The Solfeggio Frequencies, as they are commonly understood in alternative and New Age healing circles, are a set of specific frequencies (174 Hz, 285 Hz, 396 Hz, 417 Hz, 528 Hz, 639 Hz, 741 Hz, 852 Hz, and 963 Hz) said to have various healing and transformative effects. However, these specific frequencies and their purported benefits do not have a historical basis in traditional music theory.
The original Solfeggio scale does have historical roots in music theory. It was developed by Guido of Arezzo, an 11th-century Benedictine monk, as a teaching tool for singers to learn melodies and intervals. This system became the basis for the “solmization” system, which is a method of teaching sight-singing where each note of the music is performed with a specific syllable called a “solfege” syllable (do, re, mi, fa, sol, la, ti, do).
The solmization system Guido developed was hexatonic (six-note), as opposed to the heptatonic (seven-note) scales most common in Western music today. His original Solfeggio system used the syllables Ut, Re, Mi, Fa, Sol, and La. The “Ut” was later replaced by “Do,” and “Si” (later changed to “Ti” in English-speaking countries) was added to complete the diatonic scale we know today as “Do, Re, Mi, Fa, Sol, La, Ti, Do.”
However, the specific frequencies now called the Solfeggio Frequencies (396 Hz, 417 Hz, etc.) do not correspond to these original Solfeggio notes, nor do they align with the equally-tempered scale used in most modern Western music. Instead, they seem to be based on a numerological system and the concept of “vibrational healing,” which is not recognized by mainstream music theory or science.
In summary, while the term “Solfeggio” does have historical significance in music theory, the modern concept of Solfeggio Frequencies is largely unrelated to traditional music theory.