摘要:

The development of a satisfactory, automatic, self‐testing audiometric system (based on the pulse‐tone techniques suggested by Gardner, Harris, Reger and Newbyet al.) reveals the need for an investigation of the psychophysical procedures that might be used in such a system. Preliminary studies led to selection of four practical methods of threshold determination suitable for this project. Final choice of a single method requires a determination of statistical reliability as well as operational suitability of the method. Experimental apparatus was constructed to permit automatic testing by the four methods. Young adult subjects were tested with one of the four methods (randomly assigned) at three frequencies. A three‐dimensional experimental design, permitting the use of analysis of variance, furnished an estimation of variance to be assigned to factors in the design, and also measures of reliability for comparison of the four methods. The results contribute data needed for selection of the method to be used in a final practical version of an automatic, self‐testing system. [This work was supported by the U. S. Air Force School of Aviation Medicine.]

ISSN:0001-4966    

DOI:10.1121/1.1905076

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The lumped constant theory given earlier [J. Acoust. Sec. Am.26, 947(A) (1954)] has been extended to take into account the finite area of contact between cushion and head. The modified theory is based on the premise that the cushion and flesh have infinite bulk modulus, and leads to the conclusion that there is an effective cover area which is equal to a linear combination of the “inner” and “outer” areas. The physical methods of attenuation measurement described earlier have been further developed to permit the determination of both the amplitude ratio and the phase shift in transmission. Such measurements make it possible to calculate the impedance of the flesh under the cushion at frequencies between 30 and 500 cps. The preliminary values of stiffness and resistance (8 × 107dyne‐cm−1and 3 × 105dyne‐sec cm−1) are, respectively, less by a factor of 6 and greater by a factor of 10 than the magnitudes of the corresponding mastoid parameters recently determined by Corlisset al.and Dadsonet al.This suggests that the low‐frequency impedance presented by the head to a circumaural ear defender cushion is mainly determined by the viscous and highly compliant flesh rather than the comparatively rigid skull.

ISSN:0001-4966    

DOI:10.1121/1.1905084

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Underwater hearing thresholds were measured at frequencies of 250, 500, 1000, 2000, and 4000 cps on four Aqualung equipped divers known to have normal hearing in air. In the frequency range investigated, the hearing threshold underwater is from 44 to 60 db greater than the minimum audible fields in air, and the shape of the thresholdvsfrequency curve is different. Mechanisms based upon the changed impedance relationships between the ear and the medium are invoked to explain the loss of sensitivity at 250 and 500 cps. It is suggested that the greater loss at 1000, 2000, and 4000 cps is caused by a shift in the resonant frequencies of the external meatus when it is filled with a medium having a different characteristic impedance. Evidence is presented that indicates that hearing underwater is at or near the bone conduction threshold, and this is considered as an alternate explanation for the change in shape of the threshold curve.

ISSN:0001-4966    

DOI:10.1121/1.1905086

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

After three very successful years, the authorities of the Stratford (Ontario) Shakespearean Festival are planning to replace the unique theater tent with a permanent structure. The Festival's original home is an interesting mixture of Greek amphitheatre, Elizabethan stage, and present‐day circus tent, and the new building will retain nearly all of these features, including a seating capacity of around 2000. With no proscenium arch, an “acting angle” of over 180°, circular banks of seats centered on the middle of the stage, and a small gallery, the new design presents a number of interesting and unusual acoustical problems, such as ensuring high intelligibility in sections of the audience on which an actor has turned his back. The location of an orchestra of reasonable size so that it will not interfere with the pageantry of the productions is also a matter of some difficulty. This paper details the solutions proposed for the building which is scheduled for completion before the 1957 Festival Season. It is hoped that a later paper may discuss the results achieved.

ISSN:0001-4966    

DOI:10.1121/1.1905097

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Theory. Lighthill's theory of aerodynamically generated sound is applied to the flow past a stationary circular cylinder with a fluctuating wake, a phenomenon related to “Aeolian Tones.” The main predictions of the theory are as follows: (a) A tone is produced having the same frequency as the wake. Its directionality is that of a line dipole with axis normal to the stream. This sound is associated with the fluctuating lift force acting on the cylinder. (b) A tone is produced having double the wake frequency. Its directionality is that of a line dipole with axis parallel to the stream. It is associated with the fluctuating drag force. (c) The intensity of both tones at points of the midplane in the far field varies approximately asU6, whereUis the stream velocity. (d) The acoustic power varies asUn,nlying between 5 and 6.Experiments. Measurements were made in the subsonic wind tunnel laboratory of the Institute of Aerophysics. Circular cylinders of various diameters were mounted in the tunnel test section, and sound pressures were measured at points inside and outside the tunnel over a range of speeds. Graphs are presented showing over‐all sound pressure levels, sound spectra, and equal level contours. The results obtained are in general agreement with the predictions of the theory.

ISSN:0001-4966    

DOI:10.1121/1.1905104

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The recent progress of acoustical techniques have made it possible for biologists to study the sounds produced by animals. These are of special interest since they can be correlated with specific forms of behavior. But parallel with these studies of what one might term “pseudo‐language” and the establishment of the “animal vocabulary,” an equally interesting aspect of the question is the study of the reactions of animals to sounds produced by man. My studies and those of my collaborators have led me to propose the terms “phonokinesis” and “phonotaxis” in order to classify, at least provisionally, the reactions of animals. These reactions which of course can appear with natural signals from the same animal species, are at times called forth by signals of another species. By an analytic procedure and for certain zoological groups such as the invertebrates and the lower vertebrates, we have succeeded in defining certain of the physical properties of sounds which provoke these reactions, permitting for example to attract or to drive away animals at a distance. The detailed study of different noises, used at times empirically for millenia by peoples close to nature, is extremely interesting and shows that certain types of hunting or fishing gear are actually generátors of acoustical signals to which certain species react. The forms of behavior in response to sound have more than theoretical interest; their deeper understanding may, a few years hence, lead to important applications in the protection of cultures.

ISSN:0001-4966    

DOI:10.1121/1.1905109

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

High‐level ultrasound, when properly controlled, produces quantitatively selective alterations in the central nervous system. The physical mechanism of this selective action of the sound on tissue is not presently understood. This paper describes a biological preparation and precision technique which are appropriate for accurately determining ultrasonic dosage relations. A knowledge of these relations will facilitate the understanding of the physical mechanism involved in the sonic action. Specific quantitative results obtained are reported.

ISSN:0001-4966    

DOI:10.1121/1.1905114

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

A cylindrical barium titanate element has been placed at the distal end of a specially designed catheter and used in studies of heart sounds of dogs and humans. The heart sounds have been recorded with the sensitive catheter located directly in the heart and in the pulmonary artery. The location of the catheter at each mapping station has been monitored with x‐ray photographs; simultaneous electrocardiogram and wide band sounds were recorded on a photographic galvanometer. The sounds were recorded on tape with several filter characteristics, and acoustic spectrographs were made. These studies indicate that much may be learned from an analysis of the spectra and time characteristics of sounds picked up directly within the circulatory system. [Work supported in part by National Institutes of Health H‐1425(c).]

ISSN:0001-4966    

DOI:10.1121/1.1905118

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The instrument is based on Mason's research device. A composite oscillator of the Quimby‐Rose type is made by combining the author's split tube torsional barium titanate transducer with a hollow stainless steel immersible head. Strip element ultrasonic viscometers of the magnetostrictive type have been used industrially but have been found to be somewhat fragile. The new device is far stronger at any given sensitivity; moreover the construction is readily adapted to use new stable piezoelectric materials. In a modified form hot liquids can be measured and in another form, high surface displacements can be generated; this feature may be required for testing two‐phase systems incorporating large particles. Electronics require little modification for use with either strip or torsional type transducers. Remote control and indication together with computation from multiple test heads can be effected with either.

ISSN:0001-4966    

DOI:10.1121/1.1905125

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The demand for quieter machines has led to a general procedure for calculation of sound pressure levels of polyphase induction motors. The origin of the magnetic driving forces which are responsible for the motor noise, and the method of calculating the mechanical response of the motor structure, are described in this paper. A method is developed to calculate the sound pressure levels of the magnetic noise at a specified point near the motor. The paper gives numerical results of calculations, and the corresponding sound pressure levels for a particular 4‐pole, 30‐horsepower polyphase induction motor of open frame construction under different operating conditions. The agreement is unexpectedly good.

ISSN:0001-4966    

DOI:10.1121/1.1905128

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP