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A systematic analysis is proposed to predict the performance of a typical feedforward single channel ANC headset in terms of the delay, especially the non-causal delay caused by different noise coming directions. First, the performance of a non-causal feedforward system for a band-limited noise is analyzed by using a simplified pure delay model, where it is found that the noise reduction bandwidth is narrowed and the maximum noise reduction is decreased with the increase of the non-causal delay. Second, a systematic method is developed, which can be used to predict the system performance with measured primary and secondary path transfer functions in most practical sound fields and to study the effects of the control filter length and the path delay on the performance. Then, the causality of a typical feedforward active noise control headset with the primary source at 0° and 90° positions in an anechoic chamber is analyzed, and the performance for the two locations predicted by the systematic analysis is shown in good agreements with the experiment results. Finally, an experiment of a typical feedforward active noise control headset in a reverberation chamber is carried out, which shows the validity of the proposed systematic analysis for other more practical sound fields. 相似文献
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In this paper, we introduce leptogenesis via a varying Weinberg operator from a semi-classical perspective.This mechanism is motivated by the breaking of an underlying symmetry which triggers a phase transition that causes the coupling of the Weinberg operator to become dynamical. Consequently, a lepton anti-lepton asymmetry arises from the interference of the Weinberg operator at two different spacetime points. Using the semi-classical approach,we treat the Higgs as a background field and show that a reflection asymmetry between leptons and anti-leptons is generated in the vicinity of the bubble wall. We solve the equations of motion of the lepton and anti-lepton quasiparticles to obtain the final lepton asymmetry. 相似文献
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The purpose of this work is to study computationally the possibility of the application of a hybrid active noise control technique for magnetic resonance imaging (MRI) acoustic noise reduction. A hybrid control system combined with both feedforward and feedback loops embedded is proposed for potential application on active MRI noise reduction. A set of computational simulation studies were performed. Sets of MRI acoustic noise emissions measured at the patient's left ear location were recorded and used in the simulation study. By comparing three different control systems, namely, the feedback, the feedforward and the hybrid control, our results revealed that the hybrid control system is the most effective. The hybrid control system achieved approximately a 20-dB reduction at the principal frequency component. We concluded that the proposed hybrid active control scheme could have a potential application for MRI scanner noise reduction. 相似文献
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A study is conducted on minimizing the sum of the squared acoustic pressures with a linear array of control sources and a perpendicular linear array of error sensors, placed above the top of a noise barrier. Particular angular orientations, with respect to the center of the barrier top, and spacings of the linear arrays of control sources and error sensors result in moderate to significant additional reduction of the acoustic pressure in the shadow zone. Visual inspection of the sound pressure field, with and without active noise control, found that uniform and significant additional insertion loss can be generated near the barrier. Numerical simulations were conducted to test the proposed method. For separations between control sources and error sensors much less than a quarter wavelength of the primary noise disturbance, results show that the angular orientation, of the combined linear control source and sensor arrays, is a weak factor for acoustic pressure reduction in the shadow zone. Weak angle dependence serves as an advantage to the proposed method, which yields uniform performance for any angular orientation. An angular orientation involving the alignment of the furthest error sensor with the first diffracting edge of the barrier and the primary source was observed to perform well for a variety of frequencies, since the spacing between error sensors and between control sources is of the order of a quarter-wavelength. Improved noise control in the shadow zone of a barrier is achieved by the use of two control sources and angular orientation as mentioned above. Further spatial extension of the area of reduced acoustic pressure is possible by utilizing an increased number of control sources. 相似文献
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MAA Dah-You 《声学学报:英文版》1994,(2)
I.IntroductionThereverberantnoisesmaybereducedwithanactivenoisecontrol(ANC)systcmformedbyacornermicrophonc-amplifier-1oudspcakersystemina.oom.lllThismeth-odbascdonthenormalmodccancelingprincip1chasalreadybeenclarifiedbothinthco-ryandexperimcnts,andthclimitationandpotcntialityofitsapp1icationalsodiscussedinapreviouspaper.Thediscussionsinthepastlimitedmost1ytothesteadyconditionofnoiscfield,andthisisextendedtothetransientcondihoninthcprcsentwork,viz.thein-llucnceofthecornerANCsystemwhenthenois… 相似文献
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Sound radiated by a computer cooling fan consists of tones which are phase locked with the rotation, and other less deterministic tones and broadband random noise. This paper demonstrates the feasibility of globally eliminating the rotation-locked tones by applying a very simple destructive interference to a modified cooling fan with the number of struts equal to the number of rotor blades. The rig consists of a miniature electret microphone used as a rotation sensor, an ordinary loudspeaker, and a bandpass filter with adjustable amplitude and phase delay. The microphone is located at the inlet bellmouth of the fan to pick up the fluctuating aerodynamic pressure caused by the passing rotor blades. The pressure spectrum is rich in the blade passing frequency (BPF) and its low-order harmonics. It provides much better performance than a pulse-generating tachometer. Analysis of the original fan noise shows that about 90% of the radiated tonal sound is phase locked with rotation, and this portion is almost completely eliminated in all directions. The reductions of the radiated sound power in the first two BPFs are 18.5 and 13.0 dB, respectively, and the overall sound power reduction is 11.0 dB. 相似文献
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The purpose of the study is to describe the effect of a suppressor to environmental noise with a typical Finnish rifle shooting range that has a shooting shelter and some noise berms. The noise measurements were carried out at Kyronpelto shooting range situated near Mikkeli in Finland. The range is equipped with wooden shooting shelter, the shooting distance is 150 m, and it has berms on sides and at the impact end. The terrain is relatively flat in the area. The best noise area reduction caused by a suppressor could be seen at angles of 315–45° from the shooting direction. The projectile noise dominates at angles 45–70°, and the effect of the suppressor is very small. To the side and back the shooting shelter has already gained significant noise attenuation, and therefore the suppressor cannot reduce the noise area much more. When there was a relatively tight shooting shelter to the side and back, the suppressor did not reduce the environmental noise area significantly any more. It can be calculated that the noise area of 65 dB (LAImax) is reduced from 95 ha to 50 ha (0.95 km2–0.50 km2) with the help of a suppressor. However, most of the area is situated to the shooting sector and it has to be unoccupied for safety reasons. 相似文献
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Asgedom EG Gelius LJ Austeng A Holm S Tygel M 《The Journal of the Acoustical Society of America》2011,130(4):2024-2034
The problem of locating point-like targets beyond the classical resolution limit is revisited. Although time-reversal MUltiple SIgnal Classification (MUSIC) is known for its super-resolution ability in localization of point scatterers, in the presence of noise this super-resolution property will easily break down. In this paper a phase-coherent version of time-reversal MUSIC is proposed, which can overcome this fundamental limit. The algorithm has been tested employing synthetic multiple scattering data based on the Foldy-Lax model, as well as experimental ultrasound data acquired in a water tank. Using a limited frequency band, it was demonstrated that the phase-coherent MUSIC algorithm has the potential of giving significantly better resolved scatterer locations than standard time-reversal MUSIC. 相似文献
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Small-angle X-ray scattering was used to study the mixture of C12E5 (pentaethylene glycol monododecyl ether)/H2O/n-decane microemulsion and polyethylene glycol (PEG). The size, shape and the structure factor of the microemulsion were investigated by adding the polymer (PEG) to the mixture. Attractive depletion potential was induced between the microemulsion droplets by the non-adsorb polymer. The range and strength of the attractive potential were changed by varying the molecular weight and concentration of PEG. The forward scattering, S(0), of the spherical microemulsion, declined gradually as the polymer concentration decreased. For PEG with the molecular weight of Mn = 285?315, the microemulsion morphology remained spherical, but the main peak of the structure factor moved towards a bigger q. When PEG with molecular weights of Mn = 2200 and Mn = 6000 were used, a shape transition from spherical to cylindrical was induced in line with increasing polymer concentration. 相似文献
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M. Azarpeyvand 《Acoustical Physics》2008,54(1):1-12
This paper follows up on an earlier paper of the author [1] dealing with the issue of multi-scattering in a typical active
noise control system. This work concerns the effects of the presence of a neighboring wall on the performance of an active
noise cancellation system when the dimension of sources is added to the analysis. Effect of the adjacent wall is taken into
account using the image method, and multi-scattering is also allowed for by the spherical harmonic addition theorem. The recognized
method of separation of variables and appropriate wave field expansions in spherical coordination are used to derive the required
analytical solutions. A primary spherical source radiates at different modes, and a secondary source is modeled as a radially
vibrating cap which resembles a real sound speaker. Our particular interest in this work is to investigate effects of multi-scattering
at intermediate working frequencies of ANC, e.g., about 100–500 Hz. In addition to emphasizing the importance of multi-scattering,
this work endeavors to find the appropriate cap angle of the control source to achieve acceptable noise attenuation for different
vibrating modes of the primary source (monopole, dipole). Numerical results reveal that the presence of a rigid wall will
considerably change the adequate velocity of the secondary source and also show that using a baffled spherical piston instead
of a monopole control source will obviously improve the sound minimization efficiency when the primary source vibrates in
the n = 1 mode in a low frequency range.
Published in Russian in Akusticheskiĭ Zhurnal, 2008, Vol. 54, No. 1, pp. 5–17.
The text was submitted by the author in English. 相似文献
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Peter Sutton 《Applied Acoustics》1976,9(1):17-33
The first step in the economic control of noise from a complete plant is to evaluate the contribution which each individual item of equipment makes to the total noise level. This involves determination of the sound power level of each source and estimation of the attenuation of noise between the source and the point where noise level is to be controlled. The second step is to identify the possible methods of noise reduction and to select the best by cost/benefit analysis. A computer program, based on the OCMA Specification, is helpful in this work. 相似文献
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Active noise control systems have been applied to increase the insertion loss of noise barriers where the squared sound pressure or the total acoustic energy density is used as the cost function in previous works. The absolute value of the mean active sound intensity is chosen as the cost function to obtain extra sound insertion loss in the dark area of a hybrid active noise barrier system in this note. The strategy of minimizing the near-field sound intensity at discrete locations along the edge of the passive barrier is shown to be able to provide better far-field noise reduction than that of minimizing the squared sound pressure control. Both numerical simulations and off-line experiments are carried out with a three-channel demonstration system, where the locations of the secondary sources and the error sensors are optimized and comparisons are made between the extra sound pressure attenuation of the sound intensity control and that of the squared sound pressure control. 相似文献
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Active noise control has been applied to a variety of systems in order to improve performance without the increases in size and weight that would otherwise be required by traditional passive noise control treatments. This paper investigates the application of an active noise control system to the control of generator noise in the master cabin of a luxury yacht. A multichannel, multi-tonal active noise control system employing loudspeakers and microphones in the master cabin of the yacht is investigated. It is shown that, due to the high number of engine orders produced by the generator, in order to achieve significantly perceptible levels of noise attenuation it is necessary to control at least 7 individual orders. A controller is investigated which targets 19 engine orders and it is shown to achieve in excess of 5 dB broadband attenuation, whilst achieving up to 23 dB attenuation in individual orders. This corresponds to a 23% reduction in the Zwicker loudness. 相似文献