The second input transducer supplies {HEAD ~ an electrical signal} corresponding to {TAIL ~ the residual noise} to the control circuitry to cancel the residual noise 
The second input transducer supplies { HEAD ~ an electrical signal } corresponding to { TAIL ~ the residual noise } to the control circuitry to cancel the residual noise
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH