Question: Can we chant 'Aum' inwardly without saying it out loud?Sri Chinmoy: It is quite possible. As a matter of fact, I do it very often. Sometimes when I stand in front of you people, I do not chant the sound 'Aum' aloud, but I produce the sound here, right in my heart, the real home of the soundless sound. Sometimes I can hear the sound louder, even more powerfully perhaps, than the noise of a plane crash!
Sri Chinmoy, Philosophy, religion and yoga, Agni Press, 1980