JP2002135880A - Primary sound pressure-gradient microphone and portable terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a primary sound pressure-gradient microphone which is suitable to adopt a structure where the high sensitivity side of directional characteristics in the transmission part of a portable terminal device is arranged toward a sound source at the time of speaking. SOLUTION: The CR ( the product between an acoustic capacity and an acoustic resistance) larger than that on a rear side (RSm) is set on a front side (FSm) of a primary sound pressure-gradient microphone (20) to make the rear sensitivity higher than the front sensitivity, and the microphone is used with the rear side turned toward the sound source to take out a sound signal from an output terminal (25) on the rear side. Since the high sensitivity side of the microphone is on the rear side having the output terminal, the output terminal is turned inward a casing (61) for portable terminal and cam be easily connected to a desired terminal of a circuit board (62) in the portable terminal device when the rear side as the high sensitivity side of the microphone is turned toward the sound source at the time of speaking and the front side (FSm) as the low sensitivity side is turned a rear part (RSp) of the casing (61) for portable terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret-type primary sound pressure gradient type microphone and a portable terminal device to which the microphone is applied.

[0002]

2. Description of the Related Art In recent years, mobile phones, which have been rapidly spreading,
Its size is smaller and thinner,
As a result, when the receiving part is placed on the ear, the transmitting part does not reach the position close to the mouth, and the number of products located right next to or slightly behind the mouth is increasing. Conventionally, most microphones incorporated therein are omnidirectional microphones. However, since the sound pressure difference between the target sound and the ambient noise is relatively small as compared with the case where the transmission part is near the mouth, the noise is often mixed and the transmission becomes unclear. Attempts have been made to use a sound pressure gradient type unidirectional or bidirectional microphone that is difficult to pick up ambient noise as a microphone for transmission.

[0003] However, the primary sound pressure gradient type microphone naturally needs to apply sound pressure to both sides of the front and back surfaces of the diaphragm because of its structure. It is necessary to provide a front opening 4 communicating with the front surface of the diaphragm 3 of the microphone 2 and a side opening 5 communicating with the back surface of the diaphragm 3 of the microphone 2. In this case, the directivity axis (directivity characteristic axis) is, as shown in FIG.
Therefore, the directivity direction becomes as shown in FIG. 12, and it is not possible to obtain a directivity characteristic in which the directivity axis is directed toward the mouth of the speaker. In short, ambient noise is picked up even if the primary sound pressure gradient type microphone is used.

Therefore, the inventor of the present invention mounts the front surface of the diaphragm 3 of the microphone 2 on the casing 6 of the portable telephone as illustrated in FIG. 11 in order to obtain a directivity characteristic in which the directivity axis is directed toward the mouth of the speaker. And a rear opening 8 communicating with the back surface of the diaphragm 3 of the microphone 2 were examined. Thereby, as illustrated in FIG. 13, it is possible to obtain a directional characteristic in which the directional characteristic axis connecting the two openings 7 and 8 of the terminal casing 6 is directed to the mouth of the speaker. The configuration shown in FIG. 11 is not publicly known.

[0005]

However, FIG.
If the microphone is oriented with the back of the microphone facing the back of the casing, the desired directional characteristics can be obtained, but since the output terminal of the microphone is located on the back of the microphone, the circuit board of the mobile phone and the It has been clarified by the present inventors that the connection with the output terminal of the microphone becomes difficult. That is, FIG.
In the configuration of 0, the output terminal 10 of the microphone 2 can be easily connected to the corresponding terminal of the circuit board 11. However, in FIG. 11, since the microphone 2 must be located on the back side of the casing 6, the microphone 2
Of the microphone 2 must be directed to a position distant from the circuit board of the mobile phone, and the output terminal 10 of the microphone 2 is connected to the circuit board irrespective of whether the circuit board is disposed at P1 or P2. The present inventor has found that the number of additional parts such as relay leads and connectors increases, the assembling process of the mobile phone becomes complicated, and the cost of the mobile phone as a whole increases.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a primary terminal suitable for adopting a structure in which a high sensitivity side of a directivity characteristic in a transmitting unit of a portable terminal device having a transmitting unit and a receiving unit is arranged toward a sound source during a call. It is to provide a sound pressure gradient type microphone.

Another object of the present invention is to eliminate the need for additional components for connecting the primary sound pressure gradient type microphone to the circuit board for a portable terminal and to reduce the ambient noise in the transmitting section without complicating the assembly process. An object of the present invention is to provide a portable terminal device that is difficult to pick up.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0009]

The primary sound pressure gradient microphone according to the present invention has an acoustic impedance formed by an acoustic capacitance Cf and an acoustic resistance Rf on the front side of a diaphragm.
An acoustic capacitor Cr is provided on the back side of the diaphragm to which the back electrode is provided.
And an acoustic impedance is formed by the acoustic resistance Rr, a microphone circuit board is disposed to face the back electrode, and an output terminal for an electroacoustic conversion signal directed to the outside is provided on the microphone circuit board, and CfRf> Cr
Rr and Cf> Cr. In short, CfR
With f> CrRr, the back sensitivity is made higher than the front sensitivity,
Use with the back side facing the sound source, and take out the audio signal from the output terminal on the back side. At this time, the acoustic capacity C
Since f and Cr are determined by the geometric size of the space, there are few errors. On the other hand, when increasing the acoustic resistances Rf and Rr, an acoustic resistance member such as cloth is used, and the acoustic resistance of such an acoustic resistance member has a large error.
The change of acoustic resistance with time is large. The relationship of Cf> Cr means that the dependence on the acoustic capacitances Cf and Cr is increased in order to obtain the necessary acoustic impedance on the front side and the rear side, respectively. This helps stabilize the relationship of CfRf> CrRr.

By employing the primary sound pressure gradient type microphone having the above structure, even when the primary sound pressure gradient type microphone is located on the back side of the casing for the portable terminal, the output terminal of the primary sound pressure gradient type microphone is provided. Can be avoided in a direction away from the mobile terminal circuit board. In short, the high sensitivity side of the primary sound pressure gradient type microphone is the back side having the output terminal, so the high sensitivity side back of this primary sound pressure gradient type microphone is directed toward the sound source during a call, and the low sensitivity front side is When the output terminal is directed toward the rear surface of the mobile terminal casing, the output terminal necessarily faces the inside of the mobile terminal casing, and can be easily connected to a desired terminal of the mobile terminal circuit board inside the mobile terminal casing. By using this primary sound pressure gradient type microphone, in a portable terminal device having a transmitting unit and a receiving unit, openings are formed in the back and bottom of the casing for the portable terminal in the vicinity of the microphone, and the pointing of the microphone is performed. If the characteristic axis is made to pass from the rear part to the bottom part of the casing for the portable terminal, it is possible to easily realize a structure in which the high sensitivity side of the directivity characteristic is arranged toward the sound source at the time of transmission. And, no additional parts are required for connection between the primary sound pressure gradient type microphone and the mobile terminal circuit board,
The assembling process is not complicated, and it is easy to realize a portable terminal device in which ambient noise is hardly picked up by the transmitting section.

The acoustic capacitance Cf is determined by the volume of an air chamber sandwiched between the front of the diaphragm and the front of the microphone casing, and the acoustic resistance Rf is a plurality of acoustic resistances Rf formed on the front of the microphone casing. And the acoustic resistance of the acoustic resistance member provided on the front side of the microphone casing. The acoustic capacitance Cr is determined by the volume of the air chamber sandwiched between the back surface of the diaphragm and the back electrode, and the acoustic resistance Rr is determined by the viscous resistance of the back electrode in which a plurality of holes are formed.

A portable terminal device such as a portable telephone according to another aspect of the present invention has a primary sound pressure gradient type microphone and a portable terminal circuit board built in a portable terminal casing, and an operation key on a front portion of the portable terminal casing. Having. The primary sound pressure gradient microphone has a sensitivity on the back side larger than the sensitivity on the front side, has an output terminal for an audio signal on the back side, and has a rear side of the primary sound pressure gradient type microphone for the portable terminal casing. Toward the front part, the directional characteristic axis of the primary sound pressure gradient type microphone passes through the bottom part from the back part of the casing for the portable terminal, and the output terminal of the primary sound pressure gradient type microphone is connected to the circuit board for the portable terminal. It is configured to face.

According to this portable terminal device, the back surface of the primary sound pressure gradient type microphone having the output terminal on the high sensitivity side is directed toward the sound source during a call, and the low sensitivity front surface is the portable terminal. The output terminal of the microphone faces the inside of the mobile terminal casing when facing the rear surface of the mobile casing, and the output terminal can be connected to a desired terminal of the mobile terminal circuit board inside the mobile terminal casing. In this portable terminal device, since the directional characteristic axis of the microphone passes through the bottom of the portable terminal casing from the back, a structure is realized in which the high sensitivity side of the directional characteristic is directed to the sound source during a call. I have. Therefore,
No additional parts are required to connect the primary sound pressure gradient microphone to the mobile terminal circuit board, and the assembly process is not complicated,
It is possible to realize a portable terminal device in which ambient noise is hardly picked up by the transmitting section.

[0014]

FIG. 1 is an axial sectional view of a primary sound pressure gradient type microphone according to the present invention. The primary sound pressure gradient microphone 20 shown in FIG. 1 has a generally button-shaped microphone casing 21 on the outside. The microphone casing 21 is made of, for example, aluminum and has a cylindrical shape, and a plurality of sound wave passage openings 22 are provided on the front side FSm.
Is formed, and the rear edge 28 is bent inward at the end of the assembling process to lock the internal structure of the casing 21 described later. An acoustic resistance member 27 made of cloth, for example, is attached to the surface of the sound wave passage opening 22 on the front side FSm.

In the cylinder of the casing 21, a front side F
Sm and a diaphragm 23 forming one pole of the condenser facing the sound wave passage opening 22 in order from the Sm.
And a microphone circuit board 26 having an output terminal 25 for an electroacoustic conversion signal by the diaphragm and the back electrode 24. The output terminal 25 is a microphone casing 2
1 at the rear side RSm.

Although the diaphragm 23 is not particularly limited,
A metal film is deposited on one surface of a dielectric film such as a polyester film, and the metal film is fixed to the diaphragm ring 30, and an insulating spacer 31 is fixed to the dielectric surface. The metal film of the diaphragm 23 may be formed on both surfaces of the dielectric film.

The back electrode 24 is fitted and fixed substantially concentrically to the inner step of the insulating ring 32, and the back electrode 24 abuts on the insulating spacer 31 in this state. Although not particularly limited, the back electrode 24 is made of a conductor, for example, nickel-plated brass, and a surface facing the vibration plate 23 is laminated with, for example, a fluorine resin for forming permanent polarization.

The microphone circuit board 26 is not particularly limited. A circuit chip 26 such as a field effect transistor used for impedance conversion is mounted on a printed wiring board 26A having an appropriate wiring pattern formed on the front and back surfaces.
B is implemented and configured. The output terminal 25 is electrically connected to a predetermined wiring pattern on the back side of the printed wiring board 26A. The back electrode 24 is electrically connected to a predetermined wiring pattern on the front surface of the printer wiring board 26A via a conductive connection ring 33. The metal film of the diaphragm 23 is conducted from the diaphragm ring 30 through the casing 21 to a predetermined wiring pattern on the back side of the printer wiring board 26A via the rear edge 28 thereof.

The printed wiring board 26A has a rear side R
A sound wave passage opening 26C from Sm is formed, and a sound wave passage opening 24A from the back side RSm is formed in the back electrode 24.

Here, the acoustic capacitance C is provided on the front side of the diaphragm 23.
f and the acoustic resistance Rf, an acoustic impedance is formed by the acoustic capacitance Cr and the acoustic resistance Rr on the back side of the diaphragm 23, and CfR
f> CrRr and Cf> Cr. The acoustic capacitance Cf is determined by the volume of the air chamber sandwiched between the front of the diaphragm 23 and the front of the microphone casing 21, and the acoustic resistance Rf is the front of the microphone casing 21 having a plurality of holes 22. Side and acoustic resistance member 27
Determined by the acoustic resistance. The acoustic capacitance Cr is determined by the volume of the air chamber sandwiched between the back surface of the diaphragm 23 and the back electrode 24, and the acoustic resistance Rr is determined by the viscous resistance of the back electrode 24 in which a plurality of holes 24A are formed. It is determined.

The relationship CfRf> CrRr means that the sensitivity of the rear side RSm of the primary sound pressure gradient type microphone 20 is higher than the sensitivity of the front side FSm. The relationship Cf> Cr is satisfied by the acoustic capacitances Cf, Cf in order to obtain the necessary acoustic impedance on the front side FSm and the rear side RSm, respectively.
This means increasing the dependency on r.

The relationship CfRf> CrRr proves that the back sensitivity of the primary sound pressure gradient microphone 20 is higher than the front sensitivity.

FIG. 2 shows the primary sound pressure gradient type microphone of FIG.
3 shows an acoustic circuit configuration of the audio signal. In the figure, r ₀, M₀, C₀Is vibration
Constant of plate 23 itself, c₁(= Cr) is
Thin fluid layer volume (acoustic capacity) with the back electrode 24, r
₁(= Rr) is the viscosity of the back electrode 24 having the opening 24A.
Sex resistance, c_Two(= Cf) is for diaphragm 23 and microphone
Acoustic volume of air chamber sandwiched between FSm on the front side of casing 21
Quantity, r_Two(= Rf) is for a microphone having an opening 22
The acoustic resistance of the casing 21 and the acoustic resistance member 27
You. The equivalent circuit of the primary sound pressure gradient microphone 20 is
As shown in FIG. In FIG. 3, p is the sound pressure, S is the diaphragm effective
Area, d is the distance between acoustic terminals, c is the speed of sound, θ is the incident angle of sound
It is.

The velocity v of the movement of the diaphragm can be obtained by equation (1). In equation (1), the part shown in equation (2) is subjected to Taylor expansion. In this, the factorial term in equation (3) does not significantly affect the calculation result, and is omitted, and is substituted as equation (4). By rearranging equation (1), equation (5) is obtained.

[0025]

(Equation 1)

Since the displacement d of the diaphragm can be obtained by integrating the velocity v, the equation (6) is obtained by indefinitely integrating the equation (5).

[0027]

(Equation 2)

Here, when the ratio A of d when θ = 0 ° and θ = 180 ° is obtained, Expression (7) is obtained. The absolute value of A (| A |) can be expressed as in equation (8), where d / c = α, r ₁ c ₁ = β, r ₂ c ₂ / r ₁ c ₁ = x and When put, the absolute value of A is expressed as in equation (9).

[0029]

(Equation 3)

Direction axis 180 ° direction (back direction) is 0 °
In order for the sensitivity to be higher than the direction (front direction), | A |>
Must be 1. The condition for this is that if both sides of equation (9) are squared and arranged as in equation (10), 4α
The condition β (x−1)> 0 can be derived.
Since α> 0, the above condition is β> 0 and x> 1. If this is rewritten, r ₂ c ₂ > r ₁ c ₁ > 0.
Considering this in terms of an equivalent circuit, in FIG.
R ₁ c ₁ on the back side of the diaphragm and r ₁ on the front side of the diaphragm
The balance of ₂ c _2, if _{r 2 c 2> r 1 c} 1 and set so made, 180 ° sensitivity (back sensitivity) 0 ° Sensitivity (front sensitivity)
Higher.

[0031]

(Equation 4)

The maximum value of | A | can be obtained by differentiating equation (9). In short, the result of equation (12) is obtained via equation (11).

[0033]

(Equation 5)

At the maximum value of the equation (12), the absolute value | A | FIG. 4 shows d = 10 mm and c = 340.
When m, ω = 2πf = 2π × 1 kHz, r ₂ c ₂ / r ₁ c ₁ and | A
Represents the relationship with | In short, the back directivity has a boundary condition.

FIG. 5 shows the structure of FIG. 1 having β / α = 1,
7 shows a difference in directional characteristics between a primary sound pressure gradient microphone having a condition of x = 1.3 and a primary sound pressure gradient microphone having the structure of FIG. 6. The primary sound pressure gradient microphone shown in FIG. 6 has a general configuration in which the sensitivity on the front side is higher than that on the back side, and no acoustic resistance member is arranged on the front surface of the casing 21. Relatively large opening 40
Are formed. Other configurations are the same as those in FIG.
From FIG. 5, the sensitivity of the back side is clearly higher in the structure of FIG. 1 as indicated by the characteristic line indicated by L1i, but the sensitivity of the front is slightly increased in the structure of FIG. 6 as indicated by the characteristic line indicated by L2i. Has been enlarged.

FIG. 7 is an actual measurement diagram of the directional characteristics of the primary sound pressure gradient type microphone 20. FIG. 5 shows ideal characteristics. Actually, the figure-shaped L1m and L2m characteristics are distorted due to manufacturing errors and measurement errors of the primary sound pressure gradient microphone 20. L1m indicates the characteristic of the primary sound pressure gradient type microphone 20 having the structure of FIG. 1, and L2m indicates the characteristic of the primary sound pressure gradient type microphone having the structure of FIG.

FIG. 8 illustrates a primary sound pressure gradient type microphone assembly (microphone assembly) having the structure of FIG. Microphone assembly 50 shown in FIG.
Is the primary sound pressure gradient type microphone 20
And the spring terminal housing 52, the front side FSm of the primary sound pressure gradient type microphone 20 faces outward from the opening 53, and the rear side RSm of the microphone 20 faces the spring terminal housing 52 via the space 54. The space 54 communicates with a side opening 55 of the rubber holder 51. A pair of contact springs 56 are mounted on the front and back surfaces of the spring terminal housing 52 so as to be able to advance and retreat, and one end of the contact spring 56 is formed on the rear side RSm of the primary sound pressure gradient type microphone 20. Is contacted.

FIG. 9 shows a partial cross section of a portable telephone incorporating the microphone assembly of FIG. The mobile phone 60 has a microphone assembly 50 and a mobile terminal circuit board 62 incorporated in a mobile terminal casing 61, and operation keys 63 are arranged on a front portion FSp of the mobile terminal casing 61. When the microphone assembly 50 is mounted on the portable terminal casing 61, the rear side RSm of the microphone casing faces the front part FSp of the portable terminal casing, and the directional characteristic axis of the primary sound pressure gradient type microphone 20. 65 passes from the rear part RSp of the portable terminal casing 61 to the bottom part BSp,
The output terminal 25 of the microphone circuit board 26 faces the mobile terminal circuit board 62. That is, the opening 70 formed in the rear portion RSp of the casing 61 for the portable terminal.
Communicates with the opening 53 of the rubber holder 51, and an opening 71 formed in the bottom portion BSp of the casing 61 for the portable terminal communicates with the opening 55 of the rubber holder 51. here,
Since the microphone assembly 50 is used, the output terminal 25 is conducted to a predetermined conductive pattern (not shown) of the portable terminal circuit board 62 via the contact spring 56.

According to the portable telephone 60 having the structure shown in FIG. 9, as shown in FIG. 13, the high sensitivity side of the directivity characteristic faces the mouth of the speaker during a call.

By employing the above-described primary sound pressure gradient type microphone 20, the high sensitivity side of the primary sound pressure gradient type microphone 20 is connected to the rear side RSm having the output terminal 25.
Therefore, the high-sensitivity back RSm of the primary sound pressure gradient type microphone 20 is directed toward the sound source at the time of a call, and the low-sensitivity front FSm is connected to the rear RS of the portable terminal casing 61.
When the terminal is turned to p, the output terminal 25 necessarily faces the inside of the casing 61 for the portable terminal, and can be easily connected to a desired terminal of the circuit board 62 for the portable terminal inside the casing 61 for the portable terminal. This primary sound pressure gradient type microphone 20
In the mobile phone, the rear part R of the casing 61 for the mobile terminal in the vicinity of the microphone 20 is used.
Openings 70 and 71 are formed in Sp and bottom surface portion BSp, and the directional characteristic axis 65 of the microphone is aligned with mobile terminal casing 6.
If the rear part RSp is passed through the bottom part BSp from the back part RSp, it is possible to easily realize a structure in which the high sensitivity side of the directivity characteristic is arranged toward the sound source at the time of transmission.

Therefore, a portable telephone which does not require additional components for connecting the primary sound pressure gradient type microphone 20 and the portable terminal circuit board 62, does not complicate the assembling process, and is less likely to pick up ambient noise in the transmitting section. Can be easily realized.

