bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound Propagation and Attenuation Characteristics over Layered Media
Authors: Pao S. P. , Evans L. B.
Published: October 2005

In dealing with wave propagation over land at below 1000 Hz, ground cover should be represented as layered media in order to assess the ground attenuation effect correctly. It is found through a theoretical analysis that a layered ground cover gives rise to strong selective absorption in certain frequency bands. Furthermore, the layer thickness has first-order effect on ground attenuation. The theoretical result agrees with those given by U. Ingard [J. Acoust. Soc. Amer. 23, 329 (1951)] in the limiting case of a semi-infinite ground cover. Experimental data has been taken under laboratory conditions over a wide range of parameters, and the results quantitatively confirm many aspects of the predictions. Both theory and experiment indicate that significant attenuation to very low frequencies can be expected for wave propagation over a thick ground cover. Other results include the confirmation of a strong sound-pressure gradient in the vertical direction near the ground cover, and that the excessive attenuation can increase at most 6 dB per doubling distance. [This work was supported by the U. S. Army Research Office—Durham, under contract.]
Comparison of Detection and Discrimination of Tones of Different Durations under Homophasic and Antiphasic Conditions
Authors: Robinson Donald E. , Blakeslee Edward A.
Published: October 2005

Using a two-alternative temporal forced-choice technique (2ATFC), the detectability of both a 64-and a 128-msec 500-Hz signal in a continuous noise masker (50 dB spectrum level) was determined. The ability of the observers to discriminate the long from the short tone was also measured using a similar psychophysical technique. Both detectability and duration discriminability were measured with both homophasic (N0-S0) and antiphasic (N0-Sπ) conditions. Under the homophasic condition, the observers require only slightly greater signal energy (approximately 3 dB) in order to perform as well in the discrimination task as they do in the detection task. With the antiphasic condition, the psychometric function for discrimination is not only displaced considerably toward greater signal energies, relative to those required for detection, but the slope of the function for discrimination is less than that for detection.
Detection of Opposed Interaural-Time and Interaural-Intensity Differences as a Function of Over-all Level
Authors: Carrier Samuel C. , Hafter Ervin R.
Published: October 2005

The binaural trading ratio (Δt/ΔI) is traditionally measured by opposing an interaural time difference (Δt) with an interaural intensity difference (ΔI) in proportions sufficient for apparent cancellation of the perceptual effects of the two cues. In a previous paper [E. R. Hafter and S. C. Carrier, J. Acoust. Sac. Amer. 46, 125 (A) (1969)], we showed that no combination of Δt and ΔI produces a dichotic tone which cannot be detected as different from an otherwise comparable diotic. In that paper we proposed a “dual-threshold” model in which intensive and temporal information are encoded by peripheral dual-threshold devices. The two sets of information are then weighted and recombined by a central processor. An important test of the model is the response to signals of levels sufficiently low as to render the high threshold device functionless. In this study, we measured the tradability of Δt and ΔI at overall levels of 20 and 40 dB SPL. At these levels, Δt and ΔI apparently do cancel, but the signal remains detectably different from diotic owing to the observer's use of monaural intensity increments. Whereas at high over-all levels monaural cues are negligible, here they are of major importance. An extension of the previous model that incorporates this feature will be presented.
Magnetometer Recording of Jaw Movements during Speech
Authors: Hixon Thomas J.
Published: October 2005

A new technique has been developed for transducing movements of the mandible during speech production. The equipment employed includes a three-coil magnetometer system that enables real-time recording of jaw movements without encumbrance to natural articulation. Theoretical principles underlying the technique will be discussed together with procedures for using and calibrating the equipment. Examples of one- and two-dimensional measurements will be presented, the latter being related to motion-motion pathways followed during nonspeech movements of the mandible. It is proposed that departures from two-dimensional passive opening-closing pathways can be interpreted in terms of the net muscular forces operating on the jaw. Beyond the technique described, it is suggested that magnetometers have attractive potential as a research tool in speech physiology. Within this framework, brief discussion is offered on the application of a miniature magnetometer unit to the study of lip, tongue, velar, and pharyngeal monitoring during speech production.
Description of Tongue and Lip Movement in a Jaw-Based Coordinate System
Authors: Mermelstein Paul , Maeda Shinji , Fujimura Osamu
Published: October 2005

The midsagittal projection of the upper tongue surface is described with reference to a jaw-based coordinate system which rotates with the mandible about a point fixed with respect to the maxilla. A jaw based coordinate system is also useful in describing the articulatory conditions of the lips. For vowels, specification of the maximal elevation point of the tongue hump is used to construct curves which approximate the tongue outline. Addition of one lip-rounding parameter allows specification of the orifice dimensions and the extent of protrusion. Subsequent consideration of the jaw angle allows computation of the midsagittal cross dimension of the vocal tract. For consonants, additional separate parameters are introduced for specification of labial, dental, and palatal constrictions.
Prephonatory Laryngeal Behavior
Authors: Allen Elizabeth L. , Shipp Thomas
Published: October 2005

Prior to the initiation of various types of phonation, intrinsic laryngeal muscle activity adjusts the vocal folds in a physiologic phonatory set to interact with the respiratory air stream. It appears that the laryngeal pattern is dependent upon the following variables: (1) type of initiation (abrupt, simultaneous, breathy), (2) voiced-voiceless initial phoneme, (3) controlled or “free” phonation, (4) frequency of phonation, and (5) intensity of phonation. Examples of the various activity patterns occurring between the termination of respiratory inspiration and the initiation of phonation will be shown.
Temporal Aspects of Audition as Correlates of Temporal Aspects of Speech
Authors: Mahaffey Robert B. , McDill Jim D.
Published: October 2005

The purpose of this study was to seek additional evidence of the temporal dependence of speech upon temporal parameters of audition. Twenty-five listeners with normal hearing each participated in three subtests during the experiment. The first subtest consisted of identifying the minimum tone-burst duration which possessed pure-tone qualities at 250 Hz and 2 kHz. The second subtest consisted of the subjects determining the minimum frequency of square-wave clicks at which the clicks fused into a tonal percept. Presentations were binaural and were presented approximately 50 dB SL. The third subtest consisted of each of the subjects talking freely about a complex stimulus picture. The recorded speech was analyzed for pause time, within time and intensity delimitations, and for average phonation time, also within delimitations. Stimulus generation and data acquisition were accomplished with a PDP-8/I computer to provide much greater accuracy than was available for earlier studies. The data revealed highly significant correlations among the pause times and phonation times of a person's speech with the measures of the auditory system's temporal integration time. The strongest relationship (r = 0.845) existed between speakers' pause times and their pure-tone-burst measures. Results suggest temporal parameters of the cybernetic relationship of speech to hearing.
Acoustic Predictions and Experimental Results
Authors: Cybulski J.
Published: October 2005

In March in the Gulf of Mexico in 3180 m of water, seven acoustic runs were conducted over a two-day period. A directional source was suspended, at 80- and 360-m depth and below a duct, from a surface ship that was essentially in a drift mode. An omnidirectional receiving hydrophone was towed at 3 kt at depths between 70 and 330 m and from 0.8 to 12 km. The acoustic energy was propagated in the form of 120-msec CW pulses at 380 and 258 Hz, alternately, every 15 sec. During these opening and closing range trials, X-BT's were taken at the receiving ship. Analysis for the received pulse levels was restricted to those coming via the refracted only and surface-reflected propagated modes. Comparisons made of ray-trace calculations from several models of the predicted acoustic signal levels with experimental results show good agreement through the Lloyd mirror interference regions with somewhat lesser accuracies for single path arrivals at the maximum ranges.
Perturbation Calculations of Propagation Loss in the Deep Ocean
Authors: Nicholas Nicholas C.
Published: October 2005

Propagation loss expressions were derived by means of perturbation theory corrections to the normal-mode series solution to the acoustical wave equation with parabolic velocity profile and sinusoidal point source. A fourth-order power series was used to approximate nonparabolic velocity profiles with coefficients determined by a least squares fit. Perturbation corrections were made to second order for the wave functions and to third order for the eigenvalues. Calculations were made for two realistic velocity profiles and an idealized nonparabolic velocity profile. Local focusing of sound in a parabolic velocity profile had been reported in previous papers [H. Überall and N. C. Nicholas, “Range Focusing in a Deep Ocean Sound Channel with Parabolic Profile,” J. Acoust. Soc. Amer. 44, 1259–1261 (1968) and N. C. Nicholas and H. Überall, “Propagation Calculations for a Parabolic Velocity Profile,” J. Acoust. Soc. Amer. 47, 101 (A) (1969)] but no local focusing was found for the nonparabolic cases computed. Numerical results showed good agreement with the few available measurements and ray-acoustic estimates of propagation loss.
Noise Control for a 60 000 BTU/h Space Heater
Authors: Rentz P. E. , Bies D. A.
Published: October 2005

A noise-reduction program for a 60 000 BTU/h military multifuel space heater is reported. A reduction of sound pressure levels in critical octave bands of 6–9.5 dB was achieved. Noise reduction measured included incorporation of a combustion blower inlet muffler, careful reconfiguration of the ventilation air inlet, reselection of the ventilating fan, and use of a new and novel boundary-layer control device in the ventilating fan venturi. The constraints of size, usage, and required performance probably preclude further noise reduction.
Snowmobile Noise: Its Sources, Hazards, and Control
Authors: Brammer A. J. , Piercy J. E. , Toole F. E.
Published: October 2005

The widespread use of snowmobiles as recreational and utilitarian vehicles has resulted in a new and significant noise problem. A survey of 50 snowmobiles in typical operation indicated that an “average” snowmobile, when cruising, produces a sound level of approximately 90 dBA at 15 ft. The range of levels was 79–102 dBA. Operators of snowmobiles are exposed to sound levels in the vicinity of 105–120 dBA, at which levels there is a serious risk of hearing damage. A representative snowmobile was examined in detail, the major noise sources were resolved and, using standard techniques and materials, the noise output of the machine was reduced by 9 dBA without affecting its mechanical performance. The modified machine produced a maximum sound level of 85 dBA at 15 ft and 103 dBA at the driver's ear. The latter level particularly is still excessive. The implications of the findings of this study are discussed with respect to the snowmobile operator, the manufacturer, and the community. [A more extensive discussion of this material is found in NRC report APS-477.]
Broad-Band Fan Noise
Authors: Kelley J. O.
Published: October 2005

The two traditional broad-band fan noise generation mechanisms are “noise due to incident turbulence” and “noise due to vortex shedding.” These might be called “aerodynamicists' mechanisms,” since they are both rooted in fluctuating lift concepts derived from two-dimensional incompressible unsteady aerofoil theory. The paper looks critically at these concepts and evaluates the practical significance of the mechanisms in current and future fan designs. Thus, it discusses their relationship to the newer “acousticians' mechanisms,” which are more intimately concerned with the acoustical properties of a compressible flow, and at the same time assesses the importance of all broad-band mechanisms compared with discrete tone generators.
Absorption of Sound in Air at Low Temperatures
Authors: Piercy J. E.
Published: October 2005

Laboratory measurements of the absorption of sound in air from the literature have been examined for their dependence on frequency, humidity, and temperature. In sufficiently dry air (<∼0.01% water molecules), which for practical purposes means at sufficiently low temperatures (<20 C° orf R.H. = 10%, <−40°C for R.H. = 100%), the measurements fit theoretical curves indicating the vibrational relaxation frequency of oxygen, for a pressure of 1 atm, to be ∼30 Hz, independent of humidity and temperature. Calculation of the relaxation frequency to be expected in dry air from acoustic measurements of binary mixtures containing oxygen yields a figure of ∼26 Hz, in agreement with experiment. This frequency, and hence the absorption in dry air, appears to be determined principally by collisions of oxygen molecules with the small number of carbon dioxide molecules normally present in the atmosphere (300 ppm). The most significant application of this analysis at present is probably to the absorption of sound at high altitudes, where some of our largest sources of noise are.
Radiation Loading of Prolate Spheroidal Surfaces
Authors: Lauchle G. C.
Published: October 2005

Prolate spheroidal coordinates and associated prolate spheroidal wave functions are used to study the acoustic radiation from arbitrarily vibrating prolate spheroidal surfaces. The theory was originally developed to study the farfield sound propagation from submerged ellipsoids of revolution with high fineness ratios (L/R). Boundary conditions are adjusted to the general wave solutions to obtain an expression for the sound pressure. The results show that a single prolate spheroidal vibration mode excites an infinite number of pressure modes. A local radiation impedance is defined and discussed. This impedance shows the effect of the strong locally variable nearfield and that the spheroid generates (L/2R) more acoustic power per unit area at the equator than at the poles. The application of the theory is demonstrated through numerical calculations of the farfield radiation from a particular submerged body of revolution in which experimental data was available. The agreement between the predicted and measured sound-pressure levels is good.
Human Auditory-Nerve Action Potentials and Cochlear Microphonics Recorded Nonsurgically
Authors: Coats Alfred C.
Published: October 2005

Auditory-nerve action potentials (APs) and cochlear microphonics were recorded from human subjects by placing a needle electrode in the external auditory canal and averaging the responses. A series of control experiments demonstrated that valid records of human auditory-nerve APs and cochlear microphonics were obtained. However, human click APs differ from those of animals in that the second peak (N2) is usually less prominent in humans. An attempt to correlate click loudness with click AP amplitude showed that AP amplitude reaches a peak at about 60 dB SL, whereas loudness continues to increase as click intensity is increased well beyond this level. However, there was a much better correlation between recovery of click loudness following masking (“auditory adaptation”) and recovery of click AP amplitude.
Report of the Acoustical Society's Committee on Education in Acoustics
Authors: Blackstock David T.
Published: October 2005

As a result of one of the recommendations of the AIP Conference on Education in Acoustics, held in March 1964, a new administrative committee of the Acoustical Society, the Committee on Education in Acoustics, was formed in October 1964. The Committee's charge was “to undertake a continuous exploration of methods of improving and expanding the teaching of acoustics.” Probably in accordance with Parkinson's law, the Committee has implemented as well as explored. It has carried out—and continues to do so—promotional efforts on behalf of acoustics education. Although the primary concern has been graduate education, there has been increasing emphasis on the undergraduate area as well. Among the Committee's projects, some finished and some continuing, are the following: (1) an acoustics laboratory manual (one published in 1967; an extensive revision is now underway); (2) a directory of acoustics education (to appear soon in the JOURNAL); (3) an acoustics manpower-needs survey (one study was done in 1966; a new one is reported later in this session); (4) a “Distinguished Lecturers in Acoustics” program (administered by the National Academy of Sciences); (5) a program of collaboration with AAPT aimed at making physics teachers aware of acoustics research problems; and (6) a modest placement program for acoustics graduates.
The Case Method in Teaching Acoustics
Authors: Boner C. P.
Published: October 2005

In the University today, there is considerable discussion of “relevance,” “environment,” and the like. The implications of architectural acoustics for society are obvious. The case method of instruction—developed by law faculties—is applicable. Field observation and measurement by students form the basis of teaching. The student is motivated by what he sees in practice. With discussions in seminar-type meetings, design principles are brought out and applied to the field situations encountered.
State of the Art in Residential Noise Control
Authors: Joiner John W.
Published: October 2005

Large technically oriented corporations often experience difficulty in keeping their various departments abreast of advancement of research in their own laboratory. Even our own Acoustical Society members are often lax in communicating with each other concerning new developments and techniques. Therefore, how much greater is the communication gap from the laboratory technician to his marketing personnel through to the distributor, to the design engineer, to his purchasing agent, to the superintendent, and then on to the workmen concerning the proper installation of materials and details intended for noise abatement in single and multifamily dwellings? An evaluation of construction workmen's understanding of important noise-control details and techniques is presented along with some recommendations for improving this communication gap. An attempt is made to show that many contractors and their workmen do not have a very clear understanding of the differences between “transmission loss” and “absorption” and that this sometimes leads to misuse of materials, which results in a very unsatisfactory installation.
Noise Reduction of a Household Refrigerator
Authors: Chanaud Robert C. , Suzuki Wayne T.
Published: October 2005

A common frostless household refrigerator was studied in anechoic and reverberation rooms to identify the relative importance of the various sound sources, the mechanism of the sound production, and methods for noise reduction. Good refrigerators are sufficiently quiet to cause measurement problems, yet, because they exist in such normally quiet environments, further noise reduction was necessary and methods for accomplishing this were found. There were four major noise sources: (1) internal circulating (evaporator) fan; (2) external (condenser) fan; (3) ice maker; and (4) compressor. The cavitation noise in the ice-maker valve was not examined. The internal fan was a significant noise source even with the door closed, owing to broad-band and discrete-frequency aerodynamic noise and also to vibrational and magnetic coupling. This result also applies to the external fan. Methods of noise reduction are discussed. Compressor noise was found to be due to radiation from the shell, which was coupled to the internal motor both vibrationally and acoustically. The high harmonic content of the compressor sound made it the most annoying of the sources, and some discussion of noise reduction is given.
Generation of Acoustic Waves During the Passage of a Shock Wave through a Heated Gaseous Element
Authors: Hamernik R. P. , Dosanjh D. S.
Published: October 2005

Experiments have been conducted in a shock tube on the interaction of a normal reflected shock wave and a cylindrical two-dimensional heated element of gas. The heated element was created in the incident-shock drift-flow by electrically exploding a wire using discharge energies between 56 and 127 J, and incident shock strengths (pressure behind/pressure ahead of shock) from 1.3 through 2.1. The interaction phenomena were synchronized to occur in a 4-in.-diam optical-glass test section. A sequence of individual μsec-spark schlieren and interferometric photographs and high-speed interferometric motion pictures (22 000 pictures/sec) were recorded. In the region behind the reflected shock wave, this interaction generated a growing cylindrical band of secondary waves (acoustic waves), centered on the transmitted heated element. The density amplitude distribution through the secondary wave system for φ = 0° (along the horizontal plane) exhibited a rarefaction nature having density extrema, 0.88⩽ρ/ρ5⩽0.98 (ρ5 = reference density behind the reflected shock). Chisnell's theory of shock interaction with a variable-density gaseous media [Proc. Roy. Soc. 232, 350 (1932)] was adapted to this interaction phenomenon to explain qualitatively the observed nature of this secondary wave system for φ = 0°. In addition, along the circumference of the secondary wave system the density-amplitude distribution was found to exhibit an alternating compression-rarefaction nature. [Partially supported by the National Science Foundation under Grant GK-1980.]
Impedance Changes in the Cochlea During Acoustic Stimulation
Authors: Honrubia V. , Strelioff D. , Haas G. F.
Published: October 2005

Two microelectrodes in the scala media, one for passing current and one for recording voltage, were used in a bridge circuit to measure impedance changes between the scala media and a reference electrode outside the cochlea of guinea pigs. In the third turn of the cochlea, a 25-Hz acoustic stimulus produced 25-Hz impedance variations which were smaller than 2% of the resting impedance (10 kΩ) when an electric test current of 600 Hz was used for the impedance bridge. The magnitude of the impedance change increased with the sound-pressure level of the sound. These variations had a phase lead with respect to the cochlear microphonics and had both resistive and reactive components. [Research supported by U. S. Public Health Service.]
Recovery of Cochlear-Microphonic Sensitivity Following Intense Pure-Tone Exposure
Authors: Price G. Richard
Published: October 2005

The cochlear microphonic (CM) can recover sensitivity following exposure to intense sounds. A previous study [G. R. Price, J. Acoust. Soc. Amer. 47, 85 (A) (1970)] indicated that, in the case of intermittent stimulation, it was likely that the amount of time available for recovery between stimuli was crucial in determining the amount of loss in CM sensitivity an ear would suffer. In order to determine the characteristics of such recovery, deeply anesthetized cats were exposed to 5.0-kHz tones ranging in duration from 10 msec to 120 sec and at intensities ranging from that necessary to produce a maximum in CM (about 102 dB SPL) up to 30 dB higher than that. Following exposure, CM output to a weak tone was monitored at the round window. In general, the half-life of the recovery was dependent on both the intensity and duration of the stimulation, with longer recoveries following longer, more intense stimuli. Recoveries to the shorter stimuli required proportionately more time than those occurring to the longer stimuli, however. This finding may explain why short-duration intermittent stimuli have greater effect than would be predicted from stimuli with equal energy but longer “off” periods.
Difference Limen for Formant Frequencies Obtained by Method of Adjustment Procedure
Authors: Horii Yoshiyuki
Published: October 2005

Difference limens (DLs) formant frequencies of steady-state signals resembling vowels have been investigated using method-of-adjustment procedure with a computer-controlled terminal-analog synthesizer. The DLs were obtained in a standard manner as a function of types of source (pulse or noise), of fundamental frequencies in the case of pulsed source, of duration, and as a function of the number and location of the formants. Values obtained under noise and pulse source conditions were about equal and smaller than those reported by Flanagan [J. Acoust. Sec. Amer. 27, 613–617 (1955)]. This difference is probably due to different procedures and signal patterns. Fundamental frequency did affect DL values significantly in the range used. In the test signals in which higher formants had smaller amplitudes, DL values tended to become larger for the higher formants. This tendency was diminished, however, in the experiments in which amplitudes of lower formants were reduced, suggesting the presence of masking by lower formants. Applications of the method-of-adjustment procedure using terminal-analog synthesizers to problems of hearing pathology are discussed.
An Investigation of the Effects of Smoothing and Quantization of the Parameters of Formant-Coded Speech
Authors: Rosenberg A. E. , Schafer R. W. , Rabiner L. R.
Published: October 2005

Schafer and Rabiner have recently developed an automatic formant and pitch analysis system for connected speech [“System for Automatic Formant Analysis of Voiced Speech,” J. Acoust. Soc. Amer. 47, 634–648 (1970)]. The formant and pitch data obtained are applied to a formant synthesizer at 10-msec intervals with values restricted to ranges appropriate for each parameter. A question of important practical and theoretical interest is the amount of smoothing and quantization of the control data that is permissible without degrading the quality of the resulting synthetic speech. To investigate this question, four all-voiced sentences spoken by male speakers were chosen for an experiment. Stimuli were pro-produced by quantizing or smoothing a specified control parameter over a wide range of values and synthesizing the utterance using the modified control parameters. Subjective evaluation of the synthetic speech was carried out by means of threshold determinations, using a Honeywell DDP-516 laboratory computer. A–B comparison presentations were used in which the reference stimulus was a synthesized version for which the control parameters were unquantized or unsmoothed. Six listeners participated in the experiment. For each experimental parameter, four threshold determinations were obtained from each subject for each of the four sentences. Quantization threshold levels obtained are: pitch period, 3.9 bits; first formant, 2.7 bits; second formant, 3.1 bits. The low-pass-filter cutoff frequency for simultaneous pitch period and formant smoothing was 12 Hz.
Asynchoronous Sampling of Speech
Authors: Babcock M. L.
Published: October 2005

A speech waveform can be sampled asynchronously, resulting in a sequence of samples which are not at all periodic nor indicative of the amplitude of the speech signal but which definitely carry sufficient information for both intelligibility and speaker identification. This method of asynchronously sampling speech is based upon the derivatives of the acoustical speech signal. The following results are apparent from experiments to date: (1) It is possible to represent speech by a string of pulses of uniform amplitude, where the only information contained in the string is the spacing of the pulses in time; (2) the string of pulses may be produced in a simple analog manner; (3) the first derivative of the original speech waveform is the most important for the encoding process; and (4) the resulting pulse train can be utilized to control an acoustical signal production system to regenerate the “intelligence” of the original speech. The paper describes the present processes involved in obtaining the pulses, some results of analysis of the pulse distributions, and a description of a simple attempt to produce the original speech from the pulse code.
Problems of Management in Multipurpose Halls
Authors: Owen Louis C.
Published: October 2005

Because of the large demands for space today, massive multipurpose buildings are being constructed. This presents a problem to architects, owners, and managers. Arenas that have temporary seating which may be changed for concerts, theatre-in-the-round, church meetings, basketball, and wrestling may use a speaker system which can be raised or lowered according to event requirements—presenting tremendous problems for management. Fixed speakers can be more than adequate for a few setups, but when the setups are changed drastically the acoustics change also. Overhead speakers work well for very large banquets, but not over a bare concrete floor such as for auto shows. The artist seldom arrives before the actual performance, and this leaves little time for the stagehands to balance the complicated systems being used. Many promoters bring in their own amplification, which, when installed by the promoter ten minutes before the doors open, creates absolute catastrophe during the event. When everything from drums to tambourines is electrified, the load may far exceed the output of the building system. Promoters are normally the last to hear of bad acoustics or amplification; however, the manager of a facility is constantly taking the heat.
Redesign of a College Field House into a Multipurpose Auditorium
Authors: Lindahl Robert
Published: October 2005

A small college wanted at minimum cost to modify its field house (100 ft×200 ft×40 ft) into a multipurpose auditorium. Projected uses included symphony, choral groups, dance recitals, solo performers, drama, individual speakers, and religious conventions where persons could speak from any point on the floor. At the same time, the building still had to serve as a single and dual gymnasium, and as an area for athletic contests. By use of (1) a dropped ceiling to reduce the volume and provide the proper ratio of sound-absorbing and reflective surfaces, (2) a demountable and adjustable stage shell with overhead surfaces, (3) a demountable stage, (4) side-wing movable barriers to cut off excess volume, (5) a versatile audio system, and (6) movable retractable bleacher seating, the goal was accomplished. Ten years of acceptable use prove that it is possible to modify such a large athletic enclosure at reasonable cost to provide fair-to-good acoustics for a large variety of uses.
Schematic Representation of Wind Instrument Oscillations
Authors: Benade A. H. , Worman W. E.
Published: October 2005

Wind instrument intonation, pitch stability, register change, and spectrum—all as a function of loudness level—are aspects of a nonlinear oscillation which may be schematized in terms of the magnitudes of the air-column input impedance Z(ω) and the reed transconductance Gr(ω). Each possible “regime of oscillation” is located near a peak of the “regeneration function” R(ω) = Σrn − (nω) ⋅ Gr(nω). The coefficients rn depend on the nature of the reed. At the pianissimo threshold, only r1 differs from zero; with increasing loudness, higher r's appear one by one. At least two terms are important for reed woodwinds and brasses above mezzopiano. Gr(ω) peaks at the reed natural frequency ωr. Woodwinds play below ωr, where Gr is roughly constant. Brasses play near ωr, which is moved about to select the desired note. Register changes in woodwinds come from selective lowering of R-peaks of undesired notes, via the register hole, which detunes the nearest Z-peak. A note played at a frequency ωp (near an R-peak) has a pressure spectrum in the mouthpiece, whose mth component has an amplitude pm(ωp) = smZm(mωp). At pianissimo threshold, s1 is the only nonzero coefficient. The others come in progressively as loudness grows. For many instruments, the mezzoforte spectrum resembles the Z curve. Conversion to concert-hall spectra is straightforward via radiation properties of the system. Examples are presented for clarinet, oboe, saxophone, trumpet, and French horn.
A Noise Exposure Meter
Authors: Partridge Gordon R.
Published: October 2005

This instrument is designed to obtain the single number representing the percentage of the day's allowed noise exposure under the Walsh-Healey Act. Sound is measured continuously, and from the continuum of levels samples of the sound level are taken at time spacings of about 12 sec. Comparators determine into which of the Walsh-Healey “bins” the sound level falls at the moment of sampling. The outputs of the comparators are injected into a counting chain at progressively more significant bit positions, depending on the weighting specified under the law. The percentage of the elapsed time (normally 8 h) and the percentage of the noise exposure accumulated up to that moment are displayed on neon indicator tubes. The sample counting chain serves to compute the answer, so that no arithmetic is required of the user. Either a self-contained microphone or a separate sound-level meter may be used as the acoustic transducer.
Auditory Sensitization in the Stapedius Reflex
Authors: Deutsch Lawrence J.
Published: October 2005

Studies of the threshold of the acoustic stapedius reflex to determine normative values and measures of stability revealed a small (approximately 2 dB), but statistically significant threshold improvement with repeated stimulation for a population of 30 normal ears. To investigate further and define the finding that acoustic stimulation may result in an increase in sensitivity of the stapedius reflex, two studies were designed. In the first, 500-msec bursts of white noise were presented in an ascending series of 2-dB increments. Contractions of the stapedius muscle were monitored by the impedance method, using a Zwislocki acoustic bridge and a specially designed electroacoustic readout system. Each of the nine normal-hearing subjects was exposed to three consecutive runs of the ascending white-noise stimuli from about 50-dB sensation level to about 10 dB above the reflex threshold; the mean threshold for the first run was 60.44 dB, while the mean for the third run was 56.67 dB. This difference was found to be significant at the 0.001 level. Phase 2 involved 10 normal ears which were exposed to 120 dB SPL of white noise for a period of 1 min. Measurements of the reflex threshold were obtained before and after the noise exposure, again by means of an impedance-monitoring technique. Threshold decreases averaging approximately 5 dB were recorded for this group.
Approximate Transfer Characteristics of a Condenser Microphone with Diaphragm Stretched over Raised Points of the Backplate
Authors: Djuric S. V.
Published: October 2005

An approximate method is presented to compute the transfer characteristics of a condenser microphone with a solid dielectric diaphragm stretched over the raised points of the backplate. It is assumed that the raised points are distributed in a regular pattern. The area of the diaphragm is divided into a finite number of small diaphragms, and the expressions for the equivalent mass, stiffness, and viscous damping resistance of the system are derived. From these expressions, the first resonant frequency and the sensitivity of the microphone can be computed. The measurements agree well with theoretical results for backplates with many raised points.
An Electromyographic Investigation of the Relationship between Abdominal Muscular Effort and the Rate of Vocal Vibrato
Authors: Smith Ethel C.
Published: October 2005

There was assumed to be a ratio relationship between the amount of muscular effort applied to muscles of exhalation and the rate of vocal vibrato. Lack of descriptive data on the physiology of the vocal vibrato led to the assumption that, when variations in body pressure are created by abdominal musculature, the subglottic air pressure within the trachea may be directly or indirectly affected by the expiratory muscles. The electromyographic record provided the measure of muscular contraction present in four muscles. The dynagraphic analysis delineated the rate of vocal vibrato. The amount of energy possible within a muscle was a measure significant to intra-abdominal pressure. Subjects were selected to sing the vowel “oh” on determined pitches at four intensity levels. The Beckman Offner type-R dynagraph recorded audio and electrical responses simultaneously. Data were recorded on dynagraph channels from surface electrodes on subjects. Findings revealed that controlled pressure applied to expiratory muscles does result in an alteration of the ratio of muscle action potential to the rate of vocal vibrato during singing.
The Relation between Vibrato and Vocal Ornamentation
Authors: Vennard William
Published: October 2005

Taped excerpts from actual lessons of a mezzosoprano are played to show that the tempo at which she is able to sing rapid scales are related to her vibrato rates. Two rates are found: 7.5 vibrati/sec and 6/sec. She can sing accurate runs at 7.5/sec or at 3/sec (each note having two vibrati at the rate of 6/sec) and is on the way to being able to sing runs at any speed. Excerpts from a lesson of a soprano are played to show the relation between her vibrato and a trill. At first, she sings a vibrato with a excessive pitch extent. The teacher suggests that a greater exaggeration would produce a trill. The singer is able, within a few minutes following this suggestion, to sing a whole-step trill, a half-step trill, and a vibrato with a normal pitch extent. All the productions are at the same rate: 6.25/sec.
Marine Engineering Applications of Seismic and Side-Scan Sonar
Authors: Van Reenan Earl D.
Published: October 2005

Underwater sound varying from low to high frequencies is used in many engineering applications in the marine environment. The sound devices that have been used are the following: (1) broad, low-frequency devices such as the sparker and boomer; (2) discrete low-frequency devices; (3) precision depth sounders; and (4) side-scan sonar. The board, low-frequency devices such as the sparker and boomer are used in applications requiring penetration of sound into the sea floor to give a continuous profile picture of the subsurface geology. The discrete low-frequency devices are also used in this application although penetrations are generally not as great. Depth sounders are employed for precision hydrographic studies. The side-scan sonar extends depth sounding from a two-dimensional profile to a three-dimensional presentation. A broad sea floor coverage is provided, which enables the sonar data to be used similarly to aerial photos over land. Examples of records and applications of the above systems are given.
Transmission of Torsional Waves in an Idealized Drill String
Authors: Barnes Thomas G.
Published: October 2005

In the exploration industry there has been a search for a means of telemetering down-hole drilling information up to the surface. Use of mechanical radiation along the drill string itself is considered as a possible telemetry link between the bottom and top of the hole. A simplified treatment is given for the transmission of sinusoidal zero-mode torsional waves in an idealized drill string. Its passbands are computed. The lowest passband begins at zero frequency, as would be expected. Additional passbands with satisfactory bandwidths exist in this “lossless” idealization. Practical limitations on the transmission of signals in an actual drill string are discussed. [Work supported by Globe Universal Sciences.]
Stability of Nonlinear Oscillations of an Elastic Rod
Authors: Haight E. C. , King W. W.
Published: October 2005

The stability of plane steady oscillations of a slender elastic rod subjected to lateral harmonic excitation is investigated. For certain values of excitation amplitudes and frequencies, the planar response is unstable, and nonplanar motions are parametrically excited. Steady nonplanar motions are characterized by each point on the rod centerline tracing an elliptical path perpendicular to the rod axis. The investigation is restricted to cantilevered rods with nearly equal principal moments of inertia of the cross section, and excitation is always in the direction of one of the principal axis of inertia. The effects of damping and of slight variations of the natural frequencies associated with motions in the two principal planes are investigated. Supporting experimental evidence is presented. Finally, the principal features of the transversely driven rod response are compared with the response for the same type rod excited axially.
Effects of Background Noise, Distance, and Speech Directivity in the Open Plan
Authors: Teplitzky Allan M.
Published: October 2005

Success of open-plan offices or schools depends upon the speech privacy between groups of conversationalists. Speech privacy can be determined by an Articulation Index (AI), which relates the speech signal at the listener's location to the background noise level. These parameters have been used to calculate contours of equal AI around a male speaker. By placing these contours on an architectural plan, the speech privacy relationship between groups can be determined. This scheme is used to compare the floor area requirements of a conventional wall school with an open-plan arrangement for a background noise level of PSIL-40.
Factors Affecting the Comparison of Theoretical and Experimental Sound Transmission Loss of Panels
Authors: Holmer Curtis I.
Published: October 2005

The sound transmission loss of homogenous isotropic panels is simply described theoretically from an infinite plate theory, in terms of the panel mass per unit area, bending stiffness per unit width and loss factor, and some a priori assumptions about the forcing sound field. In a typical transmission loss test, a number of additional factors are involved which may affect the test results. These effects include: (a) “diffusivity” of the incident sound field at the panel; (b) finite size of the test opening; (c) depth of the test opening; (d) inhomogenieties in the panel; (e) resonant response of the panel; (f) panel size compared with correlation length in the forcing sound field; (g) spectral shape of sound fields (when measured with filters of nonzero bandwidth). These variables are reviewed in view of the current state-of-the-art, and their range of effect in the region of the panel critical frequency is discussed.
An Experimental Study of Acoustic Interactions between Transducer Elements in a Model Array
Authors: Chervenak John
Published: October 2005

A model array of 100 ADP crystal transducers designed to vibrate in a fundamental longitudinal mode was fabricated for the purpose of studying acoustic interactions in the NRL Acoustic Research Tank. To promote these interactions, the transducers were designed to have radiating faces of fractional wavelength size. Measurements were made on the full array as well as on smaller arrays. The objective of the study was to learn more about the parameters that affect the velocities or displacements of individual elements and thus the nearfield pressure patterns of multielement transducer arrays. Data obtained and presented in the form of curves, charts, and patterns indicate how the phase and amplitude of the displacements of transducer radiating faces is affected by parameters such as negative admittances, electrical drive conditions, and transducer element variations, location, and separation.
Masking Effects of Competing Speech
Authors: Speaks Charles , Wigginton Virginia , Germono Joseph
Published: October 2005

Performance-intensity functions for synthetic sentences were defined in the presence of two competing signals. One was a competing speech message. The second was a noise envelope obtained by multiplying white noise and the amplitude envelope of the competing speech message that was full-wave rectified and low-pass filtered to 20 Hz. The two competing signals had nearly identical temporal masking patterns, but the noise envelope was devoid of all other speechlike properties. Mean sentence identification scores were higher for the noise envelope condition. Threshold levels (S/N ratio corresponding to 50% correct) were −29 dB for competing speech and −36 dB for the noise envelope. The area under the function for the noise envelope was approximately 22% greater than the area for competing speech. The disruptive influence of (1) the random temporal masking pattern and (2) the speechlike properties of the competing message will be discussed. The results will be compared with previous experiments in which competing messages were presented in forward and backward modes. [Research supported by grants from National Institutes of Health and University of Minnesota Graduate School.]
A Nonlinear Extension to Flanagan's Model of Vocal-Cord Oscillations
Authors: Mermelstein P.
Published: October 2005

An extension of Flanagan's model for vocal-cord oscillations [J. L. Flanagan and L. Cherry, J. Acoust. Soc. Amer. 45, 764–769 (1969)] has been used to excite a transmission-line analog of the vocal tract and thereby synthesize voiced and unvoiced stops. Postulation of a two-spring vibrating system allows the lateral compression of the vibrating vocal-cord mass to be a non-linear function of the force exerted by the air on the cords. When the supraglottal pressure is low, e.g., for an unconstricted vocal tract, the vibrating system is essentially linear and reduces to that proposed by Flanagan. When the tract is constricted, e.g., for voiced stops, the nonlinearities introduced serve to limit expansion of the glottal area in spite of the higher air pressure on the vocal cords. Unvoiced stops are modeled by an active separation of the vocal cords, which switches the oscillator from an oscillatory to stationary mode. Examples of simulations of intervocalic voiced and unvoiced stops are given.
Individual Differences and Multidimensional Scaling of Speech Perception Data
Authors: Bricker P. D.
Published: October 2005

An experimenter who performs a multidimensional analysis of speech perception data must deal with two problems: (1) differences among subjects in the data and (2) rotation of axes in the solution. The rotational problem is crucial when one seeks to determine whether the “true” perceptual dimensions correspond to a particular set of acoustic measures or articulatory features of the stimuli. A new multidimensional scaling technique devised by Carroll and Chang [Psychometrika, (1970) (to be published)] offers a solution to the rotational problem arrived at by capitalizing on individual differences: the axes derived are those that best account for variations among individuals in terms of a differential weighting model. This paper illustrates the promise this method holds for speech perception studies by an example: data on dissimilarities among nine Swedish vowels published by Hanson [Ericsson Technics 23, 3–175 (1967)] are re-analyzed. Whereas the stimulus set represented three distinctive features, the published solution recovered only two. The Carroll-Chang solution is interpretable in terms of all three features and formant frequencies as well. Additional procedures show that the two solutions differ chiefly in rotation and illustrate how other (superficially rational) rotational criteria can lead to less informative solutions.