Here’s the pattern: Standing sound waves can be established in a tube that’s closed
at one end if the tube’s length is equal to an odd multiple of λ. The resonant
wavelengths and frequencies are given by the equations
If the far end of the tube is not sealed, standing waves can still be established in the
tube, because sound waves can be reflected from the open air. A closed end is a
displacement node, but an open end is a displacement antinode. In this case, then,
the standing waves will have two displacement antinodes (at the ends of the tube),
and the resonant wavelengths and frequencies will be given by