The OM Set of 14 and the Set of 13 are our two complete sets. Both are spirals of fifths, with every neighboring pair of forks tuned in a true fifth—but they are built on different frequency foundations. The Set of 13 begins with the first Schumann resonance and climbs upward; the OM Set of 14 is built around the OM frequency of 136.1 Hz, extending both upward and downward from it. In the INNER SOUND approach, the two sets complement one another: the Set of 13 is understood as working across body, emotion, mind, and spirit, while the OM Set of 14 is often experienced as having more of a physical and emotional character. Practitioners choose which set to work with based on what their clients ask for, and over time many also develop a preference of their own. You can read more about the two sets in our Tuning Fork FAQs, or experience both in the INNER SOUND Tuning Fork Training.