As long as the falsetto is preserved in its pure form with a minimum of coordinate action with the chest register, it will present, in addition to being flexible, the widest possible extremes of intensity. Starting in the lower portion of the pure register (D, E, or F), the tone is at best soft, breathy, and incapable of swelling.
Ascending the scale, the intensity of the pure falsetto register mounts with increasing rapidity until by the time the top line of the treble staff has been reached a full forte has already been attained, after which the volume continues to increase until the very highest tones have been reached.
On all upper tones of the falsetto the singer is usually able to swell and diminish with fluency, but once the lower middle and lower tones have been reached this is no longer possible and the singer must be content to conform to the natural contour of the register outline until such time as the proper conditions have been established for increasing its volume. Once the register has been properly joined this vocal limitation is overcome."