Shiva is often described as cosmic dancer and a great musician. Shiva’s Tandavam is the cosmic dance and his Damaru (a small hourglass shape drum) represent the cosmic sound.
It is said in Shiva Mahapurana that the sounds from the damaru beats the the rhythm of the cosmic vibrations and the energy is activated by the divine Mother or Shakti.
The sound from damaru often is interpreted as the Pranavam and represent the Shabda Brahman. Pranavam or OM is supposed to the precursor to all human languages.
There’s a very beautiful strotam which mimics the sound produced by damaru called Shiva Tandava Strotam by creating a rolling effect. The first couplet is :
जटाटवीगलज्जलप्रवाहपावितस्थले
गलेऽवलम्ब्य लम्बितां भुजङ्गतुङ्गमालिकाम् |
डमड्डमड्डमड्डमन्निनादवड्डमर्वयं
चकार चण्डताण्डवं तनोतु नः शिवः शिवम् ||१||Jatatavee gala jwalapravaha pavitha sthale
Galae..valambya lambitaam bhujanga tunga malikaam
Damad damad damad damanninaadavaddamavaryam
Chakara chandatandavam tanotu naha shivaha shivam.
Damaru is a symbol of infinity (the endless time). It represents that the universe is expanding and collapsing. from where it is expanding , it is collapsing there only. its an endless process. Damru creates cosmic rhythm and influences the movement of energy in the universe.
Various legends associated with it:
Damaru is often attributed to the Shiva’s famous dancing posture—the Nataraja. It is believed by many that the damaru produced the first sound also known as ‘nada’ in the universe. It was born in the void and Shiva danced to the rhythm of damaru, which led to the creation of this universe.
Another legend has it that the top of the damaru symbolizes male creativity of procreation (the Lingam), and the downward representation stands for female creativity of procreation (the Yoni).
Also, many say that the sound produced by beating the damaru was passed onto lord Ganesha, who added more sound and thus—music was born. Some even suggest that it stands for words of the Vedas.