Sound Insulation of Orthotropic Plates

We can run into Orthotropic plates, and unlike Isotropic plates, Orthotropic plates will have different characteristics in different directions.

An example of an Orthotropic plate is wood, that have a vastly different bending stiffness parallel with the fibres if compared to the bending stiffness perpendicular to the fibres.

Another example is a corrugated steel plate.

The important difference in the sound insulation is that Orthotropic plates typically will have 2 different critical frequencies.

Some orthotropic plates will have the two critical frequencies fairly close to each other, and so the Sound reduction may look similar to that of isotropic plates.

However the illustration below is what the sound reduction may look like when the critical frequencies are far enough apart that they can be individually distinguished.
in other scenarios, like a corrugated steel plate, the critical frequencies can be very far apart.