Ground Attenuation Factor Based on Measurements

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

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Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources

Journal of Vibration and Acoustics ◽

10.1115/1.1420197 ◽

2001 ◽

Vol 124 (1) ◽

pp. 2-9 ◽

Cited By ~ 7

Author(s):

Kean Chen ◽

Gary H. Koopmann

Keyword(s):

Active Control ◽

Near Field ◽

Low Frequency ◽

Sound Radiation ◽

Sound Field ◽

Sound Power ◽

Frequency Range ◽

Sound Sources ◽

Frequency Sound ◽

Secondary Sources

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.

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Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.217-219.2590 ◽

2012 ◽

Vol 217-219 ◽

pp. 2590-2593 ◽

Cited By ~ 1

Author(s):

Yu Wang ◽

Bai Zhou Li

Keyword(s):

Sound Pressure ◽

Near Field ◽

Low Frequency ◽

Dipole Source ◽

Fluctuating Pressure ◽

Common Structure ◽

Hydrodynamic Noise ◽

Near Field Sound ◽

Equivalent Sources ◽

Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

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Incubator Noise

PEDIATRICS ◽

10.1542/peds.56.4.617 ◽

1975 ◽

Vol 56 (4) ◽

pp. 617-617

Author(s):

Gōsta Blennow ◽

Nils W. Svenningsen ◽

Bengt Almquist

Keyword(s):

Low Frequency ◽

Sound Level ◽

Noise Levels ◽

Frequency Sound ◽

Mechanical Noise ◽

Sound Levels ◽

Infant Incubator ◽

Improved Model ◽

Model C

Recently we reported results from studies of incubator noise levels.1 It was found that in certain types of incubators the noise was considerable, and attention was called to the sound level in the construction of new incubators. Recently we had the opportunity to study an improved model of Isolette Infant Incubator Model C-86 where the mechanical noise from the electrically powered motor has been partially eliminated. With this modification it has been possible to lower the low-frequency sound levels to a certain degree in comparison to the levels registered in our study.

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Noise and low‐frequency sound levels due to aerial fireworks and prediction of the occupational exposure of pyrotechnicians to noise

Journal of Occupational Health ◽

10.1539/joh.16-0064-oa ◽

2016 ◽

Vol 58 (6) ◽

pp. 593-601 ◽

Cited By ~ 1

Author(s):

Tagayasu Tanaka ◽

Ryoichi Inaba ◽

Atsuhito Aoyama

Keyword(s):

Occupational Exposure ◽

Low Frequency ◽

Frequency Sound ◽

Sound Levels

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SOFTWARE DEVELOPMENT FOR ESTIMATION OF LOW FREQUENCY SOUND PROPAGATION IN GAS GUIDES OF POWER PLANTS TAKING TO ACCOUNT ACTIVE SOUND SOURCES

Journal of Dynamics and Vibroacoustics ◽

10.18287/2409-4579-2019-5-4-36-44 ◽

2020 ◽

Vol 5 (4) ◽

pp. 36-44

Author(s):

A V Vasilyev

Keyword(s):

Sound Source ◽

Power Plants ◽

Sound Propagation ◽

Combustion Engine ◽

Source Parameters ◽

Low Frequency ◽

Sound Sources ◽

Software Application ◽

Frequency Sound ◽

Exhaust Noise

This paper is devoted to the problems of modelling and calculation of propagation of low frequency sound in gas guides of power plants taking to account active sound sources. The structure of software for prediction and calculation of low-frequency sound propagation in gas guides have described. Software uses four-pole method and takes to account radiation from additional (active) sound course. By using software it is possible to estimate sound source parameters to provide efficient sound attenuation. Examples of software application to calculation of intake and exhaust noise of internal combustion engine are described. The results of calculations show the possibilities of four-pole method software using to design acoustically the parameters of gas guides and mufflers for the different fields of applications.

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