Materials used for manipulating sound include metamaterials such as engineered composites and layered structures that have specific mechanical and acoustic properties. These materials can be designed to interact with sound waves in specific ways, allowing them to be used to control the speed and direction of sound.

Materials that can slow down sound include:

 * Soft materials such as rubber and foam, which have a low density and can absorb sound energy

 * Porous materials such as ceramics, which have small voids that can trap sound waves

 * Metamaterials with a negative refractive index, which cause sound waves to refract in the opposite direction of normal materials

Materials that can speed up sound include:

 * Hard materials such as metal, which have a high density and conduct sound waves efficiently

 * Metamaterials with a positive refractive index, which cause sound waves to refract in the same direction as normal materials
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