JP2007274313A - Speaker device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speaker device capable of increasing the degree of freedom of the design of a speaker box itself without lowering a sound pressure level in both a low-pitched sound zone and a high-pitched sound zone. <P>SOLUTION: The speaker device 1 comprises: the speaker box 2; a speaker unit 3 attached to the speaker box 2; a vibrating membrane 4 composed of an elastic body and arranged in the internal space 2a of the speaker box 2 whose peripheral part 4a is fixed; and a back air chamber 5 shut off from the internal space 2a of the speaker box 2 by the vibrating membrane 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker device, and more particularly, to a speaker device capable of improving the sound pressure level on the low sound side.

  In general, in a small and light speaker device, the internal air in the speaker box is compressed / expanded by the vibration of the diaphragm of the speaker unit to form a kind of air spring, and the vibration of the air spring has a specific frequency with the diaphragm. There is a problem of so-called low-frequency reproduction limit that resonance occurs and the low frequency is lower than the resonance frequency.

Conventionally, in order to prevent the vibration of the air spring, in the case of a sealed speaker, the speaker box is filled with a fibrous material such as glass wool or felt.
However, since the fibrous material has a property of absorbing sound in the high sound range, there is a problem that the reproduction of the high sound range is hindered.
Also, the so-called bass reflex type speaker device is less likely to cause the bass reproduction limit than the sealed speaker device, but has a problem that the bass reproduction limit problem becomes obvious when the internal volume of the speaker box is reduced.
In the design of the conventional speaker device, since the design is performed so as to prevent the resonance between the air spring and the diaphragm of the speaker unit as much as possible, the degree of freedom in designing the speaker device itself and the speaker box has been reduced.

Therefore, in Patent Document 1 below, a speaker unit attached to the baffle plate on the front surface of the speaker box, a chamber having a vent hole provided on the rear surface of the speaker box, and a vibration disposed on the speaker unit side of the chamber. A speaker device is disclosed that includes a body and a movable body such as a damper that fixes the outer periphery of the vibrating body.
Further, in Patent Document 2 below, an airtight box having one opening or duct is provided in a speaker box to which a speaker unit is attached, so that there is no change in the stiffness of air in the speaker box. A speaker device is disclosed.
Japanese Patent Laid-Open No. 11-150782 Japanese Patent Laid-Open No. 11-341595

However, since the speaker device described in Patent Document 1 uses an inelastic member as a vibrating body, it is considered that so-called Helmholtz resonance is used. When using Helmholtz resonance, for example, if the resonance frequency of the air spring and the diaphragm of the speaker unit is set to 200 Hz or less, the volume of the chamber provided on the rear surface of the speaker box is about 3375 cm ³ (the length of one side). There is a problem that it is difficult to reduce the size of the speaker device.

  Further, in the speaker device described in Patent Document 2, the compression / expansion of the air in the speaker box caused by the vibration of the diaphragm of the speaker unit is made difficult to occur due to the mass of the air itself and the mass of the airtight box itself. An attempt is made to suppress resonance between the spring and the diaphragm of the speaker unit. However, in this configuration, the vibration of the diaphragm of the speaker unit itself is suppressed, and the output (sound pressure level) with respect to the input power of the speaker device is lowered, and the energy efficiency of the speaker device is lowered. .

  The present invention has been made in view of the above circumstances, and the sound pressure level does not decrease in any of the low sound range and the high sound range, and the degree of freedom in designing the speaker box itself is increased. An object of the present invention is to provide a speaker device capable of performing

In order to achieve the above object, the present invention employs the following configuration.
The speaker device of the present invention includes a speaker box, a speaker unit attached to the speaker box, a vibration film made of an elastic body that is disposed in an internal space of the speaker box and has a peripheral portion fixed thereto, and the vibration film. The internal space of the speaker box and a closed back air chamber are provided.

In the speaker device of the present invention, the vibrating membrane is a substantially circular membrane having a radius a (m), and when the inner volume of the back air chamber is V (m ³ ), the a and the V It is preferable that the relationship is determined by the following formula (1).
f _0c = f ₀ ((3.55 × 10 ⁴ · πa ² / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (1)
However, in Formula (1), _f0c is a low frequency resonance frequency in a speaker device including only the speaker box and the speaker, a is a radius (m) of the diaphragm, and t is a thickness of the diaphragm ( m), ρ is the density (kg / m ³ ) of the diaphragm, V is the inner volume (m ³ ) of the back air chamber, and f ₀ is the resonance frequency of the diaphragm, This is a value determined by equation (2).
f ₀ = α · t · a ⁻² · (E / (ρ (1−σ ² ))) ^1/2 (2)
However, in the formula (2), alpha is a number in the range of .46 to .48, t is the thickness of said vibration film (m), the Young's modulus of E, the vibration film (N / ^{m 2} ), Ρ is the density (kg / m ³ ) of the diaphragm, and σ is the Poisson's ratio of the diaphragm.

  The speaker device according to the present invention is configured by temporarily configuring the speaker device based on the relationship between the a and the V, measuring the frequency dependence of the sound pressure level, and finely adjusting at least the V based on the measurement result. Preferably, it is configured.

In the speaker device of the present invention, the vibration membrane is a substantially rectangular membrane having a size of x (m) in the vertical direction and y (m) in the horizontal direction, and the internal volume of the back air chamber is defined as V (m ³ ). Then, it is preferable that the relationship between the x, y and the V is determined by the following formula (3).
f _0c = f ₀ ((3.55 × 10 ⁴ · x · y / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (3)
However, in Formula (3), _f0c is a low frequency resonance frequency in the speaker device including only the speaker box and the speaker, and x and y are lengths (m) of the respective sides of the diaphragm, t is the thickness (m) of the diaphragm, ρ is the density (kg / m ³ ) of the diaphragm, V is the internal volume (m ³ ) of the back air chamber, and f ₀ is the vibration The resonance frequency of the film, which is a value determined by the following equation (4).
f ₀ = π · t / 2 · (E / (12ρ (1−σ ² ))) ^1/2 · ((m / x) ² + (m / y) ² ) (4)
However, in Formula (4), t is the thickness (m) of the diaphragm, E is the Young's modulus (N / m ² ) of the diaphragm, and ρ is the density (kg / m ³ ) of the diaphragm. , Σ is the Poisson's ratio of the diaphragm, m is the number of displacement parts of vibration along the side of the length of x (m) when the diaphragm undergoes natural vibration, and n is the above This is the number of vibration displacement portions along the side of the length of y (m) when the vibration film undergoes natural vibration.

  Further, the speaker device of the present invention temporarily configures the speaker device based on the relationship between the x, y and the V, measures the frequency dependence of the sound pressure level, and finely adjusts at least the V based on the measurement result. It is preferable that it is comprised by this.

  In the speaker device of the present invention, it is preferable that the back air chamber is filled with a fibrous sound absorbing material.

According to the speaker device of the present invention, the speaker box is provided with the vibration film made of an elastic body and the back air chamber, so that the air inside the speaker box is compressed and expanded by operating the speaker unit. Even if a repulsive force is generated by the air spring, the repulsive force of the air spring is absorbed by the vibration membrane and the back air chamber, thereby suppressing resonance between the air spring and the speaker unit. As a result, an extreme increase in the sound pressure level in the vicinity of the resonance frequency can be suppressed, and the sound pressure level in the low sound range can be improved.
In addition, since the present invention employs a membrane made of an elastic material as a vibrating membrane, the volume of the back air chamber can be made relatively small compared to the case of using Helmholtz resonance, thereby realizing a reduction in the size of the speaker device. can do.
Further, by adopting an elastic membrane as the vibration membrane, the repulsive force of the air spring inside the speaker box is efficiently absorbed by the vibration membrane and the back air chamber, so that the repulsive force of the air spring is absorbed by the vibration of the speaker unit. The energy efficiency of the speaker device can be improved without reducing the output (sound pressure level) with respect to the input power of the speaker device.
Furthermore, since it is not necessary to fill the speaker box with a fibrous sound absorbing material, the sound pressure level in the high sound range is not lowered.

  Further, according to the speaker device of the present invention, when the diaphragm is a substantially circular film, the relationship between the radius a of the diaphragm and the inner volume V of the back air chamber is expressed by the above formulas (1) and (2). Therefore, the inner volume of the back air chamber can be designed to the minimum necessary size in accordance with the radius of the diaphragm, thereby reducing the size of the speaker device.

  Furthermore, according to the speaker device of the present invention, when the diaphragm is a substantially rectangular film, the relationship between the lengths x and y of each side of the diaphragm and the inner volume V of the back air chamber is expressed by the above equation (3). ) And formula (4), the inner volume of the back air chamber can be designed to the minimum necessary size in accordance with the size of the vibration membrane, and thus the speaker device can be miniaturized. .

  Furthermore, according to the speaker device of the present invention, since the fibrous sound absorbing material is filled in the back air chamber that is blocked from the internal air by the vibration membrane, the repulsive force of the internal air by the vibration membrane is used to reduce the repulsive force of the internal air. Can be absorbed more efficiently, and the sound pressure level in the low sound range can be further improved. Moreover, since the fibrous sound absorbing material is not filled in the internal space of the speaker box, the sound pressure level in the high sound range is not lowered.

  According to the speaker device of the present invention, it is possible to provide a speaker device that does not reduce the sound pressure level in any of the low sound range and the high sound range, and can increase the degree of freedom in designing the speaker box. .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings referred to in the following description are for explaining the configuration of the speaker device, and the size, thickness, dimensions, etc. of each part shown in the drawings may differ from the dimensional relationship of the actual speaker device. is there.

"Example of speaker device"
FIG. 1 is a perspective view illustrating an example of the speaker device of the present embodiment, and FIG. 2 is a schematic cross-sectional view of the speaker device of FIG.
As shown in FIGS. 1 and 2, the speaker device 1 of this example is arranged in a speaker box 2, a speaker unit 3 attached to the speaker box 2, and an internal space 2a of the speaker box 2, and its peripheral portion 4a. And a rear air chamber 5 that is blocked from the internal space 2 a of the speaker box 2 by the vibration film 4.

  As shown in FIGS. 1 and 2, the speaker box 2 is formed in a hollow rectangular parallelepiped shape, and is made of a wood material or a resin material. An opening 2c is provided in the front wall 2b of the speaker box 2, and the speaker unit 3 is attached to the opening 2c. Two fixing members 2 d for supporting and fixing the vibrating membrane 4 are provided in the internal space 2 a of the speaker box 2. Each fixing member 2d is a plate-like member provided with an opening 2e having a substantially circular shape in plan view on which the vibrating membrane 4 is mounted, and is substantially parallel to and spaced apart from the top wall 2f and the bottom wall 2g of the speaker box 2. Has been placed.

  Next, the speaker unit 3 is a so-called full-range type, and is a conversion unit 3a that electromagnetically converts an input signal into a vibration signal, and a cone-type diaphragm 3b that converts the vibration signal into a sound wave and emits it. It is roughly composed of Both the converter 3 a and the diaphragm 3 b are disposed in the internal space 2 a of the speaker box 2.

Next, the vibration film 4 is made of an elastic film (elastic body) having a circular shape in plan view, and is fixed by a fixing member 2 d provided inside the speaker box 2. As described above, the fixing member 2d is provided with the opening 2e having a substantially circular shape in plan view, and the peripheral portion 4a of the vibration film 4 is fixed by the opening 2e.
The material of the diaphragm 4 is preferably a material having a large loss factor (tan δ) and a small temperature dependency of the loss factor (tan δ), and having excellent durability. Elastic materials such as silicone resin and urethane rubber are preferable. Preferably, a silicone resin is particularly preferable. The thickness of the vibrating membrane 4 is preferably about several mm.

Next, the back air chamber 5 is cut off from the internal space 2 a of the speaker box 2 by the vibrating membrane 4. As shown in FIGS. 1 and 2, the back air chamber 5 of this example includes a vibration film 4, a fixing member 2 d that supports and fixes the vibration film 4, an upper surface wall 2 f or a bottom wall 2 g of the speaker box 2, and It is partitioned by the side wall adjacent to the top wall 2f or the bottom wall 2g.
The back air chamber 5 is filled with air in the same manner as the internal space 2 a of the speaker box 2. It is preferable that the back air chamber 5 is blocked from the internal space of the speaker box 2 by the vibrating membrane 4 in terms of not lowering the sound pressure level in the low sound range. The relationship between the inner volume V of the back air chamber 5 and the radius a of the vibrating membrane will be described later.
The back air chamber 5 may be filled with a fibrous sound absorbing material such as glass wool or felt.

Next, the operation of the speaker device 1 of this example will be described. As shown in FIG. 3, when an input signal is input to the conversion unit 3a of the speaker unit 3, the input signal is electromagnetically converted into a vibration signal. This vibration signal is propagated to the diaphragm 3b, and the diaphragm 3b vibrates toward the internal space of the speaker box 2 as shown in FIG.
The vibration of the diaphragm 3b is transmitted to the internal space 2a of the speaker box, and the compression and expansion of the internal space 2a are repeated in accordance with this vibration, and the air in the internal space 2a becomes an air spring. When the internal space 2a expands, a reaction force is generated against the diaphragm 3b and the speaker box 2 of the speaker unit 3 in accordance with the law of action and reaction.
At this time, since the vibration film 4 and the back air chamber 5 are provided in the internal space 2a of the speaker box 2, the reaction force of the air spring in the internal space 2a is also transmitted to the vibration film 4. Since the vibration film 4 is composed of an elastic body, the reaction force of the air spring in the internal space 2a is reduced by loss elasticity due to expansion and contraction of the elastic body.
By reducing the reaction force, the reaction force of the speaker unit 3 against the diaphragm 3b is weakened, and the resonance phenomenon between the diaphragm 3b and the internal space 2a is suppressed. Thereby, the peak of the sound pressure level at the resonance frequency is reduced, and a decrease in the sound pressure level in the low sound range is suppressed.

FIG. 4 is a graph showing the relationship between the sound pressure level and the frequency of the speaker device having no diaphragm, and FIG. 5 is the relationship between the sound pressure level and the frequency of the speaker device having the diaphragm (reproduced sound pressure). Frequency characteristics) are shown in a graph. The frequency characteristic of the sound pressure level was measured according to the international standard IEC 268-1, with a microphone installed on the axis of the speaker unit of the speaker device, and the distance between the microphone and the speaker unit being 1 m.
As shown in FIG. 4, in the case of a speaker device that does not have a diaphragm, a sound pressure level peak is observed near 100 Hz, and the sound pressure level sharply appears on the low frequency side (low frequency side) from this peak. It turns out that it is decreasing. The sharp decrease of the sound pressure level is particularly large after the curve of the speaker unit is below the curve of the speaker unit alone.
In FIG. 4, the speaker unit alone means that the speaker unit is attached to a standard sealed box (specified in JIS C 5531), and the relationship between the sound pressure level and the frequency is measured in accordance with the specification of JIS C 5531. It is a curve, which is a target curve when designing a speaker device.

  On the other hand, as shown in FIG. 5, in the case of a speaker device having a diaphragm, the peak of the sound pressure level is shifted to a lower sound region side than 100 Hz, and the peak itself is significantly smaller than that of FIG. . Furthermore, although the sound pressure level is decreasing on the low frequency side (low frequency side) from this peak, the slope of the decrease is smaller than that in FIG. 4, and the sound pressure level on the low frequency side is lower. It can be seen that the decrease is small.

  As described above, according to the speaker device 1 of the present embodiment including the vibration film 4 and the back air chamber 5, it is possible to reduce a decrease in sound pressure level in a low sound range of about 100 Hz.

Next, the relationship between the inner volume V of the back air chamber 5 and the radius a of the diaphragm will be described.
In the speaker device 1 of the present embodiment, the material, size (radius a), thickness, and the like of the diaphragm 4 are first determined, and then the internal volume of the back air chamber 5 is determined based on the structure of the diaphragm 4. It is desirable to do.
In the present embodiment, it is advantageous to make the area of the vibration film 4 as large as possible in order to reduce the loss of the reproduced sound pressure on the low sound side. However, in the present embodiment, as shown in FIGS. 1 and 2, the size of the vibrating membrane 4 is determined from the relationship between the vibrating membrane 4 and the upper surface wall 2f and the bottom wall 2g of the speaker box 3 being arranged. The size of the vibrating membrane 4 is limited in that it must be smaller than 2f and the bottom wall 2g. In the present embodiment, it is desirable to increase the size (radius a) of the vibration film 4 as much as possible within the range of this restriction.

As shown in FIG. 6, the radius of the vibration film 4 is a (m), the thickness of the vibration film 4 is t (m), the Young's modulus of the vibration film 4 is E (N / m ² ), and the vibration film 4 The resonance frequency f ₀ (Hz) of the vibrating membrane 4 is expressed by the following formula (5), where ρ is kg (m ³ ) and the Poisson's ratio of the vibrating membrane 4 is σ. However, in Formula (5), (alpha) is a number of the range of 0.46-0.48.

f ₀ = α · t · a ⁻² · (E / (ρ (1−σ ² ))) ^1/2 (5)

For example, when a silicone resin is selected as the material of the diaphragm 4, the Young's modulus E of the diaphragm 4 is 1.0 × 10 ⁷ (N / m ² ), and the density ρ of the diaphragm 4 is 1040 (kg / kg). m ³ ), the Poisson's ratio σ of the vibrating membrane 4 is 0.45, and α is 0.467.

Next, the relationship between the inner volume V of the back air chamber 5 and the radius a of the diaphragm is determined from the resonance frequency f ₀ of the diaphragm 4.
As shown in FIG. 7, the radius of the diaphragm 4 is a (m), the thickness of the diaphragm 4 is t (m), the density of the diaphragm 4 is ρ (kg / m ³ ), and the back air chamber 5 , V (m ³ ), and the resonance frequency of the vibrating membrane 4 obtained by the equation (5) is f ₀ (Hz), and a bass resonance frequency (for example, FIG. 4) in a speaker device including only a speaker box and a speaker unit. When the frequency of the peak value of the sound pressure level at f) is f _0c (Hz), the relationship between f _0c , a and V is as shown in the following equation (6).

f _0c = f ₀ ((3.55 × 10 ⁴ · πa ² / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (6)

As described above, the frequency characteristic of the reproduction sound pressure of the speaker device having no vibration film as shown in FIG. 4 is obtained, and the frequency at which the reproduction sound pressure reaches the peak value is set to f _0c. After determining the thickness t, the internal volume V of the back air chamber 5 optimum for the radius a of the vibrating membrane 4 is obtained by using the above formulas (5) and (6). The speaker device 1 may be configured according to the relationship between the radius a and the internal volume V.

However, in some cases, the relationship between the radius a and the internal volume V calculated by the above calculation may not be optimal.
That is, the speaker device is temporarily assembled based on the relationship between the radius a and the internal volume V, the frequency dependency curve of the sound pressure level is measured for the temporarily assembled speaker device, and the frequency dependency curve of the measured sound pressure level is When the curve of the speaker unit alone in FIG. 4 is compared, the curve of the temporarily assembled speaker device may not match the curve of the speaker unit alone.
In such a case, the inner volume V of the back air chamber is finely adjusted until the curve of the temporarily assembled speaker device matches the curve of the speaker unit alone, or the inner volume V, the radius a, and the material of the diaphragm are changed. It is desirable to make fine adjustments.

  Note that the speaker device shown in FIGS. 1 and 2 includes two sets of diaphragms and back air chambers. In such a case, the radius of each diaphragm is set to the same value, and the inner volume V of the rear air chamber is obtained from the above equations (5) and (6) based on this radius value. And what is necessary is just to set the internal volume of each back air chamber to V, respectively. By providing two back air chambers, the repulsive force of the air spring is absorbed more efficiently, and the resonance suppression effect by the air spring and the diaphragm 3b of the speaker unit 3 is further enhanced.

  The description so far is an example in which the diaphragm 4 having a substantially circular shape in plan view is applied. However, in the case of a diaphragm having a substantially rectangular shape in plan view, the size of the diaphragm and the inner volume of the back air chamber are determined according to the following procedure. Find the relationship.

Even in the case of a diaphragm having a substantially rectangular shape in plan view, the material, size (length x, y of each side) and thickness of the diaphragm are determined, and the internal volume of the back air chamber is vibrated. What is necessary is just to determine based on the structure of a film | membrane.
That is, the length of the vertical side of the diaphragm is x (m), the length of the horizontal side is y (m), the thickness of the diaphragm is t (m), and the Young's modulus of the diaphragm is E (N / m ² ), the density of the vibrating membrane is ρ (kg / m ³ ), the Poisson's ratio of the vibrating membrane is σ, and the vibration displacement along the length of x (m) when the vibrating membrane vibrates naturally When the number of parts is m and the number of vibration displacement parts along the side of the length of y (m) when the vibration film vibrates naturally is n, the resonance frequency f ₀ (Hz) of the vibration film is (7). Note that m and n are specifically natural numbers of 1 or more.

f ₀ = π · t / 2 · (E / (12ρ (1-σ ² ))) ^1/2 · ((m / x) ² + (n / y) ² ) (7)

Next, the relationship between the inner volume V of the back air chamber and the lengths x and y of each side of the diaphragm is obtained from the resonance frequency f _{0 of the} diaphragm.
The length of the vertical side of the diaphragm is x (m), the length of the horizontal side is y (m), the thickness of the diaphragm is t (m), and the density of the diaphragm is ρ (kg / m ³ ). , Where the internal volume of the back air chamber is V (m ³ ), the resonance frequency of the diaphragm obtained by the equation (7) is f ₀ (Hz), and the low frequency resonance frequency in the speaker device including only the speaker box and the speaker unit When (the frequency of the peak value of the sound pressure level in FIG. 4) is f _0c (Hz), the relationship among f _0c , x, y, and V is as shown in the following equation (8).

f _0c = f ₀ ((3.55 × 10 ⁴ · x · y / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (8)

Thus, after obtaining the frequency characteristic of the reproduction sound pressure of the speaker device having no diaphragm as shown in FIG. 4, the frequency at which the reproduction sound pressure reaches the peak value is defined as f _0c, and the length of each side of the diaphragm After determining x, y, and film thickness t, by using the above equations (7) and (8), the inner volume V of the back air chamber that is optimal for the lengths x, y of each side of the vibration membrane Is required. The speaker device may be configured according to the relationship between the lengths x and y of each side and the internal volume V.

Similarly to the case of the circular diaphragm, the relationship between x and y calculated by the above calculation and the internal volume V may not always be optimal.
In such a case, as in the case of the circular shape, the internal volume V of the back air chamber is finely adjusted or the internal volume V is adjusted until the curve of the temporarily assembled speaker device matches the curve of the speaker unit alone. It is desirable to finely adjust the side lengths x and y and the material of the diaphragm.

According to the speaker device 1 described above, since the diaphragm 4 and the back air chamber 5 made of an elastic body are provided in the speaker box 2, the air inside the speaker box 2 is activated by the operation of the speaker unit 3. Is compressed and expanded to form an air spring, and even if a repulsive force is generated by the air spring, the repulsive force of the air spring is absorbed by the vibration film 4 and the back air chamber 5, thereby vibrating the air spring and the speaker unit 3. Resonance with the plate 3b is suppressed. Thereby, the fall of the sound pressure level in a low sound range can be prevented.
Further, in the present embodiment, a film made of an elastic body is used as the vibration film 4, so that the volume of the back air chamber 5 can be made relatively small as compared with the case where Helmholtz resonance is used. Miniaturization can be realized.
Further, by adopting a film made of an elastic body as the vibration film 4, the repulsive force of the air spring inside the speaker box 2 is efficiently absorbed by the vibration film 4 and the back air chamber 5, thereby the repulsive force of the air spring is reduced. There is no possibility that the vibration of the speaker unit 3 will be hindered, and the energy efficiency of the speaker device 1 can be increased without reducing the output (sound pressure level) with respect to the input power of the speaker device 1.
Furthermore, since it is not necessary to fill the speaker box 2 with a fibrous sound absorbing material, there is no possibility of lowering the sound pressure level in the high sound range.

  Further, according to the speaker device 1 described above, when the vibrating membrane 4 is a substantially circular membrane, the relationship between the radius a of the vibrating membrane 4 and the internal volume V of the rear air chamber 5 is expressed by the above formulas (5) and (5). Since it is determined by (6), the inner volume of the back air chamber 5 can be designed to the minimum necessary size in accordance with the radius of the vibration film 4, and thus the speaker device 1 can be miniaturized.

  Further, when the diaphragm is a substantially rectangular film, the relationship between the lengths x and y of each side of the diaphragm and the inner volume V of the back air chamber can be determined by the above formulas (7) and (8). As in the case of the substantially circular membrane, the inner volume of the back air chamber can be designed to the minimum necessary size in accordance with the size of the vibration membrane, thereby reducing the size of the speaker device. be able to.

  Furthermore, when the back air chamber 5 is filled with a fibrous sound absorbing material, the repulsive force of the internal air by the vibrating membrane 4 can be more efficiently absorbed by this fibrous sound absorbing material, and the sound pressure in the low frequency range can be reduced. A decrease in level can be suppressed.

Further, in the speaker device, in addition to the resonance caused by the air spring, there may be a peak portion of the sound pressure level derived from the material of the diaphragm of the speaker unit. For example, such a peak portion can be reduced.
Further, when a plurality of back air chambers are provided, resonance at a plurality of frequencies can be prevented by making the respective internal volumes different.

"Another example of a speaker device"
Next, another example of the speaker device of this embodiment will be described with reference to FIG.
The speaker device 11 shown in FIG. 8 includes a speaker box 12, two speaker units 13 attached to the speaker box 12, and an elastic body disposed in the internal space 12a of the speaker box 12 and having a peripheral portion 14a fixed thereto. And a rear air chamber 15 that is blocked from the internal space 12a of the speaker box 12 by the vibration film 14.

As shown in FIG. 8, the speaker box 12 is formed in a hollow rectangular parallelepiped shape, and is made of a wood material or a resin material. Two openings 12c are provided in the front wall 12b of the speaker box 12, and a speaker unit 13 is mounted in each opening 12c. A cylindrical tube 12d for supporting and fixing the vibrating membrane 14 is disposed in the internal space 12a of the speaker box 12. One end of the cylindrical tube 12d is joined to the upper wall 12f of the speaker box 12, and the vibrating membrane 14 is attached to the other end.
In addition, a reinforcing plate 12e having a substantially rectangular shape in plan view is attached to the center of the speaker box 12. Two cylindrical bass reflex ports 12g are provided below the reinforcing plate 12e. The bass reflex port 12g is attached to the rear wall 12h opposite to the front wall 12b of the speaker box 12. The rear wall 12h to which the bass reflex port 12g is attached is provided with a through hole 12i, and the internal space 12a of the speaker box 12 communicates with the external space via the through hole 12i and the bass reflex port 12g.

  Next, the speaker unit 13 has substantially the same configuration as the speaker unit 3 in the speaker device 1 of the example described above. However, each speaker unit 13 in the speaker device 11 of this example is designed for a low sound range and a high sound range, respectively.

Next, as in the case of the speaker device 1, the vibrating membrane 14 is made of an elastic membrane (elastic body) having a circular shape in plan view, and the other end of the cylindrical tube 12 d provided inside the speaker box 12. It is fixed on the side. That is, the peripheral portion of the vibration film 14 is fixed by the opening on the other end side of the cylindrical tube 12d.
As the material of the vibration film 14, as in the case of the speaker device 1, an elastic body such as silicone resin and urethane rubber is preferable, and silicone resin is particularly preferable. The thickness of the vibrating membrane 14 is preferably about several mm.

  Next, the back air chamber 15 is cut off from the internal space 12 a of the speaker box 12 by the vibrating membrane 14. As shown in FIG. 8, the rear air chamber 15 of this example is partitioned by a vibration film 14, a cylindrical tube 12 d that supports and fixes the vibration film 14, and an upper surface wall 12 f of the speaker box 12. The back air chamber 15 is filled with air in the same manner as the internal space 12 a of the speaker box 12. The back air chamber 15 may be filled with a fibrous sound absorbing material such as glass wool or felt.

Further, the relationship between the internal volume V of the back air chamber 15 and the radius a of the vibrating membrane 14 may be designed in the same manner as in the speaker device 1 described above.
Further, when the diaphragm is formed in a substantially rectangular shape in plan view, the relationship between the inner volume V of the back air chamber 15 and the lengths of the sides x and y of the diaphragm is the same as in the case of the speaker device 1 described above. To design.
Similarly to the case of the speaker device 1 described above, the internal volume V or the like may be finely adjusted after the speaker device is temporarily assembled.

  According to the speaker device 11 of this example, the same effect as the speaker device 1 described above can be obtained.

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the speaker device 1 shown in FIGS. 1 and 2, two sets of vibration membranes and a back air chamber are disposed inside the speaker box. However, the present invention is not limited to this, and one set of vibration membranes and a back air chamber is provided. May be provided. Moreover, the arrangement location of the vibration membrane and the back air chamber is not limited to the position shown in FIGS.

Example 1
A rectangular parallelepiped speaker box having an inner size width of 14 cm, a depth of 18 cm, and a height of 31 cm was prepared, an opening was provided in the front wall of the speaker box, and a full-range type speaker unit was attached to the opening. In addition, two 2.1 cm-thick fixing members having a circular opening with a diameter of 10 cm were mounted in the interior space of the speaker box, 3 cm apart from each of the top wall and the bottom wall. Then, a silicone resin film having a diameter of 10 cm and a thickness of 1 mm was attached to the opening of each fixing member. As a result, the size of the internal space of the speaker box was 14 cm wide, 18 cm deep, and 21 cm high, and the size of each rear air chamber was 14 cm wide, 18 cm deep, and 3 cm high. In this way, the speaker device of Example 1 having substantially the same configuration as that shown in FIGS. 1 and 2 was manufactured.

(Comparative Example 1)
A speaker device of Comparative Example 1 was manufactured in the same manner as in Example 1 except that a stainless steel plate was fitted into the opening of the fixing member.

  For the speaker devices of Example 1 and Comparative Example 1, the frequency characteristics of the sound pressure level were measured. The frequency characteristics of the sound pressure level were measured according to the international standard IEC 268-1, with a microphone installed on the axis of the speaker unit of each speaker device, the distance between the microphone and the speaker unit being 1 m. The results are shown in FIG.

As shown in FIG. 9, in the speaker device of Comparative Example 1, a sound pressure level peak was observed near 150 Hz. The frequency at this peak is the bass resonance frequency _f0c . On the other hand, in the speaker device of Example 1, the peak of the sound pressure level as in Comparative Example 1 was not observed. Thereby, in the speaker apparatus of Example 1, it is presumed that resonance did not occur between the air in the internal space and the speaker unit due to the arrangement of the diaphragm and the back air chamber.

(Example 2)
A rectangular parallelepiped speaker box was prepared, two openings were provided on the front wall of the speaker box, and two full-range speaker units were mounted. Also, a cylindrical tube having a diameter of 8 cm and a length of 14 cm is disposed in the interior space of the speaker box, one end of the cylindrical tube is joined to the upper surface wall of the speaker box, and a 1 mm thick silicone resin film is connected to the other end. Attached. In this way, the speaker device of Example 2 having substantially the same configuration as that shown in FIG. 8 was manufactured.

(Comparative Example 2)
A speaker device of Comparative Example 2 was manufactured in the same manner as in Example 2 except that a stainless steel plate was fitted to the other end of the cylindrical tube.

  For the speaker devices of Example 2 and Comparative Example 2, the frequency characteristics of the sound pressure level were measured. Similarly to the above, the frequency characteristics of the sound pressure level were measured according to the international standard IEC 268-1 with a microphone installed on the axis of the speaker unit of each speaker device, the distance between the microphone and the speaker unit being 1 m. . The results are shown in FIG.

As shown in FIG. 10, in the speaker device of Comparative Example 2, a sound pressure level peak was observed in the vicinity of 100 Hz. The frequency at this peak is the bass resonance frequency _f0c . On the other hand, in the speaker device of Example 2, the peak of the sound pressure level as in Comparative Example 2 was not observed. As a result, in the speaker device of the second embodiment, as in the case of the first embodiment, the vibration membrane and the back air chamber were disposed, and thus resonance did not occur between the air in the internal space and the speaker unit. It is estimated to be.

