Measurement and Prediction of Sound Absorption of Sound Package Materials in Large and Small Reverberation Chambers

The paper discusses the methodology for measuring the sound absorption of sound package materials in a different sizes of reverberation chambers. The large reverberation chamber is based on test methods and requirements as per ASTM C423 and ISO 354 standards. Both the test standards are similar and recommend a reverberation chamber volume of at least 125 m³ and 200 m³ respectively for sound absorption measurements from 100 Hz to 5000 Hz. The test sample size requirements are from 5.5 to 6.7 m² as per ASTM C423 and 10 to 12 m² as per ISO 354. In the automotive sector passenger car, heavy truck, and commercial vehicle, the parts that are used are much smaller in size than the size prescribed in both the standards. The requirement is to study the critical parameters such as the chamber volume, sample size, reverberation time and cut-off frequency etc. which are affecting the sound absorption property of acoustic material. The melamine foam has been chosen for carrying out the study which is more uniform and homogeneous foam. The sound absorption of melamine foam evaluated in large and small reverberation chamber with different sample sizes. Also the intrinsic parameter of melamine foam evaluated to predict the random incidence sound absorption and study the effect of samples size based on Finite Transfer Matrix Method (FTMM). The predicted results using FTMM technique established good correlation with experimental results. The paper discuss the measurements carried out at different labs with various test conditions such as chamber sizes, sample sizes, cut-off frequency etc. Finally the suggestion has been given to arrive good agreement in sound absorption results when measured in different size of reverberation chambers.