摘要:

The intense sound output at resonance in a laminated nickel bar is calculated from static measurements of the relationship of the free magnetostrictive strain to the intrinsic induction. The limitations of the linear theory are avoided by determining the dynamic magnetostrictive stress which is taken to be the motivating influence of the mechanical vibrations. The dynamic magnetostrictive stress is obtained by graphical methods that are not limited to small excitation amplitudes, as is the case in the linear theory. Simple relationships of the dynamic magnetostrictive stress to the impedances of the transducer load system enable the sound output to be determined from the calculated magnitudes of the magnetostrictive stress. The calculated sound output is compared with the sound output measured on a laminated bar of annealed nickel, resonating longitudinally at 20 kcps, and coupled to an acoustic load consisting of a half‐wavelength stub of highly dissipative cast iron. The sound energy delivered to the load is measured by a flow calorimeter, and mechanical transformers which are either solid exponential horns or stepped stubs are used to change the acoustic load to maximize the load power. The calculated sound outputs agree to within ±10% with the sound outputs measured calorimetrically. The measured maximum of the sound intensity is 167 w/cm2, while calculations show that 492 w/cm2ultimately can be generated with the annealed nickel. Estimated intensities for a more freely mounted specimen are in excess of 1 kw/cm2.

ISSN:0001-4966    

DOI:10.1121/1.1908779

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A study is made to determine the frequency and concentration dependence of the ultrasonic attenuation in aqueous suspensions of hatched and unhatched brine shrimp in the frequency range 1–45 Mc. In both types of suspensions a linear relationship is found to exist between the excess attenuation and concentration at each frequency. The attenuation caused by hatched brine shrimp is found to be the same when the organisms are either living or dead.For both types of suspensions the major cause of the excess attenuation is attributed to a scattering mechanism. Over the range of frequencies studied, while the excess attenuation in a hatched brine shrimp suspension varies as the 1.35 power of frequency, the attenuation caused by unhatched brine shrimp exhibits a maximum. The fact that the unhatched brine shrimp can be considered as small spherical particles allows calculation of the scattering loss, which, when subtracted from the measured values, results in a resonance type loss. The measured loss maximum associated with this resonance occurs at a frequency coincident with the principle mode of oscillation calculated assuming the eggs to be spherical cavity oscillators. A simple theory of geometric scattering from unhatched brine shrimp gives attenuation values which agree exactly with those measured above 20 Mc.

ISSN:0001-4966    

DOI:10.1121/1.1908781

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An apparatus is described which facilitates the measurement of ultrasonic fields within transparent solids. This optical system makes use of the birefringence produced within the solid by the passage of an ultrasonic wave. The interaction of light with ultrasonic fields is discussed and expressions derived for the modulation of light by both transverse and longitudinal ultrasonic waves. Various detection systems are discussed and the reasons for the choice of a system, making use of a wide slit in conjunction with a pulsed ultrasonic source, are given. An electronic apparatus, assembled for the most part from commercially available components to implement the measurement, is described. The output of the system is a strip chart recording of the strength of the ultrasonic field along a line. The advantages and limitations of the electronic system are discussed. A typical measurement made with the apparatus is shown and suggestions are given to extend the range of the apparatus.

ISSN:0001-4966    

DOI:10.1121/1.1908783

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A photometric device for accurately measuring the amplitudes of sinusoidal vibrations is described. The device is designed for calibrating vibration pickups. The apparatus employs a Fizeau‐type interferometer with a photomultiplier observing the fringe pattern. The method is applied to the measurement of vibrations throughout the audio and near ultrasonic frequency range with amplitudes ranging from 72 to 4400 A. Extension to amplitudes as low as 5 A can be made with some modification to the apparatus.

ISSN:0001-4966    

DOI:10.1121/1.1908785

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Computations have been made for the effect of a nonlinearity of the hard spring type upon the fatigue damage ensuing on excitation of a resonator by a stationary, broad‐band, random Gaussian force. The fatigue theory used assumes simple accumulation of damage in proportion to a power of the peak values of response strain, without interactions between peaks. Two cases are distinguished: (a) strain proportional to displacement; (b) strain nonlinearly dependent on displacement, as is the surface fiber strain in a bar with pinned ends, responding in a single mode.Numerical results are presented that indicate for case (a) a continuous decrease, with increasing nonlinearity, of the rate of accumulation of damage, while for case (b) this damage rate increases to a maximum as large as 3.4 times the linear estimate, and then falls below the value for linear response. Probability density (in response amplitude) of damage is greater at small amplitudes, and less at large, than for the linear case. The value of response amplitude of maximum damage density is also affected by nonlinearity.

