High Sound Pressure Levels Research Articles

Assessment of temporary hearing changes related to work as a bartender

Noise in entertainment industry often reaches high sound pressure levels. Nevertheless, the risk of hearing loss in this sector is insufficiently recognized. The aim of this study was the assessment of the relationship between noise exposure and temporary threshold shifts (TTS) for people working as bartenders at a variety of entertainment venues. The study comprised a total of 18 bartenders (mean age was 25±7 years old) employed at a music club (N = 8), pub (N = 5) and discotheque (N = 5). Personal dosimeters were used for determining noise levels and frequency characteristics. Hearing was evaluated by pre- (before work) and post-exposure (up to 15 min after the end of work) pure tone audiometry. Hearing tests were carried out for bartenders during 2 or 3 sessions while working on weekends. The mean personal noise exposure level normalized to a nominal 8-hour working day was 95 dBA, above 4 times higher than the accepted legal limit. The TTS values (10 dB HL or more) were significant at 4 kHz for both ears for 77% of bartenders. People working as bartenders represent a professional group with an increased risk of hearing loss. Raising awareness of this fact and implementing hearing protection programs in this group of workers is urgently needed, in line with the European Commission Directive (EU Directive 2003/10/EC). Med Pr. 2019;70(1):17-25.

Evaluation of on-the-job noise exposure in the case of bartenders

In places associated with the entertainment industry in which music is performed or played, sounds with high sound pressure levels may occur. Such exposure is a threat to both people spending their free time at concerts, in discos or pubs, as well as employees in these places. The aim of the research conducted in 2017 was to assess on-the-job noise exposure in the case of bartenders at various premises of the entertainment industry. The measurements included 15 entertainment venues in Łódź, out of which 3 were selected: a music club, disco and pub. The exposure measurements were taken together for 4 work stations for bartenders using individual dosimetry in accordance with the PN-EN ISO 9612: 2011 standard. A total of 64 measurements were carried out, which showed that the equivalent sound levels A at the bartenders' workplaces vary considerably depending on the type of premises and the day of the week and the range of 67.6-108.7 dB. The highest sound levels occurred during the weekend (Fridays and Saturdays). The determined daily noise exposure levels exceeded the threshold of preventive action (80 dB) in 95% of the analyzed cases. Exceeding the maximum permissible noise level (NDN = 85 dB) was found in 66% of cases. It has been found that on-the-job noise levels in the case of bartenders significantly exceed the acceptable values of exposure levels and pose a risk of hearing damage. Med Pr 2018;69(6):633-641.

Fabrication and investigation of a thermoacoustic loudspeaker based on carbon nanotube coated laser-scribed graphene

In spite of being known since a century ago, high operational voltage and low sound pressure level have limited wide applications of thermophones. In recent years, utilizing graphene in thermophones has been proposed as an attractive solution, which is benefiting from high electrical and thermal conductivity and inherent high surface area, to enhance the heat transfer and lowering the required electrical input power. In this paper, a laser-scribed graphene (LSG) layer is utilized to realize graphene-based thermophones, which provide a considerably high sound pressure level of about 80 dB (Pin = 0.6 W). Furthermore, a layer of carbon nanotubes (CNTs) is incorporated on the prepared LSG sheets, which benefits from both randomly oriented CNTs over the surface of reduced graphene oxide (rGO) sheets and suspended CNTs, which act like heat exchanger nano-fins on rGO sheets and efficient heat generators, respectively. The input voltage for CNT/LSG based thermophones is measured 7 times lower than the prepared LSG samples, in order to generate the same sound pressure level (75 dB). The achieved sound pressure, normalized to the input power, has increased about 80 dB by incorporating CNTs which entitles the proposed structure as a promising candidate for novel thermophones.

Noise comparison of centrifugal pump operating in pump and turbine mode

Investigations regarding the relation of noise performance for centrifugal pump operating in pump and turbine modes continue to be inadequate. This paper presents a series of comparisons of flow-induced noise for both operation modes. The interior flow-borne noise and structure modal were verified through experiments. The flow-borne noise was calculated by the acoustic boundary element method (ABEM), and the flow-induced structure noise was obtained by the coupled acoustic boundary element method (ABEM)/structure finite element method (SFEM). The results show that in pump mode, the pressure fluctuation in the volute is comparable to that in the outlet pipe, but in turbine mode, the pressure fluctuation in the impeller is comparable to that in the draft tube. The main frequency of interior flow-borne noise lies at blade passing frequency (BPF) and it shifts to the 9th BPF for interior flow-induced structure noise. The peak values at horizontal plane appear at the 5th BPF, and at axial plane, they get the highest sound pressure level (SPL) at the 8th BPF. Comparing with interior noise, the SPL of exterior flow-induced structure noise is incredibly small. At the 5th BPF, the pump body, cover and suspension show higher SPL in both modes. The outer walls of turbine generate relatively larger SPL than those of the pump.

Electrospun poly(vinylidene fluoride)-zinc oxide hierarchical composite fiber membrane as piezoelectric acoustoelectric nanogenerator

Nanogenerators which efficiently convert mechanical forces, vibrations and sound to electrical energy have attracted much attention and showed potential application as sustainable energy source for powering miniature devices. In this work, we fabricated a piezoelectric acoustoelectric nanogenerator using poly(vinylidene fluoride)-zinc oxide composite fiber membrane with hierarchical microstructure by electrospinning and hydrothermal techniques. The prepared PVDF–ZnO acoustoelectric nanogenerator (PVDF–ZnOANG) was able to generate voltage and current output of 1.12 V and 1.6 μA with a power density output of 0.2 μW cm−2 (50 μW cm−3) in optimized sound condition (140 Hz, 116 dB). Under the optimized sound condition, the electric energy generated by the prepared PVDF–ZnOANG could charge a capacitor up to 1.3 V in 3 min. The PVDF–ZnOANG generated higher voltage output under sound of low frequency and high sound pressure level and therefore might be a promising power source for noise energy harvesting.

Uncertainty analysis on free-field reciprocity calibration of measurement microphones for airborne ultrasound.

Airborne ultrasound has been used for various purposes, including object detection and pest repellent systems. Recently, it has been used in haptic technology for virtual reality. The safety of exposure to airborne ultrasound has been studied as its use has increased. Although airborne ultrasound cannot be directly perceived by humans, some research has found that exposure to very high sound pressure levels can harm the human body. Thus, quantitative characterization of airborne ultrasound is essential. To contribute to the safe use of airborne ultrasound, this paper established the acoustic standards in Japan in terms of sound pressure from 20 to 100 kHz. This paper evaluates the measurement uncertainty in the free-field reciprocity calibration of quarter-inch condenser microphones, following the document "Guide to the Expression of Uncertainty in Measurement," and describes a few significant uncertainty components, such as deviation from the plane sound field. As a result, it is realized that the expanded uncertainty of 0.3-0.7 dB in a frequency range from 20 to 100 kHz.

Effects of very high-frequency sound and ultrasound on humans. Part II: A double-blind randomized provocation study of inaudible 20-kHz ultrasound

Some people have reported symptoms such as nausea, dizziness, and headaches that they attribute to ultrasound (US) emitted by devices in public places. The primary aim of the present study was to investigate whether inaudible US can provoke adverse symptoms compared to a sham presentation, under double-blind conditions. A second aim was to investigate whether the expectation of US being present could provoke adverse symptoms (a nocebo response). The US stimulus was a 20 kHz tone presented continuously for 20 min set to at least 15 dB below the participants' detection threshold, giving a typical sound pressure level (SPL) of 84 dB. No evidence that US provoked symptoms was found, but there was evidence of small nocebo effects. A case study on an individual with high self-reported sensitivity to US gave similar results. The present study did not reproduce the severe symptoms reported previously by some members of the public; this may be due to the SPL or duration of the stimulus, or strength of the nocebo stimulus. These findings cannot be used to predict outcomes from exposures to sounds that are audible to the individual in question, or to sounds with higher SPLs, longer durations, or different frequency content.

Feature Maps of the Acoustic Spectrum of the Voice

The change in the spectrum of sustained /a/ vowels was mapped over the voice range from low to high fundamental frequency and low to high sound pressure level (SPL), in the form of the so-called voice range profile (VRP). In each interval of one semitone and one decibel, narrowband spectra were averaged both within and across subjects. The subjects were groups of 7 male and 12 female singing students, as well as a group of 16 untrained female voices. For each individual and also for each group, pairs of VRP recordings were made, with stringent separation of the modal/chest and falsetto/head registers. Maps are presented of eight scalar metrics, each of which was chosen to quantify a particular feature of the voice spectrum, over fundamental frequency and SPL. Metrics 1 and 2 chart the role of the fundamental in relation to the rest of the spectrum. Metrics 3 and 4 are used to explore the role of resonances in relation to SPL. Metrics 5 and 6 address the distribution of high frequency energy, while metrics 7 and 8 seek to describe the distribution of energy at the low end of the voice spectrum.Several examples are observed of phenomena that are difficult to predict from linear source-filter theory, and of the voice source being less uniform over the voice range than is conventionally assumed. These include a high-frequency band-limiting at high SPL and an unexpected persistence of the second harmonic at low SPL. The two voice registers give rise to clearly different maps. Only a few effects of training were observed, in the low frequency end below 2 kHz. The results are of potential interest in voice analysis, voice synthesis and for new insights into the voice production mechanism.

Concave surfaces and acoustics of performance spaces—Part II —Wave analysis

Conventional wisdom states that having concave surfaces as the envelope of any occupied space does not produce good sound. The focussing effect of concave surfaces can cause high sound pressure levels, coloration, and echoes. However, throughout history there have been many enclosed rooms with large curved surfaces as envelopes that seem to produce good acoustics. Recent research suggested that wave analysis must be undertaken to establish the impact of concave surfaces. In contrast to Part I of the current investigation, evaluation of the sound pressure level distribution, in rooms with concave surfaces, was performed by solving the governing wave equation. The main reason is that the image-ray theory is valid only at frequencies greater than the Schroeder cut-off frequency. The wave theory is used for frequencies lower than 100 Hz. Finite element modelling was applied to solve for the sound pressure level distribution within rooms with concave surfaces. Three spaces, the Paul Crocker Gallery in Ryerson University, Toronto, St. Pauls Anglican Church in Toronto and Wigmore Hall in London were investigated in this study. The results for three low frequencies (25 Hz, 50 Hz, and 100 Hz) as well as their combination will be presented in this paper.Conventional wisdom states that having concave surfaces as the envelope of any occupied space does not produce good sound. The focussing effect of concave surfaces can cause high sound pressure levels, coloration, and echoes. However, throughout history there have been many enclosed rooms with large curved surfaces as envelopes that seem to produce good acoustics. Recent research suggested that wave analysis must be undertaken to establish the impact of concave surfaces. In contrast to Part I of the current investigation, evaluation of the sound pressure level distribution, in rooms with concave surfaces, was performed by solving the governing wave equation. The main reason is that the image-ray theory is valid only at frequencies greater than the Schroeder cut-off frequency. The wave theory is used for frequencies lower than 100 Hz. Finite element modelling was applied to solve for the sound pressure level distribution within rooms with concave surfaces. Three spaces, the Paul Crocker Gallery in Ryerson ...

Large eddy simulation of serration effects on an ultra-high-bypass-ratio engine exhaust jet

Serrated jet nozzles are considered to be an efficient and practical passive control approach for jet noise. However, some fundamental mechanisms of serration effects on jet noise are not fully understood, especially in terms of the sound source. In this paper, a high-fidelity simulation framework using large-eddy simulation (LES) is demonstrated to predict near-field turbulence and far-field acoustics from an ultra-high-bypass-ratio engine with round and serrated nozzles. Far-field sound is predicted using Ffowcs Willams–Hawkings (FWH) integration. The results show that the serrated nozzle increases mixing near the nozzle and hence the turbulence decay rate, reducing the turbulence level downstream. The serrations shift the energy from the low frequencies to the high frequencies and decrease overall sound pressure levels by about 3 dB over the low-frequency range. Sound sources are analysed based on fourth-order space–time correlations. There are six major source components (R1111, R2222, R3333, R1313, R1212, and R2323) inside the jet shear layers. The serrations are able to reduce the amplitude of these source terms, causing them to decay rapidly to a level below the round nozzle jet within 2D downstream of the nozzle.

Bass Extension of Microspeaker System on Mobile Device

ABSTRACTThis study provides a solution for the bass extension of a microspeaker system in a mobile device that involves using a resonant combination of a front chamber and a rectangular, long, pipe-shaped port. The efficient resonant coupling of the microspeaker system to the acoustic load in this structure enables a microspeaker with modest cone displacement to achieve a high sound pressure level (SPL) and bass extension below the resonance of the microspeaker in free air, and the total dimensions of the structure are minimized. A combination of electro-mechanic-acoustic and finite element methods was applied to determine the SPL and bass extension levels for mobile devices. Simulation results show acceptable agreement with experimental results. A suitable extended-range microspeaker system was applied in a 10 inch tablet. The audio frequency response could be extended from 630 to 300 Hz with the greatest loudness. As much as possible add low bound frequency extension to make the article more clear. Finally, five cases of parameter settings for the front chamber volume, rear chamber volume, rectangular pipe-shaped port, cross-sectional area, and opening area were studied. The results can be applied for optimizing a suitable extended-range microspeaker system.

Modeling of acoustic lined duct with and without grazing air flow by an analytical method

An analytical method is proposed to characterize the sound acoustic transmission in a rectangular lined duct with and without grazing air flow. The acoustic wave number in the duct is determined using Taylor series expansion. The proposed method is validated by comparison with a finite element method in grazing air flow environment and experimental measurements at grazing sound incidence for the case with no flow. Excellent agreement is found in both configurations. The proposed method is used for sensitivity analysis of acoustic duct lined with micro perforated panel absorber in order to evaluate the impacts of the inputs parameters on the transmission loss of the duct. It is shown for a constant sound pressure level that the transmission loss of the duct is very sensitive to the cavity depth of the absorber while the resonance of the transmission at high sound pressure level is controlled by the perforation ratio of the panel. The effects of the perforation diameter and the plate thickness are negligible for higher pressure excitation and the impact of the sound pressure level on the transmission is preponderant.

Intracochlear pressure measurements during acoustic shock wave exposure

IntroductionInjuries to the peripheral auditory system are among the most common results of high intensity impulsive acoustic exposure. Prior studies of high intensity sound transmission by the ossicular chain have relied upon measurements in animal models, measurements at more moderate sound levels (i.e. < 130 dB SPL), and/or measured responses to steady-state noise. Here, we directly measure intracochlear pressure in human cadaveric temporal bones, with fiber optic pressure sensors placed in scala vestibuli (SV) and tympani (ST), during exposure to shock waves with peak positive pressures between ∼7 and 83 kPa. MethodsEight full-cephalic human cadaver heads were exposed, face-on, to acoustic shock waves in a 45 cm diameter shock tube. Specimens were exposed to impulses with nominal peak overpressures of 7, 28, 55, & 83 kPa (171, 183, 189, & 192 dB pSPL), measured in the free field adjacent to the forehead. Specimens were prepared bilaterally by mastoidectomy and extended facial recess to expose the ossicular chain. Ear canal (EAC), middle ear, and intracochlear sound pressure levels were measured with fiber-optic pressure sensors. Surface-mounted sensors measured SPL and skull strain near the opening of each EAC and at the forehead. ResultsMeasurements on the forehead showed incident peak pressures approximately twice that measured by adjacent free-field and EAC entrance sensors, as expected based on the sensor orientation (normal vs tangential to the shock wave propagation). At 7 kPa, EAC pressure showed gain, calculated from the frequency spectra, consistent with the ear canal resonance, and gain in the intracochlear pressures (normalized to the EAC pressure) were consistent with (though somewhat lower than) previously reported middle ear transfer functions. Responses to higher intensity impulses tended to show lower intracochlear gain relative to EAC, suggesting sound transmission efficiency along the ossicular chain is reduced at high intensities. Tympanic membrane (TM) rupture was observed following nearly every exposure 55 kPa or higher. ConclusionsIntracochlear pressures reveal lower middle-ear transfer function magnitudes (i.e. reduced gain relative to the ear canal) for high sound pressure levels, thus revealing lower than expected cochlear exposure based on extrapolation from cochlear pressures measured at more moderate sound levels. These results are consistent with lowered transmissivity of the ossicular chain at high intensities, and are consistent with our prior report measuring middle ear transfer functions in human cadaveric temporal bones with high intensity tone pips.

Numerical modelling of unsteady cavitation and induced noise around a marine propeller

The objective of this paper is to numerically investigate the cavitating flow around a marine propeller and to explore the intrinsic relationships between the sheet cavitation and its radiation noise. The k-ω SST turbulence model with the turbulence viscosity correction and the Zwart cavitation model are introduced to the simulation of cavitating flow around a propeller in a non-uniform wake. The loading noise and cavitation noise have been predicted based on the theory for acoustic fan source and the sound radiation theory for spherical bubble respectively. The periodic cavitation development has been captured, and the periodic large pressure fluctuation around the blade has been analyzed with the dominant frequencies in accordance to the first order of the blade passing frequency. For the non-cavitation case, the high sound pressure levels mainly concentrate in the low frequency stage and decrease from the low-order to the high-order blade passing frequency. While for the sheet cavitation case, the sound pressure level at the high-order of blade passing frequencies are enhanced. The sound pressure induced by the cavitation development is periodically varied accompanied with the periodic pulsating cavity evolution, and the acoustic energy mainly focus on the low order of blade passing frequencies.

Sound absorption of a porous material with a perforated facing at high sound pressure levels

A semi-empirical model is proposed to predict the sound absorption of an acoustical unit consisting of a rigid-porous material layer with a perforated facing under the normal incidence at high sound pressure levels (SPLs) of pure tones. The nonlinearity of the perforated facing and the porous material, and the interference between them are considered in the model. The sound absorptive performance of the acoustical unit is tested at different incident SPLs and in three typical configurations: 1) when the perforated panel (PP) directly contacts with the porous layer, 2) when the PP is separated from the porous layer by an air gap and 3) when an air cavity is set between the porous material and the hard backing wall. The test results agree well with the corresponding theoretical predictions. Moreover, the results show that the interference effect is correlated to the width of the air gap between the PP and the porous layer, which alters not only the linear acoustic impedance but also the nonlinear acoustic impedance of the unit and hence its sound absorptive properties.

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

We present a high-speed single-mirror double-pass coincident schlieren system and corresponding algorithms for the visualization of acoustic waves and recovery of their associated audio signals. Schlieren systems are extensively used to visualize strong shockwaves, such as those from supersonic motion or explosions. Recently, they have also been used to visualize lower amplitude non-linear acoustic phenomena, such as the weak shockwaves arising from impact events including hand claps, belt snaps, and towel cracks. Time-invariant sounds produced by loudspeakers have also been imaged, in one case leading to frequency analysis, although these have been limited to high-frequency signals at very high sound pressure levels. The research presented here shifts the focus from sound-field visualization towards audio signal recovery. A comprehensive exploration of several parameters for imaging sound sources, including frequency, wave form, and amplitude, is presented. In addition, we address for the first time the recovery of phase information, which would be essential for speech intelligibility, and the more general case of non-contact sound field reconstruction. Through image and signal processing, it is shown that audio signals can be recovered from high-speed schlieren video whose acoustic waves appear to be below the limit of visibility, and were previously deemed unrecoverable by virtue of their frequency and sound pressure level. This includes sounds at frequencies and loudnesses relevant for human hearing, producing the first ‘schlieren microphone’.

Numerical study on non-locally reacting behavior of nacelle liners incorporating drainage slots

For acoustic liners used in current commercial nacelles, in order to prevent any liquid accumulating in the resonators, drainage slots are incorporated on the partition walls between closely packed cavities. Recently, an experimental study conducted by Busse-Gerstengarbe et al. shown that the cell interaction introduced by drainage slots causes an additional dissipation peak which increases with the size of the slot. However, the variation of damping process due to drainage slots is still not fully understood. Therefore, a numerical study based on computational aeroacoustic methods is carried out to investigate the mechanism of the changed attenuation characteristics due to drainage slots in presence of grazing incident sound waves with low or high intensities. Different slot configurations are designed based on the generic non-locally reacting liner model adopted in the experimental investigation. Both 2-D and 3-D numerical simulations of only slit resonators are carried out. Numerical results indicate that the extra peak is a result of a resonance excited in the second cavity at specific frequency. Under high sound pressure level incoming waves, the basic characteristics of the acoustic performance remain. However, vortex shedding transpires at the resonances around both the slits and the drainage slot. Vorticity contours show that the connection of two coupled cavities decreases the strength of vortex shedding around the basic Helmholtz resonance due to a higher energy reflection. Meanwhile, the cell interaction significantly increases the vorticity magnitude near the extra resonant frequency. Finally, a semi-empirical model is derived to predict the extra attenuation peak frequency.

Engineering-oriented design strategy to obtain linear micro-perforated panel absorbers at high sound pressure environment

The nonlinear effect at high sound intensity not only degrades the absorption performance of a micro-perforated panel (MPP) absorber, but also makes its performance prediction and structure design become difficult and unreliable due to the absence of accurate nonlinear impedance models. Hence, it is desirable to develop a linear MPP absorber. Based on this, this paper presents an investigation on an engineering-oriented design method of a linear absorber according to practical needs for a specific high sound pressure level (SPL) application. The strategy actually involves a reverse design method and process and the output is a set of structure parameters that uniquely determine an MPP absorber. The input is the characteristic parameters of an MPP absorber which are associated with environment parameters, such as the most undesirable frequency and the maximum SPL. Firstly, the detailed process of design for a linear MPP absorber is expatiated in this study. Then a concrete design example based on the current approach is present and finally, the reliability of the design results is validated by experiment. This study provides a new thought and method for the effective application of MPP absorbers in high SPL environments.

A Method to Estimate Students’ Exposure to Road Traffic Noise Events

The correlation between exposure to traffic noise and students’ performance and annoyance has been investigated in literature mainly considering the relationship between indoor equivalent A-weighted sound pressure level (LAeq) and students’ cognitive impairment. Annoyance is frequently related to the effect of short-duration noise events characterized by high sound pressure levels, such as those due to aircraft fly-over and pass-by of buses, heavy trucks, motorcycles, or street sweepers. These noise events are often described, over specific measurement periods, in terms of maximum A-weighted sound pressure level, LAmax, or statistical levels, such as LA1 or LA10. This aspect is not considered in the noise maps drawn in accordance with the European Environmental Noise Directive, as they provide the LAeq only, determined over day, evening, and night periods. In this paper, students’ exposure to road traffic noise is analyzed by means of regression equations obtained by the authors between LAeq and A-weighted maximum and statistical levels due to road traffic noise. The traffic noise of 28 urban streets was monitored during the opening period of Italian schools. A method is described to estimate students’ exposure to noise from data made available on noise maps by the municipalities of metropolitan areas. The application of this method to the case study of Florence shows that almost 60% of students from municipal primary and lower secondary schools could be exposed to the maximum sound pressure level (SPL) inside the classroom greater than 55 dB(A) every hour, probably exceeding the typical background noise in classrooms by more than 10 dB.

Numerical and experimental study of acoustically enhanced heat transfer from a single particle in flue gas

ABSTRACTTo investigate the heat transfer of pulverized coal particles under the effect of an acoustic field (without a superposed steady component), we derived and solved the two-dimensional, unsteady, laminar conservation equations for mass, momentum, and energy transport in the flue gas phase of a power plant boiler. The local, space-averaged, and space- and time-averaged Nusselt (Nu) numbers for the coal particles are discussed for the full audible frequency range. Experiments were also conducted to study the heat transfer, in particular the heat exchange at the surface, considering the effect of the acoustic wave around a stationary copper sphere. The sphere was exposed to different sound pressure levels of acoustic waves in air, and the temperature of the sphere was recorded. The range of the studied sound frequencies is between 500 Hz and 3 kHz. Both, numerical and experimental investigations indicate that the acoustic field can increase the heat transfer significantly. Higher sound pressure levels cause higher heat-transfer rate. However, there is a special frequency, at which Nu reaches a maximum, due to the flow separation caused by flow acceleration. This special frequency increases with increasing sound pressure level.