On vocalising Mantra's

Each are effective and useful, but different.

On retreats, we teach all of these. We also explain that it is more effective to learn how to use mantras silently.

Vocalizing mantras aloud stimulates physical matter and energy. This can provide healing, stimulation, etc. However, we are easily distracted by physical sensations (sound) and often are focusing on how good we sound, or are distracted by sounds around us, rather than focusing on directing the energy.

Using mantras silently is more effective than aloud, but for some, it is more difficult, because it requires more concentration. It is stated in Hinduism and Buddhism that silent mantras are more effective, because the attention and energy are focused internally, which is ultimately where we need the mantras to take effect anyway: on the consciousness itself, on the chakras, on the mental or astral body, etc. Most of the time we are using mantras to have internal experiences, so it makes sense to relax and still the entire physical body, and be working only silently, internally, so the body can be left behind.

Using mantras with the heart is simply to focus the attention and the energy in your heart, to feel the mantra, to open your emotional center to work with that energy. This is a very powerful technique, but many find it difficult because their hearts are cold, they are too intellectual, etc.