Abstract:

By using the four-load method, one-port source characteristics can be determined in the duct system. In this study, a modification is made to avoid the instability problems occurring in the conventional four-load method. In the present method, the acoustic power spectra are measured at the inside or outside of the duct varying the acoustic loads, and an error function based on the linear time-invariant source model is obtained. It is numerically shown that the method is less sensitive to input errors compared to the conventional four-load method. The two methods are utilized to obtain the source parameters of a loudspeaker and a centrifugal fan using various types of loads. The estimated impedance values are compared with those obtained from the direct measurement method. As a direct measurement method, the multiple sensor method is adopted using three microphones. It is observed that the conventional four-load method results in large errors, whereas the present method yields far better agreement with the actual source characteristics.