摘要:

The detectability of auditory signals in reproducible random noise was studied under two conditions: a single noise used throughout a block of 288 trials, and 12 noises occurring at random, but with equal frequency, throughout a block of trials. Both two‐interval forced‐choice judgments and judgments of the presence or absence of the signal in single‐noise samples were obtained in separate blocks of trials. On individual trials of the forced‐choice judgments, the same noise appeared in both intervals. Signal detectability was found to be significantly better when a single noise was present in a block of trials. Introducing variability in the stimulus by altering the number of different signal levels presented during a block of trials did not affect detection. The results support the importance of memory for the noise from trial to trial in the detection process.

ISSN:0001-4966    

DOI:10.1121/1.1910856

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Acoustic impedance at the eardrum was measured on three subjects as a function of frequency (20 cps to about 1000 cps) and intensity (minimum 65 dB SPL; maximum 150 dB SPL, at eardrum) of a sustained ipsilateral sinusoidal stimulation by means of an inversely driven Zwislocki acoustic bridge. At lower intensity levels, acoustic impedance was independent of level, resistance and reactance varying with frequency according toR = af−1/2andX = bf−3/4, respectively, from 20 cps to about 300 cps; above 300 cps, resistance remained essentially constant, and negative reactance decreased rapidly. At higher levels, one subject showed variations in impedance attributable to the acoustic reflex. At levels above 120 dB SPL, all subjects showed a rapid decrease of both impedance components at all frequencies. Middle‐ear attenuations calculated from the magnitude of the acoustic impedance, together with previously obtained equal‐loudness contours for the participating subjects, support the hypothesis that equality of loudness between two tones is attained when both generate the same total number of neural impulses within about 200 msec. The decrease in impedance at the highest levels is attributed to subharmonic radiation from the eardrum and/or a shift in the axis of rotation of the ossicles.

ISSN:0001-4966    

DOI:10.1121/1.1910857

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Three assumptions constitute the basis for a research program of which this study is a part. Vocal fry (1) is a normal mode of laryngeal production; (2) it consists of a register of very low fundamental frequencies, and (3) it consists of a train of relatively discrete laryngeal pulses with nearly complete damping between successive glottal excitations. In order to obtain perceptual evidence relevant to the latter point, listeners were asked to match the repetition rate of a variable pulse train (electronically produced) to the fundamental of eight samples of vocal fry. The resultant data supported the hypothesis that repetition rate can be successfully assigned to vocal fry. In addition, evidence was obtained indicating that vocal fry occurs within a low‐frequency phonatory register, is perceived similarly in relation to single or double glottic pulses, and is regular, rather than aperiodic, in nature.

ISSN:0001-4966    

DOI:10.1121/1.1910858

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Sound absorption and velocity measurements have been made inCO2/D2Omixtures at 300°, 400°, and 500°K. The results show thatD2Ois from13to15as efficient asH2Oin de‐exciting the bending‐mode vibration ofCO2in a molecular collision. The collision efficiency ofD2Ofor de‐excitingCO2decreases with temperature at an even greater rate than does that ofH2O. The large difference betweenD2OandH2Oinvalidates the chemical affinity explanation of effect ofH2OonCO2. An approximate semiclassical calculation of the transition probability indicates that it is possible to attribute the relaxation to an interchange between the vibration of theCO2and the rotation of theH2OorD2O.

ISSN:0001-4966    

DOI:10.1121/1.1910859

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A perturbation expansion is formulated for the one‐dimensional, nonlinear, acoustic‐wave equation with dissipative term describing the viscous and thermal energy losses encountered in a rigid‐walled, closed tube with large length‐to‐diameter ratio. The resulting set of iterative, linear equations is solved for a finite‐amplitude standing wave. Solutions lead to a steady‐state distribution of harmonics of the fundamental, the amplitude and phase of each term being strong functions of frequency and the absorptive process. Necessary features of the approach include characterizing all absorptive processes by a bulk absorption coefficient and requiring a boundary‐layer depth much less than the tube diameter. The solution, while strictly limited to the preshock régime, can be used to predict certain features of the onset of shock. Intense longitudinal standing waves were generated within a rigid‐walled tube of 6‐ft length and212‐in.diam. The tube contained air, at ambient pressure and temperature, which was excited into vibration by a piston at one end. A microphone at the rigid end of the tube was used to observe the pressure as a function of time. For input frequencies around either the fundamental or the first overtone of the tube, the amplitudes of the second and third harmonics of the finite‐amplitude wave were in excellent agreement with the predictions of the theory. Waveforms reconstructed from the predicted amplitudes and phase angles of the solution compared very well with the observed microphone output. An extension of the theory to the shock régime provided qualitative agreement with observations of the frequency dependence of both the intensity needed to produce shock and the phase of the onset of shock.

ISSN:0001-4966    

DOI:10.1121/1.1910860

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Measurements have been made of the absorption of sound in air as a function of humidity in the frequency range from 2500 to 8000 Hz at pressures in the range from 0.2 to 0.9 atm, at a constant temperature of 20°C, employing measurement techniques of an earlier study at atmospheric pressure. The results show that, at a given frequency, a plot of molecular absorption versus humidity has a maximum value that is independent of pressure in the range of pressures from 0.4 to 1.0 atm. The effect of lowering the pressure is to shift the peaks in the curves of absorption versus humidity to lower values of relative humidity.

ISSN:0001-4966    

DOI:10.1121/1.1910861

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The linearized transverse vibrations of a moving thin rod between two supports is investigated. Since the governing differential equation in the steady state is not self adjoint, the vibration frequencies and mode shapes are obtained via infinite systems of simultaneous equations using the mode functions of the corresponding stationary rod. Detailed calculations are performed for both end supports fixed and for both end supports simply supported. The energy of vibration is also investigated.

ISSN:0001-4966    

DOI:10.1121/1.1910862

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Longitudinal vibration of a bar of general taper is analyzed subject to the inclusion of the effect of Poisson's ratio. The resulting differential equation may be used to treat bars of general taper. Numerical results are presented for bars of conical taper. It is found that if the length of the bar exceeds the diameter then inclusion of a value of Poisson's ratio equal to 0.3 leads to the prediction of fundamental resonant frequencies and velocity gains that are only a few percent less than the predicted values that result when Poisson's ratio is ignored.

ISSN:0001-4966    

DOI:10.1121/1.1910863

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Time‐average statistics of the response of the bilinear hysteretic system to an excitation with approximately white‐power spectral density and approximately Gaussian probability distribution are determined, using electronic‐analog techniques. Results are presented for the mean‐squared amplitude, the power spectral density, and the probability distribution of the response. The applicability of the Krylov‐Bogoliubov method of equivalent linearization to this problem is investigated by comparing predicted and experimentally measured values of the mean‐squared level of response.

ISSN:0001-4966    

DOI:10.1121/1.1910864

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

The equation of mean power flow between two groups of randomly excited oscillators is derived from first principles. Subject to the coupling satisfying certain requirements, it is shown that a new parameter—the average natural frequency shift of the oscillators owing to the coupling—determines the power flow between the two groups. Power flow is directly proportional to the natural frequency shifts and to the oscillator densities (modal densities) in each group. It is suggested that this formulation has advantages over the conventional “coupling‐loss‐factor” equation of the statistical energy approach to noise‐transmission problems.

ISSN:0001-4966    

DOI:10.1121/1.1910865

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP