Audible Frequency Range Research Articles

How artificial intelligence applied to sound recognition can help gas leak detection in acoustically complex environments?

From production to storage and transport, detecting leaks of flammable gases is a major challenge, particularly in terms of occupational safety and health, and environmental considerations. The emergence of hydrogen as an energy source makes acoustic-based technologies a key element in this value chain. For these reasons, Metravib Engineering, in collaboration with the R&D Safety Project of TotalEnergies One Tech, has been developing since 2019 the AGLED system, for the early detection, localization and classification of these leaks. The system performs acoustic detection in the audible frequency range, using antennas consisting of 4 microphones and physics-based artificial intelligence. Over 5,600 signals were recorded on a site fairly representative of gas production and storage facilities in order to build a robust learning database. Several algorithms were implemented to limit the number of false detections delivered by the system. A relearning strategy was developed to handle unexpected disturbances relative to specific noise environment. This paper describes the overall architecture of the system, from signal acquisition to gas leak detection and 3D localization. It delves into the relearning algorithm and its performance during two full-scale industrial pilots of TotalEnergies - La Mède (France) and Tempa Rossa (Italy) - that included nitrogen controlled leaks tests campaigns.

Measuring audible acoustic frequencies parameters of rigid porous media via an innovative impedance tube method - Solving the inverse problem

This study introduces an experimental approach to measuring audible acoustic frequency parameters of a rigid porous medium using an impedance tube. Grounded in the equivalent fluid model, a derivative of Biot's theory, our investigation delves into the propagation of waves within porous media, emphasizing the importance of effective density and dynamic compressibility of the saturated fluid. Our primary focus is on resolving the inverse problem by minimizing both experimental and theoretical absorption coefficient expressions within the audible frequency range. Concurrently, we determine four pivotal parameters: viscous and thermal permeability, the inertia factor introduced by Norris, and the thermal tortuosity introduced by Lafarge. The outcomes include a comparative analysis between experimental and simulated absorption coefficients, leveraging optimized parameters, across two distinct polyurethane foam samples.

Sound absorption coefficient in the audible and ultrasonic frequency range measured in a reverberation chamber with an omnidirectional parametric loudspeaker

An omnidirectional parametric loudspeaker (OPL) is a sound source that contains hundreds of ultrasonic transducers set on the surface of a sphere. Each transducer emits an ultrasonic collimated beam consisting of an audible exponential sweep sine (ESS) modulated in amplitude. This results in hundreds of ultrasonic sound waves emitted in all directions, but also audible sound waves generated by the parametric acoustic array (PAA) phenomenon, by which a modulated signal returns to the audible range thanks to nonlinear propagation in the air. This work examines how the OPL performs in assessing room acoustics, specifically in determining material sound absorption coefficients within reverberation chambers. The ISO 354 standard requires measuring reverberation times with the chamber empty and with the material sample. These are measured using ESS, which has proven effective for the OPL performance. This signal concentrates all the sound power into a single frequency, which improves ultrasonic power levels and thus the signal-to-noise ratio of the audible sound field. The absorption coefficient is next evaluated following the standard, and the results are compared with those obtained using a standard dodecahedral loudspeaker. Finally, the absorption coefficient in the ultrasonic range is examined to evaluate the OPL performance in this frequency range.

Optimised implicit methods for audio rate wave-based acoustic simulation

Wave-based room acoustic computation at an audio rate (i.e., covering the complete range of audible frequencies) is computationally intensive. There is thus a great incentive to develop simulation methods that allow for "accurate" simulation at the lowest possible computational cost, taking into account requirements for massively parallel implementation. Though often formal measures of order of accuracy are employed, in this paper, we examine the optimisation of a locally-defined implicit family of schemes against wideband measures of accuracy, based on the minimisation of numerical dispersion over a specified frequency range. The resulting optimised scheme is defined over a Cartesian grid, and allows performance gains over standard schemes (such as the basic rectilinear scheme, or schemes defined over face-centered cubic grids, and other implicit designs presented in the literature). Numerical stability conditions are easily formulated, and can be built into the optimisation, alongside the computational cost of linear system solution. Simulation results and comparisons of computation times against other known methods are presented.

An Extensive Parametric Analysis and Optimization to Design Unidimensional Periodic Acoustic Metamaterials for Noise Attenuation

The presented research delineates an extensive study aimed at obtaining and comparing optimal designs and geometries for one-dimensional periodic acoustic metamaterials to attenuate noise within the audible frequency range of 20 Hz to 20 kHz. Various periodic designs, encompassing diverse geometric parameters and shapes—from Basic-Periodic to Semi-Periodic, Tapered-Diverging, and Tapered-Converging unit cells of repeated patterns—are examined to identify the most effective configurations for this application. A thorough parametric analysis is executed employing FE-Bloch’s theorem across these four configurations to determine their bandgaps and to identify the most effective geometry. A normalization process is utilized to extend the domain of the analysis and the range of the system parameters studied in this work, totaling 202,505 design cases. Finally, the optimal design is identified based on achieving the best bandgaps coverage. The study concludes with the presentation of frequency domain acoustic pressure responses at multiple sensing points along the filters, validating the performance and the obtained bandgaps through these optimal geometries.

Modal approach to the dynamics of string instruments over the audible range

The present theoretical analysis addresses the dynamics of the bow instruments in the whole audible range of frequencies. Several scenarios are considered for the string-bridge-soundbox system: natural vibrations and frequency spectrum, external periodic excitation on some bridge point, and vibration induced by the bow rubbing. The single parts of the musical artifact are conveniently modelled and the bridge interfacing between the strings and the top plate of the soundbox is studied considering two possible vibrating modes of the bridge: a translational mode along its symmetry axis and a rotational mode around the waist centre. The bridge mechanical model is thus definable from both the kinematical and the dynamical aspects, and the relations between the forces and displacements of the strings and the sound box are formulated.The coupled natural modes of vibration are obtained in non-dissipative conditions, finding that the whole frequency spectrum is roughly given by the union of the uncoupled spectra, of the strings and the harmonic box. Then, introducing some level of dissipation, the frequency response to a transverse harmonic excitation on an arbitrary bridge point and the admittance on another arbitrary point of the instrument are studied, obtaining a useful tool to identify or verify the mechanical characteristics of the system. At last, the response to the bow excitation is analysed introducing an appropriate model for the nonlinear stick-slip contact between the bow and the strings and solving the motion equations by modal decomposition.

A Reduced Order Series Expansion for the BEM Incorporating the Boundary Layer Impedance Condition

When modeling sound waves in fluids it can be important to include the viscous and thermal losses originating from the fluids’ interaction with boundaries. In the audible frequency range, the thickness of the boundary layers is between a micrometer and a millimeter. As such the viscous and thermal losses are important when simulating the properties of small acoustical devices such as e.g. hearing aids or transducers. However, the inclusion of viscous and thermal losses is a computationally demanding task as it requires a fine discretization of the boundary layer in order to fully capture the complicated physical phenomena happening on the microscale. Recently, there has been developments to ease the computational demands using both the Finite Element Method and the Boundary Element Method, by approximating the losses using the Boundary Layer Impedance (BLI) boundary condition. In this paper, we extend previous developments for multi-frequency analysis using the Reduced Order Series Expansion Boundary Element Method to handle the BLI condition. This model follows a two-step procedure: Using a series expansion to decrease the assembly time of the BEM matrices and a projection to reduce the overall memory consumption of the model. Results from two acoustic interior problems show that the model decreases the total computational time by around 96% while using less than 15% of the memory. For both test setups the limiting factor of the accuracy was the reduction and not the series expansion.

Micro-perforated mufflers based on the Acoustic Black Hole effect

Attenuation of acoustic disturbance with compact and low-weight acoustical devices is a demanding requisite in industries such as vehicle exhaust mufflers, turbofan liners or ventilation systems. Acoustic Black Holes (ABH) is a concept that has been studied originally in the field of vibration control for the design of a structure based on a power-law thickness profiles along its edges. The idea of wave trapping and dissipation has been extended to the field of duct acoustics using compact devices that avoid blocking the air flow. Based on this idea, in this work we propose the study of a micro-perforated silencer that should prevent reflection and transmission of the sound waves over a wide range of audible frequencies. The use of micro-perforations over the facing cavities should help to extend performance towards the low frequency range. The acoustic behavior of the ABH is assessed from theoretical and numerical modeling. The performance can be greatly improved when the physical constituting parameters are optimized simultaneously. Particle swarm optimization is a computational method inspired by the behavior of natural systems that is able to provide a satisfactory solution with enhanced total dissipation.

Ventilated silencer based on layered Helmholtz resonators

This study investigates the performance of a multilayer sound-attenuating metamaterial with ventilation capabilities. The design incorporates arrays of Helmholtz resonators embedded within the wall structure. Each cell of the barrier's front wall is a Euclidean polygon, triangular, square, or hexagonal, housing a parallel array of resonators interconnected via an axial ventilation duct. The sound attenuation performance of these barriers is meticulously examined using the lumped parameter theory and the transfer matrix method (TMM), complemented by finite element (FE) simulations. The results indicate that sound attenuation in the audible frequency range (300–2000 Hz) can be significantly enhanced by employing multiple layers of resonators, each layer assigned a unique peak resonance frequency. Despite the design's inherent trade-offs between barrier thickness, ventilation capacity, operational frequency range, and overall sound attenuation, its structural simplicity and straightforward theoretical performance estimation methods make it a promising candidate for applications requiring a specific attenuation spectrum. The sound-blocking performance of the design is further validated through impedance tube experiments, which show a reasonable agreement with the numerical predictions, thereby affirming the efficacy of the proposed design. The performance of multilayer design is also compared with the similar ventilated barriers proposed in the recent studies.

Enhancing heart disease diagnosis through precise heart sound including infrasound

Recent research has been pushing the frontier of diagnosing cardiovascular diseases, which have a high mortality rate globally. The need for swift responses to acute diseases has underscored the importance of continuous health monitoring and the development of monitoring diagnostic technology. Our work focused on an overlooked aspect—the microphones used to measure heart sounds. Existing ones, particularly capacitive MEMS types, measure only heart sounds primarily within the audible frequency range, potentially limiting the diagnostic accuracy. To overcome these limitations, we used microphones capable of measuring down to infrasound areas. We also designed an experimental environment to capture the precise heart sounds. The crux of our approach was using the full information of heart sounds through infrasound measurements. A convolutional neural network-based deep learning model was employed for algorithm development and validated using the PhysioNet 2016 CinC’s open-source heart sound data. We conducted an experiment on the impact of low-frequency components on heart sound diagnosis using a new infrasound dataset measured at Seoul St. Mary's Hospital of the Catholic University of Korea. Accuracy and sensitivity, respectively, improved on average by 2% and 4%, showing that datasets including low-frequency components generally performed better.

Piezoelectric properties of [001]-textured (K, Na)(Nb, Sb)O3-CaZrO3-(Ag, Bi)ZrO3 ceramics and their application in panel loudspeakers

A [001]-textured 0.96(K0.5Na0.5)(Nb0.93Sb0.07)O3-0.02CaZrO3-0.02(Ag0.5Bi0.5)ZrO3 [KNNS-0.02CZ-0.02ABZ] piezoceramic exhibited a large d33 of 760 pC/N, which is close to the largest d33 reported in literature. The large d33 of this sample can be explained by the existence of nanodomains and the tetragonal-orthorhombic-rhombohedral (T-O-R) structure, with a large portion of the O-R structure. Piezoelectric loudspeakers were produced using [001]-textured KNNS-(0.04 – x)CZ-xABZ piezoceramics (0.0 ≤ x ≤ 0.04). The loudspeaker with an actuator fabricated using the [001]-textured KNNS-0.02CZ-0.02ABZ piezoceramic exhibited the largest sound pressure level (SPL) owing to its large d33. The average SPL of the loudspeaker was 68.5 dB at a distance of 30 cm in the audible frequency range with an input of 6 Vrms. The loudspeaker produced using the bimorph-type actuator with the KNNS-0.02CZ-0.02ABZ piezoceramic exhibited an improved average SPL of 75.6 dB. Therefore, the [001]-textured KNNS-0.02CZ-0.02ABZ piezoceramic is an excellent material for loudspeakers.

Theoretical Study of Rampwise DPWM Technique to Reduce Motor Acoustic Noise

Motor acoustic noise generated near living environments such as elevators and electric vehicles may cause discomfort. In order to reduce the acoustic noise, the switching frequency is set to the high side of the audible frequency range. In this case, however, the switching loss is increased. The conventional discontinuous PWM (DPWM) method is widely used since it can reduce the switching loss drastically. However, it produces larger acoustic noise than the conventional sinusoidal PWM method. The authors have previously proposed Rampwise DPWM techniqueh which can reduce both acoustic noise and switching loss. In this paper, the line-line voltage with the proposed Rampwise DPWM technique is expanded into a real-valued Fourier series, and the frequency characteristics are analyzed. It is theoretically confirmed that the rampwise part in the Rampwise DPWM technique can achieve reduction of motor acoustic noise. Furthermore, the reduction effect of motor acoustic noise with the Rampwise DPWM technique is theoretically and experimentally verified.

Studying the high frequency seismic signals for enhanced knowledge of the shallow Earth structure and soil investigation

The Earth acts like a low-pass filter to earthquake energy so that frequencies higher than 10 Hz are rapidly attenuated. This intrigues seismologists about the seismic waves in the frequency domain 1–10 Hz, which is crucial to correctly assess the impact of seismic shaking on structures. However, not much attention has been paid to higher frequencies, probably due to its low significance and structural damage. The Earth has high frequency seismic signal (HFSS) in the audible frequency range 20–20,000 Hz and maybe higher (Gamal et al., 2020). These seismic signals result from the transformation of any energy into HFSS energy which is propagated inside the Earth, this energy may be winds, the crustal structure movement, movement due to gravitational force or any mechanical energy transformed into high frequency seismic vibrations. Fifteen different geological environments were tested in Egypt, to monitor the high frequency seismic signals (HFSS) of the subsurface soil. The present study used very high digitising frequency seismographs, not less than 8,000 to 16,000 sample per second, and a set of horizontal and vertical geophones of natural frequencies in the ranges of 4 Hz to 100 Hz. It was found that consolidated rocks have high-pitch that may reach 4,000 Hz, while weak fractured soils sound have a low-pitch, in the frequency range of 20–70 Hz. Speech and audio processing methods have been used to differentiate between these HFSS preserved inside soils and to produce the “unified HFSS map”. The “Soil HFSS map” was considered as avail science could be used in the future to give deep insight on the shallow Earth's interiors.

Modeling coupled oscillators: Applications for musical sequencing and synthesis

There are many naturally occurring systems of coupled oscillators, e.g., the synchronization of firefly flashes, frog calls, and electrical impulses in the brain. The behavior of a large system of coupled oscillators can be approximated using the Kuramoto-Daido model. The model shows that phase calculations for each oscillator can be simplified by comparing each oscillator’s phase to the average phase of the collection, eliminating the need to sum over the whole group. In this session, we will explore this algorithm in Max/MSP. We will look at simple systems with a small number of low frequency oscillators, both free-running and rhythmically quantized/Euclidean, as a means of generating rhythmic patterns and sequences. Then we will look at larger collections of oscillators within the audible frequency range and explore how the algorithm can be used to modulate audio signals for timbral effects. This example will delve into how the coupling algorithm affects oscillators that have frequency relationships drawing from the overtone series. We will also see how delaying the averaged signal simulates a proximity effect that more closely resembles the localized synchronization that occurs in natural systems.

A linear non-Hertzian unsteady tangential wheel-rail contact model

The increase in computational capacity has considerably reduced the use of linear models for wheel/rail tangential contact, being currently replaced by theories that adopt non-linear formulations able to address the most complex conditions realistically. However, linear formulations are difficult to replace in certain applications such as acoustic problem modelling, in which case a linear formulation of the track-contact-vehicle system is needed. The vibration that appears in this type of problem covers a wide range of audible frequencies, so, in addition to linearity, these theories are required to be non-stationary. The literature in contact mechanics gives response to this problem through models that consider low creepage levels, but it remains to cover other conditions in which the mean creepage is not small, such as when a railway vehicle negotiates a curve.This work presents a new theory of unsteady linear tangential rolling contact for non-Hertzian areas that considers kinematics as the sum of a constant creepage resulting from large stationary forces (such as those that occur when the vehicle negotiates a curve with constant radius) and small variable creepage due to a high-frequency phenomenon (e.g. the dynamic interaction between the vehicle and the track). The model is based on the Variational Theory (i.e. the CONTACT method for tangential problems), from which a linear formulation with variable creepage is deduced. According to this formulation, the non-steady state contact problem can be solved for any shape of the wheel/rail contact region, requiring a much smaller computational effort than the general unsteady CONTACT approach. The results show a satisfactory agreement of the proposed model to the unsteady CONTACT version, hence confirming the soundness of the proposed contact model.

A comparison between the high-frequency Boundary Element Method and Surface-Based Geometrical Acoustics

The audible frequency range covers many octaves in which the wavelength changes from being large with respect to dominant features of a space to being comparatively much smaller. This makes numerical prediction of a space's acoustic response, e.g. for auralisation, extremely challenging if all frequencies are to be represented accurately. Different classes of algorithm give the best balance of accuracy to computational cost in different frequency bands - 'wave solvers' such as Boundary Element Method (BEM) at low frequencies and Geometrical Acoustics (GA) methods at high frequencies. But combining their output data can be an awkward process due to their very different formulations. This is particularly important for early reflections, which give crucial spatial perceptual cues. Hence there is a need for a unified full audible bandwidth algorithm for early reflections. This paper will describe ongoing research to develop such an algorithm by exploiting synergies between high-frequency BEM and GA. It will describe how appropriately chosen oscillatory basis functions in BEM can produce leading-order GA behaviour at high frequencies and explore how interactions between these compare to the same interactions arising in a surface-based Geometrical Acoustics scheme.

Individual and interactive effect of ultrasound pre-treatment on drying kinetics and biochemical qualities of food: A critical review.

One of the earliest and most prevalent processing methods to increase the shelf-life of foods is drying. In recent years, there has been an increased demand to improve product quality while lowering processing times, expenses, and energy usage in the drying process. Pre-treatments are therefore effectively used before drying to enhance heat and mass transfer, increase drying efficiency, and lessen degradation of final product quality. When food is dried, changes are expected in its taste, color, texture, and physical, chemical, and microbial properties. This has led to the need for research and development into the creation of new and effective pre-treatment technologies including high-pressure processing, pulsed electric field, ultraviolet irradiation, and ultrasound. Sound waves that have a frequency >20kHz, which is above the upper limit of the audible frequency range, are referred to as "ultrasound". Ultrasonication (US) is a non-thermal technology, that has mechanical, cavitational, and sponge effects on food materials. Ultrasound pre-treatment enhances the drying characteristics by producing microchannels in the food tissue, facilitating internal moisture diffusion in the finished product, and lowering the barrier to water migration. The goal of ultrasound pre-treatment is to save processing time, conserve energy, and enhance the quality, safety, and shelf-life of food products. This study presents a comprehensive overview of the fundamentals of ultrasound, its mechanism, and how the individual effects of ultrasonic pre-treatment and the interactive effects of ultrasound-assisted technologies affect the drying kinetics, bioactive components, color, textural, and sensory qualities of food. The difficulties that can arise when using ultrasound technology as a drying pretreatment approach, such as inadequate management of heat, the employment of ultrasound at a limited frequency, and the generation of free radicals, have also been explained.

Shape-preserving average frequency response curves using rational polynomials: A case study on human stapes vibration measurements

The vibration of the human middle ear shows sharp variations in the amplitude and phase over the audible frequency range. Measurements often differ between subjects, and it is difficult to determine the average response of the human middle ear. However, such an average response curve is of great value in detecting pathological ears. Simply averaging the amplitude and phase for each frequency results in a “washed-out” view due to differences in the locations of the maxima and minima of the curves. Therefore, a method is required to consider each individual curve's shape in the average.This paper discusses a novel method based on frequency-response transfer functions. Each of the individual measurements is fitted with a rational polynomial. The average frequency response is determined by a weighted averaging of the individual curves' numerator and denominator polynomial coefficients. Such an average preserves the shape of the individual curves. The method is applied to vibrational data of the human stapes. As expected from the literature, two resonance frequencies at 1.14 ± 0.13 kHz and 3.61 ± 0.43 kHz were found. A comparison with other methods is made to discuss the method's advantages and disadvantages.

Measurement of airborne ultrasound using laser Doppler vibrometry

The speed of light in air is dependent on the air's instantaneous density. Since air density is modulated by sound, sound in the air can be observed and measured using optical methods. One such optical method is Laser Doppler Vibrometry (LDV). Most commonly, LDVs measure the mechanical velocity of a surface. However, by placing a rigid reflector beneath a sound beam in air, it is possible to measure the time rate-of-change of optical refractive index and thus to measure dynamic changes in air density, or sound. In prior demonstrations, this method has been used to visualize sound fields in the audible frequency range and ultrasonic range underwater. Here, we present the first measurements of high-intensity airborne ultrasound beams in the frequency range spanning 100 kHz–300 kHz. We observe accumulated distortion, wave steepening, and weak shock formation as high intensity sound beams propagate. LDV measurements are compared against numerical simulations of the sound field. Advantages of the LDV technique are discussed, and we also attempt to quantify limitations of the technique which include spatial averaging of the measurand along and normal to the optical beam path.

Effect of binaural beat in the inaudible band on EEG (STROBE).

This study aimed to determine the effects of the binaural beat (BB) on brainwave induction using an inaudible baseline frequency outside the audible frequency range. Experiments were conducted on 18 subjects (11 males [mean age: 25.7 ± 1.6 years] and 7 females [mean age: 24.0 ± 0.6 years]). A BB stimulation of 10 Hz was exerted by presenting frequencies of 18,000 Hz and 18,010 Hz to the left and right ears, respectively. A power spectrum analysis was performed to estimate the mean of the absolute power of the alpha frequency range (8–13 Hz). The variation in the mean alpha power during the rest and stimulation phases in each brain area was compared using the Wilcoxon signed-rank test. Compared to the rest phase, the stimulation phase with BB showed an increasing trend in the mean alpha power across all 5 brain areas. Notably, a significant increase was found in the frontal, central, and temporal areas. This is a significant study in that it determines the effects of only BB without the influence of auditory perception, which has been overlooked in previous studies.