Experimental Investigation of Sound Power Radiation From Partly Open Enclosure With Numerous Interior Objects

Paper in proceeding, 2007

The radiated sound power from an engine of a passenger car is highly dependent on the acoustical properties of the engine bay. The engine bay is a densely packed and partly open enclose where standard room acoustics models do not directly apply. It has a complex geometry of numerous accessory parts, cables, pipes, screens, and absorbers that all together affect the wave field and the radiated sound power. Radiated sound power from a simplified hardware model has been measured for various configurations of interior objects. The measurements have been preformed in an anechoic environment using a reciprocal technique where source and receiver positions are interchanged. The results show a clear tendency with higher reduction of the radiated sound power at higher frequencies as the number of objects is increased. There is a reduction of about 10 dB at higher frequencies when 10% of the empty volume is filled with objects. Screens partly covering openings are needed in the modal range to get a significant reduction. Differences in sound radiation between specific source positions show clear variations. Models combining deterministic and statistical approaches are needed to cover the local behaviour in a wide frequency range.