Improvements to the Johnson–Allard model for rigid-framed fibrous materials

详细信息    查看全文

• 作者：Naoki Kino ; Takayasu Ueno
• 关键词：Flow resistivity ; Tortuosity ; Viscous characteristic length ; Thermal characteristic length
• 刊名：Applied Acoustics
• 出版年：2007
• 出版时间：November-December 2007
• 年：2007
• 卷：68
• 期：11-12
• 页码：1468-1484
• 全文大小：1706 K

文摘

Measurements of the surface impedance and the physical parameters of seven glass wool samples and six polyester fibre samples with flow resistivities between 4100 and 69,900 Pa s m⁻² have been made. Comparisons of measured absorption coefficients and those predicted from the Johnson–Allard formulae using the measured and deduced physical parameters show discrepancies that exceed 20 % for some samples and frequencies. By modifying the Johnson–Allard formula for effective density and by introducing a correction factor that is a function of flow resistivity based on data fitting, it has been found possible to improve the predictions. However, it has also been found that a similar modification of the formula for bulk modulus is necessary to reduce the discrepancies with data to below 5 % in the frequency range between 800 Hz and 5 kHz.