To activate the root chakra and the perineum, the Indian mantra LAM is commonly used. In China, the mantra BIN or BING is also used for this area. Another option is the mantra PAI, which has a broader effect, extending from the lower torso downward through the legs.
The mantra KU can also be used to stimulate the root chakra and the perineum. When this sound is used, the energy tends to move upward, which means it also partially affects the genital area, the abdomen, and the parts of the legs closest to these chakras. The effects of this mantra are therefore less focused on a single point and more distributed across a wider area.
The Mystery of Numbers, Luck, Worlds and Planets 