Providing an optimal porous absorbent pattern to reduce mid to low-frequency sounds.

Noise is definitely a nuisance to the quality of people's lives and health. In recent decades the public has suffered from industrial and environmental noise and its control has had a desirable impact on people's lives. Though noise cannot be completely eliminated, it can be mitigated to a level that it is less harmful to people's health. One of the ways for obtaining these pleasing environment is to design and use the absorbing sound materials. Fibrous and porous materials are the ordinary absorptive materials that are not good absorbers for low and mid frequency sounds. In this study, we examined the different parameters that affect the quality of absorbers, which could provide the best pattern for mid to low frequencies with the numerical and analytical models. For this purpose, three methods including measurement of absorption coefficient by impedance tube, analytical and numerical methods were used. Accuracy was determined by comparing measurement and two prediction methods. The results showed that the experimental and analytical methods provided by the Delany and Bazely and finite element (COMSOL) modeling have good adaptation. The best thickness of porous sound absorbers for low to mid frequencies f:[80-5000]Hz is about 10 cm with the air flow resistivity of 10,000-30,000 Ns/ m4 .