Point a speaker or buzzer at a wall or reflecting plate with some angle (45 degrees) of incidence with respect to the wall.  Use the cardboard tubes to make the sound emitted from the speaker more directional.  Place the microphone at an equal reflecting angle from the wall and note that the maximum sound intensity angle reflecting from the wall is at the same incidence angle as the speaker and wall.  You may also use a directional tube over the microphone to help cut down on unidirectional interference.  

This shows that sound reflecting from a wall does so at equal angles just as light does reflecting from a mirror or the angle of incidence equals the angle of reflection.