639 Hz benefits: the claims about connection

What are the claimed benefits of 639 Hz?

The benefits claimed for 639 Hz are about other people. It is called the frequency of relationships, of connection and communication, and of the heart chakra, and it is said to help people understand each other and get along.

Harmonance's own page names it the same way, connection and communication, and suggests it as a quiet backdrop while you think about someone you would like to understand better. None of these descriptions comes from a measurement. The number came from verse numbers in the Bible, the link to relationships from a hymn syllable, and no study has tested whether the tone changes how people relate to each other.

Where does 639 Hz come from?

639 Hz is one of the six numbers in Healing Codes for the Biological Apocalypse, a 1999 book that began the modern Solfeggio set. Its publisher's press release says the numbers were found in the Book of Numbers, chapter 7, verses 12 to 83, by

reducing the verse numbers to their single digit integers

Numbers 7 lists the gifts that twelve leaders brought on twelve days, six verses to each day from verse 12. The fourth verse of each of the first three days, verses 15, 21 and 27, gives 1 + 5 = 6, 2 + 1 = 3 and 2 + 7 = 9: 639. The same three digits come round every three days, four times in all, which is why the press release calls the six numbers "repeating codes". The 528 Hz guide works through the rule for all six numbers.

The verses themselves say nothing about people getting along. In the King James Version all three read, word for word:

One young bullock, one ram, one lamb of the first year, for a burnt offering

Why is 639 Hz linked with relationships?

639 Hz is linked with relationships through its syllable, FA. The six syllables of the old scale come from a hymn to John the Baptist, Ut queant laxis, which is credited to Paul the Deacon in the late eighth century. Guido of Arezzo used its tune to teach the steps of the scale: each half-line begins one note higher than the last, and its first syllable became that note's name. FA opens the words famuli tuorum, and the line as a whole reads, in the classicist Richard Tarrant's translation:

So that your servants may sound forth the wonders of your deeds with loosened hearts

So in the hymn FA names a step in a scale, not a pitch, and its word means servants. The guide to the Solfeggio frequencies tells the story of the hymn and the whole set.

The meanings came from a dictionary. The 1999 press release says the first syllable "is defined in Webster's Dictionary" and gives its definition, and a tuning fork maker, David Hulse, explained the method in 2006: he looked at "the definitions of each of the original syllables, using hidden entries from Webster’s Dictionary", citing the 1999 book. The use he gives FA is "connecting with spiritual family". By the end of 2002 his site already listed FA, 639 Hz, as "Connecting/Relationships", the meaning the tone carries today.

The likeliest bridge is the Latin. Famulus, a servant, is probably formed from familia, the Latin household with its servants, the word that gave English family. Read through an English dictionary, the servants of the hymn become a family, and a spiritual family becomes relationships. That is our reading of the step: the book's own pages on it were not seen, and no source says it in so many words.

Is 639 Hz the heart chakra frequency?

Only in modern charts, and they do not agree. A 2024 study of young adults states that "the solfeggio frequency of 639 Hz is dedicated to the Heart Chakra", and modern charts colour that centre green, as Harmonance colours 639 Hz. A 2025 chanting study gives "639 Hz for Root and 396 Hz for Heart" in its summary, and later in the same paper pairs the heart, green, with 639 Hz again.

The older texts give the heart centre a sound but no pitch. In Arthur Avalon's 1924 translation, The Serpent Power, the heart lotus, Anahata, sits

in the region of the heart, which is red like a Bandhuka flower

and takes its name from the "sound (Anahata shabda) which comes without the striking of any two things together". The centre is named after an unstruck sound, it has twelve petals, and it is red: the green and the 639 Hz both arrived much later. The guide to chakras and frequencies follows how the modern pairings were made.

What happened when researchers played 639 Hz to people?

Four studies have played 639 Hz to people and could be read in full. All are small, none measured anything about relationships, and between them they point in no single direction.

Four studies of 639 Hz in people

Study	Who and how	At 639 Hz
Kumar, 2022	37 adults online, twelve pure tones for 20 seconds each, rated against each other	Ninth of twelve for calm, about 2.5 out of 10
Rawat, 2024	15 young adults, three weeks of a mantra, the tone and deep breaths	More self-awareness in their answers, the authors say; no comparison group
Presley, 2026	18 adults, six pure tones for 5 minutes each, in rising order	No significant change in skin conductance
Wago, 2026	2 adults, 5 minutes of sound, then the sound with a video	Relaxation 8 and 9 out of 10 for one, 0 and 0 for the other

How it sounded to 37 listeners

In an online test run from the Australian National University, 37 adults heard twelve pure tones for 20 seconds each, the nine Solfeggio tones among them, and rated how happy, sad, calm and angry each sounded, from 1 to 10 (Kumar, Abhayapala and Samarasinghe, 2022). The tones came in rising order, and each was judged against the one before and the one after.

The four ratings crossed between 417 and 440 Hz, a range the authors call neutral. Above it, calm fell and anger rose as the pitch climbed. Read from the paper's graph, 639 Hz scored about 2.5 for calm, ninth of the twelve, and about 7.4 for anger. The test asked how each tone sounded, not how anyone felt, and its order always put higher tones later, so it says little about listening for twenty minutes. It does suggest that many people hear 639 Hz as a bright tone rather than a soothing one.

What the skin did in 18 adults

A university team in the United States played six pure tones, 396 to 852 Hz, to 18 healthy adults aged 17 to 75, five minutes each in rising order, from a speaker about 15 cm away at 75 to 79 dB, and recorded their skin conductance, a sign of arousal (Presley, Stamps and Davis Alexander, 2026). It rose steadily from tone to tone, and the rise was significant only for 741 and 852 Hz, for the six played together and afterwards. At 639 Hz there was no significant change.

Before the session no one described feeling annoyed or tired; afterwards, five of the 18 said they felt "annoyed, tired, and less calm". Because the tones always came in the same order, a slow climb over half an hour cannot be told apart from an effect of the higher tones, and the authors' next step is "randomizing frequencies to account for sequential increases versus exposure".

Two listeners and two opposite answers

A pilot in Japan gave each of five Solfeggio tones to two healthy adults: five minutes of the sound alone, then the sound with a colour video, pink for 639 Hz, while the researchers recorded brainwaves and heart rhythm and asked for a relaxation score out of 10 (Wago, Bando and others, 2026). Everyone knew what they were hearing, and there was no comparison group.

The two people who heard 639 Hz could hardly have answered more differently. The first scored their relaxation 8 out of 10 with the sound alone and 9 with the video, and their eyes-closed alpha brainwaves, which the authors read as a sign of relaxation, rose a little with the sound (8.5 to 9.6) and sharply with the video (10.2 to 24.7). The second scored 0 both times, yet their alpha rose from 34.1 to 60.1 with the sound alone. The body and the answer disagreed, and in a second paper the group writes that the traditional reading of 639 Hz, as a "frequency of harmony and interpersonal connection",

should be regarded as a hypothesis rather than an established neuroscientific fact

Three weeks of a heart chakra programme

A study from Amity University in Lucknow followed 15 young adults aged 18 to 22 through a three-week programme meant to open the heart chakra: a seed mantra before sleep, 639 Hz each morning on waking, and deep breaths while it played (Rawat, Gupta and Pal, 2024). They answered open questions about love, compassion and their feelings before and after, and the authors report more self-awareness at the end. There was no comparison group and no measurement, and the mantra, the breathing and the tone all came together, so the study cannot say what the tone itself did.

What the four add up to

None of the four shows that 639 Hz brings people closer, and none set out to test it. One found no change in the body, one found that listeners heard the tone as less calm than lower ones, one found two people who answered in opposite ways, and one cannot separate the tone from everything around it. A 2026 review of music, healing frequencies and binaural beats after brain injury and stroke reaches the same place for 639, 741 and 852 Hz together: "there is currently little direct empirical evidence supporting these individual frequencies". The US National Center for Complementary and Integrative Health says much the same of music research as a whole: "much of the research on music-based interventions is preliminary".

Does music bring people closer together?

Making music together can, though the studies are about singing, drumming and moving in time with other people, not about listening to a tone. In one study, 96 four-year-olds who sang, danced and played percussion together in a game helped and cooperated more afterwards than children who played the same game without music (Kirschner and Tomasello, 2010). A repeat with 84 children in four kindergartens in Hamburg found no effect, and its authors write that it remains possible "the original effect found in 2010 might be overestimated".

With adults the picture is similar. In three experiments, "people acting in synchrony with others cooperated more in subsequent group economic exercises" (Wiltermuth and Heath, 2009). In new adult education classes followed over seven months, people in singing classes felt close to their class sooner than people in craft or writing classes, and the others caught up by the seventh month: in the authors' words, "singers experienced much faster bonding" (Pearce, Launay and Dunbar, 2015).

So if connection is what you want from 639 Hz, the research points to sharing it. Listen with someone, or hum along: 639 Hz itself is high for most voices, but its octaves at 319.5 and 159.75 Hz are easier to match, and the page's Strings mode plays them.

What does 639 Hz sound like?

639 Hz is a clear, fairly high tone. On a piano tuned to A at 440 Hz it falls between two keys in the octave above middle C: 46 cents above the E flat at 622.25 Hz and 54 cents below the E at 659.26 Hz, where a cent is a hundredth of a semitone (the note frequencies, UNSW Sydney). Halve it again and again for its lower octaves, the same note further down: 319.5, 159.75 and 79.875 Hz.

The 639 Hz page plays it in two ways, and we measured both from the page's own audio files.

The numbers behind the chart

Pitch	Strings off	Strings on
79.875 Hz, three octaves down	none	10.4 dB under the loudest
159.75 Hz, two octaves down	none	2.2 dB under
319.5 Hz, one octave down	none	0.6 dB under
402.9 Hz, a major third above 319.5 Hz	none	the loudest
639 Hz, the tone itself	the loudest	9.7 dB under
1,278 Hz, one octave up	23.1 dB under	more than 24 dB under

Download the measurements (CSV)

With Strings off, the page plays the tone alone: 99.5% of its energy sits at 639 Hz, with two faint overtones above it, at 1,278 Hz, 23.1 dB quieter, and at 1,917 Hz, 34 dB quieter.

With Strings on, the strings play a chord built on 79.875 Hz, three octaves below the tone, and almost all of the sound, 97.8%, lies between 79 and 810 Hz. Only 24% of it falls on 639 Hz and its octaves; most of the rest is the harmony around them, notes a fourth, a fifth or a third above those octaves. The loudest single pitch is 402.9 Hz, a major third above 319.5 Hz, and the exact 639 Hz tone plays underneath, 35.5 dB below the music. The page's name for 639 Hz, harmonising relationships, is a tradition's label; in Strings mode the harmony is literal, other notes sounding with the tone.

Is 639 Hz safe, and how long should you listen?

No study sets a length for 639 Hz: the rating test played it for 20 seconds, the skin and brainwave studies for five minutes, and the heart chakra programme each morning for three weeks. Harmonance's page suggests fifteen to twenty minutes as a calm backdrop, at a low volume, and you can stop whenever it no longer feels comfortable.

Loud listening is the one risk that is well established, and the skin study played its tones at 75 to 79 dB from close range. The US National Center for Complementary and Integrative Health notes that "listening to music at too high a volume can contribute to noise-induced hearing loss", and the World Health Organization's safe listening advice is that "you can safely listen to a sound level of 80dB for up to 40 hours a week", with your device's volume at no more than 60% of maximum.

How do you listen to 639 Hz on Harmonance?

Press play on the 639 Hz page. With Strings off it plays the tone alone; switch Strings on beside the player and the strings carry the chord around it. Nothing plays until you press play, and no account is needed.

Listeners hear it differently, as the two people in Japan did. Under Harmonance's video of 639 Hz harmonics on YouTube, one wrote

this is so good

and another

Didn't vibe right with me ,.....I must need another htz

If it does not suit you, its neighbours in the set are 528 Hz and 741 Hz, the Solfeggio collection plays all nine, and in Harmonance Studio you can set 639 Hz beside other tones and shape your own mix. The Feeling disconnected? page pairs it with the Venus tone, and the Carrying grief? page offers it as quiet company.

For the wider field, what the science of sound healing shows sets out what research on sound and music has and has not found, and the 963 Hz guide follows the same two research groups to the highest tone of the set.

Sources and limits

The history of the number and its meaning rests on the 1999 press release, the King James text, a scholar's translation of the hymn, a dictionary entry and two archived pages from a tuning fork maker, each read in its original or archived form; the step from famuli to family is our reading. The research is four small studies, two of them uncontrolled, and none measured relationships. The measurements of the 639 Hz page are Harmonance's own, made from the page's audio files. The listeners' words are public comments under Harmonance's own video, quoted whole without names.

1. Tetrahedron Publishing (1999), press release for Healing Codes for the Biological Apocalypse, Internet Archive copy: the verse rule and the dictionary.
2. Numbers 7, King James Version (eBible.org): verses 15, 21 and 27.
3. Richard Tarrant, Lyricus vates: musical settings of Horace's Odes (Harvard DASH): the hymn, its translation and Guido's syllables.
4. Wiktionary, familia: the household, famulus and the English family.
5. David Hulse, SomaEnergetics, The Solfeggio Scale Frequencies, Internet Archive copy from 2002: FA, 639 Hz, "Connecting/Relationships".
6. David Hulse, SomaEnergetics, What are the Solfeggio Frequencies, Internet Archive copy from 2006: the meanings from dictionary definitions.
7. Arthur Avalon (1924), The Serpent Power, Internet Archive: the heart centre, Anahata.
8. Rawat, Gupta and Pal (2024), The Heart Chakra as a Gateway to Self-Awareness in Young Adulthood, IJFMR: 15 young adults and three weeks.
9. Malik, Rampal and Malik (2025), chakra meditation and seed mantra chanting and root and heart chakra behaviours in young adults, International Journal of Yogic, Human Movement and Sports Sciences: two pairings for 639 Hz in one paper.
10. Kumar, Abhayapala and Samarasinghe (2022), frequency cues for human emotions, in Acoustics: 37 adults rating twelve pure tones.
11. Presley, Stamps and Davis Alexander (2026), pure tone Solfeggio frequencies and skin conductivity, Journal of Scientific Exploration: 18 adults.
12. Wago, Bando and others (2026), Frequency-related Exploratory Research No. 1: the pilot and its two 639 Hz listeners.
13. Wago, Bando and others (2026), Frequency-related Exploratory Research No. 2: the group's reading of 639 Hz.
14. Whitney and others (2026), music, healing frequencies and binaural beats after brain injury and stroke: a review, Cureus: little direct evidence for 639, 741 and 852 Hz.
15. Kirschner and Tomasello (2010), joint music making and prosocial behaviour in 4-year-old children, Evolution and Human Behavior.
16. Baier, Wöllner and Wolf (2021), musical synchronisation and prosocial behaviour in children: no effects in a controlled field experiment, Frontiers in Psychology: 84 children in Hamburg.
17. Wiltermuth and Heath (2009), synchrony and cooperation, Psychological Science (PubMed).
18. Pearce, Launay and Dunbar (2015), the ice-breaker effect: singing and fast social bonding, Royal Society Open Science.
19. Joe Wolfe, note names, MIDI numbers and frequencies (UNSW Sydney): the piano keys with A at 440 Hz.
20. National Center for Complementary and Integrative Health, music and health: the state of music research, and loud listening.
21. World Health Organization, safe listening: weekly limits and device volume.
22. Listeners' comments under Harmonance's 639 Hz harmonics video on YouTube, quoted without names.