The Physics of College Tour Guides

So we were touring an unnamed university's engineering department this weekend. It was pretty cool, the vibe was positive, the people were well adjusted and friendly, and all seemed well.

Things took a turn for the dire as we stepped into the acoustics laboratory. Tragically, our tour guide uttered an utterly unforgivable sentence... "If I stood back to back with you inside this acoustically silent room and talked, you couldn't hear me because the sound-proofing is so great!"

My first thought? "That's so cool!!"

My second thought? "Wait... that's completely false, even in the most acoustically silent room around," and here's why....

His premise for the statement was that the walls reflected no sound waves, and thus by standing directly behind someone you couldn't hear them speak. False. If you stand back to back with someone in the middle of a football field and say something, they will hear you immediately. There's nothing for sound waves to reflect off of (anything that might reflect them is far enough away that the time it takes sound to travel there and back would create a noticeable lag), yet one can still hear.

So basically, no, nothing will reflect off of the walls, but sound will still travel throughout the room. This is because, unlike light, sound is not line-of-sight reception dependent. One vibrating air molecule will vibrate all those around it, not just the ones in the direction of projection, and so on.