摘要:

In recognition of the need for a better high‐intensity acoustic source capable of simulating rocket engine noise and in‐flight aerodynamic noise, Lockheed conducted an experimental program during 1966 in an attempt to develop such a source. Most of the experiments performed were of a “Combustion Modulation” principle whereby acoustic energy is produced through control of the reactants in a combustion process. Peripheral tests were made including attempts to modulate low‐volume air flow. In one peripheral experiment, a discovery was made that a worthwhile acoustic source is achieved when a stream of hydrogen and oxygen in detonatable proportions is subjected to a repeating electrical spark. Sonic pulses are produced at the frequency of the spark repetition rate. The device, called the “sonic detonator,” promises early application as a source of high‐intensity, high‐energy acoustic pressure. The paper describes the tests performed and results achieved.

ISSN:0001-4966    

DOI:10.1121/1.2144244

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The excessive heat development on the exterior structure of hypersonic reentry vehicles necessitates the use of heat‐resistant pressure transducers for the measurement of boundary layer pressure fluctuations on the vehicle's surface. An appropriate acoustic probe configuration was developed and tested in windtunnel experiments. The frequency response of the probe configuration to flow excitation was studied under subsonic (M = 0.055) and supersonic (M = 2.92) flow conditions and was found to depend both on the probe interior geometry and on the physical characteristics of the flow. In addition, the influence of heat‐shield ablation on the frequency response was studied under these same conditions. Widnall and Lyon's theory of the dynamics of the probe in the presence of hypersonic flow was confirmed by the experimental findings. [This work was sponsored by the Space and Missile System Organization.]

ISSN:0001-4966    

DOI:10.1121/1.2144251

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

In Part 1, university students enrolled as music majors served as subjects to determine discrepancies between frequencies of pure tones presented through either a bone oscillator or earphones (monaurally and binaurally) and the fundamental frequency of vocal limitations of pitches of the pure tones. All vocalizations were recorded on magnetic tape and analyzed to determine fundamental frequency. In Part II, pure tones were presented at one of two intensities through a bone oscillator placed on the mastoid bone and matched in pitch with a pure tone (variable in frequency by the subject) presented through earphones (monaurally and binaurally). Discrepancies of responses in hertz from the stimulus were recorded by the examiner. Results indicated minimal differences among responses to stimuli through the bone oscillator and monaurally and binaurally through earphones. However, an increase in intensity of the stimuli through the bone oscillator raised the matched frequency of pure tones through the earphones presented either monaurally or binaurally. An increase in intensity of stimuli presented binaurally through the earphones lowered the fundamental frequency of vocal limitations of those pitches. Analyses of pitch matching responses to other stimulus conditions were also computed.

ISSN:0001-4966    

DOI:10.1121/1.2144259

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The purpose of this experiment was to plot equal pitch‐modulation contours as statistical functions of duration, direction, and extent of frequency modulation. Twenty college students listened to 66 quasipure tones each of which was a combination of one of six durations (40–1000 msec) and one of 11 extents of modulation (−10 to +10 semitones). Duration and direction as well as extent of frequency modulation affected pitch modulation as evaluated by a method of magnitude estimation. A regression line was fitted to the listeners' responses plotted on a coordinate of pitch modulation (psychological) and frequency modulation (physical) for each combination of duration and direction. Expected mean values on the regression lines rather than the actual mean values were used to plot the contours for each extent, duration, and direction. The nearest but significantly different mean values from the expected mean of zero were used to determine the thresholds of pitch modulation. The distance between the threshold value and zero mean was determined by calculating confidence intervals for the expected mean values of zero by using the variance of the observed data.

ISSN:0001-4966    

DOI:10.1121/1.2144261

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

This paper discusses the bandwidth requirements for accurate estimates of cross‐spectral density. The common way to reduce the statistical fluctuations occurring in measurements of auto‐and cross‐spectral density is to increase the analysis bandwidth and accept the resulting decrease in resolution. For cross‐spectral estimates, however, there is a danger that the estimates will be low, low by perhaps orders of magnitude, if the analysis band is too wide. The band must be so narrow that both the phase angle and the magnitude of the cross spectrum remain relatively constant over the band. Because of the phase requirement, estimates of cross spectra usually require narrower bands than do autospectral estimates (which are insensitive to phase). This limitation is common to both digital and analog estimates. Several case histories are discussed where errors resulted from excessively wide bands. The bandwidth limitations associated with several physical systems are discussed in terms of phase velocities. It is shown that estimates of ocean‐wave cross spectra require that the bandwidthdecreasewith increasing frequency. Finally, it is shown how the errors can be reduced by use of phase equalization.

ISSN:0001-4966    

DOI:10.1121/1.2144267

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

A brief review of Powell and Stetson's original work on vibration holography [R. Powell and K. Stetson, J. Opt. Soc. Am.55, 12 (1965)] will be given and the mathematics discussed for determining the relative displacement of the transducer surface from the vibration hologram. Experimental results of tests of a prototype sonar transducer (several models) using holographic interferometry are given. Hologram vibration patterns at various drive frequencies will be shown and corresponding displacement or flexure diagrams shown. Experimental comparison of unloaded (in air) and loaded (in water) operation [R. M. Grantet at., “Underwater Holography,” J. Opt. Soc. Am.56, 8, 1142 (1966)] will also be given. The feasibility of predicting performance under loaded operation from unloaded holographic measurements will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2144277

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP