Comparison between ensemble averaged absorption characteristics of materials using an in-situ technique and those of conventional methods

In order to create comfortable indoor sound environment, it is important to comprehend sound absorption characteristics of building materials. These are generally obtained using the reverberation room method and/or the impedance tube method which are standardized by ISO, JIS and so on. However, it is known that the values measured by such conventional methods have uncertainties due to the diffuseness of sound fields and the installation condition of materials to the tube, respectively. On the other hand, the authors have proposed the sound absorption measurement method using ensemble averaging technique, i.e., EA method. The method is a simple and efficient in-situ measurement method of surface normal impedance of materials at random-incidence. However, little has been reported on the relationship between value measured by the EA method and those of the conventional methods. This study is carried out to clarify those relationships. The absorption characteristics for several kinds of materials with different sound absorption performances are measured by the three methods, and the sound absorption coefficient by EA method is compared with those of the reverberation room method and the impedance tube method in the frequency range of 100 Hz to 3150 Hz.