The statistical energy analysis (SEA) is an effective method to predict noise and vibration in the high-frequency band. To predict vibration and noise accurately by using SEA, it is important to estimate parameters called loss factors and modal density. The power injection method (PIM) is an effective experimental method to estimate SEA parameters accurately. In this experimental method it is necessary to take a lot of vibration measurement points because the number of measurement point influences the estimated result using PIM. However, there is no concrete guideline concerning the number of measurement points. In addition, it is necessary to measure the vibration in all subsystems to estimate parameters when the structure is changed. In this paper, we verified the influence of the number of measurement points on the analytical result. Furthermore, as an example of structural modification, we estimated the loss factors of a structure when attached with damping material using the experimental result of a single subsystem. As a result, we can present the concrete guideline concerning decision of the number of measurement point and it is possible to omit the process of estimating the loss factors after a structural modification using the proposed technique in the study.
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