论声压级平均算法

本文阐述了求声压级平均值的几种算法,特别论述了对声压级数据直接进行算术平均的运算方法。  

微光成型法微细光束紫外光源的研制

简要介绍了光成型法的原理以及在微细加工领域应用所需解决的关键问题。着重就选取经济性好的球形高压汞灯作为光源发光体 ,通过对聚光系统结构和聚光能力 ,导光光路的传导方式和光能传递效率以及缩微光路的成像性质的综合分析 ,并结合各级传输的光束特性进行优化设计 ,选取两平凸透镜聚光系统和光纤导光方式 ,并利用显微物镜的微缩特性 ,研制成紫外光光源。该光源可产生直径为数微米的微细光斑 ,现已应用于微细光成型法进行微型结构的成型制造研究  

A Supercoherent State and a New Inhomogeneous Differential Realization of the SPL(2,1) Superalgebra

The supercoherent state of the SPL(2,1) superalgebra is constructed and its properties are discussed in detail. The new inhomogeneous differential realizations of the SPL(2,1) superalgebra are obtained.  

中型多功能体育馆声学设计的探讨

本文从应用角度探讨了中型多功能体育馆声学设计中的一些问题，并提出了一些有用的经验数据和建议。  

Research on the evolution model of an energy supply–demand network

A universal bipartite model is proposed based on an energy supply–demand network. The analytical expression of SPL distribution of the node weight, the “shifting coefficient” α$\alpha$ and the scaling exponent γ$\gamma$ are presented without edge weight growth by using the mean-field theory approach. The numerical results of SPL distribution of the node weight, the “shifting coefficient” α$\alpha$ and the scaling exponent γ$\gamma$ with edge weight growth are also presented. The production’s SPL distribution of the US coal enterprizes from 1991 to 2009 is obtained from the empirical analysis. The numerical results obtained from the model are in good agreement with the empirical results.  

Reduction of motor fan noise using CFD and CAA simulations

Motor fans used for cooling electric motors have long been recognized as one of the major noise sources. Current paper focuses on design of motor fan for electric motors that are used in submarines for pumping sea water. Noise reduction at source is very important and the critical task, for under water applications. An attempt has been made for reduction of motor fan noise by modification of noise sources. For this purpose computational fluid dynamics and computational aeroacoustics code FLUENT package is used to identify the noise sources and to know the overall sound pressure level of motor fan. From these results it is observed that aerodynamic noise is the dominate fan noise source. Aerodynamic noise of motor fan can be reduced by modifying fan geometry. The aerodynamic noise level of motor fan has been reduced by replacing the straight blades with various digits of NACA (National Advisory Committee for Aeronautics) 65 series airfoil sections. From the numerical results it is observed that the minimum sound pressure level for NACA 65-010 is 65.4 dB(A). These numerical results are compared with measurements in a semi-anechoic chamber. It is found that there is good agreement between numerical and experimental results.  

Chinese speech intelligibility at different speech sound pressure levels and signal-to-noise ratios in simulated classrooms

The speech intelligibility in classroom can be influenced by background-noise levels, speech sound pressure level (SSPL), reverberation time and signal-to-noise ratio (SNR). The relationship between SSPL and subjective Chinese Mandarin speech intelligibility and the effect of different SNRs on Chinese Mandarin speech intelligibility in the simulated classroom were investigated through room acoustical simulation, auralisation technique and subjective evaluation. Chinese speech intelligibility test signals recorded in anechoic chamber were convolved with the simulated binaural room impulse responses, and then reproduced through the headphone by different SSPLs and SNRs. The results show that Chinese Mandarin speech intelligibility scores increase with increasing of SSPLs and SNRs within a certain range in simulated classrooms. Chinese Mandarin speech intelligibility scores have no significant difference with SNRs of no less than 15 dBA under the same reverberation time condition.  

On the sound field of a vault with two open ends

The sound field in a vault with two open ends is studied and its sound pressure distribution is compared with that in an enclosure and a long space. The accuracy of estimation on this kind of space by the classic Sabine Formula, the modified Sabine Formula and the ray tracing method are compared through numerical simulations and experiments. It is found that the sound field in this type of non-close space is not uniform, SPL declines faster near the openings, and RT values have a large span when the source is not at the center. Non-exponential decay is also found in this open vault, and the reason and precondition of its occurrence are discussed.  

Effect of listening level and background noise on the subjective decay rate of room impulse responses: Using time-varying loudness to model reverberance

Room impulse responses (RIRs) are used very widely to characterize the acoustic conditions of rooms, such as in the derivation of reverberation time, early decay time and clarity index. This study investigates the subjective decay rate (or reverberance) of RIRs when directly listened to (rather than convolved with a dry signal such as speech or music). Through a subjective experiment, it investigates the effects of gain (or listening level) and background noise level on the reverberance of RIRs that had been measured in three concert auditoria. The task of the experiment was to match the decay rate of RIRs to that of a reference RIR by ear, by adjusting the RIRs’ exponential decay rate. Based on objective loudness modeling, gain should have a positive effect on reverberance, and background noise has a negative effect. This is confirmed in the results of the experiment. Furthermore, the objectively calculated loudness decay function provides an effective predictor of subjective decay rate, which performs better than conventional early decay time or reverberation time for the RIRs tested.  

Statistical comparison of reverberation times measured by the integrated impulse response and interrupted noise methods, computationally simulated with ODEON software, and calculated by Sabine, Eyring and Arau-Puchades’ formulas

This paper evaluates several procedures to determine the reverberation time, RT, in a classroom. These procedures are: (1) measurement by the integrated impulse response method, (2) measurement by the interrupted noise method, (3) computer simulation using ODEON Version 9.0 software, and (4) calculations using the Sabine, Eyring, and Arau-Puchades formulas. The resulting data are analyzed statistically to verify their similarity. No statistical difference was found between the values obtained by the two measuring methods. The computer simulation produced accurate data. The best formula for calculating RT in the classroom in question is Eyring’s formula.