ACOUSTICAL PROPERTIES OF THE YONGLE BELL

the Yongle Bell is the largest bell in china.Experimenta study on the bell has been carriedout in two aspects:modal analysis and characterstics of bell sound.A method for modal analysisunder transient state is presented in this paper.The lowest natural frequency is 16 Hz.The soundof bell is harmonious.Frequences of some partial tones which are important in sensation are inconformity with the standard pitches.     

古编钟的声学特性

编钟是中国古代的重要乐器。通过对模型编钟振动方式、共振频率和声频谱的测量来分析编钟的声学特性,证实了编钟是发两个基音乐音的乐器,阐明了决定敲钟位置和古人调音方法的声学原理。用FFT做实际和模型编钟声的短时频谱分析,应用了信号处理中线性预测等方法来分析编钟声,实验表明用线性预测法计算基音频率是有足够高的准确度的。     

ACOUSTICAL PROPERTIES OF CMME BELLS

The acoustic characteristics of chime bells have been studied by the measurements of vibrationalmodes and the power spectra of bell sound.Each of the chime bell has two tones depending on thestriking positions on the bell.At the tone frequencies,the modes of vibration are similar,but thepositions of nodal lines are different.The short-time sound spectra of chime bells were measured bythe use of FFT.The sound of chime bell can also be analyzed by the method of linear predictionused in signal processing.     

北京机场周围1984年的飞机噪声

本文介绍了1984年11月对北京机场飞机噪声的测量评价及噪声等值线图.对控制机场噪声提出了一些措施.     

ACOUSTIC ABSORPTION CHARACTERISTICS OF FOAMED ALUMINUM

The acoustic absorption characteristics of foamed aluminum and the effect of its structural parameters on the characteristics have been in vestigated. The results indicate that the acoustic absorption behavior of foamed aluminum has an uncertain relation with its porosity, the effect of pore size is non-monotonous, while the flow resistance, which characterizes the structural coefficients, might be the most important factor. It is also found that the absorption peak is widened and the noise reduction coefficient can be increased through suitable compressive deformation.     

北京市1986年居住环境噪声状况

本文介绍了在1986年对北京规划市区居住环境噪声的测量结果和噪声级的统计分布,叙述了海淀、西城、东城、宣武和崇文等九个行政区和七个不同功能区的噪声概况和全市环境噪声污染图.     

城市居住环境噪声暴露的研究

1986年3月到8月,在北京的规划市区,用噪声自动测量仪器,按每1km~2取一测点的原则,共对353个点的环境噪声进行了24小时的连续测量,得到了各测点每10分钟的L_(eq)值和L_(50)值.在测量的同时进行了社会调查,收集了与声环境有关的资料及其居民对噪声的反应.根据测量和调查所得数据,本文就环境噪声、影响环境噪声的主要因素及居民对噪声反应等问题进行讨论和分析.     

轻结构隔声测量的新方法

本文提出了小试件轻结构隔声测量的一种新方法。这种方法,声源放在一个混响室内,而接收室是一个小的消声箱。详细地描述了测量的装置。测量了几个试件,结果与“质量定律”很好地一致。在需要测量具有高隔声量的小试件时,这个方法更加有用。另外还讨论了装置的限制与精度。 关键词：     

FLEXURAL VIBRATION OF TRUNCATED ELLIPTICAL CONE AND CHINESE CHIME BELLS

In this paper,we consider the Chinese chime bell as a truncated elliptical cone.The flexcuralvibration of an elliptical cone is analysed for the fundamental modes of vibration of chime bells.The approximate expression of frequency for the two tones of a chime bell is: f=K(1/2)(E/3ρ(1-σ~2))t/b~2where t is the bell thickness,b is the long axis of elliptical cone base and factor K is a functionof the bell shape parameters.This expression shows the influence of bell shape and size uponthe frequencies.From the frequency relations of the two fundamental tones we can suggest indetail the method of tuning used in ancient times.As an example,the relations between tonefrequencies and bell size are studied for a group of ancient chime bells.     

椭圆截锥的弯曲振动和编钟

本文将编钟近似为椭圆截锥壳体,分析了椭圆锥的弯曲振动,从而得出编钟隧音和鼓旁音频率的近似表示式。讨论了编钟形状和尺度对频率的影响以及调音步骤等有关编钟的一些基本问题。