1. 40c. BELL, LOUIS.-On the Ultra Violet Component in Artificial Light. 2 pls. May, 1912. pp. 1-29. 2. 3. 4. CHIVERS, A. H.- Preliminary Diagnoses of New Species of Chaetomium. 81-88. July, 1912. 20c. pp. 5. 6. 30c. WALCOTT, HENRY P.- Alexander Agassiz. pp. 31-44. June, 1912. KENT, NORTON A.- A Study with the Echelon Spectroscope of Certain Lines in the Spectra of the Zinc Arc and Spark at Atmospheric Pressure. pp. 91-109. 2 pls. August, 1912. 50c. KENNELLY, A. E., and PIERCE, G. W.-The Impedance of Telephone Receivers as affected by the Motion of their Diaphragms. pp. 111-151. September, 1912. 70c. Proceedings of the American Academy of Arts and Sciences. THE IMPEDANCE OF TELEPHONE RECEIVERS AS AFFECTED BY THE MOTION OF THEIR DIAPHRAGMS. By A. E. KENNELLY AND G. W. PIERCE. THE IMPEDANCE OF TELEPHONE RECEIVERS AS AFFECTED BY THE MOTION OF THEIR DIAPHRAGMS. BY A. E. KENNELLY AND G. W. PIERCE Received July 16, 1912. I. INTRODUCTION. THE writers have made a series of measurements of the resistance and inductance of several forms of telephone receivers over a wide range of frequency of current. In the course of the measurements some interesting results have been obtained, which form the subject of this paper. As the period of the e. m. f. used in the measurements approaches the natural period of the diaphragm, the note emitted by the telephone receiver increases markedly in loudness, and the resistance and inductance of the receiver undergo wide deviations from values obtained when the diaphragm is prevented from vibrating by being damped. That is to say, the motion of the diaphragm has an effect upon the resistance and inductance of the receiver, and this effect grows rapidly as the electrical period approaches the mechanical period. In the tests to be described, the resistance and the inductance of a given receiver were measured, first with the diaphragm free and sounding, and, second, with the diaphragm damped, or arrested. The values when the diaphragm is free may be called free values; the values when the diaphragm is damped may be called damped values. The difference obtained by subtracting the damped values from the corresponding free values may be called the motional values of resistance, inductance, etc.; since such differences are due to the motion of the diaphragm. It is found that when the impressed frequency differs widely from the natural frequency of the diaphragm, the motional resistance and inductance are very small. In the neighborhood of resonance, which is often very sharply marked, these motional values become relatively large, and one or both pass through a change of sign, in such a manner that, when the motional impedance for different frequencies is drawn vectorially from a fixed point as origin, all the points given by the observations lie upon a circular graph, which may be called the mo tional impedance circle, or for brevity, the circular graph of the receiver. Different telephone receivers have very different circular graphs, and the circular graph of any given receiver defines its characteristics in various important practical respects, both mechanical and electrical. Also, from a theoretical standpoint, the reactive influence of the motion of the diaphragm upon the current through the coils of a tele FIGURE 1. Diagram of connections of the Rayleigh Bridge and Vreeland Oscillator. phone is interesting from its analogy to the effects of an optical medium upon transmitted light in the neighborhood of an absorption band. The experiments also give information regarding the natural period of vibration, and the natural damping factor of the diaphragm, and the power drawn by the instrument when it is sounding and when it is damped. II. METHOD AND APPARATUS. Measurement of Resistance and Inductance. The measurements of resistance and inductance were all made with a Rayleigh equal-arm bridge, with connections as indicated in Figure 1. The arms AD and DC of the Bridge were 5-ohm non-inductive resistances. The Arm AB contained the telephone receiver T under test. The arm BC contained the adjustable non-inductive resistance R and the adjustable Ayrton-Perry Variometer L. A head telephone H served to determine a balance. |