JPH0121680B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring method for easily and accurately measuring internal acoustic impedance viewed from an acoustic output section of a telephone receiver or the like.

Conventionally, the internal acoustic impedance of a handset is measured by attaching another calibration handset to the coupling air chamber of the coupler pressed against the receiver under test and driving it acoustically. was measured using a probe tube microphone, etc. (for example, Research and Practical Application Report Vol. 30, No. 4, page 923, published by Nippon Telegraph and Telephone Public Corporation Telecommunications Research Institute, April 1981). (See the paper “Real Ear Loss of Handsets” on pages 935 to 935). Therefore, as a measurement device for determining impedance, a device that measures the absolute value and phase of the sound pressure in the coupled air chamber is required.
In particular, the phase measurement requires an expensive measuring device, so it has the disadvantage that it cannot be easily carried out.

The present invention has been made to overcome the drawbacks of the prior art as described above, and an object of the present invention is to provide a measuring method that can accurately and easily measure the internal acoustic impedance of a telephone receiver. It is in.

The gist of the present invention is to press a coupler against the receiving surface of a handset driven by alternating current at a constant frequency, change the volume of the coupled air chamber of the coupler in at least three stages, and change the volume of the coupled air chamber at each stage. The present invention is characterized in that the ratio of the sound pressures is determined by measurement, and the internal acoustic impedance of the handset is calculated from the determined ratio by a predetermined calculation.

The reason why it is necessary to measure the internal acoustic impedance of the handset is as described in the above-mentioned document for the following reason. In other words, when trying to determine the speech quality of a telephone using an objective calculation method, it is necessary to take this into consideration, since the received sound will leak through the gap between the earlobe and the earpiece, degrading the receiving quality. It won't happen. Therefore, it is necessary to find the leakage loss L _e as a parameter for evaluating such deterioration, but this leakage loss L _e can be easily calculated from the internal acoustic impedance of the handset and the equivalent circuit constant of the leakage loss. It is of a quality that can be sought. Furthermore, by reducing the internal impedance of the handset, it is possible to receive a desired call without being influenced by the influence of leakage. Due to such circumstances, it may be necessary to determine the internal acoustic impedance of the handset.

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an outline of the configuration of a measuring device necessary for carrying out the measuring method according to the present invention.
In the same figure, 1 is a cylinder constituting the coupler, 2
is a cylinder that can be moved left and right within the cylinder 1, and the cylinder 2 contains a condenser microphone 21 and a preamplifier 22 for impedance conversion, and a pointer is provided at the rear end of the cylinder 2. 23 is attached. 3 is a scale, and the scale position indicated by the pointer 23 that moves together with the movement of the cylinder 2 indicates the volume of the combined air chamber 4 inside the cylinder 1 at that time. In addition, 6 is a telephone receiver, 7 is an earpiece against which the cylinder 1 is pressed, 8 is a lead terminal connected to the telephone receiver 6, and 10 is a vent provided in the cylinder 1, which is inserted into the joint air chamber 4 by the movement of the piston 2. 11 is a code for taking out the output from the preamplifier 22.

FIG. 2 is a sectional view taken along line A-A' in FIG.

Next, the measurement method according to the present invention will be explained, but before that, the measurement principle will be explained.

Fig. 3 is a circuit diagram showing the electrical equivalent circuit of the measurement system shown in Fig. 1.The internal acoustic impedance seen from the coupled air chamber side of the handset is determined by the electrical impedance shown in Fig. 3 based on Ho and Thevenin's principles. Given using an equivalent circuit. where P ₀ is the driving sound pressure of the handset, ZR
is the internal acoustic impedance of the receiver, C _i is the compliance of the combined air chamber volume, and the relationship with the combined air chamber volume V _i is C _i = V _i /k (where k is the bulk modulus of air). Therefore, if the volume V _i of the combined air chamber is known, the compliance C _i can be found immediately. Also, let P _i be the sound pressure within the volume of the combined air chamber.

Now, in this measurement, it is necessary to change the volume V _i of the combined air chamber in at least three stages (i = 1, 2, 3), and the volumes V ₁ and V ₂ of each stage are
and compliance corresponding to V ₃ for C ₁ , C ₂
and C ₃ , and the sound pressure in the volume of each stage is
Let P ₁ , P ₂ and P ₃ . Then, A and B of the internal acoustic impedance ZR=A+jB of the receiver are given by the following equation. However, (j ² = -1) and A is
B indicates the real part of ZR, and B indicates the imaginary part of ZR.

Note that ω represents an angular frequency, and A≧0.

Here, we will explain how to derive the above equations (1), (2), and (3).

In the equivalent circuit of Figure 3, compliance C _i
Since the current flowing through is jωC _i P _i , the following equation holds.

Po=(ZR+1/jωC _i )jωC _i P _i ...(a) Here, ω is the driving angular frequency, and j=√−1.

Here, if we set ZR=A+jB and rewrite the above equation (a), we get the following equation.

Po=(A+jB+1/jωC _i )jωC _i P _i =(1−ωC _i B+jωC _i A) P _i ...(B) Now, P _i is a complex number as in (B), but the value obtained by measurement is the absolute value.

Therefore, the absolute value of P _i is calculated from equation (b) and becomes the following equation.

｜Po／P _i ｜ ² = (1-ωC _i B) ² +ω ² C _i ² A ² ...(C) By finding A and B from equation (C), we can obtain the internal impedance ZR = A + jB. , now P _i ,
Considering three levels of C _i (i=1, 2, 3), the following equation (d) is obtained.

Thereby, A and B can be uniquely determined by measuring P ₁ to P ₃ and C ₁ to C ₃ .

Rewriting equation (d) using |ZR| ² = A ² + B ² results in the following equation.

To further organize, ω ² {(P ₁ /P ₂ ) ² C ₁ ² −C ₂ ² } | ZR | ² −2ω {(P ₁ /P ₂ ) ² C ₁ −C ₂ }B=(P ₁ /P ₂ ) ² −1 ω ² {(P ₁ /P ₃ ) ² C ₁ ² −C ₃ ² } | ZR | ² −2ω {(P ₁ /P ₃ ) ² C ₁ −C ₃ }B=(P ₁ /P ₃ ) ² -1 From the above equation, when B and A are solved by simultaneous equations, equations (1) to (3) are obtained.

As can be seen from equations (1), (2), and (3) above, the compliances C ₁ , C ₂ , and C ₃ can be immediately determined from the volumes V ₁ , V ₂ , and V ₃ at each stage of the combined air chamber, respectively. Therefore, what needs to be measured is the ratio of the sound pressures P ₁ , P ₂ , and P ₃ (P ₁ /P ₂ ) in the volume of each stage,
(P ₁ /P ₃ ), and once these are determined, the desired internal acoustic impedance of the receiver can be easily determined by calculation.

What should be noted here is that it is not necessary to find the absolute values of the sound pressures P ₁ , P ₂ , and P ₃ within the volume of each stage, but only the sound pressure ratios (P ₁ /P ₂ ), (P ₁ /P ₃ ) is sufficient, and this makes the measurement itself extremely simple, which will be explained later.

Returning to FIG. 1, the measurement method according to the present invention will be explained.

First, an oscillator (not shown) generates a sine wave alternating current of a constant frequency, and this is applied to the receiver 6 via the lead terminal 8 to drive it. As a result, the handset 6
generates a sound pressure P ₁ into the joint air chamber 4. A condenser microphone 21 placed at the tip of the cylinder 2 detects the sound pressure P ₁ and converts it into an electrical signal. It is measured by

Next, move the cylinder 2 to change the volume of the combined air chamber 4, measure the electrical signal corresponding to the sound pressure _P2 at that time, and then move the cylinder 2 further to change the volume of the combined air chamber 4. change the sound pressure at that time
Measure the electrical signal corresponding to P ₃ . Sound pressure P ₁ , P ₂ ,
If it were necessary to find the absolute value of _P3 , it would be extremely troublesome to calibrate the electrical signal to the sound pressure, since the sensitivity of the microphone 21, the gain of the amplifier 22, etc. would become a problem. In the measurement method, as mentioned earlier, the sound pressure ratio (P ₁ /P ₂ ),
Since it is sufficient to find (P ₁ /P ₃ ), the sound pressure ratio can be found from the ratio of the corresponding electrical signals, so the troublesome problem described above does not occur.

Figure 4 shows the absolute value of the internal acoustic impedance of the receiver obtained from the absolute value and phase using the conventional method.
This is a graph showing the results obtained by the measurement method of the present invention as indicated by the marks and the values determined by the measurement method of the present invention shown as the ○ marks for comparison, and it can be seen that there is good agreement in the low frequency range.

As explained above, according to the measurement method of the present invention, there is no need for an expensive phase meter as required in the past.
Furthermore, the sensitivity and characteristics of the condenser microphone, amplifier, electric meter, etc. used in carrying out the present invention need only be constant and unchanging during the measurement period; Since it does not affect the ratio, it has the advantage that measurement can be carried out very easily.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an outline of the configuration of a measuring device necessary to carry out the measuring method according to the present invention, FIG. 2 is a cross-sectional view taken along line A-A' in FIG. 1, and FIG. FIG. 1 is an electrical equivalent circuit diagram of the measurement system shown in FIG. 1, and FIG. 4 is a graph showing a comparison between the measured values by the conventional method and the measured values by the method of the present invention. Explanation of symbols, 1... Cylinder forming Katsupura, 2
... Cylinder, 21 ... Condenser microphone, 22 ... Preamplifier, 23 ... Pointer, 3 ...
Scale, 4... Combined air chamber, 6... Receiver, 7... Earpiece, 8... Lead terminal, 10... Ventilation hole, 11
……code.

Claims (1)

[Claims] 1. A coupler is pressed against the receiving surface of a handset driven by alternating current at a constant frequency, and the volume V in the coupled air chamber of the coupler is varied in at least three stages to V ₁ , V ₂ . , V ₃ and the ratio of the sound pressures P ₁ , P ₂ , P ₃ in the combined air chamber at each stage (P ₁ /P ₂ ), (P ₁ /P ₃ )
is determined by measurement, and the internal acoustic impedance ZR (=A+jB) of the handset is calculated from the determined ratio using the following arithmetic expressions (1) to (4). . Record however C _i =V _i /k where (i=1, 2, 3)...(4) Note that k represents the bulk modulus of air, ω represents the angular frequency, and A≧0.