Generally kirtana is performed with mrdanga and karatalas, but if somebody is expert instrument player, he can be admitted to join Sankirtana.
Letter to Jadurani — New Vrindaban 26 May, 1969.
Performing kirtana and hearing the vibration of the sound Hare Krishna is actually seeing the Supreme Personality of Godhead directly.
Purport on Srimad Bhagavatam 7.4.25-26
When a Vedic mantra is chanted within the mouth so that only the chanter can hear, the chanting is called japa. But when such mantras are chanted loudly, it is called kirtana.
Purport on Srimad Bhagavatam 3.14.32
Devotional service is called kirtana-yajna, and by practicing the sankirtana-yajna, one is very easily elevated to the planet where the Supreme Lord resides.
Purport on Srimad Bhagavatam 4.24.7