Modeling of Rocking Modes in Electroacoustic Transducers

The rocking of the radiator is a severe problem in headphones, micro-speakers, and other kinds of loudspeakers causing voice coil rubbing, which limits the maximum acoustical output at low frequencies. The root causes of this problem are small imbalances in the distribution of the stiffness, mass, and magnetic field in the gap. Modal analysis and lumped parameter modeling is used in this paper to explain the generation of rocking modes. This theory is the basis for a new measurement technique using laser vibrometry to quantify the rocking behavior and to identify the dominant root cause in the design or manufacturing process.