摘要:

Beranek's bookMusic Acoustics and Architecture(pages 550– 551) gives three curves that allow one to predict the reverberation time for an occupied concert hall from the measured reverberation time for the unoccupied hall. Beranek fitted these curves by eye to his tabulated data (Appendix 2) on the reverberation times measured (at 125, 500, 1000, and 2000 Hz) in approximately 50 unoccupied and occupied halls, built before 1960. This paper presents least‐squares regression curves fitted to Beranek's data, establishes the probable reliability of the revised prediction (in terms of correlation coefficients and standard errors of estimates), and extends the prediction to other frequency bands of interest. Comparison with measured data from unoccupied and occupied halls shows good agreement with the predicted values.

ISSN:0001-4966    

DOI:10.1121/1.2018427

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The effective absorption coefficients, in the one‐third‐octave frequency bands from 125 to 10 000 Hz, obtained from measurements on three different materials in a reverberation room were studied as a function of the geometry of the test sample. The measurements were designed to isolate the effects of the sample area, perimeter, and shape, making use of the precision available at the NBS reverberation room facility [T. W. Bartel and E. B. Magrab, J. Acoust. Soc. Am.63,1841–1850 (1978)]. Measurements made with the sample edges exposed and with the edges covered with reflecting material were compared. The measured absorption coefficients, which increase approximately linearly with the ratio of the sample perimeter to the sample area, were compared with a theoretical model [T. D. Northwood, J. Acoust. Soc. Am.35,1173–1177 (1963)] using values of the acoustical admittance obtained from impedance tube measurements performed on the same material. The agreement was within the order of 15%. It was found that if the area and the perimeter of the sample were held constant, the shape of the sample had a small effect on the measured absorption coefficients, which decreased by a few percent as the number of corners in the sample configuration increased.

ISSN:0001-4966    

DOI:10.1121/1.2018430

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The reconstruction of the Harvard Square (Cambridge, Massachusetts) rapid transit station and its associated tunnel work, scheduled for completion in 1983, will have resulted in sustained construction activity over a five‐year period. A number of Harvard University dormitory, classroom, and other academic buildings directly abut work sites and a great many more buildings have shielded or partially shielded exposure to construction noise. The potential problems of long term activity interference, occupant annoyance, and sleep disturbance were recognized and addressed early in the planning phases of the project. Extensive noise monitoring both before and after the construction commenced was carried out in dormitory rooms, classrooms, and faculty offices with open and closed windows. On the basis of analysis of the existing noise environments and the proposed construction activity scenarios, a program of sound attenuation measures for most severely affected buildings was developed and implemented. This paper reviews the development of criteria for permissable interior noise levels produced by construction noise sources, the noise monitoring program, the design and implementation of building noise attenuation features, and general results observed to date.

ISSN:0001-4966    

DOI:10.1121/1.2018435

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The effect of air loading on the normal modes of a vibrating membrane may be systematically calculated by making use of the relevant Green's functions for the air medium. Formal and numerical results have been obtained for the case of rectangular membranes with and without rectangular‐box and split‐cylinder air enclosures, and of circular membranes with and without cylindrical and hemispherical air enclosures. Our analysis may be used to assess the relative importance of bowl shape, enclosed‐air loading, and outside‐air loading on the normal modes of the kettledrum.

ISSN:0001-4966    

DOI:10.1121/1.2018441

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Noise generated by ball bearings has been of considerable interest from various points of view. A noiseless ball bearing has become a necessity in many applications. Noise generated by ball bearings is very complex in nature and depends on a large number of parameters. Lubricant is one of these parameters. This paper deals with the experimental investigation carried out in a specially designed anechoic chamber to determine the effect of various types of lubricants on ball bearing noise. The lubricants used for the investigation include different grades of SAE oils, sodium‐, lithium‐ and calcium‐based greases. Noise spectrum obtained during the investigation indicate that due to inefficient and improper lubricants both the magnitude of noise levels as well as the characteristic frequencies are considerably changed. From the present investigation it is concluded that some lubricants behave very well in reducing the overall noise levels. Ball bearings running with sodium‐based greases are found quieter than those with lithium and calcium‐based greases. Therefore, it is suggested that proper lubricant is necessary for quiet running of ball bearings.

ISSN:0001-4966    

DOI:10.1121/1.2018446

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The importance of unobstructed and controlled airspace in proximity to airports was one of the prime factors that influenced the siting of military air installation and the retention and expansion of these facilities. Over the past few years, however, rapid urbanization has adversely effected both military and civilian airports. For example, communities are becoming more critical of aircraft noise and increasing pressure is being applied by local government and of all the military services, the navy has faced the most intense pressure because the majority of its air stations are located in costal areas which have experienced growth rates far exceeding the natural metropolitan average. The Department of Defense responded to this problem by initiation of the Air Installation Compatible Use Zones (AICUZ) Program to protect the public's safety, health, and welfare while forestalling degradation of the operational capability of military air installations. The main intent of AICUZ program is to insure that development of surrounding land will be compatible with the noise levels and accident potential associated with airfield operations. The Navy endeavors to achieve this compatibility through an appropriate mix and locally adopted land use controls such as zoning, easements, and sound attenuation measures.

ISSN:0001-4966    

DOI:10.1121/1.2018448

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The vibrations of the cat eardrum are being modelled using the finite‐element method. The three‐dimensional, linear, low‐frequency model previously reported [W. R. J. Funnell, J. Acoust. Soc. Am.63,1461–1467 (1978)] has been further developed by the addition of inertial terms. The first several natural frequencies have been calculated as functions of various parameters of the model, including drum curvature and ossicular load. The ossicular moment of inertia strongly affects the lowest natural frequency, but has little effect on the higher ones. The three‐dimensional curvature of the eardrum affects the higher modes most strongly. The importance of quantitative eardrum shape measurements [W. R. J. Funnell, J. Acoust. Soc. Am.65,S9 (1979)] is discussed. [Work supported by the Medical Research Council of Canada.]

ISSN:0001-4966    

DOI:10.1121/1.2018454

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Anatomical studies using light microscopy have shown that mice affected by thedeafnessorjerkergenes develop cochlear hair cells which at first appear to be normal. The hair cells then begin to degenerate, and by about three months of age most of the organ of Corti has degenerated. The object of the present study was to determine whether the cochleas of affected animals are functionally normal during the period when they appear structurally normal. Mice from the two strains aged between 12 and 50 days were anaesthetized and audiograms were determined by measuring thresholds for detecting the compound action potential recorded at the round window. No action potentials or cochlear microphonics could be recorded from affected animals at any age but littermates unaffected by the respective genes had normal thresholds. These results indicate that the apparent structural integrity of the cochleas of youngdeafnessandjerkermice is not accompanied by normal function. Mice affected by these genes appear to be completely deaf at all stages of cochlear development.

ISSN:0001-4966    

DOI:10.1121/1.2018460

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The present electrophysiological study was done to confirm an expected low‐tone dysfunction in guinea pigs poisoned with cumulated doses of methylmercury. Forty young‐adult Hartley strain guinea pigs were fitted stereotaxically with permanent recording electrodes having tips in the auditory tubercle and on the dural surface of the cerebrum. Twenty animals were injected subcutaneously with cumulated doses (2 mg/kg/day) of methylmercury chloride solution five times per week for periods ranging from 10 to 38 days. Twenty control subjects were injected with comparable volumes of sterile water. Click‐ and pure‐tone‐evoked responses were recorded during the waking state using a summing computer. Neither input‐output functions nor visual detection levels for tones from 0.125 through 16 kHz provided any evidence for low‐tone dysfunction in methylmercury‐treated subjects. Supranormal evoked response amplitudes were seen at 8 and 16 kHz. Contrary to earlier conclusions based only on morphological data, the guinea pig as a species appears to be an inappropriate model for methylmercury‐induced deafness reported in human victims.

ISSN:0001-4966    

DOI:10.1121/1.2018475

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Hyperlipidemia has been implicated as a cause of sensorineural hearing loss. Forty‐five subjects (25 male, 20 female), age 6 to 57, from families with familial hypercholestcrolemia were prospectively evaluated with pure‐tone audiometrics (from 0.25 to 8 kHz) and serum lipoprotein quantification. Twenty had no lipid abnormality (N); 25 had familial hypercholesterolemia (FHC). All had clinically normal hearing and tympanometry. In 13 FHC and 11 N under 18, hearing at 6 and 8 kHz was reduced compared to age/sex adjusted values (NL) (p<0.001). FHC compared to N were not significantly different. In 12 FHC and nine N over 18, there was reduced hearing compared to NL at selected frequencies. FHC vs N revealed reduced hearing in higher frequencies for males (3–8 kHz) (p<0.01) and in lower frequencies for females (0.25–1 kHz) (p<0.01). FHC and N from FHC families compared to NL had decreased hearing at selected frequencies at all ages. The difference between FHC and N was more pronounced in subjects over 18.

ISSN:0001-4966    

DOI:10.1121/1.2018479

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP