斜置微穿孔板结构声学特性计算与试验研究

采用声电类比法计算斜置微穿孔板结构吸声性能存在误差.运用阻抗转移法计算斜置结构的吸声系数,用假想平面将斜置微穿孔板结构离散为若干个等宽定空腔的吸声单元,建立简化模型,采用阻抗转移计算每个吸声单元的吸声系数,综合各单元吸声系数,获得整个结构的吸声系数.设计相应的实验比较计算结果表明,采用阻抗转移法计算结果与实验结果吻合良好,声电类比法计算结果偏离实验结果较大.声电类比法采用集中参数分析,需将空腔声阻抗进行近似,造成误差;阻抗转移法不存在这一误差,计算更合理和准确.     

胶粘剂在扬声器中的应用

介绍了应用在扬声器中的不同部位胶粘剂特性以及在扬声器中的特殊应用,提出胶粘剂对改善扬声器音质的重要作用,分析了不同特性的胶粘剂在扬声器不同部位的应用对音质产生的不同影响。通过常规的频响曲线对比、音质对比评价,总结出不同特性的胶粘剂在满足可靠性前提下,可利用其特性来改善扬声器的音质。     

使用EASE软件中一些误区的讨论(待续)

在厅堂扩声系统工程设计中,大多采用声学模拟软件EASE进行室内声环境设置和扬声器布置,进而对工程完成后的室内一些声学参量做出预测,用于厅堂扩声系统工程投标中。然而这里最重要的一点就是要正确使用EASE软件。有鉴于此,就需要对使用EASE软件中存在的一些误区进行深入讨论。这些误区涉及正版EASE软件的版本配置,涉及适用房间的大小,涉及到吸声材料数据库和扬声器数据库等诸多方面。只有走出这些误区才能正确把握EASE的使用,使该软件更好地服务于厅堂声学设计。     

Isentropic compressibilities of the mixture chlorobenzene + n-hexane + (n-heptane or n-octane) at 298.15 K

In this work, the applicability of the free length and the collision factor theories (FLT and CFT, respectively) to predict multicomponent changes of isentropic compressibilities is analysed and compared. To this end, appropiate expansions for ternary mixtures were derived from the original works, and then applied to a mixture containing unlike compounds in terms of functional molecular groups. Experimental data of excess molar volumes from open literature and new experimental isentropic compressibilities of the mixture chlorobenzene?+?n-hexane?+?(n-heptane or n-octane) were used to compute the parameters. A good accuracy was obtained when ternary prediction is attempted in this partially soluble mixture at different temperatures by the collision factor theory. These results show the versatility of this model for estimation in complex multicomponent mixtures with phases splitting.     

Design of electrospun polyacrylonitrile nanofiber–coated nonwoven structure for sound absorption

Acoustic felts are commonly used in white goods. Bearing that into mind, this paper aims to enhance sound absorption behavior of such felts, in particular, within the low and medium frequency ranges. In doing so, wool and jute felt samples were coated with electrospun polyacrylonitrile nanofibrous membrane. These nanocoated felts were studied in terms of their sound absorption performance, air permeability, and surface morphology. The results indicated that the air permeability of the felts could be drastically decreased by coating with nanofibers, which was required for better acoustic performance of felt‐like structures. Moreover, the samples having higher amount polyacrylonitrile nanofibers tended to demonstrate better sound absorbency.     

Partial molar isentropic compressibilities and volumes of selected electrolytes and nonelectrolytes in dimethylsulfoxide

Precision densities and sound velocities for solutions of selected univalent electrolytes and nonelectrolytes in DMSO have been measured at 25°C, and apparent molar isentropic compressibilities and volumes evaluated. The data were extrapolated to infinite dilution to obtain standard state partial molar quantities, K _s,2 ^° , and V ₂ ^° . Values of V ₂ ^° and K _s,2 ^° for alkali metal halides in DMSO are very similar to those in water. The results confirm conclusions derived from data in water and other nonaqueous solvents that K _s,2 ^° and V ₂ ^° for alkali metal halides are strongly dependent on solvent compressibility. K _s,2 ^° becomes more negative and V ₂ ^° decreases as solvent compressibility increases. Attempts to determine ionic K _s,2 ^° values suggest that a significant dissymmetry exists between ₄P⁺ and ₄B^– in DMSO, whereas in water and MeOH, these large ions appear to behave similarly. Ionic V ₂ ^° values support this conclusion. Steric hindrance in the DMSO molecule is believed to be responsible for this dissymmetry.     

Topological and thermodynamic investigations of binary mixtures: Molar excess volumes, molar excess enthalpies and isentropic compressibility changes of mixing

Molar excess volumes, V^E, molar excess enthalpies, H^E, and speeds of sound, u, of o-toluidine (i) + cyclohexane or n-hexane or n-heptane (j) binary mixtures have been determined over entire range of composition at 308.15 K. Speeds of sound data have been utilized to predict isentropic compressibility changes of mixing, of (i + j) mixtures. The observed V^E, H^E and data have been analyzed in terms of Graph theory. The analysis of V^E data by Graph theory reveals that o-toluidine exists as an associated molecular entity and (i + j) mixtures contain 1:1 molecular complex. It has been observed that V^E, H^E and values calculated by Graph theory compare well with their corresponding experimental values. The observed data have also been analyzed in term of Flory theory.     

Prediction of sound velocity and compressibility via molecular simulation at fixed entropy

A molecular-level simulation route is proposed to compute the isentropic thermodynamic properties in a fluid system by Monte Carlo simulation at fixed entropy. The method involves computation of the pressure response of a system to an infinitesimal change in system density by introduction of a single molecule, while retaining the system volume as well as the absolute molar entropy. The probability for accepting a change in temperature during the Monte Carlo moves was weighted against the argument proposed by Smith et al. [W.R. Smith, M. Lísal, I. Nezbeda, Chem. Phys. Lett. 426 (2006) 436–440]. Application to fluid argon has confirmed superior accuracy for the technique within the gas state to yield results within 1.2% of the measured values for the range of thermodynamic conditions investigated.     

Volumetric behaviour of the (2,2,4-trimethylpentane + methylbenzene + butan-1-ol) ternary system and its binary sub-systems within the temperature range (298.15–328.15) K

Densities and speeds of sound of the (2,2,4-trimethylpentane + methylbenzene + butan-1-ol) ternary system as well as all its binary sub-systems were measured at four temperatures, namely 298.15 K, 308.15 K, 318.15 K, and 328.15 K at atmospheric pressure by a vibrating-tube densimeter DSA 5000. The binary (isooctane + toluene) system was studied previously. Excess quantities (molar volume, adiabatic compressibility, and isobaric thermal expansivity) of the mixtures studied were calculated from the experimental densities and speed of sounds. The excess molar volume data were correlated using the Redlich–Kister equation. Both the positive and S-shaped excess molar volume curves were found for the systems studied. The excess molar volumes versus concentration of binary systems differed in the shape and temperature dependence. The experimental binary data were compared with literature data. The experimental excess molar volumes were analyzed by means of the Extended Real Associated Solution (ERAS) model. The experimental data and the ERAS model can help to estimate real behaviour of the systems studied.