Development of thin sound absorber by parameter optimization of multilayer compressed porous metal with rear cavity

Improving and Optimizing Sound Absorption Performance of Polyurethane Foam by Prepositive Microperforated Polymethyl Methacrylate Panel

“…According to the Johnson-Champoux-Allard model [15][16][17], calculation of sound absorption coefficient α p f of the polyurethane foam was obtained by the Equation (1). For the convenience of following the calculation of the sound absorption coefficients for the composite structures, the transfer matrix method was utilized in this research [21][22][23], and that for the polyurethane foam T p f was calculated by Equation (2). In the Equation (1), Re( ) and Im( ) represented the real part and imaginary part of one complex number respectively; ρ 0 was the density of the air with the room temperature and atmospheric pressure, 1.21 kg/m 3 ; c 0 was the acoustic velocity in the air with the room temperature and atmospheric pressure, 340 m/s; T p f 11 and T p f 21 were the two components of transfer matrix T p f for the polyurethane foam.…”

“…It was well known that the microperforated panel could achieve an outstanding low-frequency sound performance [18][19][20]. Thus, in order to improve low-frequency sound absorption properties of the polyurethane foam, a prepositive microperforated polymethyl methacrylate panel was fixed in front, which formed the composite sound-absorbing structure, and its sound absorption coefficient could be calculated through the transfer matrix method [21][22][23].…”

“…According to the derived transfer matrix T p f of the polyurethane foam in Equation (2) and the calculated transfer matrix T mpma of the microperforated polymethyl methacrylate panel in Equation (8), total transfer matrix T cs of the composite structure was obtained based on the transfer matrix method [21][22][23], as shown in Equation (16). Moreover, similar to the calculation of sound absorption coefficient α p f of the polyurethane foam through Equation (1), theoretical sound absorption coefficient α cs of the composite structure could be calculated by Equation (17).…”

“…When the incident sounds wave reached the composite sound-absorbing structure, some of them were absorbed and the others were reflected. Through detecting the sound pressures of the incident sound wave and those of the reflected sound wave at the two microphones in Figure 3, the sound absorption coefficient could be calculated based on the standing wave tube method [22]. By this method, sound absorption characteristics of the composite sound absorbing structures were simulated in this study.…”

“…Therefore, improving and optimizing sound absorption performance of the polyurethane foam by prepositive microperforated polymethyl methacrylate panel was conducted in this study. The sound absorption mechanism of the polyurethane foam and that of the composite sound absorbing structure were investigated according to their structures, and their theoretical sound absorption models were constructed based on the Johnson-Champoux-Allard model [15][16][17] and Maa's theory [18][19][20] by the transfer matrix method [21][22][23]. Afterwards, identification of acoustic characteristic parameters of the polyurethane foam and optimization of structural parameter of the composite structure were realized through the cuckoo search algorithm [24][25][26][27].…”