How to plan AV for a classroom or training room
A classroom is judged from the back row. If students there cannot read the screen or hear the teacher, the room does not work.
Size the display for the back row
Classrooms are deep. With the back row 28 feet from the screen, text needs a picture about 56 inches tall, which is a 114-inch diagonal. That means a projector, or more than one flat panel.
If lessons include spreadsheets, code or fine diagrams, size for detailed work instead, which calls for a larger picture still.
Projector or flat panel
Flat panels are brighter in a lit room and need no lamp or filter care, but they top out around 98 to 110 inches. Projectors cost less per inch above that.
Pick projector brightness for a lights-on room. An ultra short throw model mounted above the board keeps the teacher's shadow off the picture.
Voice and sound
Ceiling speakers give every row the same level. In rooms deeper than about 25 feet, a microphone for the teacher helps the back rows without raising the volume at the front.
Cable runs from the lectern
The run from the lectern to the display is often 25 to 50 feet, well past the limit for a passive 4K HDMI cable. Plan an active optical cable or an HDBaseT extender from the start.