Regular Article

Optimization of double-layer sound absorber in a broadband frequency range using transfer matrix method and Evolution Strategies algorithm

Department of Marine Technology, Amirkabir University of Technology, Tehran, Iran

^* e-mail: pghadimi@aut.ac.ir

Received: 11 June 2016
Accepted: 10 June 2017

Abstract

Curtailment of the ambient noise level for providing a better living environment is immensely important. Accordingly, acoustic isolation via different combinations of porous materials is the most widely used passive soundproofing system. The present study focuses on the optimization of single and double-layer absorbers in different frequencies. To this end, the transfer matrix and the Evolution Strategy (ES) method are firstly explained. Afterward, the optimization of single and double-layer absorbers is considered for up to 10 parameters (material porosity, air gap, perforated plate characteristics among others) at 350 Hz frequency and has been compared with the results obtained through other methods (Genetic Algorithm among others). It has been illustrated that ES algorithm provides better optimization in this field. Subsequently, since the incident sound in most cases is a correlation of different frequencies, the broadband optimization of the single and double-layer absorbers is considered in three frequency ranges (100–800 Hz, 800–1600 Hz, 1600–3000 Hz), with an increment of 1 Hz, for three different materials (polyester, fiber and foam). After the optimization, the resulting optimum parameters are presented in form of characteristics charts of the optimized materials for different frequency ranges, as a reference for material designers and manufacturers. Also, the absorption coefficient of all optimized cases are calculated and presented in range of 100 Hz to 3 kHz as a reference for the absorber selection for different situations. Finally, by presenting the improvement chart of double layer versus single layer combinations, it has been shown that double layer combination can improve the absorption coefficient of different materials up to 4% in different frequencies depending on the material (4% for polyester and foam for under 800 Hz, 3–4% for polyester and fiber for 800–1600 Hz and 2.6% for foam in 1600–3000 Hz).