bluuebunny/crossref_metadata_2025 huggingface dataset:
Response to steady signals
Authors: Kuemmel Theodore J.
Published: July 2002

The level of a steady sinusoidal signal indicated by a sound-level meter should be linearly related to the level of the corresponding signal at the input. Small level-linearity errors over a wide range of input signal levels and signal frequencies are a powerful indicator of the ability of a sound-level meter to square and form the time integral of the sound-pressure signal properly. Errors in level-range controls as well as level linearity are specified in proposed IEC 61672 relative to a fixed reference level difference at the reference frequency for the reference sound-pressure level on the reference level range. At 1 kHz, the extent of the linear operating range is to be at least 60 dB. The Instruction Manual is to state the nominal sound levels at the lower and upper boundaries of the linear operating ranges at specified frequencies. The new standard requires an instrument to have overload and under-range indicators. Level-linearity errors are to be within the tolerance limits up to the first indication of overload. Data will be presented to demonstrate that modern designs for sound-level meters can conform to the specifications for the response to steady sinusoidal electrical signals.
Response to nonsteady signals
Authors: Bjor Ole-Herman
Published: July 2002

A sound-level meter should respond correctly to the frequency-weighted energy of the sound signal, no matter whether the signal comes from a pistol shot or a fan. Most sound signals of interest are transients, some with very short durations and high peak amplitudes. A major part of the proposed IEC 61672 standard describes requirements for the response of a sound-level meter to short duration signals of various levels and durations. Compared with the present standards for sound-level meters, the requirements for measurements of short-duration signals have been improved considerably. After considerable discussion, the Working Group decided to specify and test a sound-level meter with electrical toneburst signals of various durations as extracted from a steady 4-kHz sinusoidal signal. The specifications apply to all kinds of sound-level meters; hence, they are given in terms of maximum F- and S-weighted sound level and in terms of sound exposure level or time-average sound level. The response of the microphone is specified separately. Examples will be shown to demonstrate the ability of modern-design class 1 and class 2 sound-level meters to conform to the specifications of the proposed International Standard.
Environmental considerations for sound-level meters
Authors: Tyler Richard G.
Published: July 2002

A sound-level meter should operate as intended over a wide range of environmental conditions. To ensure this objective, IEC 61672 sets limits for the influence of atmospheric conditions and radio-frequency (rf) fields. A limit is also established for the rf emissions from a sound-level meter. Specifications in IEC 61672 for the influence of temperature and humidity on the performance of a sound-level meter are more stringent for class 1 instruments than corresponding specifications in existing standards. The extremes of the temperature–humidity range are reduced for class 2 instruments. Requirements for the effects of atmospheric pressure remain similar. New specifications were added for the effects of static discharges up to 8 kV and for the influence of exposure to a moderate rf field. Limits for the influence on instrument performance of a given rf field, with carrier frequencies from 25 MHz to 1 GHz, should satisfy most existing national and European Union requirements. Tests to demonstrate conformance with these requirements are specified in the proposed International Standard. Test results will be presented, as available, to demonstrate that modern designs for sound-level meters are able to conform to the environmental specifications in IEC 61672.
Uncertainties of measurement and IEC 61672
Authors: Dowson Susan P.
Published: July 2002

No measurement is ever exact; there is always an uncertainty associated with it. In the past, international specification standards for the performance of acoustical instruments have not included uncertainties of measurement of the testing laboratory when specifying tolerance limits. However, to demonstrate conclusively whether or not a particular instrument conforms to the specifications of a standard, it is essential that these measurement uncertainties be taken into account. In a recent change of policy, the international committee responsible, IEC TC-29 ‘‘Electroacoustics,’’ has decided that all its future standards must include uncertainties of measurement in the tolerance limits specified. This paper will discuss different types of measurement uncertainty and likely contributions to uncertainty budgets. It also explains the difficulties in accumulating the necessary data for inclusion in IEC 61672, and of incorporating the data into the tolerance limits. The reasoning behind the decision to quote a maximum permitted expanded uncertainty of measurement for the testing laboratory separately for each test will also be discussed. Examples will be presented of the determination of expanded uncertainties of measurement for acoustical and electrical signals and their application in assessments of conformance.
Numerical analysis and active control of wake/blade-row interaction noise
Authors: Hwang C. J. , Kuo J. Y.
Published: July 2002

A computational approach for investigating and controlling the wake/blade-row interaction noise through the use of actuators or blowing/suction on the stator blade surfaces is presented in this paper. This approach includes a solution-adaptive finite volume upwind scheme, adaptive/dynamic mesh technique, boundary treatments for aeroacoustic computations, and an active noise control algorithm. A two-dimensional section of a fan stage, which is composed of an upstream rotor and a downstream fan exit guide vane (FEGV), is investigated. By utilizing a rotor wake model, the acoustic fields of the FEGV are presented and analyzed to understand the accuracy and suitability of the present adaptive scheme. Also, the noise generation mechanics are studied. Finally, the active noise control algorithm is introduced. From the computational results, the reduction of noise due to actuators on the blade surfaces is more significant than that of using blowing/suction. The downstream propagating acoustic waves are more difficult to control than the upstream propagating waves. [Work supported by NSC.]
Performance of acoustic liners for jet engine intake ducts
Authors: Greaves Matthew J. , Petersson Björn A. T.
Published: July 2002

In order to meet current and future noise emission regulations, it is necessary to reduce the noise generated by aircraft engines. One method is to line the duct with an attenuating configuration, and acoustic liners employing the Helmholtz resonator concept are now commonplace in jet engine intake ducts. Based on reports of core failure, the question of the mechanisms behind such failures, being the interaction of high sound pressure levels and shock waves with the liners, is addressed. Full-scale experimental pressure data are presented. Moreover, using the experimental data as input to a numerical model for nonrigid cavity walls, the induced stresses are analyzed. Results for typical liner configurations are given, and the nonlinear orifice effects considered. Possible alternative designs are examined and their advantages and disadvantages from an acoustic viewpoint discussed.
Acoustical forced oscillation diagnosis method of cracks for turbomachinery
Authors: Gelman Leonid M. , Kondratyuk Lyudmila V.
Published: July 2002

A new acoustical forced oscillation diagnosis method of fatigue cracks for turbomachinery is proposed. The method uses nonstationary vibration excitation with variable frequency. Turbomachinery rotating details with fatigue cracks were considered as piecewise-linear systems. A new analytical approach and new analytical expressions of spectral density of narrow-band noise of rotating details are proposed. Experimental results of diagnostics of gas-turbine engine compressor blades based on noise emission are presented.
The effects of flanking transmission on sound attenuation in a finite-length lined duct, with mean flow
Authors: Kirby R. , Cummings A.
Published: July 2002

The acoustic performance of lined air-conditioning ducts is known to be compromised by the effects of flanking sound transmission. Two separate flanking paths have been identified; the first involves sound transmitted directly through the duct walls (sometimes termed radiation-by-pass) and the second involves the axial transmission of structural/acoustic waves along the duct walls. The attenuation of the internal sound field, particularly in relatively long ducts, is known to be limited by the effects of noise transmission caused by the formation of flanking paths. A model is described here which predicts the effect of both forms of flanking transmission on the attenuation of sound in a lined air-conditioning duct with mean flow in the central airway. Since most air-conditioning ductwork contains only a finite section of porous material, attenuation in both lined and unlined sections is included here. A finite-element eigenvalue solution is employed to couple the acoustic pressure field in the duct to the duct wall displacement. The principle of reciprocity is then used to model the effects of break-in. Finally, mode-matching techniques are employed to match the modal expansions across the discontinuity between the lined and unlined sections. [Financial support provided by the European Commission, BRITE/EURAM project FLODAC, Project No. BRPR CT97-0394.]
Negative resistances in nonlinear lumped acoustic systems and IC-engine source data
Authors: Albertson Fredrik
Published: July 2002

Negative real parts of impedances can be found in IC-engine source characterization measurements. There is an obvious problem with the physical interpretation of negative resistances, and consequently there have been many questions about the validity of such results. This paper is an attempt to explain the origin of the mentioned negative acoustic resistances. To this end, a simple nonlinear lumped acoustic system, that is, a force-driven damped mass-spring system, is analyzed. Since this is a common case in acoustic measurements, linear analysis is performed in spite of the obvious nonlinear properties. It is shown that the degree of nonlinearity in the system is crucial to the values of the acoustic impedance. Furthermore, it is shown that it is possible to achieve negative resistances already in a simple lumped system. Finally, these results are also compared to simulated and measured IC-engine source impedances.
The Rayleigh-like collapse of a conical bubble
Authors: Leighton Tim G. , Cox Ben T.
Published: July 2002

This paper describes an experimental investigation of the collapse of a conical bubble, with measurement of the liquid and bubble gas pressures, and sonoluminescence, generated during the collapse. A theoretical analysis, based on the 1917 formulation of Rayleigh, adequately predicts the pressures, and the time scales as measured by high-speed photography, within the limitations of both theory and measurement. One implication of this novel apparatus lies in the ability to control the inertia associated with the liquid without changing its other properties. The inertia is key to the dynamics of the type of bubble collapse which is associated with sonoluminescence and the emission of strong rebound pressures into the liquid. Another implication of this study is the ability to image the collapsing meniscus and the gas and, to a certain extent, place sensors within the gas of the collapsing bubble.
Bubble response to the amplitude modulation signal near the threshold of dynamical stability
Authors: Maksimov Alexey O. , Sosedko Ekaterina V.
Published: July 2002

There is a range of acoustic techniques for characterizing bubble populations within liquids [Leighton et al., Ultrasonics 34, 661–667 (1996)]. The linear resonant backscattering was the first detection technique. The great difference between the compressibility of gas in the bubble and surrounding liquid leads to the easy manifestation of nonlinear effects, the simplest of which is the presence of harmonics at 2ωp, 3ωp, etc., of the pure tone driving frequency ωp in the scattering signal. However, bubble pulsation of finite amplitude results not only in the harmonics generation. The nonlinear resonance characterized by multistable oscillation states arising from the saddle-node bifurcations is a significant example. The emphasis of this study is to propose a technique for bubble sizing by using the ability of a bubble as a nonlinear oscillatory system to amplify weak signals near the threshold of dynamical stability. The analytical as well as numerical solutions have been derived for the nonlinear bubble response to the modulation driving pressure. The magnitude and the form of the acoustical signal reradiated near the threshold of dynamical stability are drastically different from the modulation of incident wave and enable the characterization of the bubble population in liquid.
A closed formulation of sound fields in front of periodical absorbents
Authors: Holmberg Dag , Nilsson Erling
Published: July 2002

Periodic resonant absorbers are known to give excessive back scattering for frequencies above a limit which is governed by the geometric proportions of the periodicity. One way to model this phenomenon is to transform the geometry into the wave number domain and solve the corresponding equation with respect to the pressure field. A drawback is that the equation matrix consists of an infinite (but relatively fast converging) set of harmonic components and therefore has to be truncated in order to be solved. However, it is possible to make use of the Poisson sum formula and obtain a closed formulation which can be solved in the wave domain without truncation. Furthermore, it is possible to transform the exact solution back to the spatial domain. This will yield an infinite series consisting of components which can be designated a physical interpretation. These components, i.e., partial pressures related to corresponding geometry, which constitute an exact solution, can then be truncated in a controlled and physical way.
Sonic band structure and surface localized modes in a density-modulated system: An experimental and theoretical study
Authors: Carr Christopher , Yu Roger
Published: July 2002

As a result of the Bloch theory, the eigenstates of an electron in a strictly periodic potential are extended and the eigenenergy levels form allowed energy bands separated by forbidden gaps. In the study reported here, a finite air-filled tube with arbitrary mass density modulation is considered which allows the inclusion of the effect of disorder. Since this theoretical model is finite, it was possible to make direct comparisons with the experiment. The baffled tube is excited with the sound source emitted at one end. The source can deliver short pulses as well as harmonic oscillations. Both normal modes analysis (NMA) and pulse analysis (PA) were used. The spectra obtained from both methods are compared with the theoretical prediction. For the tube with evenly spaced baffles, three passing frequency bands were found. More interestingly, a few ‘‘surface’’ localized resonant modes whose frequencies lie in the gaps were discovered. The wave functions of the surface modes are confined within a few sections of divided tube at both ends. It was found that the acoustic intensity of higher frequency bands is drastically lower than that of the lowest band, which suggests that the baffled tube can be used as a frequency filter.
Time-of-flight measurements on high-frequency surface acoustic phonons in silicon
Authors: Photiadis D. M. , Ding J.
Published: July 2002

Results from time-of-flight measurements of high-frequency surface acoustic phonons (50–500 GHz) in (001) silicon wafers at low temperatures are reported. Pulsed laser excitation is used for the generation of the high-frequency surface acoustic phonons and aluminum edge bolometers are used as detectors. The times defined by the fast initial response of the edge bolometer correspond to surface acoustic delays in silicon. Late time responses consistant with echoes from the back face of the wafer were also observed. These results and the accompanying analysis will be discussed.
Effects of aging on sound localization and speech understanding in realistic listening situations
Authors: Koehnke Janet , Besing Joan
Published: July 2002

The ability to localize sound in quiet and noise and understand speech in noise was measured for four groups of subjects including adults under 50 years old and over 60 years old with normal hearing, and adults under 50 years old and over 60 years old with hearing loss. Performance was measured in anechoic and reverberant listening environments at two stimulus levels (25 dB SL and 70 dB SPL). Head-related transfer functions were used to create spatialized stimuli that were presented to subjects via earphones. Results indicate that performance on both tasks is affected by age and hearing loss. Localization errors are larger in older adults than younger adults with normal hearing, and larger in older adults with hearing loss than older adults with normal hearing. The intelligibility gain is smaller in older adults than younger adults with normal hearing, and smaller in older adults with hearing loss than older adults with normal hearing. Speech understanding in noise shows a large effect of reverberation, but localization is not affected by the same amount of reverberation. Overall, results suggest that in realistic environments these tasks are more difficult for older adults. [Work supported by the American Hearing Research Foundation.]
Estimating the phase characteristic of the auditory system from masking by harmonic complexes
Authors: Lentz Jennifer J. , Leek Marjorie R.
Published: July 2002

As shown by several recent studies of positive and negative ‘‘Schroeder-phase’’ stimuli, masking by harmonic complexes is strongly affected by the temporal waveform of the masker [e.g., V. Summers and M. Leek, Hearing Res. 118, 139–150 (1998)]. Differences in masking by the Schroeder waves provide a starting point for estimating the phase response of the auditory system. In this study, the gradient of phase change across masker bandwidth was varied by altering the Schroeder-phase algorithm. Depending on signal frequency (ranging from 500 to 4000 Hz), differences in masking could be 5–10 dB for phase gradients changing by only 10%. The phase gradient that resulted in a minimum amount of masking varied systematically with signal frequency, with low frequencies masked least effectively by waveforms with rapidly changing component phases, and high frequencies by waveforms with more shallow phase gradients. This relationship between phase gradient and signal frequency is taken to reflect the phase response of the auditory filter at that frequency. The phase gradients associated with minimal masking at each frequency can be used to construct a piecewise-estimate of the phase characteristic of the auditory system for individual listeners. [Work supported by NIH DC00626.]
Gap detection within and across perceptual channels
Authors: Oxenham Andrew J.
Published: July 2002

The ability to detect gaps is degraded when the stimuli (markers) on either side of the gap have different power spectra. This may be due to peripheral frequency selectivity: when no transient is audible in the no-gap condition (e.g., when the markers have the same intensity and spectrum), listeners detect the transient introduced by the gap; when the markers fall into different auditory filters or are at different intensities, transients are audible regardless of the presence of a gap and listeners must perform a timing judgment. It has recently been suggested that changes in other, more central, perceptual dimensions, such as perceived location, may also affect gap detection. This study was designed to test whether a peripherally based model could also account for such data. Lateralization differences between the two broadband-noise markers were achieved using interaural time and intensity differences independently. Monaural gap detection with level differences between the markers was also tested. Results indicate that gap detection is poor only when level differences exist between the markers, independent of perceived location. Thus the data can in principle be accounted for by peripheral mechanisms. No evidence was found for the influence of higher perceptual channels. [Work supported by the NIDCD.]
A hybrid passive/active system for control of the noise radiated by a small generator
Authors: Cuesta Maria , Cobo Pedro
Published: July 2002

The aim of this work was the design and implementation of a hybrid passive/active system to control the noise radiated by a small generator. The fundamental frequency of the periodic radiated noise depends on the electrical load plugged into the generator. Passive control is afforded by a rectangular enclosure with dimensions 1000×710×530 mm3. The wall panels of the enclosure (steel 1.5 mm thick) are lined with a 30-mm layer of sound absorbing material. Special attention is paid to technical aspects such as air refreshing and temperature inside the enclosure. The measured insertion loss is higher than 20 dB above 500 Hz. Low-frequency noise escapes the enclosure via intake and exhaust openings. Active control is applied to the exhaust noise. The reference signal is supplied by an accelerometer over the air filter case of the generator. A high-temperature loudspeaker is used as control source. The error signal is picked up by a cheap electric microphone. Since noise along the exhaust is too loud, the microphone sensitivity had to be reduced by taping its diaphragm. A commercial system is used to implement active noise control. [Work supported by CICYT, Project AMB97-1175-C03-01.]
Sound scattering by moving inhomogeneity
Authors: Semenov Andrew G. , Alexeyev Vadim N.
Published: July 2002

This report considers the propagation of sound in the vicinity of a rather general class of localized flows induced by the motion of spherically symmetric structures of the type of solid spheres and droplets or vortices in the liquid, say, ocean environment. Acoustic scattering from such inhomogeneities, situated inside various flows, is analyzed with the aid of the M. J. Lighthill equation boundary value problem solution—both in the presence of vorticity and without it. The role of a moving body generating inhomogeneity as well as the role of the surface at which the tangential component of flow velocity could suffer a discontinuity are demonstrated in a most general form. Comparison of body and flow contribution to the observed scattered field is presented. The physical condition of flow presumably yields in a forward scattering direction—a situation of the type encountered in a conventional ocean tomography system, comprising a source–detector line, is proposed. The angular structure of the scattering amplitude and the frequency dependence of the scattered sound are evaluated.
GEOSTAR benthic observatory: Technological results
Authors: Gerber Hans W. , Favali Paolo , Smriglio Giuseppe , Gasparoni Francesco , Marvaldi Jean , Coudeville Jean-Michel
Published: July 2002

GEOSTAR (GEophysical and Oceanographic STation for Abyssal Research) is a project funded by European Commission, MAST III. The aim of the project was the development of the first prototype of an innovative deep-sea benthic observatory capable of carrying out long-term scientific observations at abyssal depths (up to −4000 m). The prototype has been realized and tested successfully in Adriatic Sea in late summer 1998. GEOSTAR is made up of two main subsystems: Bottom Station and Mobile Docker. The Bottom Station includes the acquisition and power systems, all the scientific sensors and hosts the Communications. The Mobile Docker is a dedicated tool for surface-assisted deployment and recovery. GEOSTAR is characterized by a lightweight and modular frame, autonomous mission control capabilities, and multiple possibilities of interfacement with external devices. The Bottom Station is presently equipped with geophysical, geochemical, and oceanographic instruments (a triaxial seismometer, vectorial and scalar magnetometers, CTD, transmissometer, ADCP, and an electrochemical package), but it can easily host other sensors for different experiments. The observatory was deployed in the Adriatic Sea on 13 August 1998 and recovered on 2 September 1998. The observatory worked properly, recording 440 hours of scientific data. Data were processed, elaborated, and interpreted based on a multidisciplinary approach.
Low-frequency dispersion computations by compound-matrix propagation
Authors: Ivansson Sven
Published: July 2002

The basic propagating waveguide modes in underwater acoustics have lower cutoff frequencies. As the frequency is decreased below the cutoff frequency, the modal horizontal slowness typically becomes complex and tends to infinity while the modal wave number tends to a nonvanishing complex number. In certain laterally homogeneous fluid–solid media, there also exist slow P−SV modes for which the horizontal slowness tends to infinity along the real axis while the horizontal wave number tends to zero as the frequency tends to zero. The flexural wave for an ice sheet on top of the ocean is a particular example. To investigate the low-frequency behavior of the modal horizontal slowness for these kinds of modes, computations of dispersion curves by propagator techniques are attempted for media composed of homogeneous fluid and solid layers. However, loss of numerical precision by cancellation effects appears for the needed elements of the solid-layer compound-matrix propagators. Guided by theoretical results for the asymptotic growth of these elements, cancellation-free expressions are derived. The harmful contributions causing loss of numerical precision at low frequencies are eliminated analytically. As an application of the new expressions, a numerical case study is performed. Improved results on low-frequency asymptotic expansions of the modal slownesses are obtained.
Validation and application of an effective medium theory to heterogeneous anisotropic structures
Authors: Stamoulis Catherine , Komatitsch Dimitri , Jordan Thomas , Tromp Jeroen
Published: July 2002

The polarization anisotropy in the upper mantle requires inhomogeneities with small scale lengths. To represent heterogeneous anisotropic structures, such as ocean basins, Jordan et al. (1996) formulated stochastic models for small-scale heterogeneities, as samples of a random field of fourth-order hexagonally symmetric elasticity tensors Cijkl. The random field has a characteristic horizontal wave number κ, independent of azimuth, and a characteristic vertical wave number ηκ. The medium is therefore statistically transversely isotropic with horizontal heterogeneity scale 1/κ, aspect ratio η, and self-affine scaling at high wave numbers specified by a fractal dimension D. The propagation of seismic waves with lengths ≫ 1/κ is described by five effective elastic constants, calculated to second order in the scattering by contracting the static fourth-order Green’s strain tensor with the eighth-order variance tensor for Cijkl. The validity of this self-consistent effective medium theory is tested by comparing the propagation characteristics that it predicts, as a function of range and frequency, with those measured from synthetic seismograms computed for realizations of the medium using a spectral element method [Komatitsch and Vilotte (1998)]. In particular, the theoretical, frequency-independent phase delays are compared with the frequency-dependent phase delays from the synthetic seismograms.
Laser optoacoustic diagnostics of sea ice
Authors: Maksimov Alexey O.
Published: July 2002

The emphasis of the current study is the analysis of the mechanisms of generation and propagation of optoacoustical (OA) signals in the upper ocean for the winter season or Arctic sea, when the water surface is covered by ice sheet. Modulated or pulsed laser radiation, being absorbed in a layer of ice, results in the excitation of elastic perturbations, propagating on large distances over the surface and in the bulk of the ice canape and in the adjoining layer of liquid. Analytical expressions for the far-field acoustic field have been derived for the wavelengths of a laser source from decimal up to several microns. The diagram of directivity of acoustic radiation in liquid was computed for the frequency interval of modulation of laser intensity of 100 Hz to 15 kHz [A. O. Maksimov, Tech. Phys. Lett. 22, 52–55 (1996)]. The particular attention was devoted to the description of radiation near the Mach angles of eigenmodes, propagating with velocities exceeding the sound speed in liquid. It happened that the interference pattern near the Mach angle is very informative for the diagnostics of physical parameters of the ice plate [A. O. Maksimov, Acoust. Phys. 43, 577–582 (1997)].
Comparison of simulation and measured sound system performance in the German Reichstag Debate Hall, Berlin
Authors: Loewer Volker
Published: July 2002

For the design of the new sound system for the Reichstag Debate Hall, Berlin, the ulysses computer aided acoustic design program has been used. The 3-D model of the room consisted of more than 1000 faces treated with different absorption in octave bands according to the architect’s plans. Simulation of direct sound coverage, RT60, intelligibility, energy decay via ray-tracing, etc., was done to evaluate different solutions of the sound system designs and their interaction with room acoustics. It is intended to compare actual acoustic test results to simulated predictions and to discuss conformity and deviations. The software was also used to predict directivity balloons of the complex speaker arrays located in the debate hall. The balloons were derived from measured balloons of the single devices used in the arrays. Considering relative mechanical locations, acoustic centers, acoustic power, and delays, the predictions showed good conformity with polar measurements of a real cluster.
A computer auralization and ‘‘real world’’ comparison using the computer programs e
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Authors: Coffeen Robert C. , Caunt Gabriel
Published: July 2002

In order to compare a ‘‘real world’’ acoustic environment with a computer auralization of the same space, an Episcopal Church located in Prairie Village, Kansas (near Kansas City, Missouri) was selected as the ‘‘real’’ space. Anechoic speech and music recordings were reproduced in this space and recorded binaurally. The same anechoic recordings were introduced into a computer model of this room with auralizations produced by the computer programs ease and ears. The ‘‘real world’’ binaural recordings are compared with the computer-generated audio using both objective and subjective methods. The measured impulse response of the room and the computer-predicted impulse response are compared. Comparisons are also made between the measured and the predicted reverberation periods of the room.
On the utility of extending the low-frequency range of standards for sound isolation in buildings
Authors: Lind Stephen J. , Pearsons Karl S. , Fidell Sanford A.
Published: July 2002

Frequencies above 100 Hz are commonly considered in sound insulation computations as specified by ASTM E413 and ISO 717. This is appropriate for concerns about speech privacy in interior spaces. However, aircraft ground operations (including takeoff roll, engine run-ups, and thrust reverser deployment) may expose buildings near runways to appreciable amounts of energy at yet lower frequencies. Several studies of low-frequency aircraft noise levels have recently been completed in the United States, and the U.S. Federal Aviation Administration is paying for architectural treatments to reduce low-frequency aircraft noise in residences near one airport. This paper describes the findings of a recent social survey of residential annoyance caused by low-frequency runway sideline noise, including noise in the 25 to 80 Hz one-third octave bands, and reviews other evidence about the role of low-frequency energy in sound isolation metrics.
Method of the main informative components for acoustic tomography
Authors: Kalyuzhnyi Alexander Ya. , Krasny Leonid G.
Published: July 2002

Techniques for an ocean acoustic tomography are based on the representation of the sound-speed field (SSF) by an expansion of some orthogonal basis functions. It is usually assumed that the most efficient basis functions for the SSF expansion are so-called empirical orthogonal functions (EOF). Meanwhile, the experiments show that algorithms based on the EOF can be extremely sensitive to slight errors in the assumed signal and noise characteristics. A new improved algorithm for acoustic tomography will be presented which minimizes output statistical errors of the SSF estimation. The concept of this algorithm is to use eigenvectors of the Fisher information operator as the basis functions into the SSF expansion. The algorithm involves a quadratic inequality constrain on the SSF expansion coefficients to select the most informative components among all the eigenvectors. It is shown that it leads to a robust algorithm in which statistical errors do not accumulate. The performance of the proposed algorithm will be illustrated both for deterministic and random signals.
Piano string excitation: The question of gravity influence on the sound spectra
Authors: Stulov Anatoli
Published: July 2002

The influence of gravity on the process of the grand piano hammer–string interaction was appreciated by D. E. Hall [J. Acoust. Soc. Am. 79, 141–147 (1986)]. Using the reasonable physical assumptions, it was shown that the gravity influence is small and may not be taken into account. It is obvious, but it is important to know exactly what this influence is. The vibration spectra of different flexible strings excited by piano hammers in the gravity field and without gravity were analyzed here. Of course, the influence of gravity increases with the increasing of the contact time. Its depends on the hammer velocity; therefore, the string excitation by hammers with velocities less than 0.5 m/s was considered. It was shown that: the gravity influence is greater for the smooth hammers, and this influence is more essential for the middle range of notes; for the small velocities of hammers the gravity changes the mode energy levels of the primary harmonics up to 10 dB, if the hammer strikes only one string of the triple set; the gravity must be taken into account definitely, if the contact time is greater than 5 ms.
The major historical events in the relating of noise-induced hearing loss to noise exposure
Authors: Johnson Daniel L.
Published: July 2002

One event was the recognition of ‘‘boilermaker’s disease.’’ Another was some of the threshold shift studies during and after WWII that led to the BENOX report. After these developments, there were a series of key events and decisions that have led up to our current state of knowledge and procedures. How Henning von Gierke was influential in most of these and how his decisions have consistently proven to be correct will be demonstrated. For example, he contributed to the 1953 BENOX report, promoted the ‘‘equal energy concept,’’ conceived and patented the first noise dosimeter, oversaw the EPA ‘‘levels’’ and criteria documents, and was the chair of the working group that wrote the current international standard (ISO-R1999) that relates noise exposure to noise-induced hearing loss. He was also instrumental in supporting many key research issues such as fetal noise exposure, asymptotic temporary threshold shift, and the longitudinal hearing of children. Henning’s perseverance and dedication has provided society with an answer to one of his favorite questions, ‘‘how much noise is too much?’’
Analysis and capability of a noncompact integration method for rotor noise prediction
Authors: Prieur J.
Published: July 2002

Rotor noise computations starting from CFD input data using either the Kirchhoff or the generalized Ffowcs Williams–Hawkings surface integral methods in unsteady conditions may be very lengthy. This is the case for directivity studies or noise level contour calculations for which a high number of observer locations is required. To overcome this drawback, a fast integration method has been designed. It starts from the emission time which avoids having to solve the retarded time equation and uses directly as integration grid the CFD rotating grid (a priori not adapted to acoustic calculations). This is made possible thanks to a noncompact treatment of each grid element. The method has already been successfully applied in a transonic rotor case using indifferently a subsonically or supersonically rotating CFD grid for the surface integration (G. Rahier and J. Prieur, 53rd Forum of the American Helicopter Society, 29 April–1 May 1997). The method is made more understandable based on a new and clearer justification and its possibilities of extension are discussed.
Recent developments in helicopter rotor noise prediction at NASA
Authors: Brentner Kenneth S.
Published: July 2002

Significant progress has been made recently toward the efficient and robust prediction of helicopter high-speed impulsive noise. The far-field approximation to the Ffowcs Williams–Hawkings (FW–H) quadrupole has been augmented with a rigorous mathematical development. Two new quadrupole formulations—a retarded-time formulation known as Q1A and an emission-surface formulation known as Q2—have been developed and implemented for subsonic and supersonic source motion, respectively. A key numerical advantage of the far-field approximation is that volume integration of the source region surrounding the rotor blades is only performed once in a preprocessing stage. The resulting quadrupole noise computation is reduced to surface integration over the rotor disk in the vicinity of the blades. The solution-adaptive marching-cubes integration algorithm used for the emission-surface formulation will be described. Another recent advance in helicopter noise prediction is the use of the FW–H equation on a permeable integration surface surrounding the source region. This application of the FW–H equation has been shown to be both analytically and numerically superior to the Kirchhoff approach. Furthermore, numerical evidence is presented to demonstrate that the Kirchhoff method is inappropriate when a wake convects through the surface.
Passive–active low-frequency vibroacoustical fault diagnosis method
Authors: Bouraou Nadejda I. , Gelman Leonid M. , Marchuk Pavel I.
Published: July 2002

The presented work is dedicated to the development of the new passive–active low-frequency automatic vibroacoustical early fault diagnosis method of helicopter engine units (compressor stages, turbine stages). The proposed method is based on signal processing of the rotating details of acoustic noise in the low-frequency range (0–25 kHz). There are two important characteristics of this method: (a) it uses a nonstationary narrow-band vibration excitation with variable central frequency, and (b) this excitation is provided by rotating rotor, and user of the method will vary the central frequency, and (b) this excitation is provided by rotating rotor, and user of the method will vary the central frequency of rotor rotation. The basis for using this method is the fact that, at the presence of fault (for example, fatigue crack) in testing details, parameters of arising free and forced oscillations change (nonzero spectral amplitudes of higher harmonics). The new analytical dependencies of testing object oscillation parameters from the relative crack size and parameters of nonstationary excitation are received. A multidimensional testing data vector for diagnostics and evaluation of faults is proposed and investigated.
An advanced field measurement system for rotorcraft flight noise
Authors: Yu James C. , Wright Kenneth D.
Published: July 2002

A Langley-developed field acoustic measurement system has been extensively employed to support the NASA aircraft and rotorcraft flight noise research programs since the early 1980s. The system was first successfully used in the NASA Forward Flight Effects on Turbofan Noise program. Starting from the late 1980s, driven by the increased demand on expanded measurement capabilities for rotorcraft flight noise, an advanced field measurement system development program was initiated to support the rotorcraft flight noise measurement, reduction, and prediction. The paper reviews the three major stages of this extensive development program: the analog measurement system stage, the digital measurement system stage, and the digital remote acquisition and storage system stage. The data processing technology associated with these different stages of the system will be presented. The paper will discuss the research drivers for the measurement system development, the development strategy used to meet the system requirement, and lessons learned at each stage of the development. Discussion will also be given on the future rotorcraft flight noise measurement challenges and the advanced measurement systems required to meet these challenges.
Computational aeroacoustics of ducts using parallel computers
Authors: Long Lyle N.
Published: July 2002

This paper will discuss recent attempts at using computational aeroacoustics (CAA) algorithms on parallel computers to solve duct propagation problems. The algorithms are higher-order accurate methods for solving the Euler and Navier–Stokes equations. As computer speed increases, more and more of the physics can be simulated. This talk will discuss the current status and trends of parallel supercomputers. While hardware trends allow us to solve more complicated problems, algorithm developments are also essential. This talk will address some new methods for solving aeroacoustics problems. Most of these new developments involve hybrid schemes that couple CAA methods with integral methods or traditional CFD codes with CAA codes. Since aeroacoustics problems involve length and time scales that are beyond computer power at the present time, clever schemes must be developed for using appropriate algorithms for the various physical phenomena. One very promising scheme [J. Comput. Phys. 133 (1997)] is the nonlinear disturbance equation (NLDE) method, which uses a traditional CFD code to predict the steady-state portion of the problem, and then a higher-order method to solve for the disturbances. The steady-state portion is included in the coefficients and source terms in the NLDE. [Work supported by NASA Langley.]
Experimental study of acoustic impedance of a Helmholtz resonator submitted to a grazing flow
Authors: Frikha Slaheddine , Hennion Pierre Yves , Boukhari Samir
Published: July 2002

Helmholtz resonators are usually used in ducts or in engines inlet and exhaust systems in order to reduce radiated noise. Their efficiency may be strongly affected since they are submitted to a fully turbulent grazing flow. An experimental analysis of a branched Helmholtz resonator composed by a circular neck and a circular cavity is presented here. An attempt is made to understand the evolution of entry impedance modification with respect to mean flow and the shear layer characteristics at the vicinity of the resonator aperture. An inverse method is used to identify the impedance of 25 resonators. This method presents the advantage that it is completely nonintrusive and does not require source control. The grazing flow modifies the orifice resistance and the effective neck length. A parametric study of these corrections is performed using experimental results obtained for a set of 25 resonators and a flow Mach number varying from 0 up to 0.25. The mean flow structure is also analyzed using a numerical model. The dimensions of the tested resonators are similar to those usually used in the exhaust and inlet systems of automotive engines. That leads to a new parametric model of these corrections more suitable to engine applications.
A ‘‘missing-data’’ model of F0-invariance in vowel perception
Authors: de Cheveigne Alain
Published: July 2002

In steady-state voiced speech production, the vocal tract transfer function is sampled at multiples of the fundamental frequency (F0). At high F0, sparse sampling causes two problems: (a) a gradual loss of information defining the spectral shape, and (b) F0-dependent distortion due to aliasing. If the shape of the spectral envelope contains lag-domain components (spatial frequencies) beyond the Nyquist limit, they are folded relative to the Nyquist limit and mixed with in-band components. The Nyquist limit (T0/2, where T0=1/F0) depends on the spacing between sampling points along the spectral envelope, and thus on F0. Distortion is thus F0-dependent, and all the more severe as F0 is high. Smoothing or interpolation are ineffective in dealing with this problem, and cannot produce an F0-invariant pattern. A solution is proposed based on the concept of ‘‘missing feature theory,’’ recently proposed for speech recognition. Pattern matching is limited to available data (F0-spaced sample points) using an F0-dependent weighting function. All other points are ignored. The model is proposed in two versions, one that operates on the short-term spectrum or excitation pattern, the other on the autocorrelation function. The model ensures F0-independent vowel identification, at the cost of an F0 estimate.
Investigation at a top counter weight of a washing machine
Authors: Heise Ulrich , Harbich Wolfgang
Published: July 2002

During the development of a new washing machine a problem came up in spite of the durability of the newly designed top counter weight. The top counter weight is necessary to balance the drum of the machine. The problem was caused by the dynamical behavior of the system. A modal analysis was made at the compensation weight in the machine. Several different modes and eigenvalues were detected. The disturbing mode was found. It was caused by the stiffness of the fastening and the mass of the weight. The top counter weight was fastened in the axial direction of the drum. The disturbing mode was eliminated due to the change of fastening from axial to radial fastening. The problem is now solved. Another point of view are the other eigenvalues of the weight. The size of the weight looks like a xylophone bar and, in the same manner, it can vibrate. These modes of the weight itself are not disturbing modes, because the excitation forces are too small in this area and at this frequency range for exciting the compensation weight.
Evaluation of the air particle velocity signal from the binaural pressure impulse response
Authors: Stanzial Domenico , Bonsi Davide
Published: July 2002

From the Lagrangian theory in linear acoustics one clearly infers that the generalized momenta of the sound field are the acoustic pressure and the three components of the air particle velocity. This means that only through the knowledge of the full set of these four quantities a complete physical identification of the sound field can be achieved. The binaural technology represents an important tool for this goal, since it offers a method for reconstructing the pressure sound field by means of a couple of pressure impulse responses measured in two close points. An additional improvement of the binaural signal processing can be obtained using the two pressure input signals for evaluating the velocity component along the direction determined by the measurement points. First the velocity impulse response component is evaluated by means of the Euler equation and then, by convolving this signal with the usual anechoic signal, the velocity is reconstructed. In this paper the rigorous mathematical procedure for accomplishing the above task is presented.