摘要:

Electronic technology has permitted many advances in acoustical measuring instruments over the years. Generally, size and weight have been reduced and speed and convenience greatly increased. The important technological advances are discussed and some examples are given of how coupling technologies with need has produced changes. The characteristics of some specific old and new instruments are contrasted and, finally, some ideas about future instruments are presented.

ISSN:0001-4966    

DOI:10.1121/1.384504

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The Acoustical Society of America has created the most important forum for advanced discussions and presentations on instrumentation and measurement techniques over the past 50 years. We have all had great benefit from this—not least within the area of transducer development. It is the intention of this paper to give a brief summary of important steps in transducer development and the state of the art in calibration accuracy, where absolute calibration today is reported with standard deviations less than ±0.01 dB. New mircophone development is reported and a history of analog detectors brought up to date.

ISSN:0001-4966    

DOI:10.1121/1.384505

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

This is a brief report of the final Plenary Session of the anniversary meeting of the Acoustical Society of America in Cambridge, Massachusetts in June 1979. It summarizes briefly conjectures about the future of acoustics with special reference to interdisciplinary technology, hearing problems, noise, and physical acoustics.

ISSN:0001-4966    

DOI:10.1121/1.384506

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Measurements of ultrasonic velocity and attenuation require ’’diffraction corrections’’ for the finite size of the source and receiver. These diffraction corrections depend on the area of the source which is usually taken as the physical area of the piezoelectric element of the the transducer. Measurements are reported which indicate that the effective area of a disk‐shaped element may vary with the exciting frequency and may differ by 40% from the physical area of the disk. The method reported may be of value in the selection of transducers, in accurate diffraction correction calculations, and in the field of ultrasonic exposimetry.

ISSN:0001-4966    

DOI:10.1121/1.384507

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A new imaging technique based on scatter at right angles from tissue has been investigated. Separate transmitting and receiving transducers are employed. The transmitting transducer generates a cylindrical wavefront that converges to a line focus in the object. A receiving transducer, aligned coaxially with the line focus, detects the ultrasound waves scattered at 90° from structures in the object. Because of the high degree of cylindrical focusing, the scatter is treated as if it arises from points on or very near the line focus. This allows the use of a ranging approach similar to that employed in conventional pulse–echo imaging. A tomographic image is generated by translating or rotating the two transducers as a unit while appropriately displaying the scatter information. This approach eliminates the depth‐of‐field problem inherent in pulse–echo imaging without sacrificing the speed or simplicity of the imaging process. The distribution of ultrasound in the field of the cylindrical transducer is treated theoretically for cylinder angles ranging from 30° to 360°. Experimental verification of theory was performed using a 120° cylinder. Here the full width at half maximum of the amplitude of the main lobe was 0.5 λ by 2.3 λ (0.15 mm × 0.7 mm at 5 MHz). An experimental scatter scanner is described, and images of a simple phantom and aninvitrotissue sample are given.

ISSN:0001-4966    

DOI:10.1121/1.384508

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The compilation of the literature on ultrasonic propagation properties of mammalian tissues [J. Acoust. Soc. Am. 64, 423 (1978)] is continued with the addition of 45 papers yielding over 700 lines of parametric data.

ISSN:0001-4966    

DOI:10.1121/1.384509

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A functional model of a simplified clarinet has been developed and implemented on a digital computer. The simplified clarinet consists of a standard clarinet mouthpiece and reed attached to a straight cylindrical tube. In the model, the tube and mouthpiece are represented by a lumped element approximation to a transmission line and the reed is represented as a nonuniform bar, clamped at one end. Differential equations for the system are solved numerically on a digital computer to obtain pressures and volume velocities of the air in the tube and mouthpiece, and positions of the reed at successive time increments. The model exhibits self‐sustained oscillations, threshold blowing pressures, frequency shifts, and spectra of mouthpiece and radiated pressures which are similar to those of an actual simplified clarinet. A previously unreported dependence of volume velocity in the reed aperture on the initial or rest opening of the aperture was also found.

ISSN:0001-4966    

DOI:10.1121/1.384635

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

This paper describes the modification and extension of an ultrasonic through‐transmission technique for examining vocal fold activity. The purpose was to achieve improved lateral resolution in the cranio‐caudal dimension. A transducer was specially designed to produce an eliptical beam, so that a measurable signal might be received through the extreme upper and lower edges of the vibrating vocal folds. An interpretation of amplitude variation within the ultrasonic waveform is offered, with illustrative data shown for a single subject.

ISSN:0001-4966    

DOI:10.1121/1.384637

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The acuity of auditory localization in Old World monkeys (Macaca) was determined psychophysically for 44 noise bands graded in bandwidth and center frequency. The acuity of localization was assessed through the method of constant stimuli under free‐field conditions in an anechoic chamber. Monkeys were trained through positive‐reinforcement operant‐conditioning procedures to report a change in azimuth of the signal by releasing a response disk. The results show that localization thresholds are dependent upon the bandwidth of the signal over much of the macaque’s range of audibility. Thresholds for the detection of a change in location varied from 18° (for a signal 250 Hz in bandwidth centered at 11 200 Hz) to 4° (for a signal 8000 Hz in bandwidth centered at 8000 Hz). The results suggest that the localization of spectrally complex signals is determined by a mechanism sensitive to periodicity (time‐domain) information across the monkey’s range of audibility.

ISSN:0001-4966    

DOI:10.1121/1.384638

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Responses to sinusoidally amplitude modulated (AM) tones were recorded in single auditory nerve fibers of anesthetized chinchillas. The tones chosen were of a class which, in humans, gives rise to a percept of low subjective pitch. It was found that, for high‐frequency stimuli, neurons tuned to high frequencies signaled waveform envolope periodicity when the stimulus was of sufficient intensity. Neurons tuned to low frequencies responded to low‐frequency AM tones in an orderly manner which ranged, as overall intensity was raised, from signaling all frequency components to signaling only the component to which the neuron was most sensitive. This result was interpreted to indicate the presence of two‐tone suppression. Variation of modulation frequency and modulation depth produced response patterns which were generally predictable based on the relative effectiveness of each of the component frequencies in eliciting discharges. Neurons tuned to low frequencies did not respond at low and moderate intensities to higher‐frequency AM tones, even though the subjective pitch of the tones corresponded to frequencies to which the neuron was sensitive. At high intensities, distortion products locked in‐phase to the frequency of the subjective pitch were observed. Responses to a single AM tone recorded from different neurons in the same animal displayed considerable diversity in their responses. Response diversity was correlated with neuronal tuning characteristics, stimulus intensity, and intrinsic factors such as suppression. Neurons retained stimulus finestructure information in the temporal patterns of their discharges as stimulus components were varied from a harmonic relationship to an inharmonic relationship. The data indicate that responses of auditory nerve fibers contain sufficient information for extraction of the subjective pitch of AM tones by a central auditory processor which operates on temporal features of the responses.

ISSN:0001-4966    

DOI:10.1121/1.384639

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP