箏の立奏台に関する研究 : 反射板取付の効果

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In the usual and traditional way of the performance, the So is placed directly on the tatami floor and is played by a musician kneeling close to the instrument. However, in some cases of performances or personal studies in modern buildings; the musician prefers to sit on a chair and play the instrument with a stand which holds it at an appropriate hight from the floor. Among the various existing types of stands, the one having a sound reflecting board might be considered as an attempt to have the traditional musical instrument adapted to the modern situations of performances such as that of a large concert hall. Differences in the acoustical properties of three typical resting conditions of the instrument (placed on the floor, on a stand without a sound reflector, and on a stand with a sound reflector) have been recognized bysome players and the audience in general. In this report the results of the first study to evaluate these issues are given. The angles of approach in this study are: 1) the comparison of the sound pressure level 'distribution in the near field for the 1/1 octave band stationary noise excited by an electromagnetic vibrator, and 2) the evaluation of the subjective difference by the comparative judgement method using the recorded real sounds of the instrument. 1) The sound pressure level distribution The measurement was carried out' in an anechoic room (volume: 135m^3), in which plywood boards had been laid as a sound reflecting floor to simulate the real conditios of the sound field around the instrument. Instead of moving the microphones, the instrument itself was moved slowly on the floor so that the continuous recording of sound pressure could be registered along two lines simultaneously, using two fixed microphones connected to a two channel tape recorder. The position of the bridge for the seventh string (the most central one) was chosen as the driving point for an electromagnetic vibrator, as shown in Fig.1. Considering the complicated motion of the bridge, the measurements were taken on two axes of vibration. The sound pressure level contours, for each measuring condition, were drawn on the basis of the readings at 252 points in the front space of the instrument, each measuring condition being associated with: the resting situation, the direction of the axis of the vibrator and frequency. As shown in Fig. 5〜8 for instance, the pattern of the sound pressure level distribution depends very much on the three factors mentioned adove. In the two resting situations of the instrument, other than the traditional one-directly on the floor-, the patterns are very complex, having maxima and minima. These patterns show that the sound fields where the stand was in volved, should be recognized as interferent fields, and not as simple fields of a single progressing wave. In the case where the instrument was placed on the stand without reflector, the results at 250Hz show remarkably the effect of reflection from the floor surface while inserting an angled board in the stand beneath the instrument, results in drastic change of contour patterns. The relative sound pressure level of contour lines is indicated in the figures. Reference values were taken at the nearest measuring points from two vibrating axes separately, in the case where the instrument was placed directly on the floor. The region where the measurement was carried out from might be considered too close to the instrument for the real performance situation. However, this region includes the position where the microphones are placed for recordings or broadcasting and also that of an intimate listener. In order to examine the generalized relative characteristics, the 252 readings of sound pressure level resulting from a certain measuring condition were averaged arithmetically. Taking the situation with the instrument placed directly on the floor as the standard, the change of the value at 250Hz and 500Hz is significant as shown in Fig 10. Looking at these and Fig. 11 which is a similar expression of the results of measurements taken from the position of the head of the musician, it can be clearly seen that the sound reflecting board results in significant change of the acoustical properties of the instrument for listeners but not so much for the musician. 2) The evaluation of the subjective difference. Test sounds were recorded in a recording studio (320m^3); the microphone was located in front of the instrument, 7.7m away from it, since that position had been found to be suitable for our purpose by the results of the preleminary examination. An adequately experienced musician played the instrument in the three different resting situations in as much the same manner as possible. The test sounds played were the following five: Low Arpeggio, Middle Arpeggio, High Arpeggio (2 seconds each), Slow Music (7 seconds), Fast Music (12 seconds). High quality professional equipment was used throughout for sound recording and reproduction. Twelve bipolar rating scales had been prepared on the basis of the results of a preliminary listening test using a group of students other than that involved in the main examination. Twenty-five students of the So -kyoku were taken as subjects and so they would naturally be expected not only to be used to the sound of the instrument but also to be experienced critics of it. In the case of the main examination, out of the twelve scales, six rating scales for the listening test of the sound of the Arpeggio, and four for the segment of music, were selected by each subject as relevant, and so the options were reduced, according to his impression of the characteristics of the test sounds by listening to them several times, before the comparative test began. As a result of this experiment, it can be generally concluded that there is a clearly recognizable contrast in the tone quality of the sound when the instrument is played in the three different situations. The change of tone quality resulting from the change of situation can be expressed as follows. The arrow symbol indicates change in the situation of the instrument and the resulting trend in the subjective judgements. I - POSITION: directly on the floor → on the stand without sound reflecting board SOUND QUALITY: [table] II - POSITION: directly on the floor → on the stand with sound reflecting board SOUND QUALITY: [table] III - POSITION: placed on stand without sound reflecting board → placed on stand with sound reflecting board SOUND QUALITY: [table] Each triangle in Fig. 15 shows the relative difference of the three situations in relation to one particular rating scale of sound characteristics. The length of the sides of the triangles shows the difference between each pair of situations. Investigating the shape of those figures, the characteristics of tone quality for each situation can be explained as follows, [table]
東京芸術大学の論文

箏の立奏台に関する研究 : 反射板取付の効果

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東京芸術大学 | 論文

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