Index of content:
Volume 120, Issue 4, October 2006
- TRANSDUCTION 
Modeling of the influence of a prestress gradient on guided wave propagation in piezoelectric structures120(2006); http://dx.doi.org/10.1121/1.2336989View Description Hide Description
The objective of this study is to model the propagation of guided waves in piezoelectric structures subjected to a prestress gradient. The constitutive equations for a piezoelectric bulk material are first modified to take into account a uniform prestress on a given cross section. Then, these modified constitutive equations are used to derive a formalism for the propagation of guided waves in piezoelectric structures under a prestress gradient. In particular, we modify the recursive stiffness matrix method to introduce a gradient of stress in a piezoelectric structure. Numerical studies are then led for a bending and for an exponential stress profile. For a piezoelectric plate, the Lamb and shear horizontal modes are found to be sensitive to the prestress gradient. In particular, some key features of dispersion curves appearing in the presence of a gradient of properties are highlighted. In the last part, these results are extended to a piezoelectric film laid down on a substrate in order to model the importance of the stress gradient on the behavior of an integrated structure. Lithium niobate is used for the plate and film material, and a silicon crystal is used as the substrate.
Objective and subjective analysis of effects of listening angle on crosstalk cancellation in spatial sound reproduction120(2006); http://dx.doi.org/10.1121/1.2257986View Description Hide Description
A comprehensive study was conducted to explore the effects of listening angle on crosstalk cancellation in spatial sound reproduction using two-channel stereo systems. The intention is to establish a sustainable configuration of crosstalk cancellation system(CCS) that best reconciles the separation performance and the robustness against lateral head movement, not only in theory but also in practice. Although crosstalk can in principle be suppressed using multichannel inverse filters, the CCS does not lend itself very well to practical application owing to the fact that the sweet spot is being so small. Among the parameters of loudspeaker deployment, span angle is a crucial factor that has a profound impact on the separation performance and sweet spot robustness achievable by the CCS. This paper seeks to pinpoint, from a more comprehensive perspective, the optimal listening angle that best reconciles the robustness and performance of the CCS. Two kinds of definitions of sweet spot are employed for assessment of robustness. In addition to the point sourcemodel, head related transfer functions (HRTF) are employed as the plant models in the simulation to emulate more practical localization scenarios such as the high-frequency head shadowing effect. Three span angles including 10, 60, and are then compared via objective and subjective experiments. The Friedman test is applied to analyze the data of subjective experiments. The results indicate that not only the CCS performance but also the panning effect and head shadowing will dictate the overall performance and robustness. The 120-deg arrangement performs comparably well as the standard 60-deg arrangement, but is much better than the 10-deg arrangement.