A voice communicates in many more ways than just with the words that are voiced. Each voice has rhythm, there is character and there is quality. I have known many people who were cursed with the wrong voice. Big burley men with high squeaky voices, little guys with a deep baritone and people who are very bright who happen to have an accent or a word usage pattern that that detract from their intelligence.
I spent my youth listening to the radio. The announcers or personalities all had distinctive voices to which my mind would draw a picture of how they looked. Most of the time my mind lead me to believe they were much better looking than they were in reality. Late night radio was populated with soothing voices of friends in the night that you just couldn’t see. These voices kept me awake while I worked nights putting myself through college. Long after that I stayed on as a night owl, and these voices were my companions and probably rounded me out into the calm character I am today.
There are some soothing voices in the musical world as well. I’ve kept a short list in my head and I’ve found Dock Watson, Don Williams, Mel Torme, and Dianna Krawl to be the most soothing in my book.
Oddly Leonard Cohen's voice is soothing to me as well. However if his voice gets any deeper it will only be audible through elephant feet across the plains along with other earthly deep rumbles.