摘要:

Criteria are suggested for ensuring the proper use of ultrasound in physical therapy and in particular for avoiding damage to patients.

ISSN:0001-4966    

DOI:10.1121/1.1907274

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907276

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907277

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907279

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Average sound attenuation and fluctuations caused by wind have been studied by transmission measurements over distances varying from 20 feet to 320 feet and with frequencies from 200 to 7000 cps. Curves showing the fluctuation as a function of distance and frequency as well as attenuation due to wind are presented. It is found that the fluctuation in the sound is practically independent of wind direction, but the attenuation depends on the wind direction.

ISSN:0001-4966    

DOI:10.1121/1.1917753

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The rigorous solution for the acoustic field due to a line source located between two planes intersecting at an arbitrary angle is presented for both planes rigid, both pressure release, and one rigid and one pressure release. Angularly stratified media cannot be treated by usual methods because the wave equation is not separable in this case. A solution can be effected, however, if the stratification is due only to changes in density. The rigorous solution for this case will also be discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917757

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

A highly flexible synthesizer, designed primarily to permit rapid and convenient exploration of certain aspects of speech synthesis will be described. It utilizes three variable tuned filters, whose inputs may be either buzz or hiss signals (or both) and whose resonant frequencies are independently controllable by signal voltages. The device was designed to facilitate the investigations of the effects of such spectrographic variants as the extent and duration of formant transitions. It is especially suited to studies in which the isolation of the significant speech cues requires the generation of long series of comparatively simple syllabic sounds which differ from one to the next only in small changes of a single pattern element.

ISSN:0001-4966    

DOI:10.1121/1.1917768

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

Although it has long been the general belief that phase distortion produces no audible effect upon speech, it is easy to set up artificial phase distortions (time delays) that do affect both quality and intelligibility. In order to be sure that the effects of filters result from their selective action upon the amplitudes of the various frequency components, and not to the phase shifts they introduce, it is important, therefore, to have an empirical test. The test was made by playing each speech sample twice through each filter to obtain the effect of two filters in cascade. A recorded word list was played through a filter and re‐recorded on a second tape. The second tape was then played through the same filter and presented through earphones to an articulation test crew of five. In half the tests, the tape was always run in the forward direction, and the phase shifts introduced by the filter and tape recorder were doubled. In the other half, the first run through the filter was made with the tape reversed end‐for‐end, and the phase shifts of the first run canceled those of the second. The two procedures were followed with high‐pass and with low‐pass commercial electronic filters set at the nominal cut‐off frequency of 1800 cps. By cascading units, we obtained cut‐off slopes of 48, 96, and 288 decibels per octave. In all, 288 articulation tests were run, each with five listeners. There was no difference at all attributable to phase distortion.

ISSN:0001-4966    

DOI:10.1121/1.1917771

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The application of a dc bias has been found to reduce the dielectric loss factor of prepolarized barium titanate. This finding has lead to the expectation that a dc bias equal to the negative peak of the driving ac field will reduce the heating effects which commonly limit the power output of thickness type barium titanate transducers. To verify this assumption both the temperature rise and ultrasonic power output of barium titanate disks have been measured near thickness resonance as a function of frequency with and without bias. Also, the onset of polarization in a biased disk which is heated by an rf field at the frequency of mechanical resonance has been determined. These measurements indicate that near mechanical resonance, both fundamental or harmonic, the effect of dielectric losses is largely over‐shadowed by the electromechanical losses associated with the motion of the transducer. It was found that under certain conditions the application of the bias increases these losses and that rather high dc fields are required to maintain polarization in the presence of the resulting high temperatures. Additional observations have revealed an electromechanical response at the second harmonic under the influence of a reversed bias. This seems to call for the same type of coupling between local mechanical strains and local domain polarization as was evidenced by earlier work.

ISSN:0001-4966    

DOI:10.1121/1.1917778

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP

摘要:

The techniques which comprise the mobility method of vibration computation are introduced into the classical impedance analogy; instead of drawing an analogous classical electrical schematic, a new set of mechanical and acoustical symbols is introduced which permits the drawing of a (classical)hydraulic schematicdirectly by cautious inspection of the structure to identify the elements and their terminals. In a mobility schematic, a straight line represents an ideal rigid massless rod; in a hydraulic schematic, a line represents a tube of unit cross section filled with ideal massless incompressible liquid which can sustain either tension or compression. Revised mobility schematic symbols are provided for mechanical and acoustical elements, and hydraulic schematic symbols for the same elements have been visualized as tubes filled with mercury or molasses, or chambers filled with methane (or air); all of these symbols resemble their analogous electrical symbols. Rigid and hydraulic junctions are distinguished by different symbols. Correct mobility schematics are obtained by inspection through considering each mass as having one terminal fixed in a frame of reference called theground, which has zero mobility and infinite mass; correct hydraulic schematics are obtained by inspection through considering each spring as having one terminal fixed in a force of reference (P0etc.) called thesky, which has zero impedance and infinite compliance (in both cases the analogous electrical element is a conducting sphere in free space, not a condenser). While it is recommended that analogous electrical circuits not be used, they can be copied directly from a mobility schematic by considering mechanical ground analogous to electrical ground, or copied directly from a hydraulic schematic by considering mechanicalskyanalogous to electrical ground.

ISSN:0001-4966    

DOI:10.1121/1.1917782

出版商:Acoustical Society of America    

年代:1954

数据来源: AIP