In-situ impedance measuring method that uses environmental noise, i.e. EA-Noise method, has been developed by some of the authors recently. In this paper, a room acoustic improvement method that utilizes both the in-situ measurement impedances obtained by the EA-Noise method and the authors' large scale finite element sound field analysis (LsFE-SFA) is proposed, and it is intended to show effectiveness of the improvement method. At first, acoustic impedances of materials in an actual seminar room are measured by the EA-Noise method on four sound source conditions: (a) all windows are closed and supplemental sound source is not used; (b) all windows are opened and supplemental sound source is not used; (c) all windows are opened and a vacuum cleaner is used; (d) all windows are opened and a loud speaker is used. As a result, the use of some supplemental sound source, i.e. sound source condition (c) and (d), gives stable measurement results. Next, some absorption installation patterns to improve room acoustic characteristics are investigated by the LsFE-SFA with the impedances measured by EA-Noise method, and one of the patterns is actually installed in the room. Finally, effects of room acoustic improvement by the absorption installation pattern are measured and compared with those predicted by the analysis.
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