| Noise pollution is considered to be the fourth largest pollution threatening human health.Traditional acoustic materials are mainly used for noise reduction by porous sound absorption or resonance sound absorption.The porous sound absorption mechanism has a significant effect for sound waves on higher frequency.Therefore,the traditional porous sound absorption materials have excellent sound absorption performance at high frequency,but the poor sound absorption at mid-low frequency.Conventional noise reduction panels such as thin plate and perforated plate based on resonance sound absorption mechanism can achieve good sound absorption at mid-low frequency,but their sound absorption frequency band is narrow and only effective for specific frequency noise.In the life scene,due to the barrier effect of the wall,the noise entering the room is mostly mid-low frequency.More importantly,the human ear is most sensitive to noise of 1000～3000 Hz.Therefore,it is of great significance to improve the quality of people’s life to realize the high-efficiency and broadband absorption of mid-low frequency noise.In this study,a fiber-based composite sound absorber with diversified sound absorption mechanisms is constructed based on the porous sound absorption mechanism of the fiber assembly,and combines the resonance sound absorption mechanism and the damping noise reduction mechanism.This enables the lightweight and thin flexible fiber sound absorber to achieve high-efficiency absorption of noise over a wideband frequency.In addition,the noise reduction mechanism of the fiberbased composite sound absorber is explored.(1)Based on the design of the porous structure of the fiber assembly,a dual-gradient noise reduction fiber sound absorber was prepared.The gradient distribution of the acoustic functional filler and the gradient distribution of the pore structure were realized in the fiber assembly.It is found that the fiber sound absorber shows a significant double anisotropic acoustic performance.When the sound wave incident direction is opposite to the distribution gradient direction of the acoustic functional filler,the sound absorption performance is significantly improved,and the sound absorption coefficient can reach up to 0.942,about 2 times of that of the control sample.When the sound wave incident direction is consistent with the distribution gradient direction of the acoustic functional filler,the sound insulation performance improvement is more significant,the sound transmission loss can reach up to 37 d B,and the maximum improvement effect is 30 times that of the control sample.(2)Based on the theory of membrane resonance sound absorption,lightweight flexible membrane composite fiber sound absorber was prepared,and the asymmetric sound absorption effect was found.When the sound wave enters from the membrane surface,the structure produces remarkable membrane resonance sound absorption,and the sound absorption coefficient is increased to 0.995,about 5.6 times that of the control fabric.(3)A perforated membrane composite fiber sound absorber was prepared by introducing the sound absorption theory of perforated resonance structure.The results show that the fiber sound absorber has a significant low frequency effect,the effective sound absorption frequency band moves to the low frequency,the minimum can be1205 Hz,and at the same time,adjusting the perforation structure parameters can achieve high-efficiency absorption of mid-low frequency noise,and the maximum sound absorption effect is increased to 3.5 times of that of the control sample.(4)The acoustic impedance model of the flexible micro-perforated membrane was established by integrating the mechanism of porous sound absorption and resonant sound absorption,and the gradient micro-perforated membrane laminated fiber sound absorber was designed and fabricated.It was found that the sound absorber had excellent broadband sound absorption performance,and its effective sound absorption frequency moved to the low band,up to 350 Hz. |
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