Diffraction is defined as the process by which waves spread out as a result of passing through a narrow slit or across an edge. It occurs only if the slit dimension is comparable to that of the wavelength of the wave.

The wavelength of sound wave is ranging from few millimetre to few metres, where the wavelength of light is in the nanometre range .So sound wave can diffract through a slit having opening in the millimetre –metre range which is seen everywhere .However it is difficult for light waves to find nanometre range opening to diffract , So the diffraction of sound waves more evident in daily experience than that of light wave.