Photo from https://www.bustle.com/articles/149928-the-evolution-of-androgynous-fashion-throughout-the-20th-century-photos

Transgender people are, naturally, concerned either about how feminine or masculine their voices sound. An interesting cultural phenomenon has occurred in western society that actually has a positive influence on how transgender voices are perceived. Basically, the pitch range of ciswomen has lowered over the past several decades, as women become more competitive in the workplace. See https://www.bbc.com/worklife/article/20180612-the-reasons-why-womens-voices-are-deeper-today

This lowering of average speaking pitch brings the gender-neutral pitch range more easily within reach for transwomen. The Cismale speaking pitch range is 100-140 Hz. The Cisgender neutral range is 145-175 Hz. An excerpt from the website from University of Iowa Voice-Academy reads, There probably is more overlap between female and male voice pitches than you thought: males often speak at 65 to 260 Hertz, while females speak in the 100 to 525 Hz range. Thus, a voice of 100 to 260 Hz is just as "masculine" as it is "feminine."

In addition to Margaret Thatcher, consider some famous women with infamously low speaking voices:

Nina Simone (singer)
Toni Braxton (singer)
Marlene Dietrich (actress)
Brett Butler (American actress)
Geena Davis (American Actress)
Candice Bergen (American model and actress)
Lauren Bacall (American actress)
Pink (American singer)
Jazmine Sullivan (singer)

Interestingly, with the exception of Marlene Dietrich, all these women are American, suggesting the possibility of a cultural influence on pitch range of speaking voices. I shall be exploring this possibility in future posts.