The design and evaluation of a semi-anechoic engine test room

A low-cost hemi-anechoic laboratory for study of diesel engine emissions has been constructed. The laboratory has been equipped for research in acoustics as well as on exhaust emissions. The facilities for acoustic research are described. A low-budget wall absorber with durable, inexpensive and easily exchangeable wedges has been designed. Various ways of evaluating the acoustic properties of hemi-anechoic rooms are investigated. Finally, measurements are presented that show sound level decay with distance from a source and the standard deviation for sound level when the source and microphone are rotated in a so-called carousel measurement. For sound level decay measurements a special extremely low loudspeaker must be used to avoid interfering floor reflections. Carousel measurements give good results even for a standard loudspeaker. Our carousel measurements show that the absorbers are as appropriate as other more expensive absorbers for measurements up to 2 m from a sound source.