Journal of the Acoustical Society of America最新文献

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

With the vigorous development of maritime trade, the frequency band from 100 to 1500 Hz of shallow-sea ambient noise is not only affected by surface wind-induced noise but also the contribution of ship noise. Shallow-sea ambient noise can be described by a linear combination of surface wind-induced noise sources and ship noise sources. By using the correspondence between the real part of the vertical coherence and vertical energy flux, this work establishes a combined noise source model based on vertical coherence. A 64-element vertical array is used to measure the ocean ambient noise 103 m deep in an area of the South China Sea. Two scenarios, one dominated by surface wind-induced noise and one dominated by wind-induced noise and ship noise, are selected for investigation. By comparing the theoretical and measured values, the accuracy of the model proposed in this paper and its ability to remove the ship noise reliably are verified. This approach can be used to quantify the proportion of ship noise power in shallow-sea low-frequency environments and evaluate the contributions of wind-induced noise and ship noise at different times.

The dispersion of circumferential waves propagating around cylindrical and spherical underwater targets with an arbitrary number of elastic and fluid layers is modeled using the spectral collocation method. The underlying differential equations are discretized by Chebyshev interpolation and the corresponding differentiation matrices, and the calculation of the dispersion curves is transformed into a generalized eigenvalue problem. Furthermore, for targets in infinite fluid, the perfect matched layer is used to emulate the Sommerfeld radiation condition. For solid targets, a transformation of potential functions, along with the corresponding boundary condition, is introduced to eliminate the singularity of the low-order modes at the origin. Numerical results are presented and compared with results obtained by the winding number integral method to verify the accuracy and efficiency of the approach.

In acoustics, an artificial head generally comprises two pinnae and occasionally a torso, which are useful for recording binaural signals and acquiring head-related transfer functions (HRTFs). Currently, most artificial heads are designed based on the anthropometric parameters of specific populations. However, anthropometric parameters do not accurately express head surface shapes, and thus, typical HRTFs are difficult to generate. Thus, this study presents a statistical shape model-based average head of 100 Chinese adults and comprehensively presents its repeatable design process. Furthermore, to validate the representativeness of the statistical shape model-based average head in terms of the head surface shape features and acoustical characteristics, its anthropometric parameters are compared with those of the 100 subjects. Moreover, the representativeness of statistical shape model-based average head's HRTFs is verified through the typical HRTFs clustered from the entire HRTF database. Owing to the clear and concise design process, the proposed method can be easily applied and promoted to a new population.

Threshold estimation procedures are widely used to measure the stimulus level corresponding to a specified probability of response. The weighted up-and-down procedure, familiar to many due to its use in standard pure-tone audiometry, allows the experimenter to target any probability of response by using different ascending and descending step sizes. Unfortunately, thresholds have a signed mean error that made using weighted staircases inadvisable. The current study evaluated a correction to eliminate the error. Monte Carlo simulations of weighted staircases were used to test the effectiveness of the proposed correction for yes-no and forced-choice tasks with Gaussian and log-Weibull psychometric functions. Results showed that the proposed correction was effective over a wide range of step size magnitudes and ratios with a symmetric psychometric function and less effective when there was asymmetry due to the shape of the function or a high guess or lapse rate. The proposed correction facilitates the use of weighted staircases to target an arbitrary probability of response.

The flextensional transducer (FT) is a typical low-frequency transmitting transducer that is capable of high-power operation due to its capacity for displacement amplification. This article uses the structural configuration of the class IV FT as the basis for designing a ring transducer, which is a circular structure comprising a multitude of class IV flextensional structures as well as circular acoustic radiation structures. The flextensional structure drives the circular acoustic radiation structure, which in turn generates sound waves at low frequencies. It concurrently enhances the intensity of the sound source. Moreover, the acoustic radiation structure is designed to operate with two resonances that can be coupled with each other to extend the bandwidth of the transducer. A finite element model of the low-frequency broadband ring transducer was developed, and its structural parameters were optimized to achieve the optimal bandwidth. The optimization of the transducer was followed by the fabrication of its prototype, which was then used to evaluate its underwater acoustic performance. The results of measurements showed that the proposed transducer could successfully couple two modes of vibrations to yield an in-band fluctuation of approximately 12 dB in the range of frequencies of 540 to 1580 Hz.

An approach is proposed for reduction index measurement where impulse response data are utilised directly without relying on intermediate reverberation time estimation. The theoretical framework is presented and the main result is substantiated by shown equivalence to the conventional method for ideal exponential decay curves of acoustic energy. Additionally, the study introduces a formula for estimating effective reverberation time in cases of non-exponential decay curves. Further formulas for determining effective values of reverberation time and absorption area for general decay curve shapes are also suggested.

The shear wave speed is often small compared to the compressional wave speed in the top part of the seabed, where acoustic normal modes penetrate. In sediments with weak but finite shear rigidity, the strongest conversion from compressional to shear waves occurs at interfaces within the sediment. Shear wave generation at such interfaces and interference within sediment layers lead to first-order perturbations in the normal mode phase speed and contributions to sound attenuation, which vary rapidly with frequency. Weak shear rigidity is shown to lead to unexpectedly strong mode group speed perturbations that retain finite magnitudes for very small shear speeds in range-independent waveguides. Variation of the waveguide parameters with range affects shear-induced attenuation and mode travel time perturbations in a different manner, depending on whether shear wave interference conditions vary appreciably along the propagation path. In horizontally inhomogeneous ocean, weak shear magnifies the horizontal refraction of adiabatic normal modes due to sloping intra-sediment interfaces. In contrast to normal modes, attenuation of lateral waves with range is insensitive to weak shear. Concurrent measurements of normal mode and lateral wave attenuation can be potentially used to identify and separate the contributions of dissipation and shear waves into observed sound attenuation.

Characterising acoustic fields in rooms is challenging due to the complexity of data acquisition. Sound field reconstruction methods aim at predicting the acoustic quantities at positions where no data are available, incorporating generalisable physical priors of the sound in a room. This study introduces a model that exploits the general time structure of the room impulse response, where a wave-based expansion addresses the direct sound and early reflections, localising their apparent origin, and kernel methods are applied to the late part. This late energy is considered to follow a sinc-like spatial correlation, in accordance with the random wave field theory. Synthesised pressure points, which follow the observed statistics of the sound field, are introduced to enable extrapolation over large distances. The model is evaluated experimentally in a lecture room and an auditorium, demonstrating a successful reconstruction of the sound field across a 5 m aperture using three microphone arrays of only 4.2 cm radius each. These results indicate that the proposed methodology enables volumetric extrapolation over several orders of magnitude, which is significant in the context of navigable sound field reproduction, "6-degrees of freedom" spatial audio and sound field analysis in rooms.

To date, there is strong evidence indicating that humans with normal hearing can adapt to non-individual head-related transfer functions (HRTFs). However, less attention has been given to studying the generalization of this adaptation to untrained conditions. This study investigated how adaptation to one set of HRTFs can generalize to another set of HRTFs. Participants were divided into two groups and trained to localize a speech stimulus reproduced binaurally using either individual or non-individual HRTFs. Training led to an improved localization performance with the trained HRTFs for both groups of participants. Results also showed that there was no difference in the localization performance improvement between the trained and untrained HRTFs for both groups, indicating a generalization of adaptation to HRTFs. The findings did not allow to precisely determine which type of learning (procedural or perceptual) primarily contributed to the generalization, thus highlighting the potential need to expose participants to longer training protocols.