After detecting the residual noise, the second input transducer outputs {HEAD ~ a signal} to the electrical circuitry in the control unit of {TAIL ~ the invention} so that an opposing sound wave 180° out of phase with the residual noise will be input into the ear canal cavity by the output transducer 
After detecting the residual noise , the second input transducer outputs { HEAD ~ a signal } to the electrical circuitry in the control unit of { TAIL ~ the invention } so that an opposing sound wave 180 ° out of phase with the residual noise will be input into the ear canal cavity by the output transducer
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