Directivity of a rectangular piston on a baffle

Directivity

For a rectangular piston in a baffle, the directivity for Lx=3 Ly and KLx=30 is plotted. x and y are the directions along the plate and z is the direction normal to the baffle.

Plane wave propagation: Sweeping Kx

Sweeping Kx from -K to K and its effect on the plane wave solution. Choosing kx can be physically done by controlling the wave number of the membrane at z=0.
All the following animations are for frequency 2000 Hz which means the membrane is vibrating at the same rate in all of these cases. The peaks and valleys are corresponding to that in a medium with c=340 m/s and density 1.23 kg/m^3.

Evanescent wave problem

Evanescent wave:

A physically accurate particle motion animation of an evanescent wave is given here. Two oppositely travelling waves in a membrane with kx=+2k and -2k forming a standing wave were taken. Assumed values: speed of sound = 340 m/s, frequency = 1000 Hz, density of medium = 1.23 kg/m^3

Propagating wave:

If kx is +k/2 and -k/2 , the wave would propagate in the positive z.

Wave Motion

This is how peaks and valleys are distributed in a 1000 Hz sound wave propagating in air with c=340 m/s. Time is in seconds. Indeed, particle velocities are exaggerated.