摘要:

Theoretical considerations have led to the design and completion of three acoustically successful open‐plan offices. With but minor compromises, each was treated with highly absorptive materials to reduce and to localize the sounds of speech and other activities. In two of the three cases, a steady level of background noise is generated and distributed electronically. Partial‐height barriers are employed to maximize privacy between work stations. This paper briefly reviews the acoustical principles employed, methods adopted, and results achieved. Specifically, it deals with the questions of surface absorptivity and background noise. The findings include observations on the level and uniformity of background noise, the level of activity sounds, sound attenuation with distance, and barrier performance. While there has been no opportunity to collect and tabulate occupant response, the over‐all results are very encouraging. They largely substantiate the validity of the approach taken and reinforce the value of exact acoustical design.

ISSN:0001-4966    

DOI:10.1121/1.1977813

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The paper reports on part of the extensive research program sponsored by ASHRAE on the sound field in reverberant chambers generated at single frequencies. The statistical properties of the sound field characterized by cumulative distributions and autocorrelation function are discussed. Experimental data obtained for various damping of modes and boundary conditions varying with time are presented. Practical conclusions with respect to the sound power measurements are considered.

ISSN:0001-4966    

DOI:10.1121/1.1977818

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

For the full potential of ultrasonic energy to be realized as a medical diagnostic and therapeutic tool, and in order to assure safe and efficacious procedures, the mechanisms by which this form of energy interacts with living systems must be well understood. The processes by which ultrasound is absorbed in biological media are basic to the understanding of these interaction mechanisms. Until the mid 1950s, investigators devoted much attention to studies of the frequency dependence of the ultrasonic absorption coefficient in biological tissues, and it was found that the loss per cycle α/fwas largely constant, at least within the frequency range 0.2–10 MHz, and that as the complexity of the biological media increased, so did the ultrasonic absorption behavior. An additional early finding was that the protein content was largely responsible for the observed ultrasonic absorption, although contributions from the structural features of tissue were also apparent. The more recent studies have dealt with molecular models to explain the latter observations. To date the ultrasonic properties of only a few biologically important macromolecules in solution have been examined extensively, mainly globular proteins, and to a much lesser extent carbohydrates and nucleic acids. Three mechanisms have been suggested to explain the excess ultrasonic absorption in aqueous protein solutions, viz., proton transfer reaction, solvent‐solute interaction, and shear viscosity relaxation, and a fourth mechanism, helix‐coil transition, has been suggested in reference to polyaminoacids.

ISSN:0001-4966    

DOI:10.1121/1.1977821

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The characterization of the female breast by ultrasonic visualization techniques presents unique problems in comparison to visualization of other body areas. Basic to this uniqueness is the fact that, not only does the breast contain a variety of types of tissues, but the amount of each type of tissue is a variable. Correct identification, from the echogram presentation, of abnormalities located within any of these tissue structures is partly dependent on the ability to correctly identifynormalechogram patterns over the full range of this variability; such identification necessitates precise correlation of the normal echogram pattern with the specific tissues and with their orientation in the path of the sound beam. However, this type of correlation is difficult to obtain in thein vivobreast. This paper discusses possible source of errors in such attempts. The basic data required to prevent such errors of interpretation of breast echograms can be obtained by carrying out a detailed acoustic visualization study ofexcisedwhole breast tissue, followed by correlation of the echogram patterns with the gross and histological sections of the breast tissue. Data obtained to date, using this approach for both normal excised breast tissue and excised tissue containing malignant abnormalities, will be presented.

ISSN:0001-4966    

DOI:10.1121/1.1977429

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Measurements were made at sea of the changes in acoustic intensity in passing from a shadow zone through the limiting ray and into the directly ensonified region. These measurements were made under conditions where a strong negative velocity gradient, extending from the surface, caused downward refraction of acoustic energy from a near‐surface source. The experiments were conducted in the Mediterranean off Corsica and in the Pacific off San Diego, using narrow‐band signals centered at 3.5 and 11 kHz. In passing downward from the shadow zone into the directly ensonified region, changes in acoustic level of from 10 to 25 dB were observed in a 500‐Hz band and over a depth interval of several hundred feet. Source levels of 73–77 dB/μbar and horizontal ranges of 1–6 kyd were employed. The shapes of the intensity profiles around the limiting ray are discussed in the context of previous theoretical work [C. L. Pekeris, J. Acoust. Soc. Amer.18, 295–315 (1946); R. W. Morse, J. Acoust. Soc. Amer.22, 857–860 (1950)]. [This work was supported by Code 00V1, U. S. Navy Ship Systems Command, under contract.]

ISSN:0001-4966    

DOI:10.1121/1.1977436

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Sonic booms laid down by Navy fighter aircraft flying at Mach 1.1–1.2 have been observed below the surface of the sea by means of a string of hydrophones 195 ft long dangling from a surface ship. The underwater booms were found to decay about as the−32power of the depth below the surface, to have the same spectral content as the boom in air, and to travel down the string with the velocity of sound in water. These findings contradict the theory of an “inhomogeneous” wave incident beyond the critical angle, as originally stated by Rayleigh and as recently extended to sonic booms by Sawyer [J. Acoust. Soc. Amer.44, 523–524 (1968)] and Cook [J. Acoust. Soc. Amer.47, 1430–1436 (1970)]. They suggest, instead, that the underwater sonic boom is a wave scattered by the rough sea surface into the sea below. Its decay with depth is so rapid that it is not likely to be perceptible against the ambient‐noise background at depths greater than one or two thousand feet in the deep sea.

ISSN:0001-4966    

DOI:10.1121/1.1977440

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

After a survey paper on the principles of noise control, 10 contributed papers dealing with several areas of acoustics were presented in the session on physical principles of noise control. Radiation and propagation from sources of various kinds, analysis of vibrations, and studies of techniques for evaluating acoustic power were discussed. Of particular interest was a study of the radiation from incoherent sources, a holographic analysis of vibrations, and a paper on the visualization of the sound pressure distribution in a reverberant room [The work of U.I. is supported by the U. S. Navy Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1977445

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

There were two significant themes in this session. One was that new electronic technologies allow more complex noise‐rating criteria to be instrumented as practical, relatively inexpensive devices. It was suggested that it is no longer necessary to use theA‐scale reading of a sound‐level meter in place of a direct loudness measurement. A new loudness meter was proposed that includes a set of octave‐band filters and is somewhat more complex than the present sound‐level meter. Another device was discussed that simulates the TTS effect in normal hearing and can be conveniently worn. It would be used to assess the probability of hearing damage in a given noisy environment. In another paper, it was shown that a relatively simple analog circuit will detect the rms level over a wide dynamic range. The other theme of the session was the measurement of vehicle pass‐by noise. Four papers considered various aspects of the measurement problem. Equipment must automatically monitor and collect data and it must be designed for continuous unattended use in adverse environments.

ISSN:0001-4966    

DOI:10.1121/1.1977448

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Schoch has pointed out that an ultrasonic beam incident on a liquid‐solid interface is displaced appreciably when the angle of incidence is such that Rayleigh surface waves are generated on the interface. This theory has been extended by Brekhovskikh. Examination of the reflected beam near this angle using a precision goniometer reveals that the energy is redistributed into multiple beams, one of which may be dominant. Experimental results obtained with a Gaussian amplitude distribution across the incident beam are discussed. [Research supported by the Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1977455

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

In previous work on computer speaker verification [Doddington, J. Acoust. Soc. Amer.49, 139(A) (1971)], low error rates were obtained when nonlinear time transformation was used for temporal registration of sample and reference utterances. In that study, utterances were represented by their pitch, amplitude, and formant‐frequency profiles. The present study considers how well one might do only with measures which can be obtained in real time. The procedure differs from that of the previous study in the following respects: (a) utterances are represented only by pitch and amplitude profiles, (b) these functions are smoothed by low‐pass filtering, and (c) a greater number of dissimilarity measures are computed. Because formants are not extracted, the verification is accomplished about 100 times faster than in the previous study. Performance was measured with the same speech material used in the earlier study. Included are utterances from eight “true” speakers and 32 “casual impostors.” A casual impostor is one who makes no attempt to mimic the true speaker. The acceptance‐rejection criterion was adjusteda posteriorifor equal rates of false acceptance and false rejection. The resulting error rate, averaged over speakers, was 1.0%.

ISSN:0001-4966    

DOI:10.1121/1.1977459

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP