摘要:

In this paper, the partial differential equations governing the motion of plates when transverse shear and rotary inertia are considered are solved for plates bounded by parabolic cylinders. Three cases have to be considered, depending on the shape of the plate. They are:Case I:a plate bounded by two parabolic arcs (v=v1,u=u1,u= −u1);Case II:a plate bounded by three parabolic arcs (v=v1,v=v2,u=u1,u= −u1);Case III:a plate bounded by four parabolic arcs (v=v1,v=v2,u=u1,u= −u2). After converting the partial differential equations and boundary conditions into parabolic coordinates, product solutions are assumed and solutions of the resulting ordinary differential equations appear as definite integrals. The eight different types of boundary conditions entering into the theory, for each case, are satisfied by taking linear combinations of products of these definite integrals. The elimination of the arbitrary constants in each boundary problem leads to the frequency equation for the normal modes of vibration. The frequency equations for Case II and Case III are given by determinants of the 12th order equaled to zero, whereas for Case I the determinant is of the 6th order. In the classical theory, the frequency equations far Case II and Case III are given by determinants of the 8th order equated to zero, whereas for Case I a determinant of the 4th order is required.

ISSN:0001-4966    

DOI:10.1121/1.1909369

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The concept of a transducer diffraction constant as the ratio of the blocked diaphragm pressure to the incident free‐field pressure is examined for meaning, definition, and application in the general case. The concept is extended to a transmitting transducer, and a transmitting diffraction constant that is equal in value but reciprocal in concept to the conventional or receiving constant is developed from the acoustical reciprocity theorem. The relationship among the diffraction constantD, the radiation resistanceR, and the directivity factor δ is given asD2=Rδ/R0, whereR0is the radiation resistance of a simple source. The electrical analog of the diffraction constantDis found to be an ideal transformer with the turns ratioD:1. The electrical analog of a complete and reciprocal projector medium hydrophone system is presented.

ISSN:0001-4966    

DOI:10.1121/1.1909371

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The scattering of acoustic radiation by limited regions of pressure fluctuations is considered. The hydro‐dynamic equations are expanded into a hierarchy of acoustic equations of increasing nonlinearity and the first three of these is solved for the particular scattering problem. The scattered energy is given in terms of correlation functions for the pressure of two different points and for the pressure and its time derivative at two different points.

ISSN:0001-4966    

DOI:10.1121/1.1909373

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

Perturbation analysis is used to obtain expressions for the harmonic content of finite‐amplitude waves propagated in a relaxing liquid. Comparison is made with similar expressions for the nonrelaxing case. Experimental measurements were made with 2.57‐MHz rf pulses in a 0.2‐Maqueous solution ofMnSO4to test the theoretical results. Agreement is excellent for the fundamental frequency. The second‐harmonic curves have the correct shape but are 10% 15% smaller in absolute magnitude.

ISSN:0001-4966    

DOI:10.1121/1.1909375

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The phenomenon of Doppler invariance in an FM signal is discussed first. This is followed by a description of how this signal may be detected by passive sampling, a variable sampling rate being chosen to make each sample correspond to a signal peak. This results in signal folding, which reduces the total number of samples required to detect the signal. Certain characteristics of the signal are described and a formula is derived for the output of the detector when a weighting function designed to reduce the sidelobes is applied to the taps. The output is a discontinuous function because the signal is not always present at all of the taps all of the time, and the nature of this function is illustrated by means of graphs drawn for a number of typical weighting functions.

ISSN:0001-4966    

DOI:10.1121/1.1909377

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

The acoustic modes of a hard‐walled hemisphere are derived. Inside the enclosure the standing waves for the velocity potential are described byΨ(r,θ,φ)=cossin(mφ)[Plm(cosθ)]j1(ωlqrc), wheremandlare positive integers,m⩽l,cis the sound velocity,Ptmare the associated Legendre functions,jtare the spherical Bessel functions, and ωlqare the ordered radian frequencies of the allowed modes. The eigenvalues are roots of[∂∂rjl(ωrc)]r=a = 0, whereais the radius of the hemisphere. Only the standing waves for which (m+l) is even are shown to satisfy the hemispherical boundary. Implications of the results to acoustic treatment for a hemispherical room are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909379

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

It has been said that the ISO tapping machine does not yield data on representative flooring materials that accurately relate to the impact‐noise isolation provided for real, foot‐fall impacts. To understand this problem, we have measured the impact force under both the ISO hammer and a woman's shoe heel. The hammer force is found to be much more intense and generally to contain more high‐frequency components than the heel force. The differences between hammer and heel forces are found to arise from the different mechanical internal admittances and from the different approach velocities. Radiated sound levels for the measured force spectra applied to a concrete slab are calculated and found to agree closely with measured impact sound levels. We conclude that the ISO machine grossly misrepresents the impact isolation provided by some typical floor surfaces.

ISSN:0001-4966    

DOI:10.1121/1.1909381

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

In the present investigations, auditory threshold shifts for either constant or pulsed pure tones were observed while a steady or pulsed narrow band of white noise was delivered to the contralateral ear via an insert receiver. The narrow‐band masker, centered around 4000 cps, was presented at intensity levels of 50, 70, and 90 dB SPL while thresholds were obtained from the test ear at 4000, 1000, and 250 cps. The results demonstrate, first, that larger threshold shifts occur when the test signal and the masker are pulsed simultaneously than when the masker is continuous; second, that a continuous masker may be as effective as the pulsed masker if the test tone is also continuous; third, that more contralateral masking is found when the test tone and masker are close in frequency; and, last, that a small increase in the average threshold shift occurs as the intensity level of the masker increases. Several interpretations are offered in explanation of the threshold shifts for the continuous continuous and pulsed pulsed (simultaneous) conditions.

ISSN:0001-4966    

DOI:10.1121/1.1909383

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

To evaluate the possibility that one ear can be eliminated from a masking experiment by use of noise, certain relevant facts were determined. These are: (1) if a tonal signal mixed with noise is received at one ear, the addition of a noise to the other ear slightly reduces the threshold for the tone if the noises are statistically independent; (2) in contrast, the noise added to the nonsignal ear distinctly reduces the threshold for the tone if the noises are perfectly correlated (+1.0); (3) these effects, (1) and (2) above, are observed whether the level of the masking noise at the ear that receives the tonal signal is less than, equal to, or greater than the level of the added noise at the ear that does not receive the tone; (4) if identical tones are presented to the two ears and if the signal‐to‐noise ratio is about 25 dB lower in one ear than in the other, the effect of the signal at the ear with the lower signal to noise ratio is eliminated from the masking experiment.

ISSN:0001-4966    

DOI:10.1121/1.1909385

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP

摘要:

There is a long history of controversy concerning the locus and mechanism of harmonic‐distortion processes in the cochlea. This controversy has importance for theories of frequency analysis along the basilar membrane and concepts of the transduction process in the hair cells, as well as for the clinical significance of psychophysical tests of aural harmonics. The cochlear‐microphonic response to a pure tone recorded at the round window of the guinea pig was led into three wave analyzers tuned to the 1st‐, 2nd‐, and 3rd‐harmonic frequencies, each component then driving one channel of a pen recorder. The various components exhibit shifts through time, which were studied at various frequencies and intensities, and during recovery from fatiguing and damaging levels of tonal and random‐noise stimulation and anoxia. The data are discussed in terms of mechanical versus transduction concepts of harmonic distortion in the cochlea.

ISSN:0001-4966    

DOI:10.1121/1.1909387

出版商:Acoustical Society of America    

年代:1965

数据来源: AIP