摘要:

Recorded speech or music signals experience considerable degradation when reproduced by a loudspeaker in a room. This work aims to differentiate between the effects of the normal‐mode structure of the room and the loudspeaker. We have produced a tape of speech and music samples as they would be recorded in a room if reproduced through an ideal pulsating sphere. We have developed a spherical speaker with the property that speech and music samples reproduced through it in a room are subjectively indistinguishable from those that would be reproduced through the ideal pulsating sphere. The latter samples are generated by a digital convolution involving the Green's function of the room, which is obtained by a linear operation on signals generated by a spark discharge. This research indicates that a transducer can be designed that is subjectively equivalent to the ideal pulsating sphere; for this trandsucer, the normal‐mode structure of the room—not that of the transducer—is the limiting factor in reproduction of speech and music signals. [Work supported ill part by the U. S. Army, U. S. Navy, and U. S. Air Force under contract DA06‐039‐AMC‐03200(E); National Science Foundation (grant GP2495); National Institutes of Health, U. S. Department of Health, Education, and Welfare (grant MH‐04737‐04); and National Aeronautics and Space Administration (grant Xs(;‐496).]

ISSN:0001-4966    

DOI:10.1121/1.1939328

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Measurements are presented of the sound power radiated by panel excited by turbulent boundary layers with air velocities up to Mach number 0.64. The test panels were mounted in a test section of an acoustically quiet air duct that was enclosed in a concrete reverberation room. The mean‐square exciting pressure fluctuation of the wall and the mean‐square panel displacement in broad and narrow bands were measured. The radiated sound power and mean‐square displacement was found to vary proportional to (Mach No.)A× (panel thickness)−B, depending on the predominant modes of vibration. Some of these results are compared with flight‐test data.

ISSN:0001-4966    

DOI:10.1121/1.1939335

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The flexural motion of a rectangular sandwich panel with mass attachments is investigated both analytically and experimentally. Differential equations are derived that include the effects of rotatory inertia of the panel and masses, transverse‐shear deformation of the core, damping, and in‐plane loading. The influence of the concentrated masses on the natural frequency is first obtained and compared with experimental values. The dynamic response of a simply supported panel with mass attachments to a point sinusoidal excitation is then calculated and compared with experimental values. The effect of in‐plane loading on the natural frequencies and response to a point loading is considered. The variation of the natural frequencies due to the rotatorv inertia of the panel and mass attachments is discussed in detail. The results of a number of special cases are discussed and compared with experimental values.

ISSN:0001-4966    

DOI:10.1121/1.1939342

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The purpose of this investigation was to study the acoustical characteristics of the school instrumental music rooms that have been adjudged satisfactory by the music teachers who use them. Public‐school band and orchestra directors long have realized that special acoustical considerations must be given to the rehearsal space assigned to them for teaching purposes if they are to teach critical listening, intonation, musical balance, tone production, and dynamic control of tonal intensity. These attributes cannot be taught within the same acoustical conditions as that of the normal classroom or performance situation. This study located six rehearsal rooms that were reported as being satisfactory acoustically for teaching purposes. These rooms were analyzed for their acoustical characteristics. The study revealed that the several common factors existing among the six rooms differ considerably from the present standards of school musicroom construction.

ISSN:0001-4966    

DOI:10.1121/1.1939346

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The problem of locating submarine self‐noise sources is approached from the phase technique rather than the usual method of observing high amplitudes in certain frequency ranges. IndividualSONARhydrophones were simultaneously recorded at sea during various no‐target speed events and subsequently digitized in the laboratory. A digital computer was programmed to calculate the phase angle between selected pairs of hydrophones as a function of frequency, using the real and imaginary parts of the crosspower spectral density function. Low ship speeds exhibited broad frequency ranges having linear changes of phase as a function of frequency, indicating the dominance of a coherent source. High ship speeds showed more dispersion in the phase plots, but did display general groupings of points. If a velocity of propagation is assumed, then the slope of this line can be used to determine the bearing of the coherent noise source with respect to the hydrophones.

ISSN:0001-4966    

DOI:10.1121/1.1939352

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In an electronic ultrasonic image converter, a plate of piezoelectric or polarized electrostrictive material transduces the ultrasonic image into an alternating surface potential that can be detected by a scanning electronic beam. The conversion characteristics of the plate are explored for various forms of electrical loading, including the conditions necessary for the retrieval of the energy stored mechanically in a resonant plate. The parameters for the high‐conductance electron‐beam scanning necessary for this energy retrieval are developed. An image tube employing these principles is described.

ISSN:0001-4966    

DOI:10.1121/1.1939362

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

A perforated metal plate covered with an adhered thin elastic sheet has been studied as a possible anechoic surface for underwater sound. Assuming that those portions of the sheet covering holes in the plate behave as driven damped circular membranes clamped at their edges, expressions for the acoustic impedance of a single membrane and the specific acoustic impedance of the surface have been derived in terms of the tension in the membrane, the number of holes per unit area, the hole size, and damping constant. The results of calculations showing how the impedance varies as these parameters are changed and the possibility of obtaining an impedance match with water, using available materials, are discussed. [This work supported by the U. S. Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1939367

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP