Books › On the Function of the Sound-Post and on the Proportional Thickness of the Strings of the Violin, 1883 › scan 1
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On the Function of the Sound-Post and on the Proportional Thickness of the Strings of the Violin, 1883
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1'f' holes. One foot of the bridge rests upon a comparatively firm support, namely, the sound-post, which is a solid rod inserted between the two plates, back and belly, of the instrument. It is only the other leg which agitates the elastic wooden plates, and through them the included mass of air."*
3The experiments† which follow have been made for the purpose of ascertaining whether it be any part of the function of the sound-post to convey vibrations to the back, or whether this post acts solely as a prop supporting the belly, so that its elasticity is not injured by the pressure from the strings, and also, as Daguin states, affords the firm basis which he considers necessary for one foot of the bridge.
5Mr. Hill, and other practical men, maintain that the quality of the wood of which the sound-post is made affects the tone of the violin, as undoubtedly do very minute differences of position. If the quality of the wood is important we must admit that vibrations are conveyed by the post.
7Whether or not the sound-post exercises the function of transmitting vibrations, it is obvious (1) that it performs the important duty of contributing to the support of the belly; (2) that the nodal arrangement of the belly, and also that of the back, are influenced by the pressure of the ends of the post against the upper and lower plates; (3), that Helmholtz is right, at least so far that the leg of the bridge under the 4th or G string has much more power than the other, in setting the belly into vibration.
9The usual way of investigating vibrations by the scattering of sand over the surface of the agitated body is difficult of application to the violin, on account of the curved form of the upper and lower plates. I found a convenient method to be by the use of what I may call a touch-rod. It consists of a small round stick of straight-grained deal a few inches long; the forefinger is placed on one end, and the other end is put lightly in contact with the vibrating surface. The finger soon becomes very sensitive to small differences of agitation transmitted by the rod.
11The experiments were made on a strongly made modern violin, and in some cases repeated on a fine violin by Stradiuarius in the possession of the writer.
13The sand method, and also the touch-rod, showed that the position of maximum vibration of the belly is close to the foot of the bridge under the 4th or G string. The place of least vibration is exactly over the top of the sound-post behind the other foot of the bridge. The back is strongly agitated, the vibrations being least
15* "Sensations of Tone," translated by Ellis, p. 137. In the 4th German edition this passage remains unaltered.
16† I wish to express my indebtedness to Mr. A. J. Ellis, F.R.S., for some suggestions in connexion with these experiments.
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