High Sound Pressure Levels Research Articles

Sound attenuation performance at high sound pressure level of micro-perforated panel sound absorber with embedded resistive screen

In this paper, a composite sound absorber made of a micro-perforated panel (MPP), an air cavity with embedded resistive screen and a rigid back plate is investigated at high sound pressure level (SPL). The sound absorption coefficient predicted theoretically is compared with the experimental measurement at 150 dB and a good agreement is obtained. It is demonstrated that the incorporation of resistive screen within the air cavity improves significantly the sound absorption that presents a large frequency band and remains almost identical with respect to the SPL compared to a classical MPP absorber whose sound absorption peak varies with the SPL. The MPP absorber with the resistive screen glued on the MPP is studied and different resistive screens are compared at 150 dB and it is observed that the sound absorption coefficient increases with a large frequency band, which depends on the airflow resistivity of the screen. A sensitivity analysis shows that the resistance per unit area of the screen affects the acoustic properties of the absorber at low SPL while at high SPL, the acoustic properties are mainly controlled by the perforation ratio of the MPP and the acoustic orifice Mach number.

Comprehensive analysis of the seismic wave fields generated by offshore pile driving: A case study at the BARD Offshore 1 offshore wind farm.

Offshore pile driving not only generates high sound pressure levels, but also induces ground vibrations and particle motions that have the potential to affect fish and invertebrates living near or in the seabed. In particular, the seismic wave field in the form of interface waves is thought to be responsible for causing these particle motions and ground vibrations. However, the magnitude and spatial extent of the seismic wave field resulting from pile driving has not been clearly established. To fill this knowledge gap, this paper analyzes and illustrates in detail the seismic wave field at a construction site of the BARD Offshore 1 wind farm. For this purpose, the measured data from the construction site are compared to the results of a seismo-acoustic model. The measured and modeled data in combination provides a potential benchmark case for subsequent studies and other authors. The computed seismic wave field is investigated in terms of wave generation, mode composition, and propagation range of individual modes. The different seismic wave forms and their contribution to the particle motions in the seabed vicinity are discussed. The results indicate that, for the considered case, interface waves dominate the particle motion at the seafloor level up to a distance of 200 m.

Modelling the Propagation of Underwater Acoustic Signals of a Marine Energy Device Using Finite Element Method

Today a large number of marine based energy devices are been deployed rapidly across coastal areas of the world’s oceans to harness the huge natural energy and power potential provided by nature. These devices produce sound signals at high sound pressure levels across a wide range of frequencies that could be detrimental to the health and livelihood of marine animals. This paper proposes a computer model that simulates the emission of acoustic signals produced by a wave energy device. It analyses these signals with the aid of the audiogram of marine mammals, in this case the Harbour seal. This enables us to estimate the levels of acoustic noise experienced by marine mammals due to the presence of ocean deployed devices. Propagation of the acoustic signals underwater was modelled with boundary conditions using the finite element method. These include the bathymetry (features of underwater terrain) of the deployment site and properties of the propagation media. The type of spreading of the acoustic signals, and their interaction with the bottom surface interface of the acoustic enviroment was also taken into consideration. The effect of the bottom surface of the acoustic medium was seen to affect the sound pressure level (SPL) values as the sound receiver moves away from the source.

Time-domain simulation of the acoustic nonlinear response of acoustic liners at high sound pressure level

Time-domain simulation of the acoustic nonlinear response of acoustic liners at high sound pressure level

Influence of Acoustic Streams on the Efficiency of Ultrasonic Particle Agglomeration

The article is devoted to the study of ultrasonic agglomeration of PM 2.5 in homogeneous and inhomogeneous ultrasonic fields. The possibility of increasing the efficiency of ultrasonic agglomeration by initiating acoustic streams in a resonant inhomogeneous ultrasonic field is shown. A inhomogeneous ultrasonic field with zones of high and low sound pressure levels formed using a bending-oscillating disk transmitter made it possible to initiate acoustic vortex-type streaming that promotes the movement of particles into the nodal areas of a standing wave and between them. Due to the formation of a inhomogeneous ultrasonic field, the efficiency of particle collection is increased: for PM 2.5, the efficiency reaches 95%; PM 1.5—92%; PM 0.5—85%. The results were obtained under the following conditions: concentration 2 × 10−2 g/m3, sound pressure level 165 dB, flow rate 6.2 m3/h. For comparison, when a homogeneous ultrasonic field is formed in the agglomeration chamber (under similar conditions), the efficiency of particle capture by inertial gas cleaning equipment does not exceed the following: for PM 2.5—89%; PM 1.5—85%; and PM 0.5—76%. The obtained research results made it possible to propose a design for an agglomeration chamber that can greatly increase the productivity of ultrasonic flow processing.

Biodegradable, Bifunctional Electro-acoustic Transducers Based on Cellular Polylactic Acid Ferroelectrets for Sustainable Flexible Electronics.

Nowadays, humans rely increasingly on smart electronics to address grand challenges and to improve life conditions in the era of digitalization and big data. However, electronics often have a limited lifespan, and they may bring electronic waste problems after their service. To mitigate this problem, environmentally sustainable methods of electronic device production and disposal are highly recommended, where advanced functional materials should be redesigned with improved sensing performance over the entire operational life while also being naturally degradable at the end. Herein, a biodegradable and flexible bifunctional electroacoustic transducer was fabricated with the utilization of cellular polylactic acid (PLA) ferroelectret films, possessing a small acoustic impedance of ∼0.02 MRayl which is quite close to that of air and a high figure of merit (FOM: d33·g33) of ∼11 GPa-1. Such devices have a prominent signal-to-noise ratio (SNR) of ∼23.5 dB @1 kHz and can work either as a microphone by direct piezoelectric effect or a loudspeaker by reverse piezoelectric effect in air medium. When used as a microphone, the flexible device exhibits a prominent receiving sensitivity up to 4.2 mV/Pa (∼-47.5 dB/ref. 1 V/Pa) at 1 kHz. When served as a loudspeaker, it is capable of yielding high sound pressure levels (SPLs) ranging from 60 to 103 dB (ref. 20 μPa) in a broad frequency range of 1-80 kHz with an active area of 3.14 cm2. Additionally, the electrical response curve of the device is very flat in a wide frequency range from 300 to 3000 Hz. With the high-performance acoustic-electric conversion capacity, the PLA ferroelectret-based flexible and filmlike electroacoustic transducer was used to realize accurate speech recognition and control, providing a strong impetus for its advanced and eco-friendly applications in the era of the internet of things (IoT) and artificial intelligence.

A comparison of in situ and impedance eduction experimental techniques for acoustic liners with grazing flow and high sound pressure level

Several techniques are available to characterize acoustic liners when subject to grazing flow and high sound pressure level (SPL). Although the in situ technique started as the primary experimental procedure, impedance eduction techniques have gained popularity over the past years. However, there is a lack of comparison between these group of methods, especially at conditions typically found in turbofan engines. In this work, in situ and impedance eduction techniques are compared at high flow velocities and SPL using typical acoustic liner test samples and considering uniform flow. Both upstream and downstream acoustic wave propagation will also be considered in view of the discrepancies recently observed by eduction methods. A new method to compensate the instrumentation effect in the in situ technique is proposed and validated. Results are obtained for bulk Mach numbers up to 0.5 and SPLs up to 145 dB for both in situ and two eduction techniques. The three methods presents good agreement in the absence of flow. Unexpected results are observed with higher flow Mach numbers using the eduction technique.

A Guinea Pig Model Suggests That Objective Assessment of Acoustic Hearing Preservation in Human Ears With Cochlear Implants Is Confounded by Shifts in the Spatial Origin of Acoustically Evoked Potential Measurements Along the Cochlear Length.

