Studies on the Hearing Test with Speech Sound Part. 2. Discussion on the Existing Methods of Voice Test

In the voice tests, meaning words have been used for the long time and the maximum hearing distance is understood to show the degree of hearing. But when meaning words are used, the speech sounds are likely to be understood as words by the help of mental power, even though the hearing is not sufficiently enough to catch the individual speech sounds. Thus, slight impairment of hearing is liable to be overlooked and the results do not mean the true hearing, but the degree of speech understanding. When cautious considerations are brought on the facts that speech sounds are compound sounds, the clearness or intensity of the testers' voice have individual differences, and the architectural acoustics of the test room is not constant, it seems to be impossible to determine the degree of hearing simply by the distances of hearing. By various experiments the author ascertained the following facts: - (1) There is not necessarily any relation which is implied by straight line òr logarithm between the intensity of sound and the distance from the source of sound. These two factors, namely, intensity and distance are variable according to the conditions of test room. (2) Considerable individual differences are seen in the intensity of testers voice. Even when the same person carries on the test, the intensity of sound differs according to the kinds of speech sounds. (3) The maximum distances of hearing for a certain voice differ according to the conditions of the test room. By the above mentioned experiments, it can be pointed out that the exsisting methods of voice test involve various defects.