The noise reduction of the acoustic paths between two rooms interconnected by a ventilation duct

This paper describes measurements made on a system of two rooms separated by a wall but connected by a ventilation duct. Using statistical energy analysis the noise reduction of each path through the system was determined from the measured data. It was found that the most important path through the system is from the source room, into the duct cavity, along the duct and then out into the receiving room.Experiments on air flow showed that for practical purposes air flow has no effect on the system considered here.     

The prediction of airborne sound transmission between two rooms using first-order flanking paths

Airborne sound transmission between adjacent rooms can be predicted using the Standard EN 12354-1 (ISO 15712-1), which is equivalent to a first-order approximation of statistical energy analysis (SEA). This paper analyses airborne sound transmission between adjacent rooms in a masonry building, by comparing results obtained from EN 12354-1 to SEA predictions and measurements. It is shown that the restriction of the Standard to first-order flanking paths can lead to large errors in predictions when compared to measurements and SEA results taking into account all transmission paths. This is observed both for individual flanking paths and overall transmission between rooms, for which the Standard provides results similar to those obtained by the first-order approximation of SEA. The paper also looks at possible reasons why previous studies using the approach in EN 12354 have generally shown good agreement with measurements.     

复式降噪块地铁车轮减振降噪特性

为探究一种复式降噪块装置及其组合形式对某S型辐板地铁车轮的减振降噪效果和机理,在半消声室内,分别对1种自由状态下的标准车轮和3种形式的复式降噪块车轮开展阻尼特性及振动声辐射特性试验,并通过有限元建模对其进行了模态计算。结果表明:复式降噪块装置可在全频段内提高车轮阻尼比,并对车轮各部位有良好的减振效果,以轮辋和踏面的减振效果最为显著;其中,6个制振阻尼片形式的降噪块对车轮的降噪效果最显著,径向激励下的降噪量为13.1 dB(A),轴向激励下的降噪量为11.1 dB(A),降噪频段主要集中在1000 Hz以上中高频。该文研究结果是对列车降噪研究领域的补充和发展。     

The measurement of quantum noise reduction in squeezed states

The use of a photomultiplier to measure the reduction in counting statistics noise (from the usual N^1/2 form) which is expected to occur for squeezed coherent light is shown to lead to no reduction or to an increase of the noise unless the number of photons in a fundamental measuring time of the photomultiplier is very large. This fundamental time is estimated to be less than 10^–13 sec for ordinary detectors. A technique for using squeezed states for determining the time a photomultiplier takes to detect the presence of a photon is presented.     

Determination of sound reduction indices in the presence of flanking transmission

Unlike the standard sound insulation test method, which requires diffuse sound fields in both source room and receiving room, the sound intensity method only requires the source room to be diffuse. Flanking may, in some cases, cause large errors in the sound reduction indices obtained by the standard method, even if the flanking power is measured separately and subtracted from the total power. The sound intensity method allows selective determination of sound reduction indices for test objects surrounded by flanking surfaces, provided the measurement surface in the receiving room is defined in such a way that it encloses nothing but the test object.     

皮层脑电的非线性降噪

引入基于对非线性动力学局部线性拟合的局部投影非线性降噪方法对Spragure-Dawley大鼠的皮层脑电进行降噪.为了提高降噪效果，利用返回图法对皮层脑电降噪时所需要的最佳局部邻域尺度进行了估计.首先以被50%的高斯白噪声污染的Lorenz方程x轴为例进行降噪，说明根据降噪理论所编写的计算程序的正确性.然后将此降噪方法分别应用于被麻醉的大鼠的皮层脑电和青霉素溶液诱发癫痫发作的皮层脑电时间序列，并采用非线性预报分析说明降噪的效果. 关键词： 皮层脑电 返回图法 非线性降噪 非线性预报     

Nonlinear noise reduction for electrocardiograms

The electrical activity of the heart usually shows dynamical behavior which is neither periodic nor deterministically chaotic: The interbeat intervals seem to contain a random component. Although long term predictions are thus impossible, good predictions can be made for times smaller than one heart cycle. This fact is used in order to suppress measurement errors by a local geometric projection method which was originally developed for chaotic signals. The result constitutes evidence that techniques of time series analysis based on chaos theory can be useful despite the fact that very few natural phenomena have been actually established to be deterministically chaotic. (c) 1996 American Institute of Physics.     

The reduction of camera fan noise in a photoprint room

The noise level produced by a fan was reduced by 21 dB(A) by enclosing it in a ‘soundproof box’. The general problems of designing such a box, and, in particular, that of preventing the enclosed fan from overheating, are discussed. The construction of the box is described in detail and its actual performance compared with that theoretically attainable.     

Detectability of interaural delays over select spectral regions: effects of flanking noise

Zurek [P. M. Zurek, J. Acoust. Soc. Am. Suppl. 1 78, S18 (1985)] noted what he termed "spectral dominance" in sensitivity to interaural delay for broadband stimuli. He found that interaural delays presented solely within high-frequency spectral regions were difficult, if not impossible, to detect in the presence of spectrally flanking, gated, diotic noise. In order to see if spectral dominance is a general result of the processing of interaural delays in broadband stimuli, similar experiments were conducted utilizing both gated and continuous flanking noises that were interaurally identical (diotic) or completely uncorrelated. Beyond replicating Zurek's basic findings, the data strongly suggest that the processing of interaural delays was largely unaffected when the flanking sounds were continuous and diotic. When the flanking sounds were interaurally uncorrelated, sensitivity was affected, but not drastically, for both gated and continuous conditions. Consequently, it appears that any inability to cope with conflicting interaural cues across spectral regions may be observed only under restricted conditions.     

Flap side-edge noise mechanism and shape modification noise reduction design

Flap side-edge noise is a significant noise source for airplane at takeoff and landing stages. The generation mechanism of flap side-edge noise is analyzed by numerical simulation on unsteady flow field using Very Large Eddy Simulation(VLES). Two kinds of flap side-edge shape modifications are proposed, and their frequency spectrum and directivity of far-field noise are compared with the baseline configuration using permeable integral surface Ffowcs Williams and Hawkings(FW-H) acoustic analogy method to investigate their effects on noise reduction. Via the numerical simulation of flow field and acoustic field, it proves that the flap side-edge noise is broadband noise in nature. The different shapes of flap side-edge change the pattern of flow field, vortex structures and the development of vortex, thus having influences on noise source distributions and characteristics of far-field noise. The result shows that at the given 5° angle of attack, the proposed flap side-edge shape modifications can reduce the overall sound pressure level(OASPL) by 1 to 2 dB without decreasing the lift and drag aerodynamic performances.     

Train noise reduction scenarios for compliance with future noise legislation

The Technical Specification for Interoperability (TSI) for high-speed trains on the European market includes limits on noise emission. These and other future restrictions on exterior noise of high-speed and intercity trains will require that train manufacturers implement noise control measures early in the design phase.A fundamental problem faced by manufacturers during the design process is determining how much noise reduction is required for each of the various noise sources on the train in order to achieve an optimal balance. To illustrate this process, estimates are presented of the contributions from different sources on existing Bombardier trains, based on measured data, numerical calculations and empirical formulae.In addition, methods of achieving the required noise reductions for different sources are briefly discussed along with targets for future exterior noise emission.Measurement results presented demonstrate the importance of track quality in noise emission. Noise restrictions, including future legislation, must give proper recognition to this important parameter.     

水筒中涂层模型降低噪声总声级的研究

我们根据回转体模型的水筒噪声试验，分析了不同低表面能涂层模型在高，低频段代噪声总声级的效果，一些涂层模在高频噪声级降低很多时引起了噪声总声级的降低。     

Performance of personal active noise reduction devices

This paper presents the results of objective tests performed on 13 personal active noise reduction devices (earmuffs, headphones, headsets and insert earphones) divided into four groups based mainly on structure, using an acoustic test fixture (ATF). Each device was examined on its attenuation of broadband noise, overload response, internally generated noise, attenuation of impulse noise, and stability to movement. The results show a large range of responses between devices in terms of attenuation and overload, and highlight distinctive differences between the device groupings.     

Time-frequency Wiener filtering for structural noise reduction

In order to enhance the defect in relation to background noise of large grained materials different algorithms have been developed. Wiener filtering techniques have proved to be efficient for the SNR enhancement of ultrasonic signals coming from highly scattering materials. These processing algorithms are based on designing a filter that has large gain at frequencies where the SNR is high and low gain at frequencies where SNR is small. However, this technique does not consider two important ultrasonic effects: the finite-time duration of the flaw UT signal coming from a defect and the distortion of the frequency components of the traveling wave-front due to the dispersion. In this work, a time-frequency Wiener filter is proposed that takes into account these two characteristics. Experimental results are presented, showing that the proposed time-frequency algorithm has an excellent performance on SNR enhancement.     

Nonlinear noise reduction through Monte Carlo sampling

We consider the problem of nonlinear noise reduction within the framework of Bayesian Theory. This enables us to place appropriate weights on the measurement and dynamic errors and thereby avoid over cleaning the data. Using a Metropolis-Hastings sampler, we are able to achieve robust noise reduction without the introduction of ad hoc parameters but at the expense of higher computational complexity. Such an algorithm should also allow us to explore the potential and limitations of other noise reduction methods. (c) 1998 American Institute of Physics.     

Geometric noise reduction for multivariate time series

We propose an algorithm for the reduction of observational noise in chaotic multivariate time series. The algorithm is based on a maximum likelihood criterion, and its goal is to reduce the mean distance of the points of the cleaned time series to the attractor. We give evidence of the convergence of the empirical measure associated with the cleaned time series to the underlying invariant measure, implying the possibility to predict the long run behavior of the true dynamics.     

Measured light vehicle noise reduction by hedges

The acoustical effects of hedges result from a combination of physical noise reduction and their influences on perception. This study investigates the physical noise reduction so as to enable estimation of its relative importance. Different in-situ methods have been used to measure noise shielding by hedges. These include a statistical pass-by experiment where the real insertion loss of a hedge could be measured, three controlled pass-by experiments using a reference microphone at close distance, and transmission loss measurements using a point source. Thick dense hedges are found to provide only a small total A-weighted light vehicle noise reduction at low speeds. Measured insertion losses range from 1.1 dBA to 3.6 dBA. The higher noise reductions are found to be associated with an increased ground effect.     

Indoor noise reduction index with open window

Indoor noise is mainly caused by road and railway traffic, especially in summer time due to open windows. The presence of absorbent ceilings can help to reduce reverberating noise and the global mean acoustic level. The aim of this work is to define an index to evaluate the indoor noise reduction index (NRI) with open window; it is a function of the acoustic absorption coefficient of the room ceiling. It is evaluated by measurements in two reverberating rooms, which simulate the real conditions. In the emission room a noise source reproduces the road and railway noise. In the receiving room a microphone measures the noise level and its spectrum; the ceiling is treated with different absorption materials. A comparison between the values in absence and in presence of different materials and an evaluation of NRI are carried out. Experimental results are generalised and a theoretical expression of NRI is given.