Total harmonic distortion (THD) plays an important role in the performance of miniature loudspeakers used in mobile phones. Traditional nonlinear models fail to predict THD in the higher frequency domain. Significant discrepancies can be found between the prediction and measurement. In this study, an extended model considering nonlinear acoustic damping is proposed to address this issue. Flow separation occurring near the orifices of the sound port is of particular interest. read more Two velocity-dependent parameters were derived to model the nonlinear damping effect. Based on the extended model, the dynamics of miniature loudspeakers are described using the state-space method. Experiments and calculations confirm the validity of the extended model. The influence of nonlinear acoustic damping on THD is also discussed.This paper deals with the experimental study of an acoustic Parity-Time (PT) symmetric system based on the thermoacoustic amplification process. Such a system is presented and consists of two acoustic units connected through side branches to a waveguide. One unit contains a thermoacoustic core that provides an acoustic gain which balances the thermal and viscous losses taking place in the second unit. Two control parameters are set to adjust the impedance of the two units and thereby achieve the PT-symmetry condition. The results show that a good balance between gain and loss is achieved within a frequency range from 45 Hz to 60 Hz. The spontaneous PT-symmetry breaking and the existence of exceptional points, which are characteristic of the behavior of PT-symmetric systems, are explored in this frequency range. Moreover, the distance between the two units is shown to be a control parameter to slightly shift the frequency at which the exceptional points occur.Progress in instrumentation, computer hardware, and inversion methods is encouraging the development of more advanced guided wave tomography techniques, especially for nondestructive testing of plate structures to characterize corrosion. An experimental S0 tomography performance assessment in the membrane regime is reported. One of the main interests of the fundamental membrane regime is that in this regime, waves are propagated over long distances. A 2 mm thick steel disk containing calibrated sharp artificial defects (flat bottom holes) is tested in both reflection and extinction modes. A reconstruction algorithm derived from the membrane approximation is presented. We expose a complete reflection mode inversion approach that includes beam inversion, waveform deconvolution, and thickness loss calibration. Non-linear correction factors are introduced and discussed for quantitative imaging. A width-regularity-depth description of defects is introduced to put the results into perspective with other defect geometries. The results show the relevance of the inversion method to enhance the imaging performance with regard to defect localization and sizing. Crucial points concerning instrumentation such as coupling, signal-to-noise ratio, excitation mode, coupling, selection of frequency, are also discussed.This paper presents a method to characterize the effective properties of inertial acoustic metamaterial unit cells for underwater operation. The method is manifested by a fast and reliable parameter retrieval procedure utilizing both numerical simulations and measurements. The effectiveness of the method was proved to be self-consistent by a metamaterial unit cell composed of aluminum honeycomb panels with soft rubber spacers. Simulated results agree well with the measured responses of this metamaterial in a water-filled resonator tube. A sub-unity density ratio and an anisotropic mass density are simultaneously achieved by the metamaterial unit cell, making it useful in implementations of transformation acoustics. The metamaterial, together with the approach for its characterization, are expected to be useful for underwater acoustic devices.A numerical simulation of a single-reed instrument with a pressure chamber is conducted to examine the interaction among the flow, reed oscillation, and acoustic propagation. The flow and acoustic fields are predicted using the three-dimensional compressible Navier-Stokes equations, whereas the one-dimensional dynamic beam equation is solved for reed oscillation. The deforming geometry in the aeroacoustic field is expressed by the volume penalization method as an immersed boundary technique. The results showed that the waveforms of the tip opening and far-field acoustic spectra agreed well with those measured experimentally. The three-dimensional flow configuration near the tip opening was visualized, and the measurement of the instantaneous volume flow rate at the tip opening revealed that 30%-40% of the total flow rate passed through the side opening. The spectral tendencies of the time derivatives of the flow rate for different tip openings were consistent with that of the far-field sound, indicating that the slope of the flow rate waveform significantly affects the generated sound’s harmonics.Although human speech radiation has been a subject of considerable interest for decades, researchers have not previously measured its directivity over a complete sphere with high spatial and spectral resolution using live phonetically balanced passages. The research reported in this paper addresses this deficiency by employing a multiple-capture transfer function technique and spherical harmonic expansions. The work involved eight subjects and 2522 unique sampling positions over a 1.22 or 1.83 m sphere with 5° polar and azimuthal-angle increments. The paper explains the methods and directs readers to archived results for further exploration, modeling, and speech simulation in acoustical environments. Comparisons of the results to those of a KEMAR head-and-torso simulator, lower-resolution single-capture measurements, other authors’ work, and basic symmetry expectations all substantiate their validity. The completeness and high resolution of the measurements offer insights into spherical speech directivity patterns that will aid researchers in the speech sciences, architectural acoustics, audio, and communications.