A headphone system, comprising: a left earpiece; a right earpiece; a left microphone coupled to the left earpiece to receive a left acoustic signal and to provide a left signal derived from the left acoustic signal; a right microphone coupled to the right earpiece to receive a right acoustic signal and to provide a right signal derived from the right acoustic signal; and a rear microphone coupled to either earpiece and positioned to receive a rear acoustic signal, the rear acoustic signal being toward the rear of the user's head relative to either or both of the left acoustic signal and the right acoustic signal; a detection circuit coupled to the left microphone, the right microphone, and the rear microphone, the detection circuit configured to: - compare a principal signal to a reference signal, the principal signal derived from a sum of the left signal and the right signal and the reference signal derived from a difference between the left signal and the right signal, - compare the rear signal derived from the rear microphone to at least one of the left signal and the right signal to generate a rear comparison, and - produce a binary output selectively indicating that the user is speaking or not based at least in part upon those comparisons, wherein the detection circuit indicates the user is speaking when the principal signal exceeds the reference signal by a first threshold and the at least one of the left signal and the right signal exceeds the rear signal by a second threshold. a left earpiece; a right earpiece; a left microphone coupled to the left earpiece to receive a left acoustic signal and to provide a left signal derived from the left acoustic signal; a right microphone coupled to the right earpiece to receive a right acoustic signal and to provide a right signal derived from the right acoustic signal; and a rear microphone coupled to either earpiece and positioned to receive a rear acoustic signal, the rear acoustic signal being toward the rear of the user's head relative to either or both of the left acoustic signal and the right acoustic signal; a detection circuit coupled to the left microphone, the right microphone, and the rear microphone, the detection circuit configured to: - compare a principal signal to a reference signal, the principal signal derived from a sum of the left signal and the right signal and the reference signal derived from a difference between the left signal and the right signal, - compare the rear signal derived from the rear microphone to at least one of the left signal and the right signal to generate a rear comparison, and - produce a binary output selectively indicating that the user is speaking or not based at least in part upon those comparisons, - compare a principal signal to a reference signal, the principal signal derived from a sum of the left signal and the right signal and the reference signal derived from a difference between the left signal and the right signal, - compare the rear signal derived from the rear microphone to at least one of the left signal and the right signal to generate a rear comparison, and - produce a binary output selectively indicating that the user is speaking or not based at least in part upon those comparisons,