Figure 3 is the test result of the sound absorption coefficient of the double-component sound-absorber material with a thickness of 18mm and a weight of 300g/m2 under different test tube depth (0mm, 3mm, 6mm, 9mm, 13mm).

Figure 3 characteristic curve of sound absorption coefficient under different specimen tube depth

As can be seen from FIG. 3, the results of the curves measured by different specimen tube depths have different characteristicsSex; When the depth of the specimen tube was 0mm, the frequency curve of each point showed a gradual rise. When the depth of the specimen tube was 3mm and 6mm, the test results were parabolic. When the depth of the specimen tube was 9mm and 13mm, the test results were wavy and linear. The highest value appeared in the low frequency band, and the lowest value appeared at 1250Hz ~ 1600Hz. The high frequency band after 2000Hz showed relatively stable values and was not sensitive to the depth of the specimen tube. Therefore, increasing the depth of the specimen tube can significantly increase the low frequency sound absorption coefficient, which is equivalent to increasing the thickness of the sample, but reduces the medium frequency sound absorption coefficient, which has little influence on the high frequency. Therefore, it can be known that the depth of specimen tube has a great influence on the sound absorption coefficient.

FIG. 4 shows the test results of sound insulation performance under different test tube depths (0mm, 20mm, 40mm) with a thickness of 18mm and a gram weight of 300g/m2

FIG. 4 acoustic insulation characteristics at different depths of the specimen tube

As shown in FIG. 4, as the depth of the specimen tube increases, the low-frequency sound insulation performance of the material is little affected, and the regularity of changes of each sound insulation performance curve in the middle frequency band to the high frequency band is weakened, and the fluctuation and fluctuation of the curve is more obvious. In the high frequency stage after 2000Hz, the value of the sound-absorbing system tends to be concentrated, showing a relatively stable value. Therefore, the sound insulation performance is not sensitive to the depth of the specimen tube. The results show that the two-component sound-absorbing cotton has better sound-absorbing and noise-reducing effect.

The amount of space left in the pipe of the specimen has a great influence on the sound absorption performance. Because the space behind the material objectively increases the thickness of the material, which is equivalent to improving the fluffy - effect of the material, the sound absorption performance of the material also changes, especially the sound absorption performance of the low-frequency part. In addition, when sound wave enters the hollow specimen tube, it can stimulate the air of the hollow tube to generate resonance and increase the loss, thus improving the sound absorption effect of the material. This provides a reference for the design and practical application of two-component sound-absorbing cotton materials in vehicle assembly, position layout, etc.