摘要:

A reinforced concrete reverberation chamber has been constructed with diffusing cylinders of random size cast in the ceiling and walls. Energy loss in the empty chamber is low because the rigid, heavily enameled walls have a low absorption coefficient and the attenuation loss in the air is moderate for such a small volume. Materials are tested in the frequency range from 250 cps to 12 kc using half‐octave noise bands.

ISSN:0001-4966    

DOI:10.1121/1.1906968

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In contrast to the extremely acute sensitivity of a human listener to discriminate small differences in the frequency or intensity between two sounds is his relative inability to identify (and name) sounds presented individually. When the frequency of a single tone is varied in equal‐logarithmic steps in the range between 100 cps and 8000 cps (and when the level of the tone is randomly adjusted to reduce loudness cues), the amount of information transferred is about 2.3 bits per stimulus presentation. This is equivalent to perfect identification among only 5 tones. The information transferred, under the conditions of measurement employed, is reasonably invariant under wide variations in stimulus conditions.

ISSN:0001-4966    

DOI:10.1121/1.1906969

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A new determination was made of the way in which differential sensitivity for frequency varies both with loudness level (up to 30 phons) mud with frequency (60–4000 cps). The effect of loudness level is independent of frequency, but sensitivity (in terms of cycles discriminable) improves continuously as frequency decreases. These results are in sharp contrast with those of the most widely‐quoted study in the field, and call for some reinterpretation of the relation between pitchDLs and such psycho‐acoustic phenomena as the pitch scale, the masking of tones by noise, and frequency localization within the auditory system.

ISSN:0001-4966    

DOI:10.1121/1.1906970

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The probable shape of a limiting spectrum for noise in a working environment where there is long daily exposure is determined by reasoning from previously determined data of the hearing mechanism. It is assumed that hearing loss is due to a progressive fatigue phenomenon, the fatigue being a direct function of the energy stimulus in the inner ear. From the characteristics of this stimulus as a function of frequency, it is shown that the most sensitive region for loss is around 3000 cps, the low frequencies being as much as 20 db less sensitive than this region. The 4000 cps “notch” in audiograms of industrial workers is thereby explained. The limiting spectra are essentially equal‐loudness contours for broad‐band noise when the noise spectrum is plotted in octave bands.Two limiting loudness curves and their corresponding spectra are tentatively suggested as damage risk criteria. If the noise exceeds 100 sones inanyoctave band, it appears very probable that long time daily exposure will result in hearing damage and in a frequency region slightly above the frequencies of maximum stimulus. If the sound does not exceed 50 sones inanyoctave band, it appears to be unlikely that damage will occur even with long exposure. These criteria are confirmed by the few literature references which have enough data to be used. The need for more research to test these conclusions is emphasized.

ISSN:0001-4966    

DOI:10.1121/1.1906971

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In the construction of ear plugs the chief problem is to combine the necessary sound insulation with comfort and sufficient speech intelligibility. Ear plugs are described which fulfill these requirements to a reasonable degree. They can be used for the attenuation of all audible frequencies or, with minor adaptation, as low‐pass filters attenuating the more dangerous high frequencies only. For maximum speech intelligibility, both kinds of sound insulation are adequate for steady noises, whereas the low‐pass filter is better for intermittent noises, detonations, and noise that can be interrupted to permit communication. Extensive experiments in industry and the armed forces have shown that low‐pass filters with a cut‐off frequency of 1000 cps provide sufficient hearing protection in most situations.

ISSN:0001-4966    

DOI:10.1121/1.1906972

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Two generally accepted facts are: 1. Noise can cause hearing loss. 2. The noise which will cause a hearing loss in one individual may not be the cause of a hearing loss in another.These immediately suggest two unsolved problems. 1. Why does a noise cause hearing loss in one person and none in another? 2. How much noise will cause a hearing loss?The only logical answer to the first question must be that there is a variation in the sensitivity of ears to noise. Discovery of reliable tests which will predict which ear will be sensitive to noise and which will not, is an important unsolved problem, but if solved would do much to clear many disputed questions.The answer to the second question, “How much noise?,” involves the following: the intensity of the noise, the kind of noise, the duration of the exposure to noise, the amount and character of the hearing loss which noise creates.Noise in intensities of 120 to 150 decibels are conceded to be injurious to hearing. Noise less than 80 decibels is not a problem. Where between these two limits does noise become injurious to some ears? Noise with predominance of higher frequencies apparently is more injurious to hearing than one with predominance of low frequencies.The length of exposure to noise depends upon so many factors that it is certainly an unsolved problem. The character of the loss is an injury to the nerve of hearing and presents no problem except the differentiation between loss due to fatigue and permanent hearing loss.The paper ends with a plea for all who are interested to join in solving these questions so that noise can be less injurious to hearing.

ISSN:0001-4966    

DOI:10.1121/1.1906973

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Many of the basic unsolved problems in noise research could be attacked by the application of statistical mathematics and techniques instead of use of the conventional “sine wave” approaches. Such techniques could be applied to many sound radiation and diffraction problems. The fields of aerodynamics and acoustics should be brought closer together, which would result in better understanding of the noise of a turbulent medium. Among the various unsolved noise measurement problems are the design of meters for measuring transients, intensity meters, and better sound level meters. Several other basic projects are mentioned briefly.

ISSN:0001-4966    

DOI:10.1121/1.1906974

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906976

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Noise‐control problems in connection with turbo‐jet engine testing as well as operation are experienced by the engine manufacturer, the airframe manufacturer, and the operators of aircraft and of airports. Some of these noise‐control problems can be solved by isolation of the noise source, others require reduction of the noise at the source. The important still unsolved problems are stated, together with background information, which may be useful to know when attempting their solution.

ISSN:0001-4966    

DOI:10.1121/1.1906977

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An experimental study of the noise produced by a single cavitation bubble has been made. The noise consists principally of a transient pressure pulse associated with the collapse of the bubble. The motion of the bubble has been photographed simultaneously with the measurement of the pressure pulse.

ISSN:0001-4966    

DOI:10.1121/1.1906978

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP