摘要:

Talking computers are likely to become a fixture in modern society. The range of information services that can be provided by voice from computers depends largely upon how clever computers become at imitating human speech. This, in turn, depends upon the fundamental acoustic and linguistic knowledge that can be imparted to the machine. This article summarizes the principles of human speech generation, traces some historical interests in speaking machines, and indicates present capabilities of talking computers.

ISSN:0001-4966    

DOI:10.1121/1.1912988

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Earphone enclosures are described which embody an improved acoustical network for enhanced noise reduction and efficient performance for an earphone. The network uses two chambers, one adjacent to the ear and the other contained in a reentrant expanded portion of the enclosure. The two chambers are connected byparallelpassages, one defining predominantly a resistance and the other an inertance. It is shown that this form of network is more effective than an arrangement of inertance and resistance in series. Cushions filled with nonfluid gel provide high wall impedance for improved noise attenuation and conformance with circumaural contours of the head. Values of noise attenuation are given, measured by artificial head and psychoacoustic methods. Performance of a typical earphone in the enclosure is shown.

ISSN:0001-4966    

DOI:10.1121/1.1912989

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The velocity of sound in helium was measured to be 972.49±0.11 m/sec. The measurements were made using a resonance tube method at standard pressure and at 0°C. The tube, unique because of rigid plates at both ends, with acoustic coupling through small holes in one plate, is described. Corrections are made for the sound speed decrease caused by viscothermal absorption at the tube walls. A detailed description of the methods used in making the measurements is included, and the possible sources of errors are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1912990

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Systematic surveys of both the near and far noise fields were made for a supersonic (nozzle design Mach number 1.5) cold model jet. The operating conditions selected for this investigation were (a) shock‐free mode at operating pressure ratio (reservoir pressure/ambient pressure), ξ=3.57 and (b) underexpanded mode at ξ=4.74. The experiments were conducted in an anechoic chamber. The purpose of this investigation was to extend the existing understanding of the noise field of a supersonic shock‐free jet at a moderate exit Mach number and the variations in its acoustic behavior when the nozzle was operated at its underexpanded mode, where strong shock waves were present. The main experimental results are presented. It was found that the broad‐band pressure spectra of apparent sources in each of the individual characteristic flow regions were grossly similar. The strongest source for the shock‐free jet was located in the region between the laminar core tip and the supersonic core tip, whereas for the underexpanded jet the strongest source was found near the middle of the flow region containing repetitive shock waves. It is shown that the significant increase in the noise output at the underexpanded mode of operation was primarily due to high‐frequency components.

ISSN:0001-4966    

DOI:10.1121/1.1912991

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Experiments and theory relating to fan noise sources are reviewed with emphasis on axial flow machines. At supersonic rotor speeds, the steady shock pattern attached to a rotor is an efficient radiator of sound. In most practical cases of subsonic rotor operation, however, direct radiation from the rotor‐locked pressure field is negligible compared with the indirect radiation, or scattering, caused by circumferential distortions in the steady flow field surrounding the rotor. Random timewise modulation of the distortion changes the scattered spectrum from discrete to continuous with a gradual progression from narrow‐band tones to broad‐band noise as the modulation bandwidth is increased. Similar scattering occurs when a nonuniform unsteady flow impinges on stator vanes, but here the radiated frequency is that of the impinging flow. Finally, for blades operating in flows free from circumferential distortions, self‐generated turbulence becomes an important source of noise. The paper describes the physical mechanisms involved in each of these processes, including the generation of unsteady lift by turbulence. Order‐of‐magnitude sound‐power estimates are compared where possible with experiment.

ISSN:0001-4966    

DOI:10.1121/1.1912992

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Different aspects of multiple‐pure‐tone (MPT) “broadband” noise generation in high‐speed fans are discussed. An analytical model for multiple‐pure‐tone generation is presented. Experimental evidence indicates that the MPT generation does not seem to be a function of the presence of shock waves. It is also shown that fan “broadband” noise is not broadband in character and could be attributed to the modulation of the blade‐passing‐frequency tones, their sub‐ and higher harmonics.

ISSN:0001-4966    

DOI:10.1121/1.1912993

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The propagation and interaction of acoustic modes in ducts is of importance for the measurement and control of sound generated by ducted fans and compressors. A method is presented by which the modal spectra (pressure and power spectral densities) for the first nine cross modes can be determined from pressure cross‐spectrum measurements in the duct. The flow noise, a potential source of errors, is suppressed by placing the two microphones sufficiently far apart in the duct. The modal spectra and some of the modal interaction terms (modal correlations) for a number of fans are presented. The method should have many applications in verifying modal propagation, absorption of linings, and scattering of modes as well as in identifying sound sources.

ISSN:0001-4966    

DOI:10.1121/1.1912994

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

Lined ducts containing flow and intense sound have been extensively studied in recent years. Parametric studies have revealed so many variables that design procedures are obscured. Analysis by solution of the convected wave equation has been complicated by uncertainties about the actual modal distribution and by uncertainties about the actual boundary impedance. As a result, when discrepancies occur between experimental and analytical results it is difficult to interpret whether the wave‐equation solution, the modal assumption, the impedance value, or the test procedure is deficient. The simultaneous refinement of all four factors has resulted in a very satisfactory correlation between theory and duct test results and provides a basis for lucid duct design procedures and the evolution of new liner materials. A duct test facility has been built which appears to provide equipartition of energy. The impedance of nonlinear materials has been redefined and measurement methods modified. Contours of equal duct attenuation in the impedance plane have been generated and prove to be simple in shape. From these, a design methodology is deduced which may be applied to any liner material and which eliminates many redundant parameters. The new methodology has led directly to the creation of new liner materials.

ISSN:0001-4966    

DOI:10.1121/1.1912995

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The discrete‐frequency noise radiation from a single‐stage lifting fan is analytically estimated from measured steady and unsteady aerodynamic data on the fan and compared with the measured noise levels. Unsteady forces acting on the stator blades are calculated from measurements of the rotor blades' wake, using a hot‐wire anemometer. The viscous interaction noise estimated is compared with the potential interaction noise from the rotor blades. Rotor potential‐flow interaction and stator viscous interaction noise both seem to be important in the case of close rotor‐stator spacing. The estimated results show a reasonable agreement with the measured results.

ISSN:0001-4966    

DOI:10.1121/1.1912996

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP

摘要:

The production of tones by an isolated rotor interacting with fluctuating and steady flow distortions is first discussed and a method of separating the steady components is explained. Circumferential, radial, and axial microphone traverses have been made in the duct of a 1‐m‐diam four‐bladed subsonic ventilation fan with no stators. The steady components of the rotor tones were measured and phase related to the shaft rotation. The results show that the acoustic field close to the rotor is dominated by its steady force field: at any multiple of rotational frequency, the basic mode is present, having a number of lobes equal to the rotational frequency harmonic order. At greater axial distances from the rotor, the basic mode decays, leaving only modes of low circumferential order at the intake. The estimated power in these modes is in agreement with the acoustic power measured from farfield traverses. The loading spectrum of the fan is determined from the acoustic modes in the intake and compared with the spectrum used in helicopter noise theory.

ISSN:0001-4966    

DOI:10.1121/1.1912997

出版商:Acoustical Society of America    

年代:1972

数据来源: AIP