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To test this sizing, the size distributions of two monodisperse microbubble populations ( R = 2.1 and 3.5 μm) acquired with the AC were matched to the distribution acquired with a Coulter counter. As a result of measuring the absolute size of the microbubbles, this "extended AC" can capture the full radial dynamics of single freely floating microbubbles with a throughput of hundreds of microbubbles per hour.The purpose of this study is to model a circular planar loudspeaker placed near a spherical reflector to broaden its directivity pattern, which would otherwise become increasingly narrow at high frequencies. Through ray tracing, it seems intuitively feasible to thus create a virtual point source at very high frequencies, but we provide a more rigorous analysis to determine what will happen at intermediate frequencies where the wavelength is of a similar magnitude to the diameter of the disk or sphere. We show that a smoother off-axis response is obtained with a dipole pressure source, which does not obstruct the scattered sound, rather than a monopole velocity source. Hence, an electrostatic loudspeaker, for example, would be more suitable than a dynamic one. The sphere may also serve as a spherical approximation of a human head, in which case the loudspeaker would become an open headphone that is not sealed to the ear.The practicality of the finite-difference time-domain (FDTD) method was confirmed by comparing head-related transfer functions obtained from a three-dimensional (3D) digital model of a bat (Rhinolophus ferrumequinum nippon) head with acoustic experiments using a 3D printed physical model. Furthermore, we simulated the auditory directionality using a 3D digital model that was modified based on the pinna movement of a bat during echolocation and found that the alternating movements of the left and right pinna result in a binaural sound pressure difference for vertical sources. Using the FDTD method, suitable for simulating acoustics in large spaces, we could analyze in detail the binaural echoes that bats receive and the acoustic cues they use for echolocation.An alternative approach to acquire transmission travel time data is proposed, exploiting the geometry of devices commonly used in ultrasound computed tomography for medical imaging or non-destructive testing with ultrasonic waves. The intent is to (i) shorten acquisition time for devices with a large number of emitters, (ii) to eliminate the calibration step, and (iii) to suppress instrument noise. Inspired by seismic ambient field interferometry, the method rests on the active excitation of diffuse ultrasonic wavefields and the extraction of deterministic travel time information by inter-station correlation. see more To reduce stochastic errors and accelerate convergence, ensemble interferograms are obtained by phase-weighted stacking of observed and computed correlograms, generated with identical realizations of random sources. Mimicking an imaging setup, the accuracy of the travel time measurements as a function of the number of emitters and random realizations can be assessed both analytically and with spectral-element simulations for phantoms mimicking the model parameter distribution. The results warrant tomographic reconstructions with straight- or bent-ray approaches, where the effect of inherent stochastic fluctuations can be made significantly smaller than the effect of subjective choices on regularisation. This work constitutes a first conceptual study and a necessary prelude to future implementations.The concept of acoustic impedance is often difficult for students in introductory acoustics courses to make sense of, especially students without advanced mathematics backgrounds. This work summarizes a laboratory activity for students in a general education musical acoustics class where a simplified brass musical instrument is examined, focusing on how the geometry of the air column affects the input impedance of the instrument. Students are guided through making bore profile measurements for use in a computation of the input impedance. Options for making experimental measurements of the simplified instrument are explained. The laboratory activity was successfully used with students who reported their increased understanding of the acoustics of brass musical instruments.Previous literature suggests that musical performers may be influenced to some extent by the acoustic environment in which they sing or play. This study investigates the influence of room acoustics on singers' voice production, by analyzing consecutive sung performances of classically trained students in five different performance spaces. The analyzed voice parameters were vibrato rate, extent, and pitch inaccuracy. Nine classically trained student-singers performed the same aria unaccompanied on a variable starting pitch that was consistent between spaces. Variance in vibrato rate and pitch inaccuracy was primarily explained by individual differences between singers. Conversely, the variance attributable to the rooms for the parameter of vibrato extent was larger compared to the variance attributable to the performers. Vibrato extent tended to increase with room clarity (C80) and was inversely associated with early decay time (EDT). Additionally, pitch inaccuracy showed a significant negative association with room support (STv). Singers seem to adjust their vocal production when performing in different acoustic environments. Likewise, the degree to which a singer can hear themself on stage may influence pitch accuracy.In this work, an iterative method based on the four-microphone transfer matrix approach was developed for evaluating the sound speed and attenuation constant of air within a standing wave tube. When the air inside the standing wave tube is treated as the material under test, i.e., as if it were a sample of porous material, the transfer matrix approach can be used to identify the air's acoustic properties. The wavenumber within the tube is complex owing to the formation of a visco-thermal boundary layer on the inner circumference of the tube. Starting from an assumed knowledge of the air properties, an iterative method can be applied in the post-processing stage to estimate the complex wavenumber. Experimental results presented here show that although the results are sensitive to ambient temperature, a semi-empirical formula previously proposed by Temkin [(1981). Elements of Acoustics (John Wiley & Sons)] matches closely with the measured sound speed and attenuation constant, as does a theoretical formulation proposed by Lahiri et al. [(2014). J. Sound Vib. 333(15), 3440-3458]. Further, it is shown that the Temkin [(1981). Elements of Acoustics (John Wiley & Sons)] and Lahiri et al. [(2014). J. Sound Vib. 333(15), 3440-3458] predictions accurately represent the variation of sound speed with frequency, in contrast to the formula recommended in the ASTM E1050 standard [(2019). American Society for Testing and Materials], in which the sound speed is assumed to be independent of frequency.Vector acoustic field properties measured during the 2017 Seabed Characterization Experiment (SBCEX17) are presented. The measurements were made using the Intensity Vector Autonomous Recorder (IVAR) that records acoustic pressure and acceleration from which acoustic velocity is obtained. Potential and kinetic energies of underwater noise from two ship sources, computed in decidecimal bands centered between 25-630 Hz, are equal within calibration uncertainty of ±1.5 dB, representing a practical result towards the inference of kinematic properties from pressure-only measurements. Bivariate signals limited to two acoustic velocity components are placed in the context of the Stokes framework to describe polarization properties, such as the degree of polarization, which represents a statistical measure of the dispersion of the polarization properties. A bivariate signal composed of vertical and radial velocity components within a narrow frequency band centered at 63 Hz representing different measures of circularity and degree of polarization is examined in detail, which clearly demonstrates properties of bivariate signal trajectory. An examination of the bivariate signal composed of the two horizontal components of velocity within decidecimal bands centered at 63 Hz and 250 Hz demonstrates the importance of the degree of polarization in bearing estimation of moving sources.In this paper, a data augmentation aided complex-valued network is proposed for underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) channel estimations, wherein empirical mode decomposition based data augmentation is proposed to solve the current dilemma in the deep learning embedded UWA-OFDM communications data scarcity and data-sampling difficulties in real-world applications. In addition, the significance of high-frequency component augmentation for the UWA channel and how it positively influences the following model training are discussed in detail and demonstrated experimentally in this paper. In addition, the complex-valued network is specially designed for the complex-formatted UWA-OFDM signal, which can fully utilize the relationship between its real and imaginary parts with half of the spatial resources of its real-valued counterparts. The experiments with the at-sea-measured WATERMARK dataset indicate that the proposed method can perform a near-optimal channel estimation, and its low resource requirements (on dataset and model) make it more adaptable to real-world UWA applications.The acoustic black hole (ABH) effect in waveguides is studied using frequency-domain finite element simulations of a cylindrical waveguide with an embedded ABH termination composed of retarding rings. This design is adopted from an experimental study in the literature, which surprisingly showed, contrary to the structural counterpart, that the addition of damping material to the end of the waveguide does not significantly reduce the reflection coefficient any further. To investigate this unexpected behavior, we model different damping mechanisms involved in the attenuation of sound waves in this setup. A sequence of computed pressure distributions indicates occurrences of frequency-dependent resonances in the device. The axial position of the cavity where the resonance occurs can be predicted by a more elaborate wall admittance model than the one that was initially used to study and design ABHs. The results of our simulations show that at higher frequencies, the visco-thermal losses and the damping material added to the end of the setup do not contribute significantly to the performance of the device. Our results suggest that the primary source of damping, responsible for the low reflection coefficients at higher frequencies, is local absorption effects at the outer surface of the cylinder.The complete decomposition performed by blind source separation is computationally demanding and superfluous when only the speech of one specific target speaker is desired. This letter proposes a computationally efficient blind source extraction method based on the fast fixed-point optimization algorithm under the mild assumption that the average power of the source of interest outweighs the interfering sources. Moreover, a one-unit scaling operation is designed to solve the scaling ambiguity for source extraction. Experiments validate the efficacy of the proposed method in extracting the dominant source.