Passive noise reduction decreases the transmission of noise and vibrational energy without altering or changing the noise generating components and mechanisms. The lessening of the transmission of noise and vibrational energy is achieved through the use of noise control materials and parts which provide vibration damping, insulation, or sound absorption.Noise sources radiate sound power and vibrate. The airborne noise propagates to the exterior and causes a particular maximum “A” weighted level to be measured during pass-by tests. Exterior or pass-by noise, and interior or in-cab noise are the two major noise problems for trucks. The major tasks of soundproofing a truck include the definition of treatments for exterior and interior noise and the choice and application of damping insulation and absorption materials in the cabin and engine compartment.