How much understanding is there between a barbarian and a cultured man?
There is no understanding whatsoever between a barbarian and a cultured man. The text states that between an uncivilized person and a cultured man like Paul, there is nothing, absolutely nothing. Since neither can understand the other's voice or meaning, no communication or comprehension occurs.
Les explains that the passage deals with communication and understanding. It asks how much understanding will come between a barbarian, an uncivilized person, and a cultured man like Paul. The answer is nothing, absolutely nothing. Les points out that the purpose of sound is to communicate, and God gave us that ability. If someone does not know the meaning of the voice, he is like a barbarian to the speaker and the speaker like a barbarian to him. Les also notes that unless the sound can be reduced to something understandable, it is like beating the air. He says he is not condemning tongues people because the last verse of the chapter does not forbid it, but without interpretation, there is no edification of the whole congregation.
Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me.