摘要:

A carbon microphone is shown to have 5 dB less low‐frequency sinusoidal output than a magnetic microphone, both judged to have approximately the same voice output level and tonal quality. Evidence is offered to show that the sinusoidal characterization of a carbon microphone does not properly describe its response to a complex, wide‐band signal having a high peak factor, such as speech. This results from a greater‐than‐unity slope for the input‐output curve of the carbon instrument. An improved characterization for estimating the subjective performance with speech input was obtained with an excitation signal consisting of a sinusoid plus white noise, the latter being filtered from the output. With this technique, the response curves for the two microphones became comparable and reasonably similar. This information is particularly important for testing carbon microphones designed to have a steep input‐output characteristic to exclude farfield sounds.

ISSN:0001-4966    

DOI:10.1121/1.1913380

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In two experiments on normals we presented CV nonsense syllables both dichotically and monotically, with onsets of the syllables separated by 0, 15, 30, 60, and 90 msec (first experiment) and 0, 90, 180, 250, and 500 msec (second experiment). We found that when one of the CV's trailed the other by 30–60 msec, the trailing CV became more intelligible than when it was given simultaneously; the leading syllable's intelligibility dropped from its “simultaneous” level when leading by 15 and 30 msec. The leading message was more intelligible between 15 and 250 msec when the two channels were mixed monotically. In the dichotic simultaneous conditon, voiceless consonants were more intelligible than voiced, especially in voiced‐voiceless pairs. When the voiced CV trailed the voiceless CV, the former became almost as intelligible as its voiceless counterpart. A left hemisphere “speech processor” was postulated, with suppression of information from ipsilateral sources during contralateral stimulation. The postulated “speech processor” may be involved in acoustic‐signal‐vocal‐tract control functions.

ISSN:0001-4966    

DOI:10.1121/1.1913381

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Electromagnetic leakage or cross talk between transmitter and receiver represents a severe limitation on the usefulness of continuous‐wave (CW) ultrasonic methods at high frequencies. The problem of leakage is, however, entirely eliminated by use of a scheme known as the sampled‐CW technique. The role of the sampled‐CW technique in eliminating leakage is explicitly demonstrated by contrasting the results of CW and sampled‐CW measurements under a variety of conditions.

ISSN:0001-4966    

DOI:10.1121/1.1913382

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The velocity and absorption of ultrasound at 19.5 MHz were studied as a function of the concentration in binary solutions of pyridine with water, methanol, and ethanol. In addition, the compressibility and volume viscosity were calculated. Molecular processes are suggested to explain the variation of the ultrasonic properties of these binary solutions with respect to concentration.

ISSN:0001-4966    

DOI:10.1121/1.1913383

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An incident scalar plane wave is scattered from a surface, corrugated in one dimension, and given by an infinite number of periodically spaced semi‐infinite parallel plates of zero thickness (thin plates). The surface is a parallel‐plate grating. An additional plate is placed between two adjacent (in period) plates, thus dividing the periodicity interval into two regions, one of which has the same (constant) density and wavenumber properties as the material above the plates, while the second (inhomogeneous) region is filled with a material which has a different (constant) wavenumber and density from the surrounding media. The solutions of the Helmholtz equation are assumed to be upgoing plane waves above the plates and, between the plates, standing waves along the periodicity direction for either soft (Dirichlet) or hard (Neumann) boundary conditions, and downgoing waves down the slots between the plates. Continuity of pressure and velocity across the common boundary yield linear equations relating the wave amplitudes in the various regions. The equations are shown to be similar to the residue series of integrals of certain metamorphic functions. The amplitudes are expressed as values or residues of these functions, which are explicitly constructed from properties of the linear equations. Two examples are done in detail: (1) no inhomogeneity structure with arbitrary incident angle, and (2) arbitrary inhomogeneity values at normal incidence. Numerical results are presented for backscatter (specular) reflection coefficientsR0for normal incidence as a function of frequency for various values of the inhomogeneity parameters. The Rayleigh anomaly and the wavenumber threshold effects for the modes between the plates are the most prominent effects.

ISSN:0001-4966    

DOI:10.1121/1.1913384

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A method is presented whereby the pressure variations at any point in the field of a baffled piston may be efficiently calculated. If a solution for the impulse response of a piston of a given geometry is known, then for harmonic excitation the steady‐state field may be computed by evaluating the driving‐frequency component of the Fourier transform of the impulse response. This method involves a single integration, whereas the direct numerical solution requires a double numerical integration. An exact, closed‐form solution for the impulse response of a rectangular piston is derived. With this solution and the known solution for the impulse response of a circular piston the steady‐state solutions for these two geometries are obtained. Three‐dimensional and contour plots of data obtained for a circular piston and for a plane of symmetry of a rectangular piston field are presented. The plots for the circular piston compare favorably with previously published plots of data calculated by a double integration.

ISSN:0001-4966    

DOI:10.1121/1.1913385

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The leading terms in the low‐frequency expansions for acoustically soft and hard bodies are examined and the relevance of the magnetic polarizability tensor is discussed. For a hard, rotationally symmetric body, two tensor elements, functions only of the geometry, are now sufficient to specify the entire low‐frequency scattering behavior in just the same way as the electrostatic capacity suffices for a soft body. Even these quantities are subject to known constraints and computed data for a variety of bodies are presented.

ISSN:0001-4966    

DOI:10.1121/1.1913386

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A free‐ and forced‐vibration analysis is made of a three‐layer laminated ring consisting of an inner and outer elastic layer with a core capable of transmitting only shear. The Variational Method is used to obtain the equations of motion. Analytical expressions are obtained for the response and the natural frequencies of the laminated ring having an elastic core material. Curves are obtained which demonstrate the variation of the natural frequencies of the laminated ring for specific values of the core thickness and shear parameters with a change in the elastic thickness parameter for the first four circumferential bending modes. The resonance response is investigated and analytical expressions are obtained for the system having a viscoelastic core. Curves are obtained relating the resonant‐frequency parameter and the composite‐loss factor to the geometrical and physical properties of the ring vibrating in the fundamental circumferential bending mode.

ISSN:0001-4966    

DOI:10.1121/1.1913387

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Under proper conditions, the response of two coupled nonlinear oscillators, driven by a sinusoidal input, contains a pair of fractional‐harmonic frequency components. The frequenciesf1andf2of the fractional‐harmonic pair correspond approximately to the resonance frequencies of the system, and the sumf1+f2equals the driving frequency. Conditions for the occurrence of fractional harmonics are examined by an analysis that relates them to a pair of coupled Mathieu equations. Fractional‐harmonic components were observed in several nonlinear electrical, mechanical, and acoustical systems. The observations are consistent with qualitative predictions of the analysis.

ISSN:0001-4966    

DOI:10.1121/1.1913388

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The method of multiple scales is used to analyze the nonlinear transverse vibrations of inhomogeneous beams including the effects of transverse shear and rotary inertia. First‐order uniform perturbation expansions are derived for the displacements, shear force, and frequency in terms of the ratios of maximum transverse displacement to cross‐sectional radius of gyration and cross‐sectional radius of gyration to wave length.

ISSN:0001-4966    

DOI:10.1121/1.1913389

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP