Swaram means note and Mandal means group it means that the Swarmandal indicates a large number of notes which can be produced by it. It is used in Hindustani vocal music.
The instrument is tuned to produce a particular Raaga and to create a sound space during a break for taking a breath. It is used by classical singers.
Swaramandal is a stringed instrument having 21 to 36 strings which are fixed to a wooden box. There is no standard tune so you may repeat a particular Raaga.
A lead vocalist plays the Sawarmandal. The individual raga is sung. At schools of the Hindustani music, the Swarmandal is taught to play.
Some points to be noted about mandal is that there are no particular standard number of strings and there is no standard size of for mandal so everyone plays from different keys. The rags may differ from each other.