And they're the people most likely to want to hear every word.

184

And you have to visualize it in three dimensions. Because that's the way sound behaves.

164

If we have echoes, those echoes step on top of the spoken word, and then you can't understand it. And if you can't understand the words here, there's no reason for a convention.

127

Concrete is a very hard, dense surface that sound bounces off, almost like a billiard ball would bounce off a hard edge. Or if you think of a sound wave as a wave of water, it hits a wall and splashes back as an echo. Or if you think of a flashlight pointed at a mirror, that light would bounce right off and create a glare -- an echo is like an acoustical glare.

107

Slate's very, very hard. If too much sound from the crowd hits that stage wall, it will bounce back and hit the speaker at the podium from behind as a giant echo, and that could really disturb them as they're delivering a speech.

100