Wind Noise and Motorcycle Crash Helmets

1994 ◽  
Vol 13 (2) ◽  
pp. 49-57 ◽  
Author(s):  
A.W. Mccombe ◽  
J.A. Binnington ◽  
D. Nash
Keyword(s):  
Low Frequency ◽  
Sound Attenuation ◽  
Wind Noise ◽  
Vehicle Noise ◽  
Sound Levels ◽  
Rate Of Increase ◽  
Noise Measurements ◽  
Motorcycle Helmets ◽  
Crash Helmet ◽  
Attenuation Characteristics

An investigation was undertaken into the source and levels of wind noise in motorcycle helmets, and their sound attenuation characteristics. All noise measurements increased in a linear fashion when plotted against log10 speed. Low frequency wind noise displayed a greater rate of increase than vehicle noise and surpassed it and the recommended 8 hour occupational maximum of 90dB(A) at approximately 17m/s (40mph/68kph) to reach levels of 111dB(A) at 44m/s (100mph/170kph). There were no statistical differences in the sound levels for different motorcycles, riding position or helmet fit. There were small but significant differences between helmet types. A wind tunnel analysis indicates a turbulent boundary layer as the sound source. As currently designed, a typical motorcycle crash helmet provides no useful sound attenuation below 2000 Hertz and thus little protection against the damaging effects of wind noise. It is suggested that improvements in helmet attenuation characteristics would go some way to addressing this problem.

Ground Attenuation Factor Based on Measurements

2021 ◽  
Vol 263 (3) ◽  
pp. 3436-3447
Author(s):  
Dan Lin ◽  
Andrew Eng
Keyword(s):  
Near Field ◽  
Attenuation Factor ◽  
Measurement Data ◽  
Low Frequency ◽  
Sound Sources ◽  
Frequency Sound ◽  
Sound Levels ◽  
Different Types ◽  
Noise Measurements ◽  
Field Sound

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.

Wind turbines noise measurements inside homes

2018 ◽  
Vol 25 (4) ◽  
pp. 339-350
Author(s):  
Gino Iannace
Keyword(s):  
Wind Velocity ◽  
Wind Farm ◽  
Wind Farms ◽  
Weather Conditions ◽  
Sound Level ◽  
Rapid Expansion ◽  
Wind Noise ◽  
Wind Speeds ◽  
Sound Levels ◽  
Noise Measurements

The rapid expansion of energy produced by wind power has increased the interest in the possible harmful effects on the health of the residents in the areas near to wind farms. It is therefore important to understand how to reduce these effects. This article analyses the results of noise measurements carried out in homes located near a wind farm in Southern Italy. Two sound level metres for the contemporary acquisitions of noise levels were used, placed in two different homes: three wind towers were visible from one measurement point, while only one wind tower could be seen from the other point. The acoustic measurements were performed under different weather conditions as well as with different wind speeds and directions. The same conditions were measured when the system was on and off. The measured sound levels were then compared so as to establish the wind velocity ranges where the part of noise generated by the rotating of the blades (ambient noise) prevails as well as the wind velocity ranges where the wind noise (background noise) prevails. The analysis of the data shows how for low wind speeds, the noise generated by the rotating of the blades is considered an annoyance by the people who live near the farm. While for greater wind speeds, the noise generated by the rotation of the blades is covered by the noise of the wind, with it therefore not being perceived.

scholarly journals LOW-FREQUENCY NOISE MEASUREMENTS OF IR PHOTODETECTORS WITH VOLTAGE CROSS CORRELATION SYSTEM

Measurement ◽  
2021 ◽  
pp. 109867
Author(s):  
Krzysztof ACHTENBERG ◽  
Janusz MIKOŁAJCZYK ◽  
Carmine CIOFI ◽  
Graziella SCANDURRA ◽  
Krystian MICHALCZEWSKI ◽  
...  
Keyword(s):  
Cross Correlation ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Ir Photodetectors ◽  
Noise Measurements ◽  
Correlation System

Nonlinear behavior of Helmholtz resonator with a compliant wall for low frequency, broadband noise control

2021 ◽  
pp. 1-29
Author(s):  
Maya Pishvar ◽  
Ryan L Harne
Keyword(s):  
Dynamic Response ◽  
Low Frequency ◽  
Nonlinear Behavior ◽  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Sound Attenuation ◽  
Wall Material ◽  
Modeling Framework ◽  
Compliant Wall ◽  
Broadband Sound

Abstract Low frequency sound attenuation is often pursued using Helmholtz resonators (HRs). The introduction of a compliant wall around the acoustic cavity results in a two-degree-of-freedom (2DOF) system capable of more broadband sound absorption. In this study, we report the amplitude-dependent dynamic response of a compliant walled HR and investigate the effectiveness of wall compliance to improve the absorption of sound in linear and nonlinear regimes. The acoustic-structure interactions between the conventional Helmholtz resonator and the compliant wall result in non-intuitive responses when acted on by nonlinear amplitudes of excitation pressure. This paper formulates and studies a reduced order model to characterize the nonlinear dynamic response of the 2DOF HR with a compliant wall compared to that of a conventional rigid HR. Validated by experimental evidence, the modeling framework facilitates an investigation of strategies to achieve broadband sound attenuation, including by selection of wall material, wall thickness, geometry of the HR, and other parameters readily tuned by system design. The results open up new avenues for the development of efficient acoustic resonators exploiting the deflection of a compliant wall for suppression of extreme noise amplitudes.

Incubator Noise

PEDIATRICS ◽  
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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