Examination of the performance of anechoic chambers and reverberation rooms at low frequencies

Determination of sound power level of the noise source is based on sound pressure and sound intensity measurements. ISO 3740 series standards are used in that purpose. Measurements are performed in anechoic chamber or hemi-anechoic chamber satisfying the free field condition and reverberation room obeying the free diffusivity condition. The lower frequency (cut-off frequency) for the measurement is directly related to the physical structure of the rooms. The inverse square law is examined in determining the cut-off frequency for anechoic and hemi-anechoic chambers. For reverberation rooms, on the other hand, diffusivity control that is the adjacent band value difference, standard deviation and reverberation time measurements are performed. Sound pressure level measurements of a sound source can be performed in a verified anechoic, hemi-anechoic and a reverberation rooms. In addition, absorption coefficient measurements can also be performed in the reverberation rooms. The aim of this thesis is to examine the performances of TUBITAK UME anechoic chamber built according to ISO 3745 standard and TUB¨ ˙ITAK UME reverberation room built according to ISO 3741 standard below their cut-off frequencies. Concurrently, the other aim of thesis is to compare the measurement surfaces describes in ISO 3744 and ISO 3746 standards for the anechoic chamber based on the sound power level, the level of uncertainty contribution due to the measurement surface, the level of uncertainty contribution due to the number of microphones and directivity indices.