bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer simulations of mutable psychometric functions
Authors: Leek Marjorie R. , Hanna Thomas E. , Marshall Lynne
Published: October 2005

The psychometric function of an experimental subject is almost certainly not fixed, but varies in response to nonsensory factors such as attention and learning. This is particularly true when the subject is inexperienced, or the complexity of the task requires a substantial allocation of attentional resources by the subject. With commonly used psychometric procedures it is impossible to know whether a shallow psychometric function slope is a true reflection of the sensory process, or is a result of “averaging” a highly variable underlying function. Computer simulations were used to assess the ability of a 2IFC adaptive procedure with two interleaved tracks to monitor the stability of the underlying psychometric function over the course of an experiment. Variability due to the slope of the underlying function and the measurement procedure will be reflected in the average level difference between the two tracks (across-track measurement), while the additional variability due to a changing psychometric function will be reflected in the within-track level differences. Simulated psychometric functions were either fixed across all. trials, shifted along the “stimulus” axis according to either a sinusoidal or square-wave movement (to simulate drifts or lapses of attention, respectively), or shifted by a negative exponential function to simulate learning effects. The across-track variability remained nearly constant across all attentional conditions, and was dependent almost entirely on the underlying slope of the function. However, within-track variability was strongly affected by the changes in psychometric function location. An estimate of underlying slope may be obtained from the across-track variability, and an indication of the relative stability of the underlying function can be extracted from within-track variability. [Work supported by the VA.]
Effect of threshold on the growth of loudness at low frequencies
Authors: Jesteadt Walt , Humes Larry E.
Published: October 2005

Loudness is generally thought to increase as a function of intensity at a more rapid rate at frequencies below 500 Hz than at higher frequencies. It is well established that loudness increases at a more rapid rate near threshold for all frequencies. To what extent can the pattern of loudness growth at low frequencies be accounted for by a combination of the threshold effect and the marked increase in threshold below 500 Hz? To answer this question, equations incorporating the threshold effect were fitted to several sets of data in the literature describing growth of loudness at low frequencies. Two such equations are generally used: ψ = k(φ − φ0)β or ψ = k(φβ − φ0β), where ψ represents the psychological magnitude, φ represents the stimulus intensity, and φ0 represents stimulus intensity at threshold. With the exponent β held constant across frequencies and k allowed to vary, either equation can account for very high percentages of variance in the data and the residual error variance is not systematic as a function of frequency. This analysis suggests that the exponent of the loudness function does not change with frequency. [Work supported by NIH.]
The slope of the loudness function for individuals and groups with normal and impaired hearing
Authors: Hellman Rhona P. , Meiselman Carol H.
Published: October 2005

The slope of the loudness function for pure tones is derived at a frequency in the region of impaired hearing for more than 90 people with bilateral moderate-to-severe cochlear hearing losses. Calculations of the slopes are obtained over the stimulus range where cochlear impairment steepens the loudness function. Slope distributions for impaired hearing, determined from magnitude estimation and production and from cross-modality matching, are compared to those obtained in a similar manner for 51 people with normal hearing. Values of the slopes reveal two distinct populations. Most of the slopes in normal hearing vary from 0.4 to 0.7 with a mean close to 0.6; in cochlear impairment they vary from 1.1 to 2.8 with a mean close to 2.0. In accord with loudness matching, much of the greater variability of the impaired distributions arises from the heterogeneity of thresholds. The results also show that group loudness functions generated from cross-modality matching are consistent with theoretical functions determined from an equation for loudness suggested by Zwislocki [Handbook Math. Psychol. 3, 3–97 (1965)]. [Work supported by the Rehabilitation Research and Development Service of the VA.]
Perceived distance and loudness-softness functions
Authors: Guirao Miguelina
Published: October 2005

Experiments were designed to investigate the relation between auditory-perceived distance and sound intensity. A pure tone at 1000 Hz and a wide band of noise were heard through earphones in a soundproof room. Sounds were presented at random and at continuously increasing or decreasing levels over a stimulus range from 20 to 80 dB SPL. Naive listeners with normal hearing estimated distance by judging nearness (proximity) and farness (remoteness). They also judged loudness and softness. Judgments were made by a conventional and two modified versions of the method of magnitude estimation. According to preliminary results, the effect of stimulus level on the responses depends on whether the subjects are instructed to judge the sound in terms of its nearness to or distance from them. The nearness and farness functions are similar in shape to the loudness and softness functions, respectively. Results are discussed in relation to the auditory attributes of density and volume. [Work supported by NIH.]
On the pitch of mistuned harmonics in a complex tone
Authors: Hartmann William Morris , Smith Sandra L.
Published: October 2005

Four listeners matched the pitch of a single mistuned harmonic in an otherwise periodic complex tone, whose fundamental frequency was near 200 Hz. In individual experiments, harmonics numbers 1, 2, 3, 4, 5, 7, 9, and 11 were individually mistuned, by 11 different amounts ranging from − 8% to + 8%. The experiment thus measured the shift in the pitch of a sine component caused by other components of the complex tone. The experiments showed that for mistuned low-order harmonics a positive mistuning produces a positive pitch shift while a negative mistuning produces a negative pitch shift. For mistuned high-order harmonics the pattern is similar except that the pitch shifts caused by positive mistunings become large. These data were compared with a place theory in which the peak in the excitation pattern for an individual harmonic is partially masked by peaks due to neighboring harmonics. Although the model correctly predicts the results for positive mistunings, it fails dramatically for negative mistunings. The data are also compared with a theory whereby pitch is determined by peaks in an interspike-interval histogram per the MIT model. This theory can account for all the data, except for the mistuned fundamental, though filter bandwidths must be considerably enlarged compared to the MIT model to obtain agreement. [Work supported by the National Institutes of Health.]
An indoor sound-power test for light vehicles
Authors: Hickling Robert , Bolen Lee N.
Published: October 2005

There is a need to develop sound-power tests as standards for the noise of manufactured products, such as automobiles. For uniformity of testing, the tests have to be independent of the test location. Sound-intensity measurements can be used for this, as has been demonstrated in tests with six automobiles. The sound power of each vehicle was measured for different loads and engine speeds, using a semicircular array of sound-intensity probes rotated around the vehicle on a dynamometer roll. The tests were conducted at Clark Laboratory Services in a large work area with a hard floor and high ceiling, with partially absorbent material on the walls. There were no room resonances apparent in the A-weighted vehicle sound-power spectra. Also, theoretical estimates with point sources in a reverberant room showed that the presence of the walls and ceiling has a negligible effect on the A-weighted sound power of the vehicles. Good agreement was obtained with a standard reference source. The results with the six vehicles indicated that the peaks in narrow-band sound-power spectra can be used to identify noisy components in a vehicle power train. [Work supported by the United States Office of Naval Research.]
Education, research, and acoustic levity: Miscellaneous demonstrations
Authors: Maynard J. D.
Published: October 2005

During the course of teaching and conducting research in acoustics, a number of demonstrations have been developed. Some have been for classroom education, some have been for our own education, some have been for entertainment, and some have led to serious research projects. These demonstrations include the sonic motor, acoustic levitation, the projected Chladni plate, shock inception, noise riding sound, following a mass and spring to chaos, acoustic Anderson localization, and tuning up a quasicrystal. The demonstrations will be presented as permitted by time and transportation limitations.
Videotape demonstrations of auditorium design principles using acoustic scale models
Authors: Siebein Gary W.
Published: October 2005

A videotape demonstration was developed to illustrate acoustical design principles for auditoria to undergraduate architecture students. An acoustical scale model of an auditorium was constructed with removable walls, floor, and ceiling. Starting with a microphone in free space, an enclosure is built in steps around the source and receiver. An echogram is recorded at each step so students can see the effect of increased enclosure on the sound that arrives at the listener's position. Theater seating, various quantities of absorbent material, acoustically shaped ceiling panels, and diffusing elements are added to the enclosure as the demonstration progresses. Echoes, excessive loudness, flutter, and other basic acoustical problems and their solutions are presented. The demonstrations show changes in the impulse response of the room as changes are made in the shape and volume of the room. It serves as an introduction to acoustical modeling and auditorium design for the students.
Focusing of an N wave by an ellipsoidal reflector: An experiment in air
Authors: Cheng Stephen T. W. , Jones Matthew R. , Blackstock David T. , Wright Wayne M.
Published: October 2005

An airborne experiment to model the intense pulse field developed by a lithotripter is in progress. The reflector is half an ellipsoid, machined from an aluminum block and having the following dimensions: major axis 280 mm, minor axis 140 mm, eccentricity 0.866, distance from aperture plane to either focus 121 mm. An electric spark at the interior focal point generates an N wave pulse. The reflected wave in the exterior region is observed with the aid of a condenser microphone having a very wide bandwidth. Of particular interest is the sequence of axial measurements from the aperture to the exterior focus and beyond. Expectations based on linear theory were that the pulse would start out N-shaped near the aperture, become U-shaped in the neighborhood of the focus (because of phase changes characteristic of three-dimensional focusing), and take on the shape of an inverted N beyond the focus. Measurements confirm expectations for the prefocal and focal regions. Beyond the focal region, however, the shape is not an inverted N. Instead it more closely resembles the U-shaped pulse recorded at the focus. [Work supported in part by Office of Naval Research and Texas Advanced Research Program.]
A method for measuring dynamic properties of soils
Authors: Farstad Jerry E.
Published: October 2005

A method is proposed for measurement of the elastic and damping properties of soils in the 100- to 1000-Hz frequency range. The soils are assumed to behave as linear viscoelastic materials. The measurement technique involves exciting vibration of a soil sample through fixtures of known dynamic characteristics. The mechanical impedance matrix of a system composed of sample and fixtures is measured directly. A model of this combined system permits the mechanical impedance matrix of the soil sample alone to be extracted. From this the dynamic properties of the soil material may be computed.
Comparison of complex dielectric constant with dynamic elastic moduli of several elastomers
Authors: Burns J. , Dubbelday P. S.
Published: October 2005

Complex dielectric constants were measured for several types of rubbery elastomers over a temperature range from −10 to 30 °C. The samples included a series of neoprenes with the same composition except for variable amounts of carbon black filler from 0% to 33%. These dielectric data are compared with elastic moduli measured on similar material to determine which elastic response is most closely correlated with dielectric properties. The correlation is discussed in terms of physical models of the polymers. [Work supported by ONR.]
Surface phenomena of finite amplitude, pure-tone sound on air-saturated porous materials
Authors: McIntosh Jason D.
Published: October 2005

It is well known that the flow resistance, as defined by Darcy's law, becomes a function of the fluid flow for large fluid velocities. For porous materials in air, there appears to be two separate nonlinear flow regimes; for low velocities, the resistance coefficient increases with the square of the fluid velocity; and for high velocities, the resistance coefficient increases linearly with the magnitude of the fluid velocity. In this paper, the two nonlinear flow regimes are parametrized for several porous materials. Nonlinear corrections are made to linear wave theory and numerical solutions for pure tones are obtained that then are used to predict surface admittance, absorption, and internal pressure attenuation for infinite and finite length samples. Among the phenomena predicted and also observed experimentally is a peaking and then a rolling off the surface absorption of a finite length sample as the surface pressure is increased. Also, a surface pressure criterion is put forth that gives an approximate maximum surface pressure that a porous material could be exposed to before these nonlinear phenomena become important in describing the material's characteristics. [This work was supported in part by a grant from the Defense Systems Divison of Honeywell, Incorporated.]
An omni-directional, ultrasonic acoustical source for three-dimensional position monitoring in air
Authors: Leifer Jack , Busch-Vishniac Ilene J.
Published: October 2005

An acoustically based means of tracking the position of the end effector of a moving industrial robot arm has been proposed. The system consists of an omni-directional acoustical source fixed to the robot arm, and several stationary sensors positioned throughout the robot's workspace. Based upon the time-of-flight of a 500-kHz signal traveling from the source to each sensor, the position of the end effector can be determined. This scheme is potentially an effective, yet economical alternative to the more complex optical tracking systems currently in use. The acoustical source incorporates an exponentially tapered solid Webster's horn that is driven in resonance by a commercial piezoelectric transducer mounted on its wide end. A high-amplitude vibration is produced at the narrow end of the horn, where the resulting sound field can be described by the piston equations. The pressure and omni-directional characteristics of the acoustical field produced are enhanced beyond those that could be generated by a simple flat piezoelectric source alone. Results obtained with this source confirm the feasibility of using ultrasound in air as a means of accurately determining positions in three dimensions. [Work supported by General Motors Research Laboratories.]
Improvement of reflection and transmission coefficient measurements on test panels
Authors: Audoly C. , Giangreco C.
Published: October 2005

The efficiency of acoustic materials is often evaluated by measuring the reflection and transmission coefficients on test panels in tanks. The aim is to obtain the intrinsic characteristics of the material, as if the panel were infinite. However, when the size of the panel is not large compared to the wavelength in water, the measurements are disturbed by scattering phenomena. Different techniques (use of surface hydrophones and transmitters, intensity receivers, double-layer transducers) are studied experimentally and theoretically and their use to improve the measurements is examined. For normal incidence measurements, good results are obtained with a surface hydrophone placed in the nearfield of the test panel.
Analysis of kinetic energy repartition for in-plane beam structures
Authors: Piaud J. B. , Loyau T. , Nicolas I.
Published: October 2005

In this paper, kinetic energy repartition for in-plane beam structures is analyzed using three different methods: the statistical energy analysis, the energy influence coefficient method (based on the modal approach), and the exact method (based on the wave approach). The two last methods allow the definition of a linear relation between the average kinetic energy of each beam and the excitations applied to all the structure. Therefore the contribution of each excitation to the kinetic energy of each beam can be shown. In the structure, the beam angle at a junction can take any value. A junction model with three degrees of freedom is developed to account for longitudinal and flexural motions. A comparison between the three methods is performed. The analysis results are presented for different angles, different types of junctions, and supports.
Propagation of elastic waves on thin-walled circular cylinders
Authors: Kil Hyun-Gwon , Pierce Allan D. , Ginsberg Jerry H.
Published: October 2005

This paper examines the nature of elastic waves propagating in a thin-walled circular cylinder from the viewpoint that the cylinder's geometry is a source of anisotropy. A point-excited circular cylinder is regarded as a two-dimensional anisotropic medium extending over an infinite domain formed from the stretched angular coordinate. Correspondingly, the displacement field is represented as a superposition of waves propagating out from localized sources into an unbounded medium. The excitation of waves by various types of point force is analyzed using Lighthill's theory. This leads to an expression for the farfield response of the point-excited unbounded medium, which can be expressed in a simple asymptotic form at frequencies somewhat higher than the ring frequency. Thus, in this frequency range, the farfield response of a point-excited circular cylinder can be easily obtained using the corresponding asymptotic farfield response of an unbounded medium. Using these results, it is shown that the wave motion in a thin-walled circular cylinder at moderate frequencies may be interpreted in terms of the wave motion in a thin plate. [Work supported by ONR.]
Theory and measurements of transient ultrasonic waves in a viscoelastic plate
Authors: Weaver Richard L. , Sachse Wolfgang , Niu Lin
Published: October 2005

The nearfield responses of a thick viscoelastic plate are computed for epicenter, off-epicenter receiver locations to a point step load acting normal to the surface. Analysis of these responses shows that the ray arrival behavior of a transient ultrasonic signal propagated through a thick viscoelastic plate can be analyzed to recover the plate material's dispersion and attenuation. Such measurements form the basis of the point-source/point-receiver measurement technique. Signal processing algorithms are demonstrated with synthetic and real signals obtained via this technique in elastic and viscoelastic materials.
Forced vibrations of stiffened cylindrical elastic panels
Authors: Mecitoglu Zahit , Dökmeci M. C.
Published: October 2005

The objective of this paper is to investigate the forced response of a stiffened circular cylindrical panel within the frame of Love's first approximation theory of elastic shells. The effects of stiffeners are taken into account by the orthotropic material approach, including the eccentricity of stiffeners. The variational equation of motion for the forced vibrations of thin elastic shells with clamped edges is derived from Hamilton's principle. The stiffened elastic panel is discretized by the Semiloof elements. Then, with the help of the variational equation, the matrix equation is obtained to determine the frequencies and mode shapes of the stiffened circular cylindrical elastic panel. Two types of stiffened shell panels are considered for forced-response analysis: the stiffened models by the stiffeners with rectangular cross section and with profile shape cross section. The influence of the spacings and dimensions of stiffeners on the forced response of the stiffened circular cylindrical panel is examined. The numerical results are plotted with respect to the parameters, and they are compared with certain earlier results. Further needs of research are pointed out.
Acoustical detection of insect larvae in post-harvest commodities
Authors: Webb J. C.
Published: October 2005

An acoustical system to detect insect larvae in fruit, nuts, and grain will be described. The system can detect 1-day-old fruit fly larva in grapefruit, mangos, or other similar fruit and lepidopterous and coleopteran larva in individual kernels of grain as well as bulk grain. Two types of detectors have been developed for this work. One type is based on the closed organ pipe principle that works well with both fruit and grain and a piezoelectric sensor that works primarily with grain. The signal of the feeding larvae is detected, amplified approximately 100 dB, filtered through the appropriate bandpass filters, and then stored on computer. The computer and software are capable of monitoring the larva 100% of the time through its life cycle. The system has applications both in basic research and quarantine inspection of insects in import and export commodities.
Sound and the moths that infest bee hives
Authors: Spangler Hayward G.
Published: October 2005

Two moths that infest bee hives, the lesser wax moth, Achroia grisella, and the greater wax moth, Galleria mellonella, generate ultrasonic pulses by buckling tymbals. Lesser wax moth males call continuously, producing 100-kHz sound pulses by which females orient and find them. Greater wax moth males generate a short series of 75-kHz sound pulses, but females find them by orienting to male pheromone. Females wing fan in response to male sound and may signal males to release more pheromone to guide them. In contrast, each tymbal of the related rice moth, Corcyra cephalonica, has nine striae that buckle and recover in sequence to produce 125-kHz sound in an irregular train of pulses. Female moths may not distinguish 7.5-ms pulse trains from 7.5-ms bursts of continuous sound. Both lesser wax moths and rice moths can be located and identified by detecting the sound of calling males. Acoustical traps may prove useful for monitoring or controlling populations.
Estimating sound power from discrete measurements of sound intensity on a hemisphere
Authors: Meyer W. Weston
Published: October 2005

In theory, total sound power radiated from a noise source can be determined by integrating the normal component of sound intensity over an arbitrary enclosing surface S. In practice, one must settle for approximation, taking the sound power integral to be a weighted sum of intensity measurements at certain strategically located nodes, or meshpoints, on S. What are the strategic locations, what are the weights, and what level of accuracy can be expected? The present paper attempts to answer these questions for the particular experimental setup described in a recent publication [R. Hickling and L. N. Bolen, “Indoor system for efficient measurement of the sound power of light vehicles,” NCPA Rep. RH-01-88]. Here, S is a hemisphere H plus circular base B—the latter a physical boundary that is perfectly reflective. The mesh covers H but not B: it appears rectangular in cylindrical projection, with longitudes equally spaced. Strategic positioning is therefore a matter of latitude selection. Several schemes are discussed based on different notions of optimality, the means of calculating weights for each scheme are shown, and numerical evidence is compiled to indicate that levels of accuracy attainable, by applying the quadrature formulas to various test functions (chiefly monopoles). The rapid fluctuations that can occur in the sound intensity function and the reasons for this condition are also discussed.
ANSI round robin test on determination of sound power from sound intensity
Authors: Shirahatti U. S. , Crocker Malcolm J. , Peppin Richard J.
Published: October 2005

The use of the sound intensity technique to determine the sound power output of a source has become very popular over the years. An American National Standards Institute committee, ANSI S12-21, is currently engaged in developing a suitable standard for making sound power measurements using the sound intensity technique. The draft version of the proposed standard permits the use of both fixed point measurements and also continous hand scanning on the enclosed surface. To check the validity of the sound power measurements and to help make suitable changes to the measurement procedure, many optional data quality indicators are also included in the draft. Recently, the working group ANSI S12-21 organized a round robin test on a standard reference sound power source. Various organizations across the United States participated in the round robin test. This paper summarizes and discusses the sound power measurement results obtained on the reference sound source.
Automated sound power measurement system for indoor testing of motor vehicle noise
Authors: Dietschi U. D.
Published: October 2005

Indoor noise testing of motor vehicles poses advantages not offered by the conventional outdoor pass-by test method. The sound power of a motor vehicle can be determined by measuring sound intensity over a surface enclosing the vehicle. Due to its geometric simplicity, a hemisphere was chosen for this purpose. In order to facilitate efficient measurement of sound intensity on a hemisphere, large enough to enclose an automobile situation on chassis dynamometer rolls, a special structure was designed to carry the intensity measurement probes. The structure was semicircular in shape made up of two concentric sections. The inner section with the measurement probes was hinged to the outer support structure such that it could be lowered into a position providing easy access to the microphones for calibration purposes. Truss sections were used in the construction of the microphone boom to present as small an interference to the sound field as possible. The entire structure was suspended at its apex and was driven by a stepper motor via suitable reduction gearing. Control of the stepper motor was provided by a computer programmed to complete either continuous sweeps of the hemisphere or in a discrete manner, stopping the microphone boom at equal angular increments.
Ultrasonic acoustic emissions from drought-stressed trees: Do bark beetles hear them?
Authors: Haack Robert A.
Published: October 2005

Bark beetles preferentially infest drought-stressed trees for reasons not completely understood. One possibility is that bark beetles are attracted to the ultrasonic acoustic emissions (AEs) that result from breakage of water columns in drought-stressed trees. AEs were measured from 20 to 300 kHz on cut trunk samples and on small, potted trees of several coniferous and hardwood species, using ceramic piezoelectric transducers and a four-channel AE analyzer. Mean rate of emission as well as mean signal duration, rise time, amplitude, and energy were determined at weekly intervals during periods of drying. Some of these results have recently been published [R. A. Haack et al., Florida Entomol. 71, 427–440 (1988)]. Using the mean emission rates and signal parameters to adjust the settings of an ultrasonic pulsing instrument, natural and artificial substrates were pulsed with ultrasound to simulate varying degrees of drought in the presence of bark beetles. The influence of pulsed AEs on the colonization behavior of bark beetles will be discussed. [Work supported by USDA.]
Phase sensitivity to amplitude-modulated stimuli as a function of component spacing
Authors: Sivaramakrishnan Savithri , Long Glenis R. , Tubis Arnold
Published: October 2005

The relation between phase sensitivity of a three-component amplitude-modulated (modulation index = 1) stimulus, presented at 40 dB SL, as a function of the frequency spacing of the individual components was examined. Five sets of stimuli with carrier frequency of 2000 Hz and modulation frequencies of 50, 100, 200, 300, and 400 Hz were generated. The phase of the center component was varied from 0–90 deg in steps of 10 deg to give a total of 50 stimuli. Subjects were asked to discriminate the zero phase stimulus from the other stimuli containing the same components in a 3I-2AFC paradigm. The relative pitch, and pitch strength, of stimuli containing the same components at different relative phase was determined using a paired-comparison paradigm. Measurements of each subject's auditory filter characteristics at 2000 Hz (based on the notched-noise paradigm) will be used to interpret the data. [Work supported by a David Ross Fellowship at Purdue University.]
Detection and recognition of amplitude modulation with tonal carriers
Authors: Sheft Stanley , Yost William A.
Published: October 2005

The ability of listeners to process multiple sources of sinusoidal amplitude modulation (AM) was evaluated using both detection and recognition procedures. For all conditions, the stimulus was a two-tone (909 and 4186 Hz) complex. Test-AM frequencies were 4 and 17 Hz. In the detection paradigm, d-primes obtained with simultaneous modulation of both tones were compared to the d-primes obtained with modulation of just one of the tonal components. When both tones were modulated at the same frequency, a phase disparity between the envelopes reduced AM detectability. With the envelopes in phase, results showed a linear summation of the d-primes for the individual components. With modulation of the two tones at different AM frequencies, performance approximated optimal processing of two sources of uncorrelated information. A similar result was obtained in the recognition paradigm when the task was to discriminate between the two modulation frequencies. When the AM frequency was fixed and the task was to identify which carrier was modulated, performance was near chance. Results are consistent with processing of near-threshold AM through modulation-specific channels that are broadly tuned to carrier frequency. [Work supported by NINCDS.]
Discrimination and identificaiton of modulation rate using a noise carrier
Authors: Hanna Thomas E.
Published: October 2005

Modulation-rate perception was measured with three tasks: a fixed-standard, forced-choice discrimination task with a 500-ms interstimulus interval; a randon-standard, forced-choice discrimination task with an 8-s interstimulus interval; and an identification task. Threshold were obtained for modulation rates from 14–224 Hz using noise carriers bandpass filtered from 500–4000 Hz, 500–1600 Hz, 1700–2800 Hz, and 2900–4000 Hz. The four bands yielded similar results except for modulation rates above 100 Hz, where the 500- to 1600-Hz thresholds were higher. Fixed-standard discrimination thresholds were about 3 Hz for modulation rates up to 66 Hz. Increased thresholds for modulation rates above 66 Hz are presumably due to temporal resolution limits. For modulation rates above 100 Hz, modulation rate resolution with the 500- to 1600-Hz carrier is probably limited by critical band filtering rather than temporal resolution. Resolution in the random-standard discrimination task was similar to that for the identification task. Threshold were elevated relative to fixed-standard threshold except at the extremes of the stimulus range. In the random-standard discrimination task, a pronounced criterion bias was also present for stimuli near the extremes of the range. Durlach and Hraida's [J. Acoust. Soc. Am. 46, 372–383 (1969)] model describes the data well and provides quantitative measures for modulation-rate perception in good agreement with those for intensity perception. [Work supported by ONR.]
Thresholds for the frequency discrimination of pulsed tones (DLFs) and for the detection of frequency modulation (FMDLs): Effects of noise and random variations in level
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

In experiment I, DLFs were measured in four conditions: (1) in quiet with the level fixed at 70 dB SPL; (2) in quiet with the level of each tone varied randomly over a 6-dB range around 70 dB SPL; (3) as 1, but with a continuous bandpass noise designed to mask the upper side of the excitation pattern; and (4) with bandpass noise and with the level of the signal randomized over a 6-dB range. Center frequencies from 0.5–6.5 kHz were used. Except at 6.5 kHz, the results were not consistent with the assumption that the DLFs were based on the detection of changes in excitation level on the low-frequency side of the excitation pattern. Experiment II was like experiment I, except that FMDLs (4-Hz rate) were measured, and, in conditions 2 and 4, a 4-Hz amplitude modulation (AM) with a peak-to-valley ratio of 6 dB was imposed on all signals; the phase of the AM relative to the FM was random. The results were generally not inconsistent with the assumption that the FMDLs were based on the detection of changes in excitation level on the low-frequency side of the excitation pattern. However, neither a single-band nor a multiple-band excitation-pattern model was able to account for the effect of the bandpass noise of the FMDLs. [Work supported by MRC, U.K.]
Temporal modulation transfer functions for pure tones
Authors: Yost William A. , Sheft Stanley
Published: October 2005

Temporal modulation transfer functions (TMTFs) were obtained for sinusoidally amplitude-modulated (SAM) pure tones. TMTFs were obtained by determining the depth of SAM required for modulation detection in a two-alternative, forced-choice adaptive procedure. TMTFs were obtained for 500-, 1000-, and 4000-Hz carrier frequencies; for durations of 125 and 500 ms (all stimuli were shaped with a 20-ms raised cosine); in gated and continuous background conditions; and for modulation rates ranging from 2–128 Hz. In the gated condition, the carrier tone was gated on and off and the modulation occurred over the full duration of the tone, while in the continuous condition, the carrier tone was on continuously, and it was modulated during the observation interval. Thresholds for modulation detection were lower in the continuous than in the gated condition and the thresholds were lower for the 500-ms than for the 125-ms stimuli. The TMTFs displayed a bandpass characteristic in all conditions, but the high-pass segment was steeper for the gated than for the continuous conditions. The loss in sensitivity at low modulation frequencies meant that the lowest thresholds were obtained for modulation frequencies of 4–8 Hz in the continuous condition and above 16 Hz in the gated condition. The data will be discussed in terms of other measures of modulation processing and theories of temporal processing, especially those involving envelope extraction. [Work supported by the NINCDS.]
Syllable structure and units of analysis in speech perception
Authors: DeGroot Jenny , Nusbaum Howard C.
Published: October 2005

Syllables or their constituents, such as onsets and rhymes, may be basic units in speech perception. If so, then recognition of a target phoneme might be influenced more by its syllabic context (i.e., other phonemes in the same syllable or constituent) than by other aspects of phonetic context. To investigate the influence of syllable structure on phoneme perception, subjects in three response-time experiments were instructed to identify a target phoneme, ignoring variation in an adjacent phoneme. In one condition, the adjacent phoneme was held constant; in a second condition, contextual variation was irrelevant to target identity. In two experiments, context varied either within the same syllabic onset or in an adjacent syllable. The third experiment involved varying an adjacent phoneme either in the same syllable as the target or in a neighboring syllable. If the syllable or onset is perceived as a unit, then varying context within that unit should slow target recognition more than varying context outside the syllable. The results have implications for the role of syllable structure in speech perception. [Research supported by AFOSR and BRSG.]
Malleable frequency effects in spoken word recognition
Authors: Luce Paul A.
Published: October 2005

Recent research has demonstrated that word frequency effects in spoken word recognition are primarily due to processes responsible for deciding among multiple lexical items activated in memory and not to differences in activation levels or thresholds of word units. The present study further supports this claim by demonstrating that frequency effects in the identification of spoken words are malleable and can be modified by varying the composition of the experimental stimuli. A set of high-frequeocy words was presented for identification mixed with either other high-frequency words or with low-frequency words. A set of low-frequency words was also presented with high- or low-frequency words. The results demonstrated that high-frequency words were identified more accurately when presented with other high-frequency words and that low-frequency words were identified more accurately when presented with other low-frequency words. The implications of these results for current models of spoken word recognition, in particular the neighborhood activation model, will be discussed. [Work supported by NIH Grant NS-12179 to Indiana University.]
Pitch of complex tones with many high-order harmonics
Authors: Houtsma Adrianus J. M. , Smurzynski J.
Published: October 2005

Pitch identification and pitch discrimination experiments were performed for complex tones with missing fundamentals between 200 and 300 Hz and with many successive harmonics varying from low (below the 10th) to high (above the 25th) harmonic order. Identification performance was found to degrade with increasing harmonic order from an essentially perfect to an asymptotic level that was clearly less than perfect but much better than chance. Just-noticeable differences in (missing) fundamental frequency were found to increase, with increasing harmonic order, from a fraction of 1 Hz to an asymptotic level of about 5 Hz. Influence of phase was found only for tone complexes of high harmonic order. Results support the existence of two separate pitch mechanisms in the auditory system, one based on pattern matching of resolved frequencies, the other on periodicity of nonresolved frequencies.
Comparing monotonic, diotic, and dichotic presentation modes in synchrony detection
Authors: Richards Virginia M.
Published: October 2005

In a 2IFC paradigm, listeners discriminated between sounds composed of two bands of noise whose center frequencies were 2500 and 5000 Hz, and whose envelopes were either identical or time delayed, one relative to the other. The extent of the temporal delay necessary for 70% correct discriminations was estimated. Dichotic masking noise was continuously present. Four presentation modes were employed: diotic, monotic, dichotic, and monotic with contralateral maskers. In the monotic with contralateral masker condition, bands centered at 2500 and 5000 Hz were presented to the ear contralateral to the signal bands. Those “masker” bands were independently chosen, and so were unrelated to each other and the signal bands. Performance levels were best in the diotic condition, an average delay of 3 ms being needed for discrimination. Performance levels in the dichotic, monotic, and monotic with contralateral masker conditions were only slightly poorer. [Work supported by the Air Force Office of Scientific Research and a National Institutes of Health post-doctoral fellowship.]
On the acoustic determination of the elastic moduli of anisotropic solids and acoustic conditions for the existence of symmetry planes
Authors: Norris Andrew N.
Published: October 2005

The 21 elastic moduli of a homogeneous anisotropic solid can be determined from the second-order acoustical tensors associated with wave motion in six phase directions. The acoustical tensor can be calculated from the three phase speeds and displacement polarizations for a given phase direction. The six directions may be quite arbitrary as long as they cannot be contained in less than three distinct planes through the origin and do not all lie on the curves formed by the intersection of the unit sphere with an elliptical cone. It is shown, for example, how the general procedure can be used to find the elastic moduli for a thick plate specimen, for which acoustic access is limited to inspection from the two parallel faces. Acoustic conditions that are both necessary and sufficient, that a solid possess a plane of material symmetry, will also be discussed. [Work supported by NSF.]
Transverse Pearcey patterns observed in the reflection of ultrasound from curved surfaces
Authors: Frederickson Carl K. , Marston Philip L.
Published: October 2005

This research concerns the reflection of light and sound from smooth curved surfaces to produce transverse cusp caustics (and associated wave fields) and the inference of shape information from such caustics and wave fields. From the generic wave front shape associated with transverse cusps [P. L. Marston, J. Acoust. Soc. Am. 81, 226–232 (1987)], it has been calculated that reflection of sound from a point source off of a surface whose height h(x,y) = h1x2 + h2y2x + h3y2 (with h2≠0) produces a transverse Pearcey pattern [P. L. Marston, in Acoustical Imaging (Plenum, New York, 1988), Vol. 16, pp. 579–588]. The imaging of such patterns by raster scanning of a small hydrophone in water is described. The ultrasonic burst incident on the surface is sufficiently long to simulate the reflection of a steady-state sine wave. When the sound source was replaced by a light source (and the hydrophone replaced by a photodetector), the corresponding optical cusp caustic was imaged and used to infer the shape parameter h2 for the polished metallic reflecting surface. These parameters facilitated a comparison of observed and predicted acoustic wave fields. [Work supported by ONR.]
On ambient noise generation by “soliton” surface waves
Authors: Mellen Robert H. , Middleton David
Published: October 2005

Wave-wave interaction is one of the more promising mechanisms for wind-generated ambient noise. However, levels calculated with the linear gravity/capillary dispersion model for surface waves are found to be much too low above about 10 Hz. This discrepancy may rest in the wave model rather than the mechanism itself. Surface-wave measurements in flumes show no evidence of dispersion at higher wavenumbers. To account for dispersionless propagation, a nonlinear model in which the surface fine structure is treated as a random ensemble of solitonlike hydraulic bumps rather than dispersive waves has been proposed. The “soliton” model appears to account for measured acoustic backscattering strengths and associated Doppler spectra at moderate sea states. Effects of the model on ambient noise prediction are examined.
Effect of monomolecular films on the underlying ocean ambient noise field at low sea states
Authors: Rohr Jim , Updegraff Garr E.
Published: October 2005

In sea states, two-six monomolecular films on the ocean surface have been previously reported to dramatically reduce the ambient noise field beneath them. The mechanism was presumed to be associated with ocean whitecapping. A recent series of low sea state tests with films, in the absence of whitecapping, has found an even more pronounced ambient noise reduction if the ocean surface agitation is above a certain critical level. The mechanism through which the films reduce surface noise at low sea states is explored.
Electroacoustics in the OMNIMAX® theater—Challenge and opportunity
Authors: Wales Alvis F.
Published: October 2005

IMAX® and OMNIMAX® films have significantly advanced the realism and impact of motion picture presentations. To derive full benefit from the giant screen, the theater acoustics and sound reproduction system must be equal in quality to the picture. Most IMAX and OMNIMAX theaters have seen new construction, which permits a higher level of acoustical performance and noise control than most other cinemas. OMNI-MAX theaters, in particular, pose special acoustical problems because of the focusing effect of the dome screen, combined with the tendency of architects to choose an acoustically difficult shape (such as a cylinder, a hemisphere, or even a sphere) for the enclosing building. To permit full spatial and directional effects, the theater acoustics are designed to be relatively nonreverberant, leaving the “ambience” and sound “images” to be created by the sound track rather than dominated by the theater acoustics. Particular attention is paid to the sound system in terms of frequency response, dynamic range, and imaging capability.
Electronic equipment noise in video facilities
Authors: Foulkes Timothy J.
Published: October 2005

Noise from electronic equipment is a significant problem for many video studios and ancillary facilities. Frequent efforts to control room ventilation noise are negated by noisy components that must be located within the critical spaces themselves. This paper will review acoustical design considerations for a few recent case histories. Measured data from several completed facilities and strategies for noise control will be discussed.
A stable data adaptive method for matched-field array processing in acoustic waveguides
Authors: Byrne C. L. , Brent R. I. , Feuillade C. , DelBalzo D. R.
Published: October 2005

The presence of a “modal noise” component leads to estimator instability when Capon's maximum likelihood (ML) method is applied to the processing of data from a vertical array in an acoustic waveguide. The physics of the waveguide forces signal vectors and noise vectors alike to be projected onto the span of the “mode” vectors, when the number of sensors (N) exceeds the number of propagating modes (M). The instability occurs whenever the (single snapshot) N × 1 data vectors have the form x = Us + Uγ + white noise, where the matrix U is N × M (sampling the normal modes at the hydrophone locations and independent of the actual acoustic disturbances present), and s and γ correspond to signal and ambient noise sources, respectively. This condition arises in normal-mode and local normal-mode propagation. The dominant eigenvectors of R−1 (where R is the cross-spectral matrix) are sensitive to slight inaccuracies in the calculation of R−1 in ways that affect the performance of the ML estimator. Following transformation of the N × N matrix R to the M × M modal space cross-spectral matrix T, Capon's method is applied to T to obtain the “reduced maximum likelihood” (RML) estimator. This procedure, which is a development of the sector focused stability technique of Steele and Byrne [Proceed. ISSPA 87, 24–28 August 1987, Brisbane, Australia, pp. 408–412], largely eliminates instabilities due to inaccurate inversion of R. Simulations are presented for a shallow-water environment to provide comparison between the ML and the RML estimators. These indicate that the degree of instability depends upon the level of noise (both correlated noise and white noise) and that a significant improvement in performance can be expected by use of the RML estimator in both cases.