As loudspeaker output power of mobile devices increases for better audio experience, an accurate measurement or estimation of the voice coil temperature becomes necessary in order to protect the loudspeaker from over-heating. A voice coil designed with a short ring, a metal pole piece, or under hung voice coil will most likely exhibit impedance nonlinearity. A voice coil resistance based temperature measurement method that relies on the resistance value may be adversely affected by voice coil impedance nonlinearity when the resistance is measured using high frequency probing. For this reason, the nonlinearity must be known and compensated. This paper analyzes and explains voice coil high frequency impedance characteristics due to Eddy losses and impedance nonlinearity, and develops a method to compensate voice coil impedance nonlinearity to obtain an accurate voice coil temperature measurement.
https://www.aes.org/e-lib/browse.cfm?elib=19235
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