摘要:

A criterion for the maximum radiated power delivered by a high‐efficiency piezoelectrically driven free disk, vibrating in the first symmetrical mode, has been developed. The maximum power emitted from such a transducer is necessarily limited by maximum stresses and strains to which the disk is subjected when undergoing transverse vibrations. A complete solution of the stress and strain distribution is given for this mode of vibration. Maximum values for these stresses and strains occur at the center of the vibrating plate. Assignment of a safe stress level, dependent on material, which the center of the vibrating plate must not exceed, then yields a unique value of maximum center velocity at which disk fracture occurs. The maximum power criterion is then established by the maximum safe center velocity, which is shown to be independent of plate geometry, and the radiation resistance of the disk in its operating medium. Experiment shows, as anticipated, that fracture occurs at the geometric center of the vibrating plate, with power values consistent with the theory.

ISSN:0001-4966    

DOI:10.1121/1.1908724

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

This paper gives a brief investigation of the concept of the acoustic bearing, the force of which is based on radiation pressure of a resonating sound wave. Of the principal configurations possible, a cylindrical geometry with plates on the ends of the cylinder was considered to be the most suitable. Output ratios of the order of 2640 d/w are shown to be obtainable. Experimentation reached a resonant amplification of 80; ways are shown by which amplifications of around 100 can be achieved. Beyond that internal absorption losses and cavitation present formidable obstacles which, at this point, cannot be overcome.

ISSN:0001-4966    

DOI:10.1121/1.1908726

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An analysis of the voices of sopranos, ranging from singers without any education to artists of world fame, shows a distinct correlation between level of training and vibrato of the voice. Furthermore, analysis of the voices of singers performing in rooms with short reverberation time shows that education is important for the ability to sing correct pitch in words of more than one syllable when the syllables have different pitches. In the analysis of 66 sustained notes, some irregularities were observed in the frequency variations of the overtones. A series of recordings was carried out to detect a plausible reason for these irregularities. The results of various methods of analysis confirm the author's assertion that the sustained note from a highly trained soprano may have parts where the complex wave representing the note is not composed of harmonics.

ISSN:0001-4966    

DOI:10.1121/1.1908728

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

It is known that standard procedures used by piano tuners result in a “stretched” scale (i.e., upper tones higher and lower tones lower than the equally tempered scale). Although there was anecdotal evidence of the desirability of this stretch (largely natural consequence of tuning by beats) it had not been formally demonstrated. Therefore recorded tonal and chordal sequences from a small upright piano, tuned to a typical empirical stretched scale by means of a visual device, were compared with similar sequences from the same piano (1) tuned to strict equal temperament (again by means of the visual device), and (2) tuned by a factory “fine tuner” (by the conventional auditory method). Strict equal temperament was unequivocally rejected both by musically oriented research engineers and by music students. Sequences covering the entire piano scale gave the most pronounced preferences.

ISSN:0001-4966    

DOI:10.1121/1.1908730

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Two experiments were performed to investigate one facet of the question of discriminability of melodic sequences in just intonation and equal temperament. First an ABX test was given to 20 listeners, in which prerecorded ascending diatonic scales of each type were used. Two widely different timbres were used, one flutelike and the other spectrally complex. Only three subjects gave results significantly different from chance. A second experiment employed scales deviating from equal temperament in a manner similar to the just scale, but varying in amount from −6 to −30 cents on the third, sixth, and seventh steps (mi, la, andli). These were compared to equally tempered scales by both ABX and AX procedures. Results showed that the maximum difference between the just and equally tempered scales (16 cents) lies just below the “ABX threshold,” but above the “AX threshold.” It is significant that music students used here (admittedly well conditioned to equal temperament) said that when they. were certain of a discrimination, it was because one of the scales contained tones which were “too flat.”

ISSN:0001-4966    

DOI:10.1121/1.1908732

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

According to an acoustical theory of speech production, the spectra of voiceless fricatives can be characterized by poles and zeros whose frequency locations are dependent on the vocal‐tract configuration and on the location of the source of excitation within the vocal tract. The locations of the important poles and zeros in the spectra of fricatives can be determined by a matching process whereby comparison spectra synthesized by electric circuits are matched against the spectra under analysis. This method has been used to determine the frequencies and bandwidths of the important poles and zeros for several versions of /f/, /s/, and /∫/. Based on these findings, a simplified electrical model is developed for the synthesis of voiceless fricatives. The model consists of a noise‐excited electric circuit characterized by a pole and a zero whose frequency locations can be varied. Stimuli generated by this model, both in isolation and in syllables, are presented to listeners for identification. The results of the listening tests are consistent with the data from the acoustic analyses and with the findings of other investigators.

ISSN:0001-4966    

DOI:10.1121/1.1908734

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An acoustic analysis of the rapid fluctuations that occur in the fundamental excitation rate, or “pitch,” of normal speech was conducted with a sample of six male speakers of American English, who each read a neutral test sentence in certain “emotional” modes. i.e., as a question, an objective statement, a fearful utterance, a happy utterance, etc. A statistical analysis of the durations of approximately 7000 pitch periods was performed with an IBM 709 computer. This analysis revealed that for all possible samples consisting of three consecutive periods, the duration did not remain constant, within ±0.1 msec, in 86% of the cases. The data also showed that the magnitude of the difference between the durations of adjacent periods was greater than 0.6 msec 20% of the time and greater than 1.0 msec 15% of the time. The magnitude of this difference increased with the duration of the periods until their duration reached 6 msec. The difference was independent of the period duration for periods longer than 6 msec. Somewhat greater differences between the durations of successive periods occurred in those samples associated with the onset and end of voicing and sudden spectral shifts. Smaller differences occurred with certain of the emotional modes that seemed to require greater conscious vocal control in their production.The output of the glottis often seemed to be like that of an oscillator with considerable overshoot. In 38% of the cases it produced a sequence of alternately short and long duration periods. The durations of adjacent periods were not correlated. The durations of alternate long and alternate short periods, however, were highly correlated, suggesting a hysteresis effect in which the duration of each period is determined with respect to the preceding period in a quasi random manner within a 2‐msec range.

ISSN:0001-4966    

DOI:10.1121/1.1908736

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Liveness is a quality of sound correlated with room volume, reverberation time, and distance between the sound source and listener (or pick‐up device). In this study, speech samples of varied liveness were obtained by mixing, in controlled ratios, the direct output of the talker's microphone and an output passed through a 9×7.5×6 ft reverberation chamber. In preliminary laboratory tests, the materials consisted of PB words, short phrases, and connected discourse; and varied from very low to high liveness values. The main tests were of an applied nature. Lists of sentences of low and zero (dead) liveness were transmitted over VHF radio and presented over earphones to 19 listeners in a series of intelligibility and preference tests. These lists were also presented to listeners in 105 db SPL helicopter cabin noise. The results indicated that the live speech was less intelligible and less preferred.

ISSN:0001-4966    

DOI:10.1121/1.1908738

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Aspects of wave propagation of particular importance for the measurement of elastic moduli of solids are first reviewed. Experimental techniques are then discussed, with notes on the suitability for a given application and on factors affecting the accuracy of results. Literature references to the more detailed descriptions are listed.

ISSN:0001-4966    

DOI:10.1121/1.1908740

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Theoretical results are presented which relate theQfactors (internal friction) of solid resonators to two loss parameters λiand μi. The latter are assumed to be characteristic of the energy loss in the homogeneous, isotropic material constituting the resonators. Derivations start from the appropriate frequency—or velocity dispersion—equation in which complex elastic constants,λr+jλiandμr+jμi, are substituted. The following cases are treated: torsional, fundamental longitudinal and fundamental bending modes of solid cylinders, and radial modes of solid and hollow spheres. Deviations from constancy ofQare found in regions where velocity dispersion occurs. Computed results are tabulated which show the dependence ofQμ, upon λ1/μ1(range 0.1–10) and the propagation factor τ (range 0–5 for cylinders); these apply to duralumin. Similar computations are used to interpret experimental results on polystyrene reported by Biesterfeldt, Lange, and Skudrzyk (see reference 22 in text), and an inconsistency is found in the values of λicalculated from the fundamental longitudinal and the fundamental bending modes of rods.

ISSN:0001-4966    

DOI:10.1121/1.1908742

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP