Some measurements of atmospheric noise levels at low and very low frequencies in Canada

1960 ◽  
Vol 65 (7) ◽  
pp. 1911-1926 ◽  
Author(s):  
C. A. McKerrow
Keyword(s):  
Noise Levels ◽  
Low Frequencies ◽  
Atmospheric Noise

Some Measured and Calculated Effects of Forward Velocity on Propeller Noise

1977 ◽  
Author(s):  
R. J. Pegg ◽  
B. Magliozzi ◽  
F. Farassat
Keyword(s):  
Analytical Techniques ◽  
Operating Conditions ◽  
General Aviation ◽  
Noise Levels ◽  
Forward Flight ◽  
Low Frequencies ◽  
Blade Thickness ◽  
Propeller Noise ◽  
Field Noise ◽  
Static Conditions

The results of a program investigating the sources of noise in unshrouded propellers under forward flight conditions and a comparison with theory are reported. Tests were conducted using an instrumented three-bladed propeller installed on a turbine-powered, twin-engine, general aviation airplane. Measurements included far-field noise on the ground and on the aircraft wing tip, propeller blade surface pressures, atmospheric turbulence, and aircraft operating conditions. The primary result of the full-scale flight tests was to confirm that foward-flight propeller noise levels are lower than those experienced under static conditions and that the most significant reductions occur at the mid-frequencies which dominate perceived and A-weighted noise levels. Analytical techniques have been used to predict the observed experimental trends and to provide further insight into the noise generating mechanisms. Correlation with experimental data is shown to be good at low frequencies under static conditions and at all frequencies in forward flight. It is tentatively concluded that propeller noise generation in flight may result from steady loads (including blade thickness effects). Under static conditions, the principal noise source appears to be the intersection of the propeller with persistent turbulent eddies passing through the propeller disk.

scholarly journals Method of measuring the acoustic characteristics of traffic flows in urban environments

2020 ◽  
Vol 78 (4) ◽  
pp. 273-279
Keyword(s):  
Traffic Noise ◽  
Urban Environments ◽  
Traffic Flows ◽  
Noise Levels ◽  
Acoustic Characteristics ◽  
Low Frequencies ◽  
High Frequencies ◽  
Medical Institutions

When examining doctors ' workplaces, it was found that traffic noise inside the premises exceeds sanitary standards. For medical institutions, the sanitary standards are 50 dBA, and for fullscale measurements, they were 60-63 dBA. Traffic noise levels have a maximum at low frequencies (31.5 Hz) and a minimum at high frequencies (16,000 Hz).

Quantitative Spectral Evaluation of Shimmer and Jitter

1985 ◽  
Vol 28 (2) ◽  
pp. 169-174 ◽  
Author(s):  
Fritz Klingholz ◽  
Frank Martin
Keyword(s):  
Vocal Fold ◽  
Signal To Noise Ratio ◽  
Voice Disorders ◽  
Voice Disorder ◽  
Wave Spectra ◽  
Noise Levels ◽  
Signal To Noise ◽  
Low Frequencies ◽  
Synthesized Speech ◽  
Spectral Evaluation

A vowel [a]-like, synthesized speech wave was perturbated by defined and comparable jitter and shimmer levels. The signal-to-noise ratio was calculated from the speech wave spectra. Noise emerges in those spectral regions in which the harmonics have high amplitudes, that is, at low frequencies and in the formant regions. Jitter created noise levels significantly higher than shimmer. To verify the theoretical findings, the voices of 32 women with functional voice disorders were analyzed for shimmer and jitter. It was found that only jitter is relevant for differentiating between hypo- and hyperfunctional voice disorders. Jitter was reduced in hyperfunctional voice disorder. This is presumed to be an effect of the high vocal fold tension found in the disorder.

Spectral Comparison of Pass-By Traffic Noise

2018 ◽  
Author(s):  
Zhuang Li
Keyword(s):  
Traffic Noise ◽  
Wide Band ◽  
Measurement Procedure ◽  
Test Point ◽  
Spectral Features ◽  
Vehicle Speed ◽  
Noise Levels ◽  
Low Frequencies ◽  
The Road ◽  
Generation Mechanisms

Traffic noise is a major noise source in the study of environmental noise. Various noise generation mechanisms depict different spectral features. Some are wide-band noise, such as engine knocks; some have signature frequencies, such as gear transmissions; and some are in a certain frequency region, such as tire/road noise. These spectral features affect the façade design of a building in order to achieve sufficient exterior noise insulation and satisfactory interior noise due to the traffic noise. ISO standard 11819-1 specifies the measurement procedure of statistical pass-by tests. There are three ranges of vehicle speed: slow, medium, and fast. However, it requires that the vehicle must maintain constant speed when passing by the test point. Unfortunately, a vehicle tends to generate higher noise when accelerating, especially at low frequencies. Therefore, it is necessary to distinguish the noise levels at an intersection versus middle-points of the road between two intersections. Presumably, the traffic noise levels at an intersection would be higher. This research measured the traffic noise at various locations of different speed limits. Statistical analyses were conducted to compare the spectra at these locations. This is also an effort to refine the noise map.

scholarly journals Experimental evidence for real-time song frequency shift in response to urban noise in a passerine bird

2010 ◽  
Vol 7 (1) ◽  
pp. 36-38 ◽  
Author(s):  
Eira Bermúdez-Cuamatzin ◽  
Alejandro A. Ríos-Chelén ◽  
Diego Gil ◽  
Constantino Macías Garcia
Keyword(s):  
Experimental Evidence ◽  
Signal Transmission ◽  
Low Frequency ◽  
Low Noise ◽  
Noise Levels ◽  
Short Term ◽  
Urban Noise ◽  
Low Frequencies ◽  
House Finches ◽  
Minimum Frequency

Research has shown that bird songs are modified in different ways to deal with urban noise and promote signal transmission through noisy environments. Urban noise is composed of low frequencies, thus the observation that songs have a higher minimum frequency in noisy places suggests this is a way of avoiding noise masking. Most studies are correlative and there is as yet little experimental evidence that this is a short-term mechanism owing to individual plasticity. Here we experimentally test if house finches ( Carpodacus mexicanus ) can modulate the minimum frequency of their songs in response to different noise levels. We exposed singing males to three continuous treatments: low–high–low noise levels. We found a significant increase in minimum frequency from low to high and a decrement from high to low treatments. We also found that this was mostly achieved by modifying the frequency of the same low-frequency syllable types used in the different treatments. When different low-frequency syllables were used, those sung during the noisy condition were longer than the ones sang during the quiet condition. We conclude that house finches modify their songs in several ways in response to urban noise, thus providing evidence of a short-term acoustic adaptation.

scholarly journals Effect of Environmental Noise, Distance and Warning Sound on Pedestrians’ Auditory Detectability of Electric Vehicles

2021 ◽  
Vol 18 (17) ◽  
pp. 9290
Author(s):  
Min-Chih Hsieh ◽  
Hung-Jen Chen ◽  
Ming-Le Tong ◽  
Cheng-Wu Yan
Keyword(s):  
Electric Vehicles ◽  
High Frequency ◽  
Detection Rate ◽  
Low Frequency ◽  
Environmental Noise ◽  
Noise Levels ◽  
Experimental Conditions ◽  
Low Frequencies ◽  
Detection Rates ◽  
On The Road

With developments in science and technology, the number of electric vehicles will increase, and they will even replace ICE vehicles. Thus, perceiving the presence of approaching electric vehicles on the road has become an important issue. In this study, the auditory detectability of the electric vehicle warning sound at different volumes, distances, and environmental noise levels was investigated. To this end, the detection rate was recorded in experiments with three environmental noise levels (50, 60, and 70 dBA), two sound pressure levels (SPLs) of the warning sound (46 and 51 dBA), three frequency combinations of the warning sound (5000, 2500, 1250, and 630 Hz for high frequencies; 2500, 1250, 630, and 315 Hz for medium frequencies; and 1250, 630, 315, and 160 Hz for low frequencies), and five distances (2, 4, 6, 8, and 10 m). The main results showed that the detection rate at 51 dBA was significantly higher than that at 46 dBA under a high-frequency warning sound; however, the detection rates were similar under medium- and low-frequency warning sounds. The participants’ rates of detection for warning sounds were less than 20% under all experimental conditions, and a high-frequency warning sound was not affected by environmental noise. With regard to distances, no significant effects were observed between the distances and the detection rate at any of the three frequencies. In addition, auditory thresholds based on high-, medium-, and low-frequency warning sounds were found through logistic regression analysis results. The results of this study can be used as a reference for the future design of warning sounds.

Atmospheric Noise Levels at Radio Frequencies near Darwin, Australia

1950 ◽  
Vol 3 (3) ◽  
pp. 409
Author(s):  
DE Yabsley
Keyword(s):  
Western Australia ◽  
Average Level ◽  
Radio Noise ◽  
Noise Levels ◽  
Atmospheric Noise ◽  
Continuous Record ◽  
Atmospheric Radio ◽  
Radio Frequencies ◽  
North Western ◽  
Atmospheric Radio Noise

Between August 25, 1944, and October 31, 1945, a practically continuous record of the average level of atmospheric radio noise at a frequency of 1.93 Mc/s. was obtained near Darwin, in north-western Australia. A few measurements were also made at a frequency of 5.9 Mc/s. The noise-measuring programme is described and the results obtained are presented graphically.

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