JP4540659B2 - Transmitter - Google Patents

Description

  The present invention relates to a transmitter used in, for example, a telephone handset.

  The conventional analog telephone line has an upper limit of the transmission frequency band of 3 to 3.4 kHz. However, the ISDN digital line has a wider band up to an upper limit of the transmission frequency band of about 10 kHz. Furthermore, it is possible to use a voice transmission band up to 20 kHz on the IP line. If communication is carried out using such a broadband line, the call quality is improved and voice and the like can be transmitted with high quality (clear). However, in order to improve the call quality, it is necessary to further increase the bandwidth of the transmitter. Don't be. Therefore, an electret microphone (hereinafter sometimes referred to as “microphone”) having excellent sensitivity in the high sound (high frequency) region is used, and as shown in FIG. 6, a front air chamber 20 is provided in the transmitter 10. Thus, a transmitter has been developed that achieves a wide band by allowing sound waves to reach the sound receiving surface side of the microphone 30 (for example, Patent Documents 1 and 2).

Here, the front air chamber 20 has, for example, a substantially cylindrical shape, and a plurality of sound holes are provided in the mouthpiece wall portion on one end side of the substantially cylindrical shape, and an internal sound hole is provided in the microphone side wall portion on the other end side. The sound (sound wave) enters the front air chamber 20 from the sound hole and reaches the sound receiving surface of the microphone 30 through the internal sound hole. The front air chamber 20 emphasizes the high frequency (high frequency) region of the sound wave as shown by the broken line in FIG. Here, the upper limit frequency (transmission frequency, which may be referred to as “ft” hereinafter) at which the transmitter 10 can output an electric signal with a lower sensitivity than the mid-range frequency is expressed by the following equation (1): It is known that it is proportional to the square root of the number n of sound holes and inversely proportional to the square root of the volume c of the front air chamber 20.
ft = kt (n / c) ^1/2 (1) Therefore, in the transmitter having the frequency characteristic of the broken line in FIG. 7, it is arranged on the wall of the mouthpiece as shown in FIG. If as many sound holes as possible are provided (if the number n of sound holes is increased), ft increases from about 5 kHz to about 10 kHz, for example, as shown by the solid line in FIG. .

However, even if the number n of sound holes is increased and ft is increased to, for example, about 10 kHz, the microphone output voltage in the vicinity of the ft is lower than the output voltage at the middle frequency as shown by the solid line in FIG. (The frequency response will drop to the right.) Therefore, an object of the present invention is to realize a transmitter capable of flattening frequency characteristics (eliminating or reducing the right-side descent of frequency characteristics) from the mid-frequency to the vicinity of ft while increasing ft.

In order to solve the above-described problems, a transmitter according to the present invention forms a cylindrical space by surrounding a space between a mouthpiece wall and a microphone side wall facing the mouthpiece wall with a peripheral wall. The front air chamber, a microphone having a sound receiving surface facing the internal sound hole provided in the microphone side wall portion of the front air chamber, and the mouthpiece wall portion of the front air chamber Provided with a plurality of sound holes for introducing sound waves from the outside into the front air chamber,
In particular, the first circle forming the outer shape of the inner surface of the mouthpiece wall portion in the front air chamber is the same as the center of gravity of the first circle and is half the length of the first circle. The plurality of sound holes are provided along the first circle only in a region surrounded by a second circle having a length of.
Therefore, in the transmitter having the above-described configuration, the central portion occupying a quarter of the inner surface of the mouthpiece wall is closed, and a plurality of sounds are formed along the first circle on the outer portion other than the central portion. The holes are arranged so that an external sound wave is guided to the front air chamber through the sound holes.

  Accordingly, since the sound waves from the sound holes reach the sound receiving surface of the microphone along the vicinity of the peripheral wall in the front air chamber space, the turbulence of the air flow caused by the collision of the sound waves in the front air chamber space is reduced. Since the transmitter having the above configuration can reduce the disturbance of the air flow and reduce the attenuation of the sound wave in the high frequency region, it can flatten the frequency characteristics from the middle frequency to the vicinity of ft (for example, 10 kHz).

  As described above, the transmitter according to the present invention flattens the frequency characteristics from the middle frequency to the vicinity of ft while increasing the ft by reducing the collision of the sound wave in the front air space and the attenuation of the high frequency region. It can be made.

  Hereinafter, a transmitter according to the present invention will be described with reference to the drawings.

An embodiment of a transmitter according to the present invention will be described with reference to FIGS. FIG. 1 shows an example of the appearance of a handset 1 (2 in FIG. 1 is a transmitter-side end), and FIG. 2 is a schematic cross-sectional configuration of a transmitter 10 included in the transmitter-side end 2. FIG.
The transmitter 10 according to the present invention includes a front air chamber 20 and a microphone 30. The front air chamber 20 has a mouthpiece wall portion 21 on one end side and a microphone side wall portion 22 on the other end side. A front air space 20 a of the front air chamber 20 is defined by a mouthpiece wall portion 21, a microphone side wall portion 22, and a peripheral wall 23. Here, the peripheral wall 23 has a cylindrical shape, and one of the peripheral walls 23 is inserted into the peripheral wall 1 b extending from the main body 1 a of the handset 1, and the end of the peripheral wall 23 abuts on the mouthpiece wall portion 21. A microphone 30 is inserted and held on the other side of 23. The microphone 30 is attached to the printed circuit board 31 and transmits an audio signal to a circuit (not shown) via the printed circuit board 31.

  In the transmitter 10 having the above-described configuration, the sound wave from the outside passes through the sound hole 21 a provided in the mouthpiece wall portion 21 and is guided to the front air chamber space 20 a and is further provided in the microphone side wall portion 22. Then, the sound is guided from the internal sound hole 22 a to the sound receiving surface of the microphone 30. The front air chamber space 20a is a cylindrical space having an inner diameter of 20 mm and a distance between the mouthpiece wall 21 and the microphone side wall 22 of 10 mm. The mouthpiece wall 21 has a sound hole 21a having a diameter of 2 mm. 24 are provided.

FIG. 3 shows an inner surface 21c (circular shape) of the mouthpiece wall portion when the mouthpiece wall portion 21 is viewed from the inside of the front air chamber space 20a. FIG. 4 is a schematic sectional view of the front air chamber space 20a. It is a block diagram. As shown in FIG. 3, on the circle C (sound hole arrangement circle) having the center (center of gravity) Ax at the same position as the circle C1 ( first circle ) that defines the outer shape of the inner surface 21c of the mouthpiece wall portion The center of the internal opening 21b of the sound hole 21a is located. The circle C2 ( second circle ) has a center Ax at the same position as the circle C and the circle C1, has a length that is half that of the circle C1, and is formed on the inner surface 21c of the mouthpiece wall portion 21c. A circle that marks the center. Here, the internal opening 21b is positioned closer to the circle C1 than to the circle C2.

  Therefore, as shown in FIG. 4, the sound wave 40 from the outside passes through the plurality of sound holes 21 a of the mouthpiece wall portion 21, propagates along the vicinity of the peripheral wall 23 in the front air chamber space 20 a, Since it reaches the sound receiving surface of the microphone 30 via 22a, the collision of the sound wave 40a passing through each sound hole 21a can be reduced. Here, since the circle C and the circle C1 have the center Ax at the same position (since the center of the sound receiving surface of the microphone 30 is also at the center Ax), the propagation path from each sound hole 21a to the sound receiving surface of the microphone 30 is Symmetry is the best. Therefore, the collision of the sound wave 40a in the front air chamber space 20a can be reduced satisfactorily, and the attenuation of the sound wave 40a in the high frequency region can be reduced.

An example of frequency characteristics of the transmitter 10 thus flattened will be described with reference to FIG. In FIG. 5, the horizontal axis represents the audio frequency, and the vertical axis represents the output voltage relative value (dB) of the microphone 30. The alternate long and short dash line L1 has the same front air chamber space 20 as the transmitter 10 according to the present invention, but the number n of sound holes provided over the entire area of the mouthpiece wall 21 is increased to widen the band. This is the frequency characteristic of the conventional transmitter (FIG. 6) at this time, which corresponds to the frequency characteristic of the solid line in FIG. 7 showing the frequency characteristic of the conventional example (shown for comparison). Moreover, the solid line L2 of FIG. 5 has shown the frequency characteristic of the transmitter 10 concerning this invention . According to the transmitter 10 according to the present invention, the attenuation of the sound wave 40a in the high frequency region can be reduced as described above, and therefore the frequency characteristic from the middle frequency to the vicinity of 10 kHz has the frequency structure of the conventional structure shown in FIG. More flattened . Specifically, for example , as indicated by a solid line L2 in FIG. 5, the frequency characteristic is improved by 5 to 6 dB near 10 kHz as compared with the characteristic of the conventional structure (broken line L1), and the frequency characteristic is broadened.

  Here, even if a plurality of sound holes positioned between the circle C1 and the circle C2 are not arranged on the circle C (for example, randomly arranged), the sound wave from each sound hole is not generated in the front air space. Because it reaches the sound receiving surface of the microphone along the vicinity of the inner wall, the turbulence of the air flow caused by the collision of the sound wave in the front air chamber space can be reduced (the sound wave attenuation in the high frequency region can be reduced). The frequency characteristic from the local frequency to the vicinity of ft can be flattened. Of course, if the number of sound holes is increased between the circle C1 and the circle C2 by arranging sound hole arrays on a plurality of circles or randomly, the above equation (1) clearly shows. Thus, ft can be made higher, so that the frequency characteristics can be further flattened from the middle frequency to the high frequency.

The transmitter according to the present invention is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the spirit of the transmitter. For example, sound waves from each sound hole is, as long as it reaches the sound receiving surface of the microphone to the front air chamber space along the peripheral wall near the turbulence caused by impingement of sound waves in the front air chamber space Since the attenuation of sound waves in the high frequency region can be reduced, the cross-sectional shape of the front air chamber space is not circular (the front air chamber space is a cylindrical shape) or rectangular (the front air chamber space is a rectangular parallelepiped shape) For example, even in the case of an ellipse or an egg shape, it is needless to say that the frequency characteristics from the middle frequency to the vicinity of ft can be flattened.

The example of an external appearance of the handset provided with the transmitter concerning this invention is shown. It is a figure which shows the general | schematic cross-section structure of the transmitter side end part containing the transmitter concerning this invention. It is the inner surface figure of the mouthpiece wall part which looked at the mouthpiece wall part from the inside of the front air chamber space. It is a cross-sectional schematic block diagram of a front air chamber space. It is a characteristic view which shows the frequency characteristic example of the transmitter of FIG. It is a figure which shows the general | schematic cross-section structure of the conventional transmitter which increased the sound hole and widened the band. It is a characteristic view which shows the example of a frequency characteristic of the conventional transmitter (FIG. 6).

Explanation of symbols

10 transmitter 20 front air chamber 20a front air chamber space 21 mouthpiece wall 21c inner wall 21a sound hole 21b inner opening 22 microphone side wall 23 peripheral wall 30 microphone Ax center of gravity C1 first Closed curve C2 Second closed curve

Claims (1)

A front air chamber in which a space between the mouthpiece wall and the microphone side wall facing the mouthpiece wall is surrounded by a peripheral wall to form a cylindrical space;
A microphone provided with a sound receiving surface facing an internal sound hole provided in the microphone side wall of the front air chamber;
A plurality of sound holes provided on the mouthpiece wall of the front air chamber, for introducing sound waves from outside into the front air chamber;
The first circle forming the outer shape of the inner surface of the mouthpiece wall portion in the front air chamber, the same center of gravity as the first circle, and half the length of the first circle A transmitter, wherein the plurality of sound holes are provided along the first circle only in a region surrounded by a second circle having a thickness.

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