639 Hz frequency
639 Hz carries the syllable FA and is marketed as the relationship tone. It sits a little above D#5.
- SyllableFA
- Nearest noteD#5 +46¢
- Period1.56 ms
- Wavelength in air0.54 m
At 639 Hz the sine is getting piercing. Use a triangle wave in the tone generator for a softer version with the same pitch.
What 639 Hz is claimed to do
- Promoted for harmony in relationships and communication
- Mapped to the heart chakra
- Used in partner or group meditation
What the evidence says
No studies exist. A tone cannot change another person’s behaviour. Shared listening can, however, set a calm tone for a conversation, which is a fair use.
Where the number comes from
The modern solfeggio list traces to Joseph Puleo and Leonard Horowitz in the 1990s, who derived the numbers by digit-reduction of verse numbers in the Book of Numbers. It is not the medieval scale Guido d’Arezzo taught with the hymn “Ut queant laxis”, which named pitches, not fixed frequencies.
639 Hz: common questions
What does 639 Hz do?
It is sold as a tone that improves relationships. There’s no evidence for that; it is a pleasant mid-high tone for meditation.
What note is 639 Hz?
Between D#5 (622.3 Hz) and E5 (659.3 Hz), about 46 cents above D#5.
Can I sleep to 639 Hz?
Most people find higher tones less sleep-friendly. For sleep, a lower tone or brown noise is usually easier to leave on.