Talking louder to a person with a hearing loss may not increase understanding. In fact, using a loud voice may be annoying to the listener. It involves exaggerated mouth movements, and may result in the loss of some speech information.
Communication involves active participation by both listener and speaker.
Position yourself to get a full view of the face, not just a profile view. A lot of information can be obtained by looking as well as by listening. The sounds most difficult to hear are the easiest to see. Speechreading classes and videotapes may help to further develop those skills you already have. Consider having your eyes examined.