ISSN:0001-4966    

DOI:10.1121/1.1908787

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

A maximum relative variation of the reverberation time according to the size of the audience must be stated as a design condition for a hall together with the value of the reverberation time itself (for instance, 1.3 sec at 500 cps, ±10%). It is interesting and very useful to compute, quantitatively, how a change in the type of seats, the volume of the hall, or the number of seats would affect the relative variation in the reverberation time according to the number of occupied seats. The present work gives, in the form of equations and charts, an easy way to do this.

ISSN:0001-4966    

DOI:10.1121/1.1908789

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The main arena of the Cleveland Public Auditorium is one of the largest listening chambers in the world. Built in the early 1920's, it has, since its opening, been the scene of important public functions, including presidential conventions. Criticism of its acoustic qualities had existed from its opening, but had increased rapidly since 1950, and in 1955 the city administration called for a thorough study of its acoustic qualities and recommendations for improvement. This paper consists of a description of the initial acoustic study, including articulation testing and reverberation time measurements, the problems involved in the acoustic treatment, the actual application of the treatment, and opinions of users since completion.

ISSN:0001-4966    

DOI:10.1121/1.1908791

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Measurements have been made on the performance of an anechoic chamber built for the National Research Council of Canada, adopting the inverse square law as the criterion of performance. Some deviations from the inverse square law were observed, and these were correlated with vibrational modes in the wedge bearing inner walls. It was shown that maximum amplitudes of vibration occur in certain regions of the walls and occupy frequency ranges which coincide with frequency ranges for maximum deviations from the inverse square law. The phase of the vibrations along the walls varies in the same manner as the phase of the incident sound wave in the room. Blocking all experimental points in one of the walls improved room response by a small but consistent amount. Treating regions of maximum vibration in the walls as extended sources and combining contributions from these with the sound field of the source in the room, it was possible to construct room characteristics similar to those observed.

ISSN:0001-4966    

DOI:10.1121/1.1908793

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Three experiments were conducted to measure the decrement in performance that results from uncertainty in the time of onset of a signal presented against a continuous background of noise. The fixed‐interval observation experiment was employed. A light defined an observation interval for the listener during which the signal, a tone of 1000 cps, either was or was not presented [p(SN)=0.5]. The signal, when presented, started at an instant randomly selected within the observation interval. Thus, the listener was uncertain as to (1) whether or not the signal would occur in the observation interval, and (2) the onset time of the signal, if in fact the signal occurred. The interval of time uncertainty (ITU) during which the tone might start was systematically varied from one series of trials to the next, and the listener knew the duration of ITU in each series. After each observation interval, the listener indicated his confidence that a tone was presented by using a rating scale. Operating characteristics [p(y|SN) againstp(y|N)] were plotted on normal‐normal coordinates, and measures of detectability were computed. The functional relation between the detectability indexd, and the interval of time uncertainty is presented for each experiment.

ISSN:0001-4966    

DOI:10.1121/1.1908795

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An experiment was conducted to determine how well listeners could judge whether or not a signal was presented in a noisy observation interval which had already occurred. The cardinal feature of the experiment is that the observation interval is not marked off for the listeners until some fixed time after its occurrence. The listening situation is described as follows. With a probability of 0.5, the signal (1000 cps, 0.25 sec) is presented at a randomly selected instant. A fixed time thereafter, the listener is informed (by a flash of light) of the real time at which the sinusoid may have occurred, and he responds with a rating of confidence. As compared with the typical fixed‐interval experiment in auditory detection, two sources of uncertainty are emphasized in this situation: (1) The listener has a faulty memory of his transformation of the input waveform, and (2) he has a faulty estimation of the time of onset of the signal. From the results of previous experiments on the role of time uncertainty in detection, it appears that a fair portion of the decrement in performance results from poor memory for the input waveform.

ISSN:0001-4966    

DOI:10.1121/1.1908797

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP