摘要:

The sound beam generated in a liquid by a 7.5 megacycle StraubelX‐cut quartz crystal has been investigated by the phenomenon of streaming. The streaming patterns in carbon tetrachloride have been determined by measuring the velocities of sugar particles which have very nearly the same density as the liquid. The velocity distributions produced by a cylindrical sound beam in liquid contained a concentric cylindrical tank are found to be in good agreement with those predicted by Eckart's solution of the hydro‐dynamical flow equations. Comparison measurements with squareX‐cut quartz crystals of the same frequency give poor agreement with theory. Since Eckart's analysis assumes uniform sound intensity across the beam, these experiments indicate that the sound beam radiated by a Straubel cut crystal is very uniform.

ISSN:0001-4966    

DOI:10.1121/1.1906656

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A close talking, noise canceling microphone has been developed which responds to the second order of the pressure gradient and which has only one diaphragm. Since there are four sound pressures involved in a second‐order gradient microphone it has been deemed necessary in the past to have four surfaces for the four pressures to act upon. This microphone has sound entrances to the two surfaces of a single diaphragm spaced and oriented in such a manner as to produce the second‐order effect, thereby increasing the signal‐to‐noise ratio over that obtained in a first‐order gradient microphone. Mathematical analyses are made of the microphone first as a purely theoretical microphone with infinitesimal spacing of the sound entrances, then as a microphone with dimensions between sound entrances which are practical for use in a microphone of this type.

ISSN:0001-4966    

DOI:10.1121/1.1906657

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906658

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906659

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A graphical functionW(r, c) has been determined experimentally, in whichWis word articulation,ris the relative level of unclipped speech and the noise, andcis the amount of uniform, symmetrical, speech‐peak clipping. Pre‐emphasis of the speech signal gave an approximately uniform speech spectrum prior to clipping. Uniform, random noise was mixed with the clipped speech before postequalization, making the final noise spectrum similar in shape to the speech spectrum. The real‐ear response of the earphones was compensated electrically to yield a uniform orthotelephonic response for the communication system, in the frequency range contributing significantly to articulation index. For constant clippingcnthe functionW(r, cn) approachesW(r, 0) as a limit for sufficiently large values ofr. Forc

ISSN:0001-4966    

DOI:10.1121/1.1906660

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The masking audiogram of a pure tone is complicated by phenomena that arise from the interaction of the test tone with the masking stimulus. The production of beats and of difference tones results in a masking audiogram that does not represent the pattern of activity in the cochlea or nerve due to a simple masking stimulus. In the present experiments a narrow band of noise was used to mask pure tones. The “beat” heard in the immediate vicinity of the masking noise is not prominent, and a test tone higher in frequency than the band of noise is detected in terms of the characteristic pitch of that tone rather than by means of a difference tone.With a band of noise slightly wider than a critical band (Fletcher), the amount by which the test signal at the center of the band exceeds the level/cycle of the noise is less than that obtained with a considerably wider band of noise. This smaller signal‐to‐noise ratio obtained with the narrow band of noise is probably due to “beats,” since the test tone is heard as a “buzz” or “rattle.” For purposes of deriving excitation or loudness patterns, a better estimate of the maximum amount of masking is obtained by using a wide band of noise whose pressure spectrum level is the same as that of the narrow band.

ISSN:0001-4966    

DOI:10.1121/1.1906661

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Pure tones and various bands of noise were used to mask impulsive acoustic stimuli (clicks) that were produced by electrical square pulses through a moving‐coil type earphone. Results indicate that it is difficult to generalize about the masking of clicks by pure tones from observations on only a few observers because of sizeable individual differences. The masking of clicks by noise, however, is related unambiguously to the intensity and the spectral distribution of the noise. Both pure tones and narrow bands of noise provide maximum masking in the region between 1000 and 3000 c.p.s. Generally speaking, noise is a more efficient masker of clicks than are single pure tones. Although the present measurements were made with masking frequencies below 6500 c.p.s., there is some preliminary evidence to suggest that the audibility of certain clicks in noise is markedly dependent on frequencies above 6500 c.p.s. The linear (slope = 1) relation between the masking of speech or pure tones by noise and the intensity of the noise does not apply here. Rather a trimodal function indicates that the masking of unfiltered clicks by “pinkish‐white” noise does not change over a 30‐db range of moderate intensities. Below and above this range masking increases with the intensity of noise, sometimes at a slope greater than one.

ISSN:0001-4966    

DOI:10.1121/1.1906662

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Two tones of different frequencies alternated successively five times per second. When the difference in frequency was small, the alternation sounded like a continuous up‐and‐down movement of the pitch. When the difference in frequency was large, the alternation sounded like two unrelated, interrupted tones. The transition point between these two perceptual organizations is called the trill threshold. The trill threshold was measured as a function of frequency for 14 subjects; the results are summarized in Fig. 1.

ISSN:0001-4966    

DOI:10.1121/1.1906663

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906665

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906666

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP