電話用動電形受話器の比感度について
1967 年 23 巻 2 号 p. 52-61
詳細
1967 年 23 巻 2 号 p. 52-61
The specific response of a dynamic receiver at low frequencies(within the range of stiffness control) when it is used as a telephone receiver has been studied by calculation. First, it is shown that the motional impedance of a telephone receiver is negligibly small as compared with the resistance of a moving coil. An expression of the specific response q_0 of the dynamic receiver with a vibrating system of three degrees of freedom has been worked out as a function of various constants of vibrating and driving systems on the supposition that the motional impedance and reactance of the receiver are negligibly small as compared with the resistance of a moving coil(namely, zero frequency). Then, some numerical example of the specific response q_0 are shown graphically as a function of the thickness h of a diaphragm with the mass ratio α of coil to diaphragm and the ratio of inner radius to outer radius of the diaphragm used as parameters. Further, using the expression of the response, maximum conditions of the response for the radius a of a diaphragm and the mass m_c of a moving coil have been worked out by calculating δ(q_0)/δa and δ(q_0)/δ(m_c), and numerical examples of the potimum condetion and the threshold value of response which are useful for design work are shown graphically as a function of the thickness of the deaphragm. The results are as follow;(1)If the mass of coil is held constant, a moving coil made of aluminium provides about 3 dB higher response than a moving coil made of copper. (2)The specific response can be increased by reducing the thickness of a diaphragm. (3)Both a_m and α_m are increased by reducing the thickness of a diaphragm, where the suffix m shows the maximum condition of each quantity. (4)When h<0. 09 mm and m_c>0. 4g, a_m is larger than 2. 5cm. On the basis of these results, the process of designing a dynamic receiver for telephone set is described. An experimental value of the specific response of a prototype receiver was compared with the value calculated from the above expression, resulting in good coincidence with each other.
