A method includes detecting, via a first microphone coupled to a user's left ear, a sound, detecting, via a second microphone coupled to the user's right ear, the sound, determining a time difference between detection of the sound at the first microphone and detection of the sound at the second microphone, and estimating a user's head size based on the time difference. The method also includes identifying a head-related transfer function (HRTF) associated with the user's head size or modifying, a HRTF based on the user's head size. The method further includes applying the identified HRTF or modified HRTF to audio signals to produce output signals and forwarding the output signals to first and second speakers coupled to the user's left and right ears.