Acoustic analysis of a Light Truck cab in the frequency range of 0 to 140 Hz was performed by utilizing an analytical method combined with experimental data.
The structural and acoustic modes of the cab were determined by utilizing the MSC/NASTRAN dynamic analysis capability. Chassis, powertrain, and suspension components were simulated with the experimental modal data, acquired from dynamic testing of an actual vehicle. Triaxial transfer functions were obtained at all six cab-mount locations due to shaker excitation at the pinion nose and the 4 spindles, as well as neutral engine run-ups.
The overall system model was constructed by combining analytical structural and acoustic modes with the experimental modal data using the modal synthesis technique and an in-house developed computer code called MOTRAN. The acoustic mode shapes, response at critical cab-structure locations, and interior sound level at the driver's ear were obtained.
After the validity of the model was shown, the model was used to improve the acoustic response of the cab structure in terms of noise-related problems such as boom and drone. A new post processing method was developed to identify and determine the effects of "panel deadening" on the acoustic response of the vehicle.
After extensive analytical iterations, an effective set of structural improvements were determined, and the recommended design modifications implemented on the vehicle. Subjective and objective evaluations were conducted to verify that the noise characteristics of the cab structure were indeed improved with the proposed design change.