The definition of a solid that can't transmit sound or has no effect on sound waves is an "acoustic insulator" or "soundproof material."
An acoustic insulator refers to a material or substance that restricts or prevents the transmission of sound waves. It absorbs or reflects sound energy, minimizing its propagation through the material. Acoustic insulators are commonly used in various applications such as soundproofing rooms, buildings, or machinery to reduce unwanted noise.
The effectiveness of an acoustic insulator is measured by its sound transmission class (STC) rating. Higher STC ratings indicate better sound insulation properties, indicating that the material is more effective at blocking or attenuating sound waves.
Examples of materials that can act as acoustic insulators include dense and heavy substances like concrete, brick, mass-loaded vinyl, specialized soundproofing foams, and insulation materials with high sound absorption coefficients. These materials work by absorbing sound energy or reflecting it back, reducing the sound transmission through the solid and providing soundproofing capabilities.