HRTFs introduced in this paper were measured with blocked ears. This means that the subjects' ears were blocked by rigid earplugs made by an expert (medical doctor) in otolaryngology so as to fit the shape of the entrances of the subjects' ears. Methods for the calibration due to differences in subjects and listening conditions (free-field and headphone listening) were discussed by Møller et al. Møller indicated that the HRTFs measured with blocked ears reflect less individuality than those measured with open ears, which are regarded as the normal measurement condition. Moreover, transfer function from the entrance of an ear to the eardrum involves much inidivisuality, and it makes the calibration of free-field to headphone listening condition difficult. Assuming the use of appropriate headphone, Møller suggested that HRTFs measured with blocked ears are useful for calibration required in those occasions. As for the appropriate headphone for binaural listening, please refer to the discussion by Møller et al..

References

1. Henrik Møller, "Fundamentals of binaural technology," Applied Acoustics, 36, 171-218(1992).
2. Henrik Møller, Dorte Hammershøi, Clemen Boje Jensen and Michael Friis Sørensen, "Tranfer characteristics of headphones measured on human ears," J. Audio Eng. Soc., 43(4), 203-217(1995).
3. Henrik Møller, Clemen Boje Jensen, Dorte Hammershøi and Michael Friis Sørensen, "Design criteria for headphones," J. Audio Eng. Soc., 43(4), 218-232(1995).