A damping device, consisting of an annular tail-pipe, has been developed. It is applicable in situations wherein acoustic damping is required in combination with low flow resistance. Examples are ventilation systems, turbo-engines, intake and exhaust systems for internal combustion engines. The device consists of a central tube surrounded by a narrow slit. The central tube has an acoustic mass ...

Headphones and earphones have many extremely small holes or narrow slits; they use sound-absorbing or porous material (i.e., dampers) to suppress vibratory system resonance. The air viscosity in these acoustic paths greatly affects the acoustic properties. Simulation analyses such as the finite element method (FEM) therefore require knowledge of the material properties of sound-absorbing or por...

A general expression for the transmission loss characteristics of the Herschel-Quincke tube is developed. This relationship eliminates the restrictions on duct cross-sectional rea employed in earlier analytical studies. The attenuation of sound by this configuration is also studied computationally in terms of a nonlinear one-dimensional finite-difference model that solves the balance equations ...

Results of design and simulation of a 0.2 THz traveling-wave-tube vacuum power amplifier with a sheet electron beam and grating slow-wave structure (SWS) are presented. Electromagnetic properties of the SWS such as dispersion and interaction impedance are calculated. Smallsignal and large signal gain curves are studied.

The relation between reflected waves and features of ascending aortic pressure waveforms and impedance patterns was investigated with a modified T-tube model of the systemic arterial circulation. Ascending aortic pressure and flow and descending aortic flow were measured in 10 dogs under basal conditions and under the effect of an agent (methoxamine) that caused vasoconstriction and an increase...

Broadband noise absorption, including low frequencies, may be obtained by a hybrid passive-active two-layer system. A porous layer in front of an air layer provides passive absorption, at medium and high frequencies. Active control of the input impedance of the two-layer system yields absorption at low frequencies. The active control system can implement either pressure-release or impedance-mat...

Acoustic measurements provide convenient non-invasive means for the characterisation of materials. We show here for the first time how a commercial impedance tube can be used to provide accurate measurements of the velocity and attenuation of acoustic waves in liquid foams, as well as their effective "acoustic" density, over the 0.5-6kHz frequency range. We demonstrate this using two types of l...

This paper reports the initial results of a test series to evaluate a method for determining the normal incidence impedance of a locally reacting acoustically absorbing liner, located on the lower wall of a duct in a grazing incidence, multi-modal, nonprogressive acoustic wave environment without ow. This initial evaluation is accomplished by testing the methods' ability to converge to the know...

Acoustic impedance of perforations in contact with fibrous material, as well as air alone, is experimentally determined in the absence of mean flow. Different porosities 2.1, 8.4, 13.6, and 25.2 % and hole diameters 0.249 and 0.498 cm are applied for perforations, along with two fiber filling densities 100 and 200 kg/m3 to illustrate the effect of variations in such parameters on the perforatio...

In order to progress in the area of aeroacoustics, experimental measurements are necessary. Not only they required for engineering applications acoustics and noise engineering, but also necessary developing models acoustic phenomenon around us. One measurement particular importance is impedance. Acoustic Impedance measure opposition acoustical flow due pressure. It indicates how much sound pres...