scholarly journals Broadband noise insulation of windows using coiled-up silencers consisting of coupled tubes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shuping Wang ◽  
Jiancheng Tao ◽  
Xiaojun Qiu ◽  
Ian S. Burnett
Keyword(s):  
Cross Sections ◽  
Insertion Loss ◽  
Natural Ventilation ◽  
Traffic Noise ◽  
Broad Band ◽  
Low Frequency ◽  
Broadband Noise ◽  
Frequency Range ◽  
Scale Down ◽  
Uniform Cross Section

AbstractIt has been demonstrated that a staggered window achieves better noise reduction performance than a traditional single glazing one at middle to high frequencies while maintaining a degree of natural ventilation. There is, however, little improvement in the low frequency range. In contrast, this work proposes to apply coiled-up silencers consisting of coupled tubes on the side walls of staggered windows to obtain noise attenuation in a broad band, especially in the low frequency range. Each element in the silencer consists of two coupled tubes with different cross sections so that noise at more frequencies can be attenuated than that with a uniform cross section. The simulation results show that 8.8 dB overall insertion loss can be obtained between 100 and 500 Hz after applying a combination of silencers designed at 7 different frequencies, and the insertion loss of the staggered window is increased from 6.7 to 15.6 dBA between 100 and 2000 Hz for normal incident traffic noise with the proposed silencers installed. The design is validated by the experiments with a 1:4 scale down model.

Analysis of turbulence power spectra and velocity correlations in a pipeline with obstructions

2017 ◽  
Vol 28 (02) ◽  
pp. 1750019 ◽  
Author(s):  
A. T. da Cunha Lima ◽  
I. C. da Cunha Lima ◽  
M. P. de Almeida
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Cross Sections ◽  
Power Spectra ◽  
Low Frequency ◽  
Frequency Range ◽  
Frequency Space ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Low Frequency Power

We calculate the power spectral density and velocity correlations for a turbulent flow of a fluid inside a duct. Turbulence is induced by obstructions placed near the entrance of the flow. The power spectral density is obtained for several points at cross-sections along the duct axis, and an analysis is made on the way the spectra changes according to the distance to the obstruction. We show that the differences on the power spectral density are important in the lower frequency range, while in the higher frequency range, the spectra are very similar to each other. Our results suggest the use of the changes on the low frequency power spectral density to identify the occurrence of obstructions in pipelines. Our results show some frequency regions where the power spectral density behaves according to the Kolmogorov hypothesis. At the same time, the calculation of the power spectral densities at increasing distances from the obstructions indicates an energy cascade where the spectra evolves in frequency space by spreading the frequency amplitude.

scholarly journals How well are FREQUENCY SENSITIVITIES OF grasshopper ears tuned to species-specific song spectra?

1996 ◽  
Vol 199 (7) ◽  
pp. 1631-1642
Author(s):  
J Meyer ◽  
N Elsner
Keyword(s):  
High Frequency ◽  
Broad Band ◽  
Low Frequency ◽  
Attachment Site ◽  
The Body ◽  
Frequency Range ◽  
Frequency Spectra ◽  
Interspecific Differences ◽  
Tympanal Membrane ◽  
Species Specific

Grasshoppers of 20 acridid species were examined using spectral analysis, laser vibrometry and electrophysiology to determine whether the song spectra, the best frequencies of tympanal-membrane vibrations and the threshold curves of the tympanal nerves are adapted to one another. The songs of almost all species have a relatively broad-band maximum in the region between 20 and 40 kHz and a narrower peak between 5 and 15 kHz. There are clear interspecific differences in the latter, which are not correlated with the length of the body or of the elytra. At the site of attachment of the low-frequency receptors (a-cells), the tympanal membrane oscillates with maximal amplitude in the region from 5 to 10 kHz. At the attachment site of the high-frequency receptors (d-cells), there is also a maximum in this region as well as another around 15-20 kHz. The tympanal nerve is most sensitive to tones between 5 and 10 kHz, with another sensitivity maximum between 25 and 35 kHz. The species may differ from one another in the position of the low-frequency peaks of the membrane oscillation, of the nerve activity and of the song spectra. No correlation was found between the characteristic frequency of the membrane oscillation and the area of the tympanal membrane. Within a given species, the frequency for maximal oscillation of the membrane at the attachment site of the low-frequency receptors and the frequency for maximal sensitivity of the tympanal nerve are in most cases very close to the low-frequency peak in the song spectrum. In the high-frequency range, the situation is different: here, the position of the peak in the song spectrum is not correlated with the membrane oscillation maximum at the attachment site of the high-frequency receptors, although there is a correlation between the song spectrum and the sensitivity of the tympanal nerve. On the whole, therefore, hearing in acridid grasshoppers is quite well adjusted to the frequency spectra of the songs, partly because the tympanal membrane acts as a frequency filter in the low-frequency range.

The Mathematical Modelling of the Performance of Noise Barriers

1994 ◽  
Vol 1 (2) ◽  
pp. 91-104 ◽  
Author(s):  
D. C. Hothersall
Keyword(s):  
Insertion Loss ◽  
Road Traffic ◽  
Traffic Noise ◽  
Broad Band ◽  
Road Traffic Noise ◽  
Noise Barriers ◽  
Experimental Modelling ◽  
Acoustic Performance ◽  
Source Characteristic ◽  
The Mean

Analytical and numerical methods of modelling the acoustic performance of road traffic noise barriers are discussed, in particular the solution of the wave equation using boundary elements. Results are presented for a range of barrier profiles in the form of Insertion Loss spectra and the mean Insertion Loss for a broad band source characteristic of road traffic noise averaged over a range of representative receiver positions. The performance of barriers comprising multiple screens is considered. Comparison is made with the results of experimental modelling.

Noise reduction of Parallel barrier integrated with compact flexible panel device

2021 ◽  
Vol 263 (3) ◽  
pp. 2961-2972
Author(s):  
Yat Sze Choy ◽  
Wang Zhibo ◽  
Yang Waiping
Keyword(s):  
Insertion Loss ◽  
Traffic Noise ◽  
Low Frequency ◽  
Sound Field ◽  
Sound Intensity ◽  
Rigid Wall ◽  
Diffraction Wave ◽  
Flexible Panel ◽  
Frequency Regime ◽  
Suppression Mechanism

Erection of parallel barriers to control environmental noise such as traffic noise and construction noise is commonly seen in community. Owing to the formation of multiple reflection waves between the parallel barriers, their performance may be worse than a single barrier. To improve the performance of parallel barriers, a small piece of flush-mounted panels backed by a slender cavity in an otherwise rigid wall of barriers is proposed. With the excitation of the incident wave from a sound source inside parallel barriers, the flexible panel vibrates and sound is radiated out to undergo acoustics interference with sound field between the parallel barriers so that the sound intensity in this space and diffraction wave at the barrier top edge is reduced over a broadband in the low-frequency regime. The use of the panel provides flexibility in controlling range of stopband with high insertion loss by varying mass and bending stiffness. A semi-analytical model for dealing with vibroacoustic coupling between the open cavity and vibrating panel in a two-dimensional configuration is established in order to understand the sound suppression mechanism within the shadow zone. With the optimal structural properties of the panel, the extra averaged insertion loss of about 5dB in the frequencies ranging from 50 to 1000 Hz is reached for the parallel barrier.

scholarly journals Attenuation of airborne noise by wet and dry neoprene diving hoods

2021 ◽  
Vol 38 (1) ◽  
pp. 3-12
Author(s):  
Gurmail S Paddan ◽  
Michael C Lower
Keyword(s):  
Resonance Frequency ◽  
Insertion Loss ◽  
Sound Level ◽  
Broadband Noise ◽  
Frequency Range ◽  
Broad Resonance ◽  
Airborne Noise ◽  
Spring System ◽  
Mass Spring ◽  
Insertion Losses

The insertion losses of five neoprene diving hoods of varying thicknesses (2 mm–9 mm) were measured in one-third octave bands using a Kemar manikin in a diffuse broadband noise field. The insertion losses were measured in air for both dry and wet hoods. The insertion loss was calculated as the sound level in each frequency band measured with the hood, minus the corresponding sound level measured without the hood. The insertion losses were similar for both ears of the manikin. Both wet and dry hoods neither attenuated nor amplified sound below 250 Hz. Between 315 Hz–1250 Hz, the insertion loss of each hood was negative, displaying a broad resonance with a gain of 6–8 dB. In this frequency range the hood acts as a mass-spring system, resonating like a drum skin when stretched over the ears. Above 1000 Hz, the insertion loss increased with frequency (10 dB per octave), reaching a maximum of 5000 Hz–6000 Hz. Wetting each hood did not significantly affect the insertion loss; the 'drum-skin' resonance frequency was marginally lower with a wet hood, and insertion losses may be marginally greater between 1000 Hz– 10 000 Hz. The resonance frequency decreased with increasing thicknesses of hood, and the insertion loss at frequencies above the resonance increased with hood thickness.

