Audible Frequency Range Research Articles

Fabrication and experimental demonstration of a hybrid resonant acoustic gradient index metasurface at 40 kHz

Over the past few years, acoustic gradient index metasurfaces (GIMs) have been actively studied for the numerous wave control capabilities that they facilitate. Previous research, however, has primarily focused on GIMs that operate in the audible frequency range, due to the difficulties in fabricating such intricate structures at the millimeter and submillimeter scales, for ultrasonic applications. In this work, we design, fabricate, and experimentally demonstrate the working of a hybrid resonant acoustic gradient index metasurface for airborne ultrasound at 40 kHz. The fabrication of such a GIM is made possible by projection microstereolithography, an emerging additive manufacturing technique. Numerical simulations were conducted to verify the metasurface design, and experiments were performed to corroborate these simulations. The stronger dissipation associated with airborne ultrasound is highlighted in this paper. The experimental demonstration of such a metasurface for airborne ultrasound could further its prospects as a candidate for miniaturized acoustic devices.

Analysis of the vibrational and sound spectrum of over 100,000 protein structures and application in sonification

We report a high-throughput method that enables us to automatically compute the vibrational spectra of more than 100,000 proteins available in the Protein Data Bank to date, in a consistent manner. Using this new algorithm we report a comprehensive database of the normal mode frequencies of all known protein structures, which has not been available before. We then use the resulting frequency spectra of the proteins to generate audible sound by overlaying the molecular vibrations and translating them to the audible frequency range using the music theoretic concept of transpositional equivalence. The method, implemented as a Max audio device for use in a digital audio workstation (DAW), provides unparalleled insights into the rich vibrational signatures of protein structures, and offers a new way for creative expression by using it as a new type of musical instrument. This musical instrument is fully defined by the vibrational feature of almost all known protein structures, making it fundamentally different from all the traditional instruments that are limited by the material properties of a few types of conventional engineering materials, such as wood, metals or polymers.

Neural Maps of Interaural Time Difference in the American Alligator: A Stable Feature in Modern Archosaurs.

Detection of interaural time differences (ITDs) is crucial for sound localization in most vertebrates. The current view is that optimal computational strategies of ITD detection depend mainly on head size and available frequencies, although evolutionary history should also be taken into consideration. In archosaurs, which include birds and crocodiles, the brainstem nucleus laminaris (NL) developed into the critical structure for ITD detection. In birds, ITDs are mapped in an orderly array or place code, whereas in the mammalian medial superior olive, the analog of NL, maps are not found. As yet, in crocodilians, topographical representations have not been identified. However, nontopographic representations of ITD cannot be excluded due to different anatomical and ethological features of birds and crocodiles. Therefore, we measured ITD-dependent responses in the NL of anesthetized American alligators of either sex and identified the location of the recording sites by lesions made after recording. The measured extracellular field potentials, or neurophonics, were strongly ITD tuned, and their preferred ITDs correlated with the position in NL. As in birds, delay lines, which compensate for external time differences, formed maps of ITD. The broad distributions of best ITDs within narrow frequency bands were not consistent with an optimal coding model. We conclude that the available acoustic cues and the architecture of the acoustic system in early archosaurs led to a stable and similar organization in today's birds and crocodiles, although physical features, such as internally coupled ears, head size, or shape, and audible frequency range, vary among the two groups.SIGNIFICANCE STATEMENT Interaural time difference (ITD) is an important cue for sound localization, and the optimal strategies for encoding ITD in neuronal populations are the subject of ongoing debate. We show that alligators form maps of ITD very similar to birds, suggesting that their common archosaur ancestor reached a stable coding solution different from mammals. Mammals and diapsids evolved tympanic hearing independently, and local optima can be reached in evolution that are not considered by global optimal coding models. Thus, the presence of ITD maps in the brainstem may reflect a local optimum in evolutionary development. Our results underline the importance of comparative animal studies and show that optimal models must be viewed in the light of evolutionary processes.

Use of cutting force and vibro-acoustic signals in tool wear monitoring based on multiple regression technique for compreg milling

This study focused on a computerised TCM (tool condition monitoring) system as a part of automated monitoring of the machining processes in the wood industry. The system’s principal task was to evaluate the actual state of tool wear without disrupting the normal course of machine tool exploitation for cutting force and vibro-acoustic signals analysis. During the experiment, five physical quantities that are generated during machining were measured and recorded: cutting forces in two directions (Fx, Fy), ultrasonic stress waves (acoustic emission – AE), acoustic pressure in the range of audible frequencies (noise – N), and acceleration of mechanical vibrations (V). Six pairs of tools were used in the experiment. One tool from each pair was experimental, the other was a control tool. Out of the five physical quantities generated during machining that were tested as an indirect source of information on the tool condition, signals of cutting forces and mechanical vibrations proved the most useful. Both acoustic emission and noise signals emerged as wholly inadequate as evidence to predict tool wear.

Public health impacts from subway noise: Case study Hong Kong

In cities, subway noise is often cited as a major contributor to noise pollution that impacts millions of people every day. Previous studies on this topic have shown that peak subway noise levels in some cities can be as high as 110 dB, which greatly exceeds the 70 dB level set by the World Health Organization (WHO) and EPA for safe environmental noise levels. This work aims to characterize the subway noise in Hong Kong, analyze potential source features, and make technical recommendations for consideration by government and metro companies. First, the overall noise data on all nine subway lines in the city are presented and compared with published data of other subway lines around the world. Spectra of the loudest segments are analyzed to show the effects of tunnel modes, track curvature, and other features that may play a significant role in noise radiation and reverberation. A detailed correlation study is conducted for the short-time noise level and vehicle speed. A new train speed profile that optimizes noise exposure reduction is proposed for consideration of a future auto-drive system. Finally, a study of vibroacoustic exposure by passengers is also conducted to examine the impacts beyond the audible frequency range.

Fabrication and measurement of a hybrid resonant gradient index metasurface at 40kHz

Over the past decade, gradient index metasurfaces(GIMs) have been voraciously studied for the numerous wave control capabilities that they facilitate. In this regard, a hybrid structure consisting of shunted Helmholtz resonators and a straight channel is often chosen as building blocks of the metasurface. Prior research, however, has primarily focused on GIMs that operate in the audible frequency range, due to the difficulties in fabricating such intricate structures at the millimeter and sub-millimeter scales, for ultrasonic applications. In this paper, we design, fabricate and experimentally realize a gradient index metasurface for airborne ultrasound at 40kHz. The fabrication of such a GIM is made possible by projection micro-stereolithography, an emerging additive manufacturing technique capable of micro-scale, high aspect-ratio features over a wide area. Simulations were first conducted to verify the metasurface design. Experiments were subsequently performed to corroborate the simulations and theory. The challenges faced by the thermoviscous effects, their usefulness in certain applications and optimal designs for minimal dissipation are discussed.

Vocal communication in Microtus (Terricola) schelkovnikovi and M. (T.) daghestanicus in the audible range of frequencies

Vocal communication in the audible range of sound frequencies in two species of voles from the subgenus Terricola includes two calls: squeak-type vocalizations in the context of discomfort; and courtship vocalization, although the latter is rarely used by the animals. In this study, compared with Schelkovnikov’s pine vole [Microtus (Terricola) schelkovnikovi], squeak-type vocalizations of the Daghestan pine voles [M. (T.) daghestanicus] showed higher frequency characteristics and shorter duration. The squeak-type vocalizations of the former species did not exhibit sexual dimorphism. Differences in the call characteristics of the two species could be the result of both gene drift and the effects of biotopes on the evolution of their sound signals.

Air Ultrasonic Signal Localization with a Beamforming Microphone Array

Nondestructive testing methods are used to inspect and test materials and components for discontinuities or differences in mechanical characteristics. Phased array signal processing techniques have been widely used in different applications, but less research has been conducted on contactless nondestructive testing with passive arrays. This paper presents an application of beamforming techniques analysis using a passive synthetic microphone array to calculate the origin and intensity of sound waves in the ultrasonic frequency range. Acoustic cameras operating in the audible frequency range are well known. In order to conduct measurements in higher frequencies, the arrangement of microphones in an array has to be taken into consideration. This arrangement has a strong influence on the array properties, such as its beam pattern, its dynamics, and its susceptibility to spatial aliasing. Based on simulations, optimized configurations with 16, 32, and 48 microphones and 20 cm diameter were implemented in real experiments to investigate the array resolution and localize ultrasonic sources at 75 kHz signal frequency. The results show that development of an ultrasonic camera to localize ultrasonic sound sources is beneficial.

Development and performance analysis of a low-cost MEMS microphone-based hearing aid with three different audio amplifiers

In this paper, MEMS-based capacitive microphone and low-cost amplifier are designed for low-cost power-efficient hearing aid application. The developed microphone along with the associated circuitry is mounted on a common board in the form of pocket-type (body-worn) device. The designed microphone consists of a flexible circular silicon nitrite (Si3N4) diaphragm and a polysilicon-perforated back plate with air as dielectric between them. The incident acoustic waves on the sensor cause deflection of the diaphragm to alter the air gap between the perforated back plate (fixed electrode) and the diaphragm (moving plate) which causes a change in capacitance. The acoustic pressure applied to the microphone is from 0 to 100 Pa for an operating range of 100 Hz–10 kHz which corresponds to the audible frequency range in case of human beings. The main purpose of this work is to increase the longevity of battery used in conventional hearing aids. The designed MEMS microphone with Si3N4 diaphragm is capable of identifying acoustic frequencies (100 Hz to 10 kHz) which correspond to a specific change in absolute pressure from 0 to 100 Pa for 2-micron-thick diaphragm with a sensitivity of about 0.08676 mV/Pa. The design of the sensor and the characteristics analysis are performed in FEM-based simulation software, which are later validated in real time. The prototype is designed using MEMS microphone and low-cost amplifier ICs with biasing components in the form of pocket-type (body-worn) hearing aid. In order to study the performance of proposed device, three different market-available amplifiers with controllable gain are used. Finally, the performance of the hearing aid is studied through audio spectrogram analysis to choose the best-suited amplifier among the three.

Ontogenetic change in predicted acoustic pressure sensitivity in larval red drum (Sciaenops ocellatus).

Detecting acoustic pressure can improve a fish's survival and fitness through increased sensitivity to environmental sounds. Pressure detection results from interactions between the swim bladder and otoliths. In larval fishes, those interactions change rapidly as growth and development alter bladder dimensions and otolith-bladder distance. We used computed tomography imagery of lab-reared larval red drum (Sciaenops ocellatus) in a finite-element model to assess ontogenetic changes in acoustic pressure sensitivity in response to a plane wave at frequencies within the frequency range of hearing by fishes. We compared the acceleration at points on the sagitta, asteriscus and lapillus when the bladder was air filled with results from models using a water-filled bladder. For larvae of 8.5-18 mm in standard length, the air-filled bladder amplified simulated otolith motion by a factor of 54-3485 times that of a water-filled bladder at 100 Hz. Otolith-bladder distance increased with standard length, which decreased modeled amplification. The concomitant rapid increase in bladder volume partially compensated for the effect of increasing otolith-bladder distance. Calculated resonant frequency of the bladders was between 8750 and 4250 Hz, and resonant frequency decreased with increasing bladder volume. There was a relatively flat frequency dependence of these effects in the audible frequency range, but we found a small increase in amplification with increasing excitation frequency. Using idealized geometry, we found that the larval vertebrae and ribs have negligible influence on bladder motion. Our results help clarify the auditory consequences of ontogenetic changes in bladder morphology and otolith-bladder relationships during larval stages.

Ins, Outs of Frequency-lowering Processing

Ins, Outs of Frequency-lowering Processing

A Miniature Fiber-Optic Microphone Based on an Annular Corrugated MEMS Diaphragm

A miniature fiber-optic microphone (FOM) based on a periodic corrugated microelectro-mechanical-system (MEMS) diaphragm has been developed in this paper. A micro Fabry–Perot cavity is an acoustic sensor structure made up of a single-mode fiber(SMF) end face and a MEMS diaphragm. The achieved signal-to-noise ratio (SNR) of the FOM is 79.08 dB under the sound pressure of 37.76 mPa at the 1 kHz acoustic signal, and the corresponding minimum detectable pressure is as low as 2.97 μPa/Hz1/2. In addition, the FOM has a flat frequency response and a linear sound pressure response within the audible sound frequency range. These results indicate that this FOM shows the extreme sensitivity and miniature size, making it a promising technology for acoustic detection.

Sensitivity analysis of a two-plate coupled system in the statistical energy analysis (SEA) framework

The main objective of this paper is to perform design sensitivity analysis of two right angle coupled plates, connected by various joint connections, to determine an optimum coupling loss factor (CLF) using optimization in the statistical energy analysis (SEA) framework. The theoretical analysis of obtaining such optimum CLFs can be used during the design stage of a dynamic system to specify the right type of joint. First- and second-order sensitivity analysis using theoretical equations of CLFs of two right angle plates in the SEA framework, coupled to form welded, riveted, and bolted connections, is presented in the audible frequency range. These sensitivities were determined using both analytic (direct differentiation) and finite difference methods; the sensitivities computed by the analytic method agree well with the finite difference method, indicating that the direct differentiation method can be directly used to predict variation in the CLF and the corresponding response of coupled plates joined by various joint connections. The sensitivity analysis also gives a feasible region in terms of frequency range for the determination of optimum values of CLF by selecting the right type of joint at the design stage based on its stiffness. The study presented in this paper will be very useful at the drawing board stage of designing vibro-acoustic systems to reduce vibration or noise of such systems by giving a definite direction for the modification of design parameters, thus eliminating expensive experimentation; it will be helpful in arriving at the optimum values of CLF that would eventually reduce the vibro-acoustic response of dynamic systems with a large number of subsystems connected by welded, riveted, and bolted joints.

Yanny or Laurel? Acoustic and non-acoustic cues that influence speech perception

“What do you hear?” This question that divided the masses highlights the complex nature of speech perception, which is dependent upon both acoustic and non-acoustic information available to the brain. In this talk, I will discuss some of the most recent advances in our understanding of both types of information that enable the complicated task of speech perception under adverse listening conditions. Recent research from our lab and others has revealed a surprising amount of speech signal information resides in the highest audible frequency range for humans (i.e., beyond 8 kHz), providing localization, phonetic, and other speech source information. These cues, as well as non-acoustic (e.g., experiential, visual, lexical) cues likely become increasingly important when a listener is faced with ambiguity and/or degradation of the acoustic signal. Given the diversity of prior experience from individual to individual, differences in perception of an ambiguous/degraded speech signal are to be expected.

Effect of structural vibration and room acoustic modes on low frequency impact noise in apartment house with floating floor

In today’s apartment houses, adoption of floating floor has vastly improved structure-borne floor impact noise by isolating vibration components well in excess of the major structural vibration resonant frequencies. For 20–200 Hz frequency region encompassing major structural vibratory and room acoustic modes, however, impact noise attenuation is much harder to achieve, and the problem can be exacerbated for small rooms where these modes are sparsely placed in audible frequency range. Experimental and numerical investigation of the effect of structural vibration and room acoustics on impact noise for the frequency region is undertaken. Structural vibration modes of the room with floating floor correlate well with the spectral characteristics of the impact noise, with various structural parts making different contributions in the frequency domain. For the low end of the impact noise spectrum, low density of high-energy axial room acoustic modes arising from small room size causes sound field in the room to show notable variation with measurement locations. For the mock-up typical of a small-sized living room considered in the present study, one of the vibrational mode of floor slab excites an overlapping fundamental room acoustic mode that further amplifies the impact noise. A room design that avoids overlapping of major structural and acoustic resonance modes at low end of the audible spectrum could be crucial in abating an echo commonly encountered in bare apartment rooms.

Forced-oscillation control of sound radiated from the flow around a cascade of flat plates

At specific velocities, intense tonal sound can be radiated from the flow around cascaded flat plates. This sound arises from the coupled phenomena of vortex shedding and acoustic resonance. To suppress such noise, we actively control the vortex shedding and acoustic radiation by oscillating the edges of every second plate in the cascade. The objective of this investigation was to clarify the effects and mechanism of noise reduction under this control. To understand how the amplitude and frequency of the oscillations influence the controlled flow and acoustic fields around the flat-plate cascade, we conducted direct aeroacoustic simulations using the volume penalization method. The sound pressure level at the resonance frequency was decreased by oscillating the plates at a dimensionless amplitude of 0.15. The pressure reduction failed at oscillation frequencies close to the resonance frequency, because the acoustic resonance occurs at the oscillation frequency. In the audible range of oscillation frequencies (0–20 kHz), the audible overall sound pressure level was not able to be reduced. In contrast, at oscillation frequencies beyond the audible range, both the tonal sound pressure level at the resonance frequency and the audible overall level were decreased. Consequently, the noise radiated from a cascade of plates can be reduced by forced oscillations at a frequency above the audible range. Moreover, we offset the phase of the oscillations between two plates and observed the effect on the acoustic field. At a one-quarter phase offset, the sound pressure level at the oscillation frequency exhibited a vertical asymmetrical directivity.

The Application of Tactile, Audible, and Ultrasonic Forces to Human Fingertips Using Broadband Electroadhesion.

We report an electroadhesive approach to controlling friction forces on sliding fingertips which is capable of producing vibrations across an exceedingly broad range of tactile, audible, and ultrasonic frequencies. Vibrations on the skin can be felt directly, and vibrations in the air can be heard emanating from the finger. Additionally, we report evidence from an investigation of the electrical dynamics of the system suggesting that an air gap at the skin/surface interface is primarily responsible for the induced electrostatic attraction underlying the electroadhesion effect. We developed an experimental apparatus capable of recording friction forces up to a frequency of 6 kHz, and used it to characterize two different electroadhesive systems, both of which exhibit flat force magnitude responses throughout the measurement range. These systems use custom electrical hardware to modulate a high frequency current and apply surprisingly low distortion, broadband forces to the skin. Recordings of skin vibrations with a laser Doppler vibrometer demonstrate the tactile capabilities of the system, while recordings of vibrations in the air with a MEMS microphone quantify the audible response and reveal the existence of ultrasonic forces applied to the skin via electronic friction modulation. Implications for surface haptic and audio-haptic displays are briefly discussed.

Comparison of the acoustic behavour between paper waste of HVS and carton in similar composite

One of the hazardous environmental pollution that harms human health is Noise. Porous and vibrous materials are considered can be used for reducing noise. The purpose of the investigation is synthesizing and characterizing two kinds of acoustical composites based on Activated Zeolite with Carton and Activated Zeolite with HVS Paper Waste as building material components for noise reduction. Synthesizing each composite was conducted by chemical and mechanical mixing, and characterizing process was carried out by using EDS, FTIR, SEM and Impedance Tube. The absorption coefficient was measured in the frequency range between 125 Hz up to 6000 Hz. The results show that both have significant values for absorbing noise at the audible frequency range between 1200 Hz to 2200 Hz.

Acoustic noise and vibration analysis of solid state drive induced by multi-layer ceramic capacitors

Solid-state drives (SSDs), popular information storage devices, are typical printed circuit board assemblies (PCBA). As is true of other PCBAs, SSDs feature many multilayer ceramic capacitors (MLCCs). SSD vibration accompanied by high-pitched noise reflects the piezoelectric properties of MLCCs, and may cause great inconvenience to users. Here, we developed a finite element (FE) model predicting the vibration of the substrate associated with SSD acoustic noise. Because the SSD structure is complex and the model must be valid in the audible frequency range, we systematically constructed the model that is performed modal analysis. The excitation sources of the MLCCs were also modeled from a piezoelectric viewpoint, in which vibration analysis was performed in conjunction with the SSD model. Finally, the FE model was verified by comparing predicted and actual vibrations of an operational SSD.

Integrated active noise control for open-fit hearing aids with customized filter

The open-fit hearing aids that allow air and sound into the ear canal have become popular in recent years. Unfortunately, they result in the noise leakage problem that bypasses the hearing aids toward the eardrum and will degrade the quality of desired signal. This paper proposes a modified audio-integrated adaptive feedback active noise control (ANC) system for open-fit hearing aids. Traditionally, the ANC system attenuates the total power of the unwanted noise over the entire spectrum. To increase efficiency and save power consumption of hearing aids, we design a customized filter based on the hearing threshold of hearing-impaired patient to generate the anti-noise only in audible frequency range. The performance of the proposed method is verified by both computer simulations and real-time experiments.