1 Corinthians 14:9-11

Darby Translation

⁹ Thus also *ye* with the tongue, unless ye give a distinct speech, how shall it be known what is spoken? for ye will be speaking to the air.

¹⁰ There are, it may be, so many kinds of voices in the world, and none of undistinguishable sound.

¹¹ If therefore I do not know the power of the sound, I shall be to him that speaks a barbarian, and he that speaks a barbarian for me.