摘要:

In a recent paper [M. P. Johnson, J. Acoust. Soc. Am.88, 1–6 (1990)], Johnson presented an interesting approach for connecting a finite‐element model and a multiport network model of a piezoelectric transducer. Thus using one of the several simple numerical tools designed to analyze the electromechanical behavior of a transducer described by a multiport network model, it remains possible to obtain the accuracy otherwise provided by a finite element model. To do this, Johnson built up a modal impedance matrix representation of the transducer structure, starting from finite‐element equations, but the diagonal modal stiffness part of the matrix obtained is perturbed by additional piezoelectric stiffness terms that can induce a more or less complex coupling between modes. The aim of this paper is to demonstrate that, starting with antiresonance modes instead of resonance modes provided by the finite‐element modeling to build up the impedance matrix, avoids the occurrence of these complex coupling terms and, thus, gives the desired simple formulation to the approach.

ISSN:0001-4966    

DOI:10.1121/1.401761

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The behavior of a thin transducer is analyzed when the electroded section constitutes a small part of the available areas. The principal signals are relatively short stress pulses. It will be seen that these pulses may travel close to or at the speed of sound in an unbounded medium and that circuit models may be associated with these transducers. The results also apply to the analysis of elastic properties of thin plates when the aperture of the probing beam is wider than the thickness of the plate.

ISSN:0001-4966    

DOI:10.1121/1.401762

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper describes the theory, construction, and operation of a transducer that is capable of transmitting an analog acoustic signal when driven by a digital input signal. The digital signal drives a capacitive dielectric transducer whose active surface area is proportional to the magnitude of the digital signal. The output of the transducer contains the original digitized analog signal in addition to higher frequency Fourier components that result from the sampling process. The unwanted additional signal is attenuated by coupling the transducer output into an acoustic low‐pass filter whose response is determined by using electrical circuit analysis techniques. The results indicate that the experimental transducer system is useful for generating acoustic signals that have an upper frequency limit of 8 kHz. With suitable modifications, wider frequency performance is attainable.

ISSN:0001-4966    

DOI:10.1121/1.401763

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Five studies examined the relative performance of traditional carbon‐type telephone transmitters and newer electret‐type transmitters that have come to replace the carbon‐type in contemporary telephone set designs. Focus is on the validity of the transmit objective loudness rating (TOLR) metric as a predictor of transmitter efficiency in response to real speech input. TOLR is the IEEE recommended metric (IEEE Standard 269‐1983) for objectively characterizing the efficiency with which telephone transmitters convert acoustic energy to electric energy. These studies indicate that the relationship between TOLR and transmitter efficiency for real speech is not the same for carbon and electret transmitters. Relative to what is observed with carbon transmitters, TOLR was shown to underpredict the real speech efficiency of electret transmitters by approximately 3 dB. Two mechanisms are involved in this effect. First, carbon transmitters have a lower peak‐clipping, or compression, threshold than electret transmitters. This difference is not accounted for in the measurement of TOLR where the input signal consists of a swept sine wave whose constant amplitude (sound‐pressure level of 88 dB) is below the compression threshold of carbon transmitters. Second, the efficiency of carbon transmitters, but not electret transmitters, declines during the first minutes after the telephone handset is taken off‐hook. The formal TOLR measurement protocol overestimates carbon transmitter efficiency because the transmitter is characterized immediately after being taken off‐hook, not over a broader period of time which would be more predictive of its efficiency in real use. These results have implications for the choice of TOLR design objectives for electret transmitter telephone sets. The greater relative efficiency of electret transmitters for real speech input also needs to be considered when grade‐of‐service models, which now assume the use of carbon transmitter telephone sets, are used to estimate the transmission quality of network connections.

ISSN:0001-4966    

DOI:10.1121/1.401764

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A recently developedp‐version finite‐element program [Bagusetal., IBM Res. Div., Res. Rep., RJ 7733 (71598), October 1990; Carnevalietal., in preparation] was used to simulate the dynamic behavior of an ultrasonic bonding tool. The accuracy of thep‐code was exploited to resolve high‐order modes near to the ultrasonic operating frequency (approximately 60 kHz). In particular, an undesired high‐order bending mode was found to occur at a frequency very close to the axial mode that facilitates the bonding process. An optimal operating frequency that minimizes the excitation of the deleterious mode could be determined. Frequency response simulations and experiments were performed to validate this assertion. Their nature, and the accuracy required to resolve these high‐order modes, would have made this analysis extremely difficult with other finite‐element tools.

ISSN:0001-4966    

DOI:10.1121/1.401765

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The influence of propagation medium inhomogeneities on pulsatile ultrasonic fields has been investigated experimentally. The study employed a special curved transducer to produce a hemispherical wave pulse and a linear array to measure the resulting field along a line in a plane. Translation of the array in the elevation direction yielded data over a two‐dimensional aperture. Time delay across the aperture was calculated by adding delay differences obtained by cross‐correlating signals on adjacent elements and noting the position of the cross‐correlation peaks. Received waveforms were shifted an amount given by the difference between the actual arrival time and a calculated geometric delay to isolate arrival time differences due to propagation path inhomogeneities. Waveform and time delay difference plots as well as histograms and statistics derived from them for propagation through a water path and for propagation through five specimens of human abdominal wall indicate that arrival time fluctuations in the presence of human abdominal wall specimens are significantly greater than for a water path and that degradation in focusing through human abdominal wall can be expected in ultrasonic imaging systems that operate in the low megahertz range and employ a relatively large aperture.

ISSN:0001-4966    

DOI:10.1121/1.401766

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A sonar system’s echolocation capabilities can be inferred from the ambiguity distribution (defined here in terms of the conventional signal response function) of each of its transmitted signals. Several records of sounds emitted by Hector’s dolphin are analyzed. The computed ambiguity distributions indicate that the sonar clicks of Hector’s dolphins should be capable of resolving the ranges of targets as close together as 2 cm apart, but that target velocities cannot be resolved to any useful degree from a single echo.

ISSN:0001-4966    

DOI:10.1121/1.401767

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Beams used in certain percussion instruments with definite pitch such as marimba, xylophone, and vibraphone are undercut in order to bring the frequencies of the first few overtones into a harmonic relationship with the fundamental frequency. This paper addresses the problem of determining the optimal dimensions of the undercut so that the frequencies of modes 2 and 3 of transverse motion are harmonically related with that of the fundamental (mode 1). The undercut is assumed to have a parabolic shape described by two variable parameters related to its depth and width. The rest of the beam on each side of the undercut is assumed to be uniform. Seven pairs of optimal undercut parameters are found that bring the frequencies of the first three transverse modes into the harmonic (integer) ratios 1:3:6, 1:4:8–9, and 1:5:10–13. Calculations performed with and without taking into account the effects of rotary inertia and shear stress are compared against measurements taken from a set of experimental beams. The comparison shows that including the effects of rotary inertia and shear stress results in a better prediction of the optimal parameters of the undercut.

ISSN:0001-4966    

DOI:10.1121/1.401768

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The spectral envelope is a major determinant of the perceptual identity of many classes of sound including speech. When sounds are transmitted from the source to the listener, the spectral envelope is invariably and diversely distorted, by factors such as room reverberation. Perceptual compensation for spectral‐envelope distortion was investigated here. Carrier sounds were distorted by spectral envelope difference filters whose frequency response is the spectral envelope of one vowel minus the spectral envelope of another. The filter /i/ minus /q/ and its inverse were used. Subjects identified a test sound that followed the carrier. The test sound was drawn from an an /itch/ to /qtch/ continuum. Perceptual compensation produces a phoneme boundary difference between /i/ minus /q/ and its inverse. Carriers were the phrase ‘‘the next word is’’ spoken by the same (male) speaker as the test sounds, signal‐correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backwards, and a repeated end‐point vowel. The carrier and test were presented to the same ear, to different ears, and from different apparent directions (by varying interaural time delay). The results show that compensation is unlike peripheral phenomena, such as adaptation, and unlike phonetic perceptual phenomena. The evidence favors a central, auditory mechanism.

ISSN:0001-4966    

DOI:10.1121/1.401769

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Prosodic structure and syntactic structure are not identical; neither are they unrelated. Knowing when and how the two correspond could yield better quality speech synthesis, could aid in the disambiguation of competing syntactic hypotheses in speech understanding, and could lead to a more comprehensive view of human speech processing. In a set of experiments involving 35 pairs of phonetically similar sentences representing seven types of structural contrasts, the perceptual evidence shows that some, but not all, of the pairs can be disambiguated on the basis of prosodic differences. The phonological evidence relates the disambiguation primarily to boundary phenomena, although prominences sometimes play a role. Finally, phonetic analyses describing the attributes of these phonological markers indicate the importance of both absolute and relative measures.

ISSN:0001-4966    

DOI:10.1121/1.401770

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP