High-Frequency Diffraction of a Point Source Field by a Strongly Elongated Elliptic Cylinder

The problem of diffraction of a high-frequency point source acoustic field by an infinite elliptic cylinder with a strongly elongated cross-section is studied. At every direction of propagation, the solution is shown to be similar to those of a linear source field diffraction by a cylinder with correspondingly enlarged major semiaxis.

A Review of Gunshot Noise as Factor in Hearing Disorders

The impulse noise produced by personal weapons (guns, rifles, shotguns) during military activity, and while people engage in sport, training and hunting, is a threat to the auditory systems of soldiers, civilians, policemen, hunters, forest officers, sportspeople and bystanders not actively engaged in professional or recreational firing. An overview of noise levels generated by different types of weapon is provided, and potential short-term and long-term consequences for the human auditory system are described. The mean values of LC, peak sound pressure level during the shot, at the shooter's ears, for various types of weapons are approximately 160 dB SPL. These are levels that can cause permanent, irreversible negative effects on hearing (hearing loss, tinnitus, etc.) even as a result of a single shot being fired. One of the largest groups of weapon users in Poland (about 120 thousand) are hunters and field masters. They are not obligated by any regulations to protect their auditory systems from impulse noise. This means that this group of firearm users is at particularly high risk of hearing damage. On the basis of the literature review, it is shown that hearing exposure to high-level impulse noise such as a gunshot can result in such consequences as damage to the middle ear and destruction of the outer/inner hair cells in the cochlea. Especially difficult to diagnose is 'hidden hearing loss', i.e. damage to the synaptic connections between the hair cells of the inner ear and the auditory nerve fibres, which is not reflected in the results of basic audiometric testing and can cause hearing problems many years after impulse noise exposure. The wide range of negative consequences of gunfire noise clearly indicates the need for the hearing of the shooters to be protected.

Numerical Modelling of Boundary Layers and Far Field Acoustic Propagation in Thermoviscous Fluid

To model linear acoustics in a thermoviscous fluid in open domain and time-harmonic regime, a Finite Element formulation in a bounded meshed domain is combined with the integral representation of the field for the propagative solution. The integrals are non-singular and involve the only Finite Element node values for temperature variation and particle velocity variables. To overcome the non-uniqueness of solutions at fictitious resonant frequencies, a Burton-Miller combination of integral representation is used. This formulation is suitable to compute acoustic radiation, scattering and diffraction by objects or mutual interaction between transducers. Two-dimensional computational experiments are presented in an infinite, open domain (exterior), showing that the model can be achieved in meshing only a thin domain surrounding the physical boundaries of a device.

Detection and Evaluation of Amplitude Modulation From a Wind Energy Development, Ireland

Amplitude modulation (AM) is a characteristic of wind turbine noise that has only been recognised as an issue in recent years. It is a characteristic related to aerodynamic noise and descriptions of it include "swishing", "whooshing" or less frequently a "thumping" sound. Due to increased awareness among exposed communities AM presents a potentially serious obstacle to future wind farm developments. This work reports on the application of a recently developed calculation method for AM in a practical setting. Correlations will be drawn with subjective reports of AM by nearby residents keeping a noise diary. The suitability of the method and its ability to quantitatively confirm subjective reports of AM will be assessed. A study is presented here whereby subjectively recorded occurrences of AM by residents living near a wind energy development in Ireland are correlated to calculated levels over a twenty day period. In order to detect and calculate AM a method published by the Amplitude Modulation Working Group of the Institute of Acoustics, referred to as the Reference Method, is applied. A subjective assessment of the sound recordings to confirm the presence of AM is discussed, including estimating the expected frequency range that AM occurs. The results of the Reference Method calculation are presented for periods with and without a subjective report of AM by the residents. Consideration is given to the criteria and thresholds for valid AM ratings within the Reference Method especially where intermittent periods of AM are identified. The Reference Method is shown to be highly suitable as a quantitative measure of AM which correlates well with subjective reports. Caution must be taken when using the method as valid periods of AM may be overlooked due to the rigorous detection thresholds set by the method.

Rippled Depth Thresholds: Estimates Obtained by Discrimination From Rippled and Nonrippled Reference Signals

The objective of the study was to better understand of contribution of excitation-pattern and temporal-processing mechanisms of frequency analysis to discrimination of complex-spectrum signals in various discrimination tasks. Using rippled-spectrum signals, the ripple depth thresholds were measured as functions of ripple density under conditions of rippled or non-rippled reference signals. With rippled reference signals, the ripple depth thresholds were as low as 0.11 at low ripple densities (2–3 cycles/oct) and rose to 1.0 at a ripple density of 8.9 cycles/oct. For non-rippled reference signals, ripple depth thresholds were nearly the same as for rippled reference signals at ripple densities of up to 7 cycles/oct; at ripple densities of 10 cycles/oct and higher, ripple depth thresholds rose slowly and reached 1.0 at a ripple density of 26 cycles/oct. The results hypothetically suggest contributions of the excitation-pattern processing and temporal-processing mechanisms of frequency analysis to discrimination of rippled signals. The excitation-pattern mechanism featured low depth thresholds at low ripple densities but could not function at ripple densities above 10 cycles/oct. The temporal-processing mechanism manifested at higher ripple densities and non-rippled reference stimuli.

Performance of a Low-Height Acoustic Screen for Urban Roads: Field Measurement and Numerical Study

Field measurements and numerical modelling were used to study the acoustic performance of a low screen in an urban road setting. The results show the usefulness of low screens as well as suggests improvements in screen design. For the measurements, an acoustic screen built up from concrete modules was temporarily installed beside a small park on the reservation between a two-lane road and a track for walking and cycling. A larger traffic system, of which the two-lane road is a part, determines the daytime equivalent noise level within the urban area. The screen height was about 1.4 m as measured from the level of the road surface and the width of the screen top was 0.3 m. Measurements were carried out both at 20 m distance from the road (within the park) and at 5 m distance from the road (at the cycle track). Insertion loss in maximum level, using controlled lightvehicle pass-by at 50 km/h, was measured to 10 dB at 5 m distance and to 6 dB at 20 m distance, at 1.5 m height. Insertion loss in equivalent level was measured within the park to 4 dB at 1.5 m height. A listening experiment confirmed a perceived improvement from installing the screen. The measured results were also compared with predicted results using a boundary element method (BEM) and a noise mapping software, the latter showing good agreement, overestimating the equivalent level insertion loss by 1 dB in the park. The BEM comparison showed reasonable agreement in maximum level insertion loss considering that facade reflections were excluded, with an overestimation of 5 dB at the cycle track, and good agreement in the park, overestimating by up to 1 dB the equivalent and maximum level insertion losses. BEM predictions were used to also investigate other screen designs, showing a positive effect of an acoustically soft screen top, significant for a screen width of 0.2 m and increasing for wider screens.

Study on the Properties of Aerodynamic Reference Sound Sources

Towards the establishment of traceability in sound power in airborne sound, the present study focuses on the dissemination procedure. Aerodynamic reference sound sources were studied as potential transfer standards. Initially, the sources were examined in the up-to-present requirements. The core of the study is the correction required for the transition from calibration to in situ conditions. The influence of atmospheric pressure, ambient temperature and fan rotation speed was investigated and the corresponding correction was determined. A comparison to an existing correction was also performed. Near field effects were another part of the study. The related uncertainty was estimated in a transparent approach. The dependency of the uncertainty on the in situ and calibration condition values is also presented.

Acoustic Scattering from Bi-Layered Cylindrical Shells: Influence of the Layers Thicknesses on the Guided Waves

The current work focuses on the study of acoustic scattering from bi-layered stainless steel-copper and copper-stainless steel cylindrical shells filled with air and immersed in water. This paper is interested in revealing the effects of physical and geometrical characteristics of the layers constituting the shells on the scattering phenomenon. The object of this work, is to study the influence of the layers thicknesses on guided waves, the overall thickness of the shells is fixed. The plane of modal identification was chosen to analyze the scattering phenomenon. We investigate the resonance trajectories of the guided waves, especially the curves change. The investigation and comparison made on resonance trajectories, show a shape change, a gradual deviation, or both, appear on the resonance trajectories of different guided waves, for the reduced cutoff frequencies of guided waves a sliding to higher and lower value are noticed. The interaction between guided waves is also manifested in the scattering phenomenon. The findings for the bi-layered cylindrical shells are then compared with those obtained for the mono-layered stainless steel and copper cylindrical shells. Then, this work is completed by an investigation on the reduced cut-off frequencies of the A1 wave, that have been extracted for different possible values of the intermediary radius. In this part, to understand the observed phenomena, other examples of bi-layered cylindrical shells are introduced. The obtained results are analyzed and investigated.

Influence of the "Ghost Reed" Simplification on the Bifurcation Diagram of a Saxophone Model

This paper presents how the bifurcation diagram of a saxophone model is affected by the contact force limiting the displacement of the reed when it strikes the mouthpiece lay. The reed impact is modeled by a nonlinear stiffness and damping activated by contact with the lay. The impact model is compared with the "ghost reed" simplification, where the reed moves through the lay unimpeded. Bifurcation diagrams in both cases are compared, in terms of amplitude of the oscillations and location of the bifurcations, on the solution branches corresponding to the first and second register. The ghost reed simplification has limited influence at low values of the blowing pressure parameter: the diagrams are similar. This is true even for "beating reed" regimes, in which the reed coincides with the lay. The most noticeable discrepancies occur near the extinction of the oscillations, at high blowing pressure.

The Acoustics of Kabuki Theaters

The study presents a room acoustical investigation of a representative sample of eight Kabuki theaters as the most important public performance venues of pre-modern Japan. Room acoustical parameters according to ISO 3382 were measured for the unoccupied and simulated for the occupied condition. In comparison with European proscenium stage theaters, they have lower room heights in the auditorium, with usually only one upper tier, and no high stage house for movable scenery. The lower volume per seat results in lower reverberation times, The wooden construction and the audience seating arrangement on wooden straw mats on the floor instead of upholstered seats leads to a mostly flat frequency response up to 4 kHz, resulting in an excellent speech intelligibility, as documented by values for definition (D50) and the speech intelligibility index (STI). The acoustical conditions support the dynamic acting space created by pathways extending the stage from the front through the audience to the rear of the auditorium. They allow great contrasts in the perceived acoustical proximity depending on the selected acting position, and support a high degree of immersion of the audience into the dramatic action.