摘要:

The use of supersonic stationary waves for the determination of the velocity of sound in liquids is well known. With water, and frequencies of the order of 106per second, the acoustic velocity is independent of the viscosity and is the reciprocal of the square root of the product of the density and the compressibility. Stewart has shown that the solution of strong electrolytes in water alters the liquid structure of the solute and has suggested an arbitrary x‐ray diffraction method of estimating the magnitude of the change of the structure. Measurements of compressibility have been made with aqueous solutions ofNH4C2H3O2,NH4Cl, NaCl, KCl,MgCl2,CoCl2,Co(NO3)2,Co(C2H3O2)2. It has been found that the rate of change of compressibility with mole fraction of the strong electrolyte has a correspondence in relative magnitude with the rate of change. of liquid structure per mole fraction as crudely estimated by x‐ray diffraction methods. This adds evidence to the view that the structure of the water is altered by the ions.

ISSN:0001-4966    

DOI:10.1121/1.1902159

出版商:Acoustical Society of America    

年代:1940

数据来源: AIP

摘要:

Computations are carried out for typical rooms of widely different volumes having one surface completely covered with absorbing material. The object of the computations is to demonstrate the application of the theory of normal modes of vibration of rectangular rooms to delineate the range of variation likely to be encountered in the shape of the decay curves. For each of the different rooms an ideal normal impedance curve for the treated surface is computed such that the decay curves would be logarithmic and the frequency‐reverberation characteristic flat up to a certain limiting frequency. This limiting frequency depends on the dimension perpendicular to the absorbing surface. Approximate values of normal impedance of several standard acoustical materials were obtained and used in computations showing the acoustical characteristics of various rooms treated with these materials. Partial coverage of the treated surface is discussed and possible means of estimating the results from the theory of completely covered walls are suggested. The distortion of the distribution of points in frequency space caused by added absorption is discussed as a possible criterion for acoustical design.

ISSN:0001-4966    

DOI:10.1121/1.1902161

出版商:Acoustical Society of America    

年代:1940

数据来源: AIP

摘要:

Recent experimental investigations by W. Trendelenburg, H. Wullstein, W. Hartmann and F. Trendelenburg are reviewed. Three experiments on fresh calf and human larynx preparations and one on human subjects are described.W. Trendelenburg and Wullstein made simultaneous recordings of glottal lip movement, shadowgraphs of the glottal chink, and oscillograms of air vibration at various points above and below the glottis. The vocal cords constituted the moving plate of a condenser microphone for registration of the lip movements. An optical system sent a beam of light from the trachea through the glottal chink and this photographed shadowgraphs above when the cords were brought into vibration by means of a controlled current of air up through the trachea. A condenser microphone was used to record air vibrations. Plastellin forms approximating the shapes of the supralaryngeal cavities for the vowels “a” and “o” were placed above the larynx. The recordings showed that, with or without the resonators, the lip movements were essentially sinusoidal, that there was no back‐coupling between cavities and cords, that the glottis was open for a relatively short portion of the cycle, that the formant frequencies were especially noticeable immediately following the glottal opening and closure and were highly dampened during the closure phase of the glottal cycle.Hartmann bored through the side of the larynx at the level of the cords and obtained simultaneous shadowgraphs of the lateral and vertical movements of the cords. The maximum glottal opening coincided with the highest point reached in the vertical movement. After closure the downward movement of the cords continued to a minimum at about the middle of the glottal closure phase. Averages: total vertical movement = 1.25 mm; glottal opening = 1.43 mm; ratio = 1:1.15.Hartmann and Wullstein recorded glottal shadowgraphs and light density variations simultaneously. Maximum density coincided with maximum glottal opening. On the human preparation, light density decreased after the glottal closure, indicating a pressing together of the cords. When the cords were made opaque by staining, light density variations coincided with the area of the aperture.Following up the observation that formant frequencies were especially prominent immediately following the glottal opening and closure, W. Trendelenburg found subjects who were able to intone vowels so that the first cycle was essentially the same as the succeeding ones in frequency, intensity and overtone structure. The typical energy maximum coinciding with the opening phase of the glottis was again apparent in the first cycle and was named the “initial group.” Further work with F. Trendelenburg utilizing octave filters showed that it is possible to determine the time of glottal closure in any cycle of a vowel. The records from the octave filters will show two vibration groups or vibration maxima which can be related to the opening and closure of the glottis.

ISSN:0001-4966    

DOI:10.1121/1.1902167

出版商:Acoustical Society of America    

年代:1940

数据来源: AIP

摘要:

The bowing factors involved in tone production and the means of their control have been studied and measured. This makes possible a more complete understanding of their control for artistic ends. Left‐hand considerations in tone quality have also been analyzed. They likewise offer experimental bases for artistic and pedagogical procedure. The implications of these studies for the string player will be emphasized.

ISSN:0001-4966    

DOI:10.1121/1.1902169

出版商:Acoustical Society of America    

年代:1940

数据来源: AIP

摘要:

The high frequency translation losses in record reproduction which Professor Hunt has quoted from a former paper of mine apply only to soft plastic‐coated recording disks such as are used for instantaneous play‐back recording. They do not hold and are very much less on the relatively hard material of which commercial transcription records are pressed. The RCA reproducer was designed and primarily intended for use with these hard commercial pressings.With reference to the frequency characteristic which is to be adopted and which is being used for the new Orthocoustic broadcast transcription records and which Professor Hunt contends represents too much high frequency pre‐emphasis, let me say that this program was started solely with the idea of producing ultra‐high quality disks. It seems inconsistent that such a characteristic would be used if it resulted in objectionable distortion. The direct purpose in accenting the high frequency range in recording and attenuating it in reproduction is of course to reduce surface noise. Our object in demonstrating such a record at this meeting was not only to show how far the surface or background noise can be reduced but also to direct attention to the absence of distortion.As Mr. Robert Morris, of the National Broadcasting Company, indicated, the requirements for low surface noise on broadcast records are rather severe. Low distortion is not alone of paramount interest. The noise level too must be below a commercially acceptable value. This level is far below that which would be tolerated in home record reproduction. Assuming that it were possible to make a record totally free from wave form distortion the broadcasters would immediately insist on raising the recording level until the distortion was brought up to but not beyond the acceptable amount just mentioned. Thus the signal to noise ratio would be improved and no harm done.I cannot argue with Professor Hunt's calculations on distortion but think perhaps he based them upon a higher recorded level than we propose to use in Orthocoustic disks. It is intended of course that the distortion will be objectionable to no one, and for all practical considerations not audible. By this method of recording it has been found possible to make ultra‐high quality lateral transcription records which, in side‐by‐side comparison with the output from a high quality monitoring loudspeaker operating on “live” programs, defy detection, from the standpoints of frequency range, background noise and low distortion. That is all we can expect from any recording system.

ISSN:0001-4966    

DOI:10.1121/1.1902170

出版商:Acoustical Society of America    

年代:1940

数据来源: AIP