An off-ear detector (200; 310; 400) for headphone off-ear detection, the off-ear detector comprising: an audio output to transmit a headphone audio signal toward a headphone speaker in a headphone cup; a feedback, FB, microphone input to receive a FB microphone signal from a FB microphone in the headphone cup; an off-ear detection, OED, signal processor configured to: determine an audio frequency response of the FB microphone signal over an OED frame as a received frequency response, determine an audio frequency response of the headphone audio signal times an off-ear transfer function between the headphone speaker and the FB microphone as an ideal off-ear frequency response, generate a difference metric comparing the received frequency response to the ideal off-ear frequency response, employ the difference metric to detect when the headphone cup is disengaged from an ear, the difference metric including a plurality of frequency bins, and weight the plurality of frequency bins; and a tone generator configured to generate an OED tone at a specified frequency bin of the plurality of frequency bins and to inject the generated OED tone into the headphone audio signal forwarded to the headphone speaker in order to support generation of the difference metric when the headphone audio signal drops below a noise floor including acoustic and electrical noise as detected from a feedforward, FF, microphone signal. an audio output to transmit a headphone audio signal toward a headphone speaker in a headphone cup; a feedback, FB, microphone input to receive a FB microphone signal from a FB microphone in the headphone cup; an off-ear detection, OED, signal processor configured to: determine an audio frequency response of the FB microphone signal over an OED frame as a received frequency response, determine an audio frequency response of the headphone audio signal times an off-ear transfer function between the headphone speaker and the FB microphone as an ideal off-ear frequency response, generate a difference metric comparing the received frequency response to the ideal off-ear frequency response, employ the difference metric to detect when the headphone cup is disengaged from an ear, the difference metric including a plurality of frequency bins, and weight the plurality of frequency bins; and determine an audio frequency response of the FB microphone signal over an OED frame as a received frequency response, determine an audio frequency response of the headphone audio signal times an off-ear transfer function between the headphone speaker and the FB microphone as an ideal off-ear frequency response, generate a difference metric comparing the received frequency response to the ideal off-ear frequency response, employ the difference metric to detect when the headphone cup is disengaged from an ear, the difference metric including a plurality of frequency bins, and weight the plurality of frequency bins; and a tone generator configured to generate an OED tone at a specified frequency bin of the plurality of frequency bins and to inject the generated OED tone into the headphone audio signal forwarded to the headphone speaker in order to support generation of the difference metric when the headphone audio signal drops below a noise floor including acoustic and electrical noise as detected from a feedforward, FF, microphone signal.