639 Hz is a frequency that is sometimes associated with connection and relationships in some alternative healing practices and spiritual traditions.
According to some sources, 639 Hz is said to be the frequency of the heart chakra, which is an energy center in the body located in the center of the chest that is associated with love, compassion, and connection.
Some proponents of sound healing and meditation suggest that listening to music or tones played at 639 Hz can help to stimulate the heart chakra, promote feelings of love and compassion, enhance relationships with others, and improve communication skills.