Since the acoustic capacitances Cf and Cr are determined by the geometric size of the space, there are few errors. On the other hand, when increasing the acoustic resistances Rf and Rr, an acoustic resistance member such as a cloth is used, and the acoustic resistance of such an acoustic resistance member has a large error. Is big. At this time, in order to obtain the required acoustic impedances on the front side and the rear side, respectively, by increasing the dependence on the acoustic capacitances Cf and Cr according to the relationship of Cf> Cr, the CfRf
> The relationship with CrRr can be stabilized.

Although the invention made by the present inventor has been specifically described based on the embodiment, it is needless to say that the present invention is not limited to the embodiment and can be variously modified without departing from the gist thereof. No. For example, a diaphragm having a metal film deposited on both surfaces thereof may be used. In the above description, the permanent polarization is formed on the back electrode side. However, the polarization may be formed on the diaphragm side. In this case, for example, a diaphragm may be formed by depositing a metal film on a fluororesin film. In addition, the present invention provides, in addition to a cellular phone, a P
It can be widely applied to portable information communication devices such as DA (Personal Digital Assistant).

[0044]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

That is, a primary sound pressure gradient type suitable for adopting a structure in which the high sensitivity side of the directivity characteristic in the transmitting section of the portable terminal apparatus having the transmitting section and the receiving section is arranged toward the sound source during a call. A microphone can be provided.

Further, a portable terminal device which does not require additional parts for connecting the primary sound pressure gradient type microphone to the circuit board for the portable terminal, does not complicate the assembling process, and is hard to pick up ambient noise in the transmitting section. Can be realized.

[Brief description of the drawings]

FIG. 1 is an axial sectional view showing an example of a primary sound pressure gradient type microphone according to the present invention.

FIG. 2 is an explanatory diagram showing an acoustic circuit of the primary sound pressure gradient microphone of FIG. 1;

FIG. 3 is an equivalent circuit diagram of the primary sound pressure gradient microphone of FIG. 1;

FIG. 4 is an explanatory diagram showing that there is a boundary condition in the back directivity of the primary sound pressure gradient type microphone of FIG. 1;

5 is a characteristic diagram showing a difference in directional characteristics between a primary sound pressure gradient type microphone having the structure of FIG. 1 and a primary sound pressure gradient type microphone having the structure of FIG. 6;

FIG. 6 is an axial sectional view of a primary sound pressure gradient microphone according to a comparative example having a structure in which the sensitivity on the front side is higher than that on the rear side.

FIG. 7 is a characteristic diagram showing a measurement result of a directivity characteristic of each of the primary sound pressure gradient type microphones having the structures of FIGS. 1 and 6;

FIG. 8 is a cross-sectional view illustrating a microphone assembly having the primary sound pressure gradient type microphone of FIG. 1;

FIG. 9 is a partial cross section of a mobile phone incorporating the microphone assembly of FIG. 8;

FIG. 10 is a partial cross-sectional view of a mobile phone previously studied by the present inventor where a high sensitivity region deviates from a sound source during transmission.

FIG. 11 is a partial cross-sectional view of a mobile phone previously studied by the inventor of the present invention, in which a high-sensitivity region faces the direction of a sound source during transmission.

12 is an explanatory diagram illustrating a relative relationship between a directional characteristic axis and a sound source of the mobile phone of FIG. 10;

13 is an explanatory diagram illustrating a relative relationship between a directional characteristic axis and a sound source of the mobile phone of FIG. 11;

[Explanation of symbols]

 Reference Signs List 20 primary sound pressure gradient microphone FSm front of primary sound pressure gradient microphone RSm back of primary sound pressure gradient microphone 21 microphone casing 22 sound wave passage opening 23 diaphragm 24 back electrode 25 output terminal 26 microphone circuit board 27 acoustic resistance Member 50 Microphone assembly 56 Contact spring 60 Mobile phone FSp Front side of mobile phone RSp Back side of mobile phone BSp Bottom side of mobile phone 61 Casing for mobile terminal 62 Circuit board for mobile terminal 63 Operation key 65 Directional characteristic axis 70 Mobile phone Opening on back side 71 Opening on bottom side of mobile phone

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) H04R 19/01 H04B 7/26 VF term (Reference) 5D017 BC18 5D018 BB13 5D021 CC02 CC17 CC19 5K023 AA07 BB04 BB07 DD06 EE02 EE05 LL01 LL06 5K067 AA21 BB04 EE02 KK17

Claims (6)

[Claims] 1. An acoustic impedance due to an acoustic capacitance Cf and an acoustic resistance Rf is formed on the front side of a diaphragm, and an acoustic impedance due to an acoustic capacitance Cr and an acoustic resistance Rr is formed on the back side of the diaphragm on which a back electrode is provided. A microphone circuit board is disposed to face the back electrode, and an output terminal for an electroacoustic conversion signal directed to the outside is provided on the microphone circuit board. The microphone satisfies CfRf> CrRr and Cf> Cr. A primary sound pressure gradient microphone. 2. A diaphragm, a back electrode capable of forming a capacitor together with the diaphragm, and an output terminal of an electroacoustic conversion signal by the diaphragm and the back electrode are sequentially arranged in the cylinder of the microphone casing from the front side. A microphone circuit board, the output terminal of which is directed to the outside from the back side of the microphone casing, and a primary sound pressure formed by allowing sound waves to enter both surfaces of the diaphragm from both ends of the microphone casing. An inclination-type microphone, wherein an acoustic impedance is formed by an acoustic capacitance Cf and an acoustic resistance Rf between one surface of the diaphragm and a front side of the microphone casing, and between the other surface of the diaphragm and a back electrode. , An acoustic impedance due to the acoustic capacitance Cr and the acoustic resistance Rr is formed, satisfying CfRf> CrRr and Cf> Cr A primary sound pressure gradient microphone. 3. The acoustic capacitance Cf is determined by the volume of an air chamber sandwiched between the front of the diaphragm and the front of the microphone casing, and the acoustic resistance Rf is formed on the front of the microphone casing. The acoustic capacitance Cr is determined by the acoustic resistance of the plurality of holes and the acoustic resistance member provided on the front side of the microphone casing, and the acoustic capacitance Cr is determined by the volume of the air chamber sandwiched between the back surface of the diaphragm and the back electrode. 3. The primary sound pressure gradient microphone according to claim 2, wherein the acoustic resistance Rr is determined by viscous resistance of a back electrode having a plurality of holes. 4. A portable terminal device having a primary sound pressure gradient microphone according to claim 2 and a portable terminal circuit board built in the portable terminal casing, and having operation keys on a front portion of the portable terminal casing. The back side of the microphone casing faces the front part of the portable terminal casing, and the directional characteristic axis of the primary sound pressure gradient type microphone passes through the rear part of the portable terminal casing to the bottom part, and the microphone circuit board has A portable terminal device, wherein the output terminal faces the circuit board for a portable terminal. 5. A portable terminal device having a primary sound pressure gradient type microphone and a portable terminal circuit board built in a portable terminal casing, and having operation keys on a front portion of the portable terminal casing, wherein the primary sound pressure gradient is provided. The sensitivity of the type microphone is higher than the sensitivity of the front side, has an output terminal of an audio signal on the back side, the back side of the primary sound pressure gradient type microphone faces the front part of the casing for the portable terminal, The directional characteristic axis of the primary sound pressure gradient type microphone passes from the back part to the bottom part of the mobile terminal casing, and the output terminal of the primary sound pressure gradient type microphone faces the mobile terminal circuit board. Characteristic portable terminal device. 6. A portable terminal device having a primary sound pressure gradient type microphone and a portable terminal circuit board incorporated in a portable terminal casing, and having operation keys on a front portion of the portable terminal casing, wherein the primary sound pressure gradient is provided. The type microphone has a diaphragm, a back electrode capable of forming a capacitor together with the diaphragm, and an output terminal for an electroacoustic conversion signal by the diaphragm and the back electrode, sequentially from the front side in a cylinder of the microphone casing. A microphone circuit board is provided, the output terminal is directed to the outside from the back side of the microphone casing, and sound waves can enter both surfaces of the diaphragm from both ends of the microphone casing. The sensitivity to the input sound from the back side is different from the input sound from the front side of the microphone casing. The microphone has a directional characteristic that is higher than the degree, the back side of the microphone casing faces the front part of the portable terminal casing, and the directional characteristic axis of the primary sound pressure gradient type microphone is from the back part of the portable terminal casing. A mobile terminal device, wherein the output terminal of the microphone circuit board faces the circuit board for a mobile terminal, the mobile terminal device being pulled out to a bottom surface portion.