Materials that obstruct the path of acoustic waveforms in free-field to the human ear, may introduce distortions that can modify the natural Head-Related Transfer Functions. In this paper the effect of wearing commercially available Head-Mounted Displays for Mixed and Augmented Reality has been measured via a dummy head mannequin. Such spectral distortions may be relevant for mixed reality environments where real and virtual sounds mix together in the same auditory scene. The analysis revealed that the measured HMDs affected the fine structure of the HRTF (> 3–6 kHz) and also introduced non-negligible distortions in the interaural level difference range mostly at the contralateral ear. Distortion patterns in HRTFs and cue modi?cations are reported and discussed across incidence angles and frequency bands. Click here for download    or you can find it online here.