摘要:

Envelope statistics are being frequently used to describe stochastic processes when a more detailed description is either unobtainable or impractical. The response of a nonlinear oscillator subject to nonstationary stochastic excitations is described. This is accomplished by analytically computing the transition probability density of a one‐dimensional Markov process, which approximates the amplitude envelope of the response. For this purpose, an appropriate variation of the solution to the corresponding linear problem is employed. The probability density at various times as well as the mean‐square and standard deviation of the amplitude envelope are computed for specific nonlinearly damped oscillators subject to separable and nonseparable nonstationary excitations. The analytical results are compared with those obtained by a Monte Carlo simulation study. The agreement between the two supports the applicability of the method to a broad class of oscillators.

ISSN:0001-4966    

DOI:10.1121/1.2024056

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In the field of high‐frequency acoustic arrays for high‐resolution sonars, some transducers are driven with very high‐power density and long pulse length. This produces a temperature rise in the transducer, leading to the variation of the materials characteristics. This phenomenon may reach the mechanical breaking point. To study this problem, we have developed a tridimensional piezoelectric finite element computer program which takes into account radiation (Helmholtz integral equation) and losses (mechanical, dielectric, piezoelectric). After an acoustic computation, using modal analysis, heat sources due to losses are determined in all the volume of the transducer. A finite element program computes the transient evolution of the temperature. According to the obtained temperatures, materials coefficients are updated and a new acoustic calculation is performed. The process is repeated until maximum dynamic stresses or maximum temperature is reached. Several examples are discussed including transducers with and without matching layer. [Work supported by DRET, France.]

ISSN:0001-4966    

DOI:10.1121/1.2024058

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In American English, a vowel preceding a voiced consonant has frequently been shown to be of longer duration than one preceding a voiceless consonant. However, Port [J. Acoust. Soc. Am.69, 262–274 (1981)] reported no effect of postvocalic consonant voicing on the total duration of the VC unit. Port attributed this finding to an inverse relationship between vowel and consonant durations. Our study replicates and extends this work to the entire CVC syllabic unit across changes in speaking rate. Syllable and segmental durations were measured for /pVC/ target syllables. The target syllables used eight vowels and voiced or voiceless cognates of the final consonant, which was either stop or fricative. Syllables were produced in sentence contexts at three speaking rates by four female and four male native American English speakers. [Work supported in part by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2024062

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

A general descriptive framework of speech timing is proposed using a hierarchical linear (elastic) representation of speech units, with a loose linkage between different dimensions (articulators). Inherent temporal properties of phonetic units are represented by their spring constants, and prosodic properties of utterance units are represented by additional springs associated with relevant substructures. For describing a process of speech utterance, an open‐ended structure can be defined by terminal forces in place of position specifications, continuously building up the utterance structure as the speaker produces (or preprograms) the speech signal. Some examples of data from microbeam data will be discussed from this point of view, using “iceberg” patterns as timing marks [O. Fujimura, “A Linear Model of Speech Timing,” inIlse Lehiste Festschrift, edited by L. Shockey and R. Channon (Foris Publications, to be published)].

ISSN:0001-4966    

DOI:10.1121/1.2024068

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Phonetic orthodoxy treats the acoustic realization of a CVn, syllable (N.B. V = vowel or glide) as the concatenation of consecutive transitions from one element to the following one in the syllable. This study proposes an alternative view of the acoustic structure of this type of syllable, based on LPC trackings ofF2 in sets of selected Chinese and English CVnsyllables. The basic hypothesis is that the underlyingF2 transitions between any two phonologically adjacent elements in the same syllable (e.g., the C → V1, V1→ V2,…) all originate at the same temporal position—the syllable initiation. Each transition has a specified rate. The acoustic realization will be a programmed “truncation” process; that is, the phonologically preceding transition truncates the phonologically following transition (e.g., the C → V1transition truncates the V1→ V2transition; the truncated V1→ V2in turn truncates the V2→ V3transition). This model provides elegant accounts and quantitative predictions of the undershooting and overshooting phenomena in acoustic target realization. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2024073

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The in‐phase (I) and quadrature (Q) components of the seafloor backscattered acoustic returns received by a Sea Beam multibeam echo‐sounder over a manganese nodules field in the tropical northeastern Pacific have been digitized and recorded on magnetic tape. Because both theIandQcomponents of the signals were present, the sidelobe interference inherent in multibeam systems [C. de Moustier, J. Acoust. Soc. Am.79, 316–331 (1986)] was able to be removed, and a complete angular dependence function of acoustic backscattering between ± 20° of vertical incidence was obtained. These results and the sidelobe interference removal method are discussed. [Research funded by ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2024083

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Currently used robot position control systems consider only the joint angles when positioning an end effector in space. This approach can lead to serious errors due to structural deflection under load, backlash in joints, manufacturing tolerances, etc. A method is needed to directly measure the absolute position and orientation of the end effector in three‐dimensional space in order to achieve positioning accuracy. An ultrasonic ranging system is proposed to accomplish this task. It consists of: (1) one or more transmitters mounted on the robot's end effector; (2) receivers (four or more required), mounted adjacent to the robot's work envelope; and (3) analog and digital electronics to drive the transducers, process the received signals, and calculate the position of the end effector. The end effector's position is calculated using the time of flight measured from the emitter to each receiver, by an intersection of spheres algorithm. The performance objectives of this system are: (a) measure position with accuracy of ± 0.001 in. (b) up to a range of 3 m. and (c) with at least 1‐Hz update rate. A theoretical error analysis of the system is presented. Types of emitter signals are compared, operating frequency considerations are discussed, and hardware recommendations are made. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2023500

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Measurements will be presented on some primitive musical instruments that produce sound from excitations of a Helmholtz resonator. Input acoustical response measurements will be compared with the sound output when the instruments are blown. In some instruments, pitch can be altered by changing finger position, but others have constant pitch. The complicated pigeon whistle which is attached to the legs of pigeons will be described. This lightweight whistle contains a large Helmholtz resonator and several quarter wave pipes, and is excited in flight by air streaming across sharp lips on each of the parts.

ISSN:0001-4966    

DOI:10.1121/1.2023505

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Many ancient Chinese bells, by virtue of their oval shape, sound two distinctly different tones, depending upon where they are struck. These so‐calledsuiandgutones usually differ in pitch by about a minor third. The vibrational modes and sound radiation from a carefully dimensioned modern copy of a Chou dynasty (1030—221 B.C.) bell in the Dutch National Carillon Museum have been studied. The lowest modes, and many of the higher ones as well, occur in pairs, with one member having an antinode near thesuistrike point and the other near thegustrike point. The frequency separation of these doublets is determined by the shape of the bell. The modal shapes, determined by holographic interferometry, are similar to those observed in round church bells, but with more mixed modes due to the greater damping.

ISSN:0001-4966    

DOI:10.1121/1.2023507

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The two‐microphone sound intensity method is potentially a valuable tool for noise source identification, sound power determination, and for other measurements (e.g., transmission loss) that are based on sound intensity measurements. An essential ingredient in an accurate sound intensity measurement is the accurate measurement of the phase between the two microphones. Because the phase is generally small, on the order of a few degrees, the microphones must either be “phase matched,” or a phase calibration procedure must be used. This paper outlines the design and test procedures for using a plane‐wave tube to perform a microphone phase calibration with an uncertainty of less than approximately 0.2 deg. The phase calibration procedure is illustrated for a pair of condenser microphones and for a pair of miniature crystal microphones typically used in hearing aids.

ISSN:0001-4966    

DOI:10.1121/1.2023511

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP