| With the increasingly serious problem of noise pollution, the demand for sound absorption materials and structures are growing, and the requirements of sound absorption, environmental protection, economy and decorative properties of those materials and structures are also becoming higher and higher. In this study, two fold structures, opened and not opened, were used which making from insulation film fold. To improve the sound absorption performance of conventional sound-absorbing structures, the composite sound-absorbing structures, with the properties of simple, efficient, and environmentally, were made by inserting the opened and not opened fold structures into the cavity of conventional structures.According to the index of maximum absorption coefficient, bandwidth of sound absorption and noise reduction coefficient (NRC), the sound absorption performance of single opened fold structure (semifold), not opened fold structure (fold), micro perforated (MPP), perforated panel (PP), slit plate (SP), aluminum foam (AFM) and aluminum fiberboard (AFB) were studied; the sound absorption performance of the composite structures which made by inserting the fold and semifold structures into the cavity of MPP, AFM and AFB were also investigated; the effect of factors on the sound absorption performance of PP-fold and SP-fold structures were researched via Orthogonal Experiments Method (OEM). The main results are concluded as follows: Both single semifold and fold structures had certain sound absorption capability, but the overall sound absorption performance was not well. With the increase of the height of the fold, the bandwidth of sound absorption was broadened and moved to the low-frequency. The NRC values were also increased with the increase of the height of the fold, at the height of 5 cm, both fold and semifold structures showed the maximum NRC values, corresponding to 0.326 and 0.308, respectively. Compared with the fold structure, the semifold structure had a higher maximum absorption coefficient but narrower sound absorption bandwidth.The sound absorption performance of composite structures, which made by combining MPP, AFM and AFB with fold and semifold structures respectively, greatly improved. At the same plate material, the composite structures made by fold structures showed a superior performance on sound absorbing than the semifold structures, which proved by the relatively bigger NRC value and wider bandwidth of sound absorption. The three indexes, maximum absorption coefficient, bandwidth of sound absorption and NRC, were increased with the increasing of height of composite structures. The maximum absorption coefficient of MPP-fold, AFB-fold and AFM-fold were 0.943,0.937 and 0.850 respectively, and the maximum NRC values of these three composite structures were 0.460,0.478 and 0.474 respectively, both the maximum absorption coefficient and maximum NRC values appeared at the cavity height of 5 cm.PP-fold composite structure with excellent acoustic performance can be gained by combining PP with fold structures. The maximum values of NRC, low frequency average absorption coefficient (α12s-400), middle frequency average absorption coefficient (α500-1000) and high frequency average absorption coefficient (α1250-2000) of PP-fold were 0.600,0.349,0.707 and 0.728, respectively. The OEM results showed that the height of fold structures was the significant influence factor affecting the sound absorption performance of PP-fold, and the acoustic performance of the composite structure would be improved with the increase of the height. In addition, the thickness of PP and the interaction factor (H*h) of plant gap were also the significant influence factors affectingα1250-2000SP-fold composite structure with excellent acoustic performance can be gained by combining SP with fold structures. The maximum values of NRC,α125-400,α500-1000,α1250-2000 of SP-fold were 0.634,0.250,0.656 and 0.741, respectively. The OEM results showed that the height of fold structures was the significant influence factor affecting the NRC value,α125-400 andα500-1000 and the acoustic performance of the composite structure would be improved with the increase of the height. However, the height of fold structures only had a certain affect on theα1250-2000 of SP-fold composite structure. |
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