r male voice:

[Music: F2-F3]

i.e., an octave lower. These are the first eight notes of the alto of
the female voice and of the bass of the male voice. Alto and bass sing
these notes with precisely the same adjustment of the vocal tract. The
vocal cords in this register vibrate along their entire length, the
space between them, also the "cup" and the general adjustment of the
vocal tract, are open. A good soprano can come down into this register
as far as [Music: C4] and a good tenor as far as [Music: C3], and when
these voices come down into this register they too sing with the same
adjustment of the vocal tract as is used for the same tones by alto
and bass. This, therefore, constitutes the lowest register for all
voices--not because it consists of certain notes, but because these
notes require the same general adjustment of the vocal tract for their
production by all voices.

When it comes to the next or middle register:--[Music: F4-F5] for
female voices (and an octave below for male voices), soprano and
tenor sing through this entire register with ease, using a slightly
different adjustment of the vocal tract from that which they employed
when they went down into the lowest register. The ordinary alto stops
at C in this register, as does also the bass at an octave lower. When
they enter it their vocal tract adjusts itself to it and corresponds
with the adjustment employed in it by soprano and tenor. In this
register the vocal cords still vibrate along their entire length,
but as the voice progresses upward, they show a tendency to shorten
the glottic chink, and the cup, as well as the adjustment of the
entire vocal tract, tends to become less open. It is the register
of transition, placed between the lowest and highest, as if to bridge
over the interval.

The highest register: [Music: F5-C6] (an octave lower for male
voice) calls for an extraordinary change in the adjustment of the vocal
tract. The vocal cords are pressed tightly together at the rear and
sometimes both at the rear and front. These portions thus cease to
vibrate. Only the small free parts vibrate and these only at the edges.
As the voice progresses up the scale the stop action ceases, the
elliptical opening and the cup become smaller, and the entire vocal
tract is, comparatively speaking, contracted. This register practically
belongs only to sopranos and tenors. For example, although some
baritones are capable of adjusting their vocal tracts