摘要:

The following document was prepared by NAS‐NRC CHABA Working Group 46. This group was asked to specify damage‐risk criteria for exposure to sound. The paper contains graphs of maximum sound‐pressure levels and durations of exposures that the Working Group believes would be tolerable and examples of the use of these graphs in addition to background information and a discussion of the rationale, assumptions, limitations, and general problems pertinent to the development and application of a damage‐risk criterion and related exposure contours.

ISSN:0001-4966    

DOI:10.1121/1.1909912

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The pressure levels generated at the entrance to the earcanal by progressive waves from a point source at a distance of 1 m have been measured for a group of ten subjects. Individual curves are presented for all ten subjects at six azimuthal angles of incidence. Measurements at 0°, 45°, 90°, and 180° cover the frequency range 0.2–14 kcps. Measurements at 270° and 315° extend to 8 kcps. The average earcanal‐versus‐free‐field pressure levels are in good agreement with Wiener's data over the common frequency range. Certain features (maxima at 2.4 and 13 kcps, minima at 4 and 10 kcps) appear to be relatively independent of angle of incidence. Others (peak at 7 kcps) have strong azimuthal dependence. Normal modes of the concha may have an important role in the 6‐ to 10‐kcps region.

ISSN:0001-4966    

DOI:10.1121/1.1909913

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The hearing thresholds of four subjects have been measured at nine audiometric frequencies from 0.125 to 8 kcps with a probe microphone placed in the external ear. The probe‐tube pressures at hearing threshold are found to be substantially the same with the four different earphones used to generate the tone. The earcanal response curves of three circumaural and two supraaural earphones coupled with a group of ten subjects have been measured over a 0.2‐ to 15‐kcps frequency range. The groups of curves have been normalized with respect to reference response curves obtained with suitable couplers. The five groups of earphone response curves are found to have much in common with one another and with curves of earcanal pressure generated by a free sound field, using the same group of subjects; there are also significant differences. The relationships are thought to shed much light on the acoustic behavior of earphone systems. Average response curves for the five earphones permit the transfer of coupler pressure at hearing threshold; data for TDH39/MX41AR and HA10 earphones are in good agreement with published subjective data. Intra‐subject range (average range of pressure with repeated measurements on a single subject) varies from 0.2 to 10 dB, depending on earphone type and frequency. In conclusion, it is suggested that existing earphone systems, though well‐adapted for speech communication, may not provide ideal coupling for more‐exacting applications.

ISSN:0001-4966    

DOI:10.1121/1.1909914

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The use of the acoustoelectric effect in measurements of the decay of multiply reflected acoustic pulses in a specimen is described. The detector is a wafer of piezoelectric semiconductor arranged to absorb a small proportion of each successive pulse. Since the voltage generated is proportional to pulse power and is not sensitive to phase, many types of pulse decay form distortion, which may be associated with such measurements, are eliminated. The efficiency of detection is discussed, and it is shown to be comparable with that of a piezoelectric transducer.

ISSN:0001-4966    

DOI:10.1121/1.1909915

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The factor analytic model, as here applied, conceives of a numerical quality judgment of a certain program played by a given reproducing device as a weighted sum of a measure of the quality of the different reproducing properties (e.g., purity of transients, full treble) possessed by the device in question. The weights constitute measures of the requirements made by the particular program on these properties. Factor analysis splits a raw‐data matrix—consisting of, e.g., quality judgments for a number of combinations of program‐loudspeaker systems—into two matrices: a factor loading matrix consisting of the weights and a factor‐score matrix consisting of the quality of the reproducing properties. The rank of these matrices (number of factors) reflects the number of dimensions (properties) that implicitly enter into the listener's judgments. Four listeners judged, on a 7‐point scale, the quality of 24 programs (music, speech, traffic noise, etc.) played on 10 sound reproducing systems of highly different general quality. The data were factor analyzed (component analysis of covariances), and factor loadings for the programs and factor scores for the loudspeaker systems were computed. Nine factors were extracted and rotated, and 7 of them tentatively interpreted (sound level, purity of transients, environmental information, bass boost, full‐treble reproduction, high‐treble relative midrange, disturbing directional effects). An attempt at validation showed good agreement between factor scores (reproducing properties) for the 4 listeners in spite of variation of preferences between listeners reflected in the factor loadings. Despite technical imperfections, it is concluded that factor analysis is a useful instrument for the assessment of acoustical properties.

ISSN:0001-4966    

DOI:10.1121/1.1909916

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Analysis of discrepancies among current reports on ultrasonic internal conical refraction arc serious enough to cast doubt on the existence of the effect. Data have been taken on ultrasonic shear waves propagating in the [111] direction in a cubic single crystal (potassium chloride), which is large enough to show the essential details of the effect. Measurements of the distribution of energy and polarization direction around the perimeter of the base of the cone, the dependence of the amplitude on the polarization direction of the input transducer, and the angle of refraction are presented. The measurements appear to support a proposal that the results observed are, as in optics, a direct consequence of beam spread in the input radiation.

ISSN:0001-4966    

DOI:10.1121/1.1909917

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Experimental results are presented for the directions of energy flow for transverse ultrasonic waves propagated along and near theZaxis of quartz. Measurements made with an absorption‐probing technique as a function of frequency in the range 12–360 Mc/sec demonstrate the considerable variations in the spread of energy for slightly off‐axis propagation. The use of plane‐wave “Christoffel” solutions to obtain a qualitative picture of conical refraction is discussed in some detail. In general, the features of Waterman's analysis are confirmed [P. C. Waterman, Phys. Rev.113, 1240–1253 (1959)].

ISSN:0001-4966    

DOI:10.1121/1.1909918

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A torsion pendulum has been used to make mechanical measurements on linear polyethylene between −175° and +110°C at about 1 Hz. Samples in which orientation had been induced by crystallization in a temperature gradient were measured together with unoriented but otherwise comparable samples. The data are analyzed to show that the a relaxation in polyethylene is sensitive to the orientation of the deformation with respect to the structural and morphological symmetry. For shearing in thea‐cface of the unit cell and lamella boundaries the relaxation average over all directions is different from the average for shearing in all possible planes in the cell and boundaries. The γ relaxation does not exhibit this difference. Various viscoelastic parameters such as the real part of the modulus and the magnitude of the relaxations do not correlate with lamella thickness in the present samples.

ISSN:0001-4966    

DOI:10.1121/1.1909919

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Visible cavitation has been obtained readily in liquid helium using a barium titanate cylinder resonant at about 46 kc/sec. The nature of the cavitation changes in various temperature régimes, and these changes are reflected by changes in the threshold, as measured by the driving voltage of the transducer. Below about 2.13°K, the threshold for visible cavitation is an order of magnitude higher than the threshold for noise; but between 2.13°K and the λ point the visibility threshold drops and becomes comparable to the noise threshold. Static pressure has a much greater effect on the visibility threshold than on the noise threshold. The results are discussed and the conclusion is reached that the information obtained is more pertinent to the dynamics of the cavities than their nucleation.

ISSN:0001-4966    

DOI:10.1121/1.1909920

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Atomization of selected fluids has been observed to occur in a capillary at various resonance heights of the standing ultrasonic wave in the fluid. The length of fogging has been observed to be a function of the voltage applied to the transducer producing the ultrasonic wave in the fluid. A theoretical analysis is given to explain the experimental results obtained.

ISSN:0001-4966    

DOI:10.1121/1.1909921

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP