摘要:

The non‐specular or scattered reflection of plane waves of sound by various rigid, non‐absorbent non‐porous surfaces composed of either semicylindrical or hemispherical bosses (protuberances) on an infinite plane is analyzed. Exact solutions for the problem of the single boss and a plane wave at an arbitrary angle of incidence are derived through consideration of a cylinder or sphere and two simultaneously incident “image waves.” Finite patterned distributions of such bosses are then treated and the far field solution obtained subject to the restriction that the secondary excitations of the various bosses be neglected. (The equivalent problems for cylinders and spheres are also considered as well as the second‐order solution, for the cylindrical case, which takes into account the interaction of neighboring elements.) These solutions are found to contain the characteristic Fraunhofer terms for a grating or lattice. The asymptotic solutions for the single bosses (Kr≫1,Ka<1) are then extended to consider both finite and infinite uniform random distributions. The solutions for the finite distributions are found to contain the characteristic Fraunhofer terms for similarly shaped apertures. The solutions for the infinite distributions (of semicylinders or hemispheres) are found to be remarkably similar when expressed in terms of the volumetric departure from the plane per cm2of distribution. Some extensions and ramifications of the results are also considered.

ISSN:0001-4966    

DOI:10.1121/1.1906646

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The reciprocal relations between autocorrelation functions and power spectra, known as Wiener's Theorem, axe extended in a modified form to the case of experimental results obtained by means of filters with finite time constants. If the short‐time autocorrelation function φt(τ) and power spectrumGt(ω) are properly defined, it is found thatφt(τ)=eα|τ|2π∫−∞∞Gt(ω)cosωτ dωGt(ω)=∫−∞∞e−α|τ|φt(τ)cosωτ dτwhere 1/α is a time constant. These equations may be used to relate the autocorrelation‐function representation of a speech wave to the corresponding spectrographic representation.

ISSN:0001-4966    

DOI:10.1121/1.1906647

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In this paper the term hyperbolic horn is used to designate those horns whose area law is given by:S(x) = πR02[coshax+T sinhax]2. WhereS(x) is the cross‐sectional area of the horn at distance (x) from the throat, (a) is the flare constant; (T) is the shape parameter and (R0) is the throat radius.The pressure on the axis due to a circular mouth, unbaffled horn loudspeaker is derived. In this calculation use is made of the recent results of Levine and Schwinger [Phys. Rev.73, 383 (1948)] and some useful additional functions are computed from their data and presented here in graphical form.It is shown how to calculate the frequencies at which peaks occur in hyperbolic horn type loudspeaker frequency response curves.It is shown how to calculate the parameters of hyperbolic and exponential horn type loudspeakers having pre‐determined peaks in their frequency response curves.Some experimental confirmation of the theory is presented.

ISSN:0001-4966    

DOI:10.1121/1.1906648

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Expressions for the impedance components of a finite catenoidal horn are derived and a comparison with similar exponential and conical horns made. The impedance of a section of a catenoidal horn is also calculated and it is shown how, for the finite as well as the infinite horn, this approaches that of the exponential as more length is trimmed from the throat end.The assumption that the resonance characteristics of a horn are the same as that of a uniform tube, provided the higher velocity of sound for the horn is used, seems to be borne out for the catenoidal horn but for the exponential horn the agreement is not very good except at higher frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1906649

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The characteristic impedance and propagation constant of a cylindrical conduit are calculated on the basis of an equivalent electricalT‐section. Numerical values of the results are plotted for air at 20°C, for a range of values of the independent variable which includes the region of transition from isothermal to adiabatic conditions.

ISSN:0001-4966    

DOI:10.1121/1.1906650

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

If the active face, or acoustic output terminal, of a sinusoidal sound source moves as a plane piston, then the source can be characterized by a blocked pressure and an acoustic output impedance. If this piston is coupled to a microphone by means of a closed air column, the pressure at the microphone depends on the acoustic impedance of the microphone, on the impedance of the source, and on the air column. An expression for this pressure as a function of the length of the air column is developed, and data are presented which show how source impedance, tube attenuation and other quantities may be obtained.

ISSN:0001-4966    

DOI:10.1121/1.1906651

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The velocity and attenuation of sound at 1 mc/sec. were measured in helium at pressures as low as 0.1 mm Hg (sound frequency about twice mean collision rate). The observed dispersions are very large and agree well with those predicted by existing theories except at very low pressures where uncertainties are introduced by lack of gas purity.

ISSN:0001-4966    

DOI:10.1121/1.1906652

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In many acoustically coupled systems the methods of geometrical acoustics do not apply. Reverberation formulas as ordinarily used would lead to incorrect results. This paper approaches the problem of coupled rooms from the “wave” point of view, treating the coupled rooms as a boundary value problem in obtaining an approximate solution. The results explain some discrepancies noted by earlier researchers between experiment and predictions from geometrical acoustics; for example, the dependence of absorption in a room on the position of the open area which couples the room to an adjacent one. For the case where the window area which couples one room to another is comparable in size with the partition which separates the rooms, the effect of the partition will be least when it is at a particle‐velocity node. For the case where the window area is small compared with the partition which separates the two rooms, the effect of the coupling window depends on the square of the unperturbed pressure at the window. Thus the effect of the window varies with position and is least at a pressure node. Experimental data on isolated modes of vibration of a coupled system are given which check the results predicted by this application of the wave theory.

ISSN:0001-4966    

DOI:10.1121/1.1906653

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The electromechanical equations of state are written in a number of forms, extending from Voigt's formulation to the recently introduced formulation withgandhas the piezoelectric constants. Those equations that are most appropriate in the theoretical treatment of the two chief types of crystal transducer are pointed out. A detailed treatment of the thickness‐vibration transducer is then given, leading to expressions for the electrical characteristics and for the acoustic vibrational amplitude and intensity. Some special cases are also considered.

ISSN:0001-4966    

DOI:10.1121/1.1906654

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The linear piezoelectric equations of state with strain, electric displacement, and entropy, as independent variables, are derived from the principle of conservation of energy. These thirteen tensor equations are then specialized to the adiabatic case and used as the starting point for the development of all possible linear piezoelectric equations of state using in turn as independent variables, stress and electric field, strain and polarization, and stress and polarization. This process gives as a by‐product the set of relations among the elastic, electric, and piezoelectric coefficients for the various pairs of independent parameters and emphasizes the frequently overlooked fact that the piezoelectric equations of state are mutually convertible. M.k.s. units and the I.R.E. notation are used throughout the discussion and a table is given which compares the I.R.E. notation with the former notations of Cady and Mason.

ISSN:0001-4966    

DOI:10.1121/1.1906655

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP