摘要:

Parnell’s mustached bat,Pteronotusparnellii, uses echolocation to hunt for insects in the New World tropics. The sonar signals, which are emitted from the mouth, are long, constant‐frequency types with a ‘‘missing’’ fundamental, so that the second and third harmonics contain most of the pulse energy. This pulse structure implies that the supraglottal vocal tract acts as an acoustic notch filter for the fundamental. To investigate this possibility, light and heavy gases were used to obtain the vocal tract transfer function. The results show that a fundamental notch filter is present, and anatomical manipulations of the vocal tract suggest that this filtering is achieved by a combination of antiphasic reflections from the nasal passages and an area‐function filter in the throat. During these experiments, tracheal sound was also monitored to assess the acoustical role of the tracheal sac. This is an elastic section of the trachea, situated immediately posterior to the larynx, which inflates during vocalization. While demonstrating that this structure plays a significant role in determining the acoustics of the subglottal system, our results neither confirm nor dismiss the hypothesis that it reflects sound back to the larynx to improve vocal efficiency. As part of the investigation, the radiation pattern for the mustached bat was also obtained and was compared with various model sources. At the second and third harmonics, sound radiation is highly directional and consistent with the idea that the mouth acts as a conical horn.

ISSN:0001-4966    

DOI:10.1121/1.399066

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The problem of identifying reproducible frequency bands useful for the nondestructive evaluation of steel plates using the dynamic acoustical intensity scanning concept (DAIS) is addressed. Reproducible frequency bands are essential so that subsequent changes in sound intensity patterns can confidently be attributed to structural changes rather than to random fluctuations. A number of evaluation methods are tried. Stationary frequency bands are identified by all methods in the range of 100–4000 Hz. The most sensitive and practical evaluation method is deemed to be the comparison of intensity versus time data collected separate from the plate scans. This method is accurate, convenient, and can be automated to exclude all unwanted frequency bands during testing. The remanent intensity factor technique, while useful in identifying stationarity, is less sensitive and more difficult to implement.

ISSN:0001-4966    

DOI:10.1121/1.399067

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In determining the velocity and attenuation of suspensions of spherical particles, results obtained from the computationally simpler multiple scattering approach of Waterman and Truell (WTF) and from a multiple scattering formalism (MSF), which considers the pair correlation function, have been compared in order to justify the range and applicability of the former method. Although the difference between the results increases as the concentration of suspensions increases, the frequency‐dependent attenuation computed from the two approaches can be quite different particularly in the low‐frequency range even at lower concentrations. Due to the unavailability of experimental data for ultrasonic propagation, data from analogous optical experiments on suspensions of latex spheres are compared. The MSF shows excellent agreement, whereas the WTF shows large discrepancies from the experimental data.

ISSN:0001-4966    

DOI:10.1121/1.399068

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Three zebra finches were trained with operant techniques to respond to pure tones. Absolute thresholds were obtained for nine durations of a 3‐kHz tone and five durations of a 1‐kHz tone. The temporal integration functions finches were described using the negative exponential function proposed by Plomp and Bouman [J. Acoust. Soc. Am.31, 749–758 (1959)]. The time constants obtained for zebra finches are about 250 ms, which are similar to those reported for a number of species, including humans and other bird species.

ISSN:0001-4966    

DOI:10.1121/1.399069

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399071

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399018

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399019

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399020

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399021

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.399023

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP