When the motor of a classical electrodynamic loudspeaker has been replaced by a so-called magnet-only motor, current distortion caused by magnetic circuits is significantly reduced. All of the nonlinear soft-iron pieces are removed, and the magnetic field is created by a combination of permanent magnets. Two loudspeakers are compared in the study: the first sample is a mass-produced 6.5-inch loudspeaker. The second sample is built replacing the magnetic circuit of the first loudspeaker by the magnet-only structure. Thus, the moving parts, including the voice-coil, diaphragm, and suspensions are kept identical for both samples, leading to a comparison based only on their motors. The measurements on the original loudspeaker have shown a significant variation of apparent resistance and inductance of the voice-coil with current, displacement, and frequency. Conversely, the measurements on the magnet-only loudspeaker have shown almost no variation whatever the frequency, current level, or position of the voice-coil.
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