Our recent empirical findings have shown that the auditory nerve compound action potential (CAP) evoked by a low-level tone burst originates from a narrow cochlear region tuned to the tone burst frequency. At moderate to high sound levels, the origins shift to the most sensitive audiometric regions rather than the extended high-frequency regions of the cochlear base. This means that measurements evoked from extended high-frequency sound stimuli can shift toward the apex with increasing level. Here we translate this study to understand the spatial origin of acoustically evoked responses from ears that receive cochlear implants, an emerging area of research and clinical practice that is not completely understood. An essential step is to first understand the influence of the cochlear implant in otherwise naive ears. Our objective was to understand how function of the high-frequency cochlear base, which can be excited by the intense low-frequency sounds that are frequently used for objective intra- and postoperative monitoring, can be influenced by the presence of the cochlear implant. We acoustically evoked responses and made measurements with an electrode placed near the guinea pig round window. The cochlear implant was not utilized for either electrical stimulation or recording purposes. With the cochlear implant in situ, CAPs were acoustically evoked from 2 to 16 kHz tone bursts of various levels while utilizing the slow perfusion of a kainic acid solution from the cochlear apex to the cochlear aqueduct in the base, which sequentially reduced neural responses from finely spaced cochlear frequency regions. This cochlear perfusion technique reveals the spatial origin of evoked potential measurements and provides insight on what influence the presence of an implant has on acoustical hearing. Threshold measurements at 3 to 11 kHz were elevated by implantation. In an individual ear, thresholds were elevated and lowered as cochlear implant was respectively inserted and removed, indicative of "conductive hearing loss" induced by the implant. The maximum threshold elevation occurred at most sensitive region of the naive guinea pig ear (33.66 dB at 8 kHz), making 11 kHz the most sensitive region to acoustic sounds for guinea pig ears with cochlear implants. Conversely, the acute implantation did not affect the low-frequency, 500 Hz thresholds and suprathreshold function, as shown by the auditory nerve overlapped waveform. As the sound pressure level of the tone bursts increased, mean data show that the spatial origin of CAPs along the cochlear length shifted toward the most sensitive cochlear region of implanted ears, not the extended high-frequency cochlear regions. However, data from individual ears showed that after implantation, measurements from moderate to high sound pressure levels originate in places that are unique to each ear. Alterations to function of the cochlear base from the in situ cochlear implant may influence objective measurements of implanted ears that are frequently made with intense low-frequency sound stimuli. Our results from guinea pigs advance the interpretation of measurements used to understand how and when residual acoustic hearing is lost in human ears receiving a cochlear implant.

Prontuário virtual para monitoramento audiológico de exposição ao ruído ocupacional

ABSTRACT Purpose: to develop and implement an electronic medical record for managing audiological assessments of workers exposed to occupational noise at a university. Methods: a computer system - the Electronic Audiology Record Program (PPVA, in Portuguese) - was developed with Microsoft Access for a university hospital’s audiology service, encompassing functional, occupational, and audiological information. After a testing period, the system was implemented in the service. Results: the PPVA is a personalized system that registers employees, audiological exams, clinical history, and risks for hearing loss induced by high sound pressure levels. It also generates reports indicating audiological monitoring frequency. Conclusion: the PPVA proved to meet the service’s needs, adequately. Its implementation improved the usability, efficiency, and quality of the service user records. Hence, it is a potential health surveillance tool, indicating that this type of instrument can benefit occupational hearing loss prevention programs.

Visualization and analysis of multi-channel dynamic range compression in hearing aids

One main functionality of hearing aids is restoring audibility. This means that low sound pressure levels are amplified above the elevated hearing threshold, and higher sound pressure levels do not exceed the individual uncomfortable loudness level (UCL). To this end, hearing aids provide frequency-dependent dynamic range compression which is denoted as hearing aid channels (HACs) in the recently published standard IEC 60118-16. As an increasing number of HACs, among other features, is one main feature to differentiate between price or technology levels, IEC 60118-16 includes a measurement procedure to verify the number of HACs. In this work, we verify this test procedure with a research hearing aid (RHA), and evaluate six commercial hearing aids of three different manufacturers and two technology levels. These results demonstrate the possibilities and limitations of the new test procedure. Furthermore, we introduced an extension of this test procedure with a channel-specific compression setting to overcome limitations and to get a deeper insight into the functionality of HACs in hearing aids. These results show that many HACs of commercial devices are coupled to neighboring frequencies, and that different strategies are used across manufacturers to adapt the number of HACs for different technology levels.

A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

A metamaterial-based interface for the structural resonance shielding of impact-driven offshore monopiles

Underwater noise resulting from the monopile driving process can cause severe damage to marine wildlife, such as hearing injury, behavioral disturbance, or even death. Although current noise-attenuation techniques used in this process have shown a significant noise reduction at high frequency ranges, mitigating low-frequency noise is still extremely challenging. To address the problem, here we propose an elastic metamaterial-based structure composed of single-phase resonant structures. The proposed structure, which we call a meta-interface, is introduced between the monopile and the hammer and is used to remove energy from the input signal associated with high noise levels. To that end, we first identify the frequency ranges associated with high sound pressure levels, which were shown to be related to the monopile’s eigenmodes. Then we design the meta-interface’s periodic unit cells so that the elastic/acoustic waves at identified frequency ranges are attenuated. A meta-interface is then realized by replicating the unit cell along the monopile wall (matching the thickness) to form a ring-shaped layer, and then by stacking up these concentric layers. A frequency analysis of the pile driving system with the meta-interface shows that the new noise levels attain a significant attenuation in frequency ranges lower than 1000Hz. This demonstrates a novel solution for the low-frequency underwater noise issue during the hammering of offshore monopiles.

The effects of ultrasound exposure with regard to the existing TVLs - a literature review

Noise is defined as any unwanted sound, and the health effects of noise have been well documented. Exposure to high levels of sound pressure can lead to hearing loss, tinnitus, and other health problems. Recently, there has been increasing concern about the potential health effects of exposure to ultrasound. Many countries have included ultrasonic noise on the list of factors hazardous to health in the working environment. Even though the frequency range above 20 kHz has been studied, there is not enough information regarding how it affects the human body. In addition, there are not any international standards for assessing ultrasonic noise at the work stations. While recent studies have helped advance the knowledge base in this area, they are still missing a considerable amount of data. This includes research into possible health consequences and improved dosimetry.

Auditory impression of amplitude-modulated vehicle horn sounds and their detectability in noisy environment

Vehicle horn sounds, due to their high sound pressure levels, induce negative psychological reactions in listeners, especially pedestrians. In order to reduce such negative effects, a horn sound with a lower sound pressure level is desired. At the same time, a horn sound should be easily perceived by drivers, considering its use on busy roads. The amplitude-modulated horn sound may help to solve these problems. Therefore, we synthesized amplitude-modulated horn sounds, and conducted psychoacoustical experiments to investigate the relationship between the acoustic characteristics and the perceived quality of these sounds. The results showed that stimuli with shallower modulation depths were less unpleasant than those with deeper modulation depths, and stimuli with modulation frequencies below 40 Hz suppressed auditory unpleasantness more than those with higher modulation frequencies. To confirm their effectiveness for detection in noisy conditions, stimuli with different signal-to-noise ratios were created by combining the amplitude-modulated horn sound and road traffic noise. The amplitude-modulated horn sound in road traffic noise was detected even in conditions where the signal-to-noise ratio was 3 dB lower than when the horn sound was not amplitude-modulated. The results indicate that amplitude-modulated horn sounds have the potential to improve the sound environment around roads.

Experimental investigation of the effect of absorption material on the non-linear properties of perforated plates

Combinations of perforated plate and porous material are used in numerous applications for noise reduction at high sound pressure level, such as in aircraft engines and automotive mufflers. Therefore, it is important to have a better understanding of the acoustic property of these systems. A semi-empirical model is a common way to calculate and understand the sound absorption of these systems. Previous studies show that the interface between a perforated plate and porous material have direct effect on the non-linear property of the perforated plate and sound absorption. Therefore, in this study two conditions of perforated plate and porous material combinations was considered. First, when the perforated plate has direct contact to the porous material and second, when there is air gap between them. Results of this research shows that the variation of non-linear acoustic resistance in case either with or without a cavity gap of air is relatively small.

Aeroacoustic analysis of a bass-reflex loudspeaker using LES: Validation of 2D and 3D numerical model with experiment

A bass-reflex loudspeaker has a port that amplifies low frequencies through Helmholtz resonance. However, high sound pressure levels can cause fluid flow near the port tip, leading to noise and distortion. Two-dimensional axisymmetric aeroacoustic analysis is commonly used to predict these non-linear phenomena; however, it has been reported to overestimate harmonic distortion. Presently, its accuracy has not been adequately verified through three-dimensional simulations or comparison with experimental results. This study validates the numerical model by comparing results from three- and two-dimensional analyses with experimental measurements on a straight tube port axisymmetric speaker model. In aeroacoustic analysis, large-eddy simulations are adopted, and the speaker model is acoustically driven at the Helmholtz resonance frequency. The results show that while the two-dimensional axisymmetric model overestimates the harmonic distortion and noise in the frequency response of far-field sound pressure, the three-dimensional model agrees well with the experiment up to the band where the harmonic distortion and port noise appear. This indicates that three-dimensional aeroacoustic analysis is necessary to accurately reproduce the fluid-induced distortion and noise of a bass-reflex port speaker.

Experimental investigation of the effect of material on the non-linear properties of perforated plates

Perforated plates are one of the effective passive noise controllers in the aeroacoustics system and industry. Effective absorption, resistant in harsh environment and easy maintenance are main reasons for perforated plates having several applications. Literature shows that even though perforated plates are common sound absorbers, they can be relatively easy non-linear. There are many reasons for this, for instance, temperature, and high level sound pressure. High sound pressure level can have non-linear impact at fairly low levels. Therefore, identification and understanding of this phenomenon is important. This is an essential reason for this study to experimentally investigate perforated plates with different material and study the non-linear properties of them. Two perforated plates with different material, fiberglass and steel, have been studied. The results illustrate that the geometry such as perforation, its thickness and the perforated plate material affect the non-linear properties of the perforated plate.

Can an artificially generated sound design improve the subjective evaluation of a vacuum cleaner noise? Results of a listening test with two vacuum cleaners.

In this study, the sound of two vacuum cleaners was enhanced with a psychoacoustic based, artificially generated sound design. One sound design with a lower level (SD_quiet) and one with a higher level (SD_loud) were tested in addition to the condition without sound design (RB). A listening test with 32 subjects was used to evaluate if the added sound design improves subjective evaluation of loudness, annoyance, and noise quality. The results showed a significant difference between the subjective ratings of SD_loud and the subjective rating of RB for both vacuum cleaners. The operating noise with added sound design SD_loud was rated as more powerful, of higher quality, more efficient, and less howling. For one vacuum cleaner, although SD_loud was rated as significantly louder and had a higher sound pressure level than RB, it was not rated as more annoying. This shows the high potential of the use of artificially added sound design in household appliances. Furthermore, the investigation showed that a sufficient volume for an added sound design has to be chosen because there were less differences between SD_quiet and RB regarding the subjective evaluation.

Research on the Hydrodynamic Noise Characteristics of a Mixed-Flow Pump

This study presents a comprehensive investigation of the internal noise characteristics of a mixed-flow pump by combining computational fluid dynamics (CFD) and computational acoustics. The turbulent flow field of the pump is simulated using the unsteady SST k-ω turbulence model in CFD. The contributions of the volute, guide vanes, and impeller to the internal noise are analyzed and compared using the Lighthill theory, FW-H formula, and LMS Virtual Lab software for acoustic simulation. The research findings indicate that the energy of pressure fluctuations in the mixed-flow pump is predominantly concentrated at the blade passing frequency and its low-frequency harmonics. This suggests that the internal noise is mainly in the low-frequency range, with higher energy at the blade passing frequency and its harmonics. Under the 0.6Qdes flow condition, the flow inside the pump becomes more complex, resulting in higher sound pressure levels and sound power levels compared to higher flow conditions. However, for flow conditions ranging from 0.8Qdes to 1.2Qdes, the sound pressure levels gradually increase with increasing flow rate, with the sound pressure level at 1.0Qdes being nearly identical to that at 1.2Qdes. The analysis of sound power level spectra at different flow rates reveals that the distribution characteristics of internal vortex structures directly impact the hydrodynamic noise inside the mixed-flow pump. These research findings provide a significant theoretical basis for noise control in mixed-flow pumps.

Computational Aeroacoustics for a Cold, Non-Ideally Expanded Aerospike Nozzle

Abstract In supersonic aerospace applications, aerospike nozzles have been subject of growing interest. This study sheds light on the noise components of a cold jet exhausting an aerospike nozzle. Implicit large eddy simulations (ILES) are deployed to simulate the jet at a nozzle pressure ratio (NPR)=3. For far-field acoustic computation, the Ffowcs Williams–Hawkings (FWH) equation is applied. A mesh sensitivity study is performed and the jet instantaneous and time-averaged flow characteristics are analyzed. The annular shock structure displays short non-attached shock-cells and longer attached shock-cells. Downstream of the aerospike, a circular shock-cell structure is formed with long shock-cells. Two-point cross-correlations of data acquired at monitoring points located along the shear layers allow to identify upstream propagating waves associated to screech. Power spectral density at monitoring points in the annular shock-cell structure allows to identify its radial oscillation modes. Furthermore, a vortex sheet model is adapted to predict the annular shock-cells length and the BBSAN central frequency. High sound pressure levels (SPL) are detected at the determined BBSAN central frequencies. Finally, high SPL are obtained at the radial oscillation frequencies for the annular shock-cell structure.