. Elements of acoustical engineering. Electro-acoustics; Sound. TELEPHONE RECEIVERS 231 network for controlling the response. A cross-sectional view of a typical dynamic telephone receiver is shown in Fig. The equivalent electrical circuit of the mechanical system is also shown in Fig. The electrical impedance, in abohms, due to the mechanical system is given by Bl zem = — Zm where B = flux density in the air gap, in gausses, / = length of the conductor in the voice coil, in centimeters, and Zm = total mechanical impedance at/iif, in mechanical ohms. DIAPHRAGM EAR CAP 6. mo ^
. Elements of acoustical engineering. Electro-acoustics; Sound. TELEPHONE RECEIVERS 231 network for controlling the response. A cross-sectional view of a typical dynamic telephone receiver is shown in Fig. The equivalent electrical circuit of the mechanical system is also shown in Fig. The electrical impedance, in abohms, due to the mechanical system is given by Bl zem = — Zm where B = flux density in the air gap, in gausses, / = length of the conductor in the voice coil, in centimeters, and Zm = total mechanical impedance at/iif, in mechanical ohms. DIAPHRAGM EAR CAP 6. mo ^ VOICE COIL CIRCUIT EQUIVALENT CIRCUIT CASE CROSS-SECTIONAL VIEW A • V ^ ^\ / /b s,7^-" = ' 1000 FREQUENCY Fig. Cross-sectional view, the voice coil circuit and the equivalent circuit of the mechan- ical system of a dynamic telephone receiver, e the voltage of the generator, teg the resistance of the generator, yed the damped resistance of the voice coil. L the inductance of the voice coil, zem the motional impedance. In the equivalent circuit: m^ the mass of the diaphragm. C>fo and ta/o the compliance and mechanical resistance of the suspension. 7n\ and rM\ the mass and mechanical resistance of the slit. Cm\ the compliance of the cavity behind the diaphragm. Jm the force generated in the voice coil. The graph shows the pressure response frequency characteristic. A. Receiver feeding a closed cavity. B. Re- ceiver feeding an artificial ear. (After Wente and Thuras.) In dynamic telephone receivers the flux density is relatively low and %em is small compared to Veb and may be neglected. The force/m, in dynes, is given by /a Bli where /, the current in abamperes, is obtained from the electrical circuit. In general, the force/j^- is practically a constant and may be considered a constant in the equivalent circuit. The response feeding a plain cavity is indicated by A, Fig. The response measured on an artificial ear indicated by 5, Fig. , shows that th
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