摘要:

The data presented in this work area complement to a previous statistical count [M. Guirao and M. García Jurado, J. Acoust. Soc. Am. Suppl. 178, S55 (1985)]. A corpus of 68141 syllables distributed in 159464 phonemes was used. This time our attention was oriented toward (a) distribution of sounds in each one of four syllabic positions, and (b) distribution in final position according to number of elements in the syllable. The first count indicates that fricative /s/, bursts /t k d p b/, and periodic sounds /n m l r/ cover about 80% of all items in first position. The second position in syllables of two or more components (64572 syllables) is taken mainly by vowels /e a o/. In the third position (22736 syllables) predominate /s/, /e a/, and /r n/. In the remaining syllables (3956) only /n/ and /s/ were found in the fourth position. The second count indicates that final sounds in two components syllables are vowels, 96%. With three components, /s n r/ scored 58%, /a e/ 24%, and /1/ 12%. With four, /n/ 40%, /s/ 29%, and /l r m/ 16%. With five components, /n/ 58%, /s/ 30%, and /l/ 5%. Sounds are classed according to their position and distribution within and between syllables.

ISSN:0001-4966    

DOI:10.1121/1.2023897

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The simplest model noise process is Gaussian and uncorrelated. Measurements of ambient noise pressure in the ocean, however, show correlation between time samples. A stationary Gaussian random process has a correlation function that decays exponentially with time if and only if the process is Markov. Here, only stationary noise processes are considered, but the Markov assumption is relaxed. A general algorithm for constructing a non‐Markov stationary time series is described. It is assumed that the statistics are Gaussian; however, the method can also be extended to include non‐Gaussian statistics. The general algorithm is then applied to a special case. A model non‐Markov noise correlation function consisting of a linear combination of two exponentials with two different correlation time constants is fit to an experimental correlation function. Time series for uncorrelated, Markov and non‐Markov noise processes are generated from the same sequence of random numbers and compared. Comparisons are made with observed time series. Consequences regarding signal detection are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2023904

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The waveguide nature of a shallow water environment bounded below by a viscoelastic medium permits noise to couple into seismic waves. Geophone and hydrophone measurements [T. Akalet al., inOcean Seismo‐Acoustics, edited by T. Akal and J. Berkson (Plenum, New York, 1986), pp. 767–778] have shown that below a threshold frequency of about 10 Hz in 100 m of water, there is an increase in the vertical and radial components of the outputs of geophones as compared to no increase in the pressure output from an adjacent hydrophone. A previously developed wave theory of distributed noise in a stratified ocean [W. A. Kuperman and F. Ingenito, J. Acoust. Soc. Am.67, 1988–1996 (1980)] used with the appropriate viscoelastic medium Green's function [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am.77, 813–825 (1985)] explains this phenomena which occurs below the waterborne propagation cutoff frequency.

ISSN:0001-4966    

DOI:10.1121/1.2023908

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

This paper summarizes the manual prepared for the FAA to provide uniform national guidance for sound‐proofing existing buildings around airports in accordance with the goals set forth in FAR Part 150. The guidelines contained in the manual are quantitative rather than qualitative in scope. Procedures are given for estimating the noise reduction provided by existing buildings in the vicinity of airports, determining the amount of soundproofing required to achieve an adequate indoor noise environment, and for selecting cost‐effective retrofit options. Although the manual is intended for use by technical people without specific training in acoustics, computations are required. Accordingly, examples will be presented to illustrate the step‐by‐step procedures, lookup tables, and graphs used.

ISSN:0001-4966    

DOI:10.1121/1.2023912

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The National Bureau of Standards document NBS BSS 84, “Design Guide for Reducing Transportation Noise in and Around Buildings,” was adapted for use in evaluating several design options by an architect in the course of replacing a highly noise‐impacted elementary school with a new facility on the same block of land. The dominant noise sources were military fighter aircraft operating in a traffic pattern which placed them approximately 1550 ft abeam the school, some 2500 ft from the runway threshold. The predicted Shell Isolation Ratings are compared to field‐measured results at the school site in order to evaluate the method's utility as a design tool. Faculty response to the new facility is favorable, partly because a noise level reduction greater than that recommended by the military was found advisable, and was achieved. Computerization of the methodology will be presented.

ISSN:0001-4966    

DOI:10.1121/1.2023918

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Few actual sound fields are representative of ideal acoustic pressure responses and ideal boundary conditions, such as those found in anechoic or reverberant rooms. Normally encountered enclosures have complicated responses that are difficult to relate to a boundary condition that is in between these two ideal extremes. Yet, the propagating and standing wave responses associated with absorptive and reflective boundary conditions seen in the ideal cases are fundamental bases to understand these more complicated problems. An analytical method is developed to decompose a one‐dimensional acoustic pressure response associated with a specified partially absorptive boundary condition into an equivalent summation of propagating and standing waves usually associated with absorptive and reflective boundary conditions, respectively. The propagating and standing wave responses are scaled and shifted in phase by factors that are dependent on the boundary absorptivity and frequency, but are independent of the spatial location. The complicated mixed response is decomposed into varying amounts of the ideal responses, which can be helpful during a design analysis.

ISSN:0001-4966    

DOI:10.1121/1.2023924

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A measurement system will be described which allows dc flow resistances (1 to 104cgs ohms) of various samples to be determined quickly and accurately. Variable‐capacitance pressure transducers are used to measure pressure differences across both the test sample and a laminar flow element with known resistance (these being in series), so that the unknown resistance can be calculated directly. The rate of flow of air through the sample is adjusted using a mass flow controller; flows of 10−3−1 cm3/s can be contolled to better than 1%. The use of these electronic sensors permits measurements of flow resistance to be made much faster than with the traditional Leonard device. Initial measurements of flow resistance (i.e., the zero frequency limit of acoustic resistance) have been made on small, circular orifices in thin plates.

ISSN:0001-4966    

DOI:10.1121/1.2023930

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In the context of contemporary electronic media, particularly radio, what are the challenges which face both scientist and broadcaster in presenting a scientific subject—specifically in the area of acoustics—to a general audience? The aim is to inform simply and accurately, without trivializing the subject, while taking into account that the listening audience may have little—if any—background in the field being discussed. Examples will be presented from “The Sounds of Science,” an award‐winning short‐format daily radio series produced by the author for The DuPont Company, and distributed to over 100 public and commercial radio stations nationwide. The series uses a blend of interview and ambient sound to convey an experience of scientific research and ideas. Subjects treated in the domain of acoustics include early woodwind instruments, the sound of a space launch, Tibetan chant, and sound paradoxes. The preparation and conditions for interviews, which help to establish an exchange meaningful to both parties, will be discussed. A collaboration is fostered in which the scientist often plays an active role in how best to portray his or her research in sound.

ISSN:0001-4966    

DOI:10.1121/1.2023933

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Hardware and software kits (less than $350) have been developed which together with an Apple II computer can be used to make a variety of sound measurements suitable for educational purposes at the precollege level. Descriptions and demonstrations will be given of such systems including those developed by TERC (Technical Education Research Centers, Cambridge, MA) for junior high school science programs. The systems include amplifiers, A to D and D to A converters, and frequency analysis components all packaged in the form of plug‐in cards or modules connected to the game port. A microphone and a speaker are also included. When used with the included software, the systems can perform the elementary functions of a digital oscilloscope, a sound spectrograph, and a frequency counter. Laboratory tests of the response of the systems to various signals will be reported.

ISSN:0001-4966    

DOI:10.1121/1.2023937

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

It was found that every penetrable scatterer has a peculiar set of poles in the lower half of the complex‐frequency plane (x=ka). Some of these poles depend only on shape while others depend only on composition. The poles are labeled by two indices (n,l). Changes in shape for a given composition, changes the location of the “shape poles.” Symmetric pole patterns with respect to the imaginary axis (Imx) are indicative of bodies close to the spherical shape. Asymmetric pole patterns with respect to Imxare indicative of elongated cylindrical shapes viewed at normal incidence. The peculiar pole asymmetry of the cylindrical shape is due to the presence of an additional branch of poles that shifts the symmetry of all the other poles. A study of these poles is presented indicating: (1) How to distinguish poles due to body shape from those due to composition; (2) How the pole positions change as the composition changes from the very stiff to the very compliant limits for a given shape; (3) How to look for the identifying symmetries or asymetries; (4) How to recognize the shape when only a limited number of poles are available; and (5) How noise levels make the pole‐positions random, and known only within “uncertainty circles.”

ISSN:0001-4966    

DOI:10.1121/1.2023942

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP