Construction of small twin reverberation chamber for measurement of sound transmission loss

Acoustics has become fundamental in daily life of human beings. There is increasing in demand for ambient noise control. Hence, there is lot of research marketed in producing good sound absorbing materials meeting to the needs. But, the testing setup for acoustic material property determination is distantly located and costlier in several instances. There is great deal of adequacy to build testing chambers with less space and cost. The present work is intended to build a low cost reverberation chamber for measurement of sound transmission loss coefficient (STC). It consists of two 5 m3 small chambers with base and ceiling in pentagonal shape and inclined to each other. All the walls of both the chambers are constructed in such a way that no two walls are parallel to each other and fully reflective. This is to ensure complete sound diffusivity inside both the chambers. The corners of the chambers are sealed with acoustic sealant and wall panels are separated using neoprene rubber sheets to avoid any air leaks. The chambers are isolated from the ground using nylon wheels to avoid ground vibration transmissions. The chambers are made up of teak wood frames and are treated with glass wool of density 50kg/m and 50 mm thick and covered with plywood sheets which acts like walls. The outer layer of the plywood sheet is covered with fully reflective acrylic sheet. In order to ensure the correctness of measurements as per ASTM E90, Sound diffusivity measurement, Reverberation time measurement as per ASTM C423, Field transmission loss measurement as per ASTM E336 and flanking transmission loss measurement are performed. Measurements made using the twin reverberation chamber adhere to ISO 10140-2:2010 and ISO 101420-4:2010. Samples of size 2' x 2' for various thickness can be tested using the chambers. From the microphones data and using Sabine's equation the sound absorption coefficient is determined. The sound transmission loss coefficient is determined as per ASTM E90 procedure. The results from the constructed reverberation chamber are verified with standard samples.