“Mantras without consciousness are said to be mere letters. They yield no result even after a trillion recitations. Kuleshvari, the knots at the heart and throat are pierced, all the limbs are invigorated, tears of joy, goose flesh, bodily ecstasy, and tremulous speech suddenly occur for sure when a mantra endowed with consciousness is uttered even once. Where such signs are seen, the [mantra] is said to be according to tradition.” -Kula-Arnava-Tantra
According to Tantric scriptures, when the central channel is activated through the ascent of prana (life force), followed by the Kundalini serpent power, all kinds of subtle sounds can be heard internally. The body of the Kundalini serpent itself is said to be composed of the 50 Sanskrit letters of the alphabet (Kali also wears 50 skulls).
Naturally, language, sounds and intonation are more than just letters and communication. Where there is activity there is vibration, where is vibration there is sound.
When the Kundalini leaves it’s position at the coccyx bone it gathers the inscribed sounds in the four petals of the Muladhara (root) chakra, ascending and vibrating the letter energies of each subsequent chakra’s lotus, dissolving at the Ajna (third eye) chakra, leading to enlightenment.
A mantra acquires value and potency when empowered by a Tantric adept and transmitted to a disciple.
A mantra should be recited with a steady pace, not too fast not too slow, and there should be careful attention in listening to the intonation of one’s own voice. The intensity of devotion and motivation yield a more likely success in activating the mantra’s power.
Twenty-one, 108 (according to Vedic wisdom the Moon and the Sun’s average distance from the Earth is 108 times their respective diameters) or a 1,008 repetitions of a mantra are considered auspicious. Through longer and more numerous repetitions (preliminary practices) the mantra eventually recites itself spontaneously (ajapa-japa), becoming infused with an intrinsic charge of energy that surges through one’s body and consciousness.