Low-frequency interior noise in prop-driven aircrafts: Sources and control methodologies

2017 ◽  
Vol 48 (7-8) ◽  
pp. 94-98 ◽  
Author(s):  
Fathollah Ommi ◽  
Mohammadreza Azimi
Keyword(s):  
Conflicts Of Interest ◽  
Health Hazard ◽  
Low Frequency ◽  
Sound Field ◽  
Interior Noise ◽  
Low Frequencies ◽  
Modern Times ◽  
Propeller Noise ◽  
The Many ◽  
And Control

Nowadays, noise has turned into one of the most important among the environmental factors on which industry sets down a big part of its efforts and concerns. The recognition of noise as a serious health hazard is a development of modern times. Too much noise obviously impairs our physical and mental existence and therefore it is reasonable to pursue Technology Assessment concerning noisy technologies. The conflicts of interest associated with noise that arise from the operation of airports are well known. Propeller noise is most dominant at low frequencies (below 500 Hz) where traditional passive treatments have only little effect. The many factors contributing to the sound field inside propeller aircraft have led to extensive research directed toward identifying and improving techniques for interior noise reduction.

High-frequency neurons in the inferior colliculus that are sensitive to interaural delays of amplitude-modulated tones: evidence for dual binaural influences

1993 ◽  
Vol 70 (1) ◽  
pp. 64-80 ◽  
Author(s):  
R. Batra ◽  
S. Kuwada ◽  
T. R. Stanford
Keyword(s):  
Inferior Colliculus ◽  
High Frequency ◽  
Low Frequency ◽  
Sound Field ◽  
Low Frequencies ◽  
Contralateral Stimulation ◽  
Binaural Stimulation ◽  
Pure Tones ◽  
Ipsilateral Stimulation ◽  
Inferior Colliculi

1. Localization of sounds has traditionally been considered to be performed by a duplex mechanism utilizing interaural temporal differences (ITDs) at low frequencies and interaural intensity differences at higher frequencies. More recently, it has been found that listeners can detect ITDs at high frequencies if the amplitude of the sound varies and an ITD is present in the envelope. Here we report the responses of neurons in the inferior colliculi of unanesthetized rabbits to ITDs of the envelopes of sinusoidally amplitude-modulated (SAM) tones. 2. Neurons were studied extracellularly with glass-coated Pt-Ir or Pt-W microelectrodes. Their sensitivity to ITDs in the envelopes of high-frequency sounds (> or = 2 kHz) was assessed using SAM tones that were presented binaurally. The tones at the two ears had the same carrier frequency but modulation frequencies that differed by 1 Hz. This caused a cyclic variation in the ITD produced by the envelope. In this "binaural SAM" stimulus, the carriers caused no ITD because they were in phase. In addition to the binaural SAM stimulus, pure tones were used to investigate responses to ipsilateral and contralateral stimulation and the nature of the interaction during binaural stimulation. 3. Neurons tended to display one of two kinds of sensitivity to ITDs. Some neurons discharged maximally at the same ITD at all modulation frequencies > 250 Hz (peak-type neurons), whereas others were maximally suppressed at the same ITD (trough-type neurons). 4. At these higher modulation frequencies (> 250 Hz), the characteristic delays that neurons exhibited tended to lie within the range that a rabbit might normally encounter (+/- 300 microseconds). The peak-type neurons favored ipsilateral delays, which correspond to sounds in the contralateral sound field. The trough-type neurons showed no such preference. 5. The preference of peak-type neurons for a particular delay was sharper than that of trough-type neurons and was comparable to that observed in neurons of the inferior colliculus that are sensitive to delays of low-frequency pure tones. 6. At lower modulation frequencies (< 150 Hz) characteristic delays often lay beyond +/- 300 microseconds. 7. Increasing the ipsilateral intensity tended to shift the preferred delay ipsilaterally at lower (< 250 Hz), but not at higher, modulation frequencies. 8. When tested with pure tones, a substantial number of peak-type neurons were found to be excited by contralateral stimulation but inhibited by ipsilateral stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Using Time-Periodicity for Inducing Energy Transfer Between Vibration Modes

2013 ◽  
Author(s):  
Fadi Dohnal ◽  
Aleš Tondl
Keyword(s):  
Energy Transfer ◽  
Degrees Of Freedom ◽  
Vibrational Energy ◽  
Low Frequency ◽  
Vibration Modes ◽  
Present Contribution ◽  
Multiple Degrees Of Freedom ◽  
Time Periodicity ◽  
The Many ◽  
And Control

Introducing time-periodicity in system parameters may lead, in general, to a dangerous and well-known parametric resonance. In contrast to such a resonance, a properly tuned time-periodicity is capable of transferring energy between vibration modes. Time-periodicity in combination with system damping is capable of efficiently extracting vibrational energy from the system and of amplifying the existing damping affecting transient vibrations. Operating the system at such a specific time-periodicity, the system is tuned at a parametric anti-resonance. The basic principle of this concept has been studied theoretically and was proven experimentally. The physical interpretation of this concept was proposed in “Damping by Parametric Stiffness Excitation: Resonance and Anti-Resonance”, Journal of Vibration and Control, 2008, for a multiple degrees of freedom system. The present contribution highlights those findings on a multiple degrees of freedom system. It is illustrated that a parametric anti-resonance is connected to inducing an energy transfer between two of the many vibration modes of the underlying system with constant coefficients. The induced energy transfer can be utilized to transfer the vibration energy from low frequency to high frequency or vice versa or, in case of system damping, to a more efficient dissipation of vibrational energy. The achievable energy dissipation is most significant if an energy transfer is induced between a lightly damped mode and a strongly damped mode.

scholarly journals Low frequency sound field reconstruction in a non-rectangular room using a small number of microphones

Acta Acustica ◽  
2020 ◽  
Vol 4 (2) ◽  
pp. 5 ◽  
Author(s):  
Thach Pham Vu ◽  
Hervé Lissek
Keyword(s):  
Low Frequency ◽  
Sound Field ◽  
Acoustic Properties ◽  
Room Acoustics ◽  
Low Frequencies ◽  
Reverberation Chamber ◽  
Sound Fields ◽  
Accurate Knowledge ◽  
Sound Field Reconstruction ◽  
Rectangular Room

An accurate knowledge of the sound field distribution inside a room is required to identify and optimally locate corrective measures for room acoustics. However, the spatial recovery of the sound field would result in an impractically high number of microphones in the room. Fortunately, at low frequencies, the possibility to rely on a sparse description of sound fields can help reduce the total number of measurement points without affecting the accuracy of the reconstruction. In this paper, the use of Greedy algorithm and Global curve-fitting techniques are proposed, in order to first recover the modal parameters of the room, and then to reconstruct the entire enclosed sound field at low frequencies, using a reasonably low set of measurements. First, numerical investigations are conducted on a non-rectangular room configuration, with different acoustic properties, in order to analyze various aspects of the reconstruction frameworks such as accuracy and robustness. The model is then validated with an experimental study in an actual reverberation chamber. The study yields promising results in which the enclosed sound field can be faithfully reconstructed using a practically feasible number of microphones, even in complex-shaped and damped rooms.

Identification of a Sleep Bruxism Subgroup with a Higher Risk of Pain

2007 ◽  
Vol 86 (9) ◽  
pp. 837-842 ◽  
Author(s):  
P.H. Rompré ◽  
D. Daigle-Landry ◽  
F. Guitard ◽  
J.Y. Montplaisir ◽  
G.J. Lavigne
Keyword(s):  
At Risk ◽  
Cluster Analysis ◽  
Diagnostic Criteria ◽  
Clinical Diagnosis ◽  
Low Frequency ◽  
Sleep Bruxism ◽  
Masticatory Muscles ◽  
Low Frequencies ◽  
Polygraphic Recordings ◽  
And Control

Sleep bruxism research diagnostic criteria (SB-RDC) have been applied since 1996. This study was performed to validate these criteria and to challenge the hypothesis that pain is associated with lower frequencies of orofacial activities. Polygraphic recordings were made of 100 individuals presenting with a clinical diagnosis of sleep bruxism and 43 control individuals. TwoStep Cluster analyses (SPSS) were performed with sleep bruxism variables to reveal groupings among sleep bruxers and control individuals. Participants completed questionnaires during screening, diagnosis, and recording sessions. Cluster analysis identified three subgroups of sleep bruxers. Interestingly, 45 of the 46 sleep bruxers with values below SB-RDC were classified in the low-frequency cluster. These individuals were more likely to complain of pain and fatigue of masticatory muscles than were the higher-frequency sleep bruxers (odds ratios > 3.9, p < 0.01). Sleep bruxers were distributed among three heterogeneous groups. Sleep bruxers with low frequencies of orofacial activities were more at risk of reporting pain.

Research on the Interior Noise Reduction of an Elastic Cavity by the Multipoint Panel Acoustic Contribution Method Based on Moore–Glasberg Loudness Model

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Rongping Fan ◽  
Guang Meng ◽  
Zhongqing Su
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Sound Field ◽  
Interior Noise ◽  
Design Parameters ◽  
Acoustic Coupling ◽  
Acoustic Contribution ◽  
Reduction Effect ◽  
Loudness Model ◽  
Two Parameters

More and more attention has been paid to reduce the low frequency interior noise of the elastic cavity, such as automobiles, ships, airplanes, and railway vehicles, to provide the more comfortable riding environment for passengers. Identification of the interior acoustical sources in the low frequency range is vitally important for the sound quality design inside the elastic cavity. By transformation of the sound pressure level into the specific loudness, a multipoint panel acoustic contribution method based on Moore–Glasberg loudness model is proposed to identify the acoustic contribution of local structural panels of an elastic cavity. The finite element (FE) equation of vibro-acoustic coupling structure with the visco-elastic damping is formulated to evaluate the acoustic panel contribution. Two parameters of acoustic contribution sum and total sound field contribution are derived to measure the acoustic contribution of each panel at the important peak frequencies for the multiple evaluation points. A carriage of high-speed train is modeled as the elastic cavity to demonstrate the application of the developed algorithm. The bottom panel of the carriage is identified to make the most significant contribution to the loudness of evaluation points. The reduction effect of the various design parameters of visco-elastic damping layer on the bottom panel is investigated. The proposed method can efficiently arrange the visco-elastic damping layer on the bottom panel to reduce the interior loudness.

High-Frequency and Low-Frequency Spectra and the Structure of Rubber

1947 ◽  
Vol 20 (4) ◽  
pp. 910-911
Author(s):  
Pierre Girard ◽  
Paul Abadie
Keyword(s):  
Relaxation Times ◽  
Low Frequency ◽  
Single Type ◽  
Essential Difference ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Alternating Electric Field ◽  
The Many ◽  
Absorption And Dispersion ◽  
Bell Shaped Curve

Abstract Under the influence of an alternating electric field, the loss angle and dielectric constant of a sheet of rubber vary as a function of the frequency, while the conductivity remains negligible even at low frequencies. The essential difference between this behavior and that of the crystalloid liquids already studied by the authors is that, instead of a single absorption curve and a single dispersion curve extending through a narrow range of frequencies, there is a series of curves extending a considerable distance toward the low frequencies. However, the relations between absorption and dispersion remain the same as with crystalloid liquids, so here too the losses can be explained by the orientation polarization, and the same qualitative scheme of dipolar oscillators which follows, with a certain dephasing, the alternations of the field. However, instead of being a single type and individually identical, these oscillators are in this case polyisoprene chains which differ in length and consequently in their relaxation times. This variety of dipoles is evident in the many successive curves. (To develop the spectrum, the authors used chiefly absorption curves.) These curves differ in their positions on the abscissa as a function of the dimensions of the dipoles, and by their height as a function of their concentration and form. When for a group of dipoles characterized by a mean relaxation time, the lengths of the chains and the relaxation times vary progressively from one dipole to another, then the resultants of the different absorption curves representing the different dipoles unite into a single flat extended curve. On the contrary, a group of homogeneous dipoles which are identical or almost identical is represented by a single bell-shaped curve.

Computers for data, control and simulation

1988 ◽  
Vol 46 ◽  
pp. 920-921
Author(s):  
David C. Joy
Keyword(s):  
Personal Computers ◽  
Monitoring And Control ◽  
Data Logging ◽  
Data Logger ◽  
Operational Conditions ◽  
Data Control ◽  
The Many ◽  
And Control

Personal computers (PCs) are a powerful resource in the EM Laboratory, both as a means of automating the monitoring and control of microscopes, and as a tool for quantifying the interpretation of data. Not only is a PC more versatile than a piece of dedicated data logging equipment, but it is also substantially cheaper. In this tutorial the practical principles of using a PC for these types of activities will be discussed.The PC can form the basis of a system to measure, display, record and store the many parameters which characterize the operational conditions of the EM. In this mode it is operating as a data logger. The necessary first step is to find a suitable source from which to measure each of the items of interest. It is usually possible to do this without having to make permanent corrections or modifications to the EM.

Natural and man-made low-frequency magnetic fields as a potential health hazard

1998 ◽  
Vol 168 (07) ◽  
pp. 767-791 ◽  
Author(s):  
N.G. Ptitsyna ◽  
G. Villoresi ◽  
L.I. Dorman ◽  
N. Iucci ◽  
Marta I. Tyasto
Keyword(s):  
Magnetic Fields ◽  
Health Hazard ◽  
Low Frequency ◽  
Potential Health ◽  
Potential Health Hazard

scholarly journals Earless toads sense low frequencies but miss the high notes

2017 ◽  
Vol 284 (1864) ◽  
pp. 20171670 ◽  
Author(s):  
Molly C. Womack ◽  
Jakob Christensen-Dalsgaard ◽  
Luis A. Coloma ◽  
Juan C. Chaparro ◽  
Kim L. Hoke
Keyword(s):  
High Frequency ◽  
Species Differences ◽  
Low Frequency ◽  
Auditory Brainstem ◽  
Low Frequencies ◽  
Hearing Sensitivity ◽  
Sensory Pathways ◽  
Airborne Sound ◽  
Vibrational Sensitivity ◽  
Species Specific

Sensory losses or reductions are frequently attributed to relaxed selection. However, anuran species have lost tympanic middle ears many times, despite anurans' use of acoustic communication and the benefit of middle ears for hearing airborne sound. Here we determine whether pre-existing alternative sensory pathways enable anurans lacking tympanic middle ears (termed earless anurans) to hear airborne sound as well as eared species or to better sense vibrations in the environment. We used auditory brainstem recordings to compare hearing and vibrational sensitivity among 10 species (six eared, four earless) within the Neotropical true toad family (Bufonidae). We found that species lacking middle ears are less sensitive to high-frequency sounds, however, low-frequency hearing and vibrational sensitivity are equivalent between eared and earless species. Furthermore, extratympanic hearing sensitivity varies among earless species, highlighting potential species differences in extratympanic hearing mechanisms. We argue that ancestral bufonids may have sufficient extratympanic hearing and vibrational sensitivity such that earless lineages tolerated the loss of high frequency hearing sensitivity by adopting species-specific behavioural strategies to detect conspecifics, predators and prey.

Exploring ‘digital placemaking’

2021 ◽  
Vol 27 (3) ◽  
pp. 573-578
Author(s):  
Germaine Halegoua ◽  
Erika Polson
Keyword(s):  
Digital Media ◽  
Sense Of Place ◽  
Media Use ◽  
Special Issue ◽  
Social Actors ◽  
Broad Framework ◽  
The Many ◽  
And Control ◽  
Connected Spaces

This brief essay introduces the special issue on the topic of ‘digital placemaking’ – a concept describing the use of digital media to create a sense of place for oneself and/or others. As a broad framework that encompasses a variety of practices used to create emotional attachments to place through digital media use, digital placemaking can be examined across a variety of domains. The concept acknowledges that, at its core, a drive to create and control a sense of place is understood as primary to how social actors identify with each other and express their identities and how communities organize to build more meaningful and connected spaces. This idea runs through the articles in the issue, exploring the many ways people use digital media, under varied conditions, to negotiate differential mobilities and become placemakers – practices that may expose or amplify preexisting inequities, exclusions, or erasures in the ways that certain populations experience digital media in place and placemaking.

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