摘要:

Cavitation generators will be reviewed. The behavior of cavities and the consequence of such behavior will be discussed. A number of useful applications as well as undesirable effects of cavitation, will be presented and each will be associated with one or more of the consequences of cavitation. The scope and limitations of this form of energy will be covered.

ISSN:0001-4966    

DOI:10.1121/1.1930336

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Carefully filtered 250 and 500 cps tones were mixed in various phase relations, producing wave forms which are not symmetrical about the time axis. By commutating the leads to an earphone it is possible to present the resulting complex tone to the ear with a given half either a condensation or a rarefaction. Subjects attempted to distinguish between the two presentations. The 250‐cps fundamental ranged in SPL from 40 to 84 db and the 500 cps harmonic from below threshold to 73 db. For each combination of levels and phase, a random sequence of twenty presentations was used, half with the commutator in one position and half in the other. The one‐second stimuli were separated by one second of silence. The results show that subjects can not only detect a difference between the phase‐reversed signals but can identify one as “higher” or “louder” or “muffled.” The two subjects from whom most of the data were obtained responded under many conditions with 80 to 100% consistency. For some of these conditions the subjects agreed about which phase condition was higher (or louder); for others they disagreed although remaining self‐consistent. The results will be shown to have some bearing on the “best‐beat” controversy. [This work was partially supported by the Bureau of Ships.]

ISSN:0001-4966    

DOI:10.1121/1.1930342

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Three female and two male voices were taped reading sentences which were re‐recorded after being led through ten hearing aids with electroacoustic characteristics ranging from very good to poor. Normal ears and ears with varying types and degree of deafness were used. A latin square design assured proper comparisons among aids. Each listener repeated 100 colloquial sentences which were taped under a natural speaking condition, 100 under a nasal‐plus‐speeded condition, and 100 under an interrupted speech condition. Comparisons of normal and deafened groups in terms of percentage of words correctly understood show that the deafened group always did poorer even though corrective amplification was used. In most cases the hearing aids were ranked in similar orders by both groups within a speech category, but were ranked differently from the natural voice condition to the distorted conditions, especially by normals. The data have also been analyzed in terms of the minimum number of voices and types of speech distortion necessary to provide an adequate test battery for such purposes. Comparisons have been made between performance on each aid versus the many electroacoustic characteristics known for each aid. (This research is supported in part by the Office of Vocational Rehabilitation.)

ISSN:0001-4966    

DOI:10.1121/1.1930347

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Ultrasonic speed of sound and absorption measurements have been made in gaseous dibromomethane at 296°K, and at pressures between 0.5 and 15.0 mm Hg. Wide‐band transducers (solid dielectric microphone and driver) were used. A continuous selection of frequencies between 13 and 80 kc was used, generated as pulsed sine waves. Independent vibrational relaxation processes were found at 7.0 and 125 Mc/atmos, with corresponding relaxation times of 3.02×10−8and 0.146×10−8sec. A third relaxation process was not within the experimental range of the apparatus, and occurs below 0.1 Mc/atmos, with a relaxation time longer than 1.8×10−6sec. Seven of the nine vibrational modes have sufficient population at 296°K to contribute to the various relaxation processes. Primarily based upon the specific heat contributions of each mode, the assignments of the various modes relaxing at the different relaxation times were made. (Supported in part by the Office of Naval Research.)

ISSN:0001-4966    

DOI:10.1121/1.1930351

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Acoustical design will always involve a decision of the conditions required in terms of physically measurable quantities followed by design techniques aimed at achieving the required results in the final building. Studies by the authors were initially concerned with the use of acoustical models as an aid in the design techniques. The requirements for the model surfaces and two acoustical models have been studied but finally an impasse was reached when measurements sufficient for testing model similarity were not known. The response of particular listeners to music and speech in typical auditoriums and to sounds with artificially added echoes showed a reasonably broad tolerance of acoustical conditions. Different individuals had varying requirements and with program variation also the over‐all tolerance for a hall is quite large. These considerations suggest that the wealth of detail supplied by acoustical measurements is not matched by any corresponding subjective response and that further search for more critical acoustical parameters will be unrewarding.

ISSN:0001-4966    

DOI:10.1121/1.1930360

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The Ford Auditorium, designed as a multipurpose hall and completed in 1957, exhibited certain acoustical deficiencies when used as a concert hall. The reverberation time was considerably below the optimal range for orchestral music; potentially useful sound energy was dissipated in a very large stage house which had little separation from the orchestra; the organ grille of (undamped) aluminum bars resonated at note “d1”; and further problems were created by the location of the fixed organ. This paper describes steps taken recently to improve the characteristics of the hall for music. A mechanically demountable, plywood enclosure was designed with surfaces oriented to diffuse sound and distribute it to the performers and the audience. Other measures included damping of the bars in the organ grille and elimination of a large fraction of the sound‐absorptive material that was in the hall. Following modification, the reverberation time at different frequencies was increased by amounts tip to 0.6 sec above previous values. Results of the acoustical measurements and listening tests are discussed in the paper. The architect was Crane, Kiehler, and Kellogg.

ISSN:0001-4966    

DOI:10.1121/1.1930364

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP