bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic transmission loss of pipes excited by internally propagating plane waves
Authors: Rennison D. C. , Brown G. L.
Published: October 2005

A control valve constitutes a source of mechanical vibration, nearfield imcompressible pressure fluctuations and radiated acoustic waves. An ideal mechanical vibration filter placed several wavelengths from the source will remove the influence of the first two excitations from the response of the downstream pipe. The internal propagation of acoustic energy, however, is unaffected and so the transmission loss of pipes to these propagating waves is of concern. In the plane-wave region, Morfey, Heckl, and others have measured acoustic radiation far greater than their estimates. This work has been directed towards explaining these differences. Experiments with plane acoustic excitation of steel and P.V.C. pipes were performed. Different gases were used inside the P. V. C. pipe, for which the wall response was forced, to investigate the radiation from subsonic and supersonic axisymmetric wave motion. Close agreement was found, in contrast to the case of steel pipes, where a strong resonant response occurred. This theoretically unpredicted resonant response (which was about 45 dB above the forced estimate) contained all resonant modes but was dominanted by the modes with the highest circumferential mode order. The acoustic radiation, however, was greater than the forced estimate by only 25 dB, since it is determined by the most efficient radiators—the n=1 “bending” modes. Only these latter modes are damped by the pipe supports; the measured Q of these modes was about 100. Similarly these modes are most strongly coupled to the excitation, and consequently the n=1 modes control the radiation. It was found that the application of surface damping treatments caused reductions of 10 to 20 dB in response, but only 2–5 dB in power radiated. This is because surface damping treatments are particularly effective on higher-order circumferential modes and much less effective on the n=1 modes, in which there are no changes in circumferential radius of curvature. It is concluded that a significant reduction in power radiated requires damping procedures directed specifically at the n=1 modes. Experiments in progress suggest that for the pipes studied, a Q less than 20 for n=1 modes is required to achieve the lower bound power radiated corresponding to a forced response.
Speech synthesis from transitions of adjacent phonemes
Authors: Olive Joseph P.
Published: October 2005

Recent work by Olive and Spickenagel [J.P. Olive and N. Spickenaged, “Speech resynthesis from phoneme related parameters,” [J. Acoust. Soc. Am. 57, S2 (A) (1975)] has suggested that the spectral parameters of natural speech, specified in terms of LPC derived area parameters, can be linearly smoothed between phonetic boundaries without apparent loss of the resynthesized speech quality: Phonetic boundaries were defined as the end points of the “steady states” of the phonemes, and of the transitions associated with successive phonemes. We have now investigated whether the data obtained from such segmentation can also be applied to speech synthesis; in particular, whether such transitions can be used in a context different from the context from which they were obtained. Speech was synthesized in the following manner:. The end points of transitions were connected by straight lines to specify area parameters which would simulate the steady states and transition regions; the duration, amplitude and intonation were copies from natural speech. The resultant speech was highly intelligible as well as continuous.
Boundary-damped panel vibrations
Authors: Hale M. E. , Chalupnik J. D.
Published: October 2005

Boundary-layer noise generation has motivated a one-dimensional sinusoidal vibration study of a narrow flat aluminum panel. The understanding of the response of this continuous system to sinusoidal excitation yields practical information which directly relates to the random excitation of the same system. Partial coverage extensional damping layers bonded to the fixed end of the panel were investigated using traveling-wave theory, transmission-line theory, and experimental analysis. These techniques establish the useful concept of an “impedance panel,” analogous to the acoustical impedance tube, which can be used to determine the complex termination impedance of any type of attaching method used with a supporting structure, whether a damping treatment is applied or not. The boundary or termination-type damping is shown to be more effective than a total coverage extensional damping layer of equal mass. Termination damping layers which gradually introduce the damping to an incident bending wave were shown to be significantly more effective than abrupt-type flat slab damping layers of equal mass. [Part of first author's Ph.D. dissertation.]
Determination of sound power of coupled machines
Authors: Wells R. J.
Published: October 2005

Several procedures are available for the determination of the sound power level of machines in normal environments. Most of these give adequate results for single medium-sized equipment, but difficulties arise in extending the concepts to large coupled machines. [“Evaluation of Proposed ASME PTC 36 Code for Sound Power Level Determination of Large Steam Turbine Generators,” S.E. Grabkowski, J. MacDonald, and T. Van Schaick (General Electric Company), to be presented at Fall 1975 ASME meeting.] Much of the problem is because the direct acoustic field of a component machine may not extend to as much as one foot from its surface due to reverberation from other components. A procedure is suggested in which all acoustic measurements are confined to surfaces near each component machine. Correction is made for the reverberant acoustic field of the entire environment. The correction procedure utilizes reverberation time determinations from impulsive noise tests; and applies a Monte Carlo approach to the problem of correcting for nearfield effects in the evaluation of sound power. An iterative computation is employed. Comparisons with free-field sound power determinations are shown.
Reduction of acoustic and infrared emissions from a mil. std. 1.5-kW engine-generator set
Authors: Remington P. J. , Rudd M. J. , Gaddy L. , Summerson W.
Published: October 2005

This is a report of a program conducted jointly by Bolt Beranek and Newman and the U.S. Army Mobility Equipment Research and Development Center. The program was to reduce the acoustic and infrared emissions from a MIL. Std. 1.5 kW gasoline engine-generator. A goal for inaudibility at 100 m in a jungle environment is derived and a feasibility study conducted into ways of achieving it. Of equal importance is the provision of adequate cooling for the engine generator so that it can operate over the temperature range −50°F to +125°F. A new exhaust muffler was designed for the engine, an aluminum enclosure was employed, based upon a standard transit case lined with fiberglass and perforated metal, and new vibration mounts were used. Separate lined inlet and exhaust ducts were employed for the cooling air and inadvertent internal recirculation of the air was prevented. Adequate cooling was then obtained over the whole temperature range. A total noise reduction of 23 dBA was achieved for a unit with a final weight of 217 lb and a volume of 9.5 ft3.
Acoustical enclosures as an effective means of reducing noise: Four case histories
Authors: Peppin Richard J.
Published: October 2005

The use of enclosures is a standard noise reduction technique. In general, the expected insertion loss of an acoustical enclosure is usually considerably greater than that measured after the enclosure is erected. This paper presents the results of a survey of four acoustical enclosures which was undertaken to determine their acoustical effectiveness after installation. Each was manufactured and erected by a different firm and each encloses a functionally similar machine. An employee evaluation of each enclosure with respect to noise, maintenance, and production, was combined with an acoustical survey. The overall effectiveness of the enclosures ran from poor to excellent. Advantages and disadvantages of each are discussed. It is shown that it is possible to achieve a reasonably high noise reduction with enclosures. However, careful construction, design and attenuation to nonacoustical criteria are necessary in order for the enclosure to be practically useful. [Work supported, in part, by National Concrete Masonry Association.]
Measurements of energy flows in impacts
Authors: Graham Holmes D. , Kursmark Robert H.
Published: October 2005

This paper describes experiments designed to measure the spectrum of the vibratory energy injected into structures by impacts. It is felt that if the techniques prove to be feasible, the information provided might be useful in efforts to reduce the noise generated by impact-preducing machines. Two techniques are described. The first requires measurements of the reverberation time of the impacted structure, and of the energy spectrum of the transient acceleration of the structure in response to the impact, observed at many points on the structure. The second requires only a single impact response measurement, and a single measurement of the steady-state response to a steady-state excitation at the impact point. These experimental methods are tested using the impact of a small steel sphere against a large, thin free-free plate. A simple theoretical expression for the spectrum of the injected energy is available for this case. The experimental results are compared to the theoretical prediction.
Noise element of the general plan concept in California: Planning for environmental noise
Authors: Swing J. W.
Published: October 2005

This paper discusses the guidelines and procedures prepared by the California Office of Noise Control for use by local agencies in developing a noise element of their general plans as required in California Government Code, Section 65302 (g). The guidelines created by this office utilize the general plane noise element as the central framework for development of a total noise control program at the local level which includes adoption of a community noise ordinance and enforcement of minimum noise insulation standards for residential dwellings in the vicinity of major noise sources. The overall purpose of the noise element is to cause environmental noise to become a mandatory consideration in the land-use planning process and to recognize severely noise-impacted areas within a city and develop a plan for mitigation of excessive exposure. A parallel objective to correction of situations of excessive exposure is that of protecting those areas whose present noise environment is deemed acceptable. The guidelines include advice on suitable standards for compatible land use (based upon exposure presented in terms of Day-Night Average Level Contours) and recommended procedures for community noise monitoring programs.
Deconvolution of low-frequency ocean sediment acoustic signals. I. Simulation study
Authors: Herstein P. D. , DiNapoli F. R.
Published: October 2005

The previous paper described a Fast Field Program propagation model consisting of two contiguous, semi-infinite, constant sound-speed fluids (ocean and sediment). A point source and a receiver were placed in the ocean above the boundary and varied in range to simulate a (real world) relative type bottom loss measurement. A 100-msec, 50-Hz sinusoidal pulse was transmitted through the ocean to study the reflected and lateral acoustic wave interaction at the boundary. To obtain the acoustic impulse response of the simulated sediment, deconvolution was performed by dividing the spectrum of the sediment interacting acoustic signal by the spectrum of a transmitted (direct path) signal and computing the inverse Fast Fourier Transform. Controlled amounts of Gaussian noise were added to simulate ambient noise. Even low noise levels (S/N=20 dB) were found to degrade the process to a point where the deconvoled signal was no longer discernable. The degree of degradation was determined by comparing bottom reflectivity ratios and lateral and reflected waveforms, after deconvolution, obtained in the absence and presence of noise. Applying averaging and stabilization techniques reduced noise degradation significantly. A 16-mm motion picture camera is requested to show a 5-min film of the modeling results. [This work was sponsored by Naval Sea Systems Command, SEA 06H1-4, A.P. Franceschetti.]
Deconvolution of low-frequency ocean-sediment acoustic signals. II. Experimental measurements
Authors: Dullea R. K. , Herstein P. D.
Published: October 2005

Bubble pulses generated by wide band explosive sources complicate the interpretation of the arrivals from the ocean bottom. However, these arrivals can be deconvolved to remove bubble pulse contamination and yield the impulse response of the ocean sediment. The deconvolution process is degraded by noise; but methods to reduce the noise sensitivity of the process have been developed as described in the previous paper. These methods were applied to ocean-sediment interacted acoustic signals acquired in a deep-water location. Bottom loss values obtained from the deconvolution process were in close agreement with values computed prior to deconvolution. Furthermore, the deconvolution process enhanced the clarification of the acoustic path structure within the sediment and thereby provided experimental verification of the contention in a previous paper that the interaction of ocean-bottom interface reflected arrivals with subbottom reflected and subbottom refracted arrivals can result in a “negative” bottom loss interpretation. Also, as a result of this interaction bottom loss can be (1) experiment configuration dependent, and (2) processing bandwidth dependent at a given frequency. [This work was sponsored by Naval Sea Systems Command, SEA 06H1-4, A.P. Franceschetti.]
Singing corrugated pipes
Authors: Crawford Frank S.
Published: October 2005

A corrugated tube open at both ends, with air flowing through the tube, sings notes which depend on the flow velocity and the length of the tube. The notes it sings are the natural harmonics of the tube. A given note will sing when the flow velocity is such that the frequency at which the air bumps into the corrugations is close to the frequency of the note, provided that the flow velocity is sufficiently high to induce turbulent flow. Study of this phenomenon [F. Crawford, Am. J. Phys. 42, 278 (1974)] has led me to invent a new family of wind instruments I call Corrugahorns. The simplest of these is the Corrugahorn Bugle. It plays harmonics third to about tenth, plus additional notes obtained by tricks (finger flatting, whistle flatting, palm sharpening) that give it almost a complete chromatic scale. The most sophisticated is the Slide Corrugahorn, with a slide (like a trombone) that gives it a chromatic scale over its range. I will demonstrate various singing corrugated pipes, including corrugahorns and another instrument I call the Water Pipe.
Using magnitude estimation to teach about loudness
Authors: Scharf Bertram , Hellman Rhona
Published: October 2005

We have used Stevens' method of magnitude estimation in a number of classes and with individual observers to obtain estimates of the loudness of pure tones. These unpracticed observers give results that mimic the tone scale: They agree that approximately a 10-dB change in sound pressure corresponds to a twofold change in loudness. Such results convince the student of the distinction between loudness, a subjective magnitude, and intensity, a stimulus magnitude. Moreover, the consistency across groups of listeners means that untrained people are able to judge loudness ratios directly. It would then be appropriate and more informative to tell consumers about the loudness or noisiness of products by giving the relative positions of products on a true number scale of loudness, rather than by giving the positions of products on a logarithmic scale of acoustical output.
Education in architectural acoustics
Authors: Wetherill Ewart A. , Scott David M.
Published: October 2005

From everyday contact with the architectural profession, we see clearly that few practicing architects really understand enough about acoustics to apply it effectively in architectural and urban design. This shortcoming can be attributed largely to the lack of acoustics training in architecture schools. Some schools have fortunately progressed beyond the physics survey course to well-taught, practically oriented acoustics courses; but these are few in number, and there is room for much wider extension of acoustics training. This paper presents a brief outline of the information that a student could acquire in a basic acoustics course and should know before graduation.
Propagation-loss model assessment at low frequencies in a bottom-limited region
Authors: Gartrell G. , DiNapoli F. R. , Powers M. R.
Published: October 2005

One series of the Project “BILL” (B_elow and I_n L_ayer Propagation L_oss) measurements was conducted at 100 Hz during December 1973 in the Tongue of the Ocean, Bahama Islands, at a water depth of approximately 6000 ft. A pulsed CW acoustic projector was towed at a depth of 250 ft in a well-defined surface duct, along an accurately determined track to a range of 40 kyd. The pulses were received at hydrophones located both in and below the surface duct. Despite excellent experimental control, predictions from various propagation-loss models have been unable to reproduce major trends in the data. Although no firm conclusions are possible, the paper discusses several possible contributory causes for the discrepancies, major among these being inadequate bottom modeling. Implications for future trends in the development of low-frequency propagation-loss models for bottom-limited regions are briefly examined. [Work supported by Naval Material Command (MAT 03L4) and Naval Sea Systems Command (SEA 06H1).]
Preliminary investigations of the ocean bottom impulse response at low frequencies
Authors: Dicus Ronald L.
Published: October 2005

Impulse responses of an abyssal plain ocean bottom were measured at grazing angles from 82° to 5°. When low-pass filtered at 100 Hz, the impulse responses consisted of only two arrivals. First arrivals corresponded to the water-sediment interface reflection, and second arrivals were attributed to sound refracted through the ocean bottom. The Rayleigh reflection equation was fitted to the measured reflection coefficients of first arrivals to determine an effective low-frequency sediment density and interfacial sound velocity. Theoretical arrival times of the refracted signals were computer from the sediment sound velocity model c(z)/c0 = (1 – 2pz/c0)−1/2, where c0 and p are the interfacial velocity and velocity gradient at z=0, and z is the depth in the sediment. Model parameters were determined by fitting theoretical to observed arrival times of the refracted pulse. The interfacial sediment sound velocities determined from the two independent methods agreed within 1%. Based on these results theoretical impulse responses were computed using Airy functions, which were in good agreement with measured impulse responses.
Surface-ducted contributions in shallow water sound transmission
Authors: Bray A. V. , Friedman A. J. , Rosenblum Larry
Published: October 2005

The relative importance of ducted energy under shallow water isogradient propagation conditions has been estimated using an extension of a shallow water propagation model developed by P.W. Smith Jr. [J. Acoust. Soc. Am. 50, 332–335 (1971)]. The ratio, Ed/Et of the ducted energy to the total energy is theoretically predicted for given environmental conditions. The study shows that for moderately large (greater than 50) range to depth ratios and nominal positive gradients (0.01 to 0.1 sec−1) the surface ducted energy is the dominant feature of shallow water transmission loss. In positive gradient conditions Ed/Et is found to be insensitive to bottom-loss estimation errors. For a wide variety of environmental conditions it is demonstrated that transmission loss for purely ducted propagation does not differ significantly from total transmission loss. The study provides theoretical confirmation of previous heuristic results.
Tissue concentrations of ethacrynic acid and inhibition of enzymes and electrophysiological responses in the cochlea
Authors: Paloheimo S. , Thalmann R.
Published: October 2005

Tissue concentrations of 14C-ethacrynic acid (EA) were determined in cochlear structures following perilymphatic perfusion. In the stria vascularis steady state levels were reached within 30 min and closely corresponded to the concentrations of the perfusion media within the range tested (5×10−4–5×10−3 M). About 55% of the label could not be washed out. In contrast to kidney cortex, there is no evidence that the stria vascularis accumulates EA above the concentrations of the perfusion media. The I50 (50% inhibition) of the endolymphatic potential (EP) with respect to EA is about 10−5 M. Much higher concentrations are required for inhibition of strial Na+K+-ATPase (I50 about 5×10−3, with preincubation 10−3 M). It is, therefore, highly unlikely that the effects of EA upon the EP are caused by interference with Na+K+-ATPase. By contrast the I50 of strial adenylate cyclase with respect to EA is the same as that of the EP (with less than 15-min preincubation). These data are consistent with the propostion that the effects of EA upon the EP are due to interference with adenylate cyclase.
Model for production of cochlear microphonics and their relationship to basilar membrane displacement
Authors: Cannon Mark W.
Published: October 2005

A three-dimensional model of cochlear voltage sources and current pathways has been developed from a series of electrical resistance and impedance measurements made in the first turn of the Guinea pig cochlea. The model is validated by reproducing and thereby explaining a wide variety of cochlear microphonic (CM) data from the literature, including the difference in interscala CM phase behavior between the hook region and the rest of the cochlea. The model predicts that an electrode pair recording microphonics has a “field of view” which is frequency dependent. The width of this field of view gets narrower with frequency, enabling an electrode pair to record CM without interference from out-of-phase hair cells up to frequencies as high as 9 kHz in the first turn of the cochlea. The model also predicts that the known discrepancies between measured basilar membrane displacement and CM amplitude for frequencies below 9 kHz are due primarily to capacitive effects in the walls of scala media. Thus with the proper amplitude correction factor, CM can be used to measure basilar membrane displacement up to about 9 kHz in the first turn of the cochlea. Data from the literature supporting these conclusions will be presented.
Preneural electric frequency sharpening in the cochlea
Authors: Haas G. F.
Published: October 2005

An extended circuit based on the low-frequency model described previously [G.F. Haas, J. Acoust. Soc. Am. 53, 2–7 (1973)] was used to calculate cochlear microphonic voltages (CM) and current densities (i) in the vicinity of the hair-cell-neuron junction at frequencies at which membrane motion has been measured by the Mössbauer technique. Results indicate that the ratio of i to CM can increase with frequency at frequencies below the best frequency of the measurement location. These results indicate the possibility that volume-conduction from adjacent areas, due to time-varying resistive and capacitive paths along and across the basilar membrane, contributes to the sharper-than-mechanical frequency resonance of single units, and that this effect can take place without concomitantly sharp CM.
Rate response characteristics of two-tone suppression in the cat auditory nerve
Authors: Javel Eric , Geisler C. Daniel , Ravindran A.
Published: October 2005

Responses to two-tone stimuli were recorded from eighth-nerve fibers in anesthetized cats. One tone was set at a suppressive frequency above best frequency, and the second tone was set at an excitatory frequency. Various frequency and intensity combinations were used. For a given intensity, the suppressive tone always reduced the efficacy of the excitatory tone by a fixed decibel amount, regardless of the excitatory tone's intensity. As the frequencies were varied, the amount of suppression varied. When the frequency of the excitatory tone was decreased, the amount of suppression likewise decreased. As excitatory frequency was raised above best frequency, the suppressive effect first increased and then decreased. In general, the effectiveness of the suppressive tone decreased logarithmically as its frequency was raised. When the suppressive tone lay within the excitatory response area, synchronization of discharges changed systematically from one tone to the other as the excitatory intensity was raised. Under favorable conditions, responses synchronized to 2f1−f2 could be elicited, these having substantially different rate response characteristics. [Work supported by NINCDS grants.]
On the slope of psychometric functions
Authors: Jeffress Lloyd A. , Pasanen Edward G. , Clark Mark H. , McCusker Leo X.
Published: October 2005

In a recent paper, Jeffress [J. Acoust. Soc. Am. 58, 399–403 (1975)] slope of the psychometric function was dependent on the degree of randomness of the stimulus, being shallow for much randomness and steep for little randomness. The present experiment was intended as a test of that hypothesis. Four stimulus conditions were employed, each with two durations of the signal: 20 msec and 1 sec. The four conditions, from greatest randomness to least, were as follows: A narrow-band noise as both masker and signal (50 Hz at 500 Hz, N0S0, α = 0), a 500-Hz tonal signal and a wide-band noise masker, a 500-Hz tonal signal and masker (N0S0, α = 0) and finally, a 1000-Hz tonal signal in the quiet. A 2IFC procedure was employed throughout, using three subjects. The slopes varied as predicted, being shallowest for the narrow-band noise and steepest for the 1000-Hz tone in the quiet.
Forward, backward, and combined masking
Authors: Penner M. J. , Pavel Michael
Published: October 2005

Temporal masking of clicks by gated noise was investigated in forward- backward- and combined forward-and-backward-masking paradigms. In addition to the gated maskers, a continuous noise floor was also present in some conditions. For three levels of continuous noise and for a condition in which there was no continuous noise, the threshold of the click was determined as a function of the temporal separation, ΔT, between the click and the noise (1 msec ⩽ ΔT ⩽ 100 msec). Combined forward and backward masking were also explored for an interval of 30 msec between the two gated noises. In the absence of a continuous noise floor, nonadditivity of masking was obtained. In the presence of a continuous noise floor, additivity of masking was reinstated. These results are discussed in terms of a running average model of temporal processing. [This research was supported by the National Institute of Health, Public Health Service, U.S. Department of Health, Education and Welfare.]
Detection of intensity differences between brief contiguous tonal bursts
Authors: Sparks D. W. , Nixon J. C.
Published: October 2005

Two experiments have been performed to examine the relative roles of a short-term memory and temporal integration or summation mechanism in the detection of intensity differences between brief contiguous tone bursts. Tonal frequency was 1000 Hz. Two tone-burst durations (320 msec and 80 msec) and two interburst interval (IBI) durations (320 msec and 25 msec) were employed. A 2AFC presentation paradigm was employed and psychometric functions plotting percent correct vs. intensity difference between tone bursts in the variable observation interval were obtained for combinations of the signal durations and IBIs given above. In Experiment I, four bursts were employed where three had identical intensities and the fourth had an intensity decrement. This configuration resulted in unequal energy between the two observation intervals. Experiment II also used four bursts where the two bursts in the standard interval were of equal intensity; one burst in the variable interval had greater intensity and one less intensity than the bursts in the standard interval. The voltages for this experiment were set such that there would be equal energy in both observation intervals according to the equation (V12 + V12)1/2 = (V22 + V32)1/2. The results of our experiments appear to suggest that more than one mechanism underlies the detection of intensity differences between brief signals: short-term memory and temporal summation.
Nonmonotic discrimination functions for time intervals: Implications for VOT perception
Authors: Divenyi P. L. , Danner W. F.
Published: October 2005

Experienced listeners identified the longer of two unfilled time intervals, each bounded by acoustic markers. Time-difference thresholds (d′ = 1.0) were measured under a variety of conditions in a four-level, 2AFC procedure. When all four tonal markers were identical and at a high level (86 dB SPL), tonal frequency did not affect performance. For 1-kHz markers, performance deteriorated as their intensity was creased below 25 dB SL. When the markers of each interval differed in intensity or in frequency, performance also decreased and the time-difference threshold was not monotonically related to base duration. This nonmonotonicity was also observed when the time intervals were hounded by a 10-msec burst of bandpass (800–2000 Hz) noise at 71 dB SPL and by a 500-msec buzz formed from 100 pulses/sec, filtered with “formants” at 630 and 1000 Hz. The best relative threshold for base durations of 10, 25, and 60 msec, was found at 25 msec. When these CV-like, noise-buzz patterns were passed through a series of one-third octave filters, some filter conditions yielded performance as good as with the entire spectrum, while some did not. The principal factor was the intensity difference between the noise and buzz energy in the particular one-third octave band. We conclude that time-marking information is not integrated across frequency bands, and that the temporal discrimination is controlled largely by temporal masking in that spectral region where masking is smallest.
Aerodynamic noise: Acoustic model sources versus acoustic energy sources
Authors: Powell Alan
Published: October 2005

There has been considerable controversy surrounding the interpretation of the various theories of aerodynamic noise generation—those of dilatational (monopole) and of momentum flux (quadrupole), to which the vortex theory (dipole) may be added. The central issue has been the fundamental nature of the aerodynamic sound source. It is pointed out that these three theories are all of the nature of “acoustic models”, and their source terms should not be expected to have a simple one-to-one relation to the real physical sources, by which one is presumed to mean the action in those regions of the real flow in which kinetic flow energy is “transduced” to acoustic energy. One of the situations illustrated is that of the different acoustic models for aeolian tones, In which none of the three very different representations has a simple translation to the real flow. For example, the argument that fixed surfaces cannot be the origin of dipole sound relates to the real flow, but not to the acoustic model where the boundary conditions are different.
On estimating aerodynamic sound from flow fields represented by discrete vortices
Authors: Powell Alan
Published: October 2005

The sound radiated by a nearly incompressible inviscid free flow, and approximated by an incompressible one, may be expressed in terms of the vorticity movement. If the field is represented by a set of point (line) vortices, their motion and hence the sound field can be determined, precisely. The sound field is dependent upon the second derivative of the flow field, and hence the effects of the fine structure of the flow are emphasized. Thus while a real flow may be reasonably well portrayed by a distribution of point vortices, the sound field may have some dependence on the details of the distribution. This is illustrated in the extreme case of an unstable shear layer represented by a single line of vortices, where the dependence of the impulsive sound on the vortex spacing wan not at first emphasized (A. Powell, Proc. Noise-Con 75). While this is an extreme case, it serves to draw attention to this feature which may be less overt in more complex situations.
Mechanisms of nozzle lip noise and experimental investigation by causality correlation approach
Authors: Siddon T. E. , Purvis H. G. F.
Published: October 2005

Excess jet noise, arising from upstream flux unsteadiness and pressure fluctuations near the nozzle lip, may be of important consequence to the limiting performance of multi-element jet noise suppressor nozzles. The relative significance of the excess noise increases as Mach number is reduced. Important parameters include the shape of the nozzle approach cone, the velocity ratio across the lip, the nature and thickness of the boundary layer at the exit plane (laminar or turbulent), the lip thickness and the levels of nozzle-borne turbulence. In our experiments, nozzles of 2-cm diameter were instrumented with specially constructed pressure transducers implanted into the nozzle surfaces. Considerable effort was expended to devise a transducer/pinhole configuration with frequency response to 100 kHz. Our experiments yield the distribution of surface dipole strength over the nozzle lips, by cross-correlation of the pressure transducer signals with sound signals recorded in the farfield, for various angles and axial positions of the nozzle transducer [as is Siddon, J. Acoust. Soc. Am. 53, 619–633 (1973)]. Results suggest that an optimally contoured nozzle with laminar boundary layer generates insignificant lip noise, but certain types of internal flow disturbance will enhance the sideline radiation at high frequencies. The lip dipole strength is concentrated within one or two wavelengths of the exit plane, and has a circumferential distribution varying roughly as cosφ squared. [Work supported by the General Electric Company, Aircraft Engine Group, Evendale, OH.]
Analysis of screeching in a cold flow scaled model test of the space shuttle
Authors: Wang M. E. , Slone R. M. , Robertson J. E. , Keefe L.
Published: October 2005

A narrow-band screech has been observed during cold flow model test performed by the NASA Marshall Space Flight Center to study trends in Space Shuttle launch acoustic environments. An investigation to determine the source of the screech has been completed by Wyle Laboratories. An acoustic feedback mechanism resulting from interaction between the jet exhaust flow and model launch pads with several exhaust hole configurations has been identified to be responsible for generation of screech. A simple equation which permits prediction of the screech frequencies in terms of the basic testing parameters, such as the nozzle exit Mach number and the distance between the nozzle exit and the surface of the model launch pads, is presented and is found in good agreement with the subject test data. [Work supported by NASA-MSFC.]
Observation on tone “cutoff” in static test data from jet engine fans
Authors: Heidmann M. F.
Published: October 2005

A quiet design feature of many fan stages is a proportionment of the rotor and stator blade numbers so that blade passage tones caused by rotor-stator flow interactions will not propagate, i.e., are “cutoff.” The anticipated reduction in tone level has been observed in some flight test data but is generally masked in static test data. This masking is attributed to inlet flow distortions, prevalent daring static testing, which generate tones by interacting with the rotor. In this study, an evaluation of distortion tone properties is used to analyze the farfield static test data for eight full-scale jet engine fans tested at a NASA Lewis outdoor facility. The analysis involves a compensation for distortion tones of the noise propagating from the aft fan duct. The analyzed data clearly differentiate the fans which are and are not “cutoff.” The result confirms that “cutoff” is a quiet design feature which can reduce the noise of operational aircraft.
Teaching acoustics to nonscience majors
Authors: Stuart A. D.
Published: October 2005

In teaching scientific material to nonscience majors, three basic problems are encountered. One is that the students' fear of failure in dealing with totally unfamiliar material is heightened and grade-consciousness reaches a very high level. A second is an increased need to convince the students of the relevance of the course material in their preprofessional (or academic) training. A third problem is that of compensating for the students' lack of technical knowledge while trying to impart technical concepts. Instructors in a course in general acoustics at Penn State attempted to deal with the above-mentioned difficulties through a variety of approaches which included using the contract system for grades, tailoring the material for application in a particular discipline (in this case Speech Pathology and Audiology), and substituting highly visual and auditory demonstrations for technical lectures. This paper discusses the various approaches and reports the degree of their success in facilitating the learning of basic acoustics for nonscience majors.
Dimensions in diffusion of knowledge in acoustics
Authors: Johnson J. C.
Published: October 2005

The Acoustical Society of America has sponsored studies which addressed relevant purposes and means for carrying out its Charter, i.e., “…diffuse the knowledge of acoustics….” A summary of findings due to such studies is presented. Primary audiences served by knowledge of or about acoustics can be classified as technical societies (professional and scientific); scholars (students, teachers, and researchers); governing bodies (private and public); and society (the public at large). The sequel means for communication to each of these audiences are normally publications; educational institutions; written reports; and mass media; respectively. There are exceptions to these generalizations, however, such categorization assists in the consideration of a rather complex subject.
Cinéfiberscopic study of velopharyngeal function
Authors: Niimi S. , Bell-Berti F.
Published: October 2005

It has been noted that the height of the velum for oral speech segments varies with the degree of oral cavity constriction for these segments [e.g., J.F. Lubker, Cleft Palate J. 5, 1–18 (1968); F. Bell-Berti, Ph.D. thesis, City University of New York (1973)]. A cinéfiberscopic study was undertaken to describe the velar height relationships between oral stop, fricative, and frictionless consonants, and the effects of phonetic environment on the achieved velar height for each segment. Frame-by-frame measurements of velar height were made from motion pictures made of the nasal surface of the velum of one speaker of American English, speaking a set of nonsence disyllables containing oral stop, fricative, frictionless, and nasal stop consonants in a constant vowel environment. Both voiced and voiceless oral stop and fricative consonants were used, as well as a format that included both oral-consonant-nasal-consonant and nasal-consonant-oral-consonant contrasts. The data are examined and discussed with reference to earlier velar height and electromyographic data. [Supported by NIDR grant DE 01774.]
Modulation of perioral reflex sensitivity during speech movements
Authors: Netsell R. , Abbs J. H.
Published: October 2005

Electrical stimuli were delivered to the skin over the infraorbital foramen to elicit reflex action potentials in m. orbicularis oris superior (OOS). These short latency responses (10–15 msec poststimulus) are designated as the first perioral reflex component (R1) and appear to be mediated by the brain stem, probably involving two synapses. In this experiment, R1 potentials were elicited under three OOS contraction conditions: (1) with OOS passive, (2) during OOS bursts associated with labial closure for production of [p] in [pa], and (3) during the OOS shutdown with labial opening for the production of [a] in [pa]. The R1s elicited during labial closure had larger amplitudes than those elicited in the passive condition. Conversely, the R1s elicited during labial opening were smaller than those elicited in the passive condition. One interpretation of these findings is that during lip movement excitatory influence of afferents on bulbar motoneurons are modulated by suprebulbar mechanisms. From this perspective, periorial reflex techniques may hold considerable potential for understanding bulbar-suprabulbar interactions during speech production. [Supported by NINDS grants NS-09627 and NS-11780.]
Vibrations of a circular plate elastically restrained along the edge and carrying a concentrated mass
Authors: Laura P. A. A. , Luisoni L. E. , Arias A.
Published: October 2005

This investigation deals with the determination of fundamental frequencies of vibration of a circular plate carrying a concentrated mass at the center. The plate is elaatically restrained along the edge and subjected to a hydrostatic state of in-plane stress. The calculated fundamental frequencies are in excellent agreement with those available in the open literature (rigid clamp along the edge and no in-plane forces). The method of solution consists of expanding the displacement function in a simple polynomial which identically satisfies the boundary conditions. A variational method is then used to gencrate the frequency equation. The approximate solution is also valid when the mass is placed off-center.
Iterative solution for random vibration problems involving structure-fluid interaction
Authors: Lin Y. K.
Published: October 2005

In the spectral analysis of a random vibration problem, a considerable effort is devoted to the evaluation of frequency response functions. This task becomes very difficult when the interaction between the vibrating structure and the surrounding fluid must be taken into account. An iterative scheme is developed in the present paper which is applicable to extremely complicated configurations. For illustration, the scheme is used to compute noise transmission through a flexible panel into a cavity and the result is compared with some known solutions.
Numerical-perturbation technique for the transverse vibrations of highly prestressed plates
Authors: Nayfeh Ali H. , Kamat M. P.
Published: October 2005

Under the usual assumptions of small strains with moderately large rotations, the problem of the transverse vibrations of highly prestressed nonuniform annular plates is reduced to the solution of the differential equation governing the transverse vibration of the corresponding prestressed membrane subject to modified boundary conditions that account for the effects of bending. The method of composite expansions is used to determine these modified boundary conditions. The agreement of the present solution or results with known exact solutions for simple geometries demonstrates the efficiency of this method when compared with other well-known numerical techniques.
Vibration response of liquid-loaded structures to low-speed flow noise
Authors: Chandiramani R. L.
Published: October 2005

Consider a spatially homogeneous and temporally stationary random pressure field exciting a spatially homogeneous structure (plate, cylinder). It is well known that when the power exchange between the pressure field and the structure results from a “surface interaction” rather than from a scattering-induced “edge interaction,” it is immaterial whether a finite or infinitely extended model of the structure is used to calculate this power exchange. This equivalence is used to estimate vibration response of a liquid-loaded flat plate when excited by a low-speed turbulent boundary layer flow. Connections, established previously for structures in vacuo, between group velocity, modal density and point and line conductances, are also generalized to apply to liquid-loaded structures. Finally, an approximate but simple method is suggested for estimating some useful vibration characteristics of spatially nonhomogeneous structures excited by surface interactions.
Vibration and sound radiation of a plate
Authors: Hannon Robert J.
Published: October 2005

Because of their many vibratory resonances, plates are mechanically soft and their suspending structures have considerable effect on their vibration and sound radiation. Experimental evaluation of acoustic properties of plates is therefore difficult. Plates of different shapes and dimensions were supported in such a way as to eliminate the effects of the supports on the vibrations and the velocity amplitudes due to point forces were recorded by phonograph cartridges and microphones in the near sound field. The results show that the many vibratory modes generate “hotspots” on the plates. The attachment of ribs and supports disturbs the vibration field and leads to localized areas of increased sound radiation. Long wavelength acoustic holography was used to locate on the vibrating plates the sources of farfield sound. These regions were also investigated by recording the vibratory and nodal line patterns of the plates by a nearfield microphone method. This combination of techniques has a unique capability to locate acoustic sources on vibrating structure. [Work supported by NASA and ONR.]
Power radiation from point-excited plates
Authors: Toth D. D. , Holmer C. I.
Published: October 2005

The application of statistical energy analysis (SEA) techniques to predict the sound power radiated from point excited plates is well known. These techniques are typically restricted to plates for which thin plate approximations apply, and to the frequency region in which high modal overlap (M > 1, where M = model bandwidth/mode spacing) occurs. Experimental data are presented for three plates (0.95-cm transite, 1.3-cm aluminum, and 4.3-cm concrete) which violate either or both of the limitations, and for which the ratio of power radiated to mean square force input is significantly (as much as 10 dB) less than the SEA theory predicts. Using Mindlin's thick plate theory, modifications to the SEA theory to account for the frequency averaged driving point impedance and mode spacing have been developed. The use of these modifications gave good agreement with the experimental results for the frequency range where the plates are thick and M > 1. Several sources for the discrepancies between analytic and experimental data for low modal overlap are under investigation and will be discussed.
An investigation of the uses of holography for the study of sound radiation from vibrating surfaces
Authors: Hansen C. H. , Bies D. A.
Published: October 2005

The radiation of the first six low-order modes of vibration of a damped circular plate mounted in an infinite baffle has been investigated both experimentally and theoretically. Time lapse holography has been used to identify modes and to determine the mean square normal velocity over the surface of the plate for the various modes. The radiated sound power has been measured in a reverberant room and the radiation efficiency computed. The use of a series of similar plates but of various thicknesses-scaling procedures has allowed a determination of the radiation efficiency over a wide range of dimensionless frequency. Theoretical predictions of the radiation efficiency have been computed using spheroidal wave functions and an evaluation of the Rayleigh integral. The experimental results are shown to compare quite favorably with the predictions of the analysis.