孔隙率(Porosity)

卷曲率(Tortuosity)： 结构因子

特点：


纤维直径：1~10 μm 流阻(Flow Resistivity)
举例：吸声材料物理属性和参数
SampleName ImpTubeCorr Porosity AirFlow Tortuosity VCL Viscous Char. Length (mm) TCL Thermal Char. Length (mm) Density (kg/m^3) Youngs (Pa) Poissons SLF Structural Loss Factor Temp Pres Thickness (mm) Slab foam 1 (24 kg/m3, 45 lb/50sinch IFD hardness, 1.3-1.8 air perm in cf/min, fine cells, 150% elasticity as elongation, 117 C glass trans temp by DMA) Viscoelastic foam 10a (1", no skin, 52 kg/m3 density, 23% compression set, 0.11 cf/min air perm, 1.5-2.5 mm cell diameter, 35% ball rebound, -52 C glass trans temp by DMA Viscoelastic foam 10c (0.5", with skin, 52 kg/m3 density, 23% compression set, 0.11 cf/min air perm, 1.5-2.5 mm cell diameter, 35% ball rebound, -52 C glass trans temp by DMA Viscoelastic foam 11 (no skin, 65 kg/m3 density, 30% compression set, 0.25 cf/min air perm, 0.4-1.0 mm cell diameter, 22% ball rebound, -35 C glass trans temp by DMA Viscoelastic foam 12 (with skin, 65 kg/m3 density, 30% compression set, 0.25 cf/min air perm, 0.4-1.0 mm cell diameter, 22% ball rebound, -35 C glass trans temp by DMA Viscoelastic foam 13 (0.5" foam + 0.25" elastomer, 52 kg/m3 density, 23% compression set, 0.11 cf/min air perm, 1.5-2.5 mm cell diameter, 35% ball rebound, -52 C glass trans temp by DMA Molded carpet underlay foam 14 (48 kg/m3, 130 N hardness by IFD @25%, air perm and cell structure TBD, 105% elong elasticity, glass trans temp by DMA TBD) Molded carpet underlay foam 15 (59 kg/m3, hardness TBD, air perm,cell structure, elasticity as elong, glass trans temp by DMA all TBD) Molded HR foam 16 (52 kg/m3, 260-280 N hardness as IFD @ 25%, 4.2 air perm in cf/min, fine cells, 105-115% elasticity as elongation, 130 C glass trans temp by DMA) Molded HR foam 17 (52 kg/m3, 260-280 N hardness as IFD @ 25%, 1.7 air perm in cf/min, normal cells, 105-115% elasticity as elongation, 130 C glass trans temp by DMA) Slab foam 2 (48 kg/m3, 135 lb/50sinch IFD hardness, 1.08 air perm in cf/min, fine cells, 80% elasticity as elongation, 121 C glass trans temp by DMA) Molded HR foam 18 (37 kg/m3, 280-3000 N hardness as IFD @ 25%, 11.7 air perm in cf/min, normal cells, 105-115% elasticity as elongation, 130 C glass trans temp by DMA) LP 1800 Slab foam 3 polyester, 0.5" thick (64 kg/m3, 50 lb/50sinch IFD hardness, 0.37 air perm in cf/min, fine cells, 300% elasticity as elongation, n/a C glass trans temp by DMA)
22
1000
24.06
AM.2/02.12
0.8949507
137797.2
1
502.55
965.47
51.2385
48091
0.34908
0.29925
23.82
978.39
14.65
AM.2/02.13
空气传声
1. 2. 3. 4. 降低声源强度 封堵无用孔洞 阻隔噪声通道 在路径上增加声传 损失STL 5. 在路径上和车内采 用吸声措施
特征：低中频< 400Hz
特征：中高频> 250Hz
第二节

声学包常用计算公式

声传递损失STL与刚度、阻尼、质量的关系 声传损失STL的测试方法 声衰减NR与声传损失STL的互换关系 插入损失IL与声衰减NR和声传损失STL互换 关系 吸声系数α，以及特定结构对α的影响
弯曲振动平面波产生的声辐射概念

超音速弯曲振动平面波 Cw > C 边界y=0,

亚音速弯曲振动平面波 Cw < C

弯曲振动平面波 Cw = C
巧合频率，声辐射最强。
巧合频率（coincidence frequency)
举例：铝材 弹性模量 = 72E9 Pa 板材厚度 = 5 mm 材料密度 = 2.7E3 kg/m3 Poisson’s ration = 0.34 耦合频率 = 2300 Hz
AM.2/02.1
0.9868135
22808.9
1.3333
34.367
290.27
24.76583
228710
0.088191
0.11866
24.64
985.77
25.77
AM.2/02.10
0.964208
93017.93
1
3.5144
1000
48.85099
55706
0.37899
0.3007
C2
12 ∙ρ (1−υ 2 ) E
=2963 Hz
传递损失TL与刚度、阻尼、质量关系
声传损失STL的工程测试方法
STL 声传损失定义式
传递系数
反射 混响室 入射
损失 消声室 传递
插入损失IL
IL – Insertion Loss 插入损失定义式
反射 混响室 入射
损失 传递 消声室
声衰减NR
第三节

声学包 - 主体部件及结构特征
汽车声学包的分布形式 吸声材料关键的物理属性和参数 隔声材料物理特点 隔、吸声材料的多层组合形式
汽车声学包分布
仓盖/机仓吸音、地板阻尼/加强片、顶棚
防火墙 (Firewall)隔/吸声
地板 (Floor pan)
顶棚 (Headliner)隔/吸声
经典噪声控制途径
去除噪声 降低噪声 不产生噪声
源
路径
如果无法去除噪声，设法不让噪声进入
噪声控制 - 优先措施次序
1. 减少或降低噪声源 2. 堵漏 3. 结构设计改造 4. 加强隔、吸声作用
噪声控制 - 路径分类控制策略
结构传声
1. 减小作用力输入 2. 增加底盘连接点 原点动刚度 3. 减小平板件频率 响应介入 4. 在路径上减小底 盘悬置造成的贡 献
30
吸声材料
31
浸透树脂层
32
吸声材料关键的物理属性和参数

多孔吸声材料


纤维声学材料 - 物理特性

玻璃纤维 (glass) 矿物纤维 (mineral) 有机纤维 (organic) 木块、片 (wood) 椰子纤维 (coco) 棉纺织毡(felts) 开口泡沫海绵 (foam) 孔洞一般小于1mm 称为“有损均匀介质”
侧窗玻璃巧合频率
The coincident frequency of an infinite panel of tempered glass (钢化玻璃):
fc = 2π∙h �
C – sound speed of the fluid medium=344 m/sec h - the thickness = 4mm - 材料密度 = 2.44E3 （kg/m3） - 材料泊桑比 = 0.23 E – 材料杨氏模量 = 70E9 Pa