摘要:

All four of the American National Standards Committees for which the Acoustical Society holds the secretariat are active in developing standards directly applicable to the workplace. S1 (Physical Acoustics) is involved with standards for equipment used to specify noise conditions including sound level meters and personal dosimeters. S2 (Shock and Vibration) has a joint interest with S3 (Bioacoustics) in standard procedures for describing human exposure to mechanical vibrations and shock. S3 has a major concern in standards relating to measurement of hearing loss and establishing the risk posed by occupational noise to hearing. S12 (Noise) is in the process of producing standard methods for measurement of noise in the workplace, evaluating hearing protectors, and evaluating the effectiveness of industrial hearing conservation programs. The status of these standards activities as well as others which directly or indirectly have an impact on problems of occupational noise is the subject for this presentation.

ISSN:0001-4966    

DOI:10.1121/1.2022216

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The future traffic noise generation from Trans‐European Motorways still under construction throughout Europe was analyzed in a study aimed to introduce standard noise control systems into the TEM Recommendations. Different prediction techniques developed by national institutions of nine countries were employed in computations of noise levels at 15 m from curbsides for varying traffic parameters. Comparisons between results relative to the procedures demonstrated that the USA method (FHWA) yielded about 5 dBA higher levels than European models especially in mountainous terrains and at higher percentages of heavy vehicles. Applying a statistical regression analysis, a simplified mathematical model for TEM noise predictions was developed with a satisfactory correlation coefficient. A new combined parameter,T(u,s,n,h,g), corresponding to interrelated TEM traffic variables (volume, speed, number of lanes, heavy vehicle percentage, and road gradient), affecting noise generation, was analytically defined and represented in the model. Reviewing the existing traffic noise criteria in the world and TEM countries, the prediction model was then improved to establish TEM noise standards taking into account environmental factors and was implemented for the required performances of the noise abatement measures applicable in every type of TEM. [Supported by Directorate of Turkish Highways within the TEM project coordinated by United Nations, Transport Division.]

ISSN:0001-4966    

DOI:10.1121/1.2022274

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The quasicrystalline approximation (QCA) was first introduced by Lax to break the infinite heirarchy of equations that results in studies of the coherent field in discrete random media. It simply states that the conditional average of a field with the position of one scatterer held fixed is equal to the conditional average with two scatterers held fixed, i.e., 〈ψ〉iji= 〈ψ〉ii. The QCA has met with great success for a range of concentrations from sparse to dense and for long and intermediate wavelengths. In this paper, the QCA is interpreted as a partial resummation of the multiple scattering series that includes only two body correlations and yields the same dispersion equation. Explicit improvements to the QCA are presented that still require only a knowledge of the two body correlation function.

ISSN:0001-4966    

DOI:10.1121/1.2022321

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

When an ultrasonic wave propagates in a solid with a low concentration of voids the attenuation coefficient is proportional to the scattering cross section of each void multiplied by the number of voids [Gubernatis and Domany, Rev. Prog. QNDE2A, 833 (1983)]. Exact calculation was carried out for the scattering cross section of elastic waves as a function ofkafrom spherical voids in several solids. A turning point between low and highkavalues of the scattering cross section provides a turning point atka= 1. This turning point depends only on the ratio of transverse to longitudinal velocity in the solids—can be used to calculate both the pore radius and their concentration. Experimental method was developed to measure attenuation coefficient as function of frequency using ultrasonic spectroscopy system. The theoretical model was successfully tested experimentally for several aluminum cast materials containing porosity up to 6% and with average radius for 10–150μ. [This work was supported by the Center of NDE operated by Ames Laboratory for the Air Force Wright Aeronautical Materials Laboratory.]

ISSN:0001-4966    

DOI:10.1121/1.2022372

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

In an earlier paper [J. Acoust. Soc. Am. Suppl. 176, S9 (1984)] we developed the complete RST formulation for an elastic sphere in an elastic medium under shear and compressional wave incidences. We also showed how that work contained a variety of simpler cases that we have studied in the past, such as, a fluid‐filled cavity in an elastic matrix, an elastic sphere in water, a gas bubble in a liquid, etc, … as particular cases. We now develop the entire computational machinery of the RST and show the many useful plots that it can produce. These numerical displays include: (a) The SEM‐type poles with their relation to the various types of surface waves that they generate. The Franz‐zeros also fall under this category. (b) The graphs of the five types of scattering amplitudes (i.e.,fpp, fps, fsp, fss, ftt) that are pertinent to this elastic problem. (c) Their decomposition into partial waves or normal modes, (d) The decomposition of the partial waves into backgrounds and resonances, (e) The informative three‐dimensional plots of theresponse surfaceof all the scattering amplitudes, in the mode‐orderandfrequency domains, and, (f) The dispersion plots for the phase velocities of the various surface waves. All this is done for two material combinations (i.e., epoxy sphere in steel and steel sphere in epoxy) for which two different types of backgrounds are required to isolate the modal resonances. All displays are constructed in wide nondimensional frequency bands that include the resonance region for which λ≈a. Physical interpretations of all plots are given.

