I am not a voice scientist, but I am very interested in the subject, and try to find ways to bring scientific knowledge into the teaching studio. What follows is more anecdotal and general than precise and scientific.
The pubertal voice change that the typical boy goes through is well-known. As normal as it is, however, there is a lack of understanding about how to work with these singers during the change. I have written about this before. Today I want to mention a few things about girls’ changes at puberty, which are smaller, but must be understood.
At puberty, a girl’s singing voice may stay at approximately the same pitch range, or it may go lower. Speaking voices almost always descend, but it can be difficult to tell whether that is because of physical or social reasons. The current tendency for girls to speak extremely low, sometimes driving their voices into a fry production, can mask their musical potential until they have actually exercised their chest and head registers and begun to coordinate them with each other.
The bottom of the chest voice and the top of the head voice are NOT indicators of voice type! Most singers can and should be trained to extend both high and low quite far, but where they are most functional for musical purposes is the deciding factor in classifying them.
Before puberty, most girls have a pitch range down to somewhere around A3 (220Hz). The voice is typically small and may be slightly breathy. There are exceptions, of course. At puberty, the speaking voice deepens somewhat, and in the years after puberty the breathiness usually decreases through the teens, yielding more richness and overtones in the sound. We can perceive this as the voice going from sounding like a little girl to that of a young woman.
After puberty, it is often possible for many sopranos to phonate down to F#3, sometimes lower, once they find their chest voice. In functional training, where we want to exercise both chest and head registers to contribute to the overall vocal potential, going all the way to the comfortable extremes of the pitch range is helpful. Mezzos and altos typically can phonate lower than sopranos, to E3 and sometimes even lower.
On the upper end, light sopranos usually have an upper range above D6, but so may some mezzos and altos! In functional training the whole range of motion of the muscles is exercised, so you sometimes get some surprises about so-called “limits”. The very high notes above D6 or so have several names like flute, whistle, flageolet, or M3. Not all singers have this area of pitches available to them. Some deep-voiced young women may not be able to phonate much above the staff. Just work with where the voice can go, and do no harm.
Girls who are shy or not comfortable with all the changes of puberty will sometimes be afraid to “sing out”, and stay with a breathy, small sound until they are more comfortable. In exercising chest with these girls, I’ve found it helpful to take on characters, use speech, and inject humor and experimentation into the process. Girls who are very motivated to sing in some contemporary popular styles are more willing to let chest tones out, but even many of them are inhibited at first.
Often, just acknowledging that girls’ voices change as a normal part of growing up is helpful. Most of them have never heard of a female voice change before.
There are other changes that females go through, such as menopause and pregnancy, that can affect the voice. The general functional principle is that you take the voice where it is, here and now, and work with that. If the voice becomes something new, so be it. If it goes back to where it was, so be that. There is recent and pending research on voice issues of mature women that will be interesting to digest and act upon in the next few years.