The Physics of Veena
The veena is an instrument of great antiquity It commands peculiar veneration and distinction among all our musical instruments. It is a string instrument plucked like the Harp and the Guitar. Though deficient in volume its sound has a captivating tonal quality. No other instrument can approach it in its ability to produce tones which are both rapid and grace fill. Its frets are no impediment to eliciting grace notes of infinite variety. Time was when the Veena served as an accompaniment for vocal music in concerts. One will never get tired of bearing Thanam ” for any number of hours on this instrument. It is to this instrument that our Carnatic system of music owes a great deal for settling some of its problems. -In spite of its merits, however, it is lacking in acoustic output.
Stringed instruments depend on their soundboards for their intensity. it is obvious that very little sound will be heard from strings rigidly supported in the Veena.
The air is not compressed before an advancing string and rarefied behind a retreating string but to a great extent slips round from front to back of the string. Hence the strings are fixed on a soundboard to which their vibrations are communicated and as the board has a large surface it is able to pass on its vibrations to the air. We should not merely be interested in mere vibrations which the string executes but also in the vibrations which the string forces the sound-board to execute. A double duty is thus thrown on the sound-board of not only reinforcing the string vibrations but also improving them. The design of soundboards for various stringed instruments is a very complex problem. The precise dimensions of the mechanical -details of the string, bridge, sound-board etc. which would secure the desired quality of tone are still settled only on an empirical basis. For this, we owe much to the refined taste and the accumulated experience of those concerned in the making of the instruments.
The function of increasing the sound output in the vina is delegated to the large pear-shaped bowl and its associated parts. The bowl is hollowed out of one piece usually of jack-wood or rose-wood. In European stringed instruments much thinner wood like the Maple or Sycamore is used. which accounts for better reinforcement of the sound. Tanjore, Trivandrum, Mysore, and Miraj are some of the chief centers where these instruments are made. In the northern instrument, a hollow gourd resonator is used in the place of the wooden bowl.
The bridge is placed in the center of the bowl and elaborate precautions are taken to fix it. The upper metal surface is made curved. In addition to this main bridge, there is a side-bridge in the form of an arc of brass attached to it. Many small holes are bored in the bowl near the bridge which establishes communication between the air outside and inside for purposes of better transmission. The body of the instrument is also made of the same kind of wood as the belly and is hollowed out thin. This part is known as ” Dandi “. The body terminates in the neck which is usually curved downward into some weird figure. Into the body just near the neck is fixed a hollow gourd on the underside which forms a kind of rest ‘and also helps the bowl in the reinforcement of the sound. The deficiency in the volume of sound, to a large extent, should be attributed to the massive structure of the belly, body etc. It is possible to increase the output by cutting down the ornamental decorations and using still thinner wood in the construction of the bowl.
There are seven strings of which four passes over the frets and the other three are stretched at the side of the fingerboard. The first four strings constitute the main playing strings while the latter is played only to mark the time. As has been pointed out earlier the method of excitement is by plucking, that is, by drawing the tense string out of its position of equilibrium and suddenly letting it go. This is done either by the finger or with a wire plectrum. Just before being let go the string is displaced such that the two portions of the string make an angle at the plucked point. On being released the string goes through a series of evolutions. Stroboscopic examination reveals that two disturbances travel from the plucked point in opposite directions along the String; they are reflected at the ends and again meet. These evolutions go on continually until the motion dies out.
Figure showing the different stages of vibration of a plucked string.
Six different stages in half a vibration are represented in the figure; which shows on the left side the individual disturbances and the resultant motion of the string in each case on the right side, this curve when analyzed is found to contain a large number of harmonies subject to certain limitations. The initial curve is not so sharply bent as shown in the figure owing to the width of the finger and this affects the production of higher harmonics. The stiffness of the string, damping due to internal friction and movement of the points of support are some other factors which further affect the waveform and hence the quality of the sound it emits.
The fingerboard in this instrument requires special mention. It contains a number of frets made of either brass or silver secured to two ledges, running along each side of the stem of the instrument. These ledges are made of some kind of wax which can be melted by heat so that the position of the frets can be altered if necessary. There are twelve frets to the octave and this shows that Equal Temperament* has been in vogue among us for a very long time. Because of the frets, it is easy to get proficiency sooner in Veena than in other stringed instruments. Tempered intonation never the less, suffers from a serious drawback. Though the most important intervals the fourth and the fifth are not affected appreciably in the Equal Temperament system, the purity of other intervals is sacrificed for purposes of convenient playing. Our system of music depends solely on the purity of intervals. One may wonder how Equal Temperament in the Veena can suit our Carnatic Music. But the purity of tones is maintained by skillful playing. Slight alterations of pressure upon the frets enable one to secure this. The performer is able to produce graces of all kinds in this instrument in a remarkable manner by means of these frets.
Sir C. V. Raman has investigated the acoustic properties of the “Tambura” and the Veena and he has shown how the form of the bridge in each case accounts for the tonal quality of these instruments. He has attempted to give an explanation of the rich overtones of the Tambura when a silken thread of suitable thickness known as ” Jeevala ” is slipped between each string and the bridge below it. He points out, that by the insertion of this thread a finely adjustable grazing contact of string and bridge is secured. In the Veena, he has found that the curvature of the upper surface of the bridge ensures the string always leaving the bridge at a tangent. He has also found that the “Young Helmholtz law” is not obeyed in both cases. According to the law if a string is plucked at a point of division the harmonics having a node at the point of excitation should be entirely absent. He has not found this to be the case in these instruments.