Showing papers in "Applied Acoustics in 1994"

TL;DR: In this article, the authors compared various commercial methods and materials for acoustic transduction, identifying their advantages and limitations, and concluded that the piezoelectric approach offers several advantages, including design cost and simplicity.

TL;DR: The theoretical basis of the most popular state-of-the-art numerical structural-acoustic analysis techniques, the finite element methods and boundary element methods, are described in general terms.

TL;DR: In this paper, negative Poisson ratios were produced in open cell, reticulated polyurethane foams by heat setting the foam which had been three-dimensionally compressed 3·7fold.

TL;DR: In this paper, the acoustic behavior of fibrous materials which depend upon physical structural parameters has been investigated experimentally and various values of characteristic impedance and propagation constant have been determined for materials having different fibre diameter and density.

TL;DR: In this paper, the authors developed the theory of low-frequency groundvibrations by moving trains in the framework of the quasi-static wheel pressure effect using the Green's function formalism.

TL;DR: A survey of traffic noise in the city of Delhi was carried out in order to examine the nature and levels of noise inside various types of vehicle as discussed by the authors, and it was found that noise levels in auto-rickshaws are the highest, followed by trucks, buses and cars.

TL;DR: In this paper, a local active control system was investigated, in which the pressure at a point in front of a piston secondary source was driven to zero, and the spatial extent of the zone of quiet created around the point of cancellation was determined numerically, for both a uniform and diffuse primary sound field.

TL;DR: In this article, a theoretical basis for acoustically thick plates is presented, which has been confirmed through measurements of phase speed as a function of the frequency for a number of wall and slab elements.

TL;DR: In this paper, a beam with a single-sided crack or a pair of double-sided cracks is modeled as two separate beams divided by the crack, and two different sets of admissible functions which satisfy the respective geometric boundary conditions are assumed for these two fictitious subbeams.

TL;DR: In this article, the effects of stiffeners, added mass and complex support conditions along the structure boundaries are incorporated into a model of sound radiation in air from a complex, baffled, rectangular panel under harmonic point force or point moment excitation.

TL;DR: In this article, a simple model for the calculation of finite length barrier insertion loss is described, which is based on the concept of minimum diffracted paths and makes use of Maekawa's empirical curve to estimate the attenuation associated with each diffracted path.

TL;DR: In this article, a vibro-acoustic reciprocity technique was proposed for the experimental prediction of sound radiated by an internal combustion engine. But the technique is not suitable for the measurement of the volume velocity distribution of the source.

TL;DR: In this paper, a simple model is employed, assuming the total sound pressure in the diffuser plane to be constant, which is considered a reasonable approximation in the low frequency range.

TL;DR: In this article, the theoretical basis of the modal method for acoustic radiation from structures is presented, which consists of expanding structural responses on a functional basis, truncated for numerical computations.

TL;DR: In this paper, two numerical methods, i.e., transfer matrix method and a finite element method have been used to model the acoustic absorption of slotted plate type resonant absorbers where the damping is provided by a thin fabric covering the slits.

TL;DR: In this paper, a 0-3 composite piezoelectric material with active ferroelectric materials and other inert phases such as polymers was developed for the detection of acoustic signals in a hydrostatic mode.

TL;DR: The NPE model has been used for the prediction of high-intensity pulse waveforms in the time domain when propagating through water as mentioned in this paper, and more recently for weakly non-linear propagation in air.

TL;DR: It is found that the sum of the eigenfrequency shifts over a number of modes is close to zero for the duct with the blockages, and a new method is proposed to reconstruct the blockage location and its size in the duct.

TL;DR: In this article, the attenuation of an impulse excitation over-seating in an unoccupied concert hall and on scale model seats was investigated and it was found that attenuation varied over time and the width of the seating area was also important.

TL;DR: Eckoldt et al. as discussed by the authors presented a computer program that allows the calculation of the insertion loss of splitter silencers in such a way that the results are comparable to results measured according to ISO 7235.

TL;DR: In this paper, the reflection from the facade of a building is considered in terms of specular reflection and diffuse scattering, and the importance of reflected noise is evaluated by comparing it with the contribution of the direct wave and background noise.

TL;DR: In this paper, three active noise control (ANC) systems, which incorporate different arrangements of the secondary loudspeaker have been examined experimentally, based on the analysis of the characteristics of sound wave propagation in a duct.

TL;DR: In this article, the fundamental frequencies and critical buckling loads of simply supported beams with stepped variation in thickness are computed using two algorithms based on the Rayleigh-Ritz method.

TL;DR: In this article, the authors examined the influence of the pressure equalisation vents of conventional condenser microphones on the performance of sound intensity probes provided with such microphones, and they showed theoretically and demonstrated experimentally that the vent systems give rise to a bias error that is proportional to the reactive sound intensity.

TL;DR: In this article, a year-long study of the noise environment in the city of Kuopio, Finland was made to assess noise sources in an urban community in different seasons.

TL;DR: In this paper, the amplitude of the radiated noise of a four-cylinder engine is analyzed analytically and numerically, and compared to experiment. But the analysis is limited to the case where the manifold resonances are independent of the manifold shape.

TL;DR: In this article, the authors evaluated the sound absorption properties of a porous Al2O3-SiO2 system and found that the porosity and grain size of the sample can affect the sound absorbing properties.

TL;DR: In this article, the authors reported the results of a study to estimate the exposure of the Australian population to road traffic noise, and they used a sample of 264 dwellings, randomly selected throughout all Australian urban centres with a population of more than 100 000 people.

TL;DR: In this paper, the authors proposed an active noise control system with both the pick-up microphone and the cancelling loudspeaker in the corner region of the room, well within a quarter wavelength to the three adjoining surfaces.

TL;DR: In this article, an experimental evaluation of the ability of sound pressure microphones to diagnose different machinery conditions in noisy environments was performed and an adaptive filtering (ANC) routine was incorporated to reduce the noise.