By utilizing the mode propagation of sound waves in a water tube of nearly semi-circular cross section whose upper plane surface is a free surface of water and whose semi-circular wall is made of a thin foil of plastic material, the acoustic properties of an underwater sound-absorbing material at an oblique incidence of waves are measured. Theoretical considerations and experimental results of the sound reflection coefficient and the unit area acoustic impedance of wedge-shaped materials made of wood are presented.
To design a sound transmission system used mainly for the transmission of musical signals according to the specifications of the quality of reproduced sound required in the system, a consideration is given on the basic problems concerning the establishment of a comprehensive method for the evaluation of tone quality. From a standpoint that the main purpose of the transmissin of auditory information in this case, is the transmission of the emotional information, a discussion on the methodology of scaling the emotion arounsed by the sensation of reproduced sound has been made. As a result it was found that the variation of judgments of the listeners coming from the emotion evoked by listening to the reproduced sound can be reduced to the variation of the judgments on the preference or pleasantness of reproduced sound, and that it can be related stabely to the physical characteristics stabely of the transmission system by grouping the listeners according to the difference of their desire. Furthermore, as a clue of finding concrete methods of constructing a comprehensive system of evaluating tone quality, a model of the process of tone quality evaluation, in which the whole process is devided into two processes, the process of elementary sensation and that of emotion, is proposed. The former is an analytical process and rather invariant on person and on time, while the latter is a synthetic process and varies from person to person and time to time.
The purpose of the present paper is to find out the relationship between the dips on the frequency charcteristics of the sound reproducing system and its sound quality represented by the preference test. The experiment was carried out on the following schemes: (1) Paired type constant method, (2) Judgment crieterion: preference of sound, (3) Exprimental conditions: (i) Program source: music obtained from diskrecord, (ii) Objects for comparison: dips on the frequency characteristics, (iii) Factorial design including replication, (iv) Reverberation time of the listening room: about 0. 6 seconds. The results obtained are as follows: (1) It was found that there is a relatively clear relationship between the preference and their evaluation scales. (2) There was approximately a linear relationship between the probabilities of the preference and the points of the center frequencies of the dips; the maximum of the probability is about 40% at 4, 800 cps or 7, 200 cps, and the minimum is about 20% at 150 cps or 300 cps. (3) There are two groups of observers who have quite different preference patterns. The feature of one group is the maximum probability of the preference when the center frequencies of the dips are in the lower side. On the contrary, the feature of another group is the maximum probability of the preference when the center frequencies of the dips are in the higher side. The existence of the different groups was found out by the statistical method of grouping, using the tables of the number of equally-perference-matched-pairs of observers is different according to the listening levels.