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The Sound of Science - 'Why does sound reflect more in an empty room?'


The Sound of Science - 'Why does sound reflect more in an empty room?'

Welcome to The Sound of Science from WNIJ and NIU STEAM. It’s a weekly series explaining important STEM concepts. Today’s hosts are Jeremy Benson and Newt Likier.

We have a question here from Marsel, who asks “Why does sound reflect more in an empty room?”

Let’s think about a basketball. If we dribble a basketball on a wooden court, we can expect the ball to bounce back up to our hand. The hard surface doesn’t absorb much of the ball’s energy, so it bounces very well. In the same way, harder surfaces like brick walls don’t absorb as much of the sound energy that hits them. The sound waves will reflect off the surface as an echo.

Now imagine trying to dribble that basketball on a sofa. The softer surface will absorb more of the ball’s energy, and it won’t bounce much at all. You might have noticed some of your favorite Youtubers have foam panels hanging on their walls. These acoustic panels work by absorbing sound energy that would otherwise echo off the walls.

In order to best control how sound moves inside a space, sound engineers also have to consider geometry. Going back to our basketball example, if we drop our ball on uneven or rocky ground, it becomes harder to predict exactly where the ball will bounce. If we drop our ball into a series of deep, soft valleys, it becomes much more likely the ball will get trapped and not bounce back at all. This is why those acoustic panels often have angular peaks and valleys to help trap and absorb sound energy.

Using all this knowledge, scientists can even create something called an anechoic chamber. Anechoic chambers can completely absorb all reflected sound, creating an eerily quiet space with no echoes at all. These chambers can be used to test equipment like speakers or headphones, or to conduct other acoustic research like some of the professors here at NIU.

The next time you’re in a public space, like a theater or a restaurant, take a look around and see if you can spot ways the space has been designed to control the reflection of sounds.

That sounds like a pretty good answer to me.

This has been the Sound of Science on WNIJ. Where you learn something new every day.

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