Head voice is a musical term related to pitch production by a vocalist. Some vocal experts use the term to mean a specific vocal register or part of the entire vocal range. Other experts use the term to mean the set of pitches that cause vibrations to occur primarily in the bones and structures of the head, specifically the pharynx, oral cavity, and the nasal cavity.
Historically, "head voice" meant the uppermost of three accepted vocal registers: chest, passagio and head. Under this view, the range for each register was clearly defined, with some experts even asserting that all singers switched registers at exactly the same pitches. These experts saw the different registers as founded in different body areas, with all pitches in the head register supposedly generated more from the head. This view largely has fallen out of favor.
As people learned more about how the vocal mechanisms function during vocal production, experts realized that all vocal production is simply the result of laryngeal activity and that the point at which a singer transitions into head voice depends on the amount of intensity or tension in the vocal cords. In other words, only the vocal cords can produce tones. Other areas of the body simply amplify it. Under this new view, talking about head voice as a register is useless, because even though some pitches cause the majority of vibration to occur within the structures of the head, all vocal production begins in the same place. Whether a pitch falls into head voice is simply a matter of whether the pitch can match the resonance frequencies of the structures of the head and cause vibration.
Study of vocal production led to the division of the human voice into as many as seven registers, but only four are widely accepted. In order from lowest to highest, these are the vocal fry, modal, falsetto and whistle registers. Experts defined these registers as they noticed that the vocal cords behaved in very specific ways at specific pitch and intensity levels. Most speech and singing takes place in the modal register.
In the modal register, the entire vocal cord is involved in the sound production, with the glottis opening first at the bottom and then at the top. In the falsetto register, the vocal cords vibrate around the edges primarily, with the rest of the cords being relaxed. Understanding these differences, when a person sings in head voice, they do not lapse into the physiological activity of the falsetto register, although many vocal teachers and students mistakenly use the terms "falsetto" and "head voice" interchangeably. The activity of the cords stays within that of the modal register. Head voice has always implied higher pitches, so a good definition of head voice thus is the upper pitches of the modal register, which the singer produces without strain and feels primarily in the head.