Sound Pressure Level Values Research Articles

A comparative study on aerodynamic performance and noise characteristics of two kinds of long-eared owl wing models

The camber line, chord length and thickness of the airfoil are important factors affecting the aerodynamic performance and noise characteristics of the blade. In this research, the long-eared owl wing as bionic prototype and two bionic blades were constructed by using bionic reconstruction method. The one named bionic blade A is based on the long-eared owl wing, which is reconstructed according to section theory and fitting formula of the measured long-eared owl wing. The other is the three-dimensional stretched cross-sectional bionic blade B. To compare the aerodynamic performance and noise characteristics of two bionic blades, the LES method coupled with FW-H equation was adopted to simulate the flow fields and the corresponding sound fields numerically at low Reynolds number condition. The results show that the lift coefficient for the bionic blade B is larger than that for the bionic blade A when the angle of attack is in the range of 0° ~ 30°. The pressure curve of bionic blade B indicates that the pressure generated from the suction side makes a greater contribution to lift force than the pressure side, especially at the leading edge. The location of the separation bubble moves from the trailing edge to the leading edge in the suction side of the blade at α =15°. The size of vortex shedding near the surface of the bionic blade A is smaller than the bionic blade B at α = 0° and it’s caused by the deeply concaved lower surface near the wing root probably. The range of the separation bubble acts as the main influence on the noise generation. Compared with the bionic blade B, the aerodynamic noise generated by the blade A is lower and the minimum value of sound pressure level is even 12.88 dB on the y-direction. That means the special construction of the natural long-eared owl wing could suppress the unsteady pressure fluctuation on the blade surface efficiently to decrease the aerodynamic noise.

Operational noise associated with underwater sound emitting vessels and potential effect of oceanographic conditions: a Dublin Bay port area study

This study presents analysis of acoustic data of underwater sound emitting vessels (USEV) recorded during operation in the Dublin Bay port area. Investigations were carried out to assess the magnitudes of these underwater sounds, and also the potential effect of changes in tidal states on these sound signals and their propagation. Power spectral densities (PSD) and 1/3 octave band sound pressure levels (SPL) were computed for frequencies between 50–500 and 50–1000 Hz, respectively. During the presence of these vessels in the study site, broadband SPL values for a range of frequency components were calculated to be between 94 and 121 dB (re 1 µPa) at a distance of 200 m from the vessels. These values decreased by 5–21 dB during their absence. The strongest sound level recorded at this site was during the departure of vessels from the dock at 200 m from the recording system. The SPL value calculated during this operational period at 315 Hz frequency was 121 dB re 1 µPa2/Hz. Associated components’ spectral of the vessels were identified, and the effect of difference in heights of tidal ranges (Neap/Spring) on this site was investigated.

Removal of fine particles in WFGD system using the simultaneous acoustic agglomeration and supersaturated vapor condensation

The characteristics of fine particle removal from wet flue gas desulfurization (WFGD) using the simultaneous acoustic agglomeration and supersaturated vapor condensation were investigated experimentally. The impacts of supersaturation degree, residence time and acoustic intensity on the fine particle removal efficiency were demonstrated. High moisture and tiny droplets were contained in the flue gas after WFGD, which benefited the use of coupling external fields in WFGD system. The results showed that the removal of fine particles can be significantly improved in the simultaneous acoustic field and supersaturated vapor condensation. High value of sound pressure level (SPL>150dB) was needed to achieve a considerable removal efficiency using acoustic agglomeration only. While low SPL of 130–150dB can be used to remove fine particle efficiently in WFGD system using simultaneous external fields. Removal efficiency higher than 70% was obtained with S=1.15 and SPL=151dB. The residence time of the simultaneous acoustic agglomeration and condensational growth was determined by the time required by acoustic agglomeration. Particle removal efficiency increased with the residence time, but it tended to be constant as the residence time over 3s. Multiple horn numbers with low acoustic intensity benefited the improvement of fine particle removal efficiency and the reduction of energy consumption using the simultaneous external fields in WFGD system.

Analysing the vocal behaviour of teachers during classroom teaching using a portable voice accumulator

Purpose: Teachers are at a considerable risk of developing vocal health problems due to intensive voice use during teaching. This study investigated factors related to the teacher’s voice during a teaching situation.Methods: Overall, 113 teachers were recorded during a typical class lesson, lasting on average 48 min. A portable voice dosimeter (VoxLog System) was used to measure the sound pressure level (SPL) of the noise in the classroom, the teacher’s voice SPL, the fundamental frequency (fo) and the phonation time. General conditions of each lesson such as number of pupils, lesson subject and the educational level of the class were also collected. For the analysis, vocal loading doses and correlations between teacher’s voice and noise SPL were calculated.Results: Voice and noise SPL values varied across the lesson subjects, with highest levels measured in sports lessons. The mean noise SPL changed throughout a lesson with highest values at the beginning and at the end of the lessons. The correlation analysis of voice and noise SPL identified two groups of teachers with different vocal SPL behaviours. For some teachers, the voice SPL varied with the noise SPL. For others, voice SPL was constantly high. A regression model on the teacher’s voice SPL yielded a strong correlation with fo, the classroom noise SPL, and the individual vocal SPL behaviour.Conclusions: Classroom noise SPL and individual vocal SPL behaviour were significantly associated with teachers’ voice SPL during teaching. Addressing these factors could be important steps in reducing the vocal load in teachers.

Investigation of Indoor Air Quality in Houses of Macedonia.

People who live in buildings are exposed to harmful effects of indoor air pollution for many years. Therefore, our research is aimed to investigate the indoor air quality in family houses. The measurements of indoor air temperature, relative humidity, total volatile organic compounds (TVOC), particulate matters (PM) and sound pressure level were carried out in 25 houses in several cities of the Republic of Macedonia. Mean values of indoor air temperature and relative humidity ranged from 18.9 °C to 25.6 °C and from 34.1% to 68.0%, respectively. With regard to TVOC, it can be stated that excessive occurrence was recorded. Mean values ranged from 50 μg/m3 to 2610 μg/m3. Recommended value (200 μg/m3) for human exposure to TVOC was exceeded in 32% of houses. Mean concentrations of PM2.5 (particular matter with diameter less than 2.5 µm) and PM10 (diameter less than 10 µm) are determined to be from 16.80 µg/m3 to 30.70 µg/m3 and from 38.30 µg/m3 to 74.60 µg/m3 individually. Mean values of sound pressure level ranged from 29.8 dB(A) to 50.6 dB(A). Dependence between characteristics of buildings (Year of construction, Year of renovation, Smoke and Heating system) and data from measurements (Temperature, Relative humidity, TVOC, PM2.5 and PM10) were analyzed using R software. Van der Waerden test shows dependence of Smoke on TVOC and PM2.5. Permutational multivariate analysis of variance shows the effect of interaction of Renovation and Smoke.

Study on the Effect of Partition Heights in Open Plan Office to the Privacy and Distraction Level Utilizing Computational Fluid Dynamics

Open-plan office is a room designed without the use of full-height partitions to isolate a workstation from other workstations. Speech privacy is one of the acoustical problems related with communication activities of the workers. Previous studies have shown that there are several sound phenomena that were unable to be explored using computer simulation based on ray tracing method. This paper is attempted to find the influence of partition height of various designs to the privacy level based on computational fluid dynamic, especially using the acoustics diffusion equation method. The results show that variation of height partitions can lower sound pressure level value by 5% - 6%, variation of absorption coefficient can lower SPL value by 8% - 9%, and adding furniture as book shelves does not change the open-plan office privacy level significantly.

Research on numerical simulation and noise reduction of aerodynamic noise in connection section of the high-speed train

The flow field distribution characteristics of side windshields and full windshields installed in the connection section of a high-speed train were numerically computed to reduce the aerodynamic noise and improve operating environment of the high-speed train. As shown from the result, the maximum pressure was at the nose tip of the high-speed train; and the greatest flow velocity of fluid was centered in the middle section of the body, while the flow velocity at both ends of the body was relatively small. After installing a side windshield, the fluid pressure of the side was significantly lower than the upper and lower surfaces, and the pressure and turbulence intensity were greater at the corner of the connection section steps. The fluid flowed to the steps from the roof of the train, and then spread gradually down along the side, with the decreasing flow rate. Therefore, the airflow was effectively prohibited from flowing into the train through installing side windshields. However, after further installing full windshields, the pressure, flow velocity and turbulence intensity in the connection section of the high-speed train were further improved. Then, the boundary element method was applied to compute the radiation noises of two kinds of windshields installed in the connection section of the high-speed train. As shown from the result, broadband radiation noise was in the upper connection section, the maximum sound pressure level (SPL) value was between 50-100 Hz and some directivity of sound pressure was shown in the high-frequency range. A certain periodicity of sound pressure distribution was presented in the longitudinal symmetrical plane of the high-speed train. At the same observation point, the sound pressure level of full windshield was slightly reduced at most frequency points, and the maximum reduction value was 23.6 dB. Finally, the wind tunnel test was conducted on the high-speed train, and the connection section of the high-speed train was the obvious noise source, thus indicating that the research in the paper was very meaningful. Besides, from SPL comparisons of the observation point, experiments and simulations were consistent with each other whether side windshields or full windshields were installed in the connection section. As a result, the reliability of the numerical computational model and the effectiveness of the results and analysis were verified.

Innovative bootstrap approach for the estimation of minimum measurement time interval in road traffic noise evaluation

Abstract It is observed that in order to characterize the environmental noise in a site, during diurnal reference time (6–22 h) or nocturnal reference time (22–6 h), relatively at preset time window, observation period, a single value of the equivalent continuous A-weighted sound pressure level L A,eq is used. This value is determined by integrating and averaging the squared A-weighted sound pressure of fluctuating noise during the measurement time interval, in which there are representative values of acoustic event pressure levels: so it is very important accurately to select the suitable integration time. Such matter are highly relevant to the area of measuring environmental noise and this paper aims to present a statistical method, for determining the minimum measurement time interval for an accurate estimation of L Aeq . The proposed algorithm, based on CPER bootstrap method, has been experimentally verified with real data obtained from road traffic noise measurement and it showed a very good stability. The methodology is suitable for upgrading the level meter firmware in order to have the real time information on the measurand uncertainty estimation and on the minimum measurement time interval.

Effects of geometry on the sound field in atria

The atria in commercial buildings are widespread. However, the sound environment has not been given sufficient consideration. Geometry affects the acoustics in the atria. The concept of geometry in this paper includes five parameters, namely, length (l), height (h), aspect ratio of length to width (l/w), skylight form and slope, to provide suggestions for the acoustic environment design in atria. A series of computer models are simulated to analyse the effects of the form parameters on the acoustic environment, such as sound pressure level (SPL) and reverberation time (T 30 in this paper). The results indicate that with an increase in the length or height, the values of the average SPL decrease, and the trends of the curves are logarithmic. For an increasing length, the T 30 increases first sharply and then slowly. With the scattering increasing, the increment of the T 30 is smaller. For an increasing height, the changes of T 30 are determined by the absorption and scattering. In terms of the aspect ratio of l/w increasing for a given volume and area, the average SPL values approximately decrease linearly; furthermore, the T 30 decreases unless the atrium is extremely high. The T 30 is the longest for a flat skylight compared to that of other forms, and it is shorter when the skylight has a slope, including either a single or a double-pitch skylight. It can decrease nearly by 40% when the angle of the lean-to skylight is 7°. The T 30 is lower and the amount of decrease is considerably smaller for an increasing slope. When the absorption is evenly distributed in the atria, the skylight has minimal effect on the average SPL or T 30 values. Additionally, the classical formula can approximately calculate the SPL distribution unless the atrium is in a form of long space. The Arau-Purchades formula is generally appropriate to predict T 30 with uneven absorption distributions unless the absorption or scattering coefficient is low.

Monitoring of noise-induced hearing threshold shifts among adolescents: The relevance of exposure to leisure noise in the prospective Ohrkan cohort study

Introduction: Exposure to high continuous noise during leisure activities such as attending discotheques or listening to portable listening devices at high volume levels is presumed to have harmful effects on the hearing system of young adolescents. Therefore, the follow-up study Ohrkan funded by the Bavarian State Ministry for the Environment and Health was initiated to track its members over a 10 years period. Currently, the 5-year follow-up is ongoing. Objectives: Analysis of the association of hearing threshold shifts and total leisure noise exposure over five years. Methods: A total of 2,149 students of grade 9 (mostly aged 15-16 years) in the City of Regensburg were recruited from 2009-2011. In the baseline survey and in the recent survey five years later exposure to leisure noise was assessed by self-administered questionnaire and audiometric examinations were performed at the university hospital of Regensburg. The self-reported frequency of participation in noisy activities was combined with literature-based values of usual sound pressure levels of these activities to calculate the total leisure noise exposure. Two different outcomes were defined: a noise notch with a distinct audiometric pattern as well as the maximum threshold shift of both ears at 3, 4, 6 kHz. A longitudinal analysis of these data by generalized linear models (GLM) is in progress to determine the long-term effects of total leisure noise exposure. Results: Up to now, data from over 1,000 students are available. The study methods including the statistical model as well as the latest results using 5-year follow-up data will be presented. Conclusions: Results will be discussed with respect to the burden of leisure noise exposure and the association with the hearing ability of adolescents. Potential implications for the development of early prevention programs and for regulatory measures to reduce leisure noise exposure will be suggested.

Physiological and acoustic characteristics of the male music theatre voice.

Six male music theatre singers were recorded in three different voice qualities: legit and two types of belt ("chesty" and "twangy"), on two vowels ([e] and [ɔ]), at four increasing pitches in the upper limit of each singer's belt range (∼250-440 Hz). The audio signal, the electroglottographic (EGG) signal, and the vocal tract impedance were all measured simultaneously. Voice samples were analyzed and then evaluated perceptually by 16 expert listeners. The three qualities were produced with significant differences at the physiological, acoustical, and perceptual levels: Singers produced belt qualities with a higher EGG contact quotient (CQEGG) and greater contacting speed quotient (Qcs), greater sound pressure level (SPL), and energy above 1 kHz (alpha ratio), and with higher frequencies of the first two vocal tract resonances (fR1, fR2), especially in the upper pitch range when compared to legit. Singers produced the chesty belt quality with higher CQEGG, Qcs, and SPL values and lower alpha ratios over the whole belt range, and with higher fR1 at the higher pitch range when compared to twangy belt. Consistent tuning of fR1 to the second voice harmonic (2f0) was observed in all three qualities and for both vowels. Expert listeners tended to identify all qualities based on the same acoustical and physiological variations as those observed in the singers' intended qualities.

Analysing Sound Environment and Architectural Characteristics of Libraries through Indoor Soundscape Framework

Abstract This study presents the indoor soundscape framework in detail by describing the variables and factors that form an indoor soundscape study. The main objective is to introduce a new indoor soundscaping framework and systematically explain the variables that contribute to the overall evaluation of an indoor soundscape. Hence, the dependencies of physical and psychoacoustical factors of the sound environment and the spatial factors of the built entity are statistically tested. The new indoor soundscaping framework leads to an overarching evaluation perspective of enclosed sound environments, combining objective room acoustics research and noise control engineering with architectural analysis. Therefore, it is hypothesised that case spaces with certain plan organisations, volumetric relations, and spatial referencing lead to differentiated sound pressure level (SPL) and loudness (N) values. SPL and N parametric variances of the sound environments are discussed through the statistical findings with respect to the architectural characteristics of each library case space. The results show that the relation between crowd level variances and sound environment parametric values is statistically significant. It is also found that increasing the atrium height and atrium void volume, the atrium’s presence as a common architectural element, and its interpenetrating reference and domain containment results in unwanted variances and acoustic formations, leading to high SPL and N values.

Effect two grades of octane numbers on the performance, exhaust and acoustic emissions of spark ignition engine

This study presents a comparative analysis of performance, exhaust and noise emissions for a one-cylinder, four-stroke, spark-ignition engine powered by gasoline fuels of two different grades of research octane numbers (RONs), namely octane 90, and octane 95. During the experimental works, each fuel test was performed by varying the engine speed within the range from 1000 to 3600rpm. The SI engine was connected to eddy current dynamometer with electronic control unit (ECU), an exhaust gas analyzer and the sound level meter (SLM) to determine engine performance, exhaust emissions, and measuring the sound pressure level (SPL) in decibels (dBA) and one octave frequency bands in the audible human range at different engine speeds, respectively. The experimental results showed that the using gasoline with octane grades higher than the requirement of an engine will decrease the engine performance. On average, the brake power and thermal efficiency for the SI engine fuelled with octane 90 is higher than that of gasoline octane 95 by 6% and 11% respectively, and improvement of BSFC by 14%, which is mainly due to higher heating value. Even though, the volumetric efficiency of octane 95 is more 5% than octane 90 due to higher latent heat and heat capacity. In general, the exhaust emission profiles for NOx and CO of the engine improved for octane 95 by 11% and 17% respectively. On the other side, the HC and CO2 emissions concentration of gasoline octane 90 is lower than that of gasoline octane 95 by 18% and 12% respectively. Finally, the noise levels showed a trend of the increase of disturbing for higher octane number and the increase of divergence between the two values of SPL at higher speed for both fuels.

Numerical simulation of the slipstream and aeroacoustic field around a high-speed train

The flow field and sound propagation around a three-coach 1/8th scale high-speed passenger train were obtained using a detached-eddy simulation and the Ffowcs-Williams and Hawkings acoustic analogy. The Reynolds number of flow based on the train height and speed was 2,000,000. The numerical results of the flow and aeroacoustic fields were validated using wind tunnel experiments and full-scale data, respectively. Features of overall sound pressure level, sound pressure level and A-weighted sound pressure level of typical measuring points are discussed. The sound propagated by a high-speed train is shown as a broadband noise spectrum including tonal component, where high sound pressure levels are concentrated on the low-frequency range from 10 Hz to 300 Hz. The inter-carriage gap is found to cause distinct tonal noise in contrast to the other parts of the train that cause a broadband noise. The negative log law has been used to study the influence of distance from the centre of track on the sound pressure level, where a good fit is shown at low-frequency ranges. The peak values of A-weighted sound pressure level from both full-scale experiment and simulation results occur at approximately 1 kHz, where simulation results show almost the same range as the experiment. The surface of each component of the train as well as the whole train are chosen as the integral surface for the Ffowcs-Williams and Hawkings computation of the far-field noise characteristics. It was found that the sound source generated by a high-speed train is mainly dipole, and the largest noise was obtained from the leading bogie. The results of this paper provide, for the first time, a better understanding of the aeroacoustic field around a three-coach train model, and the paper has the potential to assist engineers to design high-speed trains with aeroacoustic noise reduction in a better manner.

The Road Particle Effect on Squeal Noise of Disc Braking System

This experimental work was carried out to examine the effect of road particle on squeal noise exerted at different load and sliding speed. The test was performed under dry sliding condition by utilizing brake test rig and commercial brake pad and discs. Squeal measurement was taken based on frequency, sound pressure level (SPL) value, vibration and brake torque measurement. The output signal from microphone and accelerometer was processed by Fast Fourier Transform analyzer to synchronize value SPL and vibration in the power spectrum graph. Simultaneous increase at the same value of frequency and SPL values showed the squeal occurrence for value above 70dBa and 1000Hz respectively. Result for test with road particle showed number of squeal tends to increase compared to test without road particle. SPL also showed high pitch of noise on squeal with road particle presence. Brake torque significantly increased with increasing brake line pressure and exaggerated with road particle. Higher brake torque resulted in higher coefficient of friction and showed high squeal generation.

構造変更によるSEAパラメータへの影響に関する研究

This study investigates the influence of some SEA parameters to predict the sound response by structural modification in plate structures. A simple system is used that consists of two flat plates connected in an L-shaped configuration with one cavity. Three kinds of structural modification are prepared, internal loss factor, plate thickness, and stiffness. For two SEA models, one is used with predicted input power by structural modification and original loss factors, another is used with predicted input power of original model and loss factors by structural modification being taken into consideration, are calculated by analytical SEA and FEM based SEA. As a result, it can be seen that the sound pressure level values for the SEA model using the predicted input power of original model and the loss factors by structural modification are overestimated.

Effects on Voice Fundamental Frequency and Satisfaction with Voice in Trans Men during Testosterone Treatment—A Longitudinal Study

To investigate effects of testosterone treatment regarding voice virilization, voice problems, and voice satisfaction in transsexual female-to-male individuals, referred to as trans men. Longitudinal. Fifty trans men, diagnosed with transsexualism, 18-64 years, met the inclusion criteria. Voice data before treatment and after 3, 6, or 12 months were available from 49 participants, and for 28 participants also after 18 and/or 24 months of treatment. Digital audio recordings of speech range profiles and voice range profiles were carried out in a sound-treated booth following clinical routines. Acoustic analyses of fundamental frequency (F0) and sound pressure level were made. Endocrine data and answers from questionnaires concerning voice function and voice problems were collected from medical records. Mean F0 and mode F0 of the habitual voice decreased significantly after 3 months, 6 months, and up to 12 months, when group data were congruent with reference data for males. Mean F0 was 125 Hz after 12 months with a large interindividual variation. Sound pressure level values did not change significantly. Voice satisfaction correlated with lower F0 values. Twenty-four percent of the participants reported voice symptoms, for example, vocal instability and fatigue, and had received voice therapy. F0 values did not correlate with androgen levels. Most trans men developed a male voice and were satisfied. However, it is important to detect the substantial group of trans men with voice problems and with insufficient voice virilization and who may need voice therapy. Therefore, we recommend systematic voice assessments during testosterone treatment.

A novel acoustically quiet coil for neonatal MRI system.

MRI acoustic exposure has the potential to elicit physiological distress and impact development in preterm and term infants. To mitigate this risk, a novel acoustically quiet coil was developed to reduce the sound pressure level experienced by neonates during MR procedures. The new coil has a conventional high-pass birdcage RF design, but is built on a framework of sound abating material. We evaluated the acoustic and MR imaging performance of the quiet coil and a conventional body coil on two small footprint NICU MRI systems. Sound pressure level and frequency response measurements were made for six standard clinical MR imaging protocols. The average sound pressure level, reported for all six imaging pulse sequences, was 82.2 dBA for the acoustically quiet coil, and 91.1 dBA for the conventional body coil. The sound pressure level values measured for the acoustically quiet coil were consistently lower, 9 dBA (range 6-10 dBA) quieter on average. The acoustic frequency response of the two coils showed a similar harmonic profile for all imaging sequences. However, the amplitude was lower for the quiet coil, by as much as 20 dBA.

Automating source localization and separation using sonic detection and ranging

The sonic detection and ranging (SODAR) technology developed previously (Wu and Zhu, JASA, 2013) is automated for performing blind sources localization and separation. In particular, source localization results are displayed in terms of space-frequency or space-time correlations. In other words, one can either view distributions of sound sources in three-dimensional (3-D) space versus any user-defined frequency bands, or distributions of sound sources in 3-D space versus time history. The sound pressure level (SPL) values associated with the identified sources are also calculated and displayed in these space-frequency and space-time correlation graphs. To acquire a better understanding of the distribution of sound sources together with their SPL values in 3-D space, a 3-D viewer using Google SketchUp software is employed to view these results in both space-frequency and space-time correlations. With this 3-D viewer, one is able to rotate and look at any source from any perspective, and zoom in and out to examine the details of relative positions of individual sources. The information on source locations together with windowing and filtering technologies enable us to separate the individual source signals. Examples of using this blind sources localization and separations in a non-ideal environment that involves random background noise and unspecified interfering signals are demonstrated.

Assessment of Impulse Noise Hazard and the Use of Hearing Protection Devices in Workplaces Where Forging Hammers are Used

Abstract The impulse noise is agent harmful to health not only in the case of shots from firearms and the explosions of explosive materials. This kind of noise is also present in many workplaces in the industry. The paper presents the results of noise parameters measurements in workplaces where four different die forging hammers were used. The measured values of the C-weighted peak sound pressure level, the A-weighted maximum sound pressure level and A-weighted noise exposure level normalized to an 8 h working day (daily noise exposure level) exceeded the exposure limit values. For example, the highest measured value of the C-weighted peak sound pressure level was 148.9 dB. In this study possibility of the protection of hearing with the use of earplugs or earmuffs was assessed. The measurement method for the measurements of noise parameters under hearing protection devices using an acoustical test fixture instead of testing with the participation of subjects was used. The results of these measurements allows for assessment which of two tested earplugs and two tested earmuffs sufficiently protect hearing of workers in workplaces where forging hammers are used.