Sound insulation

Low frequencies, such as engine and road noise, travel as mechanical vibrations through panels. Heavy, visco-elastic anti-drumming sheets add mass to doors, floor, roof and boot and tackle the vibration source itself: resonating body panels and rattling interior parts fall silent. Full coverage is not needed; from about 60% coverage the result is already optimal.

Higher frequencies spread as airborne vibrations and reflect between surfaces. Flexible acoustic foam catches those waves and prevents echo within the space; it also insulates heat, is oil-resistant and gives off no toxic substances. Without the anti-drumming layer the foam would pass the vibrations on, without foam sound waves keep reflecting: the combination makes the difference. How that works out in practice is in the project reports of the Karmann Ghia coupé and the Volkswagen T2B, and in the ultimate guide to sound and vibration damping.