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Sounds to Astound is an acoustics demonstration show, produced for the community twice yearly by the Brigham Young University Student Chapter of the Acoustical Society of America. The free, interactive demonstration show explores the science of sound for a target audience of fifth- to eighth-grade students. Introductory acoustics concepts, such as longitudinal wave motion, wave properties, propagation effects, and standing waves, are taught with live demonstrations, animations, and videos. The goal of this paper is to inspire and encourage readers in their outreach efforts by describing the purposes of Sounds to Astound and technical details of several entertaining and educational demonstrations. Lessons learned from a decade of these student-produced shows serve as an aid for future efforts and highlight the benefits of outreach efforts, particularly for the students involved.

Multireference partial field decomposition (PFD) can be used to generate coherent holograms for near-field acoustical holography measurements. PFD is most successful when the reference array completely senses all independent subsources, but meeting this requirement is not straightforward when the number of subsources and their locations are ambiguous (such as in aeroacoustic sources). A figure of merit based on spatial coherence lengths, called references per coherence length (RPL(C)), is a useful metric to guide inter-reference spacing in the array design. For numerical, extended, arbitrarily coherent sources one reference per coherence length results in a sufficient reference array.

Acoustic shocks have been previously documented in high-amplitude jet noise, including both the near and far fields of military jet aircraft. However, previous investigations into the nature and formation of shocks have historically concentrated on stationary, ground run-up measurements, and previous attempts to connect full-scale ground run-up and flyover measurements have omitted the effect of nonlinear propagation. This paper shows evidence for nonlinear propagation and the presence of acoustic shocks in acoustical measurements of F-35 flyover operations. Pressure waveforms, derivatives, and statistics indicate nonlinear propagation, and the resulting shock formation is significant at high engine powers. Variations due to microphone size, microphone height, and sampling rate are considered, and recommendations for future measurements are made. Metrics indicating nonlinear propagation are shown to be influenced by changes in sampling rate and microphone size, and exhibit less variation due to microphone height. [ABSTRACT FROM AUTHOR]

The viability of using reflection loss measurements for the determination of sediment parameters and the predictions of broadband acoustic behavior is studied as a function of frequency for a dispersive ocean bottom. For this study, a deterministic set of reflection loss values from an idealized dispersive sediment is calculated as a function of grazing angle over a large frequency band 100 Hz–1 MHz. In each of the four decades of frequency a simulated annealing optimization process is used to invert for the sediment parameters. In addition, a set of rotated coordinates is calculated that reveals the the relative sensitivities of the reflection data to each of the sediment parameters and therefore the ability of the inversion process to converge. The accuracy and precision of each estimate is analyzed. The predicted broadband acoustic behavior from the inverted parameters from each decade band was compared to the original model. Only the estimates obtained from data that include frequencies in the transition region can successfully predict broadband behavior. [ABSTRACT FROM AUTHOR]

A generalized inversion method is presented that uses a rotated coordinates technique [Collins and Fishman, J. Acoust. Soc. Am. 98, 1637-1644 (1995)] in simulated annealing to invert for both the location of an acoustic source and parameters that describe the ocean seabed. The rotated coordinates technique not only aids in the inversion process but also indicates the coupling of the source and environmental parameters and the relative sensitivities of the cost function to changes in the various parameters. The information obtained from the rotated coordinates provides insights into how the inversion problem can be effectively decoupled. An iterative process consisting of multiple simulated annealing runs that each use a different set of rotated coordinates is demonstrated. This multistep algorithm is called systematic decoupling using rotated coordinates and is especially helpful when inverting for a large number of unknown parameters. The cost function minimized in the inversion algorithm is model-data cross-hydrophone spectra summed coherently over frequency and receiver pairs. The results of applying this inversion method to simulated data are presented in this paper. [ABSTRACT FROM AUTHOR]

The Biot-Stoll poro-elastic model for sediments is parameterized by 13 properties. Initial investigations indicate that the individual Biot parameters influence reflection loss differently depending on the frequency range of interest. A more extensive study of the frequency dependence of the parameter sensitivities is performed by computing posterior probability distributions (PPDs) [S. E. Dosso, J. Acoust. Soc. Am. 111, 129–142 (2002)] to determine which parameters most influence reflection loss for each frequency decade from 100 Hz to 1 MHz. The sampling for the PPDs is based on the least-squares error between simulated reflection coefficient data and values modeled with the reflection module of OASES. [H. Schmidt, ‘‘OASES Version 2.1 User Guide and Reference Manual,’’ Department of Ocean Engineering, Massachusetts Institute of Technology, 1997.] The PPDs provide a quantitative value of the uncertainty in the optimum parameter estimates obtained by sampling or inversion techniques. A good value of the uncertainty is critical if one wants to use parameter estimates obtained with data from one frequency range to predict acoustic response for a different frequency range. [Work supported by the ONR.] [ABSTRACT FROM AUTHOR]