JP2008211389A - Intercom device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a speaker system which is improved in sound quality and efficiency in an audio band by suppressing a standing wave in the audio band generated in a rear air chamber. <P>SOLUTION: The speaker system includes a housing A1; a speaker SP which is accommodated in the housing A1 and configured to provide audio information from one surface side to the outside of the housing A1; and a rear air chamber Br which is defined as a space formed in the housing A1 on the side of the other surface of the speaker SP, wherein each of surfaces surrounding the rear air chamber Br has a distance of 50 mm or less between surfaces facing each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a speaker device.

2. Description of the Related Art Conventionally, there is a speaker device in which a speaker is attached to a cabinet and audio information is output from the surface side of the speaker (diaphragm) toward an external space, and is used for various acoustic devices. (For example, refer to Patent Document 1).
Japanese Patent No. 3766682

  In recent years, there has been an increasing demand for communication devices such as intercoms, mobile phones, and hands-free communication devices, and speaker devices used in these communication devices generally have sound quality and efficiency in a voice band of 600 Hz to 3 KHz used for calls. It becomes important.

  Generally, in the cabinet of the speaker device, there is a rear air chamber formed on the back surface side of the speaker, and sound waves radiated from the back surface of the speaker to the rear air chamber are reflected by the inner surface surrounding the rear air chamber, A standing wave having a frequency at which the distance between the inner surfaces facing each other is equal to an integral multiple of a half wavelength is generated. The standing wave generated in the rear air chamber has the effect of hindering the movement of the diaphragm of the speaker. Therefore, the same frequency component as the standing wave is reduced from the output of the speaker, which deteriorates the sound quality and efficiency of the speaker. It is a big factor. Thus, when such a standing wave is generated in the voice band, a speaker device that mainly outputs human voice has problems that it is difficult to hear the voice content and power consumption is increased.

  The present invention has been made in view of the above reasons, and an object of the present invention is to suppress the standing wave of the voice band generated in the rear air chamber and improve the sound quality and efficiency of the speaker in the voice band. To provide an apparatus.

  The invention of claim 1 includes a housing, a speaker that is attached to the housing and outputs audio information from one side to the outside of the housing, and a rear chamber that is a space formed on the other side of the speaker in the housing. And each surface surrounding the rear air chamber is characterized in that the distance between the opposing surfaces is 50 mm or less.

  According to the present invention, a standing wave of 3 KHz or less is not generated in the rear air chamber, and the sound quality and efficiency of the speaker in the voice band can be prevented from being deteriorated by the standing wave generated in the rear air chamber. That is, it is possible to provide a speaker device that suppresses the standing wave in the voice band generated in the rear air chamber and improves the sound quality and efficiency of the speaker in the voice band.

  According to a second aspect of the present invention, there is provided an acoustic tube according to the first aspect, wherein the acoustic tube is formed in a hollow shape having one end opened and the other end closed, and communicated with the rear air chamber through the opening.

  According to the present invention, the acoustic tube shifts the lowest resonance frequency of the speaker to the lower frequency side, and further increases the sound pressure level of the speaker. Therefore, even if the rear air chamber has a small capacity, Efficiency is improved.

  According to a third aspect of the present invention, in the sound pipe according to the second aspect, in order to increase the sound pressure level at a predetermined frequency of the speaker output, which is decreased when the capacity of the rear air chamber is small, the acoustic tube is ¼ of the frequency to be increased. The length is set based on the wavelength.

  According to the present invention, the sound pressure level of a desired frequency can be increased by appropriately setting the length of the acoustic tube.

  A fourth aspect of the present invention is characterized in that, in the second or third aspect, the acoustic tube is continuously formed over a plurality of surfaces among the surfaces surrounding the rear air chamber.

  According to this invention, the acoustic tube can be lengthened as necessary.

  According to a fifth aspect of the present invention, in any one of the second to fourth aspects, a plurality of the acoustic tubes having the same length are provided.

  According to the present invention, the sound pressure level at a predetermined frequency can be greatly improved.

  A sixth aspect of the invention is characterized in that in any one of the second to fourth aspects, a plurality of the acoustic tubes having different lengths are provided.

  According to the present invention, the sound pressure levels of a plurality of frequencies can be improved.

  A seventh aspect of the invention is characterized in that, in any one of the second to sixth aspects, the shape of the closed other end face of the acoustic tube is formed obliquely with respect to the axial direction of the acoustic tube.

  According to this invention, the frequency band of the sound pressure level that can be improved by one acoustic tube can be expanded.

  The invention of claim 8 is characterized in that, in any of claims 2 to 7, a sound absorbing material is provided in the rear air chamber or the acoustic tube.

  According to this invention, it is possible to suppress a drop in the sound pressure level that occurs in the vicinity of the frequency at which the sound pressure level is desired to be improved by the acoustic tube.

  According to a ninth aspect of the present invention, in any one of the second to eighth aspects, the acoustic tube is formed in a bent shape and provided in the rear air chamber.

  According to the present invention, the acoustic tube can be arranged in a small-capacity rear air chamber.

  As described above, the present invention has an effect of suppressing the standing wave of the voice band generated in the rear air chamber and improving the sound quality and efficiency of the speaker in the voice band.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
As an embodiment using the speaker device of the present invention, an interphone communication device will be described below as an example.

  The communication device A according to the present embodiment is shown in FIGS. 1 to 3, and includes a housing A1 (horizontal dimension X1 = 40 mm, vertical dimension) including a body A10 having an opening on the front surface and a cover A11 covering the opening of the body A10. X2 = 90 mm, thickness dimension X3 = 8 mm), and the housing A1 includes a speaker SP, a microphone board MB1, a call switch SW1, and a voice processing unit 10, and functions as an interphone capable of two-way calls between rooms. To do. Note that the power of the communication device A may be supplied from an outlet provided in the vicinity of the installation location or may be supplied via the information line Ls.

  First, as shown in FIG. 1, the speaker SP includes a support body 20 provided with a yoke, a permanent magnet, etc. (not shown), and an edge portion on the outer peripheral side of a dome-shaped diaphragm 21 is fixed to the support body 20. Yes. The diaphragm 21 is formed of thermoplastic plastic (for example, 12 μm to 50 μm in thickness) such as PET (PolyEthyleneTerephthalate) or PEI (Polyetherimide), and when an audio signal is input to a voice coil (not shown) fixed to the back of the diaphragm 21, The electromagnetic force is generated in the voice coil by the current of the audio signal and the magnetic field of the permanent magnet of the support 20, so that the diaphragm 21 is vibrated in the front-rear direction. At this time, a sound corresponding to the audio signal is emitted from the diaphragm 21. That is, an electrodynamic speaker SP is formed (for example, a diameter of 25 mm and a thickness of 3.6 mm). Since the configuration of the electrodynamic speaker is well known, detailed description thereof is omitted.

  The mounting holes 22 provided at the four corners of the support 20 of the speaker SP are placed on the four cylindrical bosses 11 formed at equal intervals on the inner surface of the cover A11, and are formed in the axial direction of the bosses 11. By screwing the attachment screw 23 into the screw hole 11a, the speaker SP is fixed in a state where the diaphragm 21 faces the inner surface of the cover A11. In addition, a plurality of sound holes 12 are drilled at locations facing the diaphragm 21 of the cover A11.

  When the cover A11 to which the speaker SP is fixed is attached to the body A10 and the housing A1 is assembled, two spaces A1a and A1b partitioned by the partition wall 13 are formed in the housing A1 by the partition wall 13 standing on the bottom surface of the body A10. And the speaker SP is disposed in the space A1a. The space A1a is formed in a space corresponding to the horizontal dimension X1 = 40 mm, the vertical dimension X2a = 30 mm, and the thickness dimension X3 = 8 mm of the housing A1, and the space A1b is the horizontal dimension X1 = 40 mm and the vertical dimension X2a of the housing A1. = 60 mm and a thickness corresponding to a thickness dimension X3 = 8 mm.

  In the space A1a, the front air chamber Bf that is a space surrounded by the inner surface of the cover A11 and the surface side of the speaker SP (diaphragm 21 side), the bottom surface of the body A10, and four inner wall surfaces (including the partition wall 13). ) And the rear air chamber Br, which is a space surrounded by the back side of the speaker SP (the support 20 side). The front air chamber Bf communicates with the outside through a plurality of sound holes 12 provided in the cover A11. The rear air chamber Br becomes a space that is insulated (not communicated) with the front air chamber Bf by the support 20 of the speaker SP being in close contact with the inner surface of the cover A11, and the cover A11 is formed in the front opening of the body A10. By being in close contact, it is a sealed space that is insulated from the outside.

  Next, the microphone substrate MB1 is configured such that the microphone M1 and the microphone M2 are mounted on one surface of the module substrate 2 and can be attached to the outer surface of the housing A1. In the present embodiment, one surface of the module substrate 2 is arranged along the outer front surface of the housing A1, and the microphone M1 is inserted through the opening 14 on the front surface of the housing A1. The sound collection surface of the microphone M1 faces the diaphragm 21 of the speaker SP toward the front air chamber Bf, has high directivity with respect to the sound from the speaker SP, and the sound emitted from the speaker SP. Can be reliably collected. Further, the microphone M2 is fitted into the recess 15 provided on the front surface of the housing A1, and the sound hole 2a of the microphone M2 formed in the module substrate 2 faces the outside (front) of the housing A1, so that the sound hole It has high directivity with respect to the voice from the speaker located in front of the communication device A transmitted through 2a. That is, the sound emitted by the speaker SP and the sound emitted by the speaker are separated and collected by the microphones M1 and M2.

  The voice processing unit 10 and the call switch SW1 are disposed in the space A1b in the housing A1, and the operation unit of the call switch SW1 is exposed from the front surface of the housing A1. The voice processing unit 10 outputs a voice signal transmitted from the call device A installed in another room or the like via the information line Ls from the speaker SP or operates the call switch SW1 to enable a call. In this case, by removing the speaker sound collected by the microphone M1 from the call voice collected by the microphone M2, a howling prevention process for canceling the sound sneak around from the speaker SP is performed, and the information line Ls The voice signal is transmitted to the communication device A installed in another room or the like.

In the communication device A configured as described above, the speaker SP is disposed in a space A1a having an approximate dimension of 40 mm × 30 mm × 8 mm (actually smaller than this dimension due to the thickness of the housing A1). The size of the rear air chamber Br which is the space on the back surface side of the speaker SP is also smaller than the above approximate size 40 mm × 30 mm × 8 mm, and in this embodiment, the capacity of the rear air chamber Br is set to 3800 mm ³ (or 3800 mm ³ or less). is doing. In general, the voice band used for calling is 600 Hz to 3 KHz, and in order to generate a standing wave of 3 KHz or less in the rear air chamber Br, the distance between the surfaces surrounding the rear air chamber Br needs to be 50 mm or more. Become. Therefore, in a small apparatus in which the distance between the surfaces surrounding the rear air chamber Br is 50 mm or less as in this embodiment, a standing wave of 3 KHz or less is not generated in the rear air chamber Br. It is unlikely that the sound quality and efficiency of communication will deteriorate due to standing waves generated in Br. However, since the capacity of the rear air chamber Br is small, the radiated sound pressure of the speaker SP is lowered, and the lowest resonance frequency fo of the speaker SP is shifted to the high frequency side, which may deteriorate the sound quality and efficiency of the speaker SP.

  Here, the minimum resonance frequency fo of the speaker SP is generally equal to the equivalent mass (diaphragm, voice coil, air added mass) Mo of the vibration system of the speaker, the stiffness So such as an edge supporting the same, and the rear air chamber Br. It depends on the stiffness Sr of the air inside,

It is represented by

FIG. 4 shows the frequency characteristics of the radiated sound pressure in front of the speaker SP, and the case where a housing (without an acoustic tube, which will be described later) having a sealed rear air chamber volume of 3800 mm ³ (or 3800 mm ³ or less) is used. The results are shown for both cases where an ideal baffle plate is used as the housing.

  First, the ideal baffle plate is a baffle plate C having an infinite size as shown in FIG. 5, and the radiated sound pressure characteristic (characteristic Y1 in FIG. 4) is the lowest resonance frequency of the speaker SP. fo1 = 600 Hz, and the lowest resonance frequency shows the same ideal characteristic as that of the speaker SP alone. When the baffle plate C is used, such excellent characteristics are provided. However, the baffle plate C has an infinite size, and the sound radiated from the back surface of the speaker SP (the back surface of the diaphragm 21) is baffled. This is the result when it is blocked by the plate C and does not go forward, and is not realistic.

Next, regarding the radiated sound pressure characteristics when a housing having a sealed rear air chamber is used, the same characteristics as the baffle plate C can be obtained if the capacity of the rear air chamber is sufficiently large. When the volume of the room is small, the stiffness Sr of the air in the rear air chamber is increased, the minimum resonance frequency of the speaker SP is increased, the radiated sound pressure is lowered, and the speech quality and efficiency are deteriorated. The radiation sound pressure characteristic (characteristic Y2 in FIG. 4) when a housing having a rear air chamber volume of 3800 mm ³ (or 3800 mm ³ or less) is used is the lowest resonance frequency fo2 of the speaker SP = 1200 Hz, and the baffle plate C is used. The lowest resonance frequency is shifted to the high frequency side compared with the case where the sound pressure level is lower, and the sound pressure level is reduced by about 5 to 20 dB compared with the case where the baffle plate C is used in the frequency band of 800 Hz or less. And efficiency is deteriorating. Increasing the capacity of the rear chamber improves the sound quality of the speaker SP. However, increasing the capacity of the rear chamber increases the size of the housing and makes it difficult to reduce the size of the communication device.

Therefore, in this embodiment, as shown in FIGS. 1 and 3, along the inner wall surface of the housing A1 surrounding the rear air chamber Br on the back surface of the speaker SP, one end is separated from the inner wall surface, and the other end is connected to the inner wall surface. A continuous tube wall 16 is erected, and a hollow acoustic tube 40 is formed by the tube wall 16, the inner wall surface of the housing A1, and the back surface of the cover A11. The acoustic tube 40 is a small capacity rear air chamber. Arranged in Br. The acoustic tube 40 is a hollow closed tube having a rectangular cross-sectional shape that is bent along the three inner wall surfaces of the rear air chamber Br and is formed over the circumference of the rear air chamber Br over approximately three quarters. (Open end 40a) and the other end is closed (closed end 40b), and the inside of the pipe communicates with the rear air chamber Br via the open end 40a. An acoustic tube uses the fact that the input impedance becomes extremely small at the resonance frequency of the closed tube (the frequency at which the total length of the tube coincides with an odd multiple of a quarter wavelength). The reflected wave has a waveform whose phase is inverted with respect to the incident wave, and the incident wave and the reflected wave cancel each other, thereby reducing the sound wave propagating from the opening end 40a to the outside. Further, by forming the acoustic tube 40 continuously over a plurality of inner wall surfaces of the rear air chamber Br, the acoustic tube 40 provided in the small air rear chamber Br can be lengthened as necessary. Further, by forming the acoustic tube 40 in a bent shape, the acoustic tube 40 can be disposed in the small-capacity rear air chamber Br. Hereinafter, the operation of the acoustic tube 40 will be described in detail. First, FIG. 6 shows a schematic configuration and a vibration model of a speaker device including the acoustic tube 40 in the rear chamber Br and a speaker device not including the acoustic tube 40, and includes the acoustic tube 40. In the housing A1, the equivalent mass Mo of the vibration system of the speaker SP is equal to the parallel circuit of the damping constant m1 and the spring constant m2 such as the edge of the speaker SP supporting the vibration system, and the damping constant m3 in the rear air chamber Br. It is connected to the fixed end via. On the other hand, in the housing A1 including the acoustic tube 40, in addition to the configuration not including the acoustic tube 40, the impedance Zp (hereinafter referred to as acoustic impedance) of the acoustic tube 40 expressed by combining the mass, the damping constant, and the spring constant. Zp) exists between the attenuation constant m3 in the rear air chamber Br and the fixed end.

  And the equivalent circuit of the vibration model at the time of providing the said acoustic tube 40 is comprised by the electrical system circuit Ke, the mechanical system circuit Ks, and the acoustic system circuit Ka like FIG. It is assumed that [the equivalent mass Mo of the vibration system of the speaker SP] = [the mass Ms of the diaphragm and the voice coil] + [the additional air mass 2Ma].

  The electric circuit Ke is composed of a voice coil impedance Ze [series circuit of a voice coil resistance Re and a voice coil inductance Le] of the speaker SP connected in series between the output terminals of the voltage source E, and the mechanical circuit Ks is a vibration circuit. The mechanical impedance Zms of the plate 21 [series circuit of the mechanical resistance Rs of the diaphragm, the weight Ms of the diaphragm and voice coil, and the stiffness So such as the edge of the speaker SP], and the electric energy of the electric circuit Ke is It is converted into mechanical energy via T1 and transmitted to the mechanical circuit Ks. Specifically, when the current I (A) flowing through the voice coil of the electric circuit Ke and the force coefficient G (N / A) at the time of conversion are given, a force Fs = GI (N) is applied to the diaphragm 21 of the speaker SP. It vibrates at the applied velocity Vs (m / s).

The acoustic circuit Ka includes a radiation impedance Za [series circuit of the mechanical resistance Ra of air in the rear air chamber Br and an additional air mass Ma] and a rear air chamber impedance Zr (stiffness Sr of air in the rear air chamber Br). ) And the parallel circuit of the acoustic impedance Zp, the mechanical energy of the mechanical system circuit Ks is converted into acoustic energy via the transformer T2 and transmitted to the acoustic system circuit Ka. Specifically, a sound wave having a volume velocity Ua (m ³ / s) is emitted from the diaphragm 21 of the speaker SP that vibrates at a velocity Vs (m / s).

The equivalent circuit composed of the electric system circuit Ke, the mechanical system circuit Ks, and the acoustic system circuit Ka is further replaced with a mechanical system equivalent circuit shown in FIG. This mechanical system equivalent circuit has a vibration source F1 of a force Fs that vibrates the diaphragm 21 at a speed Vs (m / s), and a mechanical electric impedance Zme (=) between both ends of the vibration source F1. Ze / G ² ), diaphragm impedance Zs (= Zms + Za), rear air chamber impedance Zr (stiffness Sr of air in rear air chamber Br) and acoustic impedance Zp, and parallel circuit of front air chamber Bf The air stiffness Sf and the impedance Zf of the sound hole 12 [sound hole resistance Rb and air added mass Mb] are connected in series.

  In such a mechanical equivalent circuit, the diaphragm impedance Zs in the zone H1 (see FIG. 6) in front of the rear air chamber Br is

Further, assuming that the sound source by the diaphragm 21 is a respiratory sphere having a radius D, the air density is ρ, the sound velocity is c, the Bessel function is J ₁ , the Strube function is K _{1, and the} phase constant is k, the radiation impedance Za is ,

It becomes.

  Then, the frequency characteristic Y11 of the sound pressure level of the speaker SP attached to the housing A1 and the frequency characteristic Y12 of the free impedance are calculated based on [Equation 2] and [Equation 3] as shown in FIG. It has a characteristic that peaks in the vicinity. The free impedance is an impedance viewed from the input side when the impedance of the load connected to the output side in the two-terminal pair system is zero.

  Next, regarding the action of the acoustic tube 40 in the zone H2 (see FIG. 6) behind the rear air chamber Br including the acoustic tube 40, an acoustic wave is generated outside the rear air chamber Br as shown in FIGS. 10 (a) and 10 (b). A theoretical explanation will be given using a configuration in which the tube 40 'is provided. It is assumed that the rear chamber Br is a plane wave sound field, and the housing A1 and the acoustic tube 40 'are rigid walls whose cross-sectional shapes are small compared to the wavelength.

  The pressure Pr + and the particle velocity Vr + of the traveling wave in the rear air chamber Br (sound wave traveling in the direction from the back surface of the diaphragm 21 toward the bottom surface of the housing A1) and the reflected velocity in the rear air chamber Br (the bottom surface of the housing A1) When the pressure Pr− and the particle velocity Vr− of the sound wave traveling in the direction toward the rear surface of the diaphragm 21 are set to the surface 101 near the diaphragm 21 in the rear air chamber Br (a surface having the traveling direction of the sound wave as a normal line). ) Pressure Pr1 and particle velocity Vr1 at

The pressure Pr2 and the particle velocity Vr2 on the surface 102 (surface with the traveling direction of sound waves as a normal line) located near the bottom surface of the housing A1 by the distance Xr from the surface 101 are

It becomes.

  Therefore, when the cross-sectional area of the rear air chamber Br is Qr, the volume velocity at the surface 101 is Ur1, and the volume velocity at the surface 102 is Ur2, from [Equation 4] and [Equation 5], the transfer matrix is

It becomes.

  If the opening end 40a ′ of the acoustic tube 40 ′ is provided near the bottom surface of the housing A1 by a distance Xr from the surface 101 in the same manner as the surface 102, the length of the rear air chamber Br is Lr, and the acoustic tube 40 ′ When the cross-sectional area is Qp and the length is Lp, the particle velocity at the closed end becomes 0 due to the closed tube condition. Therefore, the rear chamber impedance Zr and the acoustic impedance Zp are

It becomes.

  Then, applying the same volume velocity and pressure in the rear air chamber Br and the acoustic tube 40 'as the boundary condition at the joint between the rear air chamber Br and the acoustic tube 40', The mechanical impedance Zmr and the mechanical impedance Zmp at the acoustic tube 40 ′ are

The combined impedance Zm of the mechanical system impedances Zmr and Zmp is

It becomes.

  Although the acoustic impedance Zp in [Expression 7] does not consider the attenuation due to the viscosity of the tube wall of the acoustic tube 40 ′, hereinafter, the acoustic impedance Zp considering the attenuation due to the viscosity of the tube wall of the acoustic tube 40 ′ is obtained. . First, in consideration of the fact that the alternating force Fa expressed by [Equation 10] acts on the air, when the equation of motion in the acoustic tube 40 ′ is solved, the range δo in which the particle velocity is affected by the viscosity of the tube wall is When the wavelength of the sound wave is λ, the frequency is f, and the viscosity of the air is μ, [Formula 11] is obtained, and the range δo becomes narrower as the frequency is higher as shown in FIG.

  Then, as shown in FIG. 12, the pressure at the opening end 40a ′ of the acoustic tube 40 ′ is Pp1, the particle velocity is Vp1, and the pressure at the position near the closing end 40b ′ by the distance Xp from the opening end 40a ′ is Pp2. If the particle velocity is Vp2, α is a wavelength constant, β is an attenuation constant, γ is a propagation constant, and d is the inner diameter (radius) of the acoustic tube 40 ′, the phase of the sound wave traveling in the axial direction in the acoustic tube 40 ′ The constant k is

It becomes. In addition, the attenuation constant β and the velocity c ″ of the in-tube sound wave in [Equation 12] increase as the frequency increases as shown in FIGS. 13 and 14.

  In addition, the amplitude velocity u of the sound wave traveling in the axial direction in the acoustic tube 40 'is set to Vo when the amplitude velocity not affected by the viscosity of the tube wall of the acoustic tube 40' is Vo.

It becomes.

  Therefore, the volume velocity at the open end 40 ′ is Up1, the volume velocity at the position near the closed end 40b ′ by the distance Xp from the open end 40a ′ is Up2, and the phase constant k = −jγ is substituted into [Equation 14]. Thus, the approximate acoustic impedance Zp ′ of the acoustic tube 40 ′ is obtained as shown in [Equation 15].

  Here, considering the opening end correction value ΔL shown in [Equation 16] and the pressure loss Δp at the opening end 40a ′ of the acoustic tube 40 ′ shown in [Equation 17], the acoustic impedance Zp of the acoustic tube 40 ′ is [ Equation 18].

The frequency characteristics of the specific acoustic impedance Zp / ρc (the value obtained by dividing the acoustic impedance Zp by the characteristic impedance of air = ρc) when the length Lp = 95 mm and the cross-sectional area Qp = 9 mm ^{2 of the} acoustic tube 40 ′ are shown in FIG. 15, Y 21 is a specific acoustic impedance not considering attenuation due to the viscosity of the tube wall of the acoustic tube, Y 22 is a specific acoustic impedance considering attenuation due to the viscosity of the tube wall of the acoustic tube, and When the viscosity is not taken into consideration, the fluctuation of the maximum value and the minimum value of the specific acoustic impedance becomes large. In FIG. 15, if the specific acoustic impedance is 1 or less, the acoustic impedance is smaller than the characteristic impedance of air, which indicates that there is a sound absorbing effect.

  The operation of the acoustic tube has been described above using a configuration in which the acoustic tube 40 ′ is provided outside the rear air chamber Br as shown in FIGS. 10A and 10B. However, as shown in FIGS. Even in the configuration in which the acoustic tube 40 is provided in the air chamber Br, the operation of the acoustic tube can be explained in the same manner, and the total length Lp of the acoustic tube 40 (40 ′) is set to the frequency at which the sound pressure level is desired to be increased (this embodiment). Since the lowest resonance frequency of the speaker SP shifts to the low frequency side and further the sound pressure level of the speaker SP increases by setting the wavelength to approximately ¼ wavelength (low frequency near 700 to 800 Hz in the embodiment) Even if the air chamber Br has a small capacity, the sound quality and efficiency of the speaker SP are improved. The relationship between the frequency at which the sound pressure level is to be increased and the total length Lp of the acoustic tube 40 is shown in [Equation 19].

16 (a), 16 (b), and 16 (c) show the radiated sound pressure characteristics of the speaker SP attached to the housing A1 including the acoustic tube 40. The capacity of the rear air chamber Br: 3800 mm ² , the acoustic tube The length of 40: 95 mm is common, and only the cross-sectional area of the acoustic tube 40 is different. FIG. 16A shows characteristics when the cross-sectional area of the acoustic tube 40 is 3.8 mm ² (equivalent to φ2.2 mm). Y31 (broken line) is the theoretical value of the sound pressure level not considering attenuation due to the viscosity of the tube wall of the acoustic tube, Y32 (solid line) is the theoretical value of sound pressure level considering the attenuation due to the viscosity of the tube wall of the acoustic tube, Y33 (Δ mark) indicates the experimental result of the sound pressure level. FIG. 16B shows the characteristics when the cross-sectional area of the acoustic tube 40 is 9.0 mm ² (equivalent to φ3.4 mm), and Y41 (broken line) considers attenuation due to the viscosity of the tube wall of the acoustic tube. No theoretical value of the sound pressure level, Y42 (solid line) indicates the theoretical value of the sound pressure level considering attenuation due to the viscosity of the tube wall of the acoustic tube, and Y43 (Δ mark) indicates the experimental result of the sound pressure level. FIG. 16C shows characteristics when the cross-sectional area of the acoustic tube 40 is 12.6 mm ² (φ4.0 mm), and Y51 (broken line) does not consider attenuation due to the viscosity of the tube wall of the acoustic tube. The theoretical value of the sound pressure level, Y52 (solid line) indicates the theoretical value of the sound pressure level considering attenuation due to the viscosity of the tube wall of the acoustic tube, and Y53 (Δ mark) indicates the experimental result of the sound pressure level.

  Thus, the theoretical value of the sound pressure level in consideration of the attenuation due to the viscosity of the tube wall of the acoustic tube and the experimental result almost coincide, and in the housing A1 provided with the acoustic tube 40, the lowest resonance frequency fo0 of the speaker SP. = 800 Hz, the lowest resonance frequency shifts to the low frequency side as compared with the characteristic Y2 without acoustic tube shown in FIG. 4 (minimum resonance frequency fo2 = 1200 Hz), and the sound pressure level in the low range of 800 Hz or less The sound quality and efficiency of the speaker SP are improved. Further, according to FIGS. 16A, 16B, and 16C, it can be seen that the smaller the cross-sectional area of the acoustic tube 40, the smaller the drop in the sound pressure level near 1000 Hz.

  Further, as shown by a broken line in FIG. 1, a sound absorbing material 45 such as a nonwoven fabric is disposed in the vicinity of the opening end 40 a of the acoustic tube 40, thereby enhancing the sound absorbing effect and finely adjusting the resonance frequency of the acoustic tube 40. It is possible to suppress the drop in the sound pressure level occurring in the vicinity of 900 to 1000 Hz in FIGS. 16A, 16B, and 16C, and to increase the sound pressure level. The sound absorbing material 45 may be disposed in various places in the rear air chamber Br or the acoustic tube 40 depending on the degree of fine adjustment.

  In addition, the cross-sectional shape of the acoustic tube 40 is not limited to a rectangle, and may be a circle, an ellipse, a polygon, or the like, and different cross-sectional shapes may be continuously formed in one acoustic tube 40. (For example, the cross-sectional shape of the front half of the acoustic tube 40 is a circle and the cross-sectional shape of the back half is a rectangle).

  Further, as a form of the acoustic tube, a tubular acoustic tube 41 may be inserted into the rear air chamber Br from the outside of the housing A2 as shown in the schematic diagram of FIG. When a urethane tube or the like is used for the acoustic tube 41, the total length Lp can be arbitrarily set and changed.

(Embodiment 2)
In the first embodiment, one acoustic tube is provided in the housing. However, in this embodiment, as shown in the schematic view of FIG. 18, a plurality of acoustic tubes 42, 43, 44 (this In the embodiment, three) are provided, and if the acoustic tubes 42, 43, 44 are set to different lengths, their resonance frequencies are also different from each other. Therefore, the sound pressure level of the speaker SP can be increased at a plurality of frequencies, and desired sound quality and efficiency can be obtained by appropriately setting the overall lengths of the acoustic tubes 42, 43, and 44.

  Further, if the lengths of the acoustic tubes 42, 43, 44 are made the same, the sound pressure level at a predetermined frequency can be greatly improved.

(Embodiment 3)
In the first embodiment, the closed end 40b of the acoustic tube 40 is a closed surface formed obliquely with respect to the axial direction of the acoustic tube 40 as shown in FIG. The frequency band of the sound pressure level that can be improved by one acoustic tube 40 can be expanded.

  Further, if the closed surfaces of the other acoustic tubes 41, 42, 43, 44 of the first and second embodiments are formed in the same manner, the same effect can be obtained.

(A) (b) (c) It is a figure which shows the structure of Embodiment 1. FIG. It is a perspective view same as the above. It is a partially exploded view same as the above. It is a figure which shows the radiation sound pressure characteristic of a speaker. It is a partial side sectional view showing the composition at the time of using an ideal baffle board. It is a figure which shows the vibration model of a speaker apparatus. It is a figure which shows the equivalent circuit of a speaker apparatus. It is a figure which shows the mechanical equivalent circuit of a speaker apparatus. It is a figure which shows the frequency characteristic of the speaker in the zone ahead of a back air chamber. It is a figure which shows the structure for theoretically explaining the effect | action of an acoustic tube. It is a figure which shows the frequency characteristic of the range where particle velocity is influenced by the viscosity of the tube wall of an acoustic tube. It is a figure which shows the sound field in an acoustic tube. It is a figure which shows the frequency characteristic of an attenuation constant. It is a figure which shows the frequency characteristic of the speed of an in-tube sound wave. It is a figure which shows the frequency characteristic of the specific acoustic impedance of an acoustic tube. It is a figure which shows the radiation sound pressure characteristic at the time of providing an acoustic tube. It is side surface sectional drawing which shows another housing same as the above. 6 is a side cross-sectional view showing a housing of Embodiment 2. FIG. It is a figure which shows the shape of the obstruction | occlusion surface of the acoustic tube of Embodiment 3.

Explanation of symbols

A1 Housing SP Speaker Bf Front air chamber Br Rear air chamber 40 Acoustic tube

The present invention relates to a call device .

The present invention has been made in view of the above circumstances, and its object is to suppress the standing waves of voice band generated in the rear air chamber, thereby improving the sound quality of the speaker in the voice band, the efficiency call To provide an apparatus .

The invention according to claim 1 is a communication device capable of two-way communication, a housing, a speaker that is attached to the housing and outputs audio information from one side to the outside of the housing, and the other side of the speaker in the housing A rear air chamber, which is a space formed at the end, an acoustic tube formed in a hollow having one end opened and the other end closed, and communicated with the rear air chamber through the opening, a microphone for collecting sound, a speaker, and And a sound processing unit that transmits and receives a sound signal to and from the microphone, and each surface surrounding the rear air chamber is formed such that a distance between the surfaces facing each other is 50 mm or less.

According to the present invention, a standing wave of 3 KHz or less is not generated in the rear air chamber, and the sound quality and efficiency of the speaker in the voice band can be prevented from being deteriorated by the standing wave generated in the rear air chamber. That is, it is possible to provide a communication device that suppresses standing waves in the voice band generated in the rear air chamber and improves the sound quality and efficiency of the speaker in the voice band. In addition, the acoustic tube shifts the lowest resonance frequency of the speaker to the lower frequency side and further increases the sound pressure level of the speaker, so that the sound quality and efficiency of the voice band are improved even if the rear air chamber has a small capacity. .

According to a second aspect of the present invention, in the first aspect, the acoustic tube is ¼ of the frequency to be increased in order to increase the sound pressure level at a predetermined frequency of the speaker output, which decreases due to the small capacity of the rear air chamber. The length is set based on the wavelength.

According to a third aspect of the present invention, in the first or second aspect, the acoustic tube is formed continuously over a plurality of surfaces among the surfaces surrounding the rear air chamber.

According to a fourth aspect of the present invention, in any one of the first to third aspects, a plurality of the acoustic tubes having the same length are provided.

According to a fifth aspect of the present invention, in any one of the first to third aspects, a plurality of the acoustic tubes having different lengths are provided.

A sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the shape of the closed other end face of the acoustic tube is formed obliquely with respect to the axial direction of the acoustic tube.

A seventh aspect of the invention is characterized in that in any one of the first to sixth aspects, a sound absorbing material is provided in the rear air chamber or the acoustic tube.

The invention of claim 8 is characterized in that, in any one of claims 1 to 7, the acoustic tube is formed in a bent shape and provided in the rear air chamber.

(Embodiment 1)
As an embodiment of the present invention, an interphone communication device will be described below as an example.

The invention according to claim 1 is a communication device capable of two-way communication, a housing, a speaker that is attached to the housing and outputs audio information from one side to the outside of the housing, and the other side of the speaker in the housing A rear air chamber, which is a space formed at the end, an acoustic tube formed in a hollow having one end opened and the other end closed, and communicated with the rear air chamber through the opening, a microphone for collecting sound, a speaker, and Each of the surfaces surrounding the rear air chamber is formed with a distance of 50 mm or less between the surfaces facing each other , and the inner diameter of the acoustic tube is It is set based on the acoustic impedance in consideration of the attenuation due to the viscosity of the tube wall .

Claims (9)

A housing;
A speaker attached to the housing and outputting audio information from one side to the outside of the housing;
A rear air chamber that is a space formed on the other side of the speaker in the housing,
Each of the surfaces surrounding the rear air chamber is formed such that the distance between the surfaces facing each other is 50 mm or less.   2. The speaker device according to claim 1, further comprising an acoustic tube that is formed in a hollow shape having one end opened and the other end closed, and communicated with the rear air chamber through the opening.   The acoustic tube is set to a length based on a quarter wavelength of the frequency to be increased in order to increase the sound pressure level at a predetermined frequency of the speaker output that is reduced due to the small capacity of the rear air chamber. The speaker device according to claim 2.   The speaker device according to claim 2, wherein the acoustic tube is formed continuously over a plurality of surfaces among the surfaces surrounding the rear air chamber.   The speaker device according to claim 2, comprising a plurality of the acoustic tubes having the same length.   The speaker device according to claim 2, further comprising a plurality of the acoustic tubes having different lengths.   The speaker device according to any one of claims 2 to 6, wherein a shape of the other end face of the acoustic tube closed is formed obliquely with respect to an axial direction of the acoustic tube.   The speaker device according to any one of claims 2 to 7, wherein a sound absorbing material is provided in the rear air chamber or the acoustic tube.   9. The speaker device according to claim 2, wherein the acoustic tube is formed in a bent shape and is provided in a rear air chamber.

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