ISSN:0001-4966    

DOI:10.1121/1.2022423

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Auditory neurons typically respond to a wide range of auditory stimuli, with responses which can vary across several stimulus dimensions. This has made classification of individual auditory neurons on a functional basis somewhat difficult. Auditory neuronal responses are therefore often described by the manner in which neural populations appear to encode such stimulus dimensions as frequency, intensity, interaural differences in signal phase or intensity, and signal envelope. Of course, with most neurons encoding several dimensions, these classifications overlap extensively. Auditory neurons also vary in the rate at which they discharge spontaneously, in the absence of external stimuli. These response characteristics can vary dramatically depending upon the state of the organism. A high degree of response plasticity may be observed with changes in attention, behavior, sleep/waking state, or with anesthesia. Due to the complexity of the auditory system, the relationships between auditory neuronal responses and their underlying anatomical substrates are just beginning to be explored. [Supported by NIH/NINCDS and the Research Service of the VA.]

ISSN:0001-4966    

DOI:10.1121/1.2022473

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The Perceptual Anchor Model of Context Coding [Braidaet al., J. Acoust. Soc. Am.76, 722–731 (1984)], developed for auditory intensity, considers resolutions to be determined by both sensory and memory processes, and postulates that tasks differ in the memorial coding they require. The theory was tested with steady‐state synthetic vowels in the range /i/‐/I/‐/ɛ/. Resolution was measured in four discrimination conditions (two‐interval forced‐choice and same‐different, fixed‐, and roving‐level), and in complete identification conditions with and without a standard. In identification and roving‐level discrimination, resolution was poorer than in fixed‐level discrimination, but not uniformly so: sensitivity differences among tasks were smallest near category boundaries. The data suggest that some categorical phenomena can be understood in terms of perceptual anchors. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2022522

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Data from perceptual tests in which subjects were asked to identify tense and lax vowels are used to suggest correlates for the tense/lax distinction in general American English. Four vowel parameters were manipulated in synthetic nonsense words of the form [dVs]: formant frequency, duration, breathiness, and first‐formant bandwidth. The tense/lax pairs included [ɪ], [æɛ], [uᴜ], and [ɑʌ]. Three separate identification tests are created in which the stimuli vary only in formant frequency and one of the other three parameters. Each test was presented to five naive native speakers of general American English. Results so far indicate that shortening the vowel shifts judgments toward the lax vowel, and that this effect is greater in the low vowel pairs than in the high vowel pairs. Increased breathiness shifts judgments toward the tense vowel for high vowels. The effect of breathiness on low vowels and the effect of bandwidth of the first formant on all vowels is as yet unclear. [Supported in part by NINCDS and a NSF Fellowship.]

ISSN:0001-4966    

DOI:10.1121/1.2022577

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A model of the lexicon and how it is accessed in speech production and perception is proposed using data from both normal and aphasic subjects. Evidence will be presented from a case study of an acquired “surface dyslexic” to show that there is no direct semantic interpretation of the acoustic signal but that it must first be transformed into an abstract phonological representation before meaning is assigned. The interconnecting pathways between phonological, orthographic, and semantic representations in the lexicon of a normal speaker and a language disordered speaker are discussed, as are the various types of processing rules in reading, writing, speaking, and understanding.

ISSN:0001-4966    

DOI:10.1121/1.2022637

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A low bit rate real‐time half duplex LPC vocoder was constructed based upon the Texas Instruments TMS32010 digital signal processor IC. Approximately 2700 words of external ROM were used for program and tables. The 144 words of onboard RAM were the only words of RAM used. The analysis was performed on preemphasized windowed speech using autocorrelation accumulation and the LeRoux‐Gueguen method to generate reflection coefficients and gain. A modified Rabiner‐Gold pitch algorithm was used for pitch and voicing. The software was split into foreground computations done on each speech sample and background computations done on each frame. There were 54 LPC information bits generated per frame.

ISSN:0001-4966    

DOI:10.1121/1.2022165

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP