bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotary power lawn mower noise
Authors: Clark William D. , Williams Kent C.
Published: October 2005

The purpose of this study was to examine the noise of a typical rotary power lawn mower. Hearing loss and annoyance criteria were examined to determine acceptable mower noise limits. It was found that if reduced from its present level of 91 dBA at the operator to 85 dBA, mower noise would pose almost no damage risk for a typical exposure. When the spectral content of the mower noise had been determined it was found that structural radiation was responsible for most of the noise in the range 500–10 000 Hz and that both the blade and exhaust were major sources below 500 Hz. The spectral content of the noise when mowing was found to be similar to that when not mowing. The three major noise sources—exhaust, blade, and structural radiation—were studied seperately. Sources of blade noise were identified by applying the theories of propellor and fan noise generation. Of the blade parameters studied, which included fan lift, sharp trailing edge, and multiple blades, none reduced the A-weighted level of the blade noise. A 1-dBA reduction was observed when the blade was statically balanced. A vibration isolator was designed and built to reduce the vibrations of the blade enclosure and resulted in an additional 112-dBA reduction. Existing theories of exhaust system design were researched and used to design resonator-type systems. Within the assumptions of classical acoustics, no acceptable solutions were found. Applying the theory of acoustic radiation from a hole, a system was designed, built, and tested which resulted in an excess attenuation over the stock muffler of 212 dBA. With the isolator, a blade with less lift, and the improved muffler, the final mower noise level was 86 dBA at the operator. Cost of the solutions is estimated at less than $ 10.00 and none of them is expected to impair the mower's operation.
Noise reduction in the fly shuttle loom
Authors: Hanson William J.
Published: October 2005

The textile industry's most severe noise problem is probably that of the fly shuttle loom. Although several substitution methods have been developed for weaving various materials, much of the industry is still plagued with noise generated by shuttle-type looms. Weave room noise levels may run as high as 105 dBA, resulting in substantial hearing damage risk. By employing a package of polyurethane and nylon components plus several adjustments, significant noise reduction may be accomplished. This could mean a hearing impairment risk reduction of approximately 20% for weave room textile workers. Loom noise was investigated through the use of a scanning gate technique, in which ten or more cycles of the loom were observed for each impulse displayed. The gate scans the entire loom cycle, resulting in a graphic record of instantaneous peak sound pressure levels as a function of time during a loom cycle. These charts provided a convenient display of component peak noise for evaluating the reduction of each individual modification.
Ultrasonovision: an interferometric device for ultrasonic visualization and measurement
Authors: Mezrich R. , Etzold K. F. , Vilkomerson D.
Published: October 2005

Gabor suggested measuring acoustic wavefronts by optically measuring the displacement of a reflective membrance coupled to the medium of propagation. We have implemented this suggestion and measured acoustic wavefronts in water at frequencies from 0.5 to 5 MHz and at intensities as low as 250 nW/cm2. The response is linear to several W/cm2. The membrane is so tightly coupled to the medium that its displacement equals the displacement amplitude of the wave to within 1% up to angles of incidence of 40°. Pictures of the acoustic fields were obtained in near real time (several frames/sec) with wavelength-limited lateral resolution. The arrangement used is that of a Michelson interferometer, with one mirror rigid and external to the acoustic field and the other a thin (∼8 μ) metalized plastic film (or pellicle) suspended normal to and in the path of the acoustic wave. A narrow laser beam is raster scanned across the interferometer, and so the pellicle. The photocurrent from a photodiode has an acoustic frequency component proportional to the pellicle displacement. This component may be measured directly or used to brightness-modulate a CRT and thus produce an image of the sound field.
Evoked response correlates of auditory perception and misperception
Authors: Pinheiro M. L. , Andrews L. T.
Published: October 2005

The relation between the averaged evoked response (AER) and the accurate perception and misperception of binary auditory pattern sequences was studied in normal subjects. Stimuli were six 540-msec patterns of three temporally spaced noise bursts with an intensity difference between loud and soft elements. The PDP-12 computer randomly generated patterns and sorted the evoked potentials, recorded at vertex, according to both stimulus and perceptual response. Subjects listened binaurally, replicating each pattern on a response box. A pair of AERs was obtained for each pattern, one associated with accurate perception and the other with the misperception which entailed a reversal of acoustic cues, i.e., short for long and vice versa. Statistical analyses of these paired observations showed that the AER was of significantly greater amplitude during accurate perception than during reversed perception. Since differences between the paired AERs, consistent across patterns and subjects, were observable before termination of the first pattern burst, they could not be attributed to differences in pattern perception. Instead, the accuracy of pattern perception may depend on the state of on-going electrophysiological activity of the brain.
Electronic subject for audiometric practice
Authors: Botsford James H.
Published: October 2005

A worrisome problem in the training of audiometric technicians is the unavailability of subjects for practice testing. The usual procedure is to instruct one trainee to test several of the other trainees. This procedure is not entirely satisfactory, because it is tiring to undergo repeated hearing tests. Also, only a limited number of audiograms, mostly normal, are available which quickly become known. To overcome this difficulty, an electronic subject to be used for practice in hearing testing has been developed. It has a statistical threshold which mimics human response. The threshold response can be made normal, or sharp as in the case of sensorineural hearing loss. It can also be made vague, as in the case of a subject who is anattentive or does not understand the test procedure. All types of audiograms can be simulated. For training large groups, several electronic subjects with different audiograms can be used serially by the trainees. The audiogram of each device is known to the instructor, so trainee performance can be graded. For individual or small group practice, a single instrument which can be switched through several different audiograms may be used. The operating characteristics and applications of this device are described.
What “tips of the slung” can tell us about the production and comprehension of speech
Authors: Fromkin Victoria A.
Published: October 2005

The importance of speech errors as evidence for models of linguistic performance was discussed in papers presented to the Acoustical Society in 1970 and 1971. Additional data have since been collected and analyzed. It is shown that errors involve more than the disordering of units at various stages in production; word substitutions, lexical and syntactic blends, and the misapplication of morphological and syntactic rules also create speech errors. The analysis of these errors contributes to our knowledge of the speech production process and, in addition, may help in the construction of “automatic speech understanding” systems. Although one cannot predict when an error will occur or what the particular error will be, one can predict the kinds of errors that will occur and the frequency of different classes of errors. Errors in speech are therefore not totally random, and are constrained by the linquistic system. Such constraints prevent an exacerbation of errors on the part of the speaker and act as a filter or corrective mechanism for the hearer. The noise in the system is thereby reduced, permitting the signal to get through. [Research supported in part by a grant from the NIH.]
Children's speech timing control
Authors: Allen George D. , Tingley Beth M.
Published: October 2005

This study investigated the accuracy with which five-, seven-, nine-, and 11-year-old children could (1) repeat the lines “Twinkle, twinkle, little star; how I wonder what your are,” and (2) tap their fingers in a steady rhythm. These repeated behaviors were analyzed with respect to the statistical model proposed by Allen and Cooper [J. Acoust. Soc. Am. 53, 379(A) (1973)], with the following results: (1) the model accounted for an average of over 95% of the variance in the different children's speech data, suggesting that it is a valid description of speech tinting control for these subjects; (2) there was a clear developmental trend, with all of the 11-year-olds behaving within normal adult limits; (3) there was good agreement between speaking and tapping control, suggesting a common timing mechanism; (4) there was no evidence for peripheral speech timing feedback, even among the five-year-olds; (5) post-hoc comparison of some children's data with those of their siblings or their previously studied parents suggests a significant genetic component to (speech) motor timing control.
Corrections of ray theory
Authors: Hudimae A. A.
Published: October 2005

In previous reports it was shown that the failure of ray theory (for a case of a ray field with the amplitude function and its first derivative continuous) can be corrected by distributing sources throughout the volume having a density proportional to the Laplacian of the amplitude function. The theory still holds with the restriction relaxed. Symbolic functions may appear on surfaces, implying a source or dipole distribution on them. This has been applied to correct for diffraction on a shadow zone boundary (for which a different proof has been reported), at a caustic, and at a discontinuity of acoustic velocity distribution (e.g., corners). Some examples are discussed.
Normal-mode calculations of underwater sound propagation from transducer arrays
Authors: Graves R. D. , Überall H. , Haug A. J.
Published: October 2005

The normal-mode solution for the problem of sound propagation in an under-ocean sound channel, as discussed in the preceding abstract, has been obtained for the case of various transducer array sources. The solution is given by the Green's function integral, which is replaced by a sum over the array elements. In the farfield, the sum over azimuthal and radial modes can be obtained in closed form. The results will be illustrated using normal-mode depth functions of a parabolic profile [H. Überall and N.C. Nicholas, J. Acoust. Soc. Am. 44, 1259 (1968)]. The solution is studied as a function of the number of array elements, and for various phasing arrangements. [Supported by the Office of Naval Research.]
Propagation of a normal mode in the parabolic approximation
Authors: McDaniel S. T.
Published: October 2005

The parabolic approximation [Maury Center Non-Ray-Tracing Workshop (May 1973)] to the acoustic wave equation is studied for a case where the normal-mode solution is valid. Errors arising in the parabolic approximation are analyzed using a normal mode as the input. It is shown that two types of errors occur. The first is dependent on the choice of range increments and may be made arbitrarily small by proper choice of range steps. In contrast, the second type of error, a phase error, is inherent in the method and can be expected to be present in any practical situation. Results of a computer program confirming this analysis are presented. [Supported by Naval Ordnance Systems Command.]
Comparison of the parabolic equation method with other propagation loss models
Authors: Benthien G. W. , Gordon D. F. , McCleary L. E.
Published: October 2005

Tappert and Hardin have developed a technique for computing underwater acoustic propagation loss fields which is known as the parabolic equation method. This is a numerical matching method which leads to a relatively fast computation algorithm and permits sound speed variation in multiple dimensions. For sound speed variation in depth only, we have investigated accuracy, ease of use, and computer time requirements of this method. Reliable natural mode or ray theory computations were used as starting values at a given range and for accuracy checks at longer ranges. The parabolic equation method was found to be stable and accurate for acoustic ducts formed by refraction or surface reflections. Bottom reflections presented many problems and mode results could not be duplicated in general. The method was comparatively easy to use once starting values were available, but no way was found to determine optimum step size without some trial and error. Computer time requirements were always as large as those for mode theory and were often much greater. The primary value of the parabolic method then lies in its application to two-dimensional sound speed profiles where closed-form solutions are difficult.
Aircraft community noise research and development—an historical overview
Authors: Blumenthal V. L. , Russell R. E. , Streckenbach J. M.
Published: October 2005

This paper summarizes noise reduction research and development programs of The Boeing Company from the early 1950s to the present time. Discussions concentrate on the background for each program, present the end results obtained or progress made, and introduce detailed descriptions of key programs to be covered in three related Boeing papers during the same ASA meeting. Summary descriptions are included for acoustic treatments that have been developed, permitting all current Boeing turbofan-powered commercial aircraft models to comply with applicable U.S. Government and international noise rules. The benefits attainable through noise-abatement operating procedures are discussed, along with the related need for compatible land-use planning. The paper concludes with a discussion of unsolved problems that need attention by the scientific community to permit continuing reductions in aircraft noise.
Acoustic resistance of an annular capillary
Authors: Backus John
Published: October 2005

As reported in a previous paper [J. Acoust. Soc. Am. 55, 457(A) (1974)], input impedances of musical wind and brass instruments were measured by using a high acoustic resistance to feed a constant acoustic current to the mouthpiece of the instrument and measuring the resulting sound pressure. For quantitative results, it is necessary that the high resistance be frequency independent; the configuration used, a capillary of annular cross section, was found experimentally to be reasonably so. For low frequencies, this is to be expected, since the effective impedance of the capillary becomes the Poisueille resistance, which is frequency independent, plus a negligible inductance term. At higher frequencies, the effective impedance of such a capillary will vary with frequency; however, computer solution of the relevant transmission line equations shows that for certain values of the parameters involved, the effective impedance is reasonably frequency-independent over a usefully wide frequency range. [This work was supported by the National Science Foundation.]
Binaural interaction in the superior olivary nucleus of the green treefrog (Hyla cineria)
Authors: Feng A. S. , Capranica R. R.
Published: October 2005

Single auditory cells in the superior olivary nucleus of the green treefrog (Hyla cineria) were isolated with indium-filled micropipettes. Acoustic stimuli, consisting of tones and clicks, were delivered to each ear independently; electrode locations were verified histologically. About 50% of the cells in the superior olive receive binaural input. Almost all binaural units can be excited by contralateral stimuli and inhibited by ipsilateral stimuli. The majority of these units are sensitive to interaural intensity differences. Only low-frequency units are sensitive to interaural time differences and generally show greater response when the contralateral stimulus leads the ipsilateral stimulus; high-frequency units are insensitive to interaural time differences. The response properties of these cells are similar to cells in the superior olivary nucleus of mammals. Our results suggest, therefore, that this neural center in the frog's auditory system plays a role in sound localization. [Supported by NIH Grant NS-09244.]
Detection of insect wing beats by the bat, Pteronotus parnellii
Authors: Johnson R. A. , Henson O. W. , Goldman L. R.
Published: October 2005

An investigation was made into one possible use of the “pure tone” portion of the echolocation signals of Pteronotus parnellii parnellii (Gray). It was verified that the echo of a constant frequency 60-kHz signal from a wax moth (Galleria mellonella) contains instantaneous Doppler shifts of as much as 300 Hz due to the wing motion. The complexity of the wing motion produces these Doppler shifts for arbitrary aspect angle. The sharp sensitivity peak in the cochlear microphonic (CM) tuning curve of P. parnellii [G. D. Pollack et al., Science 176, 66–68 (1972)] could be used to detect the wing beat Doppler shifts. The frequency deviations would be converted into amplitude deviations. This effect was verified by stimulating bats with the artificial moth echo signal with the “carrier” frequency adjusted to the center of the particular bats' sensitivity peak and monitoring the CM potential. Large amplitude fluctuations occur as the frequency sweeps back and forth through the sensitivity peak. This mechanism may explain the flight speed Doppler compensation in the echolocation signals.
Discrimination of vowels and semivowels synthesized with an articulatory model
Authors: Kasuya H. , Kido K.
Published: October 2005

In order to examine the difference between perceptual manner of vowels and semivowels which are characterized by dynamic acoustic events, an articulatory model for producing both high vowels such as [i] and [w] and the syllable [ju] was first introduced. The formant frequency movements of the syllables obtained from the model were considered to be reasonable as compared with those of natural speech sounds. The difference limens (DLs) of vowels and semivowels for the changes in an articulatory point in the model were measured by an AX discrimination test. The DLs were almost the same among four semivowels having different terminal articulation points when the initial articulation points and lip opening area were kept constant. But the DLs were significantly different among four sustained vowels having the same values as the vocal tract area functions of the semivowels at a terminal point. The implications of these results for feature detecting mechanisms in the perception of vowels and semivowels are discussed with the role of phonetic framework of listeners.
Similarity structures among vowels
Authors: Bernstein Jared
Published: October 2005

Phoneticians have tried to predict phonological patterns by applying metalinguistic principles to phonetic substance. For instance, Liljencrants and Lindblom [Language (Dec. 1972)] assumed that vowel phonemes will tend to settle in maximally distinct locations in an acoustic vowel space. This presumes a knowledge of the acoustic-phonetic nature of vowel similarity. However, representations of the auditory-phonetic structure of a vowel space have usually been based on data about a stimulus set consisting of vowel sounds which approximate the phonemic norms of the language spoken by the experimental subjects. The results from these studies reflect more than the auditory qualities of the sounds, so they cannot be used without circularity for establishing phonetic explanations of phonological patterns. In the present study, 19 vowels were chosen to sample all areas of an “F1 by F2 by F3” acoustic vowel space appropriate for an adult male vocal tract. An American and a Persian subject judged the similarity of selected pairs of these sounds. Six dimensions (F1, F2, F3, F2−F1, F3−F2, F3−F1) were tested for independence and interdimensional additivity, using the ordinal properties of the subject responses. The data reject the possibility of expressing phonetic similarity over the whole vowel space as a simple combination of monotonic scales along any two or three of these dimensions. The similarity judgments among certain subsets of the stimuli, however, allow construction of simple expressions of similarity within subregions of the vowel space. [Supported by USPHS Grant 1-TO-HD00275.]
Acoustic invariance for stop consonants
Authors: Kuhl Patricia
Published: October 2005

Acoustic invariance for the six stop consonants occurring with /i/, /a/, and /u/ in naturally spoken CV syllables was investigated. Each syllable was divided into consonant and vowel fragments that were identified in isolation in Experiment I. Consonant fragments that were long enough to be identified as consonants, rather than noise, yet short enough so that the original vowel could not be identified (20-, 30-, and 40-msec fragments for voiced stops; 30-, 40-, and 50-msec fragments for voiceless stops) were recombined with their original vowels (control syllables) and with each of the two other vowels (experimental syllables) in Experiment II. Twenty-one of 54 control syllables met criteria for consistent identification. These 21 control syllables were each compared with their two experimental counterparts to form 42 control-experimental comparisons. The 22 comparisons of controls identified as voiceless stops, and their experimental counterparts, were all invariant (identified as the same consonant); the 20 comparisons of controls identified as voiced stops, and their experimental counterparts, were almost equally variant (9) and invariant (11).
Generative rules for French prosody
Authors: Vaissiere J.
Published: October 2005

In earlier work, we analyzed the fundamental frequency (F0) contour and the location of pauses in isolated sentences read by a professional mate radio announcer. Using the results of this analysis, we derived a set of rules for automatically specifying the pauses and F0 contour from the surface structure and the phonemic transcription of the sentences. Recently, we tested the validity of the rules for isolated sentences and two texts read by six other native speakers of French. Good agreement between the observed contours and the contours predicted by rules was obtained. Rules derive a prosodic structure of the sentence from the phrase marker by taking account of the number of syllables in each grammatical unit. For example, a grammatical sentence can be divided by the rules into two phonetic sentences, depending on its length; two successive short lexical words in a phrase are merged into a single phonetic word. Rules are then successively applied at the level of the phonetic sentence, at the level of the phonetic phrase, at the level of the phonetic word, and at the level of the syllables to assign F0 contour.
Sound fluctuation and inhomogeneities in shallow water
Authors: Barakos P. A. , Speidel S. L.
Published: October 2005

Acoustic amplitude and phase fluctuations depend primarily upon variations of the acoustic index of refraction of the medium. Time series of experimental data of amplitude and phase fluctuations and of index of refraction were obtained for a nearshore environment off Southern California. A fixed narrow-beam ultrasonic source radiated CW pulses at 90 kHz at a rate of four pulses per second. Vertical thermocline movements related to internal waves induce time-dependent variations in the acoustic index of refraction and, as a consequence, variations in acoustic signals propagating in the ocean. Correlation functions and variances of the amplitude and phaser fluctuations and of the index of refraction are found and a comparison is made with the Komegorov-Obukhov two-thirds law for isotropic turbulence.
Use of phase fluctuations in the scattering of electromagnetic radiation by sound as a highly directional acoustic receiver
Authors: Larson Richard S.
Published: October 2005

The phase and amplitude fluctuations of an electromagnetic wave scattered by a sound beam may be used as a highly directional sensitive (in air) acoustic receiver for low-frequency sound. The phase and amplitude changes of the electromagnetic wave as a function of the distance L traveled through the sound beam are calculated using geometrical optics. In the limit λs ≪ L where λs is the wavelength of the sound beam, the phase perturbation caused by variations in the dielectric constant of the medium is nonzero only for normal incidence of the two beams. The maximum phase perturbation at normal incidence is kΔθ = − 12η n0kL cosωst, where kΔθ is the phase change, k is the wave vector for the electromagnetic wave, n0 is the index of refraction, ωs is the angular frequency of the sound beam, and η is the parameter coupling changes in pressure to changes in the dielectric constant. The analysis is extended using Rytov's method of smooth perturbations, and the result is compared with the answer obtained for the analogous problem in the scattering of sound by sound in dispersive media. [This work was supported by the U. S. Office of Naval Research.]
Impedance measurements of acoustic duct liners with grazing flow
Authors: Armstrong D. L. , Beckemeyer R. , Olsen R. F.
Published: October 2005

The impedance properties of acoustic duct liners are affected by airflow in the duct. Measurements have shown that interactions between the duct flow and the acoustically induced flow at and within the acoustic liners can cause significant changes in the effective liner impedance. Acoustic measurements in a flow environment are used to develop acoustic impedance mathematical models for use in lining design. These impedance measurements are made in a 2 × 2-in. cross-section flow duct using waveguide principles. The design of the duct and the data analysis technique are based on solution of the convected wave equation in an infinite waveguide. The sheared boundary layer velocity profiles in the duct are measured and used to calculate the acoustic impedance of the liner. Examples of measured attenuation and phase rate data are presented which show effects of duct flow velocity and wall impedance. A comparison with standing-wave impedance tube measurements in the limiting case at zero flow is also presented.
Method of acoustic modules
Authors: Vaidya P. G.
Published: October 2005

Most theoretical studies in duct acoustics involve idealized conditions. Thus, sound propagation in semi-infinite absorbent ducts is considered and radiation from a rigid duct termination is analyzed. Very little consideration is given, in general, to matching these subproblems together to solve a specific practical problem. The method of the acoustic modules is a first step towards resolution of such discrepancies. Both these problems are analyzed in terms of the same (rigid duct) eigenfunctions. Each module has au input (pressure and velocity distributions) which uniquely determines its output. Thus, a cascade of modules could be analyzed if the source impedance of the first module and the termination impedance of the last module are known. The paper includes analysis of a rectangular module by means of a finite-length Green's function and a discussion of the applications of this method to various practical problems. [Work supported by NASA Lewis under Contract No. NAS 3-18010.]
Release of acetylcholine in cochlear nucleus upon stimulation of the crossed olivocochlear bundle
Authors: Guth P. S. , Corals S. D.
Published: October 2005

It has been established that the crossed olivocochlear bundle endings (COCB) in the cochlea release acetylcholine (ACh). According to Dale's principle, any single neuron will release the same transmitter at all its terminals. Therefore, the dorsal and ventral cochlear nuclei were perfused with a physiological salt solution and samples were collected during and in the absense of COCB stimulation to determine whether stimulation would or would not cause ACh release. Stimulation of the COCB caused a statistically meaningful increase in ACh content of the dorsal cochlear nucleus perfusates. The Ach determinations of the ventral cochlear nucleus perfusates were confounded by the presence of an unknown (but not uninteresting) agent which opposed ACh on the bioassay object. Although evidence was adduced indicating release of ACh coincidental with COCB stimulation, it cannot be said with certainty to come from COCB collaterals. Therefore, the method employed cannot be said to have asked the most incisive experimental question. Nonetheless, the research can be said to have produced provocative results and some interesting new hypotheses.
Ribonucleic acid changes in the brain, spiral ganglion, and adrenal cortex of noise-exposed rats
Authors: Anthony A. , Bennett T. , Hahn P. , Maliniak R.
Published: October 2005

Microspectrophotometric determinations of neuronal RNA levels were made in selected brain areas (auditory cortex, optic cortex, and hippocampus), in adrenal cortical cells, and in cochlear receptor elements from adult male albino rats exposed to a 60-min noise (100–120 dB re 0.0002 μbar, 350–20 000 Hz). Control animals were maintained at ambient sound pressure levels (ca. 40 dB). Animals were sacrificed at 1-, 4-, 8-, and 24-hour postexposure intervals. RNA was quantified in azure-B-stained tissue sections which were pretreated with DNase. A transient RNA elevation was evidenced in neurons from the three brain regions analyzed during the 1- to 8-hour postexposure interval. Adrenal cortical cells also exhibited increased RNA levels at corresponding postexposure time intervals, whereas no appreciable stimulation of RNA synthesis was evidenced in spiral ganglion neurons of the cochlea during a 24-hour period following cessation of auditory stimulation. The latency of RNA activation in brain elements, coupled with the similarity in the pattern of adrenal stimulation suggests that nucleic acid responses of brain neurons may be hormonally mediated and not a direct manifestation of excitation via auditory neural pathways. [Research aided by the Office of Environmental Quality Programs and the Center for Air Environment Studies.]
Some variables in the learning of auditory pattern discriminations by animals
Authors: Wegener J. G.
Published: October 2005

We have examined the role of a number of variables in auditory pattern discrimination learning: (1) species, (2) reinforcement, (3) learning sequence, and (4) internal structure of the auditory patterns. (1) In a conditioned avoidance situation cats learned a simple frequency discrimination more slowly than rhesus monkeys—and an auditory pattern discrimination at about the same rate as monkeys. (2) Four monkeys working for juice reinforcement required a mean number of 737 trials to learn the same frequency discrimination as 12 monkeys working to avoid shock learned in a mean of 55 trials. The same four monkeys learned an auditory pattern task in a mean of 451 trials for juice, while 12 monkeys in the shock avoidance situation required a mean of 159 trials. (3) Five monkeys learning three or four auditory pattern discriminations simultaneously required a mean of 11 trials to learn the same auditory pattern discrimination for which 12 monkeys required a mean of 159 trials to learn. (4) Five monkeys learned to differentiate patterns which consist of different proportions of the same frequency elements more rapidly than they learned to discriminate patterns with the same proportion of frequency elements but differently arranged. These results are discussed on the background of earlier studies of auditory pattern learning by animals. [Supported by PHS NS 06587.]
Sound transmission in the thorax
Authors: Merchant H. C. , Golden R. D. , Cobb L. A.
Published: October 2005

The use of an intracardiac sound source to determine transfer functions and propagation paths and modes for the thorax using digitial data reduction techniques is discussed. It is important to know the sound transmission characteristics of the thorax for diagnostic purposes. Studies made using naturally occurring heart sounds have not satisfactorily defined either the origin or the transmission modes and paths for the signals. An intracardiac sound source inserted by standard cardiovascular catherization techniques [“Artificial Sound Production in the Cardiovascular System,” H. C. Merchant et al., J. Assoc. Advan. Med. Inst. 7, No. 4 (Sept. 1973)] was used as the sound source. The sound source and external receiver were located in three dimensions using x-ray techniques [“Three Dimensional Location Using Planar X-ray Systems,” R. D. Golden et al., J. Assoc. Advan. Med. Inst. 6, No. 3 (May 1972)]. Preliminary experiments were performed using experimental animals. The analog data were digitated and reduced on a digital computer using correlation and spectrum analysis techniques.
Moderate frequency transposition as an aid for the moderately hearing impaired
Authors: Mazor M. , Simon H. , Scheinberg J.
Published: October 2005

The intelligibility of frequency-reduced speech was measured for four normal and eight hearing-impaired subjects with sensory-neural high-frequency loss. Hearing levels were roughly 40 dB. Four conditions of frequency reduction, 0%, 20%, 33% and 55% were obtained using a Varispeeeh compressor. The test materials were PB 50-word lists recorded by one male and one female speaker. The effect of frequency reduction was to reduce intelligibility in all cases except one, that of the female voice at 20% reduction for the hearing-impaired listeners. It is possible that even greater improvements may be obtained at smaller frequency reductions. The interpretation is that the hearing-impaired listeners have better residual hearing in the lower frequencies and, since female (and children's) speech have relatively more energy in the high frequencies, a moderate frequency transposition can bring this energy down to a frequency region typical of male speech without producing intelligibility-destroying distortion.
Backscattering and diffraction from bare and lined wedges—theory and experiments
Authors: Cohick S. M.
Published: October 2005

This report documents an experimental program to determine the ability of existing theoretical formulations to predict the diffraction field from submerged wedges. Both backscatter and diffraction measurements were conducted on two wedges measuring 75° and 90°. Tests were conducted on the bare steel wedges and on the wedges lined with a pressure release rubber. The experimental results were compared to the first-order approximation of the diffraction field from rigid and pressure release wedges. The experimental values for the bare steel and rubber-lined wedges agree to within experimental error. This combined value agrees more closely with the pressure-release wedge theory than with the rigid wedge theory. [Supported by the Naval Ordnance Systems Command.]
Backscattering of low-frequency acoustic waves from the sea surface
Authors: Welton P. J. , Boyd M. L.
Published: October 2005

In this paper, a previously developed scattering model [Boyd and Deavenport, J. Acoust. Soc. Am. 53, 791 (1973)] is extended to treat backscattering from gravity waves on the sea surface. The statistical description of the sea surface used in this work has two advantages over previous representations of the gravity wave-height spectrum. First, the wave-height spectrum used here can be Fourier transformed to yield a simple, closed-form sea surface autocovariance function, which is required in the evaluation of the scattering integrals. Second, when a low-frequency or wave-expansion technique is applied to the scattering integral, the first three terms in the expansion can be evaluated. This should be contrasted with conventional representations of the wave-height spectrum which limit the evaluation to the first two terms. The expressions derived here are valid for ratios of the rms wave height to the acoustic wavelength (h/λ) up to 0.3. Backscattering predictions based on this theory are presented and compared with low-frequency experimental backscattering data.
Acoustic volume scattering, Project Rarotonga
Authors: Batzler W. E. , Vent R. J.
Published: October 2005

Measurements of underwater volume scattering were made aboard HMNZS TUI during a cruise from Auckland, New Zealand, to Rarotonga in the Cook Islands in May 1973. Scattering data were obtained at 15 stations along the 3000-mile track which extended eastward from New Zealand about 1500 miles and then northward to Rarotonga. Directional transducers pointing downward were used at 5 and 12 kHz to obtain volume scattering strength, SV, as a function of depth. Values of SV, averaged over a depth interval of 1000 yd vary from −67 to −81 dB; at a given station, the strength at 12 kHz was usually higher than at 5 kHz, and at night the strengths at both frequencies are higher than in daytime. In a separate set of measurements, the scattering strength of a column extending from the surface to a depth of 1000 yd was obtained by use of a wide-band source (1.8 lb of TNT detonated at a depth of 60 ft) and an omnidirectional hydrophone at a depth of 30 ft. Analysis in 1/3-octave bands yielded column scattering strengths Sc over the frequency interval 1–20 kHz. The characteristic dependence on frequency observed previously at stations to the north of New Zealand and elsewhere in the Pacific and Indian Oceans was seen here also; a relatively sharp increase in column strength occurs from 1 to 6 kHz and this is followed by fairly constant strength out to 20 kHz. This pattern of frequency dependence prevails at all stations, but there is a significant station-to-station shift in the level of the scattering. This shift is gradual and is most pronounced at 3.2, 5.0, and 6.3 kHz, where column strengths for the early stations east of New Zealand are about 10 dB higher than for the most easterly stations.
Predictions of volume scattering strengths from biological trawl data
Authors: Love Richard H.
Published: October 2005

A volume reverberation model which utilizes actual fish distribution data has been developed to permit quantitative predictions of depth-dependent scattering strengths. The model was evaluated using coincident acoustic volume scattering measurements and biological trawl data collected in the Mediterranean Sea. Biological specimens were collected at discrete depths with an Issacs-Kidd midwater trawl. Each fish collected was identified and sized, and its acoustic cross section calculated utilizing regression equations relating fish species, length, and swimbladder volume at frequencies near swimbladder resonance or equations relating fish length to acoustic cross section at frequencies far above resonance. Scattering strengths for each species were then determined, indicating dominant species at each trawl depth for 1/3-octave frequency bands between 2.5 and 20 kHz. The acoustic data were obtained with surface-vented explosive sources and a shallow omnidirectional hydrophone. These data were processed to yield integrated column strength versus depth profiles, which were then numerically differentiated to produce scattering strength versus depth profiles for each frequency band. Comparison of the model predictions to the scattering strength profiles showed good agreement at the higher frequencies, with the agreement decreasing with frequency below 8 kHz. Possible causes of this disagreement are enumerated.
Amplitude shading of sonar transducer arrays
Authors: Wang H. S. C.
Published: October 2005

Amplitude shading is an important technique for controlling the beamwidth and sidelobe level of transmitting and receiving arrays in sonar and radar. The traditional method of Dolph-Tchebyscheff synthesis for the determination of array amplitude shading or weighting coefficients is, however, high restrictive despite extension and generalization by many workers following Dolph. This paper outlines an entirely new method of finding these shading coefficients by minimizing the power received by the array in an isotropic noise field exclusive of a three-dimensional spatial slice around the mainbeam direction. The method is completely general in the sense that it is applicable to any discrete array of transducers arbitrarily distributed in three-dimensional space. As an illustrative example, nonuniformly spaced linear arrays (which are necessary for reasons of economy and operation over a band of frequencies) are shown to have been successfully shaded to acceptable pattern shape and sidelobe levels. In the special case of equally spaced linear transducer arrays, the new method of shading yields a mainbeam shape essentially identical to Dolph-Tchebyscheff's for the same sidelobe level, while the total power received (or transmitted) via the sidelobes is actually slightly less than one-half of that by the latter synthesis. Necessary detailed mathematical formulas for applying the method to circular (including arc) arrays are also suggested.
Acoustics of spaces between axisymmetric structures
Authors: Apfel Robert E. , Lyon Richard H.
Published: October 2005

The acoustic behavior of a fluid in the space between two axisymmetric rigid bodies has been investigated, with emphasis placed on the determination of the resonance frequencies of this space. An approximate wave equation derived for this interspace is quite similar to the Webster horn equation. Since the interspace wave equation can be solved analytically for only a few special shapes, an approximate Rayleigh-Ritz procedure is used to predict the resonance frequencies of the space. This procedure is shown to give accurate results when applied to an exponential horn, for which the exact solution to Webster's horn equation is known. It is then applied to the practical case of the interspace region in the Apollo Command Module. The resonance frequencies so predicted are in resonable agreement with measurements on a one-tenth acoustic scale model of the Apollo Command Module. [Work performed at Bolt Beranek and Newman Inc. under the sponsorship of the National Aeronautics and Space Administration.]
Cylindrical nearfield calibration array
Authors: Van Buren A. L. , Trott W. James
Published: October 2005

The planar nearfield calibration array (NFCA) has previously been used to determine the farfield radiation of underwater transducers from nearfield measurements. We consider here a cylindrical NFCA constructed from a single line of suitably shaded reciprocal hydrophones. The transducer to be calibrated is rotated within a volume V near the line about an axis parallel to the line. The response, beth amplitude and phase, of the line is measured at N angular positions equally spaced over the 360°. In this way a virtual cylindrical array of N lines is created. The azimuthal farfield pattern of the transducer is then obtained by computer processing the N responses together with a set of complex shading coefficients. The coefficients are designed so that the entire virtual array, if driven as a source, would produce a plane wave over the volume V. Experimental results were obtained for a large piston transducer. The computed farfield patterns are in good agreement with directly obtained farfield patterns.
Solid lens collimator for high-frequency nearfield measurements
Authors: Folds D. L.
Published: October 2005

Acoustic measurements with nearfield arrays which simulate farfield conditions have been used in the past at frequencies less than 20 kHz primarily due to the difficulties of fabricating multielement transparent arrays at high frequencies. In this paper a solid lens operating as the acoustic equivalent of an optical collimator is used to produce planar waves. The acoustic collimator employs a single transducer element placed at the focal point of an acoustic lens. Amplitude shading which is required to control the diffraction rings at the edge of the field can be accomplished by proper selection of the attenuation coefficient of the lens material. Also, the directivity of the single transducer element can be designed to achieve appropriate shading of the lens aperture. This paper describes collimator lens design considerations and experimental results obtained with a 50-cm-diameter polystyrene lens used as a collimator in calibrating a 20-cm2 hydrophone in the frequency range 200–600 kHz and a 10-cm piston in the frequency range 600–1200 kHz. Farfield results and those obtained with the collimator lens in the nearfield are compared.
Determination of lip noise by correlation measurements
Authors: Regan D. R. , Meecham W. C.
Published: October 2005

An experimental investigation of lip noise has been conducted at the UCLA Aerosonics Laboratory using a 112-in.-diameter model jet. Over the range of Mach numbers M for which the experiments were performed (0.3 ⩽ M ⩽ 0.7) the lip noise intensity IL was found to vary as the sixth power of the jet velocity (IL ∼ U6) consistent with a dipole source. Cross-correlation measurements of the nearfield acoustic pressure waves emitted perpendicular to the jet axis show that lip noise originates from two lip positions (off axis), the two contributions being out of phase for frequencies significantly above 2 kHz. Cross-correlation measurements of the farfield acoustic pressure waves emitted from symmetric positions on opposite sides of the jet axis suggest that lip noise reaches maximum intensity about 70°–80° from the jet axis. Third-octave spectral analysis shows that lip noise can be characterized as a wide-band (impulsive) type of noise peaked at a frequency f ∼ U/D, where D is the jet diameter. Measurements made with a small, 2-mm-o. d. probe tube mounted flush with the inside surface of the lip show, as expected, that the hydrodynamic pressure fluctuations arising from turbulence there are proportional to the square of the jet velocity (p ∼ U2. Calculations made from the probe tube measurements yield values of 0.03 for the turbulence intensity just inside the lip of the jet. Normalized cross correlations of 0.1 were found for the lip pressure with the sound field. [Partially supported by NASA-Ames Research Center.]
Aerodynamic noise experiments in a quiet free jet
Authors: Griffith E. D.
Published: October 2005

Aerodynamic noise experiments utilizing a two-dimensional cambered airfoil extending through both the potential core and the mixing regions have been conducted in the quiet free jet facility at the Lockheed Rye Canyon Research Laboratory. Farfield noise measured in these tests differs significantly from the noise reported by other investigators in similar experiments. Specifically, the pure-tone phenomena previously observed with airfoils subjected to subsonic flows of 100–200 ft/sec have been absent in these tests. Instead the measured noise is broad band, extending from 100 to 16 000 Hz, and appears to be random in character. Two peaks are observed in the spectra near 400 and 6000 Hz. At present, it is uncertain whether the source of lower band peaking at 400 Hz is in the potential core, the mixing regions, or perhaps both. However, considerable evidence has been obtained that indicates that the source of the higher band peaking at 6000 Hz is a dipole radiation caused by fluctuating surface loads in the turbulent boundary layer of the airfoil in the potential core. This high-frequency band of noise was predicted before these experiments were conducted by the theoretical work discussed in Dr. Revell's paper.