摘要:

In this paper, a computational method for assessing the sound power characteristics of machines is presented. The method, which is based upon a Helmholtz integral formulation, requires a knowledge of the geometry and the modal characteristics of a machine's vibrating surfaces. Closed form integration of the associated surface integral is carried out in a piecewise manner over planar surface elements of simple shapes such as rectangles and triangles. This choice of element allows the grid geometries associated with the acoustic power computations to be made identical to those used in existing structural modal analysis schemes such as finite element methods or Fourier analysis methods. In this way, the sound power characteristics of a given machine can be computed in terms of the sound power radiated by each of the structural modes comprising the overall response. The structural modes can then be ranked in order of their radiation efficiency for purposes of noise control treatments.

ISSN:0001-4966    

DOI:10.1121/1.2018368

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An analytical solution is given to predict the propagation of noise from a point source to a point receiver over an infinite plane consisting of two half‐planes, each covered by a different impedance. The solution is found by the use of function theoretic methods, and is evaluated asymptotically by the method of pole subtraction. It includes a reflected wave, three diffracted (ground) waves, and a surface wave due to each impedance in addition to a direct wave. The reflection coefficient form is different than the plane wave reflection developed for a point source over an infinite impedance covered plane given in the literature. However, it reduces to the plane wave reflection coefficient once the point source position approaches infinity representing an incoming plane wave. Out of the two reflecting waves only one contributes depending on the position of the receiver. The two surface waves correspond to the two impedance half‐planes, but only one contributes depending on the location of the receiver. If the receiver is close to an impedance plane it picks up the surface wave emitting from that part of the plane, but it disappears as the receiver moves away from that surface. The diffracted (ground) waves depend on the difference of the impedances of the half‐planes. [Work supported by NCHRP.]

ISSN:0001-4966    

DOI:10.1121/1.2018372

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A theoretical analysis of the wavefield radiated by a point source in a weakly inhomogeneous one‐dimensional random medium is presented. The analysis is based on a perturbation technique, and includes all single‐ and double‐scattering terms, as well as some scattering terms of higher order. An expression for the mean intensity (i.e., the mean square of the modulus of the complex wave amplitude) of the wave as a function of source‐receiver distance, or propagation distance, has been obtained. This expression shows that, inside a certain region of space containing the source, the mean intensity of the wave is increased by the randomness of the medium, whereas outside of this region it is decreased. The result of this redistribution of mean intensity in space is a more rapid rate of decrease of the mean intensity (or the log of the mean intensity) with propagation distance than would be the case in the absence of randomness, which can be interpreted as an excess attenuation of the wave as a result of the randomness of the medium. The relation of the present theory to previous theories of attenuation of waves by randomness, or turbulence, is briefly discussed. [Work sponsored by NORDA.]

ISSN:0001-4966    

DOI:10.1121/1.2018379

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The structural organization of the middle ear in adult parakeets and neonatal chicks was examined using light and scanning microscopy. The areas of the tympanic membrane (TM) and columella footplate were ascertained, as was the columella length and angle of incidence between columella and TM. The ligaments of the TM and columella were identified, and the angular relations between the shaft of the columella, its footplate and the oval window were measured. Transmission electron microscopy was used to examine the layers of the TM. A capacative probe was further used to describe the response characteristics of the TM (measured at the tip of the extracolumella) when stimulated at 100 dB SPL between 0.2 and 10.0 kHz. The unique response properties of the TM are considered with regard to the structures of the middle ear. [Work supported by Heinrich‐Hertz Foundation, West Germany.

ISSN:0001-4966    

DOI:10.1121/1.2018387

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Pathogenesis of inner ear deafness are thought to be due largely to imbalance of potassium and sodium ions in the inner ear fluids. Such imbalance can occur with renal diseases, vascular insufficiencies, and ototoxic drugs. An ion‐specific micro‐electrode was applied to the peri‐ or endo‐lymph in chinchilla's cochlea. Simultaneous measurements of endocochlear dc potentials (EP) and K‐ion concentration were made over a period of a few hours and their changes following temporary asphyxia, following various loop diuretics, following permanent anoxia were studied. The reduction of endolymph potassium concentration was accompanied by the elevation of perilymph concentration of this cation following loop diuretics. Normal values for K+in the inner ear fluids and potassium conductance following various doses of loop diuretics will be discussed in detail.

ISSN:0001-4966    

DOI:10.1121/1.2018392

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Deaf students entering Gallaudet College routinely are evaluated audiologically. Data for 330 new students enrolled during Fall semester 1978 were analyzed. The primary purpose was to obtain descriptive statistics for 118 assessment variables. Clinical test variables included pure tone and speech audiometric responses, immitence measures, aided and unaided hearing aid performance, history of hearing aid use, speechreading scores with and without audition. auditory speech reception measures with and without hearing aids, speech intelligibility ratings, and reported information regarding onset, etiology, and family history of hearing loss. Summary descriptive data and intercorrelations among major clinical variables will be reported and discussed.

ISSN:0001-4966    

DOI:10.1121/1.2018397

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The reliability of a closed‐response set nonsense syllable test [S. B. Resnick, J. R. Dubno, S. Hoffnung, and H. Levitt, J. Acoust. Soc. Am.58,114 (1975)] was determined on a group of 38 listeners with mild to moderate sensorineural hearing loss. Eight randomizations of the 91‐item test (four trials on each of two days) were presented monaurally, under earphones, at 90 dB SPL with a cafeteria background noise set at a +20 dB speech‐to‐noise ratio. Performance under these conditions ranged from 21.4% to 91.2%, reflecting the wide range of syllable‐recognition ability of these subjects. Reliability of the eight measurements was determined by analysis of variance and analysis of covariance structure (parallel‐test modelling) for the entire test and each of 11 subtests. Overall and individual subject results failed to show any systematic differences in scores over eight trials. Likewise, no significant differences were found in performance on individual syllables, nor were changes in the relative occurrence of specific syllable confusions noted. This test is highly reliable when evaluating hearing‐impaired subjects, and thus is appropriate for use in investigations where identical items are administered under multiple experimental conditions.

ISSN:0001-4966    

DOI:10.1121/1.2018399

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Results on the perception of speech through the Tadoma method (in which the “listener” monitors the articulatory process by placing a hand on the talker's face) have been obtained on seven adult deaf‐blind, experienced Tadoma users. Six of the subjects became deaf and blind as a result of meningitis between the ages of one and seven; the seventh became deaf from a progressive hearing loss and blind from retrolental fibroplasia suffered in infancy. Performance was measured on various word and sentence tests (W‐22 words, SPIN sentences, and CID sentences), syllable tests (identification of sets of consonants and vowels), and a test of language (Quigleyet al., 1978). The results of these tests provide us with information concerning the comparative abilities of a relatively large sample of experienced Tadoma users to communicate through Tadoma. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2018408

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In a previous paper [J. Acoust. Soc. Am. Suppl. 165,S62(A) (1979)] the design of large time‐bandwidth product signals for simultaneous estimation of the range and bearing of stationary point targets from a moving platform was discussed. Examination of the range‐bearing ambiguity functions produced by a number of simple FM signals indicated marginal gains in terms of interference suppression even for relatively large TW products. In this paper the performance of a class of composite (multicarrier) FM signals which have desirable ambiguity, and interference suppression properties, will be discussed and compared with the previous results. [Work supported by NAVMAT.]

ISSN:0001-4966    

DOI:10.1121/1.2018419

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Cross‐sensor beamforming offers the potential of providing good side‐lobe suppression for sparse acoustic arrays or filled arrays which develop faulty elements during exercises at sea. To determine the sensitivity of this technique to random errors in amplitude and phase we computed the cross‐sensor beam pattern with each element in the array subject to a random amplitude and phase error. For a line array with 32 equally spaced elements, the beam pattern from the cross‐sensor method was nearly identical to that of the conventional beamformer with both subject to the same set of random errors. Repeating the same computation with four inoperative elements showed that the cross‐sensor method maintained good side‐lobe suppression while the side lobes of the conventional beamformer were elevated corresponding to the amplitude weights of the faulty elements. The mean beam pattern for the cross‐sensor method was computed analytically assuming the errors were random, independent, and uniformly distributed. The result can be expressed as the sum of the error‐free pattern and an additional angle‐independent term due to the random errors. Comparison of this expression with the corresponding one for the conventional beamformer reveals that for a filled array the two results are identical. [Work supported by NAVMAT.]

ISSN:0001-4966    

DOI:10.1121/1.2018424

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP