Compatible Tests on Earcap and Ear-Insert-Type Earphones

Abstract

This paper covers the use of the 6- and 2-cm3 ASA (Standard Z 24.9-1949) couplers employed to measure the response of earcap and ear-insert-type earphones, respectively. The investigation revealed that in order to compare the subjective loudness of the two types of earphones at any given frequency, a correlating adjustment had to be applied because the couplers measure the sound pressure developed at opposite ends of the auditory canal. In addition, to avoid a 3-dB error, the basic 2-cm3 volume had to be reduced to 1.3 cm3, coinciding with the unoccupied coupler volume. An experimental 6-cm3 coupler is described which measures the pressure developed at the tympanum end of the canal, and direct comparisons with data taken on the 1.3-cm3 coupler are presented. The necessary correlating information was obtained with ear probes projecting into the canal.