中科院声学所声础试题.doc

2006声学基础 一、名词解释： 受迫振动：系统遭周期性的外力持续作用下发生的振动。 变量器： 反射系数： 偶极子： 群速度：波包的传播速度 可听域：人类能够听到的不同的频率对应的声压的范围 凋落波 声阻抗： 互易原理： 品质因数： 二、振动系统的固有频率为，加一木块后变为，求系统质量。 解： 三、初始时对该系统加一力，放开后，固有频率为，振动模式 解：列出振动方程（设位移，位移） 令，代入上述方程 取， 振动模式 四、弦振动的基频能量和振幅 解：设弦长为l，线密度为，弦张力为T，且两端固定 则基频角频率，波数 振幅为 五、 ，，， 整理 六、脉动球源的声压级、声功率 解：脉动球源的声波方程 则p的一般解为 上式的第一项代表向外辐射 取 七、二列同向运动的波p1 p2 求能量密度、平均声能密度、平均声功率。 解： 设 八：解利用多普勒频移 中心频率 带宽 九：亥姆霍兹共鸣器定义及共振频率的推导 定义：由面积为S的截面长为的短管容积为的腔体组成的最基本的最简单的声学系统； 且满足：1共鸣器的线度远远小于波长，即、、 2短管的体积远远小于腔体的容积，即 3腔体内媒介压缩和膨胀时，腔壁是刚性的，不会把腔内的媒介的疏密过程传递出去。 共振频率的推导 设短管中媒介的质量，管壁对媒介的阻尼系数是，媒质的密度是 设短管中媒质位移为时，腔内压强由变为 得又 所以 短管中的空气柱运动方程：设外界的声压为 得： office, branch offices (jurisdiction), risk management, marketing management sector through supervision and inspection found problems, should be assigned the investigators are corrected in a timely manner. 27th the fifth chapter penalty under any of the following acts, then the relevant provisions to punish the investigators, according to the Bank. To constitute a crime shall be investigated for criminal responsibility: (A) on the business that are not involved in the investigation, issued a survey. (B) customer credit information are not thorough verification. (Iii) to participate in credit customer survey is not in place, customers and data is incomplete, untrue; he knows bear a counterfeited clients issuing credit. (D) does not provide for due diligence of credit business, pre-loan investigation form, concealing facts or providing false information or should be found in a normal investigation failed to discover the risk factors, lead to the review and approval policy errors, loan risk. (Five) on loan guarantees of survey not in place, not by provides on arrived, and pledge real for field verification, and assessment, and identification and registration, not according to provides on gua