The introduction of machine learning (ML) in the research domain is a new era technique. The machine learning algorithm is developed for frequency predication of patterns that are formed on the Chladni plate and focused on the application of machine learning algorithms in image processing. In the Chladni plate, nodes and antinodes are demonstrated at various excited frequencies. Sand on the plate creates specific patterns when it is excited by vibrations from a mechanical oscillator. In the experimental setup, a rectangular aluminum plate of 16 cm x 16 cm and 0.61 mm thickness was placed over the mechanical oscillator, which was driven by a sine wave signal generator. 14 Chladni patterns are obtained on a Chladni plate and validation is done with modal analysis in Ansys. For machine learning, a large number of data sets are required, as captured around 200 photos of each modal frequency and around 3000 photos with a camera of all 14 Chladni patterns for supervised learning. The current model is written in Python language and model has one convolution layer. The main modules used in this are Tensor Flow Keras, NumPy, CV2 and Maxpooling. The fed reference data is taken for 14 frequencies between 330 Hz to 3910 Hz. In the model, all the images are converted to grayscale and canny edge detected. All patterns of frequencies have an almost 80% - 99% correlation with test sample experimental data. This approach is to form a directory of Chladni patterns for future reference purpose in real-life application. A machine learning algorithm can predict the resonant frequency based on the patterns formed on the Chladni plate.
This work deals with the study of a plane periodic multilayer structure in which the elementary stack consists of two plates in contact: one in aluminum (AL) and the other one in polyethylene (PE). These isotropic materials, present a high acoustic impedance contrast. The attenuation of the longitudinal and transverse waves is taken into account in the polyethylene but neglected in the aluminum plate. The effect of different defects is analyzed. Firstly, we focus on the effect of the presence of grease inclusion in the polyethylene plate (considering the two plates of the elementary stack in perfect contact). Secondly, the effect of disbond simulated by the insertion of a thin Teflon layer between the interfaces of the two layers constituting the elementary stack of the multilayer structure is investigated. Finally, the effect of the stacking sequences of the multilayer is analyzed. In order to obtain the effective acoustic parameters of polyethylene layer, allowing to evaluate the reflection and transmission coefficients using the stiffness matrix method developed by Rokhlin et al., four homogenization models are analyzed, then the best one to our configuration is chosen. The comparison of the simulation results is carried out.
In musical instruments, the geometric design and material features of the instrument are the most important factors that determine the sound characteristics of the instrument. Traditional replication and experiment-based handcrafting methods are predominant in the production of Turkish Folk Music wind instruments. The instrument manufacturing and standardization approaches, which include the relevant rules of physics and engineering practices, are limited purely to prototype studies for scientific research purposes. It is almost impossible to find studies on Turkish Folk Music wind instrument design and production involving computer aided design and engineering applications. In this study, an example Turkish woodwind instrument, the Turkish Treble Recorder (dilli kaval) is considered, and the air flow behaviour and acoustic (sound) power magnitudes that occur at different air flow rates are simulated in a computer environment using a Computational Fluid Dynamics (CFD) simulation technique. In the study, numerical and visual outputs related to air behaviour at different air flow rates that may be used in the instrument manufacturing phases were obtained. Acoustic power level was also measured experimentally. Simulation outputs (the acoustic power level) were compared to experimental results in order to validate the simulation results. The comparison revealed that the highest relative difference was calculated as 13.32(%). This value indicated that the simulation results were reasonably consistent with the results of the experimental measurement. Additionally, this study was constructed as a case study that may provide reference for future research studies in this field.
The produced sound quality of guitar primarily depends on vibrational characteristics of the resonance box. Also, the tonal quality is influenced by the correct combination of tempo along with pitch, harmony, and melody in order to find music pleasurable. In this study, the resonance frequencies of the modelled resonance box have been analysed. The free-free modal analysis was performed in ABAQUS to obtain the modes shapes of the un-constrained sound box. To find music pleasing to the ear, the right pitch must be set, which is achieved by tuning the guitar strings. In order to analyse the sound elements, the Fourier analysis method was chosen and implemented in MATLAB. Identification of fundamentals and overtones of the individual string sounds were carried out prior and after tuning the string. The untuned strings showed irregular fundamental frequencies and higher partials of decay. Octaves and power spectrums have been presented and discussed in this paper.
This paper addresses the effect of high temperature on absorption performance of sandwich material coupled with microperforated panels (MPPs) in multiple configurations using a finite element model (FEM) over a frequency range from 10 to 3000 Hz. The structure is backed with a rigid wall which can either be Aluminium or Al-Alloy used in aeronautic or automobile. The wave propagation in porous media is addressed using Johnson Champoux Allard model (JCA). The FEM model developed using COMSOL Multiphysics software makes it possible to predict the acoustic absorption coefficient in multilayer microperforated panels (M-MPPs) and sandwich structure. It is shown that, when structures made by MPPs or sandwich materials are submitted to high temperature, the absorption performance of the structure is strongly modified in terms of amplitude and width of the bandgap. For application in sever environment (noise reduction in engines aircrafts), Temperature is one of the parameters that will most influence the absorption performance of the structure. However, for application in the temperature domain smaller than 50?C (automotive applications for example), the effect of temperature is not significant on absorption performance of the structure.
This paper examines the characteristics of a harmonic plane wave in 1D and applies it to a model of an auditorium in the shape of a quarter of an ellipsoid. In the application, this paper will mainly look at transmission loss, reverberation, disruption of the performers, and differences between different frequencies. The differences between different frequencies will be analyzed on both a macroscopic auditorium level as well as on a microscopic level of a single point in the audience.
Coir fibre is extracted from the husk of coconut and is used in products such as floor mats, door mats, brushes and mattresses and in many applications. Here coir fibres are used to make particle boards of densities 300, 400 and 500 kg/m3 using UF resin to determine its efficiency for interior applications like acoustic and thermal properties and also tested for Indian standard 3129. Noise Reduction Coefficient (NRC) of all the boards decreases with an increase in density. Maximum sound absorption coefficient for all three densities was found in the frequency range of 2500 to 30,000 Hz. Among three densities, 300 kg/m3 board shows the maximum absorption coefficient at frequency 3000 Hz. The thermal conductivity results of all three densities boards increase with an increase in density. Modulus of Rupture for all three densities were meeting the requirement of standard. Results reveal that particle board manufactured from coir fibre can be used for acoustic and thermal insulation applications.
In this study, noise pollution assessments were performed along Marechal Deodoro Avenue and Batel Avenue, which are two major thoroughfares in the city of Curitiba, Brazil. Eleven points were evaluated at Batel Avenue and 16 points at Marechal Deodoro Avenue. The results of the noise level measurements and the calculation of noise maps indicated that both thoroughfares are acoustically polluted. The simulated and measured noise levels, in the 27 evaluated points, exceed the limits established by law 10,625 of the city of Curitiba, which establishes acceptable levels for the comfort of the population in the external environment. With regard to the traffic composition in the areas under study, the vehicle flow was found to consist mostly of light vehicles, representing 88% of the total flow along Batel Avenue and 85% on Marshal Deodoro Street. Based on the noise maps and measured noise levels, it was found that the entire length of Marshal Deodoro Avenue and Batel Avenue are strongly affected by street noise, which is readily explained by the constant traffic, high vehicle flow (number of vehicles/hour) and high vehicle speed at some points of these thoroughfares.
It has been hypothesized that objective assessment for building acoustic conditions only may not always be representative of the users’ perception in occupied indoor spaces. This study objectively and subjectively examined indoor acoustic condition in rooms within students’ hostels in Obafemi Awolowo University, Nigeria. The objective assessment considered the physical measurement of sound pressure level in the rooms in relation to the rooms’ physical characteristics like window to external wall area and window to floor area ratios. The subjective assessment considered the occupants’ perception of the acoustic condition in the rooms in relation to their personal characteristics like age, gender, body mass index, metabolic rate, and body skin area. The sound pressure level was measured in each of the randomly selected 44 rooms at 15 minute intervals between 7 hours and 19 hours daily through a period of eight weeks. The measurement was done with High Accuracy Digital Sound Noise Level Data Loggers placed at work plane at the centre of the rooms. The geometry of the rooms was documented through physical measurements. All the occupants of the selected rooms as well as the two adjoining rooms, amounting to 696 respondents, were purposively selected to fill a questionnaire regarding activities carried out in the rooms, the frequency of fenestration opening, the personal characteristics of the occupants and the rooms’ occupancy ratio. This study established a strong correlation between the objective and subjective assessments of the acoustic condition in the spaces. Moreover, out of all the occupants’ personal characteristics considered, it was the age that has a relationship with the occupants’ perception of the acoustic condition that is closest to significant level.The relationship between their perception and measured sound pressure level was slightly more pronounced among the male gender than the female with correlation coefficients of 0.115 and 0.096 respectively. This study concluded that none of the considered occupants’ personal characteristics can effectively predict their response to indoor acoustic condition in the spaces.
Propagation of Love waves in a transversely isotropic poroelastic layer bounded between two compressible viscous liquids is presented. The equations of motion in a transversely isotropic poroelastic solid are formulated in the framework of Biot’s theory. A closed-form solution for the propagation of Love waves is obtained in a transversely isotropic poroelastic layer. The complex frequency equation for phase velocity and attenuation of Love waves is derived for a transversely isotropic poroelastic layer when it is bounded between two viscous liquids and the results are compared with that of the poroelastic layer. The effect of viscous liquids on the propagation of Love waves is discussed. It is observed that the presence of viscous liquids decreases phase velocity in both transversely isotropic poroelastic layer and poroelastic layer. Results related to the case without viscous liquids have been compared with some of the earlier results and comparison shows good agreement.
Ultrasound is used in various chemical reaction processes, and these reactions are influenced by ultrasonic frequency. A threshold power is required for the ultrasonic degradation reaction and oxidation reaction caused by hydroxyl radicals, and the cavitation threshold power is also influenced by frequency generally. In this study, the effects of frequency on the threshold power of methylene blue degradation and KI oxidation were investigated in the range between 22.8 kHz and 1640 kHz. The threshold power of KI oxidation reaction increased with increasing frequency. This phenomenon well agrees with previous study, and it is revealed that the generation of I-3 ion is caused by oxidation reaction of Iˉ ions with hydroxyl radicals. On the other hand, the threshold power of methylene blue degradation reaction was not affected by frequency. The ultrasonic degradation of methylene blue is considered to be caused by hydroxyl radicals, and there is a linear relationship between degradation rate constant and sonochemical efficiency value. However, it is guessed that the degradation of methylene blue is occurred inside cavitation bubble by pyrolysis at high frequency regions.
Cochlear implants were widely used for hearing impaired, while at the same time the devices require surgical intervention for implanting. Infrared laser neural stimulation has been investigated for overcoming the drawback because the laser can elicit neural activity without contacting tissues. The purpose of this study was to develop a speech encoding scheme for the infrared laser auditory prosthesis. A click-modulated speech sound (CMS), which is a click train with a repetition rate of formant frequencies of an original speech sound, was created as an acoustic simulation of the laser auditory prosthesis. Four Japanese speakers with normal hearing participated in the experiment. Subjects reported their perceptions of the CMS synthesized from low familiarity Japanese words. As a result, CMS replicating first and second formant frequencies created statistically significant vowel and consonant perception. The result suggests that laser auditory prosthesis replicating formant frequencies could restore the speech perception.
This experiment aims to study the effects and modifications that occurred on acoustic signal harmonics when travelling through wood. The experiment measured the output amplitudes and frequencies of the travelling signals and compared them with the original input signal. The factors under investigation in this experiment included: wood type, wood moisture content (MC), input signal frequencies, signal travelling distance and wood condition (wood with/without cracks). The experiment findings demonstrated that higher input signal frequencies results in higher attenuation of acoustic emissions (AE) travelling through the wood. The results also indicate that: wood type, MC, the signal's travelling distance, and the orientation of the travelling signal, compared to the wood's grain direction, affected the signal propagation.
Detection and localization of acoustic events in an environment are important to protect the military and civilian installations. While there are finite paths of wave propagation in simple or low reverberant environments, in complex environments (e.g. a complex urban environment) obstacles such as terrain or buildings introduce multipath propagations, reflections and diffractions which make source localization challenging. Therefore, numeric results of simulated models (simplified and Fort Benning urban models) of 3D complex environments can highly help in real applications. Some of the conventional beamformer algorithms have been used in order to localize point sound source. Analyzing results shows that MRCB beamformer has better performance than others in this issue and its accuracy superiority is more than 3 m in simplified urban model and 5 m in Fort Benning urban model with respect to the SOC. Moreover, due to possible uncertainties between the numerical model and the actual environment such as squall effect, temperature gradient etc., sensitivity of the beamformers to temperature gradient is investigated which shows higher robustness of SOC beamformer than the MRCB beamformer. According to the results, due to gradient temperature uncertainty the accuracy degradation of the SOC is about 1m while in MRCB it alters from 0.5 m to 20 m approximately at all SNRs. COMSOL Multiphysics has been used to numerically simulate the environment of wave propagation.
