After detecting the residual noise, the second input transducer outputs a signal to the electrical circuitry in {HEAD ~ 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 
of
After detecting the residual noise , the second input transducer outputs a signal to the electrical circuitry in { HEAD ~ 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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