bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering-Matrix Description and Nearfield Measurements of Electroacoustic Transducers
Authors: Kerns D. M.
Published: October 2005

Recently developed analytical techniques for the measurement of microwave antennas at reduced distances are “translated” into corresponding techniques for the measurement of electroacoustic transducers in fluids. The basic theory is formulated in scattering-matrix form and emphasizes the use of plane-wave spectra for the representation of sound fields. This theory, in contrast to those based on asymptotic description of transducer characteristics, is suitable for the formulation and solution of problems involving interactions at arbitrary distances. Two new techniques (in particular) are described: One, utilizing deconvolution of transverse scanning data, which may be taken at distances d much less than the Rayleigh distance dR(≡ a2/2λ), provides a means of obtaining complete effective directivity functions, corrected for the effects of the measuring transducer. Applicability of a (two-dimensional, spatial) sampling theorem and the “fast Fourier transform” algorithm, which greatly facilitate the necessary computations, is shown. The second technique provides a means of extrapolating received signal as a function of distance (observed with d∼dR or d≫a instead of the conventional d∼dR) to obtain on-axis values of effective directivity. Other possible applications are indicated. In these techniques, pressure data are rigorously sufficient; normal velocity data are not required.
An Ultrasonic Radiation Calorimeter
Authors: Herman Bruce , Stewart Harold F.
Published: October 2005

This paper describes a constant temperature environment calorimeter for the absolute measurement of ultrasonic power. This design uses a variation of the classical calorimetric procedure of power measurement as applied specifically to ultrasonic transducers. This measurement technique has advantages over other methods in that it is the least affected by beam shape and pulse duration. The calorimeter consists of a conical shaped calorimeter cup mounted in an outer brass cylindrical container. The calorimeter is placed in a water bath, which provides both a constant temperature environment and an effective medium for the propagation of ultrasound. The calorimeter cup is filled with Dow Corning 710 silicon fluid, which is an effective absorption medium. It has a 112-in. entrance window of gold coated nylon separating the silicon fluid from the water bath. The gold film is used as a resistance heater to maintain quasi-adiabatic conditions between the silicon absorbing fluid and the water environment at the entrance membrane. The temperature difference between the silicon absorbing fluid and the outer brass cylinder is measured with a bank of chromel-constantan thermocouples. This measured temperature difference is a measure of the ultrasonic power. Calibration of the system is accomplished with a constant resistance heating coil immersed in the Dow Corning 710 absorbing fluid.
Suppression of Transducer Sidelobes by the Use of Acoustic Baffles
Authors: Watters B. G. , Goddard G. C. , Welsby V. G.
Published: October 2005

The out-of-beam response of underwater acoustic transducers may be reduced by the use of baffle systems. This paper presents the results of experimental work carried out recently at the University of Birmingham (U.K.) on the effect of high-transmission-loss pressure-release planar baffles placed to the side of the main axis of a transducer. The height of the baffle (i.e., its projection beyond the transducer face) and the distance in wavelengths from the transducer axis have been varied over a wide range. Our results are compared to values calculated on the basis of Fresnel diffraction theory.
Frequency Response of Condenser Microphones in Gases other than Air
Authors: Semrau W. R.
Published: October 2005

Performance of scale model fan noise experiments in a unique free-field heavy gas test facility required that a method be developed for determining microphone response in the high molecular weight gas. Using an electrostatic actuator, calibration experiments in air, argon, helium, and freon-12 were conducted at several gas pressures. Results indicated that microphone pressure response is essentially independent of the test gas composition. At diaphragm resonance frequency, where the greatest sensitivity variation was observed, changes due to gas composition were only about 1 dB. Apparently diaphragm damping is governed by pressure rather than gas density. This result obviates the need for microphone calibration in gases other than air.
Computer Modeling of Vocal Cord Pathologies and Voice Registers
Authors: Titze Ingo R. , Strong William J.
Published: October 2005

A detailed study of normal vibrational patterns of the vocal cords and a preliminary investigation of simple vocal cord pathologies have been conducted. A 16-mass model described in earlier abstracts [Titze and Strong, J. Acoust. Soc. Amer. 51, 138(A) (1972); 52, 123(A) (1972)] represents mucous membrane, vocal ligament, and vocalis muscle. An 18-section vocal tract and a 12-section nasal tract are coupled to this system. Fundamental frequency, vocal dynamics, register, and vibrato are linked quantitatively with the physiological correlates, i.e., subglottal pressure, vocalic contraction, vocal cord length, and elastic properties of vocal ligament and mucous membrane. Interactions between the vocal tract and the glottal source are demonstrated for the vowels /a/ and /i/. An attempt is made to simulate localized mass increase, i.e., a vocal node, and localized stiffening to approximate the effect of a mild cancer. The perturbed vibrational patterns and the corresponding synthesized vowels art, discussed. Samples of normal utterances and slightly pathological utterances are presented for several pitches in modal and falsetto register.
Predictors of Age in the Male Voice
Authors: Ryan W. J. , Burk K. W.
Published: October 2005

Direct age estimates of 80 adult male speakers, chronologically 40–80 years of age, were made by 20 untrained listeners from recorded speech samples. Forty recordings were selected for further perceptual and acoustic analyses based upon high listener agreement of perceived age. Judgments by trained listeners of the presence or absence of selected voice characteristics, in addition to five acoustic measurements were intercorrelated. The significance of these variables in predicting perceived age was assessed through a multiple regression analysis. Results indicated that five voice characteristics: voice tremor, laryngeal tension, air loss, imprecise consonants, and slow rate of articulation, were strong predictor.of perceived age, and suggest specific areas of future study involving age related physiologic, acoustic, and perceptual changes in speech production.
Intrinsic F in Vowels: Physiological Correlates
Authors: Atkinson J. E.
Published: October 2005

It has been known for some time that different vowels characteristically have different average fundamental frequencies (F0) The most influential explanations offered to account for these “intrinsic” differences in F0 are (1) dynamogenetic radiation of muscle potentials (e.g., Taylor, 1933); (2) mechanical interaction with the supralaryngeal musculature (e.g., Lehiste, 1971); (3) aerodynamic coupling between the largynx and the oral cavities (e.g., Flanagan, 1968). In the present study, a simplified explanation of source-system interactions is given in terms of an electrical equivalent circuit. From this model several physiological parameters are predicted for different vowels. Measured physiological (air flow rate and subglottal pressure) and acoustical data are compared with these predictions. The measured data in all cases support the results predicted by the model. This study supports the Flanagan model for source-system interaction and extends its scope in terms of physiological correlates.
The Interaction of Continuous and Impulse Noise: Histological Effects
Authors: Hamernik Roger P. , Crossley James J. , Henderson Donald , Salvi Richard J.
Published: October 2005

The cochleas of the chinchillas exposed to the four noise conditions described in the previous abstract were examined using the surface preparation technique. The animals (six) exposed to the continuous noise alone, had essentially normal hair cell populations. The animals (five) exposed to the 158-dB peak impulse had hair cell losses that ranged from a scattered low level loss to approximately a 4 mm loss of OHC in the base of the cochlea. IHC losses were considerably smaller. The animals (six) exposed to the interrupted combination had nearly the same range of hair cell losses as seen in the 158-dB group, with the exception of one animal that had a large (8 mm) discrete loss of OHC and IHC. The superimposed combination produced the most severe hair cell lesions with five of the six animals showing nearly 100% losses of OHC and IHC extending throughout the basal one-third to one-half of the cochlea. The audiometric and histological findings agree in showing that the superimposed combination of the two “safe” noises produces traumatic effects that more than exceed the additive effect of either component. The existing DRC do not provide guidlines for such combinations.
An Evaluation and Description of the Electroacoustic Units Associated with the Verbo-Tonal System
Authors: Asp C. W. , Keller J. E. , Williams R. P.
Published: October 2005

The verbo-tonal method advocates working through the impaired auditory modality as the primary channel to habilitate or rehabilitate hearing-impaired people. To implement this philosophy, six electroacoustic units have been designed. The characteristics of these units are as follows: (1) Suvag I has an electrical response that extends from 12 to 20 000 Hz; it can also be utilized in low-pass filter conditions of 0.6, 1, 2, and 3 kHz. (2) Suvag II is a multichannel unit with the following modes of operation: (a} direct channel (20–20 000 Hz); (b) low-pass and also low-peaking filters of 0.07, 0.15, 0.3, 0.6, and 2 kHz; (c) high-pass and also high-peaking filters of 3, 4, 6, and 8 kHz; and (d) base and treble control of + and − 16 dB. (3) Suvag Lingua has discrete bandpass filters that correspond to the “optimal octaves” of normal-hearing people; it is utilized for teaching foreign languages. (4) The Mini Suvag hearing aid is a body-type aid with a wide frequency response. If utilized with a separate power amplifier, the unit can simultaneously drive both bone- and air-conduction transducers. (5) The audiometer is utilized to present pre-recorded filtered speech signals. (6) The Suvag Vibar is a bone vibrator that is placed at different points of the body during the therapy procedure. Electrical and acoustic frequency responses will be displayed and compared to those of other units. [Work supported by the U. S. Office of Education.]
A Simplified Description of Wind-Generated Noise for Sonar Response Applications
Authors: Huggins G. G. , Burroughs C. B.
Published: October 2005

Many current ambient noise measurement and modeling programs are aimed at improved estimates of the spatial properties of ambient noise fields. One application of these studies is the development of models for predicting sonar array response to anisotropic ambient noise. The purpose of this paper is to present a simple model developed in closed form for sonar applications, and yet which reflects the dependence on important environmental parameters. The model describes vertical directionality of wind-generated noise above and below the horizontal for a near-surface receiver. The sensitivity of the model to such factors as the strength and sign of the velocity gradient, bottom loss, and water depth are explored. Comparisons to more accurate and comprehensive models and measurements show that the model satisfactorily describes the substance of these environmental factors. For example, noise directionality above the horizontal for a shallow receiver is only weakly dependent upon the velocity gradient. Below the horizontal, results are strongly a function of bottom reflectivity and nearly independent of water depth. [Study supported by NAVSHIPS, PMS 302-4.]
Sonar Array Response to Ambient Noise Directional Fields, Comparing Numerical Results to Closed-Form Estimates
Authors: Huggins G. G. , Burroughs C. B.
Published: October 2005

Several studies have been directed towards the development of both numerical and analytical expressions of ambient noise directionality. In this paper, the results of a simplified ambient noise model are employed to examine the response of sonar arrays to directional noise fields. Expressions are found for the array gain against wind noise for near-surface arrays, employing vertical and horizontal line arrays as examples. The results are compared in each case with array gain against isotropic noise (i.e., directivity index). Array response is found as a function of array orientation, frequency (or size), and steering angle. For the broadside steered line array, a simplified beam response pattern is used to find array gain for these simple analytical noise models. Results compare very well with array gains computed using more precise models of the ambient noise field and exact array response patterns. The implications on sonar design and performance studies are discussed, as well as similar estimates for the response of more complex array configurations. [Study supported by NAVSHIPS, PMS 302-4.]
The Effect of Ice Cover on Shallow Water Ambient Noise
Authors: Collier A. J.
Published: October 2005

Ambient sea noise in the frequency range 12.5–6400 Hz was measured in the Cabot Strait, near Cape North, Nova Scotia, during the period 23 February to 16 April 1971 with a bottom-mounted hydrophone at a 350 ft depth. During this period, floe ice moved continuously, giving ice coverage that varied from 0/10ths to 10/10ths. The wind-dependent noise spectra and distributions of spectral levels are presented for various degrees of ice coverage. It was found that the spectral levels are wind dependent for all degrees of ice cover, but the under-ice spectral levels are significantly lower than the open water levels for comparable wind velocities.
Analysis-by-Synthesis Recognition of Spoken Integers Using Prosodic Information Alone
Authors: Allen J. , Willems Y. D.
Published: October 2005

A formal syntax for the spoken integers between 0 and 999 can be written using syllables as terminal elements, and which also utilizes word and syllable juncture as well as spoken variations (e.g., three versions of the lexical item “and”) of some of these terminals. A match routine is then used to generate all possible syntactic strings from left to right. As each terminal is generated, a comparison is made of the syntactic structure with the syllabic and junctural correlates determined from the waveform envelope and pitch contour. In this way, a running likelihood score is generated for each possible terminal string as it builds up from left to right. This technique returns a small number of possible utterance candidates with a high degree of correctness. These results are obtained without use of any segmental information.
A Reverberant Chamber Facility for Sound Power Measurements in Air or Water
Authors: Blake W. K.
Published: October 2005

A reverberant chamber for use with both air and water media is described. The chamber is used to investigate the acoustic coupling of simple vibrating structures under conditions of light or of heavy fluid loading. Calibration was effected by measuring 60-dB reverberation times in 13-oct bands; decay times of 2 sec in air and 0.2 sec in water were observed. These broad-band results were cross checked in water by measuring the spectrum of acoustic pressure in the chamber generated by a calibrated hydrophone source. Sound pressure levels measured in narrow (50-Hz) bands varied ±3 dB spatially in the air-filled chamber and ±5 dB spatially in the water-filled chamber.
A Tape Recorder for Use With Sound-Level Meters
Authors: Marteney Eugene R.
Published: October 2005

A tape recorder designed specifically for use with sound-level meters is described. Important considerations of recording from sound-level meters are discussed, including calibration, dynamic range, crest factor, frequency response, and flutter. Particular attention is given to the recovery of recorded sound-level range One solution is to use a second record channel and tape track to record tones representing the sound-level meter range. Four bridge “T” oscillators, multiplexed in a binary format, generate the encoding signal. The oscillators convert to filters during playback, selecting tones, which when detected, actuate a light emitting diode digital display. Encoding of tones is accomplished manually or automatically from sound-level meters that have an encoding switch as part of the attenuator selector. Convenience of a cassette recording format, and the simple setup and operate procedure make the recorder ideally suited for field use.
Sound Radiation Characteristics of Simply Supported Vibrating Beams
Authors: Moore James W. , Crocker Malcolm J.
Published: October 2005

Theories for the sound power radiated from a simply supported beam have been developed by Lyon and Maidanik [J. Acoust. Soc. Amer. 34, 623–639 (1962)], and others. In this paper, simple formulas have been derived which predict the sound power radiated and the farfield directivity pattern for an acoustically narrow beam. The results clearly show that a vibrating beam can be modeled by two interfering monopole sound sources located at the ends of the beam having equal strengths related to the vibration amplitude of the beam and a phase relationship depending on the type of mode excited. To test this theory, directivity patterns were measured for a 1-ft-long simply supported beam vibrating at its resonance frequencies. The directivity patterns for the first five modes were found to agree well with those predicted by the theory. [Work supported by American Standard Research and Development Center, New Brunswick, New Jersey, and conducted when both authors were at the Herrick Laboratories.]
Review of Noise Impact Aspects of Environmental Impact Statements
Authors: Garrelick Joel M.
Published: October 2005

The noise impact aspect of a number of Environmental Impact Statements has been reviewed for projects within the New England Region. The projects include transportation facilities, e.g., highway and airport constructions, as well as standard building construction. Different levels of effort were apparent. These ranged from complete surveys of ambient levels plus detailed predictive schemes to a few cursory remarks. Various acceptability criteria and analyses were employed. However, a number of generalizations can be made. Finally, means for improving efficiency of preparation and presentation of these statements are suggested. [This work was partially performed under contract to the Environmental Protection Agency, Categorical Programs Division, Boston.]
A-weighted Sound Levels Measured with/n the Cockpits of 339 Fixed- and Rotary-Wing Aircraft
Authors: Gasaway Donald C.
Published: October 2005

Acoustic noise levels measured within 339 aircraft are depicted for seven groups of fixed-wing aircraft and four groups of rotary-wing aircraft. These measurements are described using octave-band noise envelopes and flat and A-weighted sound levels. Also, differences between flat and A-weighted levels are identified for different types of aircraft. The noise spectra and weighted levels are reported from noise measurements obtained within the cockpits of various aircraft during conditions of normal cruise. Noise data are reported for 271 fixed-wing aircraft: 142 powered by reciprocating engines, 45 powered by turboprop engines, and 84 powered by turbojet or turbofan power plants; and for 68 rotary-wing aircraft: 28 powered by reciprocating engines and 40 vehicles mated to turboshaft engines. The purpose of this report is to provide insight concerning the acoustic character of noise exposures commonly encountered within aircraft.
Practical Considerations in the Establishment of Effective Hearing Conservation Programs
Authors: Scott C. E. , Thomas W. G. , Royster L. H.
Published: October 2005

Procedures of developing, implementing, and maintaining an effective hearing conservation program are presented. Special emphasis is placed on the employee's part and the need to develop special techniques in order to ensure the program's success.
Techniques and Results of Audiometric Testing in Hearing Conservation Programs
Authors: Thomas W. G. , Royster L. H. , Scott C. E.
Published: October 2005

Audiometric testing is an integral part of a hearing conservation program. Newer techniques, which more closely approach the state-of-the-art, including computerized testing, and telephone line operation, are available for testing large numbers of people with results that are in good agreement with standard testing techniques. These techniques, as they apply to preemployment audiograms, initial testing, and annual retests, are discussed. A large number of audiograms from several major industries have been reviewed. The results of this review indicates that approximately 50% of the employees on the initial test show significant high-frequency hearing loss, approximately 10% of the employees show hearing loss severe enough to be seen by Clinics or physicians for further testing, and approximately 5% of the employees have to be retested because of inaccurate results. On annual retests, approximately 15% of the employees show additional hearing loss with hearing conservation programs in effect. Criteria and techniques for evaluating hearing conservation programs are suggested, along with criteria for evaluating additional hearing loss on annual retests.
Comparison of Selected Damage Risk Criteria in Judging Industrial Noise Environments
Authors: Scott C. E. , Royster L. H. , Thomas W. G.
Published: October 2005

A study was made of over 500 data samples for the purpose of comparing allowed exposure times using 85 dBA, 90 dBA, and octave band spectra with the CHABA Working Group damage risk contours. The results of the study indicate that the use of octave band data spectra and the CHABA Working Group damage risk contours should be allowed in lieu of overall dBA.
A Multidimensional Analysis of the Phonemic Responses of Hard of Hearing and Deaf Subjects of Three Languages
Authors: Danhauer Jeffrey L. , Singh Sadanand
Published: October 2005

Twenty logatomes (CVCV) involving five vowels and 20 consonants were presented to 36 subjects, 18 hard of hearing and 18 deaf. Of the 18 subjects, six were speakers of English (American), six Serbo-Croatian (Yugoslavian), and six French (French). The logatomes were analyzed for both initial and medial consonants. The responses were recorded on magnetic tape and transcribed phonetically by three judges. The data were analyzed by IND-SCAL and reported in unique dimension for both stimulus and subject spaces. Twelve groups of similarity matrices mainly yielded two- and three-dimensional solutions. The interpretation of these dimensions were mainly voicing and sibilant. Additional features retrieved in some cases were nasality, fricative, and voiceless stop. Recovery of similar space for three language groups, two deviancy groups, and two positions reveal “universal” dimensionality and features of the consonants. Some features were more prominent at the initial place (sibilant and fricative), whereas others at the medial place (voicing and nasality). While hard of hearing and deaf subjects utilized voicing equally, sibilant, nasality, and fricative were utilized more by the hard of hearing and voiceless stop by the deaf subjects.
Noise Sources and Room Acoustics of Closed Circuit Subsonic Wind Tunnels
Authors: Vér I. L.
Published: October 2005

The noise aspects of subsonic wind tunnels have been studied experimentally on full-scale and model-scale tunnels. In wind tunnels without acoustical treatment, the driving fan and the boundary layer suction fan were found to be the dominant noise sources. The fan noise in the test section scales with the 6th power of the airspeed. Using this scaling, one obtains a number, the acoustical merit rating, which permits one to compare the acoustical quality of different wind tunnels. Experimental results obtained in full scale as well as in scale models of closed circuit tunnels will be presented to illustrate the impulse response and spatial distribution of the sound pressure. Also, the special instrumentation required for obtaining valid results will be discussed.
Noise Control of Closed Circuit Subsonic Wind Tunnels
Authors: Vér I. L.
Published: October 2005

The noise control measures discussed will include the design of low-noise driving fans, the acoustical design of the exterior walls, and the sound absorbing treatment of strategically located interior wall surfaces. it will be shown how scale models can be used to predict the effect of noise control measures in reducing fan noise in the tunnel proper and sound power radiated to the outside.
Pressure Waves in a Fluid Layer
Authors: Easter J. R. , Torvik P. J.
Published: October 2005

The pressure field in a layer of compressible inviscid fluid between two parallel elastic plates is considered. Each plate is described by the Timoshenko-Mindlin plate equation, and a point time-harmonic force is assumed to be applied normally to one plate. The method of solution parallels that previously applied to a semiinfinite fluid bounded by one plate [Feit, J. Acoust. Soc. Amer. 40, 1489–1494 (1966)]. The Hankel transform was applied to the plate equations and the wave equation for the fluid, with the pressure and normal velocity at the interfaces being equated. The resulting inverse Henkel transform was evaluated both by numerical integration and by an approximation using the method of steepest descent. Separate expressions were developed in each case for results near the axis of symmetry and for large distances from that axis. Results for 10-μsec pulses were also obtained by the superposition of steady-state results for 20 frequencies. Satisfactory agreement between the two methods was obtained.
Comparison of Direct and Indirect Measures of Critical Bands of the Monaural Chinchilla
Authors: Seaton W. H. , Trahiotis C.
Published: October 2005

Typically, it is found that lower forms (rats, cats, and chinchillas) require a greater S/N ratio than does man in order to detect the presence of a pure-tone signal in a broad-band noise. Assuming Fletcher's formula to be an adequate means of estimating the operating bandwidth of the auditory system, one could come to the conclusion that these lower forms have larger critical ratios, larger critical bands, and, therefore, poorer frequency resolving ability than does man. However, the behavioral index of auditory sensitivity utilized in these experiments does not permit separation of behavioral criterion and auditory sensitivity. It seems probable that lower forms are trained to maintain a “high” criterion (low false-alarm rate) and, thereby, produce threshold measures of relatively high S/N ratio. Our efforts have been directed toward measuring both critical ratios and critical bands (band narrowing paradigm) utilizing both traditional threshold measures and criterion free indices of signal detection theory. Data obtained at signal frequencies of 500 Hz, 1, 2, and 4 kHz will be discussed in terms of (1) the relationship of critical ratios to critical bands as a function of frequency and (2) the effect of criterion contamination on the estimate of the critical ratio and therefore on the estimate of the frequency resolving power of the organism.
Regulation of Voice Amplitude by the Monkey (Macaca)
Authors: Sinnott J. M. , Stebbins W. C. , Moody D. B.
Published: October 2005

Increasing voice amplitude in the presence of noise has been referred to as the “Lombard reflex.” Lane [J. Speech Hearing Res. 14, 677–709 (1971)] believes that the response is not reflexive, but that speakers learn to take their audience into consideration by raising their voices in noise. In this experiment, we determined the effect of noise on monkey vocalizations, which have long been considered to be primarily affectire in nature and con- trolled by subcortical limbic structures [Robinson, Physiol. Behavior 2, 345–354 (1967)]. Monkeys were trained by oper- ant conditioning procedures to vocalize for food reinforce- ment. Our results showed that the monkeys increased their voice level under a masking noise band of 200–500 Hz (funda- mental frequencies for these monkeys ranged between 250 and 400 Hz. The slope of the function relating vocal intensity to external noise level was approximately 0.2, comparable to our own data from humans. The monkeys' voice amplitude was not noticeably affected by a high-frequency nonmasking noise band of 8–16 kHz. Thus both humans and monkeys ap- pear to have a similar self-regulatory system of voice control in masking noise, despite alleged differences in the neural basis of human speech and monkey calls. [Research supported by grants from NIH and Sigma Xi.]
Temporal Interactions within Phrase and Sentence Contexts
Authors: Wright T. W.
Published: October 2005

Recent timing control research has shown that when a smaller linguistic segment within a repeated utterance is produced either shorter or longer than its average duration, the resulting deviation constitutes a timing error that is temporally compensated by the remaining segments in the utterance. In the present study, timing errors and the extent to which they are compensated define different levels of temporal interaction. Temporal interactions were studied within a phrase spoken in isolation and within the same phrase spoken in a sentence context. The data, presented as significant negative Pearson correlations (p < 0.05) between various adjacent segment durations, support several tentative conclusions on the timing control of repeated utterances: (1) different-sized utterances have different levels of temporal interaction; (2) temporal interaction effects extend across phoneme, syllable, word, and phrase boundaries; (3) there appears to be no basic unit of timing for English utterances, but a hierarchy of units ranging in size from a CV or VC syllable to a sentence; and (4) identical durational errors may be compensated for by a variety of adjacent segment lengths.
More Temporally Segmented Speech
Authors: Huggins A. W. F.
Published: October 2005

The intelligibility of alternated spech passes through a minimum at an alternation rate of about 3 Hz. The critical parameter defining the minimum is not the duration of the bursts of speech reaching the listener, but rather the amount of speech each burst contains [J. Acoust. Soc. Amer. 36, 1055 (1964)]. Recent work with temporally segmented speech [J. Acoust. Soc. Amer. 52, 176(A), (1972)] showed the decline and recovery of intelligibility, as switching rate is increased, to be due to different effects. The decline depends on the decreasing duration of the speech bursts, but the recovery depends on the decreasing duration of the silent intervals. Since the minimum is determined by both these effects, the amount of speech contained in the speech bursts cannot be the only critical parameter, as stated above. To resolve this conflict, an experiment was performed with temporally segmented speech. Intelligibility was measured as a function of silent interval duration, speech interval duration, and speech interval content, the latter two being varied independently by varying the playback speed of the speech. [This research was supported by NIH grant.]
Rayleigh Wave Study of Ionic Diffusion and Stress Buildup in Glass
Authors: Bucaro J. A. , Simmons J. H.
Published: October 2005

The velocity of elastic surface waves has been studied as a function of frequency on a system of ion exchanged glasses. The ion exchange was carried out by immersion in a high-temperature salt bath at several temperatures and for times ranging from 12 to 259 h. The results of this study allow the determination of the ionic diffusion coefficient and its activation energy. The mechanism of dispersion is discussed in terms of mass and volume changes and stress buildup. Since ion exchange is currently used to strengthen glass, the above technique also appears to be ideal for the nondestructive testing of glass strengths.
Reducing Blade Tonal Noise Generated by Vane-Axial Fans
Authors: Pierpoint J. V.
Published: October 2005

An experimental investigation was made to determine the effectiveness of unequally spaced blades and blade/vane interaction techniques in reducing the pure-tone aerodynamic noise generated by vane-axial fans. Balanced mirror-image and other modulated blade patterns were investigated for 13, 19, 20, and 21 blades in combination with nine equally spaced downstream stator vanes. In-duct discrete-frequency noise analyses were obtained. Blade-passing frequency and its harmonics were modulated and reduced 10–20 dB, using unequally spaced blades. Large spacing deviation had the effect of spreading the sound energy to more harmonics of rotational frequency. In some instances, significant downstream stator vane and upstream strut frequencies were observed. Predictable pure-tone multiples of rotational frequency were also detected. Elimination of inlet strut frequency and large reductions at the harmonics of blade-passing frequency were obtained upon replacement of the inlet bell and stationary nose cone and eight support struts with an inlet bell and spinning nose cone. Unequally spacing the blades of the fan had little effect on the ability of the fan to move air.
Measurements of the Wall Pressure Field in a Transition Boundary Layer on a Fiat Plate
Authors: DeMetz F. C. , Casarella M. J. , Jorgensen D. W.
Published: October 2005

Experiments have been conducted in the new anechoic flow facility at the Naval Ship Research and Development Center on the flow noise feature of the transition boundary layer on a flat plate. Measurements were made of the pressure fluctuations in the intermittent region of a naturally developing transition boundary layer over a 14 ft long flat plate in a mild accelerated flow. Results are reported of the power and cross-spectral density of the pressure field of the intermittent turbulent spots, as a function of the intermittency factor. The average burst length, burst frequency, and burst convection velocity are also computed from the data and compared with those of related studies.
Acoustic Impedance Measurements for Various Angles of Incidence
Authors: Tocci Gregory C. , Davies Huw G.
Published: October 2005

A simple correlation technique is presented for measuring acoustic absorption coefficients and impedances of surfaces for sound incident at any angle. The measurements can be made in situ; the technique is useful for measuring ground impedance and the surface impedance of buildings, as well as the impedance of acoustic absorbing material. The technique uses a simple source and one microphone, both placed a few acoustic wave-lengths away from the surface. The source signal is random noise, and the microphone output is filtered through a narrow frequency band with a suitably smooth filter shape. Values of the absorption coefficient and impedance at any frequency are obtained from the autocorrelation curve of this narrowband signal. [Work supported by NSF.]
Computer generation of sequential musical patterns
Authors: Hiller Lejaren A.
Published: October 2005

It has been thought that music is a multilayered hierarchical communication system in which relationships exist among several levels of structural significance. This view of music structure can be tested by computer synthesis of statistically converted melodic and/or harmonic sequences, starting with random music through simple stochastic music in which each musical event is affected by previous events to successively more and more complex structures that have imbedded in them whole groupings of events such as phrases, themes, and so forth. The background for this work is briefly reviewed and programming methods for a number of examples of computer-generated sequences of increasing complexity are discussed. Included in the presentation are some recorded examples of this output.
Recall of auditory patterns by monkeys
Authors: Dewson J. H.
Published: October 2005

Six monkeys have been trained to indicate the nature of a recently heard sequence of auditory events by pressing, in proper sequence, illuminated panels whose specific colors have a learned equivalence to the specific auditory events. The auditory sequences and, likewise, the spatial location of the later-presented color cues for response are randomized for each trial. Recall functions, obtained via adaptive psychophysical procedures, have been determined for both monaural and binaural monkeys. This behavioral animal preparation should prove of great value for the study of brain mechanisms which underlie cognitive abilities.
Cross-spectral densities in partially reverberant sound fields
Authors: Blake W. K. , Waterhouse R. V.
Published: October 2005

The cross-spectral densities of sound at two points in a reverberant space are shown to be sensitive to the power flow out of the space. A nearly homogeneous sound field is found to possess a co-spectral density which is nearly insensitive to the nature of the field. This spectrum is traditionally obtained as a cross correlation and its analytical form has been well established. Perhaps less well known is the imaginary part of the cross spectrum which is shown in this paper to be sensitive to the direction of propagation from a sound-scattering enclosure Specific analytical forms of the spectrum are derived for incidence included within certain cones by using a wave-function model of the scattered sound field. The co- and quadrature-spectra are then shown to be uniquely related to each other by the Hilbert transform.
Annoyance and behavioral consequences following interfering and noninterfering aircraft noise exposure
Authors: Vanderhei Sharon L. , Loeb Michel
Published: October 2005

Six groups were exposed for 15 minutes to one of three noise conditions—“quiet” (less than 40 dBA), “high noise” (47 recorded jet flyovers with peaking from 90 to 105 dB SPL), and “moderate noise” (14 flyovers). One group under each noise condition performed a listening task subject to noise interference and the other performed a cancellation task. Estimations of annoyance and ratings of unpleasantness and concentration difficulty produced were obtained, after which subjects performed on proofreading and design tracing tasks similar to those of Glass and Singer [Urban Stress (Academic Press, 1972)]. Annoyance, unpleasantness, and concentration difficulty were higher for listening than for cancellation under high noise but not under other noise conditions. Aftereffects similar to those reported by Glass and Singer were not observed. Subjective measures were intercorrelated for cancellation but not listening conditions. Generally, they did not predict performance. It is concluded that ratings of interfering noise may reflect in part reaction to the interference and that aircraft noises may not elicit the behavioral changes described by Glass and Singer.
Measurement of classroom noise environments
Authors: Simpson Myles A. , Bishop Dwight E.
Published: October 2005

As part of a study of the impact of aircraft noise intrusions within schools in the vicinity of a major airport, it was necessary to obtain a realistic assessment of the noise environment in actual classrooms. To determine typical classroom noise exposure, noise measurements in terms of equivalent levels were made with classes in session, during periods with no formal voice communication and with no aircraft intrusions, in 72 classrooms of six schools—three located close to the airport and three far removed from the airport. Analysis of the measurements showed wide variations in noise levels. Average levels were highest in the kindergartens (average equivalent level of 60 dB), with levels decreasing with grade to an average of slightly less than 50 dB in high schools. No statistically significant difference was found between the levels observed in the three schools located near the airport and the three schools far from the airport.
Acoustical modeling for site evaluation
Authors: Lyon Richard H. , DeJong Richard , Cann Richard
Published: October 2005

The positioning of building complexes that are noise sensitive (hospitals) or noise producing (factories) on a new site or changing patterns of land use around the site can result in uncertain noise exposures. Analytical or computer-based procedures for estimates of noise are useful, but limited. Acoustical scale modeling provides immediate predictions of changes in noise exposure as the positions of buildings, roadways, land profile, and other features are changed. The RANN program of NSF has sponsored MIT to develop an acoustical modeling system usable by engineering groups, environmental agencies, and developmental organizations. A prototype system has been developed and used in field/laboratory comparisons of sound propagation at various sites on the MIT campus. We are now in a “user experience” phase of the program, in which three organizations representative of prospective user groups will be provided systems for their evaluation. As a result of this user feedback, we hope to be able to provide a modeling system and associated techniques that will allow technically trained people in these organizations to use modeling as a site evaluation and design procedure. [Work supported by the RANN Program, NSF.]
Analysis of low-frequency sound channel propagation in Baffin Bay
Authors: Powers M. R. , Browning D. G. , DiNapoli F. R.
Published: October 2005

The axial arrival pattern at low frequencies (below 100 Hz) and relatively long ranges (200 km) from a sound channel propagation experiment in Baffin Bay shows an extensive series of arrivals after the refracted arrival pattern. Since the bottom at this location was relatively lossless, the hypothesis that these later arrivals represented energy that was diffracted from the sound channel was examined using the Fast Field (Modeling) Program. A comparison of sound-propagation characteristics was made for the frequency range 1–100 Hz, assuming both high and low loss bottoms. The results show that diffraction does not significantly change the average propagation loss at frequencies above 5 Hz.
Ambient noise measurements in Jervis Inlet, British Columbia
Authors: Scott Jeffery T. , Huelsdonk Robert A.
Published: October 2005

Measurements of ambient underwater noise were made in Hotham Sound, Prince of Wales Reach, and other locations in Jervis Inlet, British Columbia, during the autumn of 1974. Jervis Inlet was found to be extremely quiet; the spectra of the ambient noise between 10 and 1000 Hz lie well below the Knudsen sea state zero curve and have the same general form as the minimum Wenz curve. Data to be presented include spectral plots of the ambient noise taken at several locations at various times of the day with different tug and ferry traffic conditions. These data are compared with the noise characteristics of other well-known quiet areas. Analog tape recordings will be played to illustrate unique features of the raw acoustical data.
Demonstration to a lay audience of echo ranging
Authors: McKinney Chester
Published: October 2005

The principle of echo ranging has been demonstrated to a variety of nontechnical groups using a mechanical halloween cricket as a pulsed sound source and a microphone, horn, amplifier, and oscilloscope as a receiver. A few related demonstrations will also be described. Groups which have observed the demonstration include cub scouts, high school students, science teachers, and women's clubs.
Conducting program
Authors: Mathews M. V. , Boulez P.
Published: October 2005

A program for computer sound synthesis has been developed with which a conductor can conduct the performance of a musical score in a manner similar to the way he would conduct an orchestra. The conductor beats time and adjusts the loudness of four voices. The score is in the memory of a computer. The computer controls a synthesizer which generates the sound. The principal devices used by the conductor are an organ keyboard and a wand attached to three potentiometers which measure the three coordinates of the position of the wand. The conductor beats time on one of the keys with one hand and adjusts the overall loudness and balance of voices by moving the wand with his other hand. The program adjusts the tempo at which the piece is synthesized so as to follow the beat. Sample pieces performed with the program will be played.
Measuring linguistic stress in a continuum
Authors: Minifie F. D. , Cheung J. Y.
Published: October 2005

This study compares the results of three scaling procedures for estimating the magnitudes of linguistic stress applied syllable by syllable to sentence-length utterances, The three scaling procedures included a continuous scale, a three-level forced-choice procedure, and a rank-ordering procedure. Eight recorded sentences were presented to listeners who rated the amount of linguistic stress on each syllable with the three techniques. A second rating session was scheduled with the same listeners two weeks later. The results showed that the perceptual stress values obtained with the continuous scaling procedure compared favorably with those obtained via the three-category technique, except that the continuous-scale values provided finer gradations of stress than did the categorical ratings. The continuous ratings also corresponded well to the rank-order data. Since the temporal reliability of the continuous ratings is high and stable estimates of the continuous scale values can be achieved with less than five judges, the continuous rating procedure is recommended in perceptual studies of linguistic stress. The implications of such a rating procedure are discussed.
Open landscaped office acoustics—an engineering approach
Authors: Edwards A. T. , Kowalewski J.
Published: October 2005

The open landscaped office has received a high degree of acceptance which, a few years ago, would have surprised many acousticians. Experience has shown that a satisfactory degree of privacy is practical in open offices, provided acoustics is taken into account in the initial conceptual and the design stages. This paper discusses the acoustical requirements of each critical factor or component of an office, such as the ceiling, screens, wall and window coverings, background sound system, and distance. Analytical considerations are supported by objective and subjective testing in an anechoic room and in working offices. The quantitative performance of offices is discussed and proposals are made for standardizing this in terms of percentage speech intelligibility.
Spatial uniformity of backKround masking system in open plan offices
Authors: Harris D. A.
Published: October 2005

Performance criteria and test procedures employed by the United States Government Services Administration, Public Buildings Service, require hackground masking systems that satisfy specific design parameters such as durability, adjustability, temporal and spatial uniformity, etc. The key criterion is within the occupied space. When speakers are mounted in a ceiling plenum, the acoustical properties of the room and the ceiling system have a direct effect on the spatial uniformity of the masking sound. Thus, the achievement of user satisfaction typically involves generating equipment design, speaker design, placement, density, and room environmental conditions. Because project parameters are complex and identical conditions rarely exist from job to job, or even within the same job, the systems offeror must demonstrate compliance with subjective judgments by a jury under in-use conditions. Field-type objective test techniques have been developed that can be used to predict when compliance exists. A description of the test techniqne and comparative results with the GSA procedures are presented.