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This work is based on a current project related to auxiliary power unit (APU) exhaust silencing technology development, specifically an active exhaust noise cancellation technology. The overriding technical challenge is identified as development of a frequency and amplitude controllable noise source that can survive in a hot and corrosive exhaust environment. Installation of an APU enables vehicle platforms to turn off the main engine and still utilize auxiliary equipment that requires electrical power. An APU with a small engine potentially consumes much less fuel than a main engine at low power levels. However, past APU integrations have resulted in unacceptable noise levels, often times louder than the main engine at the equivalent operating point. Exhaust tones created by combustion pose a unique challenge to external acoustic reduction because they generally occur at low frequency, often less than 100 Hz.

Noise generated by tracked vehicles is influenced by dynamic forces generated during suspension and track interaction. The forces cause the suspension components on the exterior of the vehicle, such as road wheels and drive sprockets, to ring at resonant frequencies. A portion of the interaction forces propagate through the suspension and into the vehicle chassis, where they radiate both exterior and interior noise from vehicle panels. This paper demonstrates these phenomena using an example based on a hypothetical tracked vehicle. The results show that staggering the phase between the excitation forces generated by the track and suspension has a significant effect on the exterior acoustic levels and radiation patterns. The interior acoustic levels can also be reduced significantly.