THE INFLUENCE OF THE SOUND STIMULATING METHODS ON THE HEARING OF THE PERFORATED DRUM MEMBRANE

Since the past study it has been stated that different hearing effects occured whether the sound stimuli were given from a distant loudspeaker or a telephone receiver. This phenomenon will be explained from the different effective impedance of the ear, which is altered by the outer orifice of the meatus opened or not. And when there is a perforation on the drum membrane, the alteration of the impedance of the sound transmission system is added, and this will make the effect of the sound stimulus more remarkably. Upon these considerations, the model ear experiment, the animal experiment and the clinical hearing tests were pursued. The results are summarized as follows: (1) Both the minimum audible thresholds measured by the receiver method (a coupler method) and the speaker method (a free field method), showed some more reduction for the low tones below 1, 000cps. by the perforated drum membrane than by the none-perforated one, and an about 10_??_15db more loss existed by the receiver method than by the speaker method. (2) The difference between two methods was considered as due to the acoustical leakage according to the perforation of the drum membrane. (3) Therefore, when we considered the true hearing of a patient with a perforated drum membrane, the result of the hearing test with the telephone receiver must reduced be some db, especially in the range of low tones. (4) There was scarcely found any difference in the audiograms between the two methods, if there was no perforation. But it was suggested that some indirect bone conduction might exist at the severe conductive deafness. (5) The above results were affirmed also by some theoretical considerations.