bluuebunny/crossref_metadata_2025 huggingface dataset:
Loudspeaker requirements for electronic organs in churches
Authors: Ashley J. Robert , Pritts Roy A.
Published: October 2005

When visiting a strange church, we can identify the organ as a pipe organ or an electronic organ with just a few minutes of listening (and without visual inspection). A run on the pedal organ will show the usual organ loudspeaker to cease radiating below 60 Hz. Modulation distortion will show that the all important middle octave (261–525 Hz) is being radiated from the same cone as the low tones. The lack of high-frequency power radiation is noticeable. We deem these faults are caused by the fact that organ loudspeakers have not been designed, they have just happened. Dr. J. E. Bensen reported (in 1959) an experiment in the Sydney (Australia) Town Hall which proves this need not be true. We have repeated Dr. Bensen's experiment in the First Methodist Church, Colorado Springs, Colorado, and verified his conclusion. To prove that the recent loudspeaker revolution can make the electronic organ viable, we use a Moog Synthesizer to simulate several pedal and great organ stops.
Automatic language identification
Authors: Li K. P. , Edwards T. J.
Published: October 2005

A study on automatic language identification has recently been completed. The study included 200 talkers from ten different languages. Data from five languages were comprised of reading data from all male talkers while the other five languages were comprised of two-way conversational data from both male and female talkers. All data were band-limited to 350-3000 Hz and digitized at 8 kHz. Using an automatic segmentation program developed at TRW [J. Acoust. Soc. Am. Suppl. 1 64, S179(A) (1978)] which provided a set of six acoustic-phonetic labels, several forms of Markov types of models and classification methods were developed to identify each language independently of the talker and context. Half of the talkers were used for training the models, while the other half was used for independent test. Classification methods, statistics of the data, and identification results will be presented.
On the use of clustering for speaker-dependent isolated word recognition
Authors: Rabiner L. R. , Wilpon J. G.
Published: October 2005

Speaker-trained, isolated word recognizers have achieved notable success in a wide variety of applications. The training for such systems generally involves a single (or sometimes two) replication(s) of each word of the vocabulary by the designated talker. Word reference templates are then formed directly from these replications. In recent work on speaker-independent word recognition, it has been shown that statistical clustering procedures provided an effective way for determining the structure in multiple replications of a word by different talkers. Such techniques were then used to provide a set of reference templates based on the clustering results. In this talk we discuss the application of clustering techniques to speaker-trained word recognizers. It is shown that significant improvements in recognition accuracy are obtained when using templates obtained from a clustering analysis of multiple replications of a word by the designated talker. It is also shown that recognition accuracy did not change with time (over a 6-month period) for any of the subjects tested, thereby indicating that the reference templates were reasonably stable.
Chairman's introductory remarks
Authors: Lubman David
Published: October 2005

The recent trend toward mainstreaming the handicapped, implies that acoustical designers must now consider the needs of persons with hearing and visual handicaps. What are these needs, and how can designers meet them? Invited speakers and panelists have been assembled to address these questions. They will review evidence showing that sensorially handicapped persons have an enormous stake in the acoustical quality of interior spaces intended for work, learning, and recreation. Examples of considerate acoustical design will illustrate how the ability of the hearing impaired to understand speech, and the mobility of the blind, can be greatly enhanced. Finally, a panel of invited speakers and other experts will consider whether the prevailing standards of acoustical acceptability are adequate for sensorially handicapped persons.
Open-plan offices pose a disadvantage to hearing-impaired people
Authors: Suter A. H.
Published: October 2005

Theoretically, open-plan offices are designed so that their occupants may study without being distracted, as well as converse with each other and on the telephone. Design criteria using masking noise are based on assumptions that talkers, listeners, and listening conditions are “average.” These assumptions are reviewed, especially as they affect hearing impaired people. There is evidence that noise levels of 47–50 dBA can degrade communication of the hearing impaired without affecting those who hear normally. A study of speech discrimination in noise showed that even people with mild hearing losses had considerably more difficulty understanding speech than their normal-hearing counterparts. Using predictions based on the ANSI standard for calculating the articulation index, a mean difference in AI units of up to 0.15 was found between discrimination scores of mildly hearing impaired and normal-hearing groups for the same conditions. This value translates to a speech-to-noise ratio of approximately 4.5 dB, given similar spectra for speech and noise. Negative speech-to-noise ratios may occur, especially when talkers lower their voices out of courtesy to neighbors or because privacy is desired, thus exacerbating the disadvantage of the hearing impaired.
Silicon rubber for optical hydrophones
Authors: Shajenko Peter , Flatley James
Published: October 2005

Elasto-optic properties of materials can be used for modulating the laser beam by the acoustic pressure. The compressibility and the change of index of refraction with pressure of silicon rubber were measured using the technique of interferometry, and the results were applied to determine the voltage sensitivity and minimum detectable pressure of an optical hydrophone. Both values compare favorably with those of a conventional piezoelectric hydrophone.
Optimization study of a parametric hydrophone with a slow waveguide
Authors: Jarzynski J. , Corsaro R. D.
Published: October 2005

The performance of a parametric hydrophone with a cylindrical slow waveguide between the pump and receiver transducers was calculated as a function of the waveguide dimensions and material properties. The computer program used is described by Corsaro and Jarzynski [J. Acoust. Soc. Am. 66, 895–904 (1979)]. The parametric conversion gain and beam patterns were calculated for waveguide lengths in the range 0.1 to 9λ, where λ is the low-frequency wavelength in water; for waveguide radius/length ratios in the range 0.03 to 0.5; and for waveguide materials with sound speeds in the range 400–1500 m/s. The general conclusion is that large gains in parametric conversion efficiency (∼20 dB) and in directivity are achievable for geometries less than a few wavelengths long, with diameter/length ratios no less than 0.1, and with material sound speeds in the range 800–1200 m/s. With longer or thinner cylinders, or with materials having speeds less than 800 m/s, the side-lobe levels increase, and both efficiency and directivity are typically reduced. These effects are predictable from Jacobi's analysis of sound propagation in slow waveguides [J. Acoust. Soc. Am. 21, 120 (1949)].
The motional impedance of an electro-dynamic loudspeaker
Authors: Murray F. M.
Published: October 2005

For many years the electrical equivalent of the motional impedance of an electrodynamic loudspeaker has been represented as a lumped parallel resonant circuit with the tacit understanding that circuit elements do become distributed and that such complications are “beyond the scope of this course.” Recent experiments with high efficiency compression drivers show that these distributed elements can be analyzed and may be very important; in some cases causing cutoff characteristics similar to M-derived filters rather than the classic constant-K filters normally assumed. The author recently presented qualitative results (F. M. Murray and H. M. Durbin, Audio Engineering Society 63rd Technical Meeting, Paper D8) of experiments to control higher-order modes of the motional impedance of such transducers. This paper presents a quantitative analysis to further understand this phenomenon. Some still unresolved questions will be discussed. When fully developed this new theory promises to provide better insight into gross anomalies sometimes attributed to other sources.
A study of stretched harmonies
Authors: Marcus K. T. , Mathews M. V. , Pierce J. R.
Published: October 2005

A class of nonharmonic sounds was synthesized by stretching normal harmonic sounds. Stretching means uniformly expanding the logarithmic frequency ratios between the fundamental frequencies of the tones in a scale and between the fundamental of each tone and its overtones. Stretched passages were studied to see what properties are invariant to stretching. Stretched cords have the same coincidence of overtones as unstretched chords; hence, harmonic perceptions, which depend on overtone coincidence, should be invariant. By contrast, perceptions which depend on periodicity pitch or on the Rameau fundamental bass should be destroyed by stretching. A number of traditional pieces and chords were synthesized in stretched and unstretched forms. These samples were evaluated by (1) informal listening, (2) tests of the identification of the key of the material, and (3) tests of the perception of cadences. Results showed both similarities and differences between stretched and unstretched materials. We believe stretched sounds have perceivable structures that can be utilized in musical compositions.
Rectified diffusion in the presence of surfactants
Authors: Crum L. A.
Published: October 2005

Measurements are reported of the growth of air bubbles by rectified diffusion in water at 22.1 kHz. Values were obtained of both the threshold and the rate of growth of bubbles by rectified diffusion as a function of bubble radius, acoustic pressure amplitude, liquid surface tension, and equilibrium gas concentration. Good agreement with theory was obtained for normal values of the surface tension of water for both the rectified diffusion threshold and the growth rate. With addition of a surfactant, measured values of the threshold and growth rate deviate from the calculated values, the disagreement becoming considerable at large surfactant concentrations (low surface tension). Surface-wave activity of the bubble that would increase the diffusion rate by acoustic streaming was not observed at low bubble radii and is not thought to be the cause of the disagreement. A possible explanation is given in terms of the retardation of gas diffusion by the surfactant monolayer on the surface of the bubble. [Work supported by the Office of Naval Research.]
Maintenance of cochlear function with synthetic blood and effects of potassium deficiency
Authors: Thalmann R. , Kambayashi J. , Wada J. , DeMott J. E. , Marcus D.
Published: October 2005

We have recently described a method for the vascular perfusion of the guinea pig cochlea with synthetic blood, using the flurocarbon FC 47 as oxygen carrier [Wada et al., Laryngoscope (1979) (to be published)]. We have now determined that the endolymphatic potential (EP) and the cochlear microphonics can be maintained at normal or near normal levels for perfusion periods exceeding 300 and 150 min, respectively. However, the compound action potential (N1) cannot be maintained for longer than 60 min. This finding may be of considerable significance for blood substitute technology in general, since N1 could be the most sensitive indicator of adverse effects of synthetic blood known to date. In other experiments we found that the EP can be maintained at normal levels for 25.3 ± 6.9 (SD) minutes by K+-free vascular perfusion. By contrast, the EP starts to decline immediately if perilymph is replaced by K+-free media [Marcus et al., J. Acoust. Soc. Am. Suppl. 1 65, S13(A) (1979)]. The possible implications of these findings with regard to the mode of generation of the EP will be discussed. [Supported by the NIH and NSF.]
Levels of putative neurotransmitters, glutamate and aspartate, in cochlear fluids and cell layers of organ of Corti
Authors: Thalmann I. , Thalmann R. , Marcus D. C. , Comegys T. H.
Published: October 2005

Glutamate and/or aspartate have been proposed as transmitters in acoustico-lateralis systems. We analyzed these substances in cochlear fluids of guinea pigs and in cell layers of organ of Corti of chinchillas. Fluids were collected with utmost care to avoid contamination. Concentrations of aspartate were 2.6 ± 1.2 (SD) and 16.3 ± 3.5 μM in perilymph and endolymph, respectively. Corresponding values for glutamate were 11.9 ± 5.0 and 74.0 ± 6.5 μM. Aspartate exhibited a gradient in whole organ of Corti [52 units (mmoles/kg dry weight) in third versus 109 units in basal turn]. No specific accumulations were seen in inner or outer hair cell layers; in fact, concentrations were highest in Hensen and Claudius cells. Glutamate exhibited only a slight gradient in organ of Corti (60 units in basal versus 81 units in third turn). Levels were similar in outer hair cell layer and supporting cells, but significantly lower in inner hair cell layer. No definite conclusions about a possible transmitter role of either substance can be drawn from these data. [Supported by NIH and NSF.]
The acoustical inverse problem for the cochlea
Authors: Sondhi Man Mohan
Published: October 2005

A knowledge of the spatially varying mechanical properties of the basilar membrane (BM) allows one to compute acoustical properties of the cochlea, e.g., the transfer function from stapes to a point on the BM. However, to the best of our knowledge, direct measurements of BM properties have not been reported in the literature. Rather, these properties are “estimated” by trial and error so as to give a reasonable match to measurements of the above-mentioned transfer function. In this talk we will show how the BM stiffness K(x) may be determined directly from a time-domain measurement of the input impedance at the stapes (i.e., from a measurement of the pressure developed just inside the stapes in response to an impulse of stapes velocity).
AP responses in forward-masking paradigms and their relationship to responses of auditory-nerve fibers
Authors: Abbas Paul J. , Gorga Michael P.
Published: October 2005

The amplitude of N, peaks of whole-nerve AP was measured in cats using a tone-burst probe with tonal maskers in a forward-masking paradigm. Experiments examined the effects of masker level, frequency, and duration (Tm), as well as interstimulus interval (Δt). Results are consistent with the interpretation that amplitude of N1 reflects activity of a limited group of fibers with CF near the probe frequency. For single fibers, decrement in discharge rate (relative to an unmasked condition) is dependent upon rate to the masker [Smith, J. Neurophysiol. 40, 1088–1112 (1977)]. For the AP, decrement in probe-elicited amplitude should reflect the rate to the masker in those fibers excited by the probe. Thus, measurements of N1 decrement versus masker frequency and level are similar to single-fiber rate-versus-level functions. Since decrement in N1 reflects amount of adaptation, increasing Tm decreases probe response. N1 amplitude as a function of Tm thus resembles PST histograms of nerve fibers. Finally, plots of N1 amplitude as a function of Δt are interpreted as a measure of recovery from adaptation.
High-frequency sensitivity of the frog basilar papilla confirmed by dye injection
Authors: Leverenz E. L. , Lewis E. R.
Published: October 2005

High-frequency sensitivity (cf. in the range 1000 to 2000 Hz) has been confirmed in the basilar papilla of the bullfrog by recording the responses of single eighth-nerve axons, then injecting those axons with the fluorescent dye Lucifer Yellow, and thereby tracing them to their origins at the periphery. Dye-filled glass micropipettes were used to penetrate primary afferent axons in the posterior branch of the eighth cranial nerve medial to its emergence from the intact otic capsule with intact circulation. All axons that we have traced to the basilar papilla have been of the high-frequency type [Feng et al., J. Comp. Physiol. 100, 221–229 (1975)], while all units that we have traced to the amphibian papilla have been of the low- or mid-frequency type. So far, all primary afferent axons traced to the basilar papilla have been unbranched and have innervated one or perhaps two hair cells. Our direct observations of high-frequency sensitive fibers emanating from the basilar papilla confirm the conclusions drawn previously by Frishkopf, Capranica, and Goldstein [Proc. IEEE 56, 969–980 (1968)]; Fend et al. (op. cit.); and others.
Airborne noise reduction of surface ship propulsion gearboxes and forced draft blowers
Authors: Thomas Edward V.
Published: October 2005

Five surface ships were treated with a propulsion gearbox two-phase cladding—damping treatment. The effects of treatment installation procedures on airborne noise reduction were evaluated as a function of ships speed. Two surface ships were treated with developmental antireflective airborne noise treatments to reduce forced draft blower noise levels. A resonant sound absorber was installed in another ship to reduce forced draft blower noise.
Analysis and prediction of the planetary boundary layer using an integrated sodar-model measurement system
Authors: Thomson D. W. , Logan M.
Published: October 2005

The surface concentration at a given location of passive pollutants emitted from surface or elevated sources depends upon the effective source height and the environmental vertical wind and temperature profiles. By automated sequential application of widely used boundary-layer inversion rise and structure, and plume rise and diffusion models in the signal processing computer of the Penn State Doppler Sodar System, measurement and modeling functions have been combined. Thus, the computer outputs not only current meteorological conditions but also predicted boundary-layer development and plume characteristics. Since environmental impact data rather than raw meteorological measurements are output, application of the system for techniques such as supplementary control system technology is greatly facilitated. The hardware and software design of this unique acoustic sounding system are presented and a demonstration including a movie are given of its application to a power plant high stack diffusion problem.
Acoustically induced turbulence and shock waves in resonance tube
Authors: Chou Kiang H. , Lee Paul S. , Shaw David T.
Published: October 2005

Experimental investigations of acoustically induced turbulence and shock waves in a resonance tube are performed. Frequency (f) and intensity (I) effects of the acoustic field on turbulence and shock waves are studied using hot-film anemometer and FFT data processing unit. Measurements were made at the tube center and at approximately 1 mm from the wall at locations corresponding to loops and nodes of the standing waves. Sampled data were first conditioned then processed to estimate the characteristics of turbulence (Taylor microscale, the integral scale, autocorrelation, crosscorrelation, and power spectrum density). It is found that for sound pressure level (SPL) ≳ 162 dB and frequencies within a narrow band (∼20 Hz) around the resonance frequency, shock wave formation appears. Turbulence measurements were performed over a frequency range of 680–2740 Hz, with intensity over a range of 1.1–3.8 W/cm2. Below I = 1 W/cm2 no turbulent bursts are found. The turbulent power spectral density F and the wavenumber k are found to satisfy a power law F ∝ kα with α ≃ −1.6 to −2.1. The rms turbulent velocity u is experimentally found to have a I1/2 dependence, yet relatively insensitive to variation of f. Throughout the whole measuring range of f and I, the rate of energy dissipation per unit mass ε is estimated to be 106 ∼ 107 cm2/s3. Special emphasis on ε is made as it vastly affects the agglomeration rate of the aerosol in the physiochemical processes.
Measuring frequency response functions on operating systems
Authors: Keller Anton C.
Published: October 2005

In studying dynamic behavior of mechanical systems very often a three-step approach is used. In this classic approach, Step 1 involves analyzing actual running characteristics of a machine, structure, or process. Step 2 involves the determination of frequency response functions between various locations on the test system. Step 3 may then involve extraction of specific characteristics of the system such as structural mode shapes, damping parameters, stiffness values, or system resonant frequencies. Often it is quite possible to extract a good understanding of possible system design problems strictly from an analysis of operating data. However in most cases, the second step will usually involve a measure of selected frequency response functions through the use of external stimulus. In the past, this has almost certainly meant that the operating system would have to be shut down and basically be in a “static” state before artificial excitation could be furnished and the frequency response function measured. This has sometimes been impractical for several reasons. First, there are cases when a system must actually be operating before its real dynamic characteristics can be extracted. This would be the case, for example, if fluid film bearings represent a part of a total system dynamic. On the other hand. system operating characteristics may interfere with the very frequency response function which is to be determined. This could be the case in a rotating turbine blade where forced vibration responses would always be present in the output or in the case of a biological system measurement which might continually include the effects of heartbeat. In each of these cases, the system must continue to operate during a frequency response measurement but it is somehow necessary to eliminate the operating characteristics from measured frequency response functions. This paper examines the classical techniques which have been used to extract frequency response information and some of the reasons why it has not been possible or conveniento eliminate running data from the desired measurement. An alternative approach is then given which has now been implemented in hardware and which offers a significant signal-to-noise enhancement over traditional techniques making it entirely feasible to extract complete frequency response information from operating dynamic systems.
The impact of new technology on instrumentation for shock and vibration measurement
Authors: Huber William C.
Published: October 2005

The dramatic evolution of new acoustic and vibration instrumentation is being driven by integrated circuit technology. Development of new microprocessors and analog processing circuits has enhanced the current generation of instrumentation, and in the next few years this trend will continue. Additional capabilities and new measurement techniques are being added rapidly. Several system architectures and developments in the area of FFT (Fast Fourier Transform) and digital and analog filtering are described.
Maximizing shock response spectra by wavelet parameter adjustment
Authors: Usher Theron
Published: October 2005

The Time/Data TDV-20 is one of a number of shock synthesis systems used with power amplifier-shaker systems to provide specified shock response spectra (SRS). The TDV-20 drives the power amplifier with a signal containing a number of finite-length, weighted-amplitude, sinusoidal wavelets. The center frequencies, lengths, and relative time delays of the wavelets can be specified by the operator. Selection of these parameters within the limitations of other system constraints is discussed so that the SRS measured at the shaker table may be maximized.
Active vibration isolation systems
Authors: Wilson J. N.
Published: October 2005

The need for improved isolation for operators of off-road vehicles is discussed. Referring specifically to agricultural vehicles, a review is made of some of the approaches taken in North America and Europe to improve seat suspension systems. Data comparing the performance of active and passive systems is presented. The presentation will be supplemented with slides and film strips.
The forced vibrational response of a rectangular parallelepiped with stress-free boundaries
Authors: Hill Eric V. K.
Published: October 2005

Most of what is known about the nature of acoustic emission sources has been learned through the use of piezoelectric transducers coupled to rectangular parallelepiped or plate-type specimens. Unfortunately, the output of the piezoelectric transducer is not a true picture of the source signal; rather, it is the acoustic emission signal modified by the responses of the specimen, the specimen-transducer interface, and the transducer. As a first step in determining what acoustic emission looks like, this paper presents a closed-form normal mode solution for the forced vibrational response of a rectangular parallelepiped with stress-free boundaries. Knowing the specimen response will allow the calibration of piezoelectric transducers for all three wave types—dilational, transverse, and surface waves—and this, in turn, will allow the characterization of acoustic emission sources.
Sound-level fluctuations in a multipath environment
Authors: Neubert J. A.
Published: October 2005

For each array sensor j in a medium of M multipaths, the composite sound-level mean-squared sound-level fluctuation (χ′j2)¯ can be found by a complicated development to be constructed from the summation of the individual multipath mean-squared sound-level fluctuations (χ′mj)2)¯ and of the multipath mean-square phase fluctuation (θmj2)¯ where χ = In A, A is the signal amplitude and m = 1, 2, …, M. Applying the appropriate fluctuation relations from Tatarski [Wave Propagation in a Turbulent Medium (McGraw-Hill, New York 1961)] and Schvachoko [“Sound fluctuations and random inhomogeneities in the ocean,” Sov. Phys-Acoust. 13, 93 (1967)], the result is (χ′j)2¯ ≃ 4Mμ̄2Lnk02R, where μ̄2 is the mean-square sound-speed fluctuations, Ln is integral scale, K0 is the wavenumber and R is the range. [Work supported by NAVELEX Code 320.]
The effects of boundary condition approximations on coupled mode theory
Authors: Rutherford Steven R. , Hawker Kenneth E.
Published: October 2005

This paper examines the effect of boundary condition approximations that are inherent to the coupled mode theories proposed by Pierce [J. Acoust. Soc. Am. 37, 19–27 (1965)] and Milder [J. Acoust. Soc. Am. 46, 1259–1263 (1969)]. The boundary condition approximation that is investigated involves the replacing of the continuity of the normal component of partial velocity boundary conditions with the continuity of the z component of partial velocity boundary conditions at sloping interfaces. This approximation is necessary in order to carry out the partial separation of depth and range variables effected in the mathematical formulation of the theory. This paper will show that a consequence of this approximation is that coupled mode theory applied to propagation media with nonhorizontal boundaries does not conserve energy. It will also be shown that a correction to coupled mode theory may be derived such that the proper boundary conditions are satisfied and energy is conserved, both to first order in the local bottom slope. Numerical examples will be presented which illustrate the nonconservation of energy effect and the proposed corrections to the theory. [Work supported by the Naval Ocean Research and Development Activity and the Naval Electronic System Command.]
Comparison of range-dependent propagation models
Authors: Bucker H. P.
Published: October 2005

It is difficult to compare range-dependent propagation models because there are no known solutions that combine realistic bottom interaction and range changes. However, a necessary requirement of a useable model must be reasonable agreement between the model and exact solutions when there is no range dependence. To show this agreement, a four-step procedure is suggested: (1) range average of the sound levels to remove small scale fluctuations; (2) make contour plots of the difference in sound levels between the tests and exact solutions as a function of range and depth; (3) make continuous plots of the mean ± standard deviation of the sound level difference averaged separately over near surface, mid-water, and near-bottom depths; (4) a written analysis by an experienced acoustician explaining the significance of the above data. These procedures will be demonstrated by comparison of FFT and Crank-Nicolson solutions of the parabolic equation with the exact normal mode solution for the case of liquid layer lying over a liquid half-space. [Work supported by NORDA, Code 500.]
Exact decomposition of bottom interacting paths via a generalized reflection coefficient expansion
Authors: Deavenport R. L. , Jensen E. P. , DiNapoli F. R.
Published: October 2005

