A low voice is about pitch. Men usually have lower voices than women. Some people might use it to mean quietly. I don't.
A small voice - This is not used in my experience.
A quiet voice - This seems like a likely answer. It has a slight difference from "quietly" in that you may be a little shy or ashamed about something is you speak in a quiet voice. You speak "quietly" in a libr
Wow! They convey quite different meanings. It's very difficult to get these connotations just by looking words up in the dictionary. So your help is more than helpful:) I can't thank you enough for your detailed explanations!