In the video, Carla Mathis makes the observation (I am paraphrasing here) that if a woman has a very sweet presentation and a powerful voice, her appearance has not prepared those with whom she is interacting for what comes out of her.
IMO, the principle carries over from vocal qualities to the content of what is spoken. If you wish to be outspoken, best not dress as a pushover. Shop The Wedding Suite at NORDSTROM for Mother of the Bride dresses. Free shipping and returns on every order.
For my own application, I am just beginning to think on this subject. After all, it is really hard to even know what your own voice sounds like. One thing I do know: my voice is fairly loud and carries well. Do not put me backstage!