摘要:

The motivation of the research described was to investigate the behavior of a masking transient that indicates that masking of a short signal pulse by a longer white‐noise burst is stronger at the beginning of the masker burst than later. The threshold of signal pulses masked by masker bursts was measured as a function of different variables such as bandwidth and center frequency of the signal, delay between onset of masker and onset of signal, duration of signal and masker, level of masker, and repetition rate. The results reveal very little “overshoot” of the threshold of short pulses as a function of theONtime of the masker if the signal and the masker have the same or similar broad spectra. The overshoot increases up to 13 dB as the bandwidth of the signal decreases down to that of a tone. The size of the “overshoot” and the prior excitation seem to be related to each other. Taking this in account, the thresholds under different conditions can be calculated on the basis of detection models. The measured and the calculated values are in good agreement.

ISSN:0001-4966    

DOI:10.1121/1.1909389

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Solions are electrical components involving charge transport by solution ions as contrasted to electrons, holes, or gas ions. Four general types of solion acoustic transducers may be distinguished on the basis of mechanism underlying the transducer action. One of these, the polarized cathode type, offers a combination of advantages, which includes low threshold pressure, high power gain, stable zero, and direct‐current transmission. Individually constructed models with a nominally linear pressure response have been used successfully in the study of infrasonic disturbances transmitted through the earth and atmosphere as well as under water. Yet, design and construction methods have not previously been perfected to a degree that would ensure wide usage. The relatively sluggish motion of the charge carriers in the electrolyte of the transducer is at the same time a necessary condition for transducer action and a factor limiting the dynamic response. A theoretical analysis is presented to explain the observed behavior of the existing devices of this type and to indicate what may be expected from transducers having the benefit of more‐refined fabrication techniques.

ISSN:0001-4966    

DOI:10.1121/1.1909391

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The acoustical nature of the head joint of a transverse flute is examined in mathematical detail. The effective length of the flute is altered in the amount by an embouchure correction Δlc= (c/2πf) arctan{(e/2π) (f/r)/(2fr2 − f2)}, wherefis the playing frequency,eis the speed of sound in the contained air,rthe (17‐mm) cork‐to‐embouchure distance, andf1a parameter (near 1450 cps which is essentially the frequency of a Helmholtz resonator made by plugging the bore with a second cork a distancerbelow the embouchure. This correction is roughly constant at 42 mm over the normal playing range. Effects of cork position, lip position, and embouchure‐hole size are discussed in detail, as is the effect of cavity resonances in the player's own mouth. Tuning errors caused by the edgetone‐regeneration mechanism are shown to be correctible by a head joint taper perturbation. Three designs are analyzed, which produces a flattening at low frequencies, zero effect near 600 cps, and a maximum sharpening near 1000 cps. Above, this the correction returns smoothly to zero at the upper playing limit near 2000 cps. In the high register, the correction is produced jointly by the taper and the vent holes. The whole analysis is summarized by means of a detailed comparison of the Boehm design of flute with the older cylindrical‐head, taper‐bore model and with the purely cylindrical flute.

ISSN:0001-4966    

DOI:10.1121/1.1909393

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Speech‐intelligibility scores as a function of noise level are studied for face‐to‐face, sound‐powered‐phone, and amplified speech (earphone and loudspeaker) communication conditions. The speech‐interference level (SIL) for octaves of noise centered at 500, 1000, and 2000 cps (0.5/1/2) is used as the measure of noise level. By using this noise measure, much of the work in this field can be brought together and interpreted. It is noted that “noisy” and “very noisy” spaces are associated with SIL's such that “shouting” or “very loud” voice levels (or 95‐dB speech levels) are required for conversations at 1.5 or 3 ft, and this is the region where telephone conversations are judged to be “difficult” or “unsatisfactory.” All of these adverse noise conditions occur at the region where ear protection will aid intelligibility and at the boundary where ear protection should be used to protect against hearing losses. Where people must converse or communicate via some interior communication device, 0.5/1/2 SIL's above 70 dB should be avoided. At 0.5/1/2 SIL's greater than 90 dB, the wearing of hearing protection should be made mandatory and every noiseproofing technique (except a noise shield for the microphone) should be employed. At 0.5/1/2 SIL's above 100 dB, every noise‐proofing technique should be employed

ISSN:0001-4966    

DOI:10.1121/1.1909395

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Experimental data on sound velocity illustrate the unusual velocity‐temperature relationship of near‐stoichiometric nickel‐titanium alloys. The effect of temperature cycling, annealing, pressure, minimum exposure temperature, and time is also shown.

ISSN:0001-4966    

DOI:10.1121/1.1909397

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The current theory of Rayleigh and stochastic scattering in polycrystalline materials is reviewed and compared with (1) former theory and (2) experiment. Rayleigh scattering giving ultrasonic attenuation equal toSTf4(Sis the Rayleigh scattering factor,Tthe average scattering volume,fthe frequency) occurs when λ>2πD̄(λ is the wavelength,D̄the average grain diameter); stochastic scattering yielding ultrasonic attenuation equal to ΣD̄f2(Σ is the stochastic scattering factor) occurs when λ<2πD̄. The average scattering volume and average grain diameter must be evaluated by taking their averages over the grain‐size distribution in the metal. When this is done, the current theory accounts rather well for the scattering component of the ultrasonic attenuation in polycrystalline metals. Former theory underestimated the scattering. A tabulation is made of the scattering factorsSand Σ in various materials. The computed scattering factors show that polycrystalline samples of the following materials should have low attenuation: aluminum, chromite, chromium, magnesium, magnetite, silicon strontium nitrate, tungsten, vanadium, and YIG.

ISSN:0001-4966    

DOI:10.1121/1.1909399

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Ultrasonic‐attenuation measurements have been made on fine‐grained specimens of several metals. The grain‐size distributions and ultrasonic velocities in these metals were also determined. The experimental attenuation is in good quantitative as well as qualitative agreement with current theory. Nickel and three iron alloys, one 30% nickel reported previously, the second 12% chromium (type 416 stainless steel), and the third 17% chromium and 1% carbon (type 440‐C stainless steel), all gave good results. Brass also gave good results, but copper showed much twinning, which as yet is unaccounted for.

ISSN:0001-4966    

DOI:10.1121/1.1909401

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Vibrational relaxation times in pure oxygen have been measured over the temperature range 100°–200°C. An anomalously rapid decrease in the relaxation time is observed for temperatures above 150°C, confirming earlier conclusions based on a comparison of theory and experiment [J. G. Parker, J. Chem. Phys.41, 1600–1609 (1964)]. This decrease in the vibrational relaxation time may be interpreted as a transition in oxygen from a low‐temperature state to a high‐temperature state, although the exact nature of the physical mechanism underlying this transition remains obscure.

ISSN:0001-4966    

DOI:10.1121/1.1909403

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

A numerical solution of the Kirchhoff equation for the propagation constant of longitudinal sound waves in infinitely long cylindrical tubes has been obtained. The solution, which avoids the wide‐tube approximations, shows that the percentage errors in the von Helmholtz‐Kirchhoff tube velocity correction and tube absorption are both roughly equal to the percentage the velocity correction is of the free‐space velocity. The error in the von Helmholtz‐Kirchhoff equations can be plotted as a function offD/a,pD/ηa, and γ. (fis the sound frequency,Dthe tube diameter,athe free‐space velocity,pthe gas pressure, η the viscosity, and γ the ratio of specific heats.) Recent absorption measurements in Ar are in agreement with values calculated numerically, but measured velocities indicate the need for considering molecular slip at the tube wall. Thermal relaxation is introduced into Kirchhoff's basic equation by using the Eucken relationk/coη − (9γ−5)/4and considering γ to be the ratio of complex relaxing specific heats. Viscothermal and relaxation effects are found to be additive only if the frequency is near the cutoff frequency for the first unsymmetric mode and thef/pvalues do not extend to the megacycle/second atmospheres range.

ISSN:0001-4966    

DOI:10.1121/1.1909405

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In conventional dynamic‐thermoelastic problems, the heating rates are sufficiently slow so that the inertia terms in the equations of equilibrium are negligible and time enters as a parameter from the transient temperature in the body. In modern technology, however, one has encountered extremely high heating rates and it is necessary to reexamine the role of inertia. To this end, studies of extremely massive bodies and extremely slender bodies under rapid heating conditions have been made by others. In the former, thermal stress‐wave propagation without reflection was examined; in the latter, thermally induced vibrations were considered. It is now of interest to examine the effect of inertia in a rapidly heated body whose dimensions lie between these extremes. As an example, we consider a hollow sphere of arbitrary thickness subjected to a step change of temperature on its inner surface. In the solution, the propagation and reflection of thermal stress waves in the sphere are observed. For comparison, the results of the conventional analysis are obtained as a special case. After passing to appropriate limits, the results are compared to the results of the previous analyses of slender and massive spherical regions.

ISSN:0001-4966    

DOI:10.1121/1.1909407

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP