JPS643400B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic piezoelectric handset for ensuring quality during calls in a handset attached to a telephone handset or the like. When a ceramic piezoelectric handset with a diaphragm formed by adhering a ceramic piezoelectric material to a conductive substrate is used for a telephone, the acoustic impedance when looking inside the handset from the earpiece is higher than that of the molded diaphragm. It is more expensive than other conversion formats that can be used, such as electromagnetic type and electrodynamic type. Therefore, when the ceramic piezoelectric type handset is actually used, the amount of received sound leaks through the gap between the ear and the handset earpiece is larger than that of the electromagnetic type, electrodynamic type, etc., which is disadvantageous for communication. First, an example of the structure of a ceramic piezoelectric telephone receiver is shown in cross section in FIG. The figure shows an acoustic vibration system with three degrees of freedom, similar to a conventional telephone electromagnetic receiver. In the structure shown in FIG. 1, the diaphragm 1 is
It is formed by fixing a ceramic piezoelectric plate 1-2 to a conductive substrate 1-1. Said diaphragm 1
is fixed at the outer periphery by the frame 2. Next, the sensitivity frequency characteristic of the handset is flat,
And in order to achieve high sensitivity, the first front air chamber 5,
A first rear air chamber 6 is formed, which further communicates with the second front air chamber (here, the ear canal volume is approximately 6 cm ² ) 7 via the receiver b3, and with the outside air via the brake hole 4. It constitutes a degree 3 acoustic vibration system. The operation will be explained with reference to FIG. 1. When an electrical AC signal is input to the terminal board 9, the AC signal is applied to the ceramic piezoelectric plate 1-2 through the lead wire 8, and this is applied to the ceramic piezoelectric plate 1-2. The sound pressure is converted into a stretching vibration and the diaphragm 1 bends and vibrates, leading to the sound pressure to the second front air chamber (ear hole) 7.
Perceived by humans as sound. FIG. 1A shows an electrical equivalent circuit of the structure shown in FIG. Here, various constants of the diaphragm 1, that is, effective area, effective mass, and effective stiffness, are determined from the upper limit frequency of the telephone transmission reproduction band in order to flatten the sensitivity frequency characteristics of the handset mentioned above, and furthermore, the sensitivity By specifying the amount of deviation, each element L, C, R shown in FIG.
The equivalent circuit constants of are determined. When designing a handset, first determine the constants of the acoustic system so that the frequency characteristic of sensitivity is flat using the equivalent circuit shown in FIG. 1A (in which there is no leakage between the handset and the ear). Conventionally, this design method alone has provided almost satisfactory call characteristics even during actual use. This is because the conventional conversion format for telephone handsets in Japan was an electromagnetic type using a molded diaphragm (large effective area), so its internal acoustic conformance value was approximately 5.6 × 10 ^-6 ( cm ³ /dyn), which was relatively high, and sufficient call quality was ensured without any special measures. On the other hand, in the case of a ceramic piezoelectric type, the internal acoustic compliance determined by the above design method is approximately 0.3 × 10 ^-6 (cm ⁵ /dyn), which is an order of magnitude lower than that of the R-62 electromagnetic handset. It becomes smaller than that. For this reason,
The leakage element constant le between the handset and the ear, which corresponds to the pressing force of the handset on the ear during actual use, is determined as
If a simulation is performed by applying the equivalent circuit shown in Figure B, the characteristics will be as shown in Figures 2a and 2b. Note that FIG. 1B is an equivalent circuit diagram when there is leakage between the ear and the earpiece. In Figure 2,
a is the characteristic of the R-62 handset used in the 601 type telephone, which has the constants shown in Table 1. The solid line is the characteristic when there is no leakage, and the broken line is the characteristic when considering the leakage mentioned earlier. . Here, the "diaphragm equivalent volume" shown in Table 1
I will explain about it. The diaphragm equivalent volume has traditionally been used in the design and evaluation of audio equipment, and is the acoustic compliance (reciprocal of stiffness).
is defined as the volume expressed by the volume with the equivalent acoustic impedance. That is, specifically, the effective area of the diaphragm is A ₀ , the stiffness of the diaphragm is S ₀ ,
If the bulk modulus of air is k, then the equivalent volume of the diaphragm is
In the range where the vibration can be considered linear, _{V 0 =} kA ₀ ² /
S ₀ (e.g., Journal of the Institute of Electrical Communication Engineers, Vol.
Volume 38, No. 7, “Basic Properties of Condenser Microphones,” p526-p531, published July 25, 1955). This diaphragm equivalent volume V ₀ is a value unique to the diaphragm of the receiver, and is uniquely given.

[Table] FIG. 2b shows a similar result for a ceramic piezoelectric telephone receiver having the constants shown in Table 1, and the line types are the same as described above. from now,
Table 2 shows the so-called weighted average sensitivity value (the value when there is no leakage as the standard, i.e., zero), which is calculated by weighting the frequency by focusing on the call volume during actual use. .

[Table] It is clear from this that the lower the pressing force of the handset on the ear, the greater the decrease in the weighted average sensitivity of the ceramic piezoelectric handset, which is thought to have a negative effect on the call characteristics. The present invention improves the internal acoustic conformance of a ceramic piezoelectric receiver by
-62 electromagnetic handset, it is characterized by being improved to the same level as the
The purpose is to obtain satisfactory communication performance during actual use. The gist of the present invention is to provide a ceramic piezoelectric receiver in which a diaphragm formed by fixing a ceramic piezoelectric plate to a conductive substrate is housed in a frame, in which 4.5 cm ³ to 8 cm ³ of air inside the frame is placed in front of the diaphragm. The first front air chamber is provided with a diaphragm braking mechanism on the rear surface of the diaphragm. This diaphragm braking mechanism preferably includes a first rear air chamber that is an air chamber in the diaphragm rear frame having a volume smaller than the equivalent volume of the diaphragm, and a braking hole provided in the diaphragm rear frame. Further, this diaphragm braking mechanism may be constructed of a damping material that is installed in a first rear air chamber that is an air chamber in the diaphragm rear frame and directly presses the diaphragm. FIG. 3 is a sectional view showing the basic configuration of the present invention. Components that are the same as the conventional method, such as a method for processing lead wires from each electrode and a terminal board, but which are out of the main points of the present invention, have been omitted to make the explanation easier to understand. Further, the part numbers in the figure are the same as those explained in the conventional example, but new symbol numbers will be explained each time. As mentioned above, the main point of the present invention is to improve the acoustic conformance when looking inside the handset from the leaky end A. As an example for realizing this, FIG. 3 will first be described. FIG. 3 is a cross-sectional view showing the configuration of the telephone receiver including the earpiece 3 and the ear hole portion 7, and FIG. 3A is an equivalent circuit diagram thereof. This is the same as in FIG. 1B above.
In this example, the first front air chamber (V _-1 ) 5 is made larger in order to improve the acoustic conformance inside the receiver. The frequency characteristics at this time are shown in FIG. 3B. In the figure, the solid line shows the characteristics of the conventional example in which the first front air chamber (V _-1 ) 5 is not increased, and the broken line shows the characteristics of the first front air chamber (V -1 ) 5.
These are the characteristics when the front air chamber (V _-1 ) 5 is increased by 6 cm ³ . This value is obtained assuming that among the constants of each part of the ceramic piezoelectric receiver shown in Table 1, all of the constants other than the first front chamber volume (V _-1 )5 are constant. As is clear from this figure, increasing the acoustic convergence simply by increasing V _-1 results in loss of flatness of the frequency characteristics, so it is necessary to take the following measures. An example of this will be explained using FIG. 4, which shows an embodiment of the present invention.
The difference from the diagram is that the first rear air chamber (V ₊₁ ) 6 is set to almost zero to achieve sufficient damping of the diaphragm. To explain this situation using the equivalent circuit in Figure 4A,
By setting V ₊₁ ≒ 0 (1/5 or less of the diaphragm equivalent volume V ₀ ), the branch in the equivalent circuit of the first rear air chamber (V ₊₁ ) 6 becomes electrically open, but The diaphragm is thus damped by the resistance component created by the damping holes, achieving flat frequency characteristics. The characteristics are shown in Figure 4B. In the figure, the solid line is the characteristic when there is no leakage, the dashed line is the frequency characteristic when the pressing force of the handset is 700 g, and the broken line is the frequency characteristic when the pressing force is 250 g. Table 3 shows the weighted average sensitivity calculated from FIG. 4B. Note that Table 3 shows the values when V ₋₁ =6 cm ² .

[Table] Comparing this with the conventional R-62 handset, almost the same values were obtained, and a clear improvement effect was obtained in the ceramic piezoelectric handset. FIG. 5 shows another embodiment in which the first front air chamber (V _-1 ) 5 is made large to flatten the sensitivity frequency characteristic. As shown in FIG. 5, this is a method of braking by directly pressing the damping material 12 against the diaphragm, and its equivalent circuit is shown in FIG. 5A. According to this method,
By appropriately selecting the damping material, the first front air chamber (V _-1 ) 5 can be made larger to increase the acoustic combination of the receiver, and the reproduction frequency bandwidth can be ensured to reduce the sensitivity deviation. It has the characteristics of being able to The above two examples are examples in which the first front air chamber (V _-1 ) 5 is made large to enhance the acoustic conformance of the receiver. Next, FIG. 6 shows the equivalent volume when looking inside the handset from the leaky end A of the handset on the horizontal axis, and the change in the weighted average sensitivity on the vertical axis. In the figure, the state with no leakage is defined as zero, as in the conventional display method. From this, in order to obtain a weighted average sensitivity equal to or higher than that of the R-62 handset, the volume of the front air chamber should be set to (4.5 to 8) cm ³ . In addition,
As explained above, if there is a change in the permissible range based on subjective values due to future call quality evaluation tests, this can be dealt with by forming the room volume according to that value. It is clear from this. Furthermore, increasing the equivalent volume when looking inside the receiver reduces acoustic impedance, which is advantageous in preventing leakage of noise during actual use, and has the effect of killing two birds with one stone. As explained above, in a ceramic piezoelectric handset, by setting the volume of the first front air chamber to 4.5 to ^{8 cm3} , the quality of calls using the handset is maintained at a value equivalent to that of an R-62 handset. and can be used. In addition, when a disk diaphragm is used as the diaphragm of the handset, whether it is a ceramic piezoelectric type or an electromagnetic iron plate, the degree of freedom of the handset vibration system and its resonant frequency must be determined. If we do this, the vibration system constants will be almost the same, so it is clear that it does not depend on the conversion format. Furthermore, if the outer diameter of the handset diaphragm becomes small, even if a molded diaphragm like the R-62 handset is used, the acoustic conformance inside the handset will become smaller, making it difficult to prevent leakage. This becomes a disadvantage and requires countermeasures according to the present invention. It is obvious that the absolute value of the receiver sensitivity increases as the front air chamber volume decreases.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the structure of a ceramic piezoelectric handset, Figure 1A is a circuit diagram showing its electrical equivalent circuit, and Figure 1B is a similar equivalent circuit when there is leakage between the ear and the earpiece. Circuit diagram, Figure 2a is R
−62 Sensitivity characteristics depending on the presence or absence of leakage of electromagnetic handset,
b is a graph showing the characteristics of a ceramic piezoelectric handset depending on the presence or absence of leakage, FIG. 3 is a sectional view showing the basic configuration of the present invention, FIG. 3A is its equivalent circuit diagram, and FIG. 3B is its sensitivity frequency characteristic diagram, FIG. 4 is a sectional view showing an embodiment of the present invention, FIG. 4A is an equivalent circuit diagram thereof, FIG. 4B is a sensitivity frequency characteristic diagram thereof, and FIG. 5 is a sectional view showing another embodiment of the present invention. 5A
The figure is an equivalent circuit diagram, and FIG. 6 is a graph showing the relationship between the equivalent volume inside the receiver and the weighted average sensitivity. 1... Vibration plate, 2... Frame, 3... Earpiece, 4... Brake hole, 5... First front air chamber (V _-1 ),
6...First rear air chamber (V ₊₁ ), 7...Second front air chamber (ear hole, V _-2 ), 8...Lead wire, 9...Terminal, 1
2...braking material.

Claims (1)

[Scope of Claims] 1. A ceramic piezoelectric receiver comprising a diaphragm formed by fixing a ceramic piezoelectric plate to a conductive substrate and housed in a frame, in which a 4.5 cm ³ to 8 cm ³ area within the frame is provided on the front of the diaphragm. A ceramic piezoelectric receiver characterized by having a first front air chamber which is an air chamber, and a diaphragm damping mechanism on the rear surface of the diaphragm. 2. Claims in which the diaphragm braking mechanism comprises a first rear air chamber which is an air chamber in the diaphragm rear frame having a volume smaller than the equivalent volume of the diaphragm, and a braking hole provided in the diaphragm rear frame. The ceramic piezoelectric telephone receiver according to item 1. 3. The ceramic piezoelectric receiver according to claim 1, wherein the diaphragm damping mechanism comprises a damping material that is installed in the first rear air chamber, which is an air chamber in the rear frame of the diaphragm, and directly presses the diaphragm.