JPH0129897Y2 - - Google Patents

Description

[Detailed description of the invention] "Industrial application field" This invention is an electrostatic transmitter using an electret condenser microphone unit, especially an electrostatic transmitter that has a simple configuration and excellent transmission frequency characteristics. It is related to the speaker.

``Prior Art'' For example, as an electrostatic transmitter used as a transmitting unit of a telephone, a carbon type transmitter has generally been used. However, the carbon type transmitter has a lot of distortion due to its transmission characteristics, so its transmission sound quality deteriorates, and satisfactory transmission frequency characteristics cannot be obtained. On the other hand, carbon type transmitters generally consume a large amount of power, and also have many variations and fluctuations in sensitivity, which also pose problems in use.

In contrast to this carbon type transmitter, an electrostatic transmitter using an electric condenser microphone unit has also been proposed.

In general, the rules regarding technical standards for attached equipment and connected equipment for subscriber telephones, etc., established based on Article 105, Paragraph 3 of the Public Telecommunications Act, in order to quantitatively determine the permissible range of transmitting frequency characteristics of transmitters. Article 19 stipulates electrical standards regarding telephone calls for attached equipment, etc. Figure 14 shows the permissible transmission level characteristic range of the transmission frequency of the electrical standards for telephone calls (hereinafter referred to as electrical standards), with frequency (Hz) on the horizontal axis and sensitivity (dB) on the vertical axis. In this case, it is required that a transmission level characteristic curve (hereinafter referred to as a transmission frequency characteristic curve) of the transmission frequency exists within a region sandwiched between reference lines R and Ru indicating the permissible range.

In general, the transmitting frequency characteristic of a transmitter itself is that the transmitting frequency characteristic curve has a cutoff characteristic in a low frequency band of approximately 500Hz or less, and a peak exists in the frequency characteristic curve in a frequency band of 2 to 3 KHz. is necessary.

A curve 11 shown in FIG. 14 shows an example of a transmission frequency characteristic curve of a transmitter that satisfies this electrical standard. Note that this tolerance range indicates relative characteristics, so if the measured value of the transmitting frequency characteristic of the transmitter is relatively within this tolerance range, it is recognized as satisfying the standard.

For example, the amount of electrostatic transmission using an electret condenser microphone unit is
As shown in FIG. 5, a through hole 13 is formed in the handset housing 12 of the transmitter.
A type in which an electret condenser microphone unit 14 is attached at a position so as to close the through hole 13 has been proposed.

When measuring the transmitting frequency characteristics of a transmitter configured in this way, the transmitting frequency characteristics are as shown by curve 15 in Figure 16, with frequency (Hz) on the horizontal axis and sensitivity (dB) on the vertical axis. A frequency characteristic curve is obtained. 1st
It is clear from FIG. 6 that in the transmitter having such a configuration, the transmission frequency characteristic curve deviates from the region between the reference lines R and Ru that satisfy the electrical standards, and does not satisfy the permissible conditions.

On the other hand, a type using an electret condenser microphone unit 14 and subjected to acoustic compensation as shown in FIG. 17 has also been proposed.

That is, the through hole 13 of the handset housing 12
A compensation case 16 is attached surrounding the repair case 16, and the electret condenser microphone unit 14 is fixed to this repair case 16 by, for example, adhesive means. In this configuration, a front chamber 17 is formed between the electret condenser microphone unit 14 and the compensation case 16. An opening 18 communicating from the front chamber 17 to the handset housing 12 side is formed approximately in the center of the front chamber 17, and the handset housing 12 side of this opening 18 is closed with a cloth 19. Further, the compensation case 16 is formed into a substantially cup shape, and a front chamber 20 is formed between the compensation case 16 and the handset housing 12.

When measuring the transmitting frequency characteristics of a transmitter with such a configuration, curve 22 is shown in FIG.
A transmitting frequency characteristic curve as shown in is obtained. As is clear from Fig. 18, in the transmitter with this configuration, a peak is formed in the transmitting frequency characteristic curve near 2500Hz, and the transmitting frequency characteristic of this transmitter is in the mid and high ranges. It satisfies electrical standards in the frequency band. However, the transmission frequency characteristic curve does not attenuate in the low frequency band, and is almost
The required cutoff characteristics in the low frequency band below 500Hz were not observed, and the electrical standards were not met in this respect.

In order to provide the transmitter with the configuration shown in Figure 17 with cutoff characteristics for its transmission frequency characteristic curve in the low frequency band below 500Hz, a low-cut filter is separately installed for the transmitter. Once installed, you will have something that meets electrical standards. However, with such a structure, the capacitors and resistors constituting the filter must be added to the transmitter as components, making the structure complicated.

``Problems to be solved by the invention'' This invention solves the various drawbacks of the electrostatic transmitter using the electret condenser microphone unit that has been proposed in the past. The present invention provides an electrostatic transmitter that satisfies the electrical standards for telephone calls, including Article 19 of the Ordinance on Technical Standards for Connected Equipment, etc., and achieves excellent transmission frequency characteristics.

``Structure of the device'' In this device, the closed end surface is made to protrude convexly from the closed surface side of the back cover body so as to close the open face of the cylindrical back cover body whose one end face is a closed face. The body is placed. A first through hole leading to the rear lid side is formed at approximately the center of the closed end surface of the front lid body, and an annular portion is formed in an annular shape at right angles to the closed end surface of the front lid body surrounding this first through hole. It is formed protrudingly on the closed surface side of the back cover.

With this invention, the bidirectional electric microphone unit is fixed so as to close the open surface formed on the protruding side of the annular portion protrudingly formed on the closed end surface of the front lid. A second through hole is formed on the peripheral edge side so as to communicate with the rear lid side.

In the electrostatic transmitter of this invention, by changing the volume of the first front chamber surrounded by the cylindrical peripheral surface between the open surface and the closed end surface of the cylindrical front lid, , 2~3KHz of transmitting frequency characteristic curve
It is possible to adjust and set the position of the peak in the frequency of , and also to set the cutoff frequency in the high frequency band of the transmission frequency characteristic curve.

The second front chamber is formed by being surrounded by a plate surface facing the closed end surface of the front lid of the electret microphone unit, and a closed end surface of the front lid and an annular portion in which the closed end surface protrudes in an annular shape. By changing the volume, it is possible to adjust and set the slope of the rise of the peak in the 2 to 3 KHz frequency band of the transmission frequency characteristic curve.

Furthermore, by changing the diameter of the second through hole, it is possible to adjust and set the position of a peak occurring in the low frequency band of the transmission frequency characteristic curve and the peak value of the peak. By changing the air permeability, that is, the acoustic resistance, of the cloth provided in this second hole, it is possible to suppress the peak value that occurs in the low frequency band of the transmission frequency characteristic curve. It is possible to flatten the transmission frequency characteristic curve of .

Furthermore, by changing the air permeability, that is, the acoustic resistance, of the cloth applied to the first through hole, it is possible to change the peak value occurring in the frequency band of 2 to 3 KHz in the transmission frequency characteristic curve.

Therefore, in this invention, by changing the volume of the first front chamber, the volume of the second front chamber, the diameters of the first and second through holes, and the conditions of the cloth applied therein, the transmitter can be improved. It is possible to set the characteristics of the transmission frequency characteristic curve to a desired predetermined shape. Further, in this invention, by using a configuration using a bidirectional electric microphone unit, it is possible to greatly increase the sensitivity of the transmitter.

"Example" Hereinafter, the electrostatic transmitter of this invention will be described in detail based on an example using the drawings.

FIG. 1 shows the configuration of an embodiment of this invention, in which a substantially cylindrical back cover body 25 with one end face as a closed face 24 is formed of, for example, a synthetic resin material, and an open face of this back cover body 25. A front cover body 26 made of, for example, a synthetic resin material is similarly attached to cover the front cover 26 . The front lid body 26 is formed into a substantially cylindrical shape with a closed end surface 27, and the rear lid body 25 is opened with the closed end surface 27 projecting convexly toward the closing surface 24 side.
It can be installed by fitting into the

That is, an annular recess 31 formed on the inner circumferential surface of the back cover 25 on the open side, and a rib 32 formed on the outer circumferential surface of the front cover 26 on the open side that fits into the annular recess 31. , back cover body 25 and front cover body 2
6 can be fitted into each other.

A first through hole 33 communicating with the rear lid 25 is formed at approximately the center of the front lid 26 . In the embodiment shown in FIG. 1, the inner diameter of the first through hole 33 is set to, for example, 1.0 mm. Also, the front lid body 26
For example, the distance from the open surface to the closed end surface 27 is 6 mm.
is set to The closed end surface 27 is integrally formed with the back cover body 2 at right angles to the plate surface so as to surround the first through hole 33.
An annular annular portion 27-T is formed to protrude in an annular shape in the direction of the closed surface 24 of No. 5.

A bidirectional electret condenser microphone unit 36 is fixed so as to close the open surface on the protruding side of the annular portion 27-T.

That is, a stepped portion 35 is formed on the inner peripheral surface of the annular portion 27-T, and a bidirectional electret condenser microphone unit 36 is fixed to this stepped portion 35, for example, by adhesive means. Closed end surface 2 of this stepped portion 35
The height from 7 is set to 5 mm in the example.

The bidirectional electret condenser microphone unit 36 has a configuration as shown in FIG. That is, an opening 50 is formed in the center of a substantially cylindrical capsule 41 with an outer diameter of 10 mm and a height of 7 mm, for example, and a diaphragm 43 is attached to this capsule 41 via a metal ring 42 and a spacer 42-R. . A back plate 44 is disposed facing the diaphragm 43, and the capsule 41 is held by a back plate holder 45.
held within. The opening 50 is closed with a cloth 53 to set a predetermined acoustic resistance.

The open side of the capsule 41 is closed with a substrate 46, and an IC circuit 47 having impedance conversion and amplification functions is fixed to the substrate 46 and disposed inside the capsule 41. The input end of the IC circuit 47 is electrically connected to the diaphragm 43 via the back plate 44.

The diaphragm 43 has a structure in which a thin metal film serving as a conductive layer is adhered to a polymeric dielectric film, and the entire surface of this dielectric film has a structure that can be uniformly polarized. In this invention, an opening 51 is formed in the substrate 46 which is disposed so as to close the open surface of the capsule 41, and the electret microphone unit 3
6 has bidirectional characteristics.

The electret condenser microphone unit 36 with bidirectional characteristics configured in this way is
The diaphragm 43 is fixed to the step 35 of the annular portion of the front cover 26 with the side facing the first through hole 33 . With the electret condenser microphone unit 36 attached, a back chamber R-B is formed between the front cover 26 and the rear cover 25.

In addition, when the electret condenser microphone unit 36 is installed, the plate surface facing the closed end surface 27 of the front cover 26 of the condenser microphone unit 36, the closed end surface 27, and the annular portion 27-
A first front chamber 61 is formed surrounded by T.

The front lid body 26 near the peripheral edge of the closed end surface 27
A second through hole 5 is opened so as to communicate with this back chamber R-B.
5 is formed. In the embodiment shown in FIG. 1, the diameter of the second through hole 55 is set to 1.3 mm.

For the first and second through holes 33, 55, first and second crosses 56,
57 is attached. In the embodiment shown in FIG. 1, the first and second crosses 56, 57 are each attached to the open side plate surface of the closed end surface 27 of the front cover body 26 by adhesive means. .

In this invention, the entire transmitter is used by being attached to a mount 60, such as a telephone handset housing, as shown in FIG. In the attached state, the plate surface of the mounting plate 60 closes the open surface of the front cover 26, and a second front chamber 62 is formed between this plate surface and the front cover 26. On the other hand, the front lid body 2
As described above, the first front chamber 61 is surrounded by the annular portion 27-T of 6, and is located between the closed end surface 27 of the front lid body 26 and the plate surface of the electret condenser microphone unit 36 facing the closed end surface 27. is formed.

When the electrostatic transmitter of this invention is attached to the mounting body 60 and its transmission frequency characteristics are measured, the results shown in FIG. 3 are obtained. As is clear from the measurement results, the cutoff characteristics in the low frequency band below 500 Hz are achieved in the obtained transmission frequency characteristic curve, and a peak appears in the transmission frequency characteristic curve in the frequency band around 2 to 3 KHz. . Furthermore, this transmission frequency characteristic curve also satisfies the electrical standards mentioned above, as shown in FIG. The curve indicated by a dotted line in FIG. 3 is a transmission frequency characteristic curve obtained when an omnidirectional electret microphone unit is used with other conditions being the same.

Figure 4 shows the transmission frequency characteristic curve obtained with a single figure-directional electret microphone unit used in this invention. The cutoff characteristic in the frequency band of 2 to 3 KHz cannot be obtained, and the peak characteristic required in the frequency band around 2 to 3 KHz cannot be clearly obtained. FIG. 5 shows the directivity characteristic curve for the bidirectional electret microphone unit used in this invention. As is clear from the figure,
A figure-directional electret microphone has a low sound pressure.
The microphone sensitivity at 90° and 270° directions is approximately 0dB,
It has the characteristic of receiving sound pressure only in the 0° and 180° directions.

In this invention, the front plate, the annular part 27-T, and the front surface of the bidirectional electric microphone unit 36 disposed in the back chamber formed between the back cover 25 and the front cover 26 are Lid body 2
6, a first through hole 33 formed in the closed end surface 27 of the first front chamber 61, and a first through hole 33 formed in the closed end surface 27 of the first front chamber 61, on the open surface side of the front lid body 26. The transmitter has a structure in which a second front chamber 62 is formed and a second through hole 55 is formed in the closed end surface 27 of the front lid body 26 so as to communicate with the back chamber RB. In this configuration, by further forming a cross in the first and second through holes, according to this invention, the transmission frequency characteristic curve of the electrostatic type transmitter can be set to a desired shape, and the transmission frequency of the transmitter can be set to a desired shape. It is possible to set the speech characteristics to desired characteristics.

In addition, in the electrostatic type transmitter of this invention, based on the audio signal input from the open side of the front cover 26, the sound pressure P ₁ from the first through hole 33 is obtained, so that the bidirectional The electret microphone unit 36 is driven from its front side, and the sound pressure _P2 from the second through hole 55 also drives the electret microphone unit 36 from its back side. Therefore, the sound pressure P ₁ on the front side and the sound pressure P ₂ on the back side are combined and applied to the electret microphone unit 36, and approximately twice the sound pressure is applied to the electret microphone unit 36. Therefore, the sensitivity will be improved by at least 4dB.

As a result of experiments conducted by the inventors, in the electrostatic transmitter of this invention, the above-mentioned first and second front chambers 61, 6
By adjusting and setting these volumes C _{1 and} C ₂ , the peaks in the frequency band near 2 to 3 KHz of _the transmitting frequency characteristic curve of the transmitter can be adjusted. It has been revealed that it is possible to set the characteristics of a predetermined shape.

That is, in the embodiment of the electrostatic transmitter of this invention, with other conditions constant, the volume of the first front chamber 61 C ₁
The transmission frequency characteristic obtained by changing . . . changes according to the curves shown in FIG. 7. 7th
In the figure, the horizontal axis shows the frequency (Hz), and the vertical axis shows the sensitivity (dB) of the handset obtained.
, each curve is the first front chamber 61
This is a transmission frequency characteristic curve obtained by setting the volume C ₁ of C ₁ = 113 mm ³ , 85 mm ³ , 57 mm ³ , and 28 mm ³ . Generally speaking, as is clear from FIG. 7, if the volume C ₁ of the first front chamber 61 is increased, the transmission frequency characteristic curve will change
The rise of the peak that occurs in the frequency band near Hz moves to the lower frequency side, its slope increases slightly, and the entire peak position also moves to the lower frequency side.
At the same time, the cutoff frequency in the high frequency band of the transmission frequency characteristic curve moves slightly to the lower frequency side.

Furthermore, it has been confirmed that by changing the hole diameter of the second through hole 55, the cutoff frequency in the low frequency band of 500 Hz or less of the transmission frequency characteristic curve can be adjusted.

That is, in the embodiment of the electrostatic transmitter of this invention, when other conditions are held constant and the diameter of the second through hole 55 is varied, the transmission frequency characteristics obtained are shown in _{FIG .} It changes according to the curve marked with _φ2 . In FIG. 9, the horizontal axis represents frequency (Hz), and the vertical axis represents the resulting sensitivity (dB) of the handset. In the figure, the curves marked with φ ₂ , φ _1.8 , φ _1.6 , _{φ 1.5} , and _{φ 1.4} represent the hole diameters of the second through hole _{55 ,} respectively, with φ=2.0 and φ=2.0, respectively.
This is the transmission frequency characteristic curve obtained when 1.8, 1.6, 1.5, and 1.4 are selected.

As is clear from FIG. 9, in the embodiment of the electrostatic transmitter of this invention, when the diameter of the second through hole 55 is increased, the position of the peak that generally occurs in the low frequency band of the transmission frequency characteristic curve tends to move toward the high frequency band side, and its peak height value tends to increase.

Further, in the embodiment of the electrostatic transmitter of this invention, with other conditions constant, the volume of the second front chamber 62 is C ₂
The transmission frequency characteristics obtained by changing the frequency change according to the curves shown in FIG. 8. 8th
In the diagram, the horizontal axis shows frequency (Hz) and the vertical axis shows sensitivity ( _dB ). ₂ = 6107mm ³ , 5090mm ³ , 4070mm ³ , 3050mm ³ ,
This is a transmission frequency characteristic curve corresponding to the cases where 2040mm ³ , 1020mm ³ , and 510mm ³ are selected.

As is clear from FIG. 8, in general, in the embodiment of the electrostatic transmitter of this invention, as the volume _C2 of the second front chamber 62 increases, the frequency near 3KHz on the transmission frequency characteristic curve increases. The height value of the peak occurring in the band increases, and in conjunction with this, the cutoff frequency on the high frequency side of the transmission frequency characteristic curve moves slightly to the low frequency band side.

Furthermore, as a result of experiments conducted by the present inventors, the electrostatic transmitter of this invention has a transmission frequency characteristic curve of 2.
It is clear that the shape of the peak that occurs in the frequency band around ~3KHz can be adjusted by the first cross 56, and the shape of the peak that occurs in the low frequency band of the transmit frequency characteristic curve can be adjusted by the second cross 57. It was done.

That is _, in the transmission frequency characteristic curve obtained with the embodiment of the electrostatic transmitter of this invention shown in FIG.
This is a transmission frequency characteristic curve obtained when the first and second crosses are not applied to 3 and 55. Also curve
K ₀ is a transmission frequency characteristic curve obtained when the diameter of the second through hole 55 is set to 0 and the structure is such that the second through hole 55 is not formed. In Figure 10,
A curve K ₂ shown by a dotted line shows the first and second cross holes 56,
57 is a transmission frequency characteristic curve obtained in a state where 57 is applied. In this state, when the air permeability of the first and second crosses 56, 57 is decreased and the acoustic resistance is increased, the low frequency band and high frequency band of the speech frequency characteristic curve are shown by the arrows in FIG. The peak value at is reduced, the transmission frequency characteristic curve is flattened, and the cutoff frequency on the low frequency band side is moved to the low frequency side.

Also, in FIG. 11, the frequency (Hz) is plotted on the horizontal axis and the sensitivity (dB) is plotted on the vertical axis. What is shown is the transmission frequency characteristic of the first cross 56 in the embodiment of the electrostatic transmitter of this invention. Show the effect on the curve. This is a detailed experimental effect. In this experiment, the first
All conditions except for the cross 56 were set constant.

The curve shown with K ₁ in FIG.
This is a transmission frequency characteristic curve obtained without applying the cross 56. When the acoustic resistance of the transmitter is increased by applying the first cross 56 from the state in which the first cross 56 is not applied, the transmission frequency characteristics of the transmitter change as shown in FIG. , respectively, along the curves shown with .

In this way, in the electrostatic type transmitter of this invention, by adjusting and setting the first cross 56, the 3K transmission frequency characteristic curve of the transmitter can be adjusted.
It is possible to adjust the shape of the peak that occurs in the high frequency band near Hz. As is clear from FIG. 11, in general, when the acoustic resistance of the transmitter is increased by the first cross 56, the peak that occurs in the high frequency band can be flattened as shown by the arrow in the figure. It is possible.

According to experiments conducted by the inventors, in the electrostatic transmitter of this invention, by changing only the hole diameter of the first through hole 56, the position of the peak that occurs in the high frequency band of about 3 KHz in the transmission frequency characteristic curve was determined. It is difficult to correct the shape and shape of the first cross 56.
It has been confirmed that this adjustment can be easily performed by using the acoustic resistance adjustment using the .

On the other hand, in the electrostatic transmitter of this invention, by using the bidirectional electric microphone unit as described above, the sound pressure on the front side and the back side of the electric microphone unit is synergized. pressure is applied to the electret microphone unit, and its sensitivity can be improved by more than 10 dB compared to when using an omnidirectional electret microphone unit.

Moreover, in the electrostatic type transmitter of this invention, the front cover body 26
Since the electret condenser microphone unit 36 held within the rear lid 25 is arranged at a distance of 11 mm or more from the open surface of the front lid 26, for example in the embodiment, it is protected against electrostatic damage. However, it is possible to realize an extremely strong structure.

In general, electrostatic transmitters are specified to have a withstand voltage of 10 to 15 KV DC when in use, so that they will not be destroyed by static voltage caused by electrostatic friction against a mounting body such as a handset housing. ing.

FIGS. 13A to 13E are experimental results showing the influence of electrostatic breakdown tests on the transmission frequency characteristics of the electrostatic transmitter of this invention, which were actually measured by the inventors. FIGS. 13A to 13E are measurement results obtained for separate test objects, respectively.
The solid line indicates the transmission frequency characteristic curve obtained by measurement before the electrostatic discharge test, and the dotted line indicates the transmission frequency characteristic curve obtained by measurement after the electrostatic discharge test. It is clearly confirmed that for each of the test objects shown in FIGS. 13A to 13E, the transmission frequency characteristics hardly change before and after the electrostatic discharge test.

The electrostatic discharge test in this case was conducted on a handset in which an embodiment of the electrostatic transmitter of this invention was incorporated. That is, +20KV and -20KV are applied between the mouthpiece of the handset and the circuit terminal of the electrostatic transmitter of this invention attached to the handset, respectively.
An electrostatic discharge test was conducted by applying a potential of 20 KV five times each. This electrostatic breakdown test was carried out under atmospheric conditions of either a room temperature of 10° C. and no humidity, or a room temperature of 4.5° C. and a humidity of 8%, depending on the test object.

As shown in Figures 13A to 13E, the results obtained before and after the electrostatic breakdown test show that the transmitting frequency characteristics of the electrostatic transmitter of this invention hardly change, and that sufficient static electricity is maintained. It was confirmed that it exhibited electrical breakdown voltage.

"Effect of the invention" As mentioned above, in the electrostatic transmitter of this invention, the volume C ₁ of the first front chamber 61 and the volume C 1 of the second front chamber 62 are
By changing the volume C ₂ of , the hole diameters of the first and second through holes 33 and 55, and the state of the first and second crosses 56 and 57 applied thereto, the transmission frequency characteristic curve can be changed. can be adjusted and set to the desired shape. Furthermore, since a bidirectional electret microphone unit is used, the input audio signal causes the electret microphone unit to emit sound from two directions, the front side and the back side, respectively, through the first and second through holes 33 and 55. Since pressure is applied, the transmitting sensitivity is greatly improved.

Furthermore, since the distance from the contact surface of the front cover body 26 with the mounting body 60 to the front surface of the bidirectional electric microphone unit 36 can be set large, it is resistant to electrostatic discharge damage, and has, for example, a static voltage withstand voltage characteristics of 20 KV or more in a linear voltage. A telephone transmitter is possible.

Furthermore, the total number of parts involved in manufacturing is small, and the manufacturing of each part and the overall assembly are easy, and it is possible to mass-produce electrostatic transmitters of stable quality at low manufacturing costs.

In the embodiments, a handset was mainly used as the mounting body 60 for the electrostatic transmitter of this invention, and a case where the electrostatic transmitter of this invention was incorporated into the handset was explained. However, the mounting body 60 is not limited to the handset, and can be selected from various types, and can have various configurations such as being incorporated into various transmitting units for telephones and C and B micro units. As explained in detail above, this invention has a small number of parts, a simple structure, and can be manufactured with significantly reduced production costs.
By adjusting and setting the volumes of the first and second front chambers, the diameters of the first and second through holes, and the first and second crosses, the transmission frequency characteristics can be adjusted to connect to attached equipment such as subscriber telephones, etc. Regulations on Technical Standards for Equipment No.
It becomes possible to provide an electrostatic transmitter that can be selected to comply with the electrical standards for telephone calls such as accessory equipment stipulated in Article 19.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional principle diagram showing the configuration of the main parts of an embodiment of the electrostatic transmitter of this invention, and Figure 2 is a bidirectional electric microphone used in the electrostatic transmitter of this invention. Figure 3 shows the transmission frequency characteristics of an embodiment of the electrostatic transmitter of this invention, and Figure 4 shows the transmission frequency characteristics of the bidirectional electric microphone unit alone. 5 is a diagram showing the directivity characteristics of a single figure-directional electric microphone unit, FIG. 6 is a diagram showing the transmission frequency characteristics of an embodiment of the electrostatic transmitter of this invention, and FIG. The figure shows the transmission frequency characteristics when the capacity of the first front chamber is taken as a parameter in an embodiment of the electrostatic type transmitter of this invention. FIG. 9 is a diagram showing the transmission frequency characteristics using the capacity of the second front chamber as a parameter in the embodiment, and FIG. FIG. 10 is a diagram showing the relationship between the first and second crosses and the transmission frequency characteristic in an embodiment of the electrostatic transmitter of this invention.
The figure is a diagram showing the relationship between the first cross and the transmission frequency characteristic in an embodiment of the electrostatic transmitter of this invention,
FIG. 12 is a principle diagram showing the wrap-around state of sound pressure in an embodiment of the electrostatic transmitter of this invention, and FIGS. 13A to 13E are diagrams of the embodiment of the electrostatic transmitter of this invention. Figure 14 is a diagram showing the permissible range of transmission level of transmission frequency characteristics, Figures 15 and 17 are main parts of conventionally proposed electrostatic transmitters. 16th diagram showing the configuration of
18 and 18 are diagrams showing the transmission frequency characteristics of the electrostatic type transmitters having the configurations shown in FIGS. 15 and 17, respectively. 24: Closed surface, 25: Back lid, 26: Front lid, 27: Closed end surface, 31: Annular recess, 32: Rib, 33: First through hole, 35: Step, 36: Bidirectional elect Ret condenser microphone unit, 41: capsule, 43: diaphragm, 44: back plate, 45: back plate holder, 46: printed circuit board,
47: IC circuit, 50: Open hole, 51: Open hole, 5
3: Cross, 55: Second through hole, 56: First cross, 57: Second cross, 60: Mounting body, 6
1: first volume chamber, 62: second volume chamber.

Claims (1)

[Scope of utility model registration request] A cylindrical front lid body is disposed such that one end face is a closed face and the open face of the cylindrical rear lid body is closed, and the closed end face protrudes convexly toward the closed face side. A first portion communicating with the rear lid body at approximately the center of the closed end surface.
A through hole is formed, and an annular portion is formed on the closed end surface of the front lid body surrounding the first through hole and protrudes toward the closed surface side, and closes the open surface on the protruding side of the annular portion to provide bidirectional orientation. 1. An electrostatic transmitter characterized in that an electrostatic microphone unit is fixed thereto, and a second through hole communicating with the rear lid is formed on a peripheral edge side of a plate surface of the front lid.