In Diamonds, light that enters gets trapped within due to total internal reflection, defined as: Total internal reflection is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index is lower on the other side of the boundary no light can pass through, so effectively all of the light is reflected. The critical angle is the angle of incidence above which the total internal reflection occurs. Diamonds have one of the highest index of refractions there is at a whopping n = 2.41. I'm curious to know if there is a material or apparatus that can achieve the same effect as a diamond, but for sound waves instead of light.