X.Additional experiments on moving-coil reproducers and on flexible disks

Abstract

Abstract In this paper various details of moving-coil reproducers are discussed. The modulus of elasticity of paper is determined and used to compare the stiffness of conical sheets and disks of the same radius. A series of experiments is outlined, showing the influence of reinforcing certain portions of the diaphragm. The combination modes of a reed-driven paper disk are treated, and by comparison with theory, heterogeneity of the paper is disclosed. The exact solution of a lossless reed-driven disk vibrating in vacuo is given, due allowance being made for variation in the apparent mass of the reed itself. The case of a coil-driven circular aluminium disk is examined experimentally, and the frequency band occupied by the first symmetrical mode is shown to be only 5 cycles. With constant current in the coil, the output at resonance is some 2000 times greater than at non-resonant frequencies. The influence of the magnetic field upon the output and upon the coil impedance of a reproducer is analysed. The output criterion of the magnet is stipulated in terms of total gap area, air-gap flux density, and the coil space factor. It is shown that the oscillation of a coil driven by an alternating current in a non-uniform magnetic field is accompanied by a motion of translation. This is akin to the process of rectification.