Plural layers of different materials, e.g. sandwiches

Full Title

Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general > Methods or devices for protecting against, or for damping, noise or other acoustic waves in general (G10K11/36 takes precedence) > Selection of materials > Plural layers of different materials, e.g. sandwiches