Sound waves have a frequency of 20 Hz to 20,000 Hz and a wavelength of 15 m to 15 mm, respectively. When the size of the slit is similar to the wavelength of the sound, it causes diffraction. Visible light has a wavelength of 0.4 to 0.7 microns. When the size of the slits differs from the wavelength of visible light, there is no diffraction of the light.