Fluid mechanical model of the acoustic impedance of small orifices
Abstract
A fluid mechanical model of the acoustic behavior of small orifices is presented which predicts orifice resistance and reactance as a function of incident sound pressure level, frequency, and orifice geometry. Agreement between predicted and measured values is excellent. The model shows the following: (1) The acoustic flow in immediate neighborhood of the orifice can be modeled as a locally spherical flow. Within this near field, the flow is, to a first approximation, unsteady and incompressible. (2) At very low sound pressure levels, the orifice viscous resistance is directly related to the effect of boundarylayer displacement along the walls containing the orifice, and the orifice reactance is directly related to the inertia of the oscillating flow in the neighborhood of the orifice. (3) For large values of the incident acoustic pressure, the impedance is dominated by nonlinear jetlike effects. (4) For low values of the pressure, the resistance and reactance are roughly equal.
 Publication:

Final Report Hersh Acoustical Engineering
 Pub Date:
 May 1976
 Bibcode:
 1976hae..reptQ....H
 Keywords:

 Acoustic Impedance;
 Fluid Mechanics;
 Mathematical Models;
 Orifices;
 Nonlinear Systems;
 Orifice Flow;
 Reactance;
 Resistance;
 Sound Pressure;
 Sound Transmission;
 Acoustics