Interactions in a multiple-voice-coil digital loudspeaker

A 7-bit digital multiple-voice-coil loudspeaker and a constant-current driv er have been constructed and evaluated. Two's complement coding offers the best compromise between complexity, excessive power consumption, and distor tion due to baseline drift. The effect of motion impedance and mutual coupl ing in a multiple-coil system is found to magnify the effective impedance o f an individual coil by its weighting in the binary representation. This ef fect places an unreasonable demand on the output impedance of the driver un less damping is controlled, which can be achieved most effectively by a sho rt-circuited voice coil. Optimum damping occurs when the damping resistance is equal to the negative resistance of an individual coil.