摘要:

Part A gives the results of remanent ,magnetization tests made under ordinary and anhysteretic conditions, and shows that the major anhysteretic properties of a recording tape can be expressed in terms of three easily measured constants. The design of the test equipment is discussed and test results are listed for thirteen representative types of tape. Part B reviews some of the theories of fine particle magnets that can be applied to recording tape, and gives an extensive treatment of remanent magnetization based upon the Preisach diagram. Some aspects of the Preisach diagram treatment may be of interest to workers outside the magnetic recording field. The anhysteretic properties are important in hf biased recording and a second paper describes how these properties can be used to predict certain recording performance characteristics.

ISSN:0001-4966    

DOI:10.1121/1.1907872

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

This paper discusses and enlarges on a recent theoretical paper by W.R. MacLean on the acoustics of cocktail parties. The discussion is supported by experimental evidence accumulated during the past two years. MacLean's analysis suggests that there is a critical density of participants above which a “quiet” cocktail party becomes abruptly “noisy.” It would appear that one might actually plan a quiet or noisy party as required (assuming control over the number of participants). Unfortunately the cases studied experimentally do not show this quiet‐noisy transition, and it is believed that factors not considered in the theory result in a blurring of the distinction. Indications are that there is a gradual increase in sound level to a saturation value that is independent of the properties of the room, the beverages served, and the number of participants. There is, however, dependence on the sex of the participants.

ISSN:0001-4966    

DOI:10.1121/1.1907870

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

In a turbulent boundary layer, the effective velocity fluctuations amount to about 4% of the free‐stream velocity, independent of the curvature of the body and within wide limits independent of the velocity of the flow. The fluctuations in pressure can then be computed from those of the velocity by an equation similar to the standard Bernoulli equation, except that the numerical constant is different. Vortices pass along the receiving hydrophone; they represent pressure pulses that generate a constant power spectrum at low frequencies that decreases approximately inversely proportional to the cube of the frequency at higher frequencies. This information, in conjunction with the pressure equation, makes it possible to compute the power spectrum of the flow noise as a function of the frequency, the boundary layer thickness and the speed of the flow. The flow noise at greater speeds and at higher frequencies turns out to be predominantly generated by the surface roughnesses.A small hydrophone records the local fluctuations at the pressure in the boundary layer; on the other hand, a large hydrophone is very insensitive to the small‐scale turbulence. It indicates the true sound pressure that is produced by the generation and the decay of the turbulence and by the vibrations of the walls of the vessel. A large hydrophone therefore reads the same pressure, whether it is placed inside the boundary layer or outside the near field region, not too far away from the turbulent layer. The theoretical conclusions are borne out, qualitatively and quantitatively, by the experimental results obtained with the aid of a rotating cylinder and through measurements in the test section of the Garfield Thomas Water Tunnel.

ISSN:0001-4966    

DOI:10.1121/1.1907871

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The studies reported in this paper have dealt with the responses of human observers to speech stimuli transmitted in a background of white Gaussian noise. In all cases the listeners attempted to identify the transmitted items and then made a second response in an attempt to convey additional information. It was found that when the listeners were allowed a second‐choice identification response, very little information was contained in these responses which was not already contained in the listeners' first identification response. When the second response was a confidence rating, significant amount of information was added to that which was carried by the identification response.The rating which followed each identification response was assigned by the observers in an attempt to estimate the probability that their identification response was, in fact, correct. For message sets of four items and for sets of sixteen items, it was found that the observers were quite capable of making such estimates over a wide range of speech‐to‐noise ratios. Their estimates did appear to be affected to some extent by the size of the message set and by the speech‐to noise ratio, but this interaction was slight.The observers' rating responses were used to generate ROC curves. These curves were adequately fit by straight lines when the data were plotted on normal‐normal probability paper. Regardless of the size of the message set, all curves, for all speech‐to‐noise ratios, were fit by a single slope. However, the point at which these curves intersected the abscissa was a function of both variables.Data from one set of observers in the rating experiments were used in an attempt to predict the performance of a different group of observers whose task was to monitor subsets of messages. While predictions were fairly good, discrepancies were noted. An internal check in the monitoring experiment strongly suggests that these discrepancies arose because of differences between the two groups of observers.

ISSN:0001-4966    

DOI:10.1121/1.1907873

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An approach to the design of a machine for the recognition and synthesis of speech is proposed, with particular emphasis on problems of acoustical analysis. As a recognizer, the proposed machine accepts a speech wave at its input and generates a sequence of phonetic symbols at its output; as a synthesizer it accepts a sequence of symbols at its input and generates speech wave. Coupling between the acoustical speech signal and the machine is achieved through two peripheral units: one an analog filter set or equivalent, and the other a model of the vocal tract. Between the analog filters and the phonetic output the signal undergoes an intermediate form of representation that is related to vocal‐tract configurations and excitations but is not necessarily described specifically in these terms. Each stage of analysis is performed by synthesis of a number of alternative signals or patterns according to rules stored within the machine and by comparison of the synthesized patterns with the input signals that are under analysis. Possible advantages of the proposed method of analysis are discussed. An experimental study based on the general analysis approach is described in an Appendix. In this study a method for the determination of the frequencies of vocal‐tract resonances from the speech wave is simulated on a digital computer.

ISSN:0001-4966    

DOI:10.1121/1.1907874

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Piezoelectric data on a mixed titanate system (82.0%BaTiO3, 9.1%CaTiO3, 3.6%PbTiO3, and 4.4%TiO2were obtained with an apparatus intended to measure the dynamic compressibility of materials. The calibration constant, determined from measurements on specimens of known compressibility, involves the piezoelectric and dielectric constants of the ceramics used as transducers. The method is discussed and an operating equation for the apparatus derived. Piezoelectric and dielectric constants have been measured as a function of temperature and pressure over the ranges: −25 to 37.5°C and 0 to 1000 kg/cm2. An apparant phase transition was observed near 5°C. A qualitative discussion of the results is given.

ISSN:0001-4966    

DOI:10.1121/1.1907875

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Diffraction from a fixed sphere is treated as an initial value problem rather than as a boundary value problem. By requiring only boundedness of the diffracted wave potential rather than the stronger Sommerfeld radiation condition, it is shown via use of the Laplace transform and complete inversion integral that the diffracted wave potential consists of the usual steady‐state term plus transient terms. The magnitude of the transient terms are governed by β =kawhereais the radius of the sphere andkis the wave number; however, the rate of decay is governed by the dimensionless decay parameter ωt. Both Dirichlet and Neumann boundary conditions are discussed in detail. Finally, the transient force on the sphere is computed in the Neumann case and the behavior examined for the long‐wave (β≪1) and short‐wave (β≫1) approximations.

ISSN:0001-4966    

DOI:10.1121/1.1907876

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The relation between spatial and temporal absorption for acoustic waves in a viscous medium is discussed by considering the problem of a viscous‐liquid filled tube with a piston at one end and a reflecting termination. The solution of the problem is found in terms of traveling waves from image sources, and standing waves in a tube. The phase velocity and attenuation of the steady‐state terms for both solutions are the same. The transient part of the standing wave solution gives rise to the usually plotted velocity and temporal attenuation; it is shown that these do not have the same meaning as in the spatial absorption case, since they depend upon the allowed wave numbers of the system, that is, upon the geometry and boundary condition.

ISSN:0001-4966    

DOI:10.1121/1.1907877

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A method and apparatus are described for calibrating bonded wire resistance strain gauges in the frequency range from 2 to 20 kc. The gauges are mounted on an electromagnetically excited longitudinally resonant bar whose amplitude of vibration is measured by an interferometer. Results are given for one type of bonded wire strain gauges. Factors affecting the frequency sensitivity relationship of bonded wire strain gauges are discussed. Application for calibration of accelerometers is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907878

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The problem of collision between a simple mechanical oscillator (with damping) and an adjacent rigid member, or between two adjacent simple oscillators, when both are subjected to random vibration is solved in terms of probability of occurrence and the mean time between occurrences. A complete solution is obtained for white Gaussian excitation. This solution can be applied to such problems as the mechanical design of electronic components, bottoming of resilient mounts, and collision between an equipment item and adjacent structure, when the representations of a single degree of freedom system can be used.

ISSN:0001-4966    

DOI:10.1121/1.1907879

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP