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Boundary Condition Setting

Two boundary conditions

Set the open boundary on the surface of the hemisphere, and the speed boundary on the diaphragm.

 

 

Pressure boundary or speed boundary?

The boundary condition set on the diaphragm should be chosen carefully.

The figure below shows the radiation impedance Z obtained by this analysis. It is calculated as follows.

 

Radiation impedance = force applied on the driving face/vibration velocity of the driving face

 

In this model, Z becomes maximum at 9 kHz due to the resonance of the cavity.

When driven at a constant speed, a very large pressure is applied to the diaphragm at a resonant frequency of about 9 kHz.

Conversely, if driven at a constant pressure, the speed becomes extremely small at the resonant point.

 

Considering which value should be kept constant, the right boundary condition should be set.