Prove it to yourself: how loudly we speak is so closely related to the volume of what we hear that we often try to "talk over" background noise without even thinking about it.
Are you seated in a reasonably quiet room? Make sure that your computer has a sound card and your speaker volume is at an audible level (or place your headphones on now).
Begin Audio #1, and while the sound sample is playing, say, "Students, please be seated."
Now - without the audio background - repeat, "Students, please be seated."
Did you feel the difference?