摘要:

The density‐dependent impedance and propagation constants of a lossy material are combined to yield a measure of the demerit of a given design. For absorbing sound of a single frequency, an ideal reflection‐free termination can be designed. This design yields acceptable results for all higher frequencies. The theory is compared with some experiments in which steel‐wool terminations (only 114 cm long) absorbed sounds of frequency 480 Hz and higher.

ISSN:0001-4966    

DOI:10.1121/1.1912563

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The farfield gain pattern of a shielded acoustic antenna is studied numerically by the use of Kirchhoff's integral. Circular symmetry and perfectly absorbing walls are assumed. Results are reported for a frequency of 2 kHz.

ISSN:0001-4966    

DOI:10.1121/1.1912564

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The artificial voice studied is the new model from Brüel&Kjær. The acoustic pressure obtained from it is given both in the far‐ and the nearfield. The pressure distribution in the latter case is compared with the one for the human voice; it is shown that they are similar. When telephone transmitters are tested, the question of the shift of acoustic flux due to reflection of sound waves from the transmitter arises. A measurement of this shift is given. The sound pressure varies with frequency because of cavity resonances in the air volumes within the voice. These resonances are studied by an expansion using eigenfunctions to compute the sound pressure in the volumes. From this follows a way to eliminate a standing wave that causes a disturbingly low sound pressure in a certain frequency range.

ISSN:0001-4966    

DOI:10.1121/1.1912565

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

In pulse‐type ultrasonic testing, the size of the defect or flaw in a specimen is estimated by the size of the echo reflected by the defect of flaw. By this method, the acceptability of the specimen is determined. In today's ultrasonic flaw detecting, the reflection coefficient of flaws, the characteristics of the acoustic field, the echoes from flaws in specimens, etc., are handled as those of continuous waves. However, in order to improve the resolving power, which is one of the flaw‐detecting capabilities of the ultrasonic flaw‐detecting method, it is necessary to minimize the number of waves contained in the pulses, and because of this the frequency distribution becomes wide. Under a condition such as this, it is not possible to determine the quantitativeness of echo from a flaw. With respect to the above problem, the author conducted a study especially on the probe, transmitter, receiver amplifier, etc., of the apparatus used in pulse‐type ultrasonic testing, mainly in order to obtain the quantitativeness of the echoes reflected by flaws.

ISSN:0001-4966    

DOI:10.1121/1.1912566

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The propagation of sound in a rigid‐wall rectangular duct is investigated for the purpose of determining the energy‐transmission properties of the higher pressure modes. It is known in the case of ducts with no flow that for low frequencies these higher modes are cut off and transmit no energy. This phenomenon is easily recognizable in the wave‐propagation solution by the appearance of purely imaginary wavenumbers. In ducts with a steady mean flow, the form of the solution for sound propagation is more complicated and the question of the direction of acoustic transmission is not clearly indicated. A complete investigation of this problem requires the use of the energy equation. This study uses forms of the energy density and energy flow vector in a uniform moving medium which are applicable for a linear theory of acoustic propagation. These relations are used in combination with the solution for sound propagation to identify the types of transmission which occur throughout the frequency range in a given mode of propagation.

ISSN:0001-4966    

DOI:10.1121/1.1912567

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

As a first step toward the acoustic radiation modeling of a reciprocating air compressor, the suction and exhaust valves were removed and the compressor was made to cycle air through a single circular orifice. The theoretical model incorporates the aharmonic and large piston motion by thermodynamically modeling the flow in the cylinder. The flow through the orifice was modeled as compressible. Contraction coefficients on anON‐OFFbasis were used to account for streamline effects in the orifice section. The farfield acoustic spectrum was predicted by treating the orifice as a monopole source radiating into an infinite halfspace. Agreement between theoretical prediction and experimental measurements was encouraging. A small rise in both the predicted and measured frequency spectrum was hypothesized to be a Helmholtz resonator effect, since it occurred in the expected frequency band. The theoretical calculations were carried out using both a conservation of mass and momentum approach and a conservation of mass and energy approach. Small differences in the results of these two approaches were observed. Finally, with a desire to simplify future models, influences of individual terms in the equations on instantaneous mass flow rates were evaluated.

ISSN:0001-4966    

DOI:10.1121/1.1912568

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1912569

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A temporary‐threshold‐shift reduction protocol and a speech intelligibility in noise procedure were used to evaluate the Gundefender earplug. Test results indicate the comparability of the Gundefender to the V.51R for temporary‐threshold‐shift reduction. Improved speech intelligibility scores in low‐noise and no‐noise conditions were obtained for the Gundefender.

ISSN:0001-4966    

DOI:10.1121/1.1912570

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1912571

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Sound velocity is discussed as a parameter for measuring solution concentration, solids content, specific gravity, and bulk modulus. Graphs are given for six products showing the correlation between sound velocity and concentration. Temperature dependency is discussed and an equation is given with supporting examples for determining concentration measurement error.

ISSN:0001-4966    

DOI:10.1121/1.1912572

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP