The Tanpura (also referred to as Tambura) is a musical instrument with an intriguing and also fundamental place in today's Indian Classical music. As you may well know, it is not a lead instrument on which a melody is played. Rather it is used as a background instrument to create a drone accompaniment through the repetitive plucking of four open strings. It is relatively new to Indian Classical music, having reached its modern form sometime around 1700 CE. But it has influenced Indian Classical music quite profoundly, including both the common styles of Hindustani and Carnatic music. 

A Tanpura (see Figure) has a long stem which is attached to a soundboard and a round resonating enclosure. The stem and soundboard are generally made of wood, while the resonator may be made from the shell of a pumpkin or gourd, or from wood. The Tanpura has four strings with their tuning pegs at the top end. They pass over a smooth round bridge and are attached to the base of the instrument. In addition to the tuning pegs at the top, each string has small fine tuning beads below the bridge. Finally, a cotton thread is passed between the strings and their contact point on the bridge. Using the tuning pegs, the fine tuning beads and the position of the thread on the bridge, an expert artist can finely tune the Tanpura to create just the right sound needed for their musical rendition.

The Sound of a String

There has been a lot of research into the sound of the Tanpura, starting from C. V. Raman in 1921 till the present times. Subsequently, there have been a number of works which have investigated the phenomenon of how a Tanpura string vibrates and produces sound. But before we attempt to explain the Tanpura sound, we need to look at a generic string and how it vibrates. Consider a string stretched across two points of contact. If the string is plucked, then how would it vibrate? It turns out that the string vibrates in a combination of the following modes of vibration.

It may look strange but really the string is vibrating in all of those ways at the same time. If you have a look at the vibrating string side on, what you see visually is the string vibrate in a combination of these modes of vibration. Not all of the modes vibrate with the same amount of intensity though. The most fundamental mode of vibration is the one labelled f with the single peak right in the middle. This is the most dominant mode of vibration. The intensity of vibration progressively decreases as you go to higher modes of vibration, 2f, 3f, 4f, etc.

Now each mode corresponds to a different pitch, with the mode 2f at twice the frequency as f, 3f at thrice the frequency as f and so on as the labels indicate. What we hear is the cumulative sound of all of those pitches playing out at different intensities. Since f is the loudest (or most dominant), our ears perceive the overall pitch to be f and the higher modes of vibration lend the string sound its character or what is called the timbre.

These modes of vibration are also referred to as overtones or harmonics. A typical tanpura has four strings tuned as Pa - SA - SA - Sa, where Sa denotes the fundamental, Pa the fifth and SA the octave. Sometimes some of these strings are tuned to different notes based on the Raga that is being sung/played, giving rise to a different set of overtones or harmonics.

A tanpura provides a rich envelope of harmonics as a background drone, against which a Raga is sung/played consonant with the harmonics.

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Excerpts from a more detailed article published at https://puretones.sadharani.com