![]() Instead, acoustic refraction takes other forms, and you may have even experienced it as something like an acoustic mirage. While acoustic lenses certainly do exist , they’re not nearly as ubiquitous as the optical lenses around us. For sound, examples of refraction are a little less obvious. For example, light moves more slowly through water than in air, causing it to abruptly change direction when going from air to water and back again. This is because different materials cause light to move at different speeds. Or a straw in a glass of water appears to be broken or bent when viewed from the side. Again, this effect is quite apparent with light, such as when the lens of a magnifying glass bends light to make an object appear larger. Refraction is when a material bends an incoming wave, causing it to change angles. In addition to reflection, both light and sound can undergo refraction. “If buildings reflected light like they reflect sound, every building would look like this.” These reflections (especially the first ones to reach us) are what give rooms their sonic character, and figure greatly into concert hall acoustics. But because of the speed of sound, rather than experiencing those echoes as distinct repetitions of the sounds we hear, we often experience those reflections as amplification and reverberation, making the sounds louder and causing them to die out more slowly. If buildings reflected light like they do sound, it would be as if every hard surface was a highly polished mirror. We spend our days awash in sound reflections from everything around us, to the point that we don’t even notice them. While a faraway object might allow us to pick out an echo from the original sound, pretty much every solid object generates a sound reflection. Sound reflections are much more common than those clear echoes, though. You may have experienced this with an echo, a reflection of a sound off a distant wall or mountain, loud and clear enough that it sounds like a distant copy of yourself is calling to you. When we look into a mirror we see the world duplicated within the reflection, a copy on the other side of the barrier of glass. Whether it’s our reflection in a bathroom mirror or off of the surface of a still pond, the reflection of light is incredibly common. Reflection is a simple enough concept and one that we experience pretty much every day. This time, we’ll cover reflection and refraction, and learn about the “Principle of least time” that governs things from the physical behavior of light and sound to the instinctual behavior of animals. ![]() Last time, we talked about mode shapes and the blurry line between things that are discrete and distinct and things that are continuous and fluid. Welcome to another installment of The World Through Sound. The World Through Sound: Reflection, Refraction, and the Principle of Least Time
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