. A text book of physics, for the use of students of science and engineering . ying below Ox, the ratio of theamplitudes, being negative. Sounding-board.—If a stretched string, or a tuning-fork, be setin vibration, the sound from it is very feeble, unless it be attachedto some sounding-board. Thus, if one end of the string be clamped 8 7 6 5 4 3 2 1 0-1-2-3-4-5-6-7Fig. 658. y - / / 1-51 2 0 i 0-5 1 1 ~x Graph of amplitude of forcedvibration. IM FIG. 659.—Sounding-board. in a vice and a weight hang from the other end, very little soundwill be heard when the string is plucked or bowed. If, howev
. A text book of physics, for the use of students of science and engineering . ying below Ox, the ratio of theamplitudes, being negative. Sounding-board.—If a stretched string, or a tuning-fork, be setin vibration, the sound from it is very feeble, unless it be attachedto some sounding-board. Thus, if one end of the string be clamped 8 7 6 5 4 3 2 1 0-1-2-3-4-5-6-7Fig. 658. y - / / 1-51 2 0 i 0-5 1 1 ~x Graph of amplitude of forcedvibration. IM FIG. 659.—Sounding-board. in a vice and a weight hang from the other end, very little soundwill be heard when the string is plucked or bowed. If, however,the string be stretched upon a board and passed over two bridges,A and B (Fig. 659), then, on bowing or plucking it, quite a loudsound will be heard. The string alone is in contact with only asmall quantity of air, so that when it vibrates it sets a smallquantity of air only in vibration. Also, since compression occurs onone side of the string at the same time as rarefaction on the other,interference further reduces the effective sound (p. 707). When, 716 SOUND FIG. -TuniiiK-fork ou soundiug-box. however, the string is stretched upon a board, the string exertsa periodic force upon the bridges A and B, which in turn give thesounding-board upon which they rest a periodic motion. As theboard is in contact with a comparatively large amount of air, owingto its large surface, the energy of the air set in motion in a given time is much greater than if therewere no board. Of course, the vibra-tions of the string die away morerapidly with the sounding-board, asthe energy is then radiated away inthe form of sound waves much morerapidly. The case of the tuning-fork issimilar to that of the string. Ifheld in the hand the sound from thefork is feeble, but if the stem bepressed upon a table or board, thisis set in forced vibration. The vibra-tion is thus communicated to a muchgreater quantity of air than before. Resonators. — Sometimes tuning-forks are mounted upon holl
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