The mridangam is the classical double sided drum of South India and is used as an accompaniment for vocal, instrumental and dance performances. The term mridangam is derived from the sanskrit words "Mrid Ang" which literally means "Clay-Body," indicating that it was originally made of clay. The present day mridangam is made of a single block of wood. It is made either of Jackwood or Redwood. Jackwood has more fibrous structure than the other types of wood.The packing of the fibres is also very high.The pores present in jackwood is less when compared to others. The pore size and distribution of the material can be inversely proportional to the modulus of the wood.the density of jackwood is also less when compared to other woods. V = E/P where V=velocity of sound, E=modulus, P=density Therefore the velocity of sound will be more when the pore size and distribution and density is less. In some cases the core of the coconut or palm tree is also used. It is a barrel-shaped double-headed drum, the right head being smaller than the left. The two heads are made of layers of skin. The heads are stretched by leather straps which run along the sides of the body. The pitch is adjusted by moving small wooden cylindrical pieces of wood between the wooden shell and the leather straps. The right head is made of three concentric layers of skin. The innermost layer is not visible. The outer ring is called the Meetu thol and the inner ring is called the Chapu thol. The inner ring is made of sheepskin and the outer skin is made of calf-hide. At the center of the right head is a permanent spot of black paste. This spot, called the Soru, is a mixture of boiled rice, manganese and iron filings. This black spot is responsible for the special tone of the mridangam allowing emission of harmonics. Different harmonics of the head are produced by various finger combinations. The left head, known as the 'Toppi' is made of only two layers; the inner one is made of sheepskin and the outer one is made of buffalo hide. Before playing the mridangam, a thick paste made of semolina (sooji) and water is applied to the center of this head. This is done to lower the pitch and produce a bass sound on the left head. This paste is scraped off after the performance. The right head is tuned to the Tonic. On the rims of the two heads there are spaces for the leather braces to pass through. A small, smooth stone and a small stick (wooden) are used to vary the pitch of the heads by upward or downward strokes on the rims. The pitch of the mridangam varies according to its size. The larger the mridangam, the lower the pitch and vice versa. The walls of the instrument are 2/3 centimeters thick and give it stability in the low frequencies. Mridangam uses a single resonator. Therefore the tension of the left and right sides of mridangam are inseperable unlike the Tabla where the tension of the left and right sides are seperate because of the use of two resonators. Mridangam's single resonator also produces an acoustic coupling between the two heads.  There is a hole in this outer covering which exposes the main membrane below. This annular membrane is much more prominent in the mridangam than in the tabla. Pieces of straw are placed between the main membrane and the annular membrane radically between the two skins. This actually increases the dampening and acts as a snare.