Loudspeakers and Microphones
When a voice coil is surrounded by a conductive material, such as short ring or pole piece (short-ring), in close proximity, the impedance becomes lossy and frequency dependent. When the short-ring is sufficiently thick relative to the penetration of impressed magnetic flux (Skin Depth), theory states that the lossy impedance frequency dependence is √ω. In practice, many short-rings do not have sufficient thickness for mid to low frequency. Therefore the lossy voice impedance response at the frequency range deviates from the model of theoretical impedance frequency dependence. Thus the short-ring material’s thickness and conductance is modeled. Then it is implemented in a transformer based voice coil block impedance model which successfully describes the block impedance frequency dependence.