A teacher’s voice can generally be heard just fine at almost any point in the classroom. The problem lies in providing adequate intelligibility. Audibility is essentially static, meaning that once you set the volume, it won’t vary significantly as you move about the room. It is measurable and predictable. However, intelligibility is dynamic. Teachers move around the room, and may turn to face the interactive whiteboard, for example, reducing visual cues. Student-generated noise levels change dramatically in an active classroom. Other factors impacting speech intelligibility include projector noise, HVAC noise, and traffic noise. These and more are pervasive in modern classrooms.