摘要:

The noise fields generated by a standard turbo‐jet aircraft engine have been measured for three different power settings. Measurements were made at points on circles around the engine having radii of 25 and 50 feet. For the 50‐feet distance the directional characteristic presented for the over‐all sound pressure and for the noise in the different octave bands starting at 37.5 cps. From these measurements the total acoustic power radiated from the engine is calculated to be approximately 69 kw at full engine power. The distribution of this power over the different frequency bands and space angles is shown. The highest total energy per cycle and the highest sound levels are found at frequencies near 100 cps for the higher power settings of the engine. Above that frequency range the total energy per cycle drops approximately as the reciprocal of the square of the frequency. The data should help us understand qualitatively the jet engine as a sound source and are therefore discussed in that respect. On the other hand, the data have practical significance with respect to the design of test facilities for adequate protection of personnel. They are equally important with respect to problems of noise control on an airport.

ISSN:0001-4966    

DOI:10.1121/1.1906874

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Relationships between a listener's identification of a spoken vowel and its properties as revealed from acoustic measurement of its sound wave have been a subject of study by many investigators. Both the utterance and the identification of a vowel depend upon the language and dialectal backgrounds and the vocal and auditory characteristics of the individuals concerned. The purpose of this paper is to discuss some of the control methods that have been used in the evaluation of these effects in a vowel study program at Bell Telephone Laboratories. The plan of the study, calibration of recording and measuring equipment, and methods for checking the performance of both speakers and listeners are described. The methods are illustrated from results of tests involving some 76 speakers and 70 listeners.

ISSN:0001-4966    

DOI:10.1121/1.1906875

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An example is shown of the steps in the design of the structure for noise control of a jet engine test cell from the determination of the design goal to the final acoustic treatment of the cell. An arbitrary design goal was set from a previous survey of city noise. With the expected octave band levels at a distance of 3000 feet, for 10 jet engines with afterburners the quieting necessary is 50 and 55 db, respectively, in the 150–300 and the 300–600 cps bands, these two bands being the most difficult to control. An analysis of the required volume and dependent cost of the structure is given as the function of the amount of quieting needed, the quantity of heated gases exhausted, the temperature of the gases, and the velocity of flow permitted. Two unconventional but economical systems of noise control, (1) a series of acoustically treated plenums and (2) a series of acoustical lined 180‐degree turns, are recommended. Design equations and confirming data from model studies are presented.

ISSN:0001-4966    

DOI:10.1121/1.1906876

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A convenient and theoretically satisfactory method for measuring the sound attenuation of flying helmets is described in which a miniature microphone is employed to measure the sound intensity inside the helmet capsule. A theory of sound transmission through helmet capsules is proposed the validity of which is established by a direct comparison of theoretical with experimental results.It is thus possible to design helmets which are considerably better than standard R. A. F. types. Comparison tests on one such helmet are described.

ISSN:0001-4966    

DOI:10.1121/1.1906877

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Data are presented on the dispersion of the velocity of sound and on the effect of impurities upon the rotational relaxation times determined therefrom. The attenuation due to the relaxation is shown to agree with the theory, with some evidence of multiple relaxation. Anomalous dispersions of the classical attenuation and of the Herzfeld reflection coefficient are predicted. The latter is confirmed experimentally and also yields a determination of the accommodation coefficient.

ISSN:0001-4966    

DOI:10.1121/1.1906878

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

There are two classes of liquids which show anomalous absorption of ultrasonic waves, class A1 (nonassociated liquids) and A2 (associated liquids). In mixtures of two liquids of class A1, both density and sound velocity vary almost linearly with concentration, in spite of the anomalous variation of sound absorption. The smaller the ultrasonic absorption of a liquid of class A1, the greater is the decrease of absorption per unit concentration in a dilute benzene solution of the liquid. This does not hold in liquids of class A2, such as alcohols. The inverse correlation between the absorption of ultrasonic waves and infrared radiations was found in the case of liquids of class A1. It was concluded from the above facts that the absorption of ultrasonic waves in nonassociated liquids should be a result of the so‐called “molecular absorption,” in the same way as in gases. In the case of associated liquids some part of the absorption is probably ascribed to the molecular absorption, but the remaining part may be caused by another relaxation mechanism, a slow change in local order of molecules. The contribution of the molecular absorption to that, in highly viscous liquids. is also estimated.

ISSN:0001-4966    

DOI:10.1121/1.1906879

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The transmission, through an isotropic solid plate immersed in a liquid, of ultrasonic waves incident at the critical angle for total reflection of the dilatational wave, is examined experimentally and theoretically. It has previously been held that total reflection does not occur at this angle when the thickness of the solid is less than or comparable with the wavelength of the dilatational wave in it. It is now shown that, owing to interference between the dilatational and rotational waves, total reflection does occur at or very near this angle for a considerable range of thickness in this region. It is therefore possible to use the total reflection method for the determination of the dilatational velocity in a solid even when only thin specimens of the solid are available.

ISSN:0001-4966    

DOI:10.1121/1.1906880

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Four groups of new methods of indirect ultrasonoscopy and ultrasonography are developed: those using temperature‐sensitive chromotropic compounds, those using leucobases of dyes, those using thermo‐stimulable phosphors, and those using special temperature‐sensitive phosphors. Various techniques are described and some results shown in the illustrations. Finally, a new method of direct ultrasonography is proposed. This method makes use of the possibility to detonate certain labile chemical compounds by ultrasonics.

ISSN:0001-4966    

DOI:10.1121/1.1906881

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Divergent compressional waves in solids differ from similar waves in fluids, even though the particle displacement is parallel to the direction of propagation in both media. The wave propagating from a radially oscillating spherical cavity in an infinite solid medium sees an acoustic radiation impedance which is a function of the Poisson's ratio of the medium as well as of the usual parameters. The radiation resistance has the same form as in a fluid medium, but the reactance is a negative or stiffness reactance, except at high frequencies in media of low rigidity. When an impulsive pressure is generated in the cavity, as by an explosion, the form of the radiated pulse is a damped oscillating wave train which does not closely reproduce the original pressure pulse.

ISSN:0001-4966    

DOI:10.1121/1.1906882

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In the following paper are included: the graphical synthesis which originally led to the belief that the tangential motion of a phonograph playback needle would cause distortion of the output signal; the mathematical analysis of the forces which would tend to cause such motion; and descriptions of equipment, tests, and conclusions reached.These conclusions are, in brief, as follows: In a common type of crystal pick‐up, equipped with the usual steel needle, tangential motion of the stylus tip does occur as postulated, ranging in amplitude up to 0.0012″, the amplitude of the motion being a function of the recorded frequency, the amplitude of recording, the radius of the groove in which the signal is recorded, recording speed, record and needle wear, and needle pressure. In addition to the tangential motion caused by the recorded signal, a vertical resonance occurring in the needle‐pick‐up arm system causes low frequency tangential motions of the needle tip (24 cps) with amplitudes of up to 0.0015″. Attempts to detect the distortion of the output signal caused by tangential motion were unsuccessful principally because of the presence of other distortions which masked the tangential motion distortion, and which could not be removed from the equipment used. However, since the existence of tangential motions and their amplitudes were established, it became possible to compute the cross‐modulation products caused by such motion.

ISSN:0001-4966    

DOI:10.1121/1.1906883

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP