The Effect of Fluctuations on the Perception of Low Frequency Sound

2007 ◽  
Vol 26 (2) ◽  
pp. 81-89 ◽  
Author(s):  
A T Moorhouse ◽  
D C Waddington ◽  
M D Adams
Keyword(s):  
Laboratory Tests ◽  
Sound Pressure ◽  
Hearing Threshold ◽  
Low Frequency ◽  
Fast Response ◽  
Pressure Level ◽  
Rate Of Change ◽  
Frequency Noise ◽  
The Difference ◽  
Method Of Adjustment

Results of laboratory tests are presented in which 18 subjects, including some low frequency noise sufferers, were presented with low frequency sounds with varying degrees of fluctuation. Thresholds of acceptability were obtained for each sound and each subject, using the method of adjustment. These thresholds were then normalised to individual low frequency hearing threshold. It was found that sufferers tend to set thresholds of acceptability closer to their hearing threshold than other subject groups. Also, acceptability thresholds were set on average 5dB lower for fluctuating sounds. It is proposed that a sound should be considered fluctuating when the difference between L10 and L90 exceeds 5dB, and when the rate of change of the ‘Fast’ response sound pressure level exceeds 10dB/s

scholarly journals Noise-silencing technology for upright venting pipe jet noise

2018 ◽  
Vol 10 (8) ◽  
pp. 168781401879481 ◽  
Author(s):  
Enbin Liu ◽  
Shanbi Peng ◽  
Tiaowei Yang
Keyword(s):  
Natural Gas ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Jet Noise ◽  
Pressure Level ◽  
Living Environment ◽  
Frequency Noise ◽  
Frequency Range ◽  
Expansion Chamber

When a natural gas transmission and distribution station performs a planned or emergency venting operation, the jet noise produced by the natural gas venting pipe can have an intensity as high as 110 dB, thereby severely affecting the production and living environment. Jet noise produced by venting pipes is a type of aerodynamic noise. This study investigates the mechanism that produces the jet noise and the radiative characteristics of jet noise using a computational fluid dynamics method that combines large eddy simulation with the Ffowcs Williams–Hawkings acoustic analogy theory. The analysis results show that the sound pressure level of jet noise is relatively high, with a maximum level of 115 dB in the low-frequency range (0–1000 Hz), and the sound pressure level is approximately the average level in the frequency range of 1000–4000 Hz. In addition, the maximum and average sound pressure levels of the noise at the same monitoring point both slightly decrease, and the frequency of the occurrence of a maximum sound pressure level decreases as the Mach number at the outlet of the venting pipe increases. An increase in the flow rate can result in a shift from low-frequency to high-frequency noise. Subsequently, this study includes a design of an expansion-chamber muffler that reduces the jet noise produced by venting pipes and an analysis of its effectiveness in reducing noise. The results show that the expansion-chamber muffler designed in this study can effectively reduce jet noise by 10–40 dB and, thus, achieve effective noise prevention and control.

scholarly journals Development of an on-site system for measuring the low-frequency noise and complainant’s responses

2018 ◽  
Vol 37 (2) ◽  
pp. 373-384
Author(s):  
Hiroshi Sato ◽  
Jongkwan Ryu ◽  
Kenji Kurakata
Keyword(s):  
Time Trends ◽  
Sound Pressure ◽  
Low Frequency ◽  
Dominant Frequency ◽  
Pressure Level ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Measurement Results ◽  
Frequency Components ◽  
The Relationship

An on-site system for measuring low-frequency noise and complainant's responses to the low-frequency noise was developed to confirm whether the complainant suffer from the environmental noise with low-frequency components. The system suggests several methods to find the dominant frequency and major sound pressure level spectrum of the noise causing annoyance. This method can also yield a quantified relationship (correlation coefficient and percentage of response to the noise) between physical noise properties and the complainant’s responses. The advantage of this system is that it can easily find the relationship between the complainant’s response to the acoustic event of the houses and the physical characteristics of the low-frequency noise, such as the time trends and frequency characteristics. This paper describes the developed system and provides an example of the measurement results.

Evaluation of Aerodynamic Infrasound Radiating From Upwind and Downwind HAWTs

2012 ◽  
Author(s):  
Adrian Sescu ◽  
Abdollah A. Afjeh
Keyword(s):  
Flow Field ◽  
Wind Turbine ◽  
Sound Pressure ◽  
Low Frequency ◽  
Pressure Level ◽  
Frequency Noise ◽  
Far Field ◽  
Acoustic Analogy ◽  
Horizontal Axis Wind Turbines ◽  
Tower Shadow

A Computational Fluid Dynamics tool is used to determine the detailed flow field developing around two-blade horizontal axis wind turbines (HAWT) in downwind and upwind configurations. The resulting flow field around the wind turbine is used to evaluate the low-frequency noise radiating to the far-field, using an acoustic analogy method. The influence of the variation of wind velocity and rotational speed of the rotor to the sound pressure level is analyzed. This paper shows that the tower shadow effect of a downwind configuration wind turbine generates higher aerodynamic infrasound when compared to a corresponding upwind configuration. For validation, a comparison between numerical results and experimental data consisting of sound pressure levels measured from a two-blade downwind configuration wind turbine is presented.

A Criterion for Predicting the Annoyance Due to Lower Level Low Frequency Noise

1983 ◽  
Vol 2 (4) ◽  
pp. 160-168 ◽  
Author(s):  
N. Broner ◽  
H.G. Leventhall
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Threshold Effect ◽  
Pressure Level ◽  
The Other ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Estimation Task ◽  
Noise Annoyance

In a study of the annoyance due to low frequency noise, 75 subjects (consisting of 21 complainants and 54 controls) carried out a magnitude estimation task and rated the annoyance due to lower-level low frequency noise (55dB–75dB). After allowing for a threshold effect, it was found that the E-weighted sound pressure level was, in general, the best predictor of lower-level low frequency noise annoyance. However, it was not a significantly better predictor than any of the other nine noise measures considered. The widely available dB(A) noise measure was therefore suggested as a useful predictor of group annoyance due to lower-level low frequency noise.

Process and Emergence on the Effects of Infrasonic and Low Frequency Noise on Inhabitants

1989 ◽  
Vol 8 (3) ◽  
pp. 87-99 ◽  
Author(s):  
Naoko Nagai ◽  
Masanobu Matsumoto ◽  
Yasukiyo Yamasumi ◽  
Tatsue Shiraishi ◽  
Koh Nishimura ◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Low Frequency ◽  
Peak Level ◽  
Pressure Level ◽  
Living Environment ◽  
Frequency Noise ◽  
Night Time ◽  
Questionnaire Method ◽  
Main Component

To clarify the process and emergence of the effects of infrasonic noise on man, the sound pressure level of infrasonic noise was measured in the area along a superhighway, and its effect on the inhabitants was investigated by the questionnaire method. The results are as follows: (1) The main component frequency of the infrasonic noise was 6.3 Hz. The sound pressure level (L50) of infrasonic noise (1–50 Hz) showed more than 85 dB in the daytime and more than 72 dB in the night time. It's peak level was above 100 dB under the overhead bridge of the superhighway. Indoors, the sound pressure level (L5) of infrasonic noise often went above 75 dB. (2) Answers about the living environment were given by 368 (85.6%) out of 430 families. Those about the condition of health were given by 909 cases (81.7%) out of 1113 cases who were all the inhabitants over 15 years of age. (3) 69.6% of families complained of the shaking of windows and the like. 65.8% of families complained of window rattling. More families complained of the shaking and rattling of windows in the area less than 80m distant from the superhighway, and more families also complained of the disturbance of sleep in that area. (4) The rates of the complaints as to ‘irritating’, have headaches', ‘head feels heavy’, ‘pain in arms or legs’, ‘feel languid’, ‘sleepless’, ‘dizziness’, ‘ringing in the ear’, and ‘difficulty in breathing’, were correlated with the distance from the superhighway. While the rate of complaints as to ‘have stiffness or pain on shoulders’ was highest, it had no relationship with the distance from the superhighway. From these results, it can be concluded that the inhabitants first complained of the shaking and rattling of windows by infrasonic noise, and then became chronically insomniac and excessively wearied by shaking and rattling of long continuance, and finally became highly sensitive to infrasonic noise. This increasing sensitivity might be closely connected with the emergence of the effect of infrasonic noise upon these inhabitants.

scholarly journals The Hearing Threshold of Employees Exposed to Noise Generated by the Low-Frequency Ultrasonic Welding Devices

2017 ◽  
Vol 42 (2) ◽  
pp. 199-205
Author(s):  
Adam Dudarewicz ◽  
Kamil Zaborowski ◽  
Paulina Rutkowska-Kaczmarek ◽  
Małgorzata Zamojska-Daniszewska ◽  
Mariola Śliwińska-Kowalska ◽  
...  
Keyword(s):  
Sound Pressure Level ◽  
Sound Pressure ◽  
Hearing Threshold ◽  
Spectral Composition ◽  
Low Frequency ◽  
Pressure Level ◽  
Exposure Level ◽  
Frequency Range ◽  
Threshold Levels ◽  
High Frequency Audiometry

Abstract The aim of the study was to assess the hearing threshold levels (HTLs) in employees exposed to noise generated by low-frequency ultrasonic technological equipment in comparison with the HTLs of workers exposed to audible noise at the similar A-weighted equivalent-continuous sound pressure level. The study includes measurements of ultrasonic and audible noise at workplaces and hearing tests, i.e. conventional pure-tone audiometry and extended high-frequency audiometry. The study group comprised 90 workers, aged 41.4±10.0 years (mean±SD), exposed for 17.3±9.8 years to noise generated by ultrasonic devices at mean daily noise exposure level (‹LEX,8h›) of 80.6±2.9 dB. The reference group consists of 156 subjects, exposed to industrial noise (without ultrasonic components) at similar A-weighted equivalent-continuous sound pressure level (‹LEX,8h› = 81.8±2.7 dB), adjusted according to age (39.8±7.7 years), gender and job seniority (14.0±7.0 years). This group was selected from database collected in the Nofer Institute of Occupational Medicine. Audiometric hearing threshold levels in the frequency range of 0.5-6 kHz were similar in both groups, but in the frequency range of 8-12.5 kHz they were higher in the group of employees exposed to ultrasonic noise. The findings suggest that differences in the hearing threshold (at high frequencies) in analyzed groups may be due to differences in spectral composition of noise and show the need to continue the undertaken studies.

scholarly journals Measurement and analysis of bridge expansion joint noise

2021 ◽  
Vol 293 ◽  
pp. 02053
Author(s):  
Dingtao Mao ◽  
Yong Ding
Keyword(s):  
Sound Pressure ◽  
Influence Factors ◽  
Low Frequency ◽  
Noise Pollution ◽  
Pressure Level ◽  
Frequency Noise ◽  
Expansion Joint ◽  
Expansion Joints ◽  
Measurement And Analysis ◽  
Level 3

The structure-borne noise while the vehicle passing across the bridge expansion joint is the main source of urban bridge noise. In order to control this noise pollution, 20 bridges including three types of typical expansion joints in Ningbo City were selected, and the noises were measured while vehicle passed across the bridge expansion joints. The measured results are expressed by the Z-weighted sound pressure level, which kept the effect of the low-frequency noise. Then the influence factors of this noise are discussed. The results show that: (1) The sound pressure while vehicle on the bridge expansion joints is much greater than that on the normal road or mid-span of the bridges, which results in significant environmental noise pollution; (2) The wider the gap of the bridge expansion joints, the greater the noise level; (3) The noises produced by the modular expansion joints and comb-plate expansion joints are greater than that from the single-gap expansion joints.

Aerodynamic noise from an asymmetric airfoil with perforated extension plates at the trailing edge

2020 ◽  
pp. 1475472X2097838
Author(s):  
CK Sumesh ◽  
TJS Jothi
Keyword(s):  
High Frequency ◽  
Sound Pressure ◽  
Pore Diameter ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Trailing Edge ◽  
High Frequency Noise ◽  
Displacement Thickness

This paper investigates the noise emissions from NACA 6412 asymmetric airfoil with different perforated extension plates at the trailing edge. The length of the extension plate is 10 mm, and the pore diameters ( D) considered for the study are in the range of 0.689 to 1.665 mm. The experiments are carried out in the flow velocity ( U∞) range of 20 to 45 m/s, and geometric angles of attack ( αg) values of −10° to +10°. Perforated extensions have an overwhelming response in reducing the low frequency noise (<1.5 kHz), and a reduction of up to 6 dB is observed with an increase in the pore diameter. Contrastingly, the higher frequency noise (>4 kHz) is observed to increase with an increase in the pore diameter. The dominant reduction in the low frequency noise for perforated model airfoils is within the Strouhal number (based on the displacement thickness) of 0.11. The overall sound pressure levels of perforated model airfoils are observed to reduce by a maximum of 2 dB compared to the base airfoil. Finally, by varying the geometric angle of attack from −10° to +10°, the lower frequency noise is seen to increase, while the high frequency noise is observed to decrease.

Sign in / Sign up

Export Citation Format

Share Document