Study of evaluating and measuring method of impact sound.

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Impact sounds are such sound that are characterized by their high peak levels and short duration time. Thus, it is not appropriate to evaluate and to measure the loudness and the noisiness of impact sounds by conventional methods. We have studied how to evaluate the impact sounds in cooperation with ten laboratories in Japan by Grant-in-aid for Co-operative Research. As the first stage, a round robin test, in which all the participants conduct the same experiments under very similar listening condition, was carried out. In this test, we used repeated impact sounds which are generated by a mini-computer. The stimuli synthesized by a computer were recorded on magnetic tapes by using PCM. Then the tapes were distributed among researchers. This round robin test becomes a very large experiment where the number of the subjects were more than a hundred. The experimental results obtained by the test were as follows:(1) If we express a repeated impact sound in terms of the unweighted sound exposure level, the loudness of the impact sound show rather high relation coefficient(0.97). However, to evaluate the loudness more precisely, we have to consider some time constant which is consider to represent the integral characteristic of our hearing system.(2) As a result of the experiment for noisiness evaluation, the unweighted sound pressure level showed a very high relation coefficient(0.99). This means that this measure is quite effective to evaluate the noisiness of the repeated impact sounds.