FIG. 1 is a perspective view showing a speaker device according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the speaker device of FIG. FIG. 3 is a schematic cross-sectional view illustrating the operation of the speaker device of FIG. FIG. 4 is a graph showing the relationship between the sound pressure level and the frequency of the speaker device having no vibrating membrane. FIG. 5 is a graph showing the relationship between the sound pressure level and the frequency of a speaker device having a vibrating membrane. FIG. 6 is a model diagram showing the configuration of the diaphragm when calculating the resonance frequency of the diaphragm. FIG. 7 is a model diagram showing the configuration of the diaphragm and the back air chamber when calculating the relationship between the radius of the diaphragm and the inner volume of the back air chamber. FIG. 8 is a schematic cross-sectional view showing the speaker device according to the second embodiment of the present invention. FIG. 9 is a graph showing the relationship between the sound pressure level and the frequency of the speaker devices of Example 1 and Comparative Example 1. FIG. 10 is a graph showing the relationship between the sound pressure level and the frequency of the speaker devices of Example 2 and Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11 ... Speaker apparatus, 2, 12 ... Speaker box, 2a, 12a ... Internal space, 3, 13 ... Speaker unit, 4, 14 ... Vibration membrane, 4a ... Peripheral part, 5, 15 ... Back air chamber

Claims (6)

  A speaker box; a speaker unit attached to the speaker box; a vibration film made of an elastic body disposed in an inner space of the speaker box and having a peripheral portion fixed; and the inner part of the speaker box by the vibration film A speaker device comprising a space and a back air chamber blocked. When the vibrating membrane is a substantially circular membrane having a radius a (m), and the inner volume of the back air chamber is V (m ³ ), the relationship between a and V is determined by the following equation (1). The speaker device according to claim 1, wherein:
f _0c = f ₀ ((3.55 × 10 ⁴ · πa ² / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (1)
However, in Formula (1), _f0c is a low frequency resonance frequency in a speaker device including only the speaker box and the speaker, a is a radius (m) of the diaphragm, and t is a thickness of the diaphragm ( m), ρ is the density (kg / m ³ ) of the diaphragm, V is the inner volume (m ³ ) of the back air chamber, and f ₀ is the resonance frequency of the diaphragm, This is a value determined by equation (2).
f ₀ = α · t · a ⁻² · (E / (ρ (1−σ ² ))) ^1/2 (2)
However, in the formula (2), alpha is a number in the range of .46 to .48, t is the thickness of said vibration film (m), the Young's modulus of E, the vibration film (N / ^{m 2} ), Ρ is the density (kg / m ³ ) of the diaphragm, and σ is the Poisson's ratio of the diaphragm.   A speaker device is temporarily configured based on the relationship between the a and the V, the frequency dependence of the sound pressure level is measured, and at least the V is finely adjusted based on the measurement result. The speaker device according to claim 2. The vibrating membrane is a substantially rectangular membrane having a size of vertical x (m) and horizontal y (m), and when the inner volume of the back air chamber is V (m ³ ), the x, y and the The speaker device according to claim 1, wherein the relationship of V is determined by the following equation (3).
f _0c = f ₀ ((3.55 × 10 ⁴ · x · y / (V · π ² · f ₀ ² · ρ · t)) + 1) ^1/2 (3)
However, in Formula (3), _f0c is a low frequency resonance frequency in a speaker device including only the speaker box and the speaker, and x and y are lengths (m) of each side of the diaphragm, t is the thickness (m) of the diaphragm, ρ is the density (kg / m ³ ) of the diaphragm, V is the internal volume (m ³ ) of the back air chamber, and f ₀ is the vibration The resonance frequency of the film, which is a value determined by the following equation (4).
f ₀ = π · t / 2 · (E / (12ρ (1−σ ² ))) ^1/2 · ((m / x) ² + (n / y) ² ) (4)
However, in Formula (4), t is the thickness (m) of the diaphragm, E is the Young's modulus (N / m ² ) of the diaphragm, and ρ is the density (kg / m ³ ) of the diaphragm. , Σ is the Poisson's ratio of the diaphragm, m is the number of displacement parts of vibration along the side of the length of x (m) when the diaphragm undergoes natural vibration, and n is the above This is the number of vibration displacement portions along the side of the length of y (m) when the vibration film undergoes natural vibration.   A speaker device is provisionally configured based on the relationship between x, y and V, the frequency dependence of the sound pressure level is measured, and at least the V is finely adjusted based on the measurement result. The speaker device according to claim 4.   6. The speaker device according to claim 1, wherein the back air chamber is filled with a fibrous sound absorbing material.

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