This article reviews the relationships among different acoustic measurements of the mobility of the tympanic membrane, including impedance, admittance, reflectance, and absorbance, which the authors group under the rubric of immittance measures. Each of these quantities is defined and related to the others. The relationship is most easily grasped in terms of a straight rigid ear canal of uniform area terminated by a uniform middle ear immittance placed perpendicular to the long axis of the ear canal. Complications due to variations from this geometry are discussed. Different methods for measuring these quantities are described, and the assumptions inherent within each method are made explicit. The benefits of wideband measurements of these quantities are described, as are the benefits and limitations of different components of immittance and reflectance/absorbance. While power reflectance (the square of the magnitude of pressure reflectance) is relatively invariant along the length of the ear canal, it has the disadvantage that it ignores phase information that may be useful in assessing the presence of acoustic leaks in ear-canal measurements and identifying other potential error sources. A combination of reflectance and impedance magnitude and angle give a more complete description of the middle ear from measurements in the ear canal.
1Department of Otology and Laryngology, Harvard Medical School and Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary Boston, Massachusetts, USA; 2Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden; and 3National Center for Rehabilitative Auditory Research, Portland Veterans Affairs Medical Center, Portland, Oregon, USA.
ACKNOWLEDGMENTS: The authors declare no conflict of interest.
Address for correspondence: John J. Rosowski, Eaton-Peabody Laboratory, 243 Charles Street, Boston, MA 02114, USA. E-mail: email@example.com
Received January 21, 2013
Accepted May 13, 2013