Porous sound-absorbing material has a basic sound absorption characteristics, namely low-frequency sound absorption is poor, a good high-frequency sound absorption. Qualitative characteristics of the absorption frequency in Figure 1. Near the high frequency to a certain value as shown in Figure 1, f0, absorption 
 Coefficient α reaches its maximum, the frequency continues to increase, the absorption coefficient at the high end some fluctuations. The location of the f0, f0 largely wavelength corresponding to 4 times the thickness t when the material thickness 
 Increases, to improve low frequency sound absorption characteristics. Figure 1 is greater than t2 t1, t2 when the same frequency absorption coefficient absorption coefficient is greater than t1. If t2 = 2t1, then the same frequency of the corresponding absorption coefficient 
 Rate of about f2 = f1, that is double the thickness of low frequency sound absorption coefficient of a shift to low frequency octave. But not to have increased thickness to improve the low-frequency absorption coefficient, because 
 Acoustic propagation in the material when the gap in the damping, so that increased thickness to improve the low-frequency sound absorption is limited. Different materials have different effective thickness. Good as glass wool sound-absorbing materials for a class, the general 
 With a thickness of about 5cm, 10cm or more rarely used. And as a class of more micro-fiber dense material, the material gap between fibers is very small, the damping of sound waves is very large, not only the absorption coefficient 
 And the effective thickness is very small. Generally flat-shaped low frequency acoustic absorption material is a universal law of poor performance. An improved method is to block the sound-absorbing materials cut into wedge shapes, 
 Figure 2, when the sound wave propagation to the wedge-like material, from the tip to the base, the ratio of air and material changes gradually, ie, the gradual change in acoustic impedance, sound wave propagation beyond the plate-like material on 
 Effective thickness of the restrictions to the base material, which can improve the low-frequency sound absorption performance. Absorption frequency remains similar to Figure 1 Contact: Xue-Wei Liu welcome cooperation; Phone: Email: 
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