摘要:

In the present paper a formula is developed for calculating the hearing loss for speech from an audiogram showing the hearing loss for each of a series of pure tones. The formula is based upon studies of loudness, including the determination of the relative contributions of different frequency regions to the audibility of speech at or near the threshold level. The formula is tested for each of 165 ears involving a wide variety of hearing losses. In every instance an audiogram is available and also an independent observation of the hearing loss for speech. The formula yields a calculated value which generally is in closer agreement with the observation than is the value calculated by the familiar rule of averaging the losses at 500, 1000, and 2000 c.p.s. The agreement is particularly better when the audiogram is not “flat.” A simplified computational rule, indicated by the more complete formula, is found within indicated limits to be almost as reliable as the formula. This simplified rule is to examine the hearing losses measured by means of the audiometer at the three frequencies 500, 1000, and 2000 c.p.s., and to take the average of the two smallest values of loss.

ISSN:0001-4966    

DOI:10.1121/1.1906567

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

This report presents the results of a study of the monaural masking of pure tones by white noise at eight sensation levels (SL) from 20 to 90 db. The observed values of masking were employed to determine two basic functions:(a) The critical band width of a masking noise, i.e., the ratio, in decibels, between the level of a pure tone and the level per cycle of the noise that is just able to mask the tone.(b) The function relating the amount of masking to the effective level of the masking noise.With the aid of these two functions, a set of contours was constructed to represent the masked threshold for pure tones heard monaurally against background of white noise having an ideal flat spectrum at the ear of the listener.A study was also made of the masking by white noise of speech in the form of continuous discourse. Measurements of the threshold of detectability and of the threshold of intelligibility were made at the same eight noise levels used to mask pure tones.

ISSN:0001-4966    

DOI:10.1121/1.1906581

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A piezoelectric crystal pick‐up has been designed, constructed and successfully applied to the detection of internodal distances in a solid metal rod vibrating at resonance and thus to the evaluation of configurational dispersion of ultrasonic compressional radiation in the rod. The use of the pick‐up yields results as accurate as the powder method and can be applied in certain cases where the latter fails.

ISSN:0001-4966    

DOI:10.1121/1.1906565

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Ultrasonic beams of frequencies in the range of 80 kc/sec. to 1000 kc/sec. emerge from a rectangular slit of known adjustable width into air, oxygen, or carbon dioxide. The disposition of the field in front of the slit is studied by the aid of a hot wire anemometer, which gives the angle of divergence of the beam and the intensity distribution across the main and the diffracted beams.The results obtained indicate that the laws of diffraction are valid so long as the gas is far removed from its anomalous dispersion region.CO2in the range between 100 and 200 kc/sec. shows a high degree of scattering with the result that the emergent beam loses its definition completely and becomes very diffused.

ISSN:0001-4966    

DOI:10.1121/1.1906566

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A statistical method is described which enables an analytical bubble size distribution to be formulated from the rough size grouping usually obtained with practical methods of experimental graphs of bubbly turbulent water. The resulting function is used with certain known formulas for evaluating the acoustical impedance of such a mixture. A brief physical interpretation of the effects predicted by the theory is given.

ISSN:0001-4966    

DOI:10.1121/1.1906568

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A few experiments are reported in which thirty‐millisecond signals of 24‐kc sound were emitted in the ocean every second at depths of 150, 300, 500, and 1000 ft., by a relatively non‐directional projector, and were received by similar units at the same depths after having traveled 100 to 3000 yards. A recording technique was used which made it possible to resolve the direct and surface‐reflected components. Transmission conditions near the surface were poor during the experiments, and the transmission was found to improve as the projector and receiver depths increased. The average attenuation at the greatest depths was about 6 db/1000 yd. in addition to the loss caused by an assumed inverse‐square divergence of the sound energy. Although the emitted signals had rectangular envelopes and were all of the same amplitude, the amplitudes of the received signals fluctuated from signal to signal and within each signal. The fluctuation of the directly transmitted signals showed a general tendency to increase with range in proportion to the square root of the range. The magnitude of this fluctuation changed from about 10 percent of the average amplitude at 100 yards to 45 percent at 3000 yards. The fluctuation of the surface‐reflected component was greater than that of the direct component and did not depend on range.

ISSN:0001-4966    

DOI:10.1121/1.1906569

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The Debye‐Sears method for measuring ultrasonic absorption is used for various organic liquids at room temperature and at frequencies of 3 to 15 mc/sec. The effect of molecular symmetry on absorption is studied for the pairs benzene, toluene; paraxylene, orthoxylene; and cyclohexane, methyl cyclohexane. The effect of doubleversussingle bond is given for tetrachlorethaneversustetrachloroethylene. The effect of viscosity on absorption is shown to be almost negligible for solutions of polystyrene in either toluene or benzene. Finally, a possible explanation along relaxational lines is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1906570

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Several acoustic properties of anisotropic media have been investigated by the pulsed ultrasonic method and the results analyzed in terms of plane waves traveling through an infinite medium. Single crystals of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) were the subjects of this study and in each case velocity measurements were used to compute a complete set of elastic moduli. Coupling between modes which results in the simultaneous generation of two modes by a transducer and in the transfer of energy between modes during a reflection was studied. The phenomenon of acoustical birefringence in ADP was particularly investigated and it was found that all of the three modes with wave normals in the 45° direction in theyzplane are propagated in different directions making non‐zero angles with the wave normals. A case in which the anisotropic property of the medium causes anomalous beam spreading is reported and the circumstances leading to this condition are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1906571

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

It is anticipated that some of the auxiliary equipment to be used in conjunction with the new water tunnel under construction at The Pennsylvania State College will be particularly noisy in the ultrasonic frequency region where certain low level acoustic measurements are to be made. This potentially noisy equipment includes such items as a deaerator, an energy dissipator and a pressure control system which are located in a water loop, external to the main tunnel section. To effectively isolate this loop acoustically from the remainder of the tunnel where the acoustic measurements will be made, it has been considered desirable to design an acoustic filter which can be inserted at the junctions of the loop with the tunnel. This filter should serve the multiple function of reducing the sound transmission through the pipe walls and through the water in the pipes while permitting the passage of relatively large volumes of water at small loss of pressure.The problem of isolation in the pipe path is a fairly common one and essentially requires the use of sound attenuating gasket material. However, the isolation of the water path is more complex in that water must be allowed to flow while sound is attenuated. In this case a honeycombed structure of a pressure release material is used.This paper discusses the hydraulic consideration of the problem and presents the results of acoustic transmission measurements on the filter components. The measurements include: 1. The frequency characteristics of the acoustic filter under free field conditions, 2. The transmission properties of the isolating gaskets mounted in the pipe flanges, and 3. The effective response of the filter and isolation gaskets combined.

ISSN:0001-4966    

DOI:10.1121/1.1906572

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A pick‐up device for measuring the standing wave ratio of transverse acoustic waves is described. One of the important features of this device is the elimination of interference from the residual plane wave. An experimental study of the attenuation characteristics of (1,0) transverse acoustic waves propagated in air in a rectangular metal tube employing such a pick‐up device is presented in this paper. This study reveals that three losses are important contributors to the attenuation. The results are in good agreement with a tube wall effect predicted by Kirchhoff. In evidence is a gaseous absorption in the medium due to thermal equilibrium adjustments. The remaining attenuation is appreciable and appears to vary with frequency asf2[1−fc2/f2]−12. This factor is here attributed to a vibration of the tube walls.

ISSN:0001-4966    

DOI:10.1121/1.1906573

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP