Audible Frequency Range Research Articles

Friction-induced noise in drum brakes: finite-element modeling and experiments with special focus on damping

Brake squeal in friction brakes is a typical audible noise phenomenon in vehicles leading to high development and sometimes warranty costs for the suppliers. The friction forces generated during braking are responsible for self-excited vibrations in the audible frequency range starting from 1hbox { kHz}. In the past countermeasures against friction-induced vibrations are mostly investigated for disk brakes while the present study focuses on drum brakes. Damping is in the context of self-excited vibrations often one of the key measures. Nowadays recuperative braking in electric vehicles relieves the conventional friction brake. Due to safety reasons, electric vehicles need to possess at least a second independent brake system. Therefore, simpler drum brakes are on the rise again when developing brake systems. Compared to brake disks, where damping elements can hardly be implemented, the freely accessible drum surface and the brake shoes offer so far unused potential for applying passive damping measures. The present paper focuses on how damping measures influence the noise behavior of drum brakes. Industrial and non-industrial brake components are investigated in detail. Experimental as well as numerical procedures are used to assess damping and noise characteristics.

Robustness of subwavelength devices: a case study of cochlea-inspired rainbow sensors.

We derive asymptotic formulae describing how the properties of subwavelength devices are changed by the introduction of errors and imperfections. As a demonstrative example, we study a class of cochlea-inspired rainbow sensors. These are graded metamaterials which have been designed to mimic the frequency separation performed by the cochlea. The device considered here has similar dimensions to the cochlea and has a resonant spectrum that falls within the range of audible frequencies. We show that the device’s properties (including its role as a signal filtering device) are stable with respect to small imperfections in the positions and sizes of the resonators. Additionally, under suitable assumptions, if the number of resonators is sufficiently large, then the device’s properties are stable under the removal of a resonator.

Threshold and frequency- and temporal resolutions of distantly presented bone-conducted sound in the audible-frequency range

As a vibrator needs to be pressed onto the osseous parts of the head, bone conduction is often accompanied by pain and esthetic problems. To solve these problems, a “distant presentation” that involves presenting vibrators to the neck, trunk, or upper limb was proposed. Our previous studies focused on the perceptual and propagation characteristics of distantly presented bone-conducted sounds in the ultrasonic range. However, only a few studies have been conducted in the audible-frequency range. In this study, to examine the basic properties of distantly presented bone-conduction perception in the audible-frequency range, hearing thresholds, difference limens for frequency, and temporal modulation transfer functions were measured with insulated air-conducted sounds. The results indicate that the distance attenuation is much larger than that in the ultrasonic range, and the degradation of frequency and temporal information occurring in the propagation process of bone-conducted sounds is sufficiently small for the transmission of sound information.

Vibration characteristics of channel steel-concrete composite girders: An experimental and numerical analysis

The broad application of steel and steel-concrete bridges has caused significant vibration and noise problems. Although the channel steel-concrete composite girder is a commonly used bridge type, the vibration transmission performance and structural optimization design (concrete deck, stiffeners, transverse connection components, etc.) from the perspective of vibration control have not been well studied. In this paper, experimental and numerical approaches are combined to investigate the dynamic properties of a steel-channel girder in the audible frequency range (20–2000 Hz). A steel-channel girder is tested via hammering. The effects of damping, stiffeners, and a concrete deck on structural vibration are evaluated using the finite element method. The experimental results indicate negligible differences in the vibration responses on a single plate, but large differences at different sections. The results are influenced by the effects of the distance and transmission path. The numerical results reveal that increasing the damping and stiffness (e.g., setting stiffeners) are both effective in reducing vibrations. Furthermore, increasing the stiffness has a more prominent effect on structural vibrations and their frequency dependence, whereas increasing the damping ratio can stably reduce structural vibrations. The simulation results indicate that installing a concrete deck is the most effective approach to vibration reduction, as it can decrease overall vibration by more than 10 dB. Vertical web stiffeners have stronger effects on vibration reduction than other stiffening countermeasures (e.g., transverse connection components and longitudinal bottom plate stiffeners).

Hearing status of people occupationally exposed to ultrasonic noise.

The aim of the study was to evaluate the hearing status of operators of low-frequency ultrasonic devices compared to employees exposed to audible noise at a similar A-weighted sound pressure level (SPL) but without ultrasonic components. Standard pure-tone audiometry, extended high-frequency audiometry (EHFA), transient-evoked otoacoustic emissions (TEOAE), and distortion-product otoacoustic emissions (DPOAE), as well as questionnaire surveys were conducted among 148 subjects, aged 43.1±10.8 years, working as ultrasonic device operators for 18.7±10.6 years. Their exposure to noise within the ultrasonic and audible frequency range was also evaluated. The control group comprised 168 workers, adjusted according to gender, age (±2 years), tenure (±2 years), and the 8-hour daily noise exposure level (LEX,8h) of ±2 dB. The ultrasonic device operators and the control group were exposed to audible noise at LEX,8h of 80.8±3.9 dB and 79.1±3.4, respectively. The Polish maximum admissible intensity (MAI) values for audible noise were exceeded in 16.8% of the ultrasonic device operators, while 91.2% of them were exposed to ultrasonic noise at SPL>MAI values. There were no significant differences between the groups in terms of the hearing threshold levels (HTLs) up to 3 kHz, while the ultrasonic device operators exhibited significantly higher (worse) HTLs, as compared to the control group, in the range of 4-14 kHz. The results of the DPOAE and TEOAE testing also indicated worse hearing among the ultrasonic device operators. However, the differences between the groups were more pronounced in the case of EHFA and DPOAEs. The outcomes of all hearing tests consistently indicated worse hearing among the ultrasonic device operators as compared to the control group. Both EHFA and DPOAE seem to be useful tools for recognizing early signs of hearing loss among ultrasonic device operators. nt J Occup Med Environ Health. 2022;35(3):309-25.

Favorable reverberation time in concert halls revisited for piano and violin solos.

A favorable reverberation time in concert halls is a fundamental issue for room acoustic design, and various recommendations have been suggested so far. Nevertheless, one must track back more than half a century when it comes to systematic subjective experiments on this topic. In this study, binaural room impulse responses (RIRs) measured with a dodecahedral loudspeaker in concert halls, where orchestra concerts are regularly held, are used. First, signal processing is applied to RIR to equalize the dodecahedral loudspeaker response as flat and broad as possible within the audible frequency range. Then, anechoic recordings of music by piano and violin, excerpts from cadenzas, are convoluted with the equalized RIR. Next, subjective experiments are conducted to seek favorable reverberation times. Reverberance and clarity were judged by 16 music experts. From this research, the favorable reverberation times RTM (octave band average for 500 and 1000 Hz) for piano and violin solos are from 1.2 to 2.0 s and 1.8 to 2.4 s, respectively. However, the clarity index C80,3 (octave band average for 500, 1000, and 2000 Hz) needs to range from 0 to 2.4 dB and -1.6 to 0.7 dB, respectively, to meet the optimum reverberance for piano and violin.

The acoustical absorption by air-saturated aerogel powders

The acoustical behavior of air-saturated aerogel powders in the audible frequency range is not well understood. It is not clear, for example, which physical processes control the acoustic absorption and/or attenuation in a very light, loose granular mix in which the grain diameter is on the order of a micron. The originality of this work is the use of a Biot-type poro-elastic model to fit accurately the measured absorption coefficients of two aerogel powders with particle diameters in the range 1-40 μm. It is shown that these materials behave like a viscoelastic layer and their absorption coefficient depends strongly on the root mean square sound pressure in the incident wave. Furthermore, it was found that the loss factor controlling the energy dissipation due to the vibration of the elastic frame is a key model parameter. The value of this parameter decreased progressively with the frequency and sound pressure. In contrast, other fitted parameters in the Biot-type poro-elastic model, e.g., the stiffness of the elastic frame and pore size, were found to be relatively independent of the frequency and amplitude of the incident wave. It is shown that these materials absorb acoustic waves very efficiently around the frequencies of the frame resonance.

Stretchable and ultrasensitive strain sensor based on a bilayer wrinkle-microcracking mechanism

As a fundamental component for human–machine interaction and human health monitoring, stretchable strain sensors suffer from an irreconcilable trade-off between sensitivity and stretchability. This severely limits their capability to detect both subtle and large deformations simultaneously. Here, a new class of strain sensors is proposed based on a hitherto unexploited strain-sensing bilayer consisting of a pre-wrinkled reduced graphene oxide layer and a highly susceptible layer of conformally deposited Ag nanoparticles. During straining, the pre-wrinkled interlayer guides preferential microcracking at the wavy troughs of the conformal Ag surface-layer, leading to effective integration of the irreconcilable sensitivity and stretchability. The obtained strain sensor not only shows high stretchability, but also owns unprecedented gauge factor (GF) both in subtle and large strain ranges (0–2%, GF: 420; 110–125%, GF: 1.1 × 109), ultralow strain detection limit (0.01%) and ultrafast response (0.13 ms). As demonstrated, the strain sensor has superior capabilities in diverse human motion detection and voice recognition over the whole audible frequency range (20–20000 Hz) with ultrahigh frequency resolution (0.5 Hz). It is expected that the novel wrinkle-directed dynamic patterning/structuring (e.g., microcracking in the current case) involved in the proposed bilayer design can be extended to fabricate a new generation of stretchable sensing devices with unprecedented capabilities.

Thin-Film PZT-Based Multi-Channel Acoustic MEMS Transducer for Cochlear Implant Applications

This paper presents a multi-channel acoustic transducer that works within the audible frequency range (250-5500 Hz) and mimics the operation of the cochlea by filtering incoming sound. The transducer is composed of eight thin film piezoelectric cantilever beams with different resonance frequencies. The transducer is well suited to be implanted in middle ear cavity with an active volume of 5 mm <inline-formula> <tex-math notation="LaTeX">$\times5$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times0.62$ </tex-math></inline-formula> mm and mass of 4.8 mg. Resonance frequencies and piezoelectric outputs of the beams are modeled with Finite Element Method (FEM). Vibration experiments showed that the transducer is capable of generating up to 139.36 mV<inline-formula> <tex-math notation="LaTeX">$_{{\mathrm {pp}}}$ </tex-math></inline-formula> under 0.1 g excitation. Test results are consistent with the FEM model on frequency (97&#x0025;) and output voltage (89&#x0025;) values. Device was further tested with acoustic excitation on an artificial tympanic membrane and flexible substrate. Under acoustic excitation, 50.7 mV<inline-formula> <tex-math notation="LaTeX">$_{{\mathrm {pp}}}$ </tex-math></inline-formula> output voltage generated under 100 dB Sound Pressure Level (SPL). Output voltages observed in acoustical and mechanical characterizations are the highest values reported to the best of our knowledge. Finally, to assess the feasibility of the transducer in daily sound levels, it was excited with a speech sample and output signal was recovered. Time-domain waveforms of the recorded and recovered signals showed close patterns.

Towards a remote inspection of jet engine blades using time reversal

Assessing the state of damage of jet engine blades is a burning issue in aeronautics. However, most nondestructive evaluation procedures require cumbersome installations and removal of the blades from the engines, which is time and money consuming. We present a non-intrusive acoustic monitoring technique that could be applied for fast remote inspection of selected blades inside a jet engine. The technique uses a time reversal mirror in the audible frequency range to selectively excite a targeted blade a few meters away. The resonance frequencies of the blade are measured at the location of the excitation using a laser vibrometer. The technique is first applied on a few individual blades and then inside a jet engine. Selective excitation of a difficult-to-access blade among others inside a cavity is shown. In laboratory, some damage (material removal or slit) is created on a set of initially intact blades, which cause a shift in their resonance frequencies. By evaluating these frequency shifts, we are able to remotely detect millimeter size damage on the blades. Finally, the on-site applicability and the uncertainties of the method are discussed.

Dynamic analysis of Sitar: A comparative study of operational and experimental modal analysis

Dynamic analysis of Sitar, an Indian string instrument, is important for better understanding of the instrument behavior during performance. Sitar has complex geometry, and most of its components have anisotropic material properties, which generate a lot of challenges in performing numerical modal analysis. Considering this, an experimental approach of operational modal analysis (OMA) is performed on Sitar to extract its natural frequencies using the Stochastic Subspace Identification method. Hammer or shaker excitation required for conventional experimental modal analysis (EMA) has huge limitations of using harder hammer tips and high magnitude force as the instrument is delicate. However, to validate OMA results, EMA is performed with extreme care using an instrumented hammer with soft tip and with a very low excitation force. PolyMAX algorithm is used in EMA. It is observed that most of the correlated OMA and EMA modes lie in the audible frequency range. The maximum absolute percent error observed for these frequencies is 2.14%. All the modes obtained in OMA are significant as the string excitation simulate close to the real-life performing situation. Most of these modes map to musical note frequencies. Considering the detrimental effect of excitation required for EMA, OMA is a recommended method for extracting modal characteristics of Sitar.

Basic properties of distantly-presented bone-conduction perception.

Since a vibrator needs to be pressed onto the osseous parts of the head, bone-conduction (BC) is often accompanied by pain and esthetic problems. In order to solve these problems, "distant presentation" has been proposed. In the distant presentation, vibrators are presented to the neck, upper limb or trunk. Our previous studies focused on the perception and propagation characteristics of distantly-presented BC sound in the ultrasonic range and an application to a novel audio-interface. On the other hand, a limited number of studies have been conducted on distantly-presented BC in the audible-frequency range. In this study, to examine the basic properties of the distantly-presented BC perception in the audible-frequency range, hearing thresholds, difference limens for frequency (DLFs) and temporal modulation transfer functions (TMTFs) were measured under the condition that AC sounds were insulated sufficiently. The results obtained indicated that BC sounds can be clearly perceived at distal parts of the body even in the audible-frequency range and no significant degradation of frequency and temporal information occurs in the propagation process in the body.

Four-channel ultrasonic demultiplexer based on two-dimensional phononic crystal towards high efficient liquid sensor

This paper reports numerically a high-performance phononic crystal sensor to sense the acidity of natural and industrial vinegar. The designed sensor is proposed based on a fluid-fluid phononic crystal structure in which the Mercury is selected as the host matrix and water-filled rods are the scatterers. The defect mode is introduced to the band gap by applying a cavity into the perfect phononic crystal, which, in turn, is created by eliminating one rod and modifying the radii of the two-sided rods. The resonant cavity has been constructed in the waveguide in order to introduce a super flat mode in the audible frequency range. It has been shown that by utilizing the finite element method, this sensor is capable of sensing the acidity of the natural and industrial vinegar with high accuracy. The sensitivity of the sensor is super remarkable and reached up to the value of 1275 Hz and consequently, the figure of merit could reach a value of 910. Finally, the sensor has been evolved to a tunable four-channel demultiplexer that could separate neighboring frequencies, each is relevant to a vinegar concentration. Based on the attained results, the proposed sensor can be used for evaluating the quality of many industrial foods and aqueous solutions.

Piezoelectric Ceramics with High d33 Constants and Their Application to Film Speakers.

A multilayer piezoelectric material was fabricated using piezoelectric materials with low-temperature sintering capabilities and high piezoelectric coefficients to develop a functionally superior piezoelectric speaker with a large-displacement deformation. A soft relaxor was utilized to prepare the component materials, with the optimized composition of the investigated piezoelectric ceramics represented by . was added to assist the low-temperature sintering conducted at 875 °C, which yielded a multilayer piezoelectric material with superior properties (= 500 pC N−1, = 0.63, = 44 mV N−1). A multilayer piezoelectric actuator with a single-layer thickness of ~40 µm and dimensions of 12 × 16 mm2 was fabricated by tape casting the prepared green sheets. Finite element analysis revealed that the use of a PEEK film and a smaller silicone–rubber film as a composite in the diaphragm realized optimal frequency-response characteristics; the vibrations generated by the piezoelectric element were amplified. The optimal structure obtained via simulations was applied to fabricate an actual piezoelectric speaker with dimensions of 20 × 24 × 1 mm3. The actual measurements exhibited a sound pressure level of ~75 dB and a total harmonic distortion ≤15% in the audible frequency range (250–20,000 Hz) at an applied voltage of 5.

Prepulse inhibition predicts subjective hearing in rats

Auditory studies in animals benefit from quick and accurate audiometry. The auditory brainstem response (ABR) and prepulse inhibition (PPI) have been widely used for hearing assessment in animals, but how well these assessments predict subjective audiometry still remains unclear. Human studies suggest that subjective audiometry is consistent with the ABR-based audiogram, not with the PPI-based audiogram, likely due to top-down processing in the cortex that inhibits PPI. Here, we challenged this view in Wistar rats, as rodents exhibit less complexity of cortical activities and thereby less influence of the cerebral cortex on PPI compared to humans. To test our hypothesis, we investigated whether subjective audiometry correlates with ABR- or PPI-based audiograms across the range of audible frequencies in Wistar rats. The subjective audiogram was obtained through pure-tone audiometry based on operant conditioning. Our results demonstrated that both the ABR-based and PPI-based audiograms significantly correlated to the subjective audiogram. We also found that ASR strength was information-rich, and adequate interpolation of this data offered accurate audiometry. Thus, unlike in humans, PPI could be used to predict subjective audibility in rats.

Nueva versión en Windows del sistema AUDIX para la evaluación objetiva de la audición

El presente trabajo describe una nueva versión del sistema AUDIX, diseñada como una estación de trabajo informatizada, para la audiometría objetiva y subjetiva. El sistema, esta integrado por un ordenador (PC) con una serie de programas de cómputo (“software”) el cual se conecta mediante una interfaz universal (universal serial bus USB) con un bloque electrónico especializado (“hardware”). El bloque electrónico tiene dos amplificadores bioeléctricos y un estimulador acústico digital totalmente programable con dos canales independientes. Esto permite generar de manera simultánea por ambos oídos, estímulos complejos diferentes (mezcla de tonos modulados en amplitud). Los estímulos acústicos pueden ser presentados a través de audiófonos (suprauriculares o de inserción), vibrador óseo y/o altavoces. El software programado sobre una plataforma Windows, tiene 5 módulos diferentes para la adquisición y análisis de PEA transientes y de estado estable, audiometría conductual, administración de base de datos y calibración. La base de datos del sistema permite almacenar, borrar, extraer, crear y realizar copias de respaldo. Durante la adquisición de los PEA se utilizan diferentes métodos estadísticos como indicadores para la detección objetiva de las respuestas. Puede visualizarse en forma concurrente la actividad bioeléctrica de base (monitoreo de EEG) y el resultado de la promediación (PEA). Los resultados del examen electroaudiométrico son analizados fuera de línea de una manera flexible, generándose múltiples reportes gráficos y permitiendo la comparación automática con datos normativos. En el caso de los PEAee los resultados pueden ser presentados en el formato estándar de un audiograma convencional utilizando diferentes escalas (dB: HL, SPL, nHL). El sistema AUDIX ha sido validado ampliamente en la práctica clínica resultando de utilidad para la detección temprana de las pérdidas auditivas y la caracterización precisa de la audición en toda la gama de frecuencias audibles.

Comparative study of efficiency and characteristics of FMT and DRT installed in human cadavers for round-window stimulation

Acoustic hearing aids generate amplified sound in the ear canal, and they are the standard of care for patients with mild to moderate sensorineural hearing loss. However, because of their limited frequency bandwidth, gain, and feedback, there is substantial room for improvement. Active middle ear implants, which directly vibrate the middle ear and cochlea, are an alternative approach to conventional acoustic hearing aids. They provide an opportunity to improve sound quality and speech understanding with amplification rehabilitation. For floating-mass type and direct-rod type (DRT) middle ear transducers, a differential floating-mass transducer (DFMT) and a tri-coil bellows transducer (TCBT), respectively, were fabricated to measure the output characteristics in four human temporal bones. Both were fabricated to have similar output forces per unit input and were placed in four human temporal bones to measure their output performances. The TCBT resulted in higher output than did the DFMT throughout the audible frequency range, and the output was more prominent at lower frequency ranges. In this study, we showed that DRT was a more effective method for round window stimulation. Because of its frequency characteristics and vibration efficiency, this implantation method can be utilized as a driving solution for middle ear implants.

DESIGN AND CONSTRUCTION OF A HEARING AID DEVICE

Hearing is one of the five senses, therefore, it is very important that the human ear be able to detect sound in the audible frequency range. However, in some cases, certain individuals have difficulty hearing in either or both ears. It is therefore necessary that a device that can help in correcting this be developed. In this work, a hearing aid has been constructed using readily available circuit components (transistors, capacitors, ICs). This makes the device easily accessible and affordable for anyone who needs it. The hearing aid constructed was tested under different levels of ambient noise and was found to amplify the desired sound while filtering away the noise. Hence, it can be said to function considerably well.

Ultra-thin PZT/Si chip integrated on paper substrates

This paper presents the integration process of an ultra-thin PZT/Si chip on paper and that it functions as a simple speaker by applying a voltage in the audible frequency range. The PZT/Si chip used is only 5 μm thick, so it does not interfere with the flexibility of the substrate, and it can be integrated on paper because it does not use a high-temperature process in the electrode connection process. We have revealed that a paper with an ultra-thin PZT/Si chip of only 1 × 5 mm2 in size generates a fully audible sound pressure level (SPL) of about 40 dB. It was rounded to a radius of curvature of 1 cm without breaking. The overall SPL was about the same even when the paper substrate dimension was reduced to 50 mm square. This technology is expected to be applied to electronic components such as surround speakers or haptics in electronic paper.

Broadband noise mitigation using coupled Helmholtz resonators: a numerical study

In this work we investigate a periodic structure in the frequency range from 20 Hz to 5500 Hz designed for broadband noise insulation. The considered unit cell consists of a simple structure: a pair of polymer pipes with slits carved along the axes, representing two coupled Helmholtz resonators. In order to develop a design with a broad band gap, we analyze the eigenmodes of the infinite two-dimensional structure considering their symmetry and interaction. This analysis is supported by parametric optimization of the resonator geometry. The obtained band diagram is compared with numerically determined transmission coefficient of a finite structure based on the same unit cell. The number of unit cells of the finite structure is chosen to be sufficient for demonstration of insulating properties and stop band formation. Furthermore, we analyze how the transmission coefficient is linked to the pressure field distribution inside the resonators. Owing to the simplicity of the geometry, the obtained results may become a basis for development of budget-friendly passive systems for broadband noise insulation within the audible range of frequencies.