Evaluating Damping Treatments Using Radiated Sound Power Normalized by Input Mechanical Power

The purpose of this paper is to propose a test method for measuring damping performance using radiated sound power measurements. A vehicle subsystem, such as an engine tunnel, is mounted and sealed in a transmission loss window between two reverberation rooms. On the appropriate side of the subsystem, a broadband steady-state structural vibration is injected using a shaker and the input power is measured with an impedance head and accelerometer. The resulting radiated sound power is measured with a rotating microphone in the diffuse sound field on the opposite side of the subsystem. The impedance head, accelerometer, and diffuse field microphone signals are processed with a narrowband FFT analyzer. Noise control treatments are evaluated and compared by normalizing the radiated sound power FFT by the corresponding input structural power FFT. Damping treatments can be installed and characterized quickly and easily allowing for rapid optimization of radiated noise control solutions. A steel engine tunnel from a Class 8 truck was used as the vehicle subsystem for this study.