Sound absorption by clamped poroelastic plates

Measurements and predictions have been made of the absorption coefficient and the surface acoustic impedance of poroelastic plates clamped in a large impedance tube and separated from the rigid termination by an air gap. The measured and predicted absorption coefficient and surface impedance spectra exhibit low frequency peaks. The peak frequencies observed in the absorption coefficient are close to those predicted and measured in the deflection spectra of the clamped poroelastic plates. The influences of the rigidity of the clamping conditions and the width of the air gap have been investigated. Both influences are found to be important. Increasing the rigidity of clamping reduces the low frequency absorption peaks compared with those measured for simply supported plates or plates in an intermediate clamping condition. Results for a closed cell foam plate and for two open cell foam plates made from recycled materials are presented. For identical clamping conditions and width of air gap, the results for the different materials differ as a consequence mainly of their different elasticity, thickness, and cell structure

Computational and theoretical investigation of acoustical and vibrational properties of rigid thin material

Computational and theoretical investigation of acoustical and vibrational properties of rigid thin fiberglass material was carried out for different boundary conditions. Fiberglass materials could be utilised for applications ranging from aerospace industry and automotive industry to building and construction industry. The theory of the plate vibration and acoustic radiation were applied to predict the deflection of the thin fibreglass material and sound radiation efficiency at different locations on its surface while study-controlled equation of motion known as Kirchhoff thin plate theory was applied for COMSOL simulation of thin material to determine the deflection of the plate and to obtain stress distribution, velocity contour, displacement, and acoustic pressure at first resonance of the material. The results of this paper show that thin fiberglass material could be applied to sandwich building structures to form panels in order to attenuate airborne sound and to lower noise transmission of structural borne sound, to cover noise barrier to make them more sustainable and weather resistant, to dampen the vibration of machines, and to reduce the structural vibration of buildings

Scattering of acoustic waves in air and water filled 3D stereo-lithographical (STL) porous rigid materials

The scattering of acoustic waves propagating in porous rigid 3D stereolithographical materials that are made of resin, has been investigated. 3D stereolithographical (STL) materials were obtained using a form of rapid prototyping that allows complex solid objects to be manufactured directly from3D computer models in the form of successive layers of light-cured resin. Relative variation of velocity and attenuation of 3D materials in air filled and water filled media has been predicted at normal and oblique directions. The scattering perturbation is similar to diffusion waves at low frequency while dispersion velocity and attenuation change with respect to square root of angular frequency and with respect to angular frequency at high frequency respectively

Spatial Fourier transform method to determine reflection and absorption coefficient of porous rigid materials applying Johnson-Champoux-Allard model

Sound absorption and reflection coefficients of the materials are two important parameters to understand the capacity of the materials to store acoustical energy. Spatial Fourier transform method is based on calculation of complex pressure distributions on two parallel surfaces and decomposing the complex pressure distributions into plane-wave components by using two-dimensional spatial Fourier transform which is used to separate the incident and reflected plane wave components. Johnson-Champoux-Allard model is utilized to predict effective density and bulk modulus of the air in the material, which are used to calculate wave number and characteristic impedance. Consequently, they are used to determine absorption and reflection coefficient of the porous materials at oblique angles

Sound radiation from composite plates

The vibration of the plates that are made of isotropic and homogeneous materials has been an important subject in the study of noise control, in the aeronautical industry, in the study of fluid-solid interactions and in building construction. It is aimed to investigate the vibrational and acoustical parameters of thin composite plates that are made of fibreglass. A thin, baffled plate of dimension a x b and uniform thickness h, excited by an uniform force density is considered. Vibroacoustical properties of thin clamped composite plate have been reported. The deflection of composite plate has been predicted at different locations on the plate using the classical theory of plate vibration while computational simulations have been carried out to determine deformations of the plate in 3D for different frequency ranges for two boundary conditions

Acoustic wave propagation through panels that are made of used tea bags

These days more than ever, society habits raise the necessity to consider the future of the environment. This presentation will tackle the aspect of more eco-friendly sound absorbing materials, more specifically analyzing the properties of consumed tea bags, starting from the collection up to the application and measurement of the final product. Many good options are often avoided, or not implemented for the lack of reliable properties analysis, encouraging existing materials to be chosen instead. The more information could be found about new materials, the more these could have a chance to be used, compared, or eventually improved. Sound absorbing panels that are made of tea bags were designed and developed to investigate sound transmission through tea-bag panels. Measurements were carried out on tea-bag panels in an impedance tube using a transfer function method to determine their sound absorption and transmission loss. Furthermore, the impedance gun system was used to determine acoustical properties of larger panels. Results show that 70 mm thick panels give an absorption coefficient higher than 0.8 between 500 Hz and 1600 Hz while 17 mm thick panels give an absorption coefficient that is mostly effective at higher frequencies. Up to 9 dB sound transmission loss is obtained at some frequencies

An Audio-Based Vehicle Classifier Using Convolutional Neural Network

Audio-based event and scene classification are getting more attention in recent years. Many examples of environmental noise detection, vehicle classification, and soundscape analysis are developed using state of art deep learning techniques. The major noise source in urban and rural areas is road traffic noise. Environmental noise pa-rameters for urban and rural small roads have not been investigated due to some practical reasons. The purpose of this study is to develop an audio-based traffic classifier for rural and urban small roads which have limited or no traffic flow data to supply values for noise mapping and other noise metrics. An audio-based vehicle classifier a convolutional neural network-based algorithm was pro-posed using Mel spectrogram of audio signals as an input feature. Different variations of the network were generated by changing the parameters of the convolu-tional layers and the length of the network. Filter size, number of filters were tested with a dataset prepared with various real-life traffic records and audio extracts from traffic videos. The precision of the networks was evaluated with the common performance metrics. Further assessments were conducted with longer audio files and predictions of the system compared with actual traffic flow. The results showed that convolutional neural networks can be used to classify road traffic noise sources and perform outstandingly for single or double-lane roads

Acoustic and Aesthetics: The Effect of Paint on Fabric Backed by a Sound Absorber

This project investigates the effects of paint on the acoustical properties of cotton and canvas fabrics. Polyurethane foam was used to back the fabric, and the dependencies on the type of paint, painted area, area distribution, and the type of fabric were analysed. One hundred and nine samples of cotton and canvas fabrics were used for this investigation. The impedance tube method, which is performed via the transfer function method, was employed to determine the acoustic properties. It is shown that the absorption of the samples is affected by the type of paint and fabric, and painted percentage area, and establishing an effective set of these parameters will result in the acoustic transparency of the fabric

Investigation of acoustic performance of compressed wool carpets

Sound absorbers including porous materials are used widely for noise control. The most widely-exploited and acknowledged absorption mechanism in porous materials is viscous friction due to relative motion between solid and fluid. Acoustical performance of carpet made of wool by using a traditional compression technique has been investigated. The results are very interesting

Determining mechanical parameters of the bone using a vibro-acoustic method

Human bones are energy absorbing complex composite structures that have an irregular hollow structure filled with marrow and surrounded by soft tissue and muscles. Current recommendations for the assessment of patients for bone mineral density (BMD) and fracture risk have several difficulties, and they are not suitable for international use. To date, no satisfactory evidence exists either supporting or refuting the usefulness of the vibro-acoustic technique. The aim of this paper is to use the vibro-acoustic technique to analyse and assess the acoustical and mechanical properties of human bone by demonstrating if variations in sound propagation through the bone can be detected. Firstly, a viscoelastic bone system is modelled to estimate mechanical properties of the bone. modal analysis of the human bone and sawbones are carried out using the viscoelastic bone system to estimate mechanical properties of the bone from acoustical parameters deduced from frequency dependent transfer function