Motor Vehicle Exterior Sound Quality Improvement for Indoors

2006 ◽  
Author(s):  
Masao Ishihama ◽  
Hiromitsu Sakurai
Keyword(s):  
Engine Speed ◽  
Motor Vehicle ◽  
Traffic Noise ◽  
Low Frequency ◽  
Sound Quality ◽  
Sound Insulation ◽  
Frequency Range ◽  
Sound Environment ◽  
Frequency Components ◽  
Driving Conditions

The objectives of this study are these three items. 1) To find better indices than dB(A) for representing annoyances caused by motor vehicle traffic noise along highways. 2) To find the frequency range of motor vehicle exterior noise that should primarily be controlled to achieve better indoor sound environment along highways. 3) To find suitable vehicle driving conditions for evaluating indoor sound environment. To obtain the desired results psycho-acoustic experiments were conducted. Firstly, sound samples were collected with microphones placed at such locations as on a sidewalk, in front of a small house and at the center of a room inside of the house. The number of test vehicles was fifteen, consisting of six motorcycles and nine passenger cars. The driving conditions were full acceleration and mild acceleration usually found in normal traffic flow. Secondly, semantic differentiation method was used. Ten pairs of adjectives were used to scale the impressions of each sound sample. Finally, physical characters of the sound samples and their subjective evaluations were compared. The results were obtained as follows. 1) Six sound samples got more uncomfortable impression at indoors. These sound samples were collected by vehicles with sport-type mufflers. 2) The samples that indoor sound quality is degraded than outdoor contain high power in low frequency range below 200 Hz. These low frequency components penetrate through the housing walls more easily than higher frequency components. 3) The degradation of comfort impression was found in mild acceleration conditions. The low frequency components of sound samples for mild acceleration are larger than those for full acceleration. Though the throttle is not fully open in mild acceleration, low engine speed generates low frequency components, and eventually increased indoor sound power in the frequency range. The conclusions drawn from these results are, 1) Indoor sound samples should be included for evaluating sound environment along highways. 2) Mild acceleration is a better driving condition for evaluating indoor sound environment along highways. In this condition, very low engine speed causes low frequency component emission that penetrate into housing more than in heavy accelerating conditions. 3) Engine exhaust systems that emit very loud low-frequency components should be focused upon in regulating traffic noise. 4) Extensive collection and analysis of housing sound insulation, absorption and resonance data along highways are necessary for further investigations. 5) Better psycho-acoustic experiment methods should be developed for investigating sound context effects on panelists.

A New Approach for Noise and Vibration Control in Locomotive Cabs

2007 ◽  
Author(s):  
Timothy P. Harrigan ◽  
Gopal Samavedam ◽  
S. K. Punwani
Keyword(s):  
Active Noise Control ◽  
Low Frequency ◽  
Broadband Noise ◽  
Frequency Range ◽  
Tonal Noise ◽  
Low Frequencies ◽  
New Approach ◽  
Nonlinear Springs ◽  
Reduction Methods

Noise and vibrations in locomotive cabs can significantly affect crew performance and cause long-term ailments, such as hearing loss, fatigue, and low back pain. Methods to reduce noise and vibrations have been implemented for the high frequency range but resulted in low frequency resonances. These resonances can exacerbate low frequency vibrations (<0.5 Hz), which can cause motion sickness. In addition, a tonal noise exists in the 50 to 200 Hz frequency range, which is more annoying than broadband noise, and which is not addressed in current noise reduction methods based on A-weighted noise metrics. To reduce vibration, the innovative approach proposed here will consider isolating only the floor of the cab rather than the whole cab as was previously reported in the literature. The isolation is achieved using nonlinear springs and dampers that provide isolation at high frequencies while avoiding resonances at low frequencies. The smaller inertia of the floor, controls, and crew, as compared to the entire cab, makes the necessary components much less expensive. To reduce the tonal noise in the range 50 to 200 Hz, active noise control is used in the vicinity of the crew seats. Analyses have shown that this new approach is very promising, and demonstrations are planned for mockups of locomotive cabs.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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