Electroacoustic converter

Abstract

To provide an electroacoustic converter that can be applied to all types of cabinets and can maintain an expansion of the low-frequency reproduction limit frequency for a long period of time.SOLUTION: An electroacoustic converter 1 according to the present invention includes a cabinet 2 having one or more speaker units 3 that emit sound waves attached to at least one surface thereof, and an enclosure 4 that contains in an airtight state a gas whose bulk modulus is less than that of air under conditions of 1 atmosphere and 20 degrees Celsius, and that is flexible enough to transmit air vibrations to the gas inside.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Regarding a technology equipped with a speaker unit 3 that emits sound waves, Patent Document 1 discloses a technology in which a cabinet with a front and back shielded is used 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 by reverse-phase compression waves generated on the back of the diaphragm. Patent Document 2 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. As a result, according to the technologies of Patent Document 1 and Patent Document 2, it is possible to expand the low-frequency reproduction limit frequency band by increasing the radiation efficiency of sound waves at low frequencies. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-117900 [Patent Document 2] JP 2007-60501 A Summary of the Invention [Problem to be solved by the invention]

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

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

[0006] As a result of intensive research into solving the above problems, the inventors have found that the above object can be achieved by providing an enclosed body containing a gas having a bulk modulus of less than 140 kilopascals in a cabinet. The inventors have then completed the present invention. Specifically, the present invention provides the following.

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

[0008] According to the above configuration, when sound waves are emitted from the speaker unit 3, the vibration of the air is propagated to the gas contained in the inclusion due to the flexibility of the inclusion. The gas to which the air is propagated is a gas with a bulk modulus smaller than that of air under the condition of 1 atmospheric pressure and 20 degrees Celsius, that is, a gas with a bulk modulus smaller than that of general air, which is 140 kilopascals. Since a gas with a small bulk modulus changes volume more easily in response to pressure changes than air, the repulsive force (spring constant, stiffness) between the air inside the cabinet that acts as a spring when the diaphragm vibrates and the gas decreases, so the minimum resonance frequency decreases and the low-frequency reproduction limit frequency band is expanded. And since such a gas that expands the low-frequency reproduction limit frequency band is provided in the cabinet while being contained in the inclusion, it is applicable to all types of cabinets and the expansion of the low-frequency reproduction limit frequency band can be maintained for a long period of time. Effect of the Invention

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

[0010] [Figure 1] FIG. 1 is a schematic diagram of an electroacoustic converter according to the present embodiment. [Figure 2A] FIG. 2A is a schematic configuration diagram of an electroacoustic converter according to this embodiment. [Figure 2B] FIG. 2B is a schematic configuration diagram of the electroacoustic converter of the present embodiment. [Figure 2C] FIG. 2C is a schematic configuration diagram of the electroacoustic converter of the present embodiment. [Figure 2D] FIG. 2D is a schematic configuration diagram of the electroacoustic converter of this embodiment. [Diagram 3] Figure 3 is a graph comparing sound pressure and frequency characteristics. [Figure 4] FIG. 4 is a schematic configuration diagram of an electroacoustic converter according to a modified example. [Diagram 5]FIG. 5 is a schematic configuration diagram of an electroacoustic converter according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0012] (Electroacoustic converter 1) As shown in Fig. 1, an 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 gas that has a bulk modulus smaller than that of air under conditions of 1 atmosphere and 20 degrees Celsius in an airtight state. The enclosure 4 also has a degree of flexibility that allows air vibrations to be transmitted 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, an electric current is passed through it, 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 inside is sealed from the outside. This prevents compression waves that are generated on the back side of the diaphragm of the speaker unit 3 and have an opposite phase to the compression waves on the front side of the diaphragm from canceling out the compression 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 with a part of the inside 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 in which an electric circuit unit 8 shown in Fig. 2C is provided inside the cabinet 2 and the operation knob is exposed to the outside, resulting in a gap between the cabinet 2 and the operation knob. The cabinet 2 may include a sound-absorbing material 6 inside for reducing standing waves, as shown in Fig. 2D.

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

[0017] (gas) In the cabinet 2, a gas having a bulk modulus smaller than that of air under the same conditions at 1 atmosphere and 20 degrees Celsius is contained and sealed in an enclosure 4. Here, the "gas having a bulk modulus smaller than that of air under the same conditions at 1 atmosphere and 20 degrees Celsius" is a gas having a bulk modulus smaller than that of general air, 140 kilopascals. For example, it is a gas containing one or more of carbon dioxide (CO2), HFCs (hydrofluorocarbons), or HCFCs (hydrochlorofluorocarbons). In this way, in a closed cabinet or an open cabinet, by having a gas having a bulk modulus smaller than that of air, that is, a gas having a bulk modulus smaller than that of general air, present inside the cabinet 2, it is possible to expand the low-frequency reproduction limit frequency by lowering the minimum resonance frequency. In addition, it is possible to easily adjust the minimum resonance frequency by changing the type, amount, and combination of gases with different characteristics. In addition, "a gas whose bulk modulus is smaller than that of air under conditions of 1 atmosphere and 20 degrees Celsius" can also be expressed as a gas whose product of density and the square of the speed of sound is lower than that of air, based on Equation 1 described below.

[0018] Here, "air" or "ordinary air" refers to a mixture of gases whose main components are nitrogen, oxygen, argon, and carbon dioxide, with trace amounts of rare gases such as neon, helium, and krypton, and water vapor, which 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 viewpoint of global warming potential (GWP), R-1234yf is preferable as the gas applied to 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 viewpoint of global warming potential (GWP), HCFC-22 is preferable as the gas to be applied to the electroacoustic converter 1 because it has a lower global warming potential value than other chemical substances.

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

[0022] (Bulk modulus of gas) The bulk modulus of a gas is a physical property that indicates how much the volume of the 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 the pressure changes, that is, ΔPV / ΔV. Furthermore, the bulk modulus can generally be expressed by the following formula (1).

[0023]

number

[0024] where κ is the bulk modulus of the gas (Pa). ρ0 is the density of the gas (kg / m 3 ), c is the speed of sound in the gas (m / s), γ is the specific heat ratio of the gas, and P is the static pressure (Pa). Equation (1) expresses the bulk modulus κ as a function of density ρ0 and the speed of sound c. In other words, the bulk modulus of a gas (Pa) is a function of the density of the gas (kg / m 3 ) and the square of the sound speed (m / s). Furthermore, because the right-hand side of formula (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 sound speed of the gas and the density as a requirement, and Patent Document 2 similarly lists the specific heat ratio as a requirement, but it can be seen that in both cases, a gas with a bulk modulus smaller than that of air is used as the means for achieving this.

[0025] (Inclusion body 4) The gas-filled enclosure 4 is airtight and flexible enough to transmit the vibration of the air to the gas inside. That is, the enclosure 4 is made of a material having a thickness that allows it to vibrate in response to the vibration of the air. For example, the enclosure 4 is made of a sheet-like bag of a polymer material such as polyethylene or polypropylene having a thickness of about 0.01 mm to 0.1 mm. The enclosure 4 may be made of thin rubber or silicone, or may be made of an elastomer or a thin cloth that is sealed or coated to ensure airtightness. Furthermore, the enclosure 4 may be made of a sheet with a layered structure in which different materials are combined in layers. For example, the enclosure 4 may be made of a sheet in which the balance between flexibility and airtightness is adjusted by combining cloth and rubber, or by combining an elastomer and a thin metal film.

[0026] Although sound waves are always reflected on the inner wall of the electroacoustic transducer 1, as shown in the above 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 there is no parameter related to sound reflection in formula 2. Therefore, the encapsulation body 4 does not need to have the property of transmitting sound waves. Stiffness is a physical concept that indicates how difficult an object is to deform against an external force, and indicates the reaction force that occurs against the deformation when an object is deformed by an external force. For example, when the bulk modulus is high, it repels changes in the volume direction caused by an external force, and deformation is reduced, resulting in high stiffness.

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

[0028] In addition, when the speaker unit 3 operates to emit sound, even when the air in the cabinet 2 expands, 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 amplitude on one side of the speaker unit 3 of the electroacoustic transducer 1 is Xmax(m), the air in the cabinet 2 can 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.

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

[0030] This lowers the lowest resonance frequency, expanding the low-frequency reproduction limit frequency band. And since the gas expanding the low-frequency reproduction limit frequency is contained in the enclosure 4 and provided in the cabinet 2, the target lowest resonance frequency can be realized in all types of cabinets 2, and the expansion of the low-frequency reproduction limit frequency band by lowering the frequency to the target lowest resonance frequency can be maintained for a long period of time.

[0031] (lowest resonant frequency) It is preferable that the inclusion body 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 lower) to twice (= one octave higher) of that frequency. The reason for this is that natural resonance is always an obstacle to the reproduction of the original sound, so it is best not to have it, but if it exists in the vicinity of the target minimum resonance frequency, it may cause mutual interference and make it impossible to achieve the purpose of the present invention, which is to lower 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 formulas (2) and (3).

[0033]

number

[0034]

number

[0035] Here, S0 is the equivalent stiffness (N / m) of the speaker unit 3. c is the equivalent stiffness (N / m) of cabinet 2 defined in equation 3. m0 is the equivalent mass of the diaphragm (kg). ρ0 is the density of the gas in cabinet 2 (kg / m 3 ) where c is the sound speed (m / s) of the gas in cabinet 2. a is the effective radius of the diaphragm (m). V 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 minimum resonance frequency of the electroacoustic transducer 1. The minimum 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, to lower the resonance frequency of the electroacoustic transducer 1, it is necessary to lower at least one of the equivalent stiffness of the speaker unit 3 and the equivalent stiffness of the cabinet 2, or to increase the equivalent mass of the diaphragm. However, in most recent products in which miniaturization of the cabinet is emphasized as a commercial value, high compliance speaker units are used, so that the minimum resonance frequency is lower than S0< C Therefore, the contribution of the equivalent stiffness S0 of the speaker unit 3 to the minimum resonance frequency is extremely low. In addition, increasing the equivalent mass m0 of the diaphragm not only reduces the minimum resonance frequency but also reduces the efficiency (output sound pressure level per unit input power) of the speaker unit 3, which is not worthy of the purpose. Therefore, the equivalent stiffness S C The reduction of the above is a means to achieve the object of the present invention.

[0037] Also, in formula 3, it can be seen that the equivalent stiffness of the cabinet 2 is equal to the square of the density and sound speed of the gas in the cabinet 2 multiplied by the square of the effective area of ​​the diaphragm, and divided by the volume of the gas in the cabinet 2. This shows that in order to reduce the equivalent stiffness of the cabinet 2, it is necessary to lower the product of the density and sound speed of the gas in the cabinet 2, reduce the effective radius of the diaphragm, or increase the volume of the gas in the cabinet 2. However, reducing the effective radius of the diaphragm leads to a decrease in the minimum resonance frequency and a decrease in the efficiency of the speaker unit 3 (output sound pressure level per unit input power), which is not conducive to the purpose. Also, increasing the volume of the gas in the cabinet 2 contradicts the premise that the volume of the cabinet 2 is not changed. On the other hand, from the relationship between equations 2 and 3, the lowest resonant frequency foc of the electroacoustic converter 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 resonant frequency of the electroacoustic converter 1 can be lowered. ​

[0038] Also, the volume V of the gas to be enclosed is such that when it is inserted and installed inside the cabinet 2, it is not compressed and the internal air pressure does not become greater than the air pressure of the surrounding air. a is smaller than the internal volume V of the cabinet c and the capacity of the enclosure 4 needs to be larger than the volume V of the gas. This is to follow without imposing a load on the change in air pressure associated with the operation of the speaker unit 3. a For this reason,

[0039] In the electroacoustic conversion device 1 configured in this way, the bulk modulus of elasticity of the entire gas inside the cabinet 2 is the weighted average of the air inside the cabinet 2 and the gas inside the enclosure 4. Therefore, the equivalent stiffness Sca of the cabinet 2 is obtained as follows from Equation 3.

