Internal Noise Reduction of a Road Bus

We are living an ecologic decade. The aspects concerning comfort and safety are emphasized, including also the commercial vehicles. The interaction between mass-machine-environment is very important. The acoustic comfort belongs to this context. This paper presents the acoustic development relative to the internal noise reduction of a road bus. The internal noise of automotive vehicles is composed by two parcels: the structureborne noise, which is characterized by the low frequencies and the airborne noise which arrives at the passenger compartment passing directly through the divisory between passenger compartment and engine compartment; this path is preferred by the high frequencies. In this work we present the technics we have applied to reduce noise coming from both paths. The quantification of the obtained results is elaborated through the measurements of sound pressure levels, specially the weighting curve “A” for the overall noise. In addition we calculate the Articulation Index starting from third octave levels, to quantify the communication/intelligibility inside the vehicle. These objective results are confirmed by subjective evaluations relative to NVH. We make conclusions concerning the efficiency of the acoustic package we have developed, and the possibilities of extending these concepts to other similar vehicles.