摘要:

Simple expressions are derived for the acoustic radiation forceFon a small rigid sphere of radiusa, volumevand density ρ suspended In a liquid or gas of density ρ0. Effects of viscosity are neglected; use is made of methods developed by King and Embleton. Results are expressed in terms of the time‐averaged densitiesT̄aandV̄aof kinetic and potential energies, respectively, in the incident sound field. Letting β be ρ0/ρ it is found. as an approximation whenais much less than the sonic wavelength, thatF = v[B∇T̄a − ∇V̄a]+Δ,B− 3 1 − β /(2+β), where Δ is given by a relatively complicated expression. The quantity Δ is important primarily in progressive waves of relatively uniform amplitude, as exist in the field of a large source; here ∇T̄aand ∇V̄a, may be relatively small while gradients of the phase exist. In a standing wave or in the neighborhood of a small source, Δ is negligible. When Δ = 0, the above expression forFagrees with one given previously by Gor'kov.

ISSN:0001-4966    

DOI:10.1121/1.1910702

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

An investigation of the sound field in a large reverberation room as influenced by a 2 in. mineral wool floor covering and or an array or 96 suspended plywood panels yielded significant results. The panels do not increase the decay rates, that is, their absorption is negligible, for frequencies below about 250 cps; their added absorption to the room increased progressively at higher frequencies to 24 sabins at 4000 cps. Decay rates for low‐frequency single modes in the empty room were linear and ranged from 2.11 to 5.7 dB/sec; the decay rates when two contiguous modes were excited were very nonlinear; their contours were predicted in terms of the decay rates and the phase differences of the two modes. With the floor absorptive, the 96 panels reduced the maximal levels of impulsive sounds (pistol shots), at frequency below 250 cps.s, for all elevations above the floor; the average decrease was 4.6 dB. With the floor absorptive, the decay rate at 250 cps was only 6.2 dB/sec when source and microphone were in the upper part of the room, and 39.3 dB/sec when source and microphone were in lower part. The influence or these decay rates on the quality of recorded speech and music was shown to be large.

ISSN:0001-4966    

DOI:10.1121/1.1910703

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The audibility threshold performance of the human ear submerged in water at ear depths of 12 and 35 ft was compared to its performance in air. Threshold SPL's at 125, 250, 500, 1000, 2000, 4000, and 8000 Hz from five male and three female divers wearing open‐circuit SCUBA equipment were obtained by the Békésy technique. Differences between water and air conduction thresholds ranged from 18 dB SPLre0.0002 μbar at 125 Hz to 56 dB at 8000 Hz. Underwater thresholds ranged between 58 and 74 dB SPL, with maximum sensitivity around 500 Hz. Maximum sensitivity for air conduction thresholds was obtained at 2000 Hz. Slightly higher thresholds were obtained at the 35‐ft ear depth than at the 12‐ft depth. Tentatively, the data suggest the importance of bone‐conduction mechanisms in underwater hearing. However, it is apparent that further research must be carried out before it will be possible to predict the character and mechanism of the human ear submerged in water.

ISSN:0001-4966    

DOI:10.1121/1.1910704

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Threshold signal‐to‐masker ratios were obtained or a 1000‐Hz signal presented with either an identical frequency sinusoidal masker or a complex masker consisting of the same frequency as the signal plus two sidetones 300 Hz on either side of the central component. Data considered include signal durations of 20, 400, and 1000 msec with masker durations either equal to that of the signal or continuous for the block up‐and‐down, two‐interval, forced‐choice threshold run. The parameters of primary interest were the level of the masker and whether the masker was gated or continuous. The thresholds appear to indicate that when the excitation pattern of the masker is increased (by shortening its duration or adding sidetones) so as to equal or surpass that of the signal, masked thresholds tend toward an inverted‐Nfunction, as related to masker level, rather than being independent of masker level. Also, differences between the gated and continuous masker thresholds do not appear to be related to changes in signal uncertainty as reflected in the slopes of psychometric functions.

