Description and validation of a muffler insertion loss flow rig

The performance of mufflers and silencers is greatly influenced by flow in many instances. Most labs, however, quantify performance sans flow with the use of an impedance tube using the two-load or two-source method. Measurements with flow are considerably more difficult. In this work, a test fixture capable of measuring insertion loss with flow is described. The flow is generated by an electric blower followed by a silencer to reduce the flow generated noise. Two loudspeakers are mounted downstream of the silencer but upstream of the tested muffler. Initial qualification of the system is detailed by comparing the transmission loss, noise reduction, and insertion loss to predictions using one-dimensional plane wave models.