However as knowledge of human physiology has increased over the past two hundred years, so has the understanding of the physical process of singing and vocal production. As a result, many vocal pedagogists have redefined or even abandoned the use of the term head voice. In particular, the use of the term head register has become controversial since vocal registration is more commonly seen today as a product of laryngeal function. For this reason, many vocal pedagogists argue that it is meaningless to speak of registers being produced in the head. The vibratory sensations which are felt in the head are resonance phenomena and should be described in terms related to vocal resonance, not to registers. These vocal pedagogists prefer the term "head voice" over the term "head register". These vocal pedagogists also hold that many of the problems which people identify as register problems are really problems of resonance adjustment. This helps to explain the controversy over this terminology. Also, the term head register is not used within speech pathology and is not one of the four main vocal registers identified by speech pathologists. The following is an overview of the two predominant views on head voice within vocal pedagogy.
In Clippinger's 1917 book, it is stated that male and females switch registers at the same absolute pitches. Clippinger also states that at about E flat or E above middle C the tenor passes from what is usually called open to covered tone, but which might better be called from chest to head voice. At the same absolute pitches the alto or soprano passes from the chest to the middle register. According to Clippinger there is every reason to believe that the change in the mechanism for male voices into head register is the same as that which occurs in the female voice as it goes into the middle register at the same pitches.
The contemporary vocal pedagogy instructor Bill Martin seconds the view that the change from chest voice to head voice occurs at around E4 in all voices, including the bass, but Martin states in the coloratura soprano it is more likely to occur at F4. A recent book by a former teacher at Oberlin College Conservatory of Music and a vocal pedagogy teacher, Richard Miller; states that in the "tenore lyrico" the higher part of the singing voice above the secondo passaggio at G4 extending upwards is referred to as "full voice in head," or voce piena in testa, effectively stating the head register begins at G4 in the "tenore lyrico," not at E4.According to Singing For Dummies, the bass changes from chest voice into middle voice around A3 or A3 below Middle C and changes into his head voice around D4 or C4 above Middle C.
According to Martin, in the head register that is above the chest register some of the bottom end leaves the voice, but it's still a voice capable of much power.
According to Clippinger, often explanations for the physiological mechanisms behind the head voice alter from voice teacher to voice teacher. This is because, according to Clippinger: "In discussing the head voice it is the purpose to avoid as much as possible the mechanical construction of the instrument".
However, not all vocal pedagogists agree with this view. In 1993 Thomas Appell published the book Can You Sing a HIGH C Without Straining? which refuted the theory that all singers switch registers at the same absolute pitch. Appell defined chest voice as resonance below the vocal folds and head voice as resonance above the vocal folds. He also recorded examples of male and female singers changing from chest voice to head voice at different pitches in an attempt to prove that the transition pitch is a function of the intensity of the vocal tone and is not absolute. At higher vocal cord tension (intensity of singing) Appell shows that the pitch at which a singer transitions from chest to head voice will be higher. At lower vocal cord tension (intensity of singing) Appell shows that the pitch at which a singer transitions from chest to head voice will be lower.