摘要:

Major stages are defined in the evolution of analytical, nonnumerical approaches to the vibrations of elastic shells and plates in an acoustic fluid and to the resulting sound field. Concepts are described in roughly chronological order: Emerging from a ‘‘prehistory’’ of interaction solutions based on the Laplace or plane‐wave approximations, analyses of structures compatible with rigorous normal mode solutions when radiation loaded; solutions in terms of wavenumber transforms whose asymptotic evaluation permits the explicit formulation of the farfield; substitution of the actual structure by an infinite, analytically tractable structure displaying a similar supersonic wavenumber spectrum, though the subsonic portions of the wavenumber spectra differ.

ISSN:0001-4966    

DOI:10.1121/1.395301

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The independent transient responses of a transducer to displacements polarized in each of the three orthogonal directions have been determined using a new method that assumes only linearity and no angular impingement dependence of the transducer response. The modeling of the transducer response is thus converted from a vector problem to three much more tractable scalar problems, thereby forming the basis for vector calibration of acoustic emission and ultrasonic transducers as receivers.

ISSN:0001-4966    

DOI:10.1121/1.395302

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The attenuation coefficient in 38 pathologically gradedinvitroliver specimens was measured over a frequency range from 1.25–8 MHz and fitted to the power law model. The attenuation in the normal group (n=17) exhibited a frequency dependence of the form 0.399f1.139; in the mild disease group (n=13), it exhibited a dependence of the form 0.395f1.212; and in the moderate/severe disease group (n=8), it exhibited a dependence of the form 0.391f1.325. Using a Student’sttest, it is shown that, due to these differences in the frequency dependence, the statistical significance level at which the null hypothesis regarding the difference between the mean attenuation slopes of any two of these categories is rejected, is a strong function of frequency in the range of 1–4 MHz. The significance level relating to the difference between the normal and moderate/severe disease group is more than one order of magnitude better than the other categories. In all cases, no substantial improvement occurs beyond 4 MHz. It is also shown that attenuation slope values at 3 MHz confirminvivoliterature results obtained via different techniques.

ISSN:0001-4966    

DOI:10.1121/1.395303

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The time it takes audible sound to travel from the trachea to the pleura in five intact, excised horse lungs and one dog lung inflated with several gases was measured. Regression estimates of sound speed at total lung capacity (TLC) using straight line distance from the carina to the pleura are: helium, 775±60.5 m/s (x̄±95% confidence limits); air, 282±23.5; carbon dioxide, 219±25.5; sulfur hexafluoride, 142±43.5. With the exception of sulfur hexafluoride, these speeds are 15%–20% less than the free‐field speed of sound in each gas. Total airway length did not predict time delay any better or worse than straight line distance, but the high correlation between these two predictors (r=0.94) prevents showing either to be the more predictive. In one lung, airway length was partitioned according to airway diameter. A regression using partitioned airway lengths significantly improved time delay prediction (p<0.001) over an unpartitioned model. Sound speed in the trachea equals free‐field sound speed. Sound speed in air‐filled airways 1 to 25 mm in diameter equals 268±44 m/s. We conclude that the first sound to reach the surface travels in the airways for at least 90% of the distance, spending at least 87% of the total travel time there.

ISSN:0001-4966    

DOI:10.1121/1.395249

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

A hammer–string interaction for the bass note (A0) of a 6‐ft grand piano is investigated by use of a lumped‐element model. The hammer head is simulated by a mass–spring system with a nonlinear spring characteristic. The string is simulated by many parallel resonant circuits, each of which consists of a mass, a linear spring, and a dashpot. The impulsive force applied by the hammer to the string lasts only approximately 1 ms for a hard‐hit key. The string deformation at the striking point also reaches near its maximum within about this time and retains its amplitude until the wave is reflected back from the closer end at approximately 4 ms. The hammer leaves the string temporarily, since the hammer is slowly moving downward after the first impact. The string reduces its displacement rapidly when the wave is reflected back from the closer end and, consequently, it pushes the hammer farther back. Effect of hammer stiffness, hammer velocity, and inharmonicity on the spectral distribution of partials and the efficiency of energy transmission are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.395250

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

This study investigated the cues for consonant recognition that are available in the time‐intensity envelope of speech. Twelve normal‐hearing subjects listened to three sets of spectrally identical noise stimuli created by multiplying noise with the speech envelopes of 19 /aCa/ natural‐speech nonsense syllables. The speech envelope for each of the three noise conditions was derived using a different low‐pass filter cutoff (20, 200, and 2000 Hz). Average consonant identification performance was above chance for the three noise conditions and improved significantly with the increase in envelope bandwidth from 20–200 Hz. SINDSCAL multidimensional scaling analysis of the consonant confusions data identified three speech envelope features that divided the 19 consonants into four envelope feature groups (‘‘envemes’’). The enveme groups in combination with visually distinctive speech feature groupings (‘‘visemes’’) can distinguish most of the 19 consonants. These results suggest that near‐perfect consonant identification performance could be attained by subjects who receive only enveme and viseme information and no spectral information.

ISSN:0001-4966    

DOI:10.1121/1.395251

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

The word recognition ability of 4 normal‐hearing and 13 cochlearly hearing‐impaired listeners was evaluated. Filtered and unfiltered speech in quiet and in noise were presented monaurally through headphones. The noise varied over listening situations with regard to spectrum, level, and temporal envelope. Articulation index theory was applied to predict the results. Two calculation methods were used, both based on the ANSI, S3.5‐1969 20‐band method [S3.5‐1969 (American National Standards Institute, New York)]. Method I was almost identical to the ANSI method. Method II included a level‐ and hearing‐loss‐dependent calculation of masking of stationary and on–off gated noise signals and of self‐masking of speech. Method II provided the best prediction capability, and it is concluded that speech intelligibility of cochlearly hearing‐impaired listeners may also, to a first approximation, be predicted from articulation index theory.

ISSN:0001-4966    

DOI:10.1121/1.395252

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Fundamental frequency (F0) information extracted from low‐pass‐filtered speech and aurally presented as frequency‐modulated sinusoids can greatly improve speechreading performance [Grantetal., J. Acoust. Soc. Am.77, 671–677 (1985)]. To use this source of information, listeners must be able to detect the presence or absence ofF0 (i.e., voicing), discriminate changes in frequency, and make judgments about the linguistic meaning of perceived variations inF0. In the present study, normally hearing and hearing‐impaired subjects were required to locate the stressed peak of an intonation contour according to the extent of frequency transition at the primary peak. The results showed that listeners with profound hearing impairments required frequency transitions that were 1.5–6 times greater than those required by normally hearing subjects. These results were consistent with the subjects’ identification performance for intonation and stress patterns in natural speech, and suggest that natural variations inF0 may be too small for some impaired listeners to perceive and follow accurately.

ISSN:0001-4966    

DOI:10.1121/1.395253

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Three new two‐mass models of the vocal cords are treated. First, the features, structure, and differential equations of motion are described for each of the new models and compared with those of previous models. Second, performances of the models are discussed in terms of glottal volume flow, glottal area, radiated sound pressure, trajectories of mass movement, running spectra of the output sound pressure, and perceptual naturalness of the output sound. Finally, the major effects of glottal source–vocal tract interaction including skewing, truncation, and superposition are investigated, using one of the simplest types of two‐mass models and two types of load representing the vocal tract.

ISSN:0001-4966    

DOI:10.1121/1.395254

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP

摘要:

Paired comparison experiments were carried out on the pitch of 18 computer‐generated complex tones synthesized by slight modification of the frequency structure of Shepard’s endless scale sounds. The results were analyzed by a multidimensional scaling technique, and simple helixes were obtained in which two components of pitch (tone height and tone chroma) were represented. Some individual differences in perception of pitch were observed according to the weight that the subject gives to each component.

ISSN:0001-4966    

DOI:10.1121/1.395255

出版商:Acoustical Society of America    

年代:1987

数据来源: AIP