PURPOSE: To measure acoustic characteristics in a frequency range close to the frequency of a noise that a real car generates by changing shapes and kinds of exciting materials inserted into a two layer tube when measuring the maximum value of a noise generated by the rotation of the two layer tube.
CONSTITUTION: Plural exciting materials 30 are inserted into the two layer tube 10 constituting by welding internal and external tubes 15 and 11 at a weld zone 19 with an interposing material 13 placed in between, and the two layer tube 10 is rotated by a rotating machine. When the rotating speed is increased gradually, the noise level rises, but when the exciting materials 30 such as steel balls and steel rods start revolving by sticking to the internal wall of the tube by centrifugal force, the noise level drops abruptly. The influence of the shape of a welding bead 19 disappears at the rotating speed where the noise level is maximum, and almost absolute acoustic characteristics are evaluated. Further, the shapes and kinds of the exciting materials 30 are changed to obtain characteristic curves A, B and C, but the frequency where the noise level has its peak is selected to evaluate the acoustic characteristics corresponding to a real car test.
ZAMA YOSHIMASA
MATSUO SHIGEMATSU
MURO YUUKICHI
