ISSN:0001-4966    

DOI:10.1121/1.1906996

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906998

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906999

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Helical wire springs have been used as one‐dimensional wave models. Sections having predetermined acoustic impedance contrasts can be wound, and then attached together. The springs are suspended horizontally. Means are described for introducing various forms of mechanical pulses into the model and for detecting and recording the resultant motion at any desired position along the model. Interfering modes of wave motion are minimized by proper design and uniform winding. Such a model has been used for experimental study of a number of plane wave propagation problems, including the verification of the formulas for the reflection and transmission of plane waves at vertical incidence, pulse propagation through a section of tapered acoustic impedance, the reflection of a pulse by a thin layer of relatively large acoustic impedance contrast, and the change in form of a pulse with time as it travels through a medium of low but finite absorption. It is concluded that the helical spring model can be used as an analog computer for many problems in plane wave propagation in applied seismology.

ISSN:0001-4966    

DOI:10.1121/1.1917549

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

There is a large amount of data in the literature describing the temperature effects on the dielectric and piezoelectric constants of barium titanate. This paper, however, describes the temperature effects on the admittance of barium titanate transducers operating near resonance. Both pure and leaded ceramic mixtures are compared over the 0°–20°C temperature range. Despite extreme fluctuations of the dielectric and piezoelectric constants over this temperature range, it is possible at a certain frequency near resonance for both the transducer conductance and susceptance to vary very little with temperature. Air and water admittance circle diagrams, sensitivity‐frequency, and efficiency curves—all plotted against temperature—are presented and analyzed from an equivalent circuit point of view. One of the significant conclusions derived from this experiment is that the radiated power of a transmitting transducer, properly matched to its source at this optimum frequency, will remain maximized regardless of the temperature variation. While the barium titanate temperature effects were studied for given underwater transducers, the information outlined is of value to anyone encountering temperature variations in a resonant barium titanate ceramic.

ISSN:0001-4966    

DOI:10.1121/1.1917554

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A new apparatus for investigation of sound propagation constants for large amplitude audiofrequency vibrations in metals is described. One novel feature of the apparatus is the use of tuned resonant supports that are tilted with respect to the specimen. The tilting minimizes the tendency to chatter due to the Poisson effect. Because the supports are driven at their resonant frequency, large amplitudes may be achieved without the occurrence of an energy loss due to slipping at the contact surfaces between supports and test specimen. Auxillary equipment permits determination of the resonant frequency of the specimen to better than 1/1000. The error in the determination of the logarithmic decrement varies between 2 percent and 5 percent. The error caused by energy dissipation due to the internal friction of the support is, in most cases, negligible. In those cases where it is not negligible, it can be closely estimated and corrected for. Preliminary results for 61S‐T6 aluminum alloy show the decrement to vary as the14power of the stress amplitude.

ISSN:0001-4966    

DOI:10.1121/1.1917558

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Single keys of a concert‐grand piano were actuated by an automatic mechanical blow‐striker. Magnetic tape recordings were made of the piano tones in Music Hall (Cincinnati), with the recording microphone located at selected positions on the concert stage and in the auditorium. A similar recording was made in an anechoic space used for acoustical measurements on pianos. High speed level recordings of the magnetic tape output reveal significant differences in scale balance at the various positions. Spectrum analyses of selected tones were also recordedvstime for the different microphone locations. The recordings show that room reverberation greatly affects the tone‐wave envelope and that piano directional characteristics influence the spectrum of the tone to a limited extent.

ISSN:0001-4966    

DOI:10.1121/1.1917566

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The materials and structures problems associated with the construction of aircraft noise silencing systems often make classical solutions to the acoustic problems extremely difficult. The associated problems of fluid mechanics and physical construction must be carefully considered along with acoustical requirements at the time of initial design. A review of some of these problems specifically associated with various types of aircraft engines will be discussed. Similarly, the various types of acoustical material suitable for broad‐band attenuation will be considered from their structural standpoint.

ISSN:0001-4966    

DOI:10.1121/1.1917573

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A noise control project has been completed by Northrop Aircraft, for the ground testing of the F89 airplane. Phases described include the prediction of performance, acoustical design considerations, correlation of acoustical and thermodynamic requirements, general construction, acoustical tests during construction, noise survey around the exposed airplane, and neighborhood survey around the completed installation. This noise suppressor is comparatively simple and inexpensive, requires no water cooling even for afterburner operation, and has proved adequate in terms of neighborhood relief and protection of operating personnel.

ISSN:0001-4966    

DOI:10.1121/1.1917580

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Routine calibration of an accelerometer is performed by comparing the open circuit voltage output of the unknown with the output of a laboratory standard which has been calibrated as described in the previous two papers. This comparison is performed with both accelerometers excited simultaneously in a special double‐ended vibration exciter. The construction of the special vibration exciter and the precautions taken to ensure that both accelerometers are exposed to the same vibration are described. The double‐ended vibration exciter is also used in part of the reciprocity calibration of laboratory standard accelerometer.

ISSN:0001-4966    

DOI:10.1121/1.1917591

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP