text: You can do this a couple ways.\n\n1.  One computer produces a constant tone and the other computer produces a tone that varies within a few Hz over a period of several seconds.  You will hear wa-wa-wa as the tones constructively and destructively interfere.\n\n2.  Set up two speakers 10 ft or so apart.  Both speakers produce a tone having a wavelength equal to the distance between speakers.  As you walk from one speaker to the other, the sound will increase and decrease as you move from the area of constructive to destructive interference.  If you change the wavelength of the sound to 1/2, 1/3, etc. of the distance between speakers, the sound will increase-decrease 2, 3, etc. times.