摘要:

As one phase of a noise survey of the Chicago area, measurements were made of the acoustic output of commonly used automobile horns. Over‐all sound levels on the axis at three feet ranged from 108 to 125 db. Loudness levels ranged from 125 to 140 phons. Fundamental frequencies of all horns ranged between 160 and 380 cps. Two types had approximately harmonic overtones, with large amplitudes below about 2000 cps and smoothly decreasing amplitudes at higher frequencies. A third type, with the most unpleasant sound, had inharmonic overtones, groups of which were greater in amplitude than the fundamental. Sound from a pair of horns at various distances was measured both inside and outside a closed automobile. The over‐all level outside was 88 db at 50 feet and 74 db at 300 feet, with corresponding loudness levels of 105 and 82 phons. The over‐all level inside was 60 db (loudness level, 72 phons) at 50 feet and 50 db (loudness level, 54 phons) at 300 feet. Filtering out overtones above 1200 cps improved the quality of horn sounds markedly, reducing the loudness level inside the automobile by four phons at 50 feet, but only one phon at 300 feet. Since the typical horn is louder than necessary at close range, use of a low pass acoustic filter on automobile horns appears desirable.

ISSN:0001-4966    

DOI:10.1121/1.1906728

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A fixed path ultrasonic interferometer for use in vapors is described, in which the stationary wave system between the quartz source and the reflector is explored by a traveling hot‐wire. The hot‐wire is calibrated for its change of resistance in terms of velocity‐amplitude in the ultrasonic wave system. A correction is made for diffraction of the ultrasonic beam.In this apparatus wavelength and absorption measurements are made in ether, ethylene, benzene, carbon disulphide, and acetaldehyde vapors. All show an absorption considerably greater than the theoretical values based on the Stokes‐Kirchhoff equations.

ISSN:0001-4966    

DOI:10.1121/1.1906729

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A reverberation method has been used to measure the absorption of sound at frequencies down to 140 kc in a number of liquids of widely different properties. For glycerol the experimental result agrees well with that predicted by classical theory. For benzene and water good agreement is found with the values calculated using the modified theory employing the values of second viscosity determined by Liebermann. The absorption in carbon disulfide agrees well with Ouang's result. For these four liquids the absorption is found to be proportional to the square of the frequency, but results indicate that toluene has a relaxation frequency of the order of 105sec−1.The reverberation method is especially useful at the lower ultrasonic frequencies, where loner wave‐lengths and lower absorption render methods used at higher frequencies less reliable or unusable.

ISSN:0001-4966    

DOI:10.1121/1.1906730

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

Experimental values are reported for the sound absorption coefficients in aqueous solutions of magnesium sulfate over the frequency range 3 to 43 megacycles. Measurements were made by an electrical method at the lowest frequency and by the pressure balance method at higher frequencies (12–43 mc). Absorption coefficients are reported as a function of frequency, concentration, and temperature. An excess absorption (relative to water) is found at the higher frequencies which cannot be interpreted by the present theory.

ISSN:0001-4966    

DOI:10.1121/1.1906731

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The ultrasonic absorption of an associated liquid, glycerin, has been measured, in the liquid and vitreous state, at 31 Mc. The value of absorption found exceeds the theoretical value at high temperatures by a factor of 2.1. This indicates that both compressional and shear viscosity contribute to the absorption process. When the liquid was cooled, a peak in the absorption was found at −6.5°C; and at still lower temperatures the absorption fell to considerably lower than classical values. The appearance of a peak in the absorption experimentally verifies the fact that both compressive and shear viscosity are associated with a relaxation phenomenon. The relaxation times for the two processes are of the same order of magnitude, and the same is true of the activation energies.

ISSN:0001-4966    

DOI:10.1121/1.1906732

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

It is shown that with or even without ultrasonic lenses or other devices for the concentration of ultrasonic energy, by ultrasonics, images can be made on photo‐sensitive emulsions. Several of the first ultra‐sonographs, as these images are called, are reproduced and some potential fields of application of the new technique are mentioned.

ISSN:0001-4966    

DOI:10.1121/1.1906734

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

Some improved sound wave interference methods for measuring the longitudinal and transverse ultrasonic velocity in opaque as well as transparent solids may be simply carried out by using the ultrasonic light‐diffraction system (as arranged for making sound beams visible on a screen). The sonic unit of the system is arranged to produce two individual traveling‐wave sound beams, by use of two generators by splitting a single beam. Three simple arrangements are described in detail. In Case A one beam travels entirely in a reference liquid, while the other beam travels a parallel path in an immersed transparent test specimen. In Case B one beam travels entirely in a reference liquid, while the other beam travels an adjacent course through an immersed, transparent or opaque test prism, and on into the liquid at an angle to the first beam. In Case C the two beams are generated at the equal edge faces of a transparent or opaque isosceles test prism (only the base edge face contacting the liquid). The two beams traverse the prism to the base, where they are refracted into the test liquid as confluent beams.In Cases A and B, simulated interference (by optical integration), and in Case C true interference, each give a light and dark band interference pattern on the screen, whose band spacing is used in calculating the velocity of sound in the test solid. The other required factors are the optical image magnification, the frequency of the sound, the angular disposition of the one or more acoustic surfaces of the test solid relative to the incident sound beams, and in Cases A and B the velocity of sound in the reference medium. Other variations of arrangement are suggested.Advantages of the improved methods are simple preparation of test specimen, directness and simplicity of measurement and calculation, good accuracy, low sonic power requirements. A table of measured velocities (and attenuations) in two metals and in numerous plastics and polymers show the wide range of materials that may be measured by the new interference methods.

ISSN:0001-4966    

DOI:10.1121/1.1906735

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A general analysis of variable resonant frequency crystal systems which utilize liquid media as backing is presented. Formulas are obtained for evaluating the effect of different geometries of backing on the resonant frequencies of the system. The various loss factors associated with such a system are related to the measurable quantity, the quality factor.The observed operating characteristics of a variable resonant system which covers a two‐to‐one frequency band (40 kc to 80 kc) are presented. The results of an experimental comparison of such a system with fixed resonant frequency systems for generation of ultrasound in liquid media are given. The theory is used to correlate the experimental observations.

ISSN:0001-4966    

DOI:10.1121/1.1906736

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906715

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906716

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP