An auditory device assembly comprising: an earpiece having an audio output device for providing sound to an ear of a user; an internal microphone arranged to detect sound emitted by the ear of the user; and an audio processing unit having: a hearing-test mode in which the audio processing unit is arranged to determine at least two ear characteristics of the ear of the user based on at least one hearing test; and an audio streaming mode in which the audio processing unit is arranged to output an audio stream via the audio output device; wherein the audio processing unit is arranged to adjust the output of the audio stream in the audio streaming mode based on at least one ear characteristic determined in the hearing-test mode wherein the audio processing unit is arranged, in the hearing-test mode, to: detect, using the internal microphone, Spontaneous Otoacoustic Emissions emitted by the ear of the user without providing any stimulus to the ear of the user; determine an ear characteristic based on the Spontaneous Otoacoustic Emissions; output, using the audio output device, an audio test signal as a stimulus to the ear of the user, wherein the audio test signal is a pre-defined audio test signal selected based on the detected Spontaneous Otoacoustic Emissions; detect, using the internal microphone, Evoked Otoacoustic Emissions emitted by the ear of the user, wherein the Evoked Otoacoustic Emissions are caused by the stimulus; and determine a further ear characteristic based on the Evoked Otoacoustic Emissions. an earpiece having an audio output device for providing sound to an ear of a user; an internal microphone arranged to detect sound emitted by the ear of the user; and an audio processing unit having: a hearing-test mode in which the audio processing unit is arranged to determine at least two ear characteristics of the ear of the user based on at least one hearing test; and an audio streaming mode in which the audio processing unit is arranged to output an audio stream via the audio output device; a hearing-test mode in which the audio processing unit is arranged to determine at least two ear characteristics of the ear of the user based on at least one hearing test; and an audio streaming mode in which the audio processing unit is arranged to output an audio stream via the audio output device; wherein the audio processing unit is arranged to adjust the output of the audio stream in the audio streaming mode based on at least one ear characteristic determined in the hearing-test mode wherein the audio processing unit is arranged, in the hearing-test mode, to: detect, using the internal microphone, Spontaneous Otoacoustic Emissions emitted by the ear of the user without providing any stimulus to the ear of the user; determine an ear characteristic based on the Spontaneous Otoacoustic Emissions; output, using the audio output device, an audio test signal as a stimulus to the ear of the user, wherein the audio test signal is a pre-defined audio test signal selected based on the detected Spontaneous Otoacoustic Emissions; detect, using the internal microphone, Evoked Otoacoustic Emissions emitted by the ear of the user, wherein the Evoked Otoacoustic Emissions are caused by the stimulus; and determine a further ear characteristic based on the Evoked Otoacoustic Emissions. detect, using the internal microphone, Spontaneous Otoacoustic Emissions emitted by the ear of the user without providing any stimulus to the ear of the user; determine an ear characteristic based on the Spontaneous Otoacoustic Emissions; output, using the audio output device, an audio test signal as a stimulus to the ear of the user, wherein the audio test signal is a pre-defined audio test signal selected based on the detected Spontaneous Otoacoustic Emissions; detect, using the internal microphone, Evoked Otoacoustic Emissions emitted by the ear of the user, wherein the Evoked Otoacoustic Emissions are caused by the stimulus; and determine a further ear characteristic based on the Evoked Otoacoustic Emissions.