摘要:

A tone burst generator is described for the production of electronically keyed oscillations free of transients. The unit consists of an oscillator, a keying circuit, and a negative pulse generator with variable duration and repetition rate. The advantages of the tone burst method in testing the frequency and transient response of amplifiers and transducers are pointed out. Some applications including reverberation time measurements are also mentioned. The almost instant rise and decay of the tone bursts was achieved by providing practically zero impedance path to ground for the keying pulses.

ISSN:0001-4966    

DOI:10.1121/1.1907255

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The sound spectrograph principle may be employed in the quantitative measurement of noise. Measurements may be made with the conventional amplitude section circuit in which, in the customary use of the sound spectrograph, each section provides observation during a few milliseconds of the signal time. A long integrating time circuit for the amplitude sectioner has been developed which provides integration over a period of as much as one or two seconds of signal time. The amplitude sectioning circuit of the sound spectrograph may be employed to determine the relationship between the level of a pure tone and the power‐per‐cycle of noise. Measurements were made for various types of amplitude analysis with the sound spectrograph. A study was made of the degree to which the section displays conform to the computed values of noise level.

ISSN:0001-4966    

DOI:10.1121/1.1907256

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A noise reduction treatment for Diesel engines is described, which, though not the ideal approach to the problem, is practical, economical, and applicable to both new engines and those already in service in the field. This treatment was designed making use of the results of a survey of the relative importance of the various noise sources on the Diesel engine. The treatment consisted of a set of sheet metal covers, lined internally with acoustical absorbing material, which were mounted directly over the noisy areas of the engine by means of built‐in vibration isolation. Noise reductions for the direct sound were at least 8 to 12 db, which were observed at a distance of one foot from the engine. The total loudness of the engine noise at six feet was reduced from 320 to 220 sones. This is a substantial improvement with regard to voice communication in the immediate vicinity of the engine. The speech interference level of the engine noise at six feet was reduced from 87 to 82 db.

ISSN:0001-4966    

DOI:10.1121/1.1907257

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The IRC scale presented herein is neither a Pythagorean scale, nor a just scale, nor an equally tempered scale, as those terms are defined inAcoustical Terminology, but it is shown to possess the major advantages of all three. In a D‐D octave, all of the notes are interconnected by a perfectly symmetrical arrangement of just fourths, and the note frequencies of the octave containing C4=256 cps are 144, 153, 162, 171, 180, 192, 204, 216, 228, 240, 256, 272, 288. A distinguishing characteristic of the IRC scale is that four ascending octaves commencing with a C embrace exactly four successive just fifths (C‐G‐D‐A‐E) immediately followed by four successive just fourths (E‐A‐D‐G‐C). The IRC scale, like the conventional just scale, is based on alternately conjunct and disjunct just tetrachords, but the IRC tetrachord intervals are the smoothly decreasing ones of 9:8, 10:9, 16:15, instead of the just scale irregularly arranged intervals of 16:15, 9:8, 10:9. The major and minor tones of the IRC scale are divided by the known superparticular proportion, giving, in addition to the just semitone 16:15, semitone ratios of 17:16, 18:17, 19:18, and 20:19. These five semitones are located in smoothly progressing order, forming three perfect harmonic series embracing a just major third, fourth, and minor third. The IRC scale is shown to be superior to the just and Pythagorean scales and to excel the equally tempered scale in modulation. If, as the author believes, Helmholtz was correct in his thesis that just intervals are musically better than equal tempered intervals, then the IRC scale is also superior to the equally tempered scale, possessing, among many other advantages, greater ease of tuning pianos and organs, and the ability to tune pianos, violins, and cellos exactly alike and play them in the same temperament.

ISSN:0001-4966    

DOI:10.1121/1.1907258

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The threshold of intelligibility for two‐syllable (spondee) words was measured in the presence of different levels of masking noise. Twelve different bands were used, one (20 to 6600 cps) approximating a white noise and each of the other eleven containing a band of frequencies corresponding to a pitch interval of 250 mels. The absolute thresholds for these bands were also measured to permit transformation of the noise level from an absolute scale to a scale of sensation level.The results show linear relations between the masked threshold and noise level for white noise and for bands of noise between 394 and 1420 cps. For noise bands above 1420 cps this masking function is accelerated, while the two bands below 394 cps yield sigmoid masking functions. Of the bands used, the most effective contained frequencies between 670 and 1000 cps. The signal‐to‐noise ratio at threshold for this band was about −25 db while for bands above or below it became gradually smaller than −25 db, reaching a minimum of −60 db for the highest and lowest bands. White noise was more effective than any band, giving a thresholdS/Nratio of −15 db.

ISSN:0001-4966    

DOI:10.1121/1.1907259

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The ears of anesthetized guinea pigs were exposed to intense tones of 135, 545, 2000, or 8000 cps at sound pressures (at the eardrum) from 138 to 148 db re 0.0002 microbar. The electrical output was recorded by differential intracochlear electrodes before, during, and after the exposures.The injury caused by 8000 cps centers in the basal turn, by 2000 cps in the second turn, by 500 and 185 cps in the third and fourth turns of the cochlea. No single tone, at the intensities and durations employed, injured all of the cochlea.The “threshold” and also the maximum voltage of the cochlear microphonic are valid indices of the anatomical injury seen under the microscope if the proper test frequencies and positions of electrodes are used.The destructiveness of a tone does not depend on its frequency. Equally severe (probably permanent) injuries were produced by a one‐minute exposure at all four frequencies tested when the intensity level was about 144 db at the eardrum.

ISSN:0001-4966    

DOI:10.1121/1.1907260

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The experience gained in fitting a large number of impaired persons with hearing aids is presented, showing illustrative ranges of impairment between 30 and 100 decibels fitted with three progressively‐powered hearing aids.General features of such hearing aids are discussed, showing circuits and arrangements for peak clipping and automatic gain control.The microphone and air and bone receivers are described, considering features developed for providing optimum reliability in service such as moisture proofing, and design arrangements providing miniaturization concomitant with ruggedness.

ISSN:0001-4966    

DOI:10.1121/1.1907261

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The sinusoidal air waves 9+6+2, shaking the skull, produce not only the commonly expected Tartini pitch 3 but also the rather surprising pitch 1, but none other. However, these occur only within a total range that barely encompasses the human voice. For this restriction a plausible evolutionary hypothesis suggested. The mathematical theory for the pitches 3 and 1 is furnished on the basis of a strictly hydraulic, i.e., nonvibratory, function of the cochlear phragma.

ISSN:0001-4966    

DOI:10.1121/1.1907262

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907263

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907264

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP