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The article presents the December 2017 issue of the periodical "Acoustics Australia." Topics include research articles on topics like sound quality experiments in a student hostel with newly designed sonic crystal window, and design and validation of a simulator tool useful for designers and policy makers in urban sound planning; news reports related to Australian Acoustical Society (AAS); and an obituary for professor Neville Fletcher.

The integration of basic geometrical acoustics into architectural design is not new. The arrival of 3D modelling packages such as Grasshopper has certainly increased the consultants' efficiency and dialogues within the design team. It has also forced the designers to go back to the basics. Efficient algorithms are complex and their development time is consuming. At first, Grasshopper's apparent limitation in complex calculus seems to confine its use to basic trigonometry, but this is not the case anymore. Much has been said about geometry analysis. But few acoustic designs are driven by actual parametric design. Recent collaborations with architects well versed in parametric design presented opportunities for the further development of acoustic concepts into real input of parametric design. Grasshopper can indeed be used to resolve inverse problems for which the output is assumed. The unknown to the problem is the 'precise geometry of the hall'. This paper describes the collaborative approach to develop a single algorithm for both acoustic and architectural form generation. [ABSTRACT FROM AUTHOR]

Present studies on the reduction of motor noise using the harmonic injection method focus on motors without mechanical brushes and commutators. Using the voltage harmonic injection method, this study proposes to reduce the noise in Rounded Square PMDC motors with mechanical brushes and commutators. The specific order and frequency of electromagnetic harmonic forces can be eliminated without losing motor performance. 2D finite element analysis and experimental testing were conducted to analyze the root cause of motor noise. Major excitation force harmonics of the motor noise were found. Theoretical and simulation models of voltage injection harmonics were built. The appropriate voltage injection harmonic was determined. The motor performance and noise was studied with and without voltage harmonic injection. It was verified that the voltage harmonic injection method was useful for noise reduction in rounded square PMDC motors. Most importantly, its performance was maintained. [ABSTRACT FROM AUTHOR]

The paper presents an experimental approach to quantify the vibrations induced due to acoustic excitation in diffuse field conditions. An empirical formulation correlating the varying sound field and vibration level generated in floors and walls in diffuse field conditions has been developed. A lower limiting frequency of 125 Hz for good diffusion is observed due to random wide band acoustic excitation in diffuse field conditions, below which lower vibration levels are registered due to discrete room modes. [ABSTRACT FROM AUTHOR]

A microperforated panel (MPP) is usually placed with a rigid-back wall to form a Helmholtz resonator with its hole and the air-back cavity. However, the authors have so far proposed an MPP space sound absorber without any backing structure. In the previous studies, as a basic form of such an MPP space absorber, multiple-leaf MPP structures without a back wall were proposed, and were theoretically and experimentally examined. In order to provide more unrestricted usage and designs for an MPP space absorber, the authors have also proposed a three-dimensional MPP space absorber, called a cylindrical MPP space absorber (CMSA). The CMSA was shown to exhibit resonance peak absorption and additional low frequency absorption. In this paper, another alternative of a three-dimensional MPP space absorber, a rectangular MPP space absorber (RMSA) is proposed. Its sound absorption performance is discussed using experimentally measured results. The results show sound absorption characteristics similar to a CMSA, and an RMSA can be effectively used if properly designed. [ABSTRACT FROM AUTHOR]

A novel methodology is presented for the simultaneous measurement of noise and personal annoyance at the exact times that the affected person is annoyed. The system is described and applied to a test case, a farmhouse close to a wind farm where the resident claims to be annoyed by noise. The system was successfully able to characterise the level and spectral content of the noise in the house when the resident was annoyed, and there was some correlation with personally recorded annoyance level. As the system cannot identify noise sources, no conclusions can be made about noise source; however, the methodology is shown to be a useful aid for diagnosing the type and severity of an indoor noise problem. To help interpret the results from this type of testing, a discussion concerning the subjective nature of noise annoyance is presented before some suggestions are made for further improvements in the measurement system. [ABSTRACT FROM AUTHOR]

This paper presents the results provided by two simulation programs for a very simple model: a cube in which all sides have the same absorption but different global scattering coefficients. Effects on merit figures of the main acoustic parameters are shown for scattering changes for a single absorption coefficient. The results are helpful for understanding the role of absorption and scattering on the values of these parameters. [ABSTRACT FROM AUTHOR]

The Pipe-in-Pipe model (PiP) is a quick and accurate tool for calculating vibration from underground railways and for assessing the performance of vibration countermeasures. The original model formulation simulates a tunnel buried in a fullspace but has recently been extended to account for a free-surface (i.e. halfspace). Results from the two versions are compared to quantify the effect of the free-surface on soil power spectral density (PSD) values. The study suggests that it is reasonable to assume the PSD surface results predicted from the free-surface model will be approximately 6dB more than those predicted by the fullspace model when the tunnel is at a depth of two tunnel-diameters or more. For tunnel depths less than two tunnel-diameters it seems beneficial to account for the free surface in the simulation as there is significant variation in the results invalidating the 6dB assumption. [ABSTRACT FROM AUTHOR]

Rotor-stator interaction has been identified as the dominant noise source of the Mupod, a vertical take-off and landing aircraft, developed by Entecho, a WA company. This paper reports field measurement results of blade passing noise of the Mupod together with its analysis and control. The blade passing event was simulated in a wind tunnel experiment. The flow speed, rotor blade position and rotor stator blade spacing were varied while the chord-wise pressure distribution of the leading surface of the rotor blade was measured by an array of 6 flush mounted microphones. The features of the pressure distribution on the rotor blade influenced by an upstream stator blade were used for the qualitative analysis of the sound radiation from the Mupod. The result of the reduction of the blade passing noise using angled stator blades is also presented. [ABSTRACT FROM AUTHOR]

Newly developed software, NoteView, is used to analyse the fundamental frequency (F0) and categorical as well as microtonal pitch from audio recordings of music performances from a single line (monophonic) instrument. The code is based on the SWIPE algorithm developed by Camacho and Harris. The features of the interface are described and a comparison of two performances of a familiar piece played by a professional French horn player is used as an example for the purpose of investigating the pitch stability of the two renditions. Results produced by NoteView indicate that pitch pairs across the two performances differed by a mean of 7 cents, and that within-note standard deviation was typically 6 cents. These results are examined using the various customisable views and statistics returned by the software. Some of the features and limitations of NoteView are discussed. The software is currently implemented in Matlab and is freely available from the UNSW Empirical Musicology web site http://empa.arts.unsw.edu.au/research-and-creative-practice/research-projects/ empirical-musicology/. [ABSTRACT FROM AUTHOR]

Mufflers are incorporated into continuous positive airway pressure (CPAP) devices to reduce noise in the air paths to and from the flow generating fan. The mufflers are very small, irregularly shaped, and are required to attenuate noise up to 10kHz. It is important that the acoustic performance of these mufflers is reliably predicted and optimised, in order to improve the user experience and maximise compliance with the CPAP therapy. In this study, the acoustic performance of three reactive muffler designs similar to those used in CPAP devices is presented. Transmission loss predictions obtained using analytical and finite element methods are compared with experimental data measured using a test rig based on the two-microphone acoustic pulse method. The analytical methods were found to be unsuitable for predicting the transmission loss of CPAP muffler designs due to the complexity of the muffler geometries. Good agreement between the finite element and experimental results were obtained. [ABSTRACT FROM AUTHOR]