Is a man's divorce valid if he uttered it in clear words, but doubts whether he made himself heard or not?

Scholars differed regarding the occurrence of divorce when someone pronounces it secretly without hearing himself. The Hanafis and Shafi'is held that it does not occur unless he makes himself hear it. The Hanbalis, however, held that it occurs merely by uttering it or moving the tongue with it, even if he does not hear himself. However, it might be argued that its occurrence is conditioned upon making himself hear it. And whoever doubts whether he made himself hear the pronouncement of divorce, his divorce does not occur, because the default is the continuation of the marriage.