[0040]

Equation

[0041] As an example, let Vc = 1 (m 3 ) and Va = 0.8 (m 3 ), and assume that a sample gas with a bulk modulus of elasticity κa of 1.2x10 5 (Pa) is created by mixing various gases. In this case, since the bulk modulus of elasticity of air κ0 = 1.4x10 5 (Pa), if the equivalent stiffness of the cabinet 2 filled only with air is Sc0, then Sca / Sc0 = 1.24 / 1.4 ≈ 0.886, and a reduction in equivalent stiffness of about 11% is obtained. When the electroacoustic conversion device 1 having a high-compliance type speaker unit 3 with a sufficiently low equivalent stiffness with respect to the cabinet 2 is equipped with an enclosure 4 containing a gas, that is, when S0 << Sc, a reduction in the minimum resonance frequency of about 6% can be obtained.

[0042] Also, the above-mentioned bulk modulus of elasticity κa is 1.2x10 5When the relationship between sound pressure and frequency characteristics was investigated using a sample gas of 100 Pa and air, 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, 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 unit were measured. The comparison is shown in Figure 3.

[0044] As a result, it was found that the minimum resonant frequency was 37.8 Hz when the cabinet 2 contained only air, whereas the minimum resonant 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 resonant frequency by approximately 6%.

[0045] (Modification) As shown in FIG. 1, an enclosure assembly may be provided in the cabinet 2, which is a combination of enclosures 4 of one or more sizes and shapes. In this case, even if the internal structure of the cabinet 2 is complicated, the enclosures 4 may be provided in the cabinet 2 as an enclosure assembly in which the enclosures 4 are selected and combined in size and shape, thereby easily achieving 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 sphere, an ellipsoid, and a flattened shape composed of flat and curved surfaces. The enclosures 4 may be made of the same material or different materials.

[0046] 4, the electroacoustic converter 1 may be configured to have flat enclosures 4 arranged in multiple layers with the length and width directions arranged horizontally. Although not shown, the electroacoustic converter 1 may be configured to have flat enclosures 4 arranged in multiple layers with the thickness and width directions arranged vertically.

[0047] 5, the electroacoustic converter 1 may be configured such that the arrangement angle (horizontal, vertical, or oblique) of one or more of the flat-shaped enclosures 4, whose longitudinal and width directions are arranged horizontally, can be changed. 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 walls to rotate the enclosure 4 via the piano wire, or by attaching a rotation knob to the end of the piano wire to rotate the enclosure 4 manually.

[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 a function similar to that of 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 inclusion body 4 made of a material according to the physical properties of the gas species to be enclosed can be selected, so that the material cost of the inclusion body 4 can be reduced.

[0049] It should be noted that within the scope of the concept of the present invention, a person skilled in the art may come up with various modifications and alterations. 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 the design of the above-described embodiment, or adds, omits, or modifies the conditions of a process, these modifications and alterations are included in the scope of the present invention as long as they include the gist of the present invention. [Explanation of symbols]

[0050] 1. Electroacoustic conversion device 2 Cabinet 3 Speaker unit 4. Inclusion bodies 5 Duct

Claims

1. A cabinet having one or more speaker units for emitting sound waves attached to at least one surface thereof, An electroacoustic transducer characterized in that it contains in an airtight state a gas having a bulk modulus smaller than that of air under conditions of 1 atmosphere and 20 degrees Celsius, and is provided with an enclosure having a flexibility sufficient to transmit vibrations of the air to the gas inside.

2. The electroacoustic transducer according to 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. 2. The electroacoustic transducer according to claim 1, wherein an enclosure assembly is provided in the cabinet, the enclosure assembly being a combination of a plurality of enclosures of one or more different sizes and shapes.

5. 2. The electroacoustic transducer according to claim 1, wherein the 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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