Heavy vehicles generate high noise levels that are increasingly put under control limits. Prominent noise generating sites from (a) to (i) in the Figure are the exhaust, tyre tread, air inlet, upper engine belts an drives, base engine, transmission, auxiliary gearboxes, rear axle and air turbulence from the cabin. Resonance from (j) and (k), empty box trays and fuel tanks can magnify the noise generated.
Because of the logarithmic addition of sound intensity, controlling one source may not be sufficient to bring down sufficiently the overall sound pressure level.
The Heavy Vehicle Noise Barrier kit is a set of bolt on noise curtains designed to block the range of dominant frequencies and solve the difficult to control noise frequencies.
The noise barriers are designed to not restrict cooling and not add excessive mass. They are robust and flexible curtain material is protected by steel panels that are functional in themselves in noise suppression.
The barriers for hanging down below the chassis are a combination of acoustic audio perforated plate, an air gap and mass filled vinyl backing a steel plate. They hang down to the lowest level of the fuel tanks in order to control sound wave diffraction by producing Fresnel values as large as possible.
Above the chassis, in the gap below the cabin, folded metal angle backed with mass filled vinyl is used without the perforated plate and air gap.