《5-3-4attenuationofcompositeatructuresoutdoordesign.ppt》由会员分享，可在线阅读，更多相关《5-3-4attenuationofcompositeatructuresoutdoordesign.ppt（33页珍藏版）》请在三一文库上搜索。
1、5.3 ATTENUATION OF COMPOSITE STRUCTURES,1. ATTENUATION OF COMPOSITE STRUCTURES,The transmission loss predicted by the mass law for a homogeneous panel can often be increased, for a given surface weight, by a “sandwich“ construction. Typical examples are:,Representative transmission-loss data for com
2、posite structures,urethane foam 聚氨酯泡沫,Composite structures using vinyl and absorption material .,Wood-stud wall,Data for steel-stud walls,2. Transmission Loss of Door and windows constructions,The effective transmission loss of a wall or panel is often determined by the Performance of a door or acce
3、ss panel. In turn, the performance of these structures depends heavily on the effectiveness of seals around the edges. Seals are usually resilient vinyl foam, or rubber constructions that are compressed when the door or panel is closed.,seals around the edges,3. Impact Performance of Floor-Ceiling C
4、onstructions,Typical improvements in STC and IIC for various floor and ceiling treatments,HUD recommendations for STC and IIC values of floors in multifamily housing,5.4 DESIGN OF PARTIAL BARRIERS FOR OUTDOOR ENVIRONMENTS,Sound Barriers Sound barriers can be installed to reduce the sound levels and
5、hide equipment from view. The barrier creates an “acoustic shadow” that reduces sound levels on the opposite side of the source.,Sound Barriers The reduction in sound level, or Insertion Loss, is based on the path length difference. The path length difference equals the path around the barrier minus
6、 direct path from the source to the receiver in feet (or meters).,Scattering and refraction of sound into the shadow zone formed by the barrierthe limiting value of about 24 dB,ft,Nomogram for design of partial barriers,In practice, we focus on the construction of barriers, not only the height! Prac
7、tical constructions, size and space restrictions often limit sound barrier performance to 10 to 15 dB.,Notice !,Partial barriers can be used indoor too.,Example: Reduction methods applied to a machine,Reduction methods applied to a machine,没有隔声措施的压风机,隔声罩设计,将噪声源封闭在一个相对小的空间内，以减少向周围辐射噪声的罩状壳体，称为隔声罩。这是在声源处控制噪声的有效措施。,计算方法,衡量隔声罩的降噪效果，通常用插入损失 来表示。它定义为隔声罩在设置前后同一接收点的声压级之差，即，,隔声罩的插入损失可由下式计算，,为罩内表面的平均吸声系数； 为隔声罩的平均透声系数。,一般情况下， ，即隔声罩的插入损失为正值。,IL,说明当隔声罩的插入损失与其材料平均固有隔声量相等时，由这种材料构成的隔声罩的隔声量达到最大值。,（ 1 ）当平均吸声系数,当隔声罩内的平均吸声系数小到与平均透声系数相等时，隔声罩的插入损失等于零。,（ 2 ）当 时,IL,IL,end,