The two mouths or apertures of the drum are covered with a goatskin and laced to each other with leather straps around the circumference of the drum. These straps are put into a state of high tension to stretch out the circular membranes on either side of the hull, allowing them to resonate when struck. These two membranes are dissimilar in width to allow for the production of both bass and treble sounds from the same drum.
The bass aperture is known as the thoppi or eda bhaaga and the smaller aperture is known as the valanthalai or bala bhaaga. The smaller membrane, when struck, produces higher pitched sounds with a metallic timbre. The wider aperture produces lower pitched sounds. The goat skin covering the smaller aperture is anointed in the center with a black disk made of rice flour, ferric oxide powder and starch. This black tuning paste is known as the satham or karanai and gives the Mridhangam its distinct metallic timbre.
The combination of two inhomogeneous circular membranes allows for the production of unique and distinct harmonics. Pioneering work on the mathematics of these harmonics was done by Nobel Prize–winning physicist C. V. Raman
Immediately prior to use in a performance, the leather covering the wider aperture is made moist and a spot of paste made from semolina (rawa) and water is applied to the center, which lowers the pitch of the left membrane and gives it a very powerful resonating bass sound. Nowadays, rubber gum is also used to loosen the membrane helping in creating the bass sound, and its advantage is that unlike semolina, it will not stick on hands. The artist tunes the instrument by varying the tension in the leather straps spanning the hull of the instrument. This is achieved by placing the Mridhangam upright with its larger side facing down, and then striking the tension-bearing straps located along of circumference of the right membrane with a heavy object (such as a stone). A wooden peg is sometimes placed between the stone and the Mridhangam during the tuning procedure to ensure that the force is exerted at precisely the point where it is needed. Striking the periphery of the right membrane in the direction toward the hull raises the pitch, while striking the periphery from the opposite side (away from the hull) lowers the pitch. The pitch must be uniform and balanced at all points along the circumference of the valanthalai for the sound to resonate perfectly. The pitch can be balanced with the aid of a pitch pipe or a tambura. The larger membrane can also be tuned in a similar manner, though it is not done as frequently. Note that since the leather straps are interwoven between both the smaller and larger aperture, adjusting the tension on one side often can affect the tension on the other.
The Mridhangam is played resting it parallel to the floor. A right-handed Mridhangam artist plays the smaller membrane with their right hand and the larger membrane with the left hand.
The Mridhangam rests upon the right foot and ankle, the right leg being slightly extended, while the left leg is bent and rests against the hull of the drum and against the torso of the artist. For a left-handed percussionist, the legs and hands are switched.
There have recently been reports of altered gait and in balance in those that play the Mridhangam for extended periods of time (more than several hours a day). This is likely due to the strength balance developed between the two sides of the upper body within the muscles of the abdomen, thorax, back and upper limbs. The issues are also caused by the asymmetrical leg positions at the hip and the torso often leaning over to the dominant side to view the head of the drum more easily. This can result in difficulty in walking and running efficiently therefore may affect the artists' ability to play sport in the future. It is not known whether all round strength training or playing the drum with the contra lateral side of the body may prevent or alleviate these problems. Therefore, it is strongly advised to notify minors and their parents of issues associated with the drum.
