Loudness discomfort level under earphone and in the free field: the effects of calibration methods

Abstract

Previous earphone LDL data from this laboratory were characterized by an intensity level increase in the low frequencies which we suggested resulted from the difference between the SPL measured in a standard coupler and that actually generated in the ear under a supra-aural earphone. The experiments reported herein were conducted to determine if the frequency effect could be explained adequately on the basis of differences between conventional and real-ear calibration methods and to extend the LDL measurement to free-field conditions. Determination of the SPL generated by an earphone and by a loudspeaker in the free field was accomplished with a probe tube at the entrance to the ear canal under earphone and free-field conditions and by conventional calibration methods. Psychophysical measurements of loudness discomfort (LDL) and loudness balance (ABLB) were conducted under earphone and in the free field. Corrections derived from differences between standard calibration procedures and probe tube measurements were applied to the psychophysical measurements. The corrected results lead to the following conclusions: (1) there is no intensity level increase in the low frequency LDL under earphone; (2) there are no differences between earphone and free field LDL and ABLB judgments. The relationships between these data and previously published MAP-MAF differences are discussed.