Preventing damage to miniature-loudspeaker by means of dynamic detection of excessive diaphragm displacement.

The rapid development of consumer electronics and the extensive use of mobile devices require the ample use of miniature-loudspeakers for audio applications. The demand for better sound pushes manufacturers to design digital signal processing (DSP) chips (smart amplifiers), which in turn could cause unpleasant sound due to distortion and parameter nonlinearity or transducer damage caused by large diaphragm excursion or voice-coil (VC) burn. This article presents a methodology for nonlinear parameter estimation using an inverse method and displacement limiter for large VC displacement-dependent transducer damage prevention. A set of transduction equations is employed to inversely determine parameters using a polynomial expression. The appropriate selection of an objective function incorporating the unknown vector of nonlinear parameters leads to the adjoint problem that requires a gradient solution. A numerical solver is provided to obtain the VC displacement, current, and derivatives using a robust hybrid spline differential method. The dynamic limiter is proposed to control the peak values of the VC velocity so as to limit an excessive displacement which prevents impulsive damage to the receiver and further application of the DSP board. Numerical and experimental results indicate that the proposed method has high efficiency and can be widely used in transducer applications.

Right miniparasternotomy may be a good minimally invasive alternative to full sternotomy for cardiac valve operations: a propensity-adjusted analysis.

BACKGROUND: Limited real-world data existed for mini-parasternotomy approach with good sample size in Asian cohorts and most previous studies were eclipsed by case heterogeneity. The goal of this study was to compare safety and quality outcomes of cardiac non-coronary valve operations by mini-parasternotomy and full sternotomy approaches on risk-adjusted basis. METHODS From our hospital database, we retrieved the cases of non-coronary valve operations from 1 January 2005 to 31 December 2012, including re-do, emergent, and combined procedures. Estimated EuroScore-II and propensity score for choosing mini-parasternotomy were adjusted for in the regression models on hospital mortality, complications (pneumonia, stroke, sepsis, etc.), and quality parameters (length of stay, ICU time, ventilator time, etc.). Non-complicated cases, defined as survival to discharge, ventilator use not over one week, and intensive care unit stay not over two weeks, were used for quality parameters. RESULTS: There were 283 mini-parasternotomy and 177 full sternotomy cases. EuroScore-II differed significantly (medians 2.1 vs. 4.7, P<0.001). Propensity scores for choosing mini-parasternotomy were higher with lower EuroScore-II (OR=0.91 per 1%, P<0.001), aortic regurgitation (OR=2.3, P=0.005), and aortic non-mitral valve disease (OR=3.9, P<0.001). Adjusted for propensity score and EuroScore-II, mini-parasternotomy group had less pneumonia (OR=0.32, P=0.043), less sepsis (OR=0.31, P=0.045), and shorter non-complicated length of stay (coefficient=-7.2 (day), P<0.001) than full sternotomy group, whereas Kaplan-Meier survival, non-complicated ICU time, non-complicated ventilator time, and 30-day mortality did not differ significantly. CONCLUSION: The propensity-adjusted analysis demonstrated encouraging safety and quality outcomes for mini-parasternotomy valve operation in carefully selected patients.

An inverse method for estimating the electromechanical parameters of moving-coil loudspeakers.

This article presents an inverse method for estimating the electromechanical parameters of a moving-coil loudspeaker with or without the eddy current and suspension creep effects. With known voice-coil displacement, voice-coil current, and stimulus signal as inputs, four calculation procedures for the direct problem, adjoint problem, sensitivity problem, and conjugate gradient method are involved in inversely solving the unknown electromechanical parameters. The proposed method features high efficiency in solving the direct problem through a hybrid spline difference method. It requires a small number of iterations for the computational algorithm, while offering excellent accuracy in parameter estimations. Analysis results demonstrate small differences between the estimated and measured electromechanical parameters under a variety of stimulus signals, excitation times, and initial guesses. The results are also confirmed by experimental measurements. These results indicate that the proposed method has a strong potential for estimating the electromechanical parameters of moving-coil loudspeakers.

Effects of porous materials in an insert earphone on its frequency response--experiments and simulations.

This article presents a promising approach to customize the sound-pressure response of an insert earphone by delicately tuning the acoustic impedance of porous materials in it. The effects of applying porous materials on and in various parts in the insert earphone were tested experimentally to determine the resulting sound pressure responses. An equivalent circuit model (ECM) is also presented to simulate the sound-pressure-level (SPL) response of the insert earphone. For each part of the earphone, the effect of applying porous materials was simulated using the ECM approach. For porous elements, modified formulae with correction factors are proposed to determine the acoustic impedance. Comparisons of the simulated responses with experimental data have verified the veracity of the ECM simulations. The present work has verified the feasibility of adjusting the aeration of the porous materials to customize the resulting SPL response of an earphone.

A simple approximate formula for the physical focal length of spherically focused transducers.

A simple approximate formula is presented to describe the relationship between the physical focal lengths and the geometric focal lengths of spherically focused transducers with ultrasonic fields. This simple expression applies regardless of whether the focus strength is strong or weak, and regardless of whether the fluids are non-attenuating or attenuating. Analysis results show that the average error of the simple approximate formula is certainly less than 2% relative to the numerical solution.