It seems that l'chatchila one should say berachot out loud to fulfill one's obligation (see for example Shulchan Aruch here). The stipulation of the SA is that if the blessing is inaudible, one is yotzei "as long as the words depart from one's lips". Does that mean sound must come out, or that the lips must move, or other? What ramifications does this have for repeating (or not) a beracha that you said 'inaudibly'?
Furthermore, the Rambam (Hilchot Berachot 1:7) holds that b'diavad, if you don't say it out loud you are yotzei i.e., you say it "in your heart":
כָּל הַבְּרָכוֹת כֻּלָּן צָרִיךְ שֶׁיַּשְׁמִיעַ לְאָזְנוֹ מַה שֶּׁהוּא אוֹמֵר וְאִם לֹא הִשְׁמִיעַ לְאָזְנוֹ יָצָא בֵּין שֶׁהוֹצִיא בִּשְׂפָתָיו בֵּין שֶׁבֵּרֵךְ בְּלִבּוֹ:
A person should recite all the blessings loud enough for him to hear what he is saying. Nevertheless, a person who does not recite a blessing out loud fulfills his obligation, whether he verbalizes the blessing or merely recites it in his heart.
From this Rambam it seems that you would not need to repeat a beracha said "in the heart" (i.e., inaudible, or no lip motion).
- What is the reason for the Rambam allowing (albeit b'diavad) blessings "in the heart"?
- Do any opinions hold that you can say berachot 'in your head' l'chatchila?
Note: Although there are similar questions (here, here, here) elsewhere in MY. Some questions deal with 'how loud'. This question is specific to berachot 'in the heart'. This also addresses the reason behind the Rambam and whether there are opinions that allow this l'chatchila.