bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Woodwinds by Tone-Hole Cutoff Frequency
Authors: Benade A. H.
Published: October 2005

Chotteau (Thesis, Case Western Reserve, 1971) remarked that a clarinet's measured tone-hole cutoff frequency fc is quite constant over the first two registers. A similar remark is found to apply to all successful woodwinds. The cutoff frequency can characterize a woodwind, since the major acoustical properties of the tone-hole system may be written as simple functions of (f/fc). In an irregular lattice fc varies from cell to cell. At log frequencies the first cell fc dominates. For f near cutoff the average fc of the first two cells dominates, thus regularizing the behavior. Cutoff frequencies were measured for oboe-family instruments of leading players and makers from the Baroque, classical, romantic, and modern periods (including Triébert and Uebel Boehm instruments). Analogous studies have been made on bassoons of Baroque, Marzoli Boehm, modern French, and German type. Similarly chosen clarinets of the major pitches and “systems” from 1830 to the present have been analyzed. Good instruments show great acoustical regularity (even bassoons). Baroque instruments have lower fc than their modern counterparts. Regardless of pitch (e.g., C, B♭, and A clarinets), overall “darker” tone is associated with lower fc. Too high fc causes harshness (e.g., Boehm bassoons and oboes).
Design of a Harpischord Soundboard and Bridge
Authors: Pyle R. W. , Warner Caleb
Published: October 2005

A harpsichord built largely of fiberglass-reinforced polyester and epoxy has been designed with a soundboard and bridge of unconventional construction inspired by the classical flat-top guitar. The harpsichord strings terminate on the bridge instead of passing over it to a hitchpin rail on the frame. The “split-level” soundboard of glass-epoxy printed circuit board material is attached to the top of the bridge at the rear and to the bottom at the front. A prototype instrument was characterized by reasonably good tone quality but inadequate loudness. A series of simple experiments on samples of various soundboard materials interpreted with the aid of some bending-wave theory showed in what directions to change the soundboard and bridge parameters. The resulting instrument is considerably louder than the prototype and is judged to have better tone as well.
Neural Control of Segmental Timing
Authors: Allen George D.
Published: October 2005

This paper attempts to specify precisely what kind of neural mechanism underlies segmental timing in speech production. One possible mechanism involves a neural “clock,” with a very short cycle time (of the order of 1 or 2 msec), which is read by a neural counting buffer. The duration of a speech segment could then be coded neurally as some number, n, of clock cycles, and timing control would be realized by the counting buffer counting up to n. A second possible mechanism involves a neural “decay” process (e.g., decreasing rate of firing of some neuron) and a neural “zero detector” to tell when the process has decayed. Segmental duration could then be coded as the starting value given to this decay process. No neural mechanism is error free, however, and the errors produced by these two hypothetical mechanisms should be different. The clock and counter model, since it involves a large number of clock cycles per segment, predicts symmetric error structure; the decay model, on the other hand, predicts positively skewed errors. Data to test these predictions are presently being collected. [This investigation was supported by PHS Research Grant No. DE 02668 from the National Institute of Dental Research and in part by General Research Support Grant No. RR 5333 from the General Research Support Branch of the National Institutes of Health.]
Interaction Between Two Factors that Influence Vowel Duration
Authors: Klatt Dennis H.
Published: October 2005

A list of 80 English words was recorded in the frame sentence “Say … instead” by three talkers. The list contained single-syllable words (e.g., “smooth”) and two-syllable words derived by appending an unstressed syllable to the single-syllable words (e.g., “smoothest”). The durations of the stressed vowels were measured from spectrograms. Vowel duration in the single-syllable words varied as a function of features of the post-vocalic consonant. For example, average vowel duration was 132 msec preceding voiceless consonants and 198 msec preceding voiced consonants. The addition of a second unstressed syllable to these words tended to shorten the duration of the stressed vowels. However, the percentage amount of shortening was strongly dependent on the voicing feature of the post-stressed consonant—vowels became 103 msec (18% shorter) before voiceless consonants and 131 msec (34% shorter) before voiced consonants. The interaction of shortening rules involving the post-vocalic consonant and the additional syllable is clearly not simple. The data suggest that a vowel that is shortened by one rule becomes less compressible to additional shortening influences than a simple ordered list of independent percentage-shortening rules would predict. [Work supported in part by National Institutes of Health and by Office of Naval Research.]
Electroencephalographic Sinusoidal Response to Rapid Periodic Click Stimuli in Waking Humans
Authors: Cohen M. M. , Schimmel H. , Rapin I.
Published: October 2005

The relation between rapid periodic click stimulation and computer-summed EEG activity, obtained from surface electrodes, was investigated in normal-hearing adult subjects. Repetition rates (R.R.) for 0.2-msec duration clicks ranged from 10/sec to 55/sec, and slightly faster in several subjects. Electrode derivations were C2, C4, C3, T4, T3, right and left mastoid, all referred to noise. Acoustic stimuli were delivered contralateral to electrode sites. In all subjects examined, a well-defined sinusoidal response corresponding in frequency to the R.R. of the stimulus was obtained at high as well as low sensation levels (SL). Various controls, to assure that responses were auditory in origin, were employed. The sinusoidal response demonstrated polarity inversion at C4 and T4, masked out when masking was sufficient to render clicks inaudible, grew in amplitude as SL of stimulus was increased, retained identical polarity regardless of polarity of clicks, and was absent when plugged transducer was energized but clicks were inaudible. A tentative explanation for the mechanism of origin of this sinusoidal response is offered on the basis of a modeling experiment, assuming temporal overlap of evoked potential componentry. The use of the sinusoidal response for the purposes of audiometry will be discussed.
A Laboratory Facility for Psychoacoustics with Computer Interaction
Authors: Braida L. D. , Kelley W. F. , Callahan D. J.
Published: October 2005

The laboratory facility of the Communications Biophysics Group supports a variety of types of psychoacoustic research involving on-line computer interaction. Two PDP-8 family computers are used to control stimuli and monitor responses from observers in two independent experiments. Special hardware permits the sharing of relatively expensive computer peripherals and the flexible assignment of stimulus generators between the experiments. Novel attenuators and electronic switches have been developed for signal control. Experiments with computer interaction are controlled by means of easily used interpretive programs that incorporate features which facilitate timing accuracy and compensate for the speed limitations imposed.
Pitch Ambiguities of Harmonic Two-Tone Complexes
Authors: Houtsma Adrianus J. M.
Published: October 2005

A tone complex comprising two arbitrary successive harmonics of low order, presented monotically or dichotically, evokes a pitch sensation which corresponds to the missing fundamental frequency. When the harmonic numbers are higher, the pitch becomes increasingly more ambiguous. These ambiguities are the major cause of incorrect responses when subjects are asked to identify musical intervals played with harmonic tone complexes of relatively high harmonic number. A detailed investigation was made of the particular confusions a subject makes when he responds incorrectly in a musical interval identification test by obtaining confusion matrices for each harmonic number. The results imply a multimodal distribution for pitch with the locations of the modes approximated by the so called “first effect” [J. F. Schouten, R. J. Ritsma, and B. L. Cardozo, J. Acoust. Soc. Amer. 34, 1418 ( 1962)]. Results are compared with theoretical performance predicted by Goldstein's Optimum Processor Theory. [Work supported by grants from the National Institutes of Health.]
An Optimum Processor Theory for the Central Formation of the Pitch of Complex Tones
Authors: Goldstein Julius L.
Published: October 2005

A theory was formulated for the central formation of the pitch of complex tones, i.e., periodicity pitch. This theory is a logical deduction from statistical estimation theory of the optimal estimate for fundamental frequency, when this estimate is constrained in ways inferred from empirical phenomena. These constraints are (1) the estimator receives noisy information on the frequencies, but not amplitudes and phases, of aurally resolvable simple tones from the stimulus and its aural combination tones, and (2) the estimator presumes all stimuli are periodic with spectra comprising successive harmonics. The stochastic signals representing the frequencies of resolved tones are characterized by independent Gaussian distributions with mean equal to the frequency represented and a variance that serves as free parameter. The theory is indifferent to whether frequency is coded by place or time. Optimum estimates of fundamental frequency and harmonic numbers are calculated upon each stimulus presentation. Multimodal probability distributions for the estimated fundamental are predicted in consequence of variability in the estimated harmonic numbers. Quantification of the variance parameter from musical intelligibility data in Houtsma and Goldstein [J. Acoust. Soc. Amer. 51, 520–529 (1972)] shows it to be dependent upon the frequency represented and not upon other stimulus frequencies. The quantified optimum processor theory consolidates existing data on pitch of complex tones. [Work supported by grants from the National Institutes of Health.]
Teaching Tape Studio Techniques for Music Synthesis
Authors: Appleton J. H.
Published: October 2005

The appearance of many electronic music installations at schools and commercial studios has necessitated introduction of instruction for these facilities. Teaching of musical composition with the new medium becomes linked with the teaching of techniques for the use of diverse audio equipment. One may have a conception of a particular objet sonore which is of little value unless its realization is as clear as the conception. The generation, routing, modification, mixing, and recording of a signal must be nearly automatic so that the composer is able to concentrate on the strictly musical problems. The author will primarily discuss the tape studio approach to electronic music generation, although live performance and all-digital synthesis are also important and interact with tape techniques. Here the student encounters synthesizing equipment and various audio processing devices as well as sophisticated tape-recording equipment. How much technical information must the student assimilate? How deep should his knowledge of acoustics be? How rapidly and in what sequence should he be introduced to the equipment? Are there any reliable indicators for predicting a student's success with the equipment? The paper will attempt to answer these questions and suggest specific instructional techniques.
A Computer Terminal for Music Instruction
Authors: Alonso S. A.
Published: October 2005

A computer terminal has been developed which assists in music instruction. Sound output from a custom digital music synthesizer and verbal input/output from a CRT/keyboard terminal are locally controlled by a 16-bit minicomputer to achieve short response times. Music and verbal data are stored in a large time-sharing computer and accessed over a 300 Baud telephone link. To the student the terminal appears similar in operation to a normal time-sharing terminal. The minicomputer, CRT/keyboard, and acoustically coupled modem are standard commercial products. The synthesizer was designed and built for this application; it requires minimal coding to produce a variety of musical timbres with accurate intonation and reproducibility. Each of eight identical channels provides a frequency source with a resolution of 16 bits driven from a common 12-MHz clock. Channels can produce ramp or triangle waves with six bits of shape resolution, and a variety of rectangular waves derived from square waves. The ramp/triangle and rectangular waves are digitally amplitude controlled with six bits of resolution each. These volume controls permit generation of a variety of envelope functions, including those with time-variable harmonic content. Channel outputs are filtered, weighted, and combined before transmission to a conventional stereo amplifier system.
Aspiration and Voice Onset Time in Word-Initial Consonant Clusters in English
Authors: Klatt Dennis H.
Published: October 2005

A list of 224 English words beginning with prestressed consonant clusters or single consonants was recorded in the frame “Say … instead” by three talkers. The timing of glottal gestures relative to supraglottal events was studied by spectrographic analysis of the data. Voice onset time (VOT) defined in this case by the onset of visible voicing striations in the spectrogram at frequencies above the first formant (relative to stop release) was measured for all words involving plosive consonants. In voiced plosives, this interval is occupied by frication noise of about 18-msec duration before a vowel and 25 msec before a sonorant consonant. In voiceless plosives, the frication noise burst is followed by an interval of aspiration noise. The sum of these two noise intervals, i.e., the VOT, was about 60 msec preceding vowels and 75 msec preceding sonorant consonants. If a voiceless plosive was preceded by [s], the VOT was much less, i.e., about 5 msec greater than the data for the analogous voiced plosive. The VOT was always about 10 msec less for labial plosives and 10 msec greater for velar plosives. The VOT was about 20% longer preceding the high vowels [i] and [u]. In [s]-sonorant clusters, an aspiration interval of 30–50 msec was observed following the disappearance of visible frication noise. [Work supported in part by National Institutes of Health and by Office of Naval Research.]
Sounds of the Spiny Lobster Panulirus argus
Authors: Mulligan B. E. , Fischer R. B.
Published: October 2005

Panulirus argus generates three types of sound and each is composed of pulses that are approximately symmetrical about peak points. The distinguishing features of these sounds are average pulse duration, average interpulse duration, pulse rate, average pulse amplitude, temporal pattern of average amplitude, and spectral composition of pulses. Two of the P. argus sound types—what we call the “popping series” and the “flutter”—are new to the literature. They apparently constitute what previous investigators designated a “slow rattle.” The third type of P. argus sound—the “rasp”—was found to conform in most respects to a sound previously identified by the same name. While the communicatory function of the “rasp” is clearly defensive, the functions of the other two sounds are unknown. We were unable to determine if P. argus is even responsive to its own sounds. Nor is the mechanism of sound generation known. One that would seem to be required on the basis of mechanical considerations does not appear to conform to the operation of the structure generally believed to be the sound-production mechanism of P. argus.
Atmospheric Absorption Considerations in Airplane Flyover Noise at Altitudes above Sea Level
Authors: Shapiro Nathan
Published: October 2005

Airplane flyover noise propagation calculations commonly include atmospheric absorption values from SAE Aerospace Recommended Practice ARP 866. These are appropriate for sea-level atmospheric pressure. The limited published data for air absorption at reduced pressures show a shift of peak absorption toward lower humidity with reduced absorption in the range of humidities of usual interest. An analysis indicates that flyover noise measured at elevations of 2500 to 8000 ft above sea level may be on the order of one PNdB higher than would be measured at sea level at the same temperature and humidity conditions. Consequently, noise data from such high-altitude measurements when corrected to sea-level conditions will give noise levels that are too high.
Demonstration of a Cross-Correlation Technique for Diagnosis of Noise Sources during Wind Tunnel Tests
Authors: Scharton T. D. , Soderman P. T.
Published: October 2005

Previous investigations have demonstrated that cross correlation of turbulence pressures and radiated acoustic pressures can be an effective technique for locating the sources of aerodynamic noise generation. Experiments were conducted using a speaker as a sound source in the NASA Ames 40×80 ft wind tunnel to determine the feasibility of using the cross-correlation technique during wind tunnel tests of flight vehicles. By using special directional acoustic microphones located 2 to 40 ft from the source, the degrading effects of wind-tunnel reverberation and background noise upon the cross-correlation data were largely alleviated.
Prediction of the Acoustic Environment Associated with Boundary-Layer Flow Transition over High-Beta Reentry Vehicles
Authors: Howe J. , Monfort A.
Published: October 2005

For the transition phase of reentry, during which aerodynamic flow changes from laminar to fully turbulent, conical-shaped vehicles are exposed to high external fluctuating pressures. In order to predict levels of acoustic excitation encountered during transition, a wind-tunnel test program was conducted wherein a smooth conical model instrumented with fluctuating pressure transducers was subjected to controlled aerodynamic environments. Through judicious choice of model orientation and wind-tunnel test conditions, stationary zones of laminar, transitional, and fully turbulent flow over the model were achieved. Tests were conducted at Mach 4, 8, and 10 for free-stream Reynolds numbers in the range 1.4×106 ft−1 −3.25×106 ft−1 and for various model angles of attack. This paper describes the formulation of expressions which relate acoustic quantities measured in the transition zone to local aerodynamic flow parameters calculated from wind-tunnel free-stream properties. Specifically, a technique for prediction of overall acoustic intensity and power spectral density encountered during transition is developed in terms of analytically determined parameters describing fully turbulent flow.
Prediction of Space-Shuttle Fluctuating Pressure Environments
Authors: Robertson Jack E.
Published: October 2005

Future developments in aerospace vehicles for manned space flight will concentrate on the Space-Shuttle vehicle concept. During launch and flight through the atmosphere, the external surfaces of the Space-Shuttle vehicles will be exposed to high-intensity acoustic and fluctuating pressure environments which will be critical to the design and success of the complete Space-Shuttle system. Definition of these environments early in the R & D phase of the Space-Shuttle program is necessary to insure the structural integrity, the reliability, and the economic operational requirements of the flight hardware. This paper will concentrate on the aeroacoustic environments which produce severe fluctuating pressures over the surface of the Space-Shuttle vehicles during flight through the atmosphere. Particular emphasis is given to the mated orbiter/booster launch configuration of a typical parallel-burn Space-Shuttle vehicle in flight at transonic Much numbers. Key features of this paper are the bringing together of data from disparate sources, combining the results to show general trends for the various unsteady flow fields, the development of prediction methods based on the combined results, and the application of the prediction methods in the final assessment of critical environments for the Space-Shuttle vehicle. Unsteady flow fields which have been analyzed consist of (1) attached turbulent boundary layers and (2) compression and expansion induced separated flows, shock-boundary layer interactions, proturberance flows, and critical interference flows between the various bodies comprising the mated launch configuration. In each case, prediction formulae have been developed for the overall fluctuating pressure levels, power spectra, and cross-power spectra. A typical Space-Shuttle launch trajectory has been used to arrive at overall sound-pressure levels and 13-oct-band spectra for critical unsteady flow fields and flight conditions. Finally, the results of the analytical study are compared with wind-tunnel test results. [This work was performed under NASA-MSFC Contract NAS8-26919.]
Perturbation Theory of Nonlinear Wave Propagation
Authors: Keller Joseph B.
Published: October 2005

The usual perturbation method yields some results about nonlinear wave propagation, but they are limited by the occurrence of secular terms. The modified perturbation method, to be described in this lecture, eliminates these terms, and thereby leads to much more useful results. These results show how the frequencies of free vibration depend upon the amplitude of vibration and how the wavelength of a periodic wave motion depends upon its amplitude. They also show how the amplitude of a forced vibration remains finite but becomes large at a resonant forcing frequency. In addition, they show that the forced vibration is often not unique, but that there are usually several possible states of motion with different amplitudes. As a consequence, jumps in amplitude can occur when the forcing frequency is varied, and different amplitudes can be reached by increasing and by decreasing the frequency. Some examples illustrating these considerations will be presented.
Cytophotometric Analysis of Noise-Induced RNA Changes in Auditory Cortical Neurons of the Rat
Authors: Maliniak R. M. , Hahn P. H. , Farwell R. W. , Anthony Adam
Published: October 2005

Male rats were exposed to white noise (350–10,000 Hz, 100 dB) for 60 min. Controls were kept at ambient sound-pressure levels (40–60 dB). Neuronal RNA levels of the auditory cortex (Brodman area 41) were determined using azure-B staining and quantitative microspectrophotometry at 1-, 4-, 8-, and 24-hour intervals after termination of noise stress. A transient 1- to 8-hour increase in RNA was evidenced in auditory cortical neurons of noise-exposed rats as compared to controls sacrificed at corresponding time intervals. Glial cells surrounding these neurons exhibited an increase in RNA at 1-, 8-, and 24 hours post exposure intervals but not in the 4 hour post exposure group. One contribution of the study is the demonstration that RNAcytophotometry can be used to assess the extent of activation of neuronal metabolism on an individual cell basis. [This research was supported by a grant from the Rockefeller Foundation].
High-Frequency Attenuation Characteristics of Ear Protectors
Authors: Bess F. H. , Townsend T. H.
Published: October 2005

The attenuation of ear protectors was examined at 8, 10, 12, 14, 16, and 18 kHz. Four different varieties of protection devices were used. These included three types of plugs—foam, rubber, and custom fitted—and a muff. Ten young normal-hearing listeners were tested (on three different days) by means of a Békésy tracking procedure. The stimulus was a pulsed 300-Hz band of noise centered around the test frequency. The results revealed a wide range of attenuation provided by the four types of protectors. The most protection was afforded by the foam plug, followed by the rubber plug and muff. The custom mold provided the least amount of attenuation. For each protector the attenuation was relatively constant between 8 to 16 kHz, with the greatest protection offered at 14 kHz.
Determination of In-Use Attenuation Values for Selected Ear Plugs
Authors: Scott C. E. , Thomas W. G. , Royster L. H.
Published: October 2005

The amount of noise attenuation offered by ear plugs in actual-use situations as compared to the attenuation measured in laboratory tests (per ANSI Standard Z24.22-1957, “Measurement of the Real-Ear Attenuation of Ear Protectors at Threshold”) has been a question of concern for a number of years. This question is especially of interest today with the recent introduction of hearing conservation programs in most industry. Almost all of these programs use ear protection as a means of temporarily protecting workers until noise reduction is accomplished. It is therefore extremely important to know the difference, if any, between published [ANSI test] and in-use attenuation values for protectors. In this study, two routines were developed to simulate in-plant work activities. Real-ear attenuation values [per ANSI] for the V51-R-type plug were determined before and after each work routine. The ten subjects were tested on three occasions for each work routine. No significant difference was found in the attenuation offered by the V51-R plug before and after each work routine.
Interactive Effects of Noise and Vibration on Human Performance
Authors: Sommer H. C. , Harris C. S.
Published: October 2005

Several studies on the combined effects of noise and vibration on psychomotor and cognitive performance are reviewed. Vibration presented alone and noise presented alone had no adverse effect on the cognitive task (mental calculation combined with short-term memory), while combined noise and vibration produced a slight increase in the number of errors. Studies in which a tracking task and two reaction-time tasks were used strongly suggest that whether noise adds to or subtracts from the effect produced by vibration depends to a large extent on the intensity level of the noise. Noise of 100 dB and 105 dB presented in combination with vibration at intensities of 0.1 gz (peak) and 0.3 gz (peak) produced subtractive effects while noise at 110 dB with vibration at 0.1 gz (peak) and 0.25 gz (peak) produced additive effects.
Rhythmic Units and Syntactic Units in Production and Perception
Authors: Lehiste Ilse
Published: October 2005

It has been claimed that spoken utterances consist of isochronous rhythmic units (metric feet), lasting from one major stress to the next. A study of 17 specially constructed sentences showed that productions of the same metric foot types have remarkably similar durations. However, there are clear differences in the average duration of different foot types in the same position, and there is neutralization of durational differences in final position. The partial isochrony found in the study leads to two further questions: the influence of syntax on the production of rhythmic units, and the perceptual nature of isochrony. If rhythmic units are independent of syntactic structure, sentences consisting of the same lexical items should have the same temporal structure regardless of syntax. A study of syntactically ambiguous sentences showed that they can be successfully disambiguated by adjusting the rhythmic units to reflect syntactic structure. The hypothesis that isochrony is primarily perceptual was tested first by having 30 listeners judge the duration of metric feet in the 17 analyzed sentences, and then perform the same task with non-speech stimuli consisting of sequences of noise bursts and noise-filled intervals duplicating the rhythmic structure of the sentences. Listener performance was significantly better in the second test, suggesting that isochrony may indeed be at least partly a perceptual characteristic of spoken English.
Degree of Phrasal Stress: A Stable Lexical Feature?
Authors: Gaitenby Jane H. , Sholes George N. , Kuhn Gary M.
Published: October 2005

Phrasal stress assignment by rule is a small but necessary step in text conversion to synthetic speech—the role of a reading machine for the blind. Specific sentence stress depends on complex semantic information, unavailable in present reading machines. Hence, most approaches to algorithmic stress assignment have taken the parsing route, using general relationships among syntax, semantics, and prosodics. A more parsimonious approach, perhaps, is advance estimation of probable semantic weight (information) of words. It is hypothesized that semantic weight and word stress degree are correlated; thus, relative prosodic value can be predicted without parsing. A further assumption is that word stress is stable in degree. Results achieved by this method are both promising and instructive. A tape of text automatically converted to synthetic speech will be played. It was produced by the Haskins reading device (using a stored dictionary, the stable stress hypothesis, Mattingly's speech-synthesis-by-rule program, and a parallel formant synthesizer). [This research was supported by the Prosthetics and Sensory Aids Service, Veterans Administration.]
A Basic Study of Automobile Tire Noise
Authors: Hillquist R. K. , Carpenter P. C.
Published: October 2005

The effects of various operating and conditional parameters of automobile tires, such as vehicle speed, vehicle load, inflation pressure, wear, size, and road surface texture, have been studied. Data were obtained in the field by coasting an automobile past a microphone varying one parameter at a time while keeping the others under rigid control. These data indicate that certain of these parameters, principally vehicle speed and road surface texture, more significantly influence the emitted noise than do the others.
Sources of Noise on a Cummins V-378, V-8 Diesel Engine
Authors: Crocker Malcolm J. , Anderkay Glen
Published: October 2005

A simple inexpensive anechoic engine noise facility has been built at the Ray W. Herrick Laboratories. Measurements of the noise from a Cummins V-378, 155-BHP diesel engine have been made in this facility. The major sources of engine noise (in dBA) as a function of load and speed are given. The relative importance of combustion noise and mechanical noise were determined by motoring the engine with an electric motor. Possibilities for noise reduction modifications are discussed. [Work supported by a grant from the National Science Foundation, Washington, D. C.]
Acoustic Enclosures for Diesel Engines on Trucks
Authors: Crocker Malcolm J. , Tree D. R. , Vaidya P. G. , Jones S. R. , Towers D.
Published: October 2005

When a heavy truck is fitted with an efficient muffler, the main sources of noise at low to moderate speeds are engine-radiated noise and fan noise. Probably the most economical method of reducing these latter sources is by complete enclosure of the engine and fan. The problems introduced are sound transmission through enclosure walls and cooling ducts, engine cooling, fire hazard, and accessibility. The transmission loss and noise reduction of a prototype enclosure measured in a laboratory experiment are given. Measurements are compared with theory. The design of the final enclosure for a diesel engine on an International Harvester truck is discussed. Practical problems encountered with this design and changes from the prototype design are reviewed. [Work supported by International Harvester, Fort Wayne, Indiana, under contract to the Office of Noise Abatement, Department of Transportation, Washington, D. C.]
Certification of Exhaust System Components
Authors: Harford K. D. , Siddon T. E.
Published: October 2005

Various regulatory agencies have recognized the need for a reliable yet uncomplicated system of certifying and identifying exhaust systems and their elements with respect to noise control capability. Experts have cautioned that such a system could prove unworkable in view of the complex mix of exhaust gas parameters and system configurations which influence the installed attenuation of individual system elements. The present paper recognizes the potential importance of these complicating factors, yet advocates that a system of toleranced muffler class ratings (M.C. ratings) that take into account frequency selective properties and attenuation capability will yield performance predictions which will remain consistent from vehicle to vehicle. The approach advocated does not attempt to develop an engineering tool for manufacturers; rather, the objective is merely one of establishing comparative classification indices which permit the selection of equivalent replacement components. A parametric study on an exhaust flow simulator would model the exhaust in an increasingly sophisticated manner until the measured insertion loss matches that measured on a sample of real engines to within an acceptable statistical tolerance, thus providing a means of assessing the relative cost/effectiveness of an increasingly complex simulation facility. Once the standard insertion loss test facility is established, insertion loss characteristics for a respresentative sample of existing mufflers would be tabulated and statistically reduced to determine the M.C. contours. Regulation of the acceptable standard deviation from these contours would provide an additional means of quality assurance on muffler performance, discouraging mufflers with passbands or extremely narrow filter characteristics.
The Effect of Test-Site Topography in Vehicle Noise Measurements
Authors: Bettis R. A. , Sexton M. Z.
Published: October 2005

The interference between sound waves directly propagated to a microphone and those reflected from the ground plane is known to influence test results. This situation is typical of vehicle pass-by noise testing, where the microphone is located 50 ft from the lane of travel and a hard surface extends from the vehicle to the microphone. Theory and data are presented indicating that small differences in ground-plane flatness and absorption can significantly alter test results. The need to specify surface flatness and absorption in test procedures is indicated.
Transducer Design Including Beam Steering and Diffraction
Authors: Szabo T. L. , Slobodnik A. J.
Published: October 2005

The physical factors of beam steering and diffraction not only affect the performance of ultrasonic surface wave devices but also are important in the initial selection of crystalline materials and orientations for a chosen application. The interrelationship of beam steering and diffraction are briefly reviewed for popular materials. Curves have been computed assessing the effect of these factors on the frequency response of typical devices on lithium niobate, quartz, and bismuth germanium oxide. Optimum transducer apertures have been calculated taking into account beam steering, diffraction, and transducer conductance. Diffraction corrections have been incorporated in the design of apodized transducers.
Ferrite Films for Shear and Surface Elastic Wave Transducer
Authors: Yamaguchi M. , Naoe M. , Yamanaka S. , Yasuda T.
Published: October 2005

Magnetostrictive Ni0.837Cu0.148Co0.015Fe2.000O4 ferrite films 10–60 μ thick were prepared on alumina and sapphire plates by vacuum-arc evaporation and by cathodic sputtering. The films of 30-μ thickness deposited on a sapphire rod, generated and detected 50-MHz shear waves by operation in conjunction with a quartz transducer. A commercial cubic magnet, of subcentimeter size, applied a bias field sufficient to operate the films. On the other hand, the films of 40-μ thickness sputtered on an alumina plate with eight-turn meander line on their surfaces generated and detected 10.8-MHz (wavelength 400 μ) surface elastic waves. It was unnecessary to apply any external bias field to operate the films, due to the use of a large internal stress induced in them during the heat treatment. Consequently, the deposited and the sputtered ferrite films can be applied to the shear and surface elastic wave transducers, respectively.
A New Horn Loudspeaker/Microphone for Personal Voice Communication Transceivers
Authors: Schumann Juergen , Abragnaro Louis A.
Published: October 2005

A highly efficient wearable horn loudspeaker/microphone for use with personal voice communication transceivers has been developed. The design incorporates an electrodynamic driver coupled to a small catenoidal horn, packaged to be protected from the environment. The electrical-to-acoustical power conversion efficiency was optimized using a computer program incorporating the parameters of the horn and driver. The prototype transducer provides 105-dB-SPL capability at the ear of the user concentrated at 800–3000 Hz for maximum intelligibility in noise.
Scattering from a Random Rough Surface Bounding an Elastic Medium
Authors: DeSanto J. A.
Published: October 2005

In a previous paper [J. Math. Phys. 13, 1903 (1972)], Feynman diagram methods were used to construct the Green's function and its first two moments for scalar wave scattering from a random rough surface with a Neumann boundary condition. This paper extends these formal diagram methods to the calculation of the Green's function and its first two moments for an elastic half-space bounded by a random rough surface considered as a free boundary. The surface height is a single-valued function with Gaussian statistics. The Dyson and Bethe-Salpeter equations, for the mean and second moment respectively, of the Green's function, are derived. Some simplifications of these integral equations and some examples are presented.
A Modified Coupled Modal Form of Burgers' Equation
Authors: Pridham Roger G.
Published: October 2005

The coupled modal form of Burger's equation is modified as follows: (1) Only the primary frequencies and first-order field (i.e., sum, difference, and double) frequencies are retained in the spectral vector. (2) The amplitudes of the first-order field components are approximated by substituting the unknown values of the primary wave attenuation into the results of first-order perturbation theory. This procedure, which is similar to Westervelt's energy conservation approach [P. J. Westervelt, in Proc. Int. Congr. Acoust., 3rd, L. Cremer, Ed. (Elsevier, Amsterdam, 1960), p. 316] results in a set of modified equations which can be decoupled. These modified equations are used to solve for the attenuation of the primary waves for several cases of interest.
The Effects of Payoffs on Sensitivity and Bias in Absolute Identification of Intensity
Authors: Lippmann R. P. , Braida L. D. , Durlach N. I.
Published: October 2005

In our previous work on the identification of intensity [e.g., L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Amer. 51, 483–502 (1972)], no attention was given to testing the implicit assumption that sensitivity and bias are independent. In the present series of experiments, sensitivity and bias were measured as a function of the payoff matrix. Maximum-likelihood estimates of sensitivity and bias were computed using an iterative procedure and the Thurstonian decision model of the preliminary theory. The results indicate that changes in payoffs cause changes in bias, but leave sensitivity invariant (consistent with the theory). Furthermore, the changes in bias were found to be similar to those that would occur for a receiver that is designed to maximize the expected value of the payoff. It is believed that these identification experiments provide a stronger test of the independence assumption than previous experiments using detection or discrimination paradigms.
Psychometric Functions in Quiet for Long- and Short-Duration Tones at 1000 Hz
Authors: Wright H. N.
Published: October 2005

The psychometric function for 500- and 20-msec tones was measured in quiet at 1000 Hz in three normal hearing listeners in an effort to determine whether differences in method have contributed to the variability among the results obtained by different investigators of temporal auditory summation at threshold. The obtained P (C) for the methods of adjustment, tracking, and PEST were related to their relative location on each psychometric function. Although the slopes of the psychometric functions, both among and within observers, were consistent (6%/dB), there was no consistency among observers in their respective P (C) positions on the psychometric functions, indicating that methodological considerations in the measurement of temporal summation are not as simplistic as they might first appear. [Supported by PHS Research Grant NS 9663 from NINDS.]
Effects of Sensation Level on Loudness Tracking
Authors: Hattler K. W. , Dixon S.
Published: October 2005

The Békésy audiometer was employed to study the effects of reference signal sensation level (SL) on recalled loudness tracking behavior. Ten trained normal-hearing subjects were given 5-sec 1000-Hz reference tones at four sensation levels from 1 to 20 dB. Subjects were instructed to maintain the recalled loudness during a 2-min compensatory tracking period. During half the trials, the comparison tone remained continuous (duty cycle, 100%). During the other half of the experiment, comparison tone was interrupted at a duty cycle of 20% (200 msec on, 80 msec off). Threshold tracings for these signals were also obtained. Results indicate that threshold tracking and loudness tracking yield remarkably different results. At threshold, continuous-tone and pulsed-tone tracing were overlapped. Beginning at 1 dB SL, loudness tracking yielded a characteristic separation of pulsed-tone and continuous-tone tracings. At 1 dB SL, continuous-tone tracings were an average of 1.8 dB lower in SPL than pulsed-tone tracings, suggesting that ongoing continuous tones are louder than repeated tones. During compensatory loudness tracking, listeners compensate for this loudness discrepancy by producing a separation of tracings with the pulsed-tone tracings at higher SPLs than continuous-tone tracings for equal recalled-loudness judgments. The size of the separation of tracings tended to increase as the SL of the reference tone was increased.
Békésy Tracings on Vibratory Sense and Hearing
Authors: Young I. M.
Published: October 2005

Békésy tracings were obtained in normal subjects for vibratory sense of finger before and after cooling by ethyl chloride and for hearing levels of pure tone following exposure to sound. When mild cooling was applied, there were no observable differences in both amplitude width and thresholds of pulsed stimuli between before and after cooling. For steady stimuli, however, there was reduction in amplitude width only at the top portion of Békésy spikes without affecting the bottom. Following deep cooling, there was an elevation of thresholds for both pulsed and steady stimuli, and reduction in amplitude width of steady stimuli. Reduction in amplitude width seemed to appear prior to threshold shift. During the course of recovery, these changes returned to original conditions in reverse order. Similar findings were found in hearing following stimulation of the ear by pure tone. The above findings were explained on the basis of perstimulatory fatigue of rapid form.
Masking by Narrow Bands of Noise in Normal Ears
Authors: Young I. M. , Wenner C. H. , Harbert F.
Published: October 2005

Threshold measurements were made by Békésy sweep-frequency audiometry for pulsed tones in the presence of five different narrow-band noises (three commercial and two laboratory sources) introduced in the same receiver for normal-hearing subjects Results indicated that masking effect for a given overall intensity was dependent not only upon the bandwidth, but also upon the cutoff slope per octave of the filter. As the bandwidth increased from that of Fletcher's, masking effect decreased. The sharper the cutoff slope up to approximately 30 dB per octave on each side of the band, the better the masking effect. However, a slope sharper than 30 dB had practically no additional masking effect. At frequencies showing the larger masking insufficiencies, the bandwidth was wider and the cutoff slope per octave was smaller than with the more efficient maskers.
Detection of Click in Noise: Peak Picking or Energy Detection?
Authors: Robinson Charles E.
Published: October 2005

Two models of signal detection were contrasted for the case of a click temporally embedded in a long noise burst. According to one possible model, the detection of a click embedded in noise depends on the amount by which the peak of the click exceeds the average value of the noise envelope. According to an energy-detection model, detection is determined by the ratio of click energy to noise power. To separate out the peak from the energy aspects of the signals, three conditions of bandpass filtering were applied to the sum of a 0.1-msec pulse and white Gaussian noise. The ratio of the square of the click's peak amplitude to its total energy varied by 4 dB over the three bandpass conditions. Thresholds were determined for two subjects. For each subject, the peak of the threshold click varied over the three conditions by only 1 dB while the energy of the threshold click varied by 3 dB. This result suggests that the peak factor may be more salient than energy in this detection situation.
A Six-Man Computerized Audiometer
Authors: Wood Thomas J. , Mahaffey Robert B. , Peters Robert W.
Published: October 2005

A computerized audiometer and its validation will be discussed. The computer system was specifically designed for mass testing in hearing conservation programs and is capable of obtaining up to six audiometric thresholds concurrently using “manual audiometric” methodologies, modified in accordance with signal-detection theory to increase threshold reliability. As part of the testing procedure, the subjects' response patterns are evaluated according to specific criteria to assess the validity and the reliability of the obtained thresholds. Following the termination of testing, pertinent personal statistics and threshold values are stored by the computer on data cassettes for subsequent processing by a central data storage and retrieval system. Emphasis will be placed on the procedural aspects of this study and on the results which demonstrate the acceptability and reliability of the testing method.
Use of a Computer Voice-Response System for Wiring Communications Equipment
Authors: Rabiner L. R. , Schafer R. W. , Shipley K. , Flanagan J. L.
Published: October 2005

Customarily, in wiring communications equipment, a production-line assembler reads and follows a complex printed list of instructions. His eyes and hands are consequently diverted from the assembly task, resulting in delays and errors. Having the wiring instructions spoken aloud, by a recorded tape, eliminates the difficulties. The tape may, of course, be recorded by a human speaker, but the procedure is burdensome. Frequent modification and updating of the instructions becomes tedious and inefficient. Also, the wire lists are typically designed by computer and exist originally in computer form. A logical step, therefore, is to have the computer speak the instructions (instead of print them), and to automatically record the computer speech on magnetic cassettes for production-line use by the assembler. We describe an automatic voice-response system implemented for this purpose. The system utilizes the Acoustics Research DDP-516 computer facility. A word library ia stored on fixed-head disk, either in data-reduced form (formant functions) or as DPCM digital waveform. A concatenation program, commanded by the input wire list, assembles, speaks, and automatically records each instruction. At this writing, eight assembly jobs have been completed for experimental use by the Western Electric Company. In the most recent, the technique has been extended from production-line assembly to central-office wiring for an ESS-1 installation.
Effects of Wind on the Propagation of Sound over Barriers
Authors: Stusnick E. , Ganley W. P.
Published: October 2005

The propagation of sound from a monochromatic source over a thick barrier has been measured in the presence of various wind conditions. Source frequency was varied over the range 250–8000 Hz. In the presence of 25–30 km/h winds, sound-pressure levels in the shadow zone behind the barrier downwind from the source are on the order of 10 dB higher than in the absence of wind and exhibit large fluctuations. Comparisons of the no-wind data with the results of various theoretical models will also be given.