Journal of the Acoustical Society of America最新文献

Thanks to recent advancements in distributed acoustic sensing (DAS) techniques, we can measure the time series of axial strains along an optical fiber at extremely dense spatial intervals. However, only a single component of a strain tensor is measured, and the partitioning of seismic energy into this component is unknown. In this study, we address this problem by formulating energy partitioning into different strain components for diffuse waves in a three-dimensional homogeneous isotropic half-space, building upon previous studies on energy partitioning into displacement components. We investigate how the contributions of both body and surface waves to the six independent components of a strain tensor change with depth. The results show that the horizontal normal strains, which surface DAS observation can measure, are primarily composed of shear horizontal-waves and Rayleigh waves at the free surface. The vertical normal strain, which borehole DAS observation can measure, is dominated by Rayleigh waves at the free surface. However, that contribution quickly decays within the depth of one shear wave-wavelength, and the shear vertical-wave contribution remains. This study serves as a reference for further extension to more realistic media, such as horizontally layered media, and opens a way to interpret the late coda of DAS strain seismograms quantitatively.

The Speech Intelligibility Index (SII) is a metric of the amount of information available in a degraded or masked speech signal. The SII is used to predict speech recognition outcomes and is part of hearing aid prescription formulae. A critical assumption in the calculation of the SII is that frequency bands contribute independently to speech recognition, i.e., the importance of a band does not change based on the context of speech cues in other bands. Prior work has challenged this assumption by demonstrating that pairs of bands can contain synergistic or redundant information. The present work extends these findings by directly measuring pairwise interactions between the 21 frequency bands defined by the Critical Band Procedure of the SII. Forty-one participants with normal hearing identified words filtered to contain pseudorandom combinations of four or five bands. Pairwise interactions indicated both synergy and redundancy and accounted for substantial variability in recognition accuracy. The importance of individual bands decreased when pairwise interactions were considered, with the largest decreases for frequency bands above 1 kHz. The spectral proximity and envelope correlation between pairs of bands predicted whether their combination was synergistic or redundant. Interactions between bands play a critical role in speech recognition.

Class III flextensional transducers have been widely used as low-frequency projectors, but their characteristics also make them promising candidates for broadband low-frequency hydrophone applications. In this study, we propose a design of Class III flextensional hydrophone featuring significant structural modifications to achieve wider receiving bandwidth and higher sensitivity in the low-frequency range. Traditional hydrophones often increase bandwidth by reducing size-a straightforward and effective approach. However, this comes at the cost of reduced receiving sensitivity, as sensitivity is generally proportional to the hydrophone's surface area. To overcome this limitation, we developed a wideband hydrophone design that maintains a similar physical size, thereby preserving high receiving sensitivity. We constructed finite element analysis models of the Class III flextensional hydrophone to investigate how various structural parameters influence its acoustic receiving characteristics. Based on the simulation results, we determined the optimal combination of the parameters to maximize bandwidth while keeping the first receiving-voltage-sensitivity peak within a specific frequency range. The designed hydrophone demonstrated a fractional bandwidth 2.51 times greater than that of the conventional model, while maintaining a comparable receiving voltage sensitivity level.

Spectrotemporal modulation tests probe spectral and temporal resolution in cochlear implant (CI) users. This study investigated how carrier type and bandpass modulations influenced modulation detection performance. Nineteen CI users performed a reaction-time task involving the detection of spectral (0.25-2 cycles/octave) and/or temporal (4-16 Hz) modulations embedded in a broadband carrier. Carriers were either (1) a complex tone composed of 87 random-phase sinusoids spaced linearly at 100 Hz and weighted by a pink spectrum or (2) pink noise. Surprisingly, stimuli with dense spectral modulations were more readily detected when paired with the complex tone carrier. In contrast, the pink noise carrier yielded the expected low-pass spectral modulation transfer function profile. Electrodogram simulations based on CI sound processing strategies suggest that using a complex tone carrier with more closely spaced, logarithmically arranged tones may reduce unintended cues, such as spectral aliasing. Additionally, 2-octave limited bandwidth stimuli with a fixed temporal modulation rate (4 Hz) and spectral densities ranging from 0-2 cycles/octave were tested within broadband pink noise, centered at frequencies from 500 to 4000 Hz. Detection sensitivity was lowest at 500 Hz-a result supported by electrodograms-suggesting potential device processing limitations for spectrotemporal modulations at apical electrode sites.

Psychoacoustic assessment of aircraft under development is hindered by the difficulty of obtaining comprehensive noise data before physical prototypes are available. For the brushless direct current motor-propeller systems that are primary noise sources on these aircraft, this study develops and validates a physics-based auralization framework that models rotational speed fluctuations induced by electromagnetic torque ripple. The model incorporates both stochastic (rotational speed fluctuation strength) and deterministic periodic [iterative polynomial function (IPF)] components. A key feature is that the IPF is mathematically derived from motor pole pairs (Nf=k·Np), linking electromagnetic physics directly to acoustic modulation. Physical validation confirmed the model's improved accuracy in predicting high-frequency tonal components compared to conventional constant-speed approaches. Perceptual validation with 61 participants was conducted through two psychoacoustic experiments. The subjective response test provided statistical evidence that listeners did not reliably distinguish between the measured sounds and the auralized sounds incorporating the ripple model. Annoyance tests confirmed loudness-dominated responses with strong psychoacoustic model correlations. These findings establish that the validated framework can effectively substitute for physical measurements in psychoacoustic assessments. This enables perception-informed design of acoustically acceptable electric vertical takeoff and landing vehicles before physical prototypes are available.

This paper presents a cylindrical shear layer model for analyzing acoustic wave propagation at the exit of a semi-infinite circular jet pipe with uniform mean flow. Building upon the Pridmore-Brown equation, the formulation is derived in cylindrical coordinates to more accurately describe the transitional region between the uniform flow inside the pipe and the quiescent outer medium by developing the coupling conditions, under low Mach number and small perturbation conditions. The proposed model improves upon earlier shear layer approaches, such as the rectangular-coordinate-based model in Yanaz Çınar, Boij, Çınar, and Nilsson [(2010). 16th AIAA/CEAS Aeroacoustics Conference], and extends beyond the classical vortex sheet model introduced in Munt [(1977). J. Fluid Mech. 83, 609-640] and Munt [(1990). J. Sound Vib. 142, 413-436]. The resulting coupling conditions are applied to the fundamental problem of areoacoustics, namely, the semi-infinite jet pipe problem. Numerical analysis carried for low-frequency range demonstrates improved agreement with experimental data, in predicting the reflection coefficient for configurations with nonzero diffuser angles. These findings confirm the enhanced fidelity of the cylindrical shear layer model and its potential applicability to a broad range of aeroacoustic engineering problems.

This paper illustrates effects of model dimensionality, and of common simplifying assumptions, regarding the geometry of the scalae, on the solution of cochlear mechanical models. We extend a previous theoretical framework from Duifhuis [(1988). Auditory Function: Neurological Bases for Hearing (Wiley, New York), pp. 189-212] to study differences between models that consider three-dimensional (3D) and two-dimensional (2D) fluid motion in the scalae, and how these differences depend on the assumed cochlear geometry. Our results show that, while cochlear mechanical responses obtained in 2D and 3D are nearly identical over the mid- and apical cochlear turn, they are significantly different in the base-where the basilar membrane (BM) is narrow-especially in the presence of active amplification. Our analysis reveals that a narrower BM intensifies the 3D short-wave "pressure-focusing" effect, which boosts the vibration of the sensory tissue at locations tuned to the stimulus frequency. Importantly, these 3D short-wave effects can be accounted for in carefully constructed 2D models, by appropriately projecting the cochlear 3D geometry in 2D. Our work shows that the cochlear 3D geometry plays a major role to high-frequency cochlear amplification-a phenomenon with a straightforward explanation and that can be included in more tractable 2D theories.

Anthropogenic noise may pose a threat to Kemp's ridley sea turtles in nearshore and offshore waters of the western North Atlantic and Gulf of America, where shipping and energy industries are widespread. Understanding hearing sensitivity is necessary for the development of effective noise impact mitigation strategies. However, data gaps currently exist. Therefore, in this study, we measured auditory evoked potentials (AEP) to determine the underwater hearing sensitivities of 13 juvenile Kemp's ridley sea turtles using hearing test frequencies ranging from 50 to 1600 Hz. We detected AEPs for hearing test signals between 50 and 800 Hz. Peak hearing sensitivity occurred between 200 and 300 Hz, followed by a decline in sensitivity above 400 Hz. The lowest hearing threshold averaged across all test subjects was 100 dB re 1 μPa at 300 Hz. No responses were detected at 1200 Hz (max received level = 143 dB re 1 μPa) and 1600 Hz (max received level = 143-165 dB re 1 μPa). Our results averaged across multiple individuals at 100 Hz (n = 9), 200 Hz (n = 8), 300 Hz (n = 5), and 400 Hz (n = 8) reveal lower hearing thresholds (greater sensitivity) than those reported in a previous study of two Kemp's ridley sea turtles at these frequencies. The results presented here should be considered a conservative estimate of hearing sensitivity, as perceptual hearing thresholds are likely lower than what can be determined with AEPs.

A formulation to introduce acoustic waves from a control surface using volumetric source terms is proposed for numerical simulations. A general expression of the source terms is derived from the non-linear Euler equations. The method is validated through three academic configurations: the injection of oblique plane waves and the radiation of a monopole source in two and three dimensions, in uniform flow. The governing equations are solved in a Cartesian grid using a low-dispersion and low-dissipation high order finite-difference numerical scheme. However, the control surface has an arbitrary shape, as demonstrated here with the use of a cylindrical surface. Numerical results show good agreement with analytical solutions in both phase and amplitude. The method is then applied to an open-fan aircraft engine configuration. The source terms are computed from a cylindrical control surface enclosing the rotor, based on data extracted from a previous fluid mechanics simulation. The radiated acoustic field is compared with the one obtained using the Ffowcs Williams-Hawkings integral formulation. The two solutions are again found in good agreement for this more realistic configuration.