A measuring method of oblique incidence absorption coefficient for a shallow incidence angle

摘要

An improved TSP (time-stretched pulse) method for measuring an oblique incidenceabsorption coefficient is proposed in this paper. The value of the absorption coefficientobtained by this method is equivalent to the value obtained by the OATSP (optimumAoshima’s time-stretched pulse) method, in which the reflected sound is extracted from thedifference in the pulse arrival time, in high reproducibility and short measuring time. Theproposed method can measure the oblique incidence absorption coefficient for a shallowerangle (larger incident angle) than the OATSP method. With this proposed method the soundthat comes directly from the speaker is measured separately in a free sound field. Therefore,there is no need to separate the arrival time between the direct sound and the reflected soundfrom the surface of the specimen.The validity of this method was ascertained by using results from numerical analysis andexperimental condition, even for incident angles larger than 45 degrees for official Japanesespecimen sizes (4 × 5 m).