There are two types of musical pillars, the tapping pillars (which produce sounds by tapping) and blowing pillars (which generate sound by blowing air in holes).
Experts further classify these pillars into,
Shruti pillars, which when tapped with fingers produce the basic notes of the swaras (sa, re, ga,
ma, pa, dha, ni) .
Gana pillars, which on tapping sound bell like notes that make classical ragas.
Laya pillars, which produce a taal (beats) when tapped.
Some musical pillars not only produce sounds but also cause adjacent pillars to vibrate in resonance to produce harmonics and create musical effects.
While the pillars at Nellaiappar are a combination of shruti, gana and laya types, those at Vittala temple are tapping pillar type. When tapped, some of the pillars produce sounds of Saptaswara (seven notes) and some others of instruments like Panchatala (five tones), Jaltarang (water instrument), Tabla, Veena, Mridanga, Ghatam, Damaru, Ghanta (bell), Shankha (conch-shell)…you name it.