Dual voice coil loudspeaker is designed for systems requiring secondary supervision using signal presence method. When the primary voice coil is excited the secondary voice coil induces output signal to a separate, dedicated supervisory line indicating "good" voice coil integrity back to the system.

Use caution when using L20-400-7 for dual source applications (separate amps feeding each voice coil in a paging or music application). No isolation between voice coils is provided (nor possible) so signal bleed between systems is likely.