Case History: Noise control in a light armored vehicle

Sound pressure levels were measured in a light armored vehicle to identify the dominant sources of noise and to develop corrective noise control treatments that would significantly reduce the overall A-weighted sound pressure levels, yet have as little effect on vehicle operation as possible, and be easy, quick, and cost-effective to implement. The A-weighted sound pressure levels from the evaporator fans in the vehicle?s two air conditioning systems were found to be up to 20 dB higher than the levels from the next most dominant source. Quiet replacement evaporator fans were installed in the vehicle. The airborne noise transmission paths from the evaporator fans to the crew locations were controlled with a lined plenum attenuator and ventilation duct silencing treatments. These simple, cost effective treatments reduced the interior A-weighted sound pressure levels from 110 dB to 92 dB and had no effect on vehicle operation.