Identification of location and strength distribution of extended noise sources is very important in the practical noise control engineering, especially in the viewpoint of dealing with the inherent nature of the noise problem in question. Recently, acoustic array techniques such as the near-field acoustic holography (NAH) method and the inverse frequency response function (IFRF) method have been developed to identify the extended noise sources, but applied mainly for exterior noise problems. The main problem in applying these techniques to interior problems is the reverberation effect due to highly reflective boundary surfaces of the enclosure, thus making the sound field very coherent everywhere inside the enclosure. In this study, experimental works by using the IFRF method are done for investigating the field characteristics and the applicability of the method in the vicinity of resonant frequencies. In order to reduce the reverberation effect, a sound absorptive body is employed within the interior space. Field conditions are checked through various field indicators such as the reactivity index level, the frequency-band coherence, the intensity-energy density ratio and the near-field indicator. A simple rectangular box and 1/2-scaled car model were taken as an example of the study. It is found that IFRF method gives information about the magnitude and phase of noise sources on the boundary, and can be easily applied to the arbitrary shaped spaces. As a result, it is thought that the present method can be applied to the noise source identification for interior spaces and might be useful in the control of various practical noise problems.
