An analysis is made of the impedance characteristic of the ear when coupled to a telephone receiver by means of an ear cap which introduces an acoustic leak at the junction. A vibrating system is also described which causes constant sound pressure to be generated in the ear cavity under such conditions. Experimental data as obtained on an artificial ear are given showing the effect of the acoustic leak on the response of various types of receivers. Subjective tests are also described and data given which corroborate the data obtained on the artificial ear.