"audible voice" is correct and usable in written English.
You can use it to refer to words that can be heard. For example, "He raised his audible voice and everyone in the room stopped to listen to him."
In a barely audible voice, she forms the word "Yes".
"LORD, forgive my sin," she says in a scarcely audible voice.
Turn the headlights on, I heard her say in a barely audible voice.
All along, Mr. Hammond speaks in a barely audible voice, though he wears a microphone.
"Can you save me from terrorists?" she asked in a barely audible voice.
"You say I did that to you?" he asks in a barely audible voice.
Irene said, "Pleased to meet you," in a sufficiently audible voice, but without expression.
Finally, he said in a barely audible voice, "I am innocent of any wrongdoing".
When asked how he felt, he replied, in a barely audible voice: "Ecstatic.
"I had a very difficult childhood," he said in a weak and sometimes barely audible voice.
I felt I could live," recalled Mr. Yamaoka, who spoke haltingly in a barely audible voice.
