Wearable audio device with head on/off state detection

A computer-implemented method of detecting a state of a wearable audio device on a user, the method comprising:

• detecting a change from one of:
• an on-head state to an off-head state, or the off-head state to the on-head state with a first sensor system, wherein the first sensor system comprises an internal microphone acoustically coupled to an ear canal of a user, wherein the internal microphone generates an electrical signal responsive to an acoustical signal incident at the internal microphone, the detecting of the change from the on-head state to the off-head state or the off-head state to the on-head state comprising determining a magnitude of an acoustic transfer function based on the electrical signal and the acoustical signal at one or more predetermined frequencies;
• calibrating a second, distinct sensor system;
• detecting a change from the other one of:
• the off-head state to the on-head state or the on-head state to the off-head state using the calibrated second sensor system, wherein the second sensor system comprises a proximity sensor;
• and
• adjusting an operating state of at least one function of the wearable audio device in response to detecting the change from the on-head state to the off-head state or detecting the change from the off-head state to the on-head state.

A wearable audio device comprising:

• an acoustic transducer for providing audio playback of an acoustical signal to a user;
• an internal microphone acoustically coupled to an ear canal of a user, wherein the internal microphone generates an electrical signal responsive to an acoustic signal incident at the internal microphone;
• and
• a control circuit coupled with the acoustic transducer and the internal microphone, the control circuit configured to:
• determine a magnitude of an acoustic transfer function based on the electrical signal and the acoustical signal at one or more predetermined frequencies;
• pause the audio signal when a change from an on-head state to an off-head state is detected;
• output an interrogation signal or narrowband noise at the acoustic transducer while the audio signal is paused;
• determine a magnitude of an acoustic transfer function based on the electrical signal and the interrogation signal or narrowband noise at one or more predetermined frequencies;
• and
• adjust at least one function of the wearable audio device in response to detecting one of:
• a change in the wearable audio device from the on-head state to the off-head state or a change from an off-head state to the on-head state.