@Ahlesaadat I don’t remember much about that loudspeaker question.AFAIK it said that if we move that spring like tube some 5cm, the sound becomes very faint as compared to that in original configuration. It means that 5cm should be the distance between the antinode and node, former being the node – which is equal to λ/2.
λ/2 = 5cm
λ = 10cm = wavelength.