Volume 128, Issue 1, July 2010
Index of content:
- ADVANCED-DEGREE DISSERTATION ABSTRACTS
128(2010); http://dx.doi.org/10.1121/1.3397653View Description Hide Description
The present work compared the physical and psychoacoustical characteristics of standard impact sources with those of human impacts, and proposed the perception models of annoyance for impact sounds with respect to temporal and spatial aspects. Impact ball (heavy/soft impact source) was selected as an appropriate standard floor impact source simulating real floor impacts based on the objective evaluation and similarity judgment. Then, measurements using impact ball were conducted in a variety of apartment buildings with different floor structure and coverings. Variations in frequency characteristics were found in the measurement results, thus these were classified into three groups, Groups A-C. Differences between Groups A-C were clarified using sound quality metrics. Finally, perception models of impact ball sounds were developed in relation to temporal aspects and spatial characteristics, respectively. When the spatial characteristics kept constant, perceptions of annoyance for impact ball sounds were affected mainly by the differences in fluctuation strength as well as loudness . Another perception model comprised of IACC (Interaural cross-correlation function) was also proposed through auditory experiments. It was found that IACC had an effect on the perception of impact ball sounds with sound pressure level, and the contribution of IACC on perception of impact ball sounds was around 20%
128(2010); http://dx.doi.org/10.1121/1.3438481View Description Hide Description
The main goals for this study were to better understand what are the acoustic conditions physically within a symphony orchestra on concert hall stages, how these physical conditions affect the players and ultimately how to design venues suitable for symphony orchestras. This was investigated through questionnaire surveys and dialogue with musicians, scale and computer modelling and measurements of existing stages. The results from the orchestra collaborations indicate that the impressions of acoustic conditions are related to complex perceptual effects. When relating these effects to acoustic conditions, a narrow and high stage enclosure with the stage highly exposed to the main auditorium appears most beneficial. Existing methods for assessing the stage acoustically by use of omnidirectional transducers without the orchestra present were found to have only limited relevance to perceived conditions. New methods and objective architectural measures have been proposed. The architectural measures successfully discriminate the most preferred from the least preferred stages of purpose-built concert halls. The results from judgements of existing stages support the finding of a narrow and high stage enclosure with a highly exposed stage being most beneficial. How to improve the assessment of acoustic conditions on stage is discussed. Copies of the thesis written in English can be obtained from Jens Jo/rgen Dammerud. E-mail address: firstname.lastname@example.org. 4
An enhanced numerical model to simulate nonlinear continuous wave ultrasound propagation and the resulting temperature response128(2010); http://dx.doi.org/10.1121/1.3455791View Description Hide Description
In this work a nonlinear CW ultrasound field propagation model based on a second-order operator splitting approach is studied and a number of significant enhancements are introduced and implemented. In this model the ultrasound field is calculated and propagated plane by plane and the effects of diffraction, nonlinearity and absorption are applied independently over incremental steps. This work completes the preceding works (Christopher and Parker 1991, Tavakkoli 1998, Zemp 2003, Williams 2006) by introducing an arbitrary source geometry and excitation definition, full diffraction solution, enhanced pressure, enhanced power deposition rate and temperature prediction capabilities. The result is a particularly useful tool in carrying out simulations of high intensity focused ultrasound (HIFU) that includes temperature rise predictions. Comparisons are made with other codes in both linear and nonlinear regimes. Different dynamics of lesion formation are obtained in linear versus nonlinear models, specially at the onset of lesion creation during HIFU exposure.
128(2010); http://dx.doi.org/10.1121/1.4808931View Description Hide Description
This thesis develops non-linear Bayesian methods for three-dimensional tracking of a moving acoustic source in shallow water despite environmental uncertainty, with application to data from a horizontal line array (HLA) of hydrophones. Focalization-tracking maximizes the posterior probability density (PPD) over track and environmental parameters. Synthetic test cases show that the algorithm substantially outperforms tracking with poor environmental estimates and generally obtains results close to those achieved with exact environmental knowledge. Marginalization-tracking integrates the PPD over environmental parameters to obtain joint marginal distributions over source coordinates, from which track uncertainty estimates and the most probable track are extracted. Both approaches are applied to HLA data from a shallow-water experiment conducted in the Barents Sea. Focalization-tracking successfully estimates the tracks of a towed source and a surface ship in cases where simpler tracking algorithms fail. Marginalization-tracking generally outperforms focalization-tracking and gives uncertainty estimates that encompass the true tracks. As a precursor, Bayesian geoacoustic inversion is applied (to both controlled-source and ship-noise data) to estimate seabed model parameters and their uncertainties. It is demonstrated that combining data from multiple, independent time-series segments in the inversion can significantly reduce geoacoustic parameter uncertainties. Geoacoustic uncertainties are also shown to depend on ship range and orientation.