摘要:

The free‐space Green's functions which satisfies the inhomogeneous scalar wave equation is derived by a simple and direct method.

ISSN:0001-4966    

DOI:10.1121/1.1908473

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908477

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908479

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Reporting audiometric threshold in terms of SPL at the entrance to the ear canal makes the assumption that equal SPL Fields equal loudness regardless of the type earphone used. This is shown not to be always the case. Loudness balances between the W.E. 552 and the W.E. 705 A phone yield data composing differences among three laboratories as to what SPL at the entrance to the ear canal constitutes American “audiometric zero.” Loudness balances and threshold measurements using the W.E. 705 A and a British earphone, Standard Telephones and Cables Ltd. Type 4026 A, show the British phone generating more SPL at the entrance to the ear canal for equal loudness. This difference must be added as a correction factor to ear canal SPL using the 705 A earphone if one wishes to compare American threshold surveys with British surveys by probe tube microphony.

ISSN:0001-4966    

DOI:10.1121/1.1908483

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908485

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Measurements were made of the masking of pure tones by bands of noise, the width of each band corresponding to a pitch interval of 250 mels, with band level varied from 40 to 120 db SPL. The masked audiograms were compared to the frequency characteristics of the bands of noise. It was found that published values for the critical bands predict the masking for tone within the band. More masking than would be predicted is found for the frequencies above a band. Below the band, the masked threshold is again predicted precisely by the critical‐band hypothesis, but only to a point beyond which, for high noise levels, a “remote” masking, which is constant as a function of frequency for any particular level, is observed and is much more than can be predicted from the effective levels (from either system noise or imperfect filtering) obtaining at those low frequencies where this masking is observed. Whereas for tone within the band masking increases linearly with level, this “remote” masking rises in an accelerated manner with level and then decelerates at the highest levels. Some speculative interpretation is attempted. [This work was supported under Contract No. AF 18(600)‐131 with the U. S. Air Force.]

ISSN:0001-4966    

DOI:10.1121/1.1904995

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Design features of an acoustic filter for use on suction and discharge of constant speed reciprocating gas compressors are presented. The filter derives its high attenuation per unit filter volume from use of Helmholtz resonators, rather than simple compliances or quarter‐wavelength tubes, in shunt branches. Direct current pressure losses are relatively small because series elements are inductive in nature. Cylinder starvation is minimized by presenting essentially equivalent impedances to all compressor cylinders. Experimental data are compared with theoretical performance predictions for an installation involving 900 horsepower compressors. In this installation a typical filter through‐put time (total filter volume/steady flow volume rate) is 0.47 second, and the fundamental frequency is 8.5 cps.

ISSN:0001-4966    

DOI:10.1121/1.1905002

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Two schemes of message storage were evaluated in a communications‐net simulation. An operator received messages, which frequently overlapped, from talkers on four channels. In a typical test problem, 32 relevant and six irrelevant messages were distributed over a five‐minute period. The operator's task was (1) to transcribe message information onto a plotting board and (2) to synthesize a problem solution from this information. In one scheme, Fixed Delay, the operator attempted to hear each message individually by appropriate use of a 9‐sec delay alternate circuit in each channel. In the other scheme, Variable Delay, messages were never heard directly; instead, message arrivals were indicated by lights and the operator summoned each message from storage individually. A third arrangement, in which all messages were heard directly as programed, served as a control condition. Performance criteria were speed, accuracy, and the number of repeats the operator had to request. The results for the Fixed Delay and control conditions were roughly equivalent. Under the Variable Delay condition more transcription and synthesis were complete and correct by the end of a programed sequence; only about half as much additional time and a third as many repeats were needed for problem solution.

ISSN:0001-4966    

DOI:10.1121/1.1905008

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

The study employed selected vowels, each combined with prevocalic or post‐vocalic consonants in consonant‐vowel or vowel‐consonant syllables. Each combination was recorded non‐contextually by several speakers and then tested by listeners for recognizability of phonemes. Oscillograms and sound spectrograms were made of all syllables correctly identified. These were used to obtain several measures of syllabic component duration and formant frequency change during transition. Measures of direction and extent of frequency change during transitions appeared to offer most promise of relationship to known physiological features of articulation and were subjected to more complete analysis. Results of the study indicate the following: (1) for the first two formants, the transitions reflect aspects of tongue placement for the vowel, and place and manner of articulation and voicing characteristics of the consonant; (2) lack of speaker agreement resulted in variations obscuring most aspects of patterning for the third formant. Specific hypotheses were tested within the limits of the experimental procedure and results are reported. Future research trends are suggested.

ISSN:0001-4966    

DOI:10.1121/1.1905014

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP

摘要:

Instrumentation for measurement of voice pitch, for automatic segmentation of voice signals, and for voice pattern‐matching, tends to be rather sensitive to the equalization of an input voice signal. A system for automatically compensating for various fixed equalizations of an input voice signal has been devised. The automatic equalizer uses a set of contiguous‐band filters. The input voice signals first pass through a fixed equalizer designed to create a relatively uniform distribution of levels among the filter channels. The output signal from each filter is rectified, and the resulting dc voltages are integrated over an interval of many seconds. In each filter channel the average dc voltage is compared with the longtime average of the mean of the voltages in the various channels, and a dc error voltage signifies the amount by which the average level in any channel deviates from the mean level. The dc error voltage in each channel is fed back to automatically control the gain of that channel. Output signals from the various filter channels are also summed before rectification to recover the ac voice signal.

ISSN:0001-4966    

DOI:10.1121/1.1905018

出版商:Acoustical Society of America    

年代:1956

数据来源: AIP