ISSN:0001-4966    

DOI:10.1121/1.1910705

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

The detectability of a monaurally presented 500‐cps signal was measured at each of several values of interaural correlation for a wide‐band noise masker. The results, when expressed in terms of masking‐level differences (MLD's), are in agreement with data reported by Whitmore and Wilbanks and show a function of similar form to that described by Robinson and Jeffress. Additionally, the detectability of a monaural signal was investigated as a function of the interaural intensive relations of a wide‐band noise masker. The data are in agreement with results originally shown by Hirsh, and since, replicated several times. That is, detectability is greatest when the level of the noise masker at the two ears is equal, and decreases as the level of the masker at the nonsignal ear is attenuated. The data are used to estimate parameters for a simple model that attempts to account for changes in detectability that occur when a monaural signal is presented with binaural, correlated noise having an interaural level difference. The model proposes that at low external noise levels, internal noise leads to a decrease in interaural‐noise correlation. Predictions from the model are in reasonable agreement with data reported previously.

ISSN:0001-4966    

DOI:10.1121/1.1910706

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Four experimental methods are described in a tutorial way for use with a laser interferometer in measuring vibrational displacements and mode shapes of a transducer face. The relative merits and experimental difficulties of the methods are discussed. Quantitative data to show the type of experimental agreement that one might expect between the various methods and two illustrative mode shape measurements are given. In general, by proper choice of one or more of the methods, displacement measurements of magnitude 0.1–6000 Å at sonic and ultrasonic frequencies can be made at a point 0.1 mm in diameter. Mode shapes are determined simply by moving the laser beam a measured distance between points. Displacement data presented show a random error for all methods of 5% in the range 0.5–80 Å and less than 5% above 80 Å.

ISSN:0001-4966    

DOI:10.1121/1.1910707

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Many physical principles have been applied to transform atmospheric pressure fluctuations of 1 sec and longer into electrical signals for the purpose of monitoring infrasonic signals. A survey of some infrasonic sensors is taken, with calibration and testing of several sensors at the UCLA calibration facility. An attempt was made to define the capabilities of each available sensor. Several experiments are described, which include the monitoring of static and dynamic firing of rockets, as well as the monitoring of explosions. The difficulties in interpretation of data are explained in relation to various instruments, taking into account wind effects, ground vibrations (observed by magnetometers), natural pressure fluctuations, and other phenomena producing noise at the frequency range of interest.

ISSN:0001-4966    

DOI:10.1121/1.1910708

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Large quantities of ultra low‐frequency acoustic data accumulated over long periods of time can be analyzed by several methods. Preliminary analysis of the analog waveform determines specific areas of primary interest prior to digital‐computer analysis. Data of no consequence can be discarded; or, the worth of such data may be graded, to scale their importance for computer processing. This technique also provides a means of expediting initial findings, and primary conclusions can be deduced. This study was conducted by the University of California, Los Angeles, and entitled, “Ionospheric Disturbance Experiment.” The raw tape‐recorded data are played back through an electronic system. Some important parts of this system are narrow bandpass filters and a Missilyzer (sound spectrograph). Some sample results are summarized.

ISSN:0001-4966    

DOI:10.1121/1.1910681

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Geo‐acoustical and geomagnetic data gathered by an array of sensors for long periods of time were recorded on magnetic tape in frequency‐modulated form. A new digitizing system was worked out for an accurate study, then data were reduced and adjusted (or “recolored” in the time domain) using a numerical‐analysis technique, which corrects for frequency attenuation due to the frequency‐response characteristics of the sensor and field recording equipment. Wavelength and wave velocity depended on frequency and statistical error estimated from study of the F‐1 engine. The mathematical techniques involved in recoloring and filtering are explained, and the statistical techniques (autocovariance, cross covariance) used in the time‐series analysis are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1910682

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP

摘要:

Analysis of the responses of a flush‐mounted transducer system to the pressure field in a turbulent boundary layer and to the boundary pressure field induced by an incident plane acoustic wave is formulated and discussed. The transducer system is considered as a spatial and a spectral filter. The properties of the filters are defined and illustrated for the case where the system consists of nominally identical transducers. The analysis is limited to geometries where the centers of the transducers are regular y placed at the centers of a plane rectangular grid. Time delays between transducers are allowed for in this analysis.

ISSN:0001-4966    

DOI:10.1121/1.1910683

出版商:Acoustical Society of America    

年代:1967

数据来源: AIP