The concept of wave fronts, defined as points of like phase, can be demonstrated by the use of an audiofrequency oscillator, a loud-speaker, a microphone, and a cathode-ray oscilloscope. The shapes of wave fronts radiated from plane, line, and point sources and the attenuation of intensity with distance can be qualitatively demonstrated. The double slit diffraction pattern can be explored as a function of the wavelength, slit spacing, and distance to the plane of observation in a simple arrangement of equipment.