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Exhaust noise is a major contributor to the radiated noise level of a vehicle, especially at idle. The radiated noise level has to meet a certain criteria based on regulation and consumer demand. In many cases, the problem appears after the vehicle is manufactured and the tailpipe noise measurement is performed indicating a high noise level that needs to be reduced. This paper describes one of those cases where the radiated noise level of a certain passenger car at idle was required to be reduced by 6 dB(A). The exhaust system consists of one main muffler and one auxiliary muffler. A 1D two-port model of the exhaust system including the two mufflers was built using commercial software. This model was validated against the measurement of the two-port matrix of both mufflers. The model was then used together with tailpipe noise measurements to estimate the characteristics of the source strength and impedance.

Flow-generated noise has recently received a lot of attention within the process of designing exhaust and intake systems. Flow-generated noise can limit the amount of sound reduction a muffler can introduce inside ducts. This is more important in the modern system design where mufflers are compact and the flow speeds become higher in different sections inside the muffler. In this paper, three measurement techniques are used to measure the flow-generated noise from a duct element. The first is based on calculating the sound power levels inside a reverberation room according to ISO 3741. The radiated noise is measured from the muffler body as a source of noise, then from the tail pipe as an active one-port source. The second is based on sound power measurements inside the ducts using the active two-port theory. The third is measuring the sound pressure radiation inside an anechoic room.