Description

electroacoustic transducer

[0001] The present invention relates to an electroacoustic transducer.

[0002] Regarding technology including a speaker unit 3 that emits sound waves, Patent Document 1 discloses a technology in which a cabinet is used that is shielded from the front and back, and the internal space of the cabinet is filled with carbon dioxide gas so that sound waves, which are air compression waves generated in front of the diaphragm when the diaphragm is driven by the speaker unit 3, are not canceled out by anti-phase compression waves generated on the back of the diaphragm. Patent Document 2 also discloses a technology in which the internal space of the cabinet is filled with a gas other than carbon dioxide gas that has a specific heat ratio of 1.28 or less. According to the technologies of Patent Documents 1 and 2, the radiation efficiency of sound waves at low frequencies is increased, thereby making it possible to expand the low-frequency reproduction limit frequency band.

[0003] Japanese Patent Application Laid-Open No. 4-117900 Japanese Patent Application Laid-Open No. 2007-60501

[0004] However, the technologies of Patent Documents 1 and 2 directly fill the cabinet with a gas such as carbon dioxide, and can only be applied to cabinets that are sealed to prevent the gas from escaping. Meanwhile, in addition to sealed cabinets, there are many other types of cabinets, such as bass-reflex (phase-inverting) cabinets with duct holes, and cabinets that are not completely sealed and have gaps for operation panels, connection terminals, etc. Furthermore, even in sealed cabinets, it is not easy to maintain a completely sealed state over a long period of time in industrial products manufactured by assembling multiple parts, and there is a possibility that gas may gradually leak through the gaps between the parts, making it impossible to maintain the originally expected expansion of the low-frequency reproduction limit frequency band.

[0005] The present invention has been made in view of the above circumstances, and its object is to be applicable to all types of cabinets and to maintain an expanded low-frequency reproduction limit frequency band for a long period of time.

[0006] As a result of extensive research into solving the above problems, the inventors have found that the above object can be achieved by providing a sealed body containing a gas having a bulk modulus of less than 140 kPa inside a cabinet. The inventors have then perfected the present invention. Specifically, the present invention provides the following:

[0007] The present invention is an electroacoustic transducer characterized in that a cabinet has one or more speaker units 3 that emit sound waves attached to at least one surface, and a gas that has a bulk modulus at 1 atmosphere and 20 degrees Celsius that is smaller than that of air under the same conditions is contained in an airtight state, and an enclosure that is flexible enough to transmit vibrations of the air to the gas inside is provided.

[0008] According to the above-described configuration, when sound waves are emitted from the speaker unit 3, air vibrations propagate to the gas contained in the enclosure due to the flexibility of the enclosure. The gas to which the vibrations propagate has a bulk modulus lower than that of air at 1 atmosphere and 20 degrees Celsius, i.e., a bulk modulus lower than that of ordinary air (140 kilopascals). Because gas with a low bulk modulus changes volume more readily than air in response to pressure changes, the repulsive force (spring constant, stiffness) between the air inside the cabinet, which acts as a spring when the diaphragm vibrates, and the gas decreases, thereby lowering the minimum resonant frequency and expanding the low-frequency reproduction limit frequency range. Furthermore, because the gas that expands the low-frequency reproduction limit frequency range is contained within the enclosure and installed inside the cabinet, the system is applicable to all types of cabinets and can maintain the expansion of the low-frequency reproduction limit frequency range over a long period of time.

[0009] According to the present invention, it is possible to apply it to all kinds of cabinets and maintain the expansion of the low-frequency reproduction limit frequency band for a long period of time.

[0010] Fig. 1 is a schematic diagram of an electroacoustic converter according to this embodiment. Fig. 2A is a schematic diagram of an electroacoustic converter according to this embodiment. Fig. 2B is a schematic diagram of an electroacoustic converter according to this embodiment. Fig. 2C is a schematic diagram of an electroacoustic converter according to this embodiment. Fig. 2D is a schematic diagram of an electroacoustic converter according to this embodiment. Fig. 3 is a graph comparing sound pressure and frequency characteristics. Fig. 4 is a schematic diagram of an electroacoustic converter according to a modified example. Fig. 5 is a schematic diagram of an electroacoustic converter according to a modified example.

[0011] Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] 1, the electroacoustic transducer 1 is configured such that an enclosure 4 is provided inside a cabinet 2 having one or more speaker units 3 for emitting sound waves attached to at least one surface. The enclosure contains, in an airtight state, a gas whose bulk modulus at 1 atmosphere and 20 degrees Celsius is smaller than that of air. The enclosure 4 is flexible enough to transmit air vibrations to the gas inside.

[0013] The speaker unit 3 comprises a diaphragm, a voice coil fixed to the diaphragm, and a magnetic circuit having a magnet for applying a magnetic field to the voice coil. By applying an audio signal voltage to the voice coil installed in the magnetic circuit, a current flows, driving the diaphragm by electromagnetic force and generating sound waves, which are air compression waves, in front of the diaphragm.

[0014] (Cabinet 2) The cabinet 2 is a sealed cabinet whose interior is sealed from the outside. This prevents compressional waves that occur on the back side of the diaphragm of the speaker unit 3 and are in opposite phase to the compressional waves on the front side of the diaphragm from canceling out the compressional waves on the front side. This makes it possible for the sealed cabinet 2 to improve sound quality.

[0015] The cabinet 2 may be an open-type cabinet whose interior is partially open to the outside. Examples of open-type cabinets include the bass reflex type shown in Fig. 2A and the double bass reflex type shown in Fig. 2B, as well as a type shown in Fig. 2C in which the electric circuit unit 8 is provided inside the cabinet 2 and the operation knobs are exposed to the outside, creating a gap between the cabinet 2 and the operation knobs. The cabinet 2 may also be provided with sound-absorbing material 6 inside to reduce standing waves, as shown in Fig. 2D.

[0016] In a bass reflex or double bass reflex open cabinet 2, a specific frequency (determined by the cabinet volume and the dimensions of the duct 5) of the compressional waves generated on the back of the diaphragm in the speaker unit 3, which are in the opposite phase to the compressional waves on the front of the diaphragm, resonates in phase inversion, making it possible to reproduce sound waves of even lower frequencies than a sealed cabinet.

[0017] (Gas) Inside the cabinet 2, a gas having a bulk modulus smaller than that of air under conditions of 1 atmosphere and 20 degrees Celsius is contained and sealed in an enclosed body 4. Here, "a gas having a bulk modulus smaller than that of air under conditions of 1 atmosphere and 20 degrees Celsius" refers to a gas having a bulk modulus smaller than that of ordinary air, 140 kilopascals. For example, carbon dioxide (CO ２ ), or a gas containing one or more of HFCs (hydrofluorocarbons), or HCFCs (hydrochlorofluorocarbons). This allows a gas with a bulk modulus lower than that of air, i.e., a gas with a bulk modulus lower than 140 kPa, the bulk modulus of ordinary air, to be present inside the cabinet 2 in a sealed or open cabinet, thereby lowering the minimum resonance frequency and expanding the low-frequency reproduction limit frequency. Furthermore, by changing the type, amount, or combination of gases with different characteristics, it is possible to easily adjust the minimum resonance frequency. Note that, a "gas with a bulk modulus lower than that of air under conditions of 1 atmosphere and 20 degrees Celsius" can also be expressed as a gas with a density and squared sound speed lower than that of air, based on Equation 1 described below.

[0018] Here, "air" or "ordinary air" refers to a gas mixture whose main components are nitrogen, oxygen, argon, and carbon dioxide, and which also contains trace components such as rare gases such as neon, helium, and krypton, and water vapor, and forms the atmosphere near the Earth's surface.

[0019] HFCs (hydrofluorocarbons) are chemical substances composed of carbon, hydrogen, and fluorine. Specific examples include R-134a, R-410a, and R-1234yf, which are defined by the nomenclature of the international standard ISO. R-134a, R-410a, and R-1234yf are often used as refrigerants, and have the characteristics of zero ozone depletion potential (ODP) and low global warming potential (GWP). From the perspective of global warming potential (GWP), R-1234yf is preferred as the gas to be used in the electroacoustic converter 1. This is because R-1234yf has a lower global warming potential (GWP) than R-134a and R-410a.

[0020] HCFCs (hydrochlorofluorocarbons) are chemical substances composed of carbon, hydrogen, fluorine, and chlorine. Specific examples include HCFC-22, HCFC-141b, HCFC-142b, HCFC-124, HCFC-141, and HCFC-142, which are defined by the nomenclature of the international standard ISO. From the perspective of global warming potential (GWP), HCFC-22 is preferred as the gas to be used in the electroacoustic converter 1 because it exhibits a lower global warming potential value than other chemical substances.

[0021] Furthermore, the "gas having a bulk modulus lower than that of air under conditions of 1 atmosphere and 20 degrees Celsius" may be, in addition to the above-mentioned HFCs (hydrofluorocarbons) and HCFCs (hydrochlorofluorocarbons), a gas containing one or more of the following gas species: hydrogen, helium, neon, acetylene, ammonia, carbon monoxide, ethylene, hydrogen fluoride, and methane. In this case, regardless of the composition of the mixture ratio at which the gas is prepared, the gas can have a bulk modulus lower than that of air under conditions of 1 atmosphere and 20 degrees Celsius.

[0022] (Bulk modulus of gas) The bulk modulus of gas is a physical property that indicates how much the volume of a gas changes when an external force is applied. Specifically, it is expressed as the ratio of the pressure change ΔP to the volume change rate ΔV / V when pressure changes, i.e., ΔPV / ΔV. Furthermore, the bulk modulus can generally be expressed by the following formula (1):

[0023]

[0024] where κ is the bulk modulus of the gas (Pa). ０ is the density of the gas (kg / m ３ ) where c is the sound speed of the gas (m / s), γ is the specific heat ratio of the gas, and P is the static pressure (Pa). Equation (1) is the relationship between the bulk modulus κ and the density ρ ０ and the speed of sound c. That is, the bulk modulus of a gas (Pa) is expressed as a function of the density of the gas (kg / m ３ ) and the square of the speed of sound (m / s). Furthermore, since the right-hand side of equation (1) includes the relationship between γ and P, it indicates that the bulk modulus κ depends on the thermodynamic properties and pressure of the gas. In other words, Patent Document 1 lists the product of the square of the speed of sound of the gas and the density as a requirement, and Patent Document 2 also lists the specific heat ratio as a requirement, but it can be seen that both use gases with a bulk modulus smaller than that of air as a means of realizing this.

[0025] (Enclosure 4) The enclosure 4 filled with the gas described above is airtight and flexible enough to transmit air vibrations to the gas inside. That is, the enclosure 4 is formed of a material thick enough to vibrate in response to air vibrations. For example, the enclosure 4 is formed as a sheet-like bag made of a polymer material such as polyethylene or polypropylene and having a thickness of approximately 0.01 mm to 0.1 mm. The enclosure 4 may be formed of thin rubber or silicone, or may be formed of an elastomer or thin cloth whose airtightness is ensured by sealing or coating. Furthermore, the enclosure 4 may be formed as a layered sheet made by combining different materials in layers. For example, the enclosure 4 may be formed as a sheet that combines cloth and rubber, or an elastomer and a thin metal film, to adjust the balance between flexibility and airtightness.

[0026] Although sound waves are always reflected from the inner wall of the electroacoustic transducer 1, as shown in the above-mentioned formula 1 and the formulas 2 and 3 described below, the reflection does not affect the lowest resonance frequency. In other words, the lowest resonance frequency is determined only by stiffness and mass, and formula 2 does not include any parameters related to sound reflection. Therefore, the encapsulation body 4 does not need to have the property of transmitting sound waves. Stiffness is a physical concept that indicates how resistant an object is to deformation by an external force, and refers to the reaction force generated against the deformation when an object is deformed by an external force. For example, if the bulk modulus is high, the object will repel changes in the volume direction due to an external force, resulting in less deformation, and therefore has high stiffness.

[0027] The enclosure 4 must also satisfy the following requirements. Specifically, the first requirement is that the internal air pressure of the enclosure 4 must be the same as the surrounding air pressure (usually 1 atmosphere) when the enclosure 4 is stationary. This is because if tension is generated in the enclosure 4, like an inflated rubber balloon, the gas inside the enclosure 4 will be compressed, causing the air pressure to become higher than the external air pressure, resulting in an increase in the bulk modulus.

[0028] Furthermore, when the speaker unit 3 operates to emit sound, even when the air in the cabinet 2 expands, the second requirement is that the internal air pressure of the enclosure 4 must always be the same as that of the surrounding air in the cabinet 2. In this case, if the maximum one-sided amplitude of the speaker unit 3 of the electroacoustic transducer 1 is Xmax (m), the air in the cabinet 2 will expand at a maximum of πa ２ Xmax (m ３ ) Since the gas will expand, the capacity of the enclosure 4 must be large enough to accommodate the volume of the gas to be filled, so that the internal air pressure of the enclosure 4 remains the same as the surrounding air pressure.

[0029] (Operation Mechanism) In the electroacoustic transducer 1 configured as described above, when sound waves are emitted from the speaker unit 3, the air vibrations propagate to the gas contained in the enclosure 4 due to the flexibility of the enclosure 4. The gas through which the sound waves propagate has a bulk modulus smaller than that of air under the same conditions, i.e., a bulk modulus smaller than 140 kilopascals, which is the bulk modulus of ordinary air at 1 atmosphere and 20 degrees Celsius. A gas with a small bulk modulus changes volume more easily than air in response to pressure changes, and so the repulsive force (spring constant, stiffness) between the gas and the air inside the cabinet, which acts as a spring when the diaphragm vibrates, decreases.

[0030] This lowers the minimum resonance frequency, thereby expanding the low-frequency reproduction limit frequency band. And because the gas that expands the low-frequency reproduction limit frequency is contained in the enclosure 4 and provided inside the cabinet 2, it is possible to achieve the target minimum resonance frequency in all types of cabinets 2, and the expansion of the low-frequency reproduction limit frequency band due to the reduction in the target minimum resonance frequency can be maintained over a long period of time.

[0031] (Minimum Resonance Frequency) It is preferable that the enclosure 4 does not have a natural resonance frequency in the vicinity of the target minimum resonance frequency, i.e., in the frequency range from half (= one octave below) to twice (= one octave above) that frequency. The reason for this is that natural resonances are always an obstacle to the reproduction of the original sound, so it is best to avoid them, but if they exist in the vicinity of the target minimum resonance frequency, they may cause mutual interference, making it impossible to achieve the objective of the present invention of lowering the minimum resonance frequency.

[0032] To explain the minimum resonance frequency of the electroacoustic transducer 1 in detail, the minimum resonance frequency foc of the electroacoustic transducer 1 is generally expressed by the following equations (2) and (3).

[0033]

[0034]

[0035] Here, S ０ is the equivalent stiffness (N / m) of the speaker unit 3. ｃ is the equivalent stiffness (N / m) of the cabinet 2 defined in Equation 3. m ０ is the equivalent mass of the diaphragm (kg). ０ is the density of the gas in the cabinet 2 (kg / m ３ ) where c is the sound velocity (m / s) of the gas inside the cabinet 2 and a is the effective radius (m) of the diaphragm. ｃ is the volume of gas in cabinet 2 (m ３ ), and κ is the bulk modulus of the gas (Pa).

[0036] Equation 2 represents the lowest resonance frequency of the electroacoustic transducer 1. The lowest resonance frequency is proportional to the square root of the equivalent stiffness of the speaker unit 3, the square root of the equivalent stiffness of the cabinet 2, and the square root of the reciprocal of the equivalent mass of the diaphragm. This shows that if you want to lower the resonance frequency of the electroacoustic transducer 1, you need to lower at least one of the equivalent stiffness of the speaker unit 3 and the equivalent stiffness of the cabinet 2, or increase the equivalent mass of the diaphragm. However, in most products in recent years where miniaturization of the cabinet is considered important as a commercial value, high-compliance speaker units are used, so S ０ <<S Ｃ The equivalent stiffness S of the speaker unit 3 is ０ The contribution of the diaphragm to the lowest resonance frequency is extremely low. ０ Increasing the equivalent stiffness S of the cabinet 2 is not in line with the objective because it lowers the lowest resonance frequency and also reduces the efficiency (output sound pressure level per unit input power) of the speaker unit 3. Ｃ The object of the present invention is achieved by reducing the value.

[0037] Furthermore, in Equation 3, it can be seen that the equivalent stiffness of the cabinet 2 is equal to the product of the density of the gas within the cabinet 2 and the square of the speed of sound multiplied by the square of the effective area of ​​the diaphragm, and divided by the volume of the gas within the cabinet 2. This shows that in order to reduce the equivalent stiffness of the cabinet 2, it is necessary to reduce the product of the density of the gas within the cabinet 2 and the square of the speed of sound, reduce the effective radius of the diaphragm, or increase the volume of the gas within the cabinet 2. However, reducing the effective radius of the diaphragm not only lowers the minimum resonant frequency but also reduces the efficiency (output sound pressure level per unit input power) of the speaker unit 3, which is not conducive to the objective. Furthermore, increasing the volume of the gas within the cabinet 2 contradicts the premise that the volume of the cabinet 2 remains unchanged. On the other hand, from the relationship between Equations 2 and 3, the lowest resonance frequency foc of the electroacoustic transducer 1 is proportional to the product of the density of the gas and the square of the speed of sound, i.e., the square root of the bulk modulus κ of the gas. Therefore, if the bulk modulus κ of the gas is made smaller than that of air, the lowest resonance frequency of the electroacoustic transducer 1 can be lowered.

[0038] In addition, the volume V of the gas to be sealed is set so that the pressure inside the cabinet 2 is not compressed when inserted and installed so that the pressure inside the cabinet 2 does not become higher than the pressure of the surrounding air. ａ is the cabinet internal volume V ｃ and the volume of the enclosed body 4 is smaller than the volume V of the gas. ａ This is to follow the change in air pressure that accompanies the operation of the speaker unit 3 without imposing a load on it.

[0039] In the electroacoustic transducer 1 configured as described above, the bulk modulus of the gas in the entire cabinet 2 is the weighted average of the air in the cabinet 2 and the gas in the enclosure 4, so the equivalent stiffness Sca of the cabinet 2 can be calculated from Equation 3 as follows:

[0040]

[0041] As an example, Vc = 1 (m ３ ), Va=0.8(m ３ ) and various gases were mixed to obtain a gas with a bulk modulus κa of 1.2 × 10 ５(Pa) sample gas is prepared. In this case, the bulk modulus of air, κ0, is 1.4 × 10 ５ (Pa), so the equivalent stiffness of cabinet 2 filled with air alone is Sc ０ If so, Sca / Sc ０ = 1.24 / 1.4 ≈ 0.886, resulting in a reduction in equivalent stiffness of about 11%. When an enclosed body 4 containing gas is mounted on an electroacoustic transducer 1 having a high-compliance speaker unit 3 whose equivalent stiffness is sufficiently low compared to the cabinet 2, that is, S ０ In the case of <<Sc, a decrease in the minimum resonance frequency of about 6% can be obtained.

[0042] In addition, the bulk modulus κa is 1.2×10 ５ The relationship between sound pressure and frequency characteristics was investigated using a sample gas of 100 Pa (Pa) and air, and the relationship shown in Figure 3 was obtained. Specifically, the relationship between sound pressure and frequency characteristics was investigated for a cabinet 2 with an internal volume Vc = 100 liters and an enclosure 4 containing a sample gas with a volume Va = 80 liters, and for a cabinet 2 without the enclosure 4, i.e., containing only air.

[0043] Specifically, a speaker unit 3 with a nominal diameter of 30 cm was attached to the cabinet 2, and a 1-watt input signal was applied, and the sound pressure-frequency characteristics obtained at a point 1 meter on the axis in front of the speaker unit 3 were measured. The results are compared in Figure 3.

[0044] As a result, it was found that the minimum resonance frequency was 37.8 Hz when the cabinet 2 contained only air, while the minimum resonance frequency was 35.7 Hz when the enclosure 4 containing the sample gas was provided, and that the provision of the enclosure 4 reduced the minimum resonance frequency by approximately 6%.

[0045] (Modification) As shown in Fig. 1, an enclosure assembly may be provided within the cabinet 2, combining a plurality of enclosures 4 of one or more sizes and shapes. In this case, even if the internal structure of the cabinet 2 is complex, by providing an enclosure assembly in which enclosures 4 of selected sizes and shapes are combined within the cabinet 2, it is possible to easily achieve an expansion of the low-frequency reproduction limit frequency by lowering the minimum resonance frequency. Examples of the shape of the enclosure 4 include a spherical shape, an ellipsoidal shape, and a flat shape composed of flat and curved surfaces. Furthermore, each enclosure 4 may be made of the same material, or may be made of different materials.

[0046] 4, the electroacoustic transducer 1 may be configured with a plurality of flat enclosures 4 arranged in layers with the longitudinal and width directions of the enclosures being horizontal. Although not shown, the electroacoustic transducer 1 may be configured with a plurality of flat enclosures 4 arranged in layers with the thickness and width directions of the enclosures being vertical.

[0047] 5, the electroacoustic transducer 1 may be configured such that the arrangement angle (horizontal orientation, vertical orientation, or oblique orientation) of one or more of the flat enclosures 4, each of which is arranged horizontally in the longitudinal direction and the width direction, is changeable. Each enclosure 4 can be changed by connecting both ends of the enclosure 4 to one end of a piano wire and attaching the other end of the piano wire to both side walls of the cabinet 2, thereby rotatably supporting the enclosure 4 with the piano wire, and attaching a rotation drive mechanism to the end of the piano wire on the outside of the side wall to rotate the enclosure 4 via the piano wire, or by attaching a rotation knob to the end of the piano wire and manually rotating the enclosure 4.

[0048] Furthermore, the multiple inclusion bodies 4 provided in the cabinet 2 may contain multiple different gas species. In this case, instead of creating a mixed gas with a desired bulk modulus by mixing multiple gas species, it is possible to obtain the same function as a mixed gas with a desired bulk modulus by setting the gas species and amount contained in the inclusion body 4 and the number of inclusion bodies 4. In this case, the material for the inclusion body 4 can be selected according to the physical properties of the gas species to be contained, thereby reducing the material cost of the inclusion body 4.

[0049] It should be noted that within the scope of the concept of the present invention, those skilled in the art may conceive of various modifications and alterations. Therefore, it is understood that such modifications and alterations fall within the scope of the present invention. For example, even if a person skilled in the art appropriately adds, deletes, or modifies components of the above-described embodiment, or adds, omits, or modifies the conditions of a process, such modifications are also included within the scope of the present invention as long as they maintain the gist of the present invention.

[0050] REFERENCE SIGNS LIST 1 electroacoustic transducer 2 cabinet 3 speaker unit 4 enclosure 5 duct

Claims

1. An electroacoustic transducer characterized in that a cabinet has one or more speaker units that emit sound waves attached to at least one surface thereof, and contains in an airtight manner a gas whose bulk modulus is less than that of air under conditions of 1 atmosphere and 20 degrees Celsius, and an enclosure that is flexible enough to transmit vibrations of the air to the gas inside is provided.

2. An electroacoustic transducer as described in claim 1, characterized in that the enclosure does not have a natural resonant frequency in the vicinity of the target lowest resonant frequency, i.e., in the frequency range from half (= one octave below) to twice (= one octave above) that frequency.

3. The gas is carbon dioxide (CO ２ 2. The electroacoustic converter according to claim 1, further comprising at least one of HFCs (hydrofluorocarbons) and HCFCs (hydrochlorofluorocarbons).

4. An electroacoustic transducer as described in claim 1, characterized in that an enclosure assembly is provided within said cabinet, the enclosure assembly being a combination of a plurality of enclosures of one or more different sizes and shapes.

5. An electroacoustic converter as claimed in claim 1, wherein said cabinet is a sealed cabinet whose inside is sealed from the outside or an open cabinet whose inside is partly open to the outside.

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