When using a closed resonator tube, why is the sound louder when the tube is at certain lengths?

Question

When using a closed resonator tube, why is the sound  louder when the tube is at certain lengths?

anonymous · Answer

sound waves have a certain distinct frequency, or how fast they oscilate.  if the length of one of these oscilations (the period) is equal to the length of the pipe or a fraction of the length of the pipe (1/2, 1/4, etc.) then the sound waves will resonate with each other and match up precisely, causing much stronger vibrations (what you hear)

anonymous · Answer

So then it depends on how it matches up right, if the frequency matches up to 1/2 of the pipe then that's where it's loudest? Would it change if it was an open tube?