Diffraction occurs with all types of waves. The amount of spreading depends on the relationship between the wavelength and the gap width.
Maximum diffraction occurs when the gap width is approximately equal to the wavelength. If the gap is much wider than the wavelength, there is very little spreading.
This explains why sound (wavelength ~1 m) diffracts through doorways but light (wavelength ~500 nm) does not noticeably diffract through the same opening.
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