Question: Will you please tell me briefly about the soundless sound?Sri Chinmoy: The most significant mantra is AUM, which is called the soundless sound, anahata nada. Anahata means 'that which is not struck'. If I strike something you will hear a sound. But the sound of AUM is created without any collision; therefore, it is called the unstruck sound, the sound that is not made by striking something. Yogis, great spiritual figures and all who are far advanced in the spiritual life hear the soundless sound in the inmost recesses of their hearts.
If you repeat the mantra AUM every day for two hours, three hours, or four hours, you will get the vibration of that sound within your heart. You will not have to strike your heart in order to hear this sound, but by repeating the word AUM outwardly, you get the sound inwardly.
When the soundless sound is vibrating constantly in your heart, your whole body is surcharged with divine knowledge, divine light, divine power. If you practise only that mantra, that is enough to take you to God. The syllable AUM is the most effective mantra. Again, if you want to hear the soundless sound, you can aspire all the time, saying, "O God, descend into me and make me hear the soundless sound." But the easiest and the most effective method is to repeat the mantra itself. AUM is the symbol of God, the Supreme.