Anyone who has ever tried to record that first feature-length album in his or her dad’s garage knows that reflecting, suppressing, and otherwise manipulating sound isn’t as simple as it might seems. We’ve got that egg-carton foam that offers some soundproofing, but beyond such muting materials we have few mature technologies that let us control the way sound travels. But Caltech researchers are working to change that via the first tunable, acoustic diode that can be used to let sound flow in one direction only.
Those one-way mirrors made famous by cop dramas aren't actually one-way. They simply play off the differences in light on each side. That is, if the lights were equally as bright behind the mirror as in front, that rattled suspect could see right through to the cops on the other side.
Hong Kong researchers have combined simple latex with some plastic buttons to create metamaterial panels that can stop sound waves very effectively, according to New Scientist. The reflected sound waves include low-frequency bass sounds that typically manage to sneak through the walls.