Unless you’re creating a stand-alone executable, your PowerPoint slides exist to supplement your presentation. You’re not there as an accessory to your slides. You must be both visible and audible to your audience.
In a small conference room, seating up to 10 people, you can talk at the volume and pace that you use in normal speech. You can also use the same gestures and movement that you use in face-to-face conversation. However, as your audience gets larger, your personal projection must also get bigger.
If you’re not wearing a mic, it’s obvious that you must speak louder in larger venues. But even if you have a sound system, you must also slow your speech down slightly and speak more deliberately. When you’re speaking with people up close, they don’t have to listen to every syllable spoken perfectly. They can fill in the blanks by relying on your facial expressions and non-verbal cues to understand what you’re saying. When someone is sitting in the back row of a large meeting room, your visual cues shrink to invisibility. So they must focus more on your voice, which they can understand only if you speak slowly and precisely.
Your gestures must also grow with the size of the room. In a conference room, the audience can see you emphasize the letter “o” with your thumb and forefinger. A larger meeting room requires that you use both hands for the same symbol. In an auditorium, you need to use both arms for the gesture to be visible.
The only way to know if your professional PowerPoint presentation is comprehensible to someone in the back is to have a colleague sit there as you go through a test run. If he can’t hear or see what you’re communicating, make your voice and actions bigger.