Journal of the Acoustical Society of America最新文献

This study aims to investigate the effects of attending a soundscape workshop on the awareness of sound as a design element for interior architects. The workshop is structured in three phases: theoretical lectures, practical applications, and discussions. In the first phase, fundamentals of architectural acoustics, the sense of place, and soundscape theory were delivered through theoretical lectures. In the second phase, participants were asked to design a sound environment for a restaurant and an office. In the third and final phase, participants discussed their sound designs from the perspectives of the lectures and sound-related topics. Additionally, participants completed an open-ended questionnaire to evaluate their workshop experience and provided suggestions for improvement. The effectiveness of the workshop in raising awareness was tested using a pre-test/post-test analysis method, with data collected through structured questionnaires completed by participants before and after the workshop. The results of the statistical analysis show that attending the workshop changed participants' evaluations of sound expectations and preferences, as well as their sensitivity to sound. The findings indicate that participating in an indoor soundscape workshop can positively influence interior architects' understanding of sound as a design element to be considered in their future work.

Acoustic thermometry is a fast, noncontact temperature measurement method that does not require heat exchange and, thus, is suitable for real-time monitoring of changes in air temperature at high altitudes where the thin air is not conducive to establishing thermal equilibrium. In this work, real-time measurements of air temperature at altitudes of up to 5200 m were achieved using a passive acoustic thermometer, which is an acoustic Fabry-Perot resonator (AFPR), consisting of an electret condenser microphone and an acoustic waveguide. The resonant frequency (fR) of the AFPR as a linear function of the mode order number (m) is measured using ambient white noise instead of external sound source, and the air temperature is determined based on the slope of the fR versus m curve. The surface air temperature changes in Beijing and the Kashgar Plateau were measured in real time over more than 15 h using the AFPR. By mounting the AFPR on a tethered balloon, the continuous monitoring of air temperature during liftoff and descent of the balloon was tested. The average deviation between the results simultaneously measured with the AFPR and commercial electronic thermometer was less than 0.5 °C, which verified the reliability of the AFPR-based passive acoustic thermometry.

Absorption of elastic waves in complex media is commonly found to increase linearly with frequency, for both longitudinal and shear waves. This ubiquitous property is observed in media such as rocks, unconsolidated sediments, and human tissue. Absorption is due to relaxation processes at the level of atomic scales and up to the sub-micron scale of biological materials. The effect of these processes is usually expressed as an integral over relaxation frequencies or relaxation times. Here, this paper argues that these processes are thermally activated. Unusually for ultrasonics and seismics, the expression for absorption from the frequency or time domains can therefore be transformed to an integral over an activation energy landscape weighted by an energy distribution. The universal power-law property surprisingly corresponds to a flat activation energy landscape. This is the solution that maximizes entropy or randomness. Therefore, the linearly increasing absorption corresponds to the energy landscape with the fewest possible constraints.

Wind instruments containing a resonator (i.e., pipe) with an open end are expected to exhibit an acoustic standing wave characterized by a density oscillation whose amplitude falls to zero a short distance beyond the end of the resonator. An extrapolation of this amplitude based on the behavior inside the resonator yields an "effective" node of the standing wave (i.e., a point at which the extrapolated amplitude vanishes), and the distance from the end of the resonator to the location of this effective node (which is commonly referred to as simply a "node") is known as the "end correction." Recent work using a novel optical technique involving optical speckle patterns surprisingly suggested instead that a node is located inside the resonator with unexpected structure in the standing wave amplitude just beyond the end of the resonator. We have studied this problem by numerically solving the Navier-Stokes equations and find that the effective node of the density oscillation is located at the expected position outside the resonator with no unexpected structure in the functional form of the standing wave. We also show how pressure gradients and the flow pattern found near the end of the resonator can account for the unexpected behavior observed in the experiments. This sensitivity of optical interference effects to flow structure may give a new experimental way to investigate vorticity and other complex flows found in the mouthpiece of a musical instrument and in other situations.

Multi-aperture ultrasound and photoacoustic imaging systems improve the imaging quality in terms of contrast, field of view, and potentially resolution in comparison to single aperture setups. However, the behavior of signal-to-noise ratio (SNR) in these systems has not been well understood. In this study, we propose a low-parameter predictive model for signal analysis based on the Fourier diffraction theorem. Furthermore, an analytical approach for SNR estimation is devised for both coherent and incoherent compounding methods. The theory is evaluated in simulations and experiments. The results show a great agreement with the theoretical expectation of k-space model for both mono-static and bi-static signals. In addition, the evaluated noise power and peak SNR results follow the analytical expectations. As the number of compounded reconstructed datasets increases, the noise power increases linearly and non-linearly for coherent and incoherent methods, respectively. Still, as demonstrated in both theory and results, for correlated sources, the SNR increases linearly with the number of coherently compounded reconstructions, while it can remain unchanged or even reduced if incoherent compounding is employed. Moreover, for uncorrelated sources, it is shown that compounding different views from several spatially diverse apertures may lead to a decrease in SNR.

Nanofiber membranes (NMs), fabricated via electrospinning of poly(vinylidene fluoride-co-hexafluoropropylene) solution, can effectively enhance the sound absorption coefficient (SAC) of porous materials with minimal mass and space requirements, making them appealing for aircraft noise reduction. The macroscopic property of a material is inherently influenced by its microscale, and therefore, this study investigates the effect of NM microscale on sound absorption and utilizes the transfer matrix method to reveal the effect of fiber diameter on the sound absorption of the membranes. The impact of the polymer concentration and solvent composition on the fiber diameter of these membranes is discussed. Experimental results demonstrate that alterations in solution parameters yield diverse fiber diameters and acoustic properties. An optimized polymer concentration and solvent composition for enhanced sound absorption are given through controlled experiments under specific stirring and electrospinning parameters. Notably, in the 1-2 kHz range, NM for melamine foam exhibits a 25% average increase in SAC, with 0.15% thickness and 0.02% weight increments. The Knudsen number and specific surface area are introduced to explain the variations in the SACs among NMs. This study provides insights into membrane acoustic properties at the microscopic level and offers guidance for producing high-performance NMs for sound absorption.

Acoustic radiation force (ARF) is a nonlinear phenomenon resulting from the wave momentum transfer to an absorbing or scattering target. ARF allows objects to be remotely manipulated, pushed, trapped, or pulled, which is used in medical applications such as kidney stone expulsion or acoustic tweezers. Such applications require development of methods for precision ARF measurements and calculations. The purpose of this paper is to present a method for direct measurement of the axial component of the ARF exerted by an ultrasound beam on its axis acting on a millimeter-sized spherical particle in a liquid. The method consists of weighing a rigid frame with a scatterer on electronic scales, similar to the radiation force balance method of measuring the total acoustic beam power. The capabilities of the method are demonstrated by applying it to spheres of different diameters (2-8 mm) and compositions (steel, glass). The additional objective is to provide experimental validation of the theoretical model of Sapozhnikov and Bailey [J. Acoust. Soc. Am. 133, (2013)], previously developed to calculate the ARF of an arbitrary acoustic beam on an elastic sphere in a liquid or gaseous medium based on the angular spectrum approach.

While Taiwan Mandarin alveolar and velar nasal codas are reported to lose their place contrast in a vowel-dependent fashion (i.e., more pervasive merging in the /iN/ context, followed by the /əN/ context, and no merging in the /aN/ context), other acoustic cues, such as vowel nasalization, have been reported to preserve the contrast. Results from our ultrasound experiment, in which Taiwan Mandarin speakers produced nasal codas in both focused and unfocused conditions, showed that the place contrast was most vulnerable to merger in /iN/ and /əN/ contexts and was not enhanced by focus. Instead, pre-nasal vowel nasalization emerged as a contrastive cue, especially in the highly merged /iN/ context in both focus conditions, suggesting a possible shift from place contrast to nasality contrast in production. A follow-up identification experiment revealed that speakers did not yet utilize the nasalization cues reliably to perceptually identify nasal codas, indicating a mismatch in the perception-production link.

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.