The exact range independent acoustic field for an arbitrarily structured multilayered medium may be expressed as a Fourier-Bessel integral involving generalized reflection coefficients. One obtains upon evaluation the total result due to all possible bottom interactions. It is desirable for some applications to decompose this total field result into path type contributions without incurring the approximations associated with ray theory. This is accomplished by first recognizing that the generalized reflection coefficient may be written in terms of partial local reflection coefficients. An infinite series of integrals results when the term in the kernel containing the local coefficients is expanded. Each term in this expansion then contains combinations of various local reflection coefficients which can be readily interpreted as the desired path contributions. The spatial amplitude and phase dependence is obtained by evaluating each term separately using the fast field program technique. Examples will be presented for a fluid subbottom structure having both constant and exponential depth dependent sound speed. [Work supported by NAVSEA 63D and NORDA 500.]
Born series sums for wave propagation in anisotropic, random media
Authors: Meecham W. C. , Tavis M. T. , Yura H. T.
Published: October 2005

The Born series for random wave propagation is considered for the physically interesting regime: the radiation wavelength short compared with the correlation lengths of the medium and the range large compared with such lengths. We treat a Gaussian medium with a Gaussian-form correlation function. These specializations lead to integrals for the moments with integrands which are themselves mainly of Gaussian form and can be performed algebraically using multivariate Gaussian distribution formulas. Specifically, for moments the, say, eighth-order Born term involves a 24-fold integration of which 16 can be done algebraically using the formulas. We are able for a two-scale anisotropic medium to sum the Born series for the first and second moments of the radiation field. The results reduce to familiar ones when we specialize to isotropic media. A novel characteristic is that for certain parameter ranges where the vertical medium scale Lv is very small compared with the horizontal scale LH diffraction effects can substantially reduce the phase variance, thus reducing the randomizing effect of the medium on the propagated field. Anisotropy also leads to an intensity dependence on angle. The fourth-order moment, the intensity correlation, is considered through fourth-order Born terms, it not being possible to sum the Born series in terms of simple functions for this moment. It is found that the propagating field is far from Gaussian for ranges of a few to many scattering lengths when diffraction effects are slight; specifically, when the Fresnel length for the vertical medium scale is much greater than the scattering length. On the other hand, the fourth-moment approaches the usually expected Gaussian form for moderate ranges in terms of scattering lengths when the Fresnel length is very small compared with that length. Validity ranges for the intensity correlation are established showing that summing through the fourth-order Born gives good results through part of the intermediate range preceding saturation of the field, depending upon the parameters discussed. For ranges where diffraction effects are not strong, the field is far from normal as judged by the intensity variance.
The directional dependence of normal mode attenuation due to scattering from a rough ocean surface
Authors: Chapman David M. F.
Published: October 2005

Using the boundary condition for the coherent component of sound at a rough ocean surface due to Kuperman and Ingenito [W. A. Kuperman and F. Ingenito, J. Acoust. Soc. Am. 61, 1178–1187 (1977)], the actual directional dependence of the normal mode attenuation coefficients can be determined for attenuation due to scattering from a rough ocean surface whose surface variance spectrum has a cos2φ anisotropy. Each normal mode has a directional attenuation of the form an + bncos2θ, with the azimuthal angle of propagation θ being measured from the wind direction, and the coefficients an and bn being calculated from the eigenfunction and eigenvalue of the nth normal mode and the radial portion of the variance spectrum, which is arbitrary.
Numerical tests of parabolic equation algorithms for field computations over totally reflective three-dimensional bottoms
Authors: Dicus Ronald L. , Wright Evan B.
Published: October 2005

Computations with two- and three-dimensional versions of the parabolic equation (PE) split-step Fourier algorithm were compared with normal mode theory and diffraction theory to ascertain the adequacy of PE computations for propagation over a totally reflective bottom. All PE computations were for 10 Hz in a constant sound speed water column with discrete depth and range steps of 20 and 100 m, respectively. Totally reflective bottom boundaries were simulated by a discontinuous fluid sound speed at grazing angles less than critical. Transmission loss over a flat 13° critical angle fluid bottom reproduced essentially the same structure as given by normal mode theory for ranges less than 200 km. PE computations of the field near the edge of a perfect reflector provided a reasonable approximation of the general features exhibited in diffraction theory results. Swept beam three-dimensional PE computations incorporating reflections from an arbitrarily inclined plane correctly displayed reflected beams at angles in agreement with geometrical considerations. Implications for computation of propagation effects over realistic bottoms composed of three-dimensional sediment or rock facets are discussed.
The effect of sediment rigidity on bottom reflection loss
Authors: Vidmar P. J.
Published: October 2005

The effect of sediment rigidity on bottom reflection loss, RL = −20 log10 (|R|) where R is the plane wave reflection coefficient, is studied using a computational model [P. J. Vidmar and T. L. Foreman, J. Acoust. Soc. Am. 65, S43 (1979)]. A single inhomogeneous turbidite layer overlying a homogeneous substrate is treated with an emphasis on low frequencies (10–200 Hz) and low grazing angles (0°–45°). We find that sediment rigidity can be neglected for thick (∼500 m) layers while it can produce significant increases in RL for thin layers (∼36 m). The frequency dependence of RL for thin layers has a low frequency regime characterized by large peaks (∼25 dB) recurring at short (∼2 Hz) intervals. At high frequencies there remains a persistent increase in RL (∼4 dB). A ray picture, based on an expansion of the reflection and transmission coefficient in the small sediment S wave speed, provides a basis for understanding these results. The most important mechanism for sediment S wave excitation is found to be compressional wave conversion at the sediment-substrate interface. [Work supported by the Naval Ocean Research and Development Activity and the Naval Electronic Systems Command.]
Three-dimensional ray trace studies over a rough ocean bottom topography
Authors: Giellis G. R.
Published: October 2005

In sea areas where long-range acoustic propagations involves repeated bottom reflection, it is essential to consider the three-dimensional aspect of the reflection. Computational methods by DeWitt [J. Acoust. Soc. Am. 62, S19(A), (1977)] have been extended to include horizontal changes in the sound speed profile and bottom loss at each reflection. It is now possible to study horizontal ray deflections in areas containing a mid-ocean ridge. An area of 120 000 km2 of sea bottom is represented by triangular facets developed from a grid of bathymetric points at one km intervals. This completely describes the bottom to the degree that it is presently known from the best existing charts. Sound speed profiles can change at large zone boundaries but horizontal refraction is neglected. Bottom reflection losses are calculated as a function of grazing angle for each bottom bounce of the ray. Rays which have accumulated a loss greater than a selected threshold can then be discontinued. Illustration and conclusions of the study will be given.
Array measurements of long-range, low-frequency signal propagation in the seabed
Authors: Baggeroer Arthur B.
Published: October 2005

Multichannel arrays and high-resolution velocity analysis have been used to measure the characteristics of low-frequency (5–20 Hz} signals propagating over long ranges (10–100 km) in the seabed. The ability to resolve the various paths both spatially and temporally has provided unique measurements of (i) the partitioning of the energy in the paths versus range, (ii) the behavior near critical angles for both refracted compressional and shear waves, (iii) multipath effects due to local inhomogeneities such as seamounts, and (iv) multiple reflected signals that are more intense than their corresponding direct paths. Multichannel data from both thickly and thinly sedimented regions has been employed in making these measurements. [Work supported by ONR.]
The structure of simple and composite convergence zones
Authors: Walkinshaw H. M.
Published: October 2005

Progressive stages in the development of RSR convergence zones were shown in the previous paper [“A Quantitative Definition of Depth Excess—How Much Is Enough?,” J. Acoust. Soc. Am. Suppl. 1 65, S15 (1979)] to form a convenient set of criteria for defining depth excess. This present paper uses both parabolic approximation and ray diagnostic codes to explore general properties of simple and composite convergence zones and to show how changes in the arrival structure of waterborne paths give rise to corresponding changes in sound transmission with range. The role of the surface grazing ray, retrograde-range smooth “caustic” ray, and recursive ray in determining RSR zone width and intensity are described. Similar ray analogs are developed for RR convergence zones with cusped caustics and for composite RR-RSR convergence zones. The effect of source/receiver geometry on zone structure asymmetry and zone width are demonstrated for shallow and deep sources with receivers at source depth and reciprocal (conjugate) depth. The supporting calculations were made at 100 Hz to 200 nmi for shallow (18 m) and deep (152 m) sources at four water depths (3840, 4145, 5030, and 5500 m).
Dispersion of sound in a combustion duct by fuel droplets and soot particles
Authors: Miles J. H. , Raftopoulos D. D.
Published: October 2005

Dispersion and attenuation of acoustic plane wave disturbances propagating in a ducted combustion system caused by fuel droplet and soot emissions from a jet engine combustor are studied. The attenuation and dispersion are due to heat transfer and mass transfer and viscous drag forces between the emissions and the ambient gas. Theoretical calculations show sound propagation at speeds lower than the isentropic speed of sound at low frequencies. Experimental results are in good agreement with the theory.
Flyover noise of a wide body aircraft
Authors: Lanter S. K. , Shivashankara B. N. , Strout F. G. , Ayyagari R.
Published: October 2005

Aircraft noise in the vicinity of airports is a well-recognized problem. Rules and regulations are in effect that set limits on the noise levels of aircraft. Although the airplanes in the commercial fleet meet the appropriate regulations, there is always a constant effort within The Boeing Company to lower the noise levels. This requires a thorough understanding of the source mechanisms and propagation effects. The total noise of an airplane is composed of engine noise and airframe noise. The engine noise itself includes various components such as jet, core, fan, and turbine noise. There has been a lack of good quality flight noise data base, especially for wide body aircraft with high bypass ratio engines. To alleviate this, several test programs have been completed within The Boeing Company. The results of one of these programs, the test of a Boeing 747 airplane fitted with Pratt and Whitney JT9D engines, are presented in this paper. From the noise results, regions of jet noise dominance, fan noise dominance, and core noise dominance are identified. Methodology that will be used for more accurate breakdown of the noise components in regions where they are not dominant is outlined.
Large scale model measurements of air frame noise using cross correlation techniques
Authors: Miller W. R. , Meecham W. C. , Ahtye W. F.
Published: October 2005

Cross-correlation techniques are used to measure the sound radiated by wing/flap airfoil configurations in the NASA-Ames 40- by 80-ft wind tunnel using a 5.8-m-high model, with three deployed flaps. The sound from flap corners exceeds other airframe noise by 10 dB and more; the noise from the leading, outbound corner of the leading flap seems to be the strongest. The sound is estimated using two formulas based on standard aeroacoustic theory and one method using the near-, farfield crosscorrelation; this last is essentially independent of such theory—all three are in fair to good agreement with one another. The classic dipole angular distribution pattern for one dipole is compared with measurements; it is found that there is qualitative but not quantitative agreement. The dependence of intensity on U0 is roughly, though not exactly, U06, where U0 is the free stream speed. The turbulence length scales on the flap surface as determined by the characteristic time of the measured correlation function and the free stream speed, are from a few to many centimeters, on the order of the flap thicknesses. Time delays from the correlation between the far field signal and the surface source are determined from the correlation functions and are in good agreement with the flow-refraction-corrected results.
Assessment at full scale of exhaust nozzle-to-wing size on STOL-OTW acoustic characteristics
Authors: Glahn U. von , Groesbeck D.
Published: October 2005

On the basis of static aero/acoustic data obtained at model scale, the effect of exhaust nozzle size on flyover noise is evaluated for different STOL-OTW nozzle configurations. Three types of nozzles are evaluated: a circular/deflector nozzle mounted above the wing, a slot/deflector nozzle mounted on the wing, and a slot nozzle mounted on the wing. The nozzle exhaust plane location, measured from the wing leading edge was varied from 10% to 46% of the wing chord (flaps retracted). Flap angles of 20° (takeoff) and 60° (approach) are included in the study. Initially, perceived noise levels (PNL) are calculated as a function of flyover distance at 152 m altitude. From these plots static EPNL values, defined as flyover relative noise levels, then are obtained as functions of nozzle size for equal aerodynamic performance (lift and thrust). On the basis of these calculations, the acoustic benefits attributable to nozzle size relative to a given wing chord size are assessed.
Intermediate range explosion airblast propagation measurements
Authors: Reed J. W.
Published: October 2005

Several hundred explosions of TNT, ranging in weight from 23 to 1134 kg, were fired at the NASA Space Center, Florida. Comprehensive meteorological measurements were made by rawinsonde balloons and on a nearby 150-m tower, including winds, turbulence, temperatures, and humidity. A cruciform array of airblast gauges was operated, with gauges at 200 m, 500 m, 1 km, 2 km, and 5 km ranges from the explosions. Airblast results will be correlated against refractive atmospheric conditions, in hopes of establishing a functional relationship between overpressure decay with distance and the sound velocity gradient with height. Preliminary results of the analyses will be presented. [Work supported by DOD, DOE, and NASA.]
Determination of two-stroke engine exhaust noise by the method of characteristics
Authors: Jones Adrian D.
Published: October 2005

A unique computational technique was developed for the method of characteristics solution of a one-dimensional flow in a duct as applied to the wave action in an engine exhaust system. By using the method it was possible to compute the detailed unsteady flow in both straight pipe and tuned expansion chamber exhaust systems as matched to the flow from the cylinder of a small two-stroke engine. The radiated exhaust noise was then determined by assuming monopole radiation from the tailpipe outlet. Very good agreement with experiment on an operating engine has been achieved in the calculation of both the third-octave radiated noise and the associated pressure cycles at several locations in the different exhaust systems. Of particular interest is the significance of nonlinear behavior which results in wave steepening and shock wave formation. The calculation method developed differs from those of others, principally that of Blair and that of Karnopp, Dwyer, and Margolis. The method computes the precise paths on the x−t plane of a finite number of C+, C−, and P characteristics, thereby obtaining high accuracy in determining the tailpipe outlet velocity and hence radiated noise.
The influence of solid bodies on low mach number vortex sound
Authors: Obermeier F.
Published: October 2005

The mechanisms of sound generation by unsteady, subsonic flows in the presence of solid boundaries are investigated. For that purpose an alternative integral representation for the radiated pressure field is applied which is different from the generally used integral representation introduced by Lighthill and Curle. The main advantage of our method consists in a linear dependence of its integrand on the time derivative of the vorticity fluctuations in the hydrodynamic near field, while the ordinary Green's function has to be substituted by a “vector Green's function.” This vector Green's function can be chosen for the flow fields appropriate in such a way that surface integrals do not appear. In particular the paper is concerned with two-dimensional flow and sound fields caused by a pair of spinning vortices and superimposed stationary potential flows along a finite plate or around a cylinder. Analytical solutions are determined by applying the method of matched asymptotic expansions.