If I was to knock on a wall or door between a pressurised room and a vacuum, would that sound different from knocking on a wall or door of the same material between two pressurised rooms?

If not, would there be any easy way to check if a room is depressurised, using only human senses and without opening the door?

  • $\begingroup$ Are you asking if you can knock twice - once when the other side is known to be pressurized, and then at some later time, to see if there is a change? Or do you mean can you tell without prior knowledge of the sound when it is pressurized? $\endgroup$
    – uhoh
    Aug 5, 2016 at 13:08
  • $\begingroup$ Knocking on a pressurized scuba tank versus an empty scuba tank may give you a similar sounding result in sound differential. 1 bar is "pretty close to a vacuum" compared to the 200 bar at which scuba tanks are pressurized. Then again, with vessel walls that thick you may honestly not hear a difference. $\endgroup$ Mar 9, 2020 at 15:21

2 Answers 2


If there is a wall between a pressurised room and a vacuum, the resulting forces to the wall are pretty strong. Strings of a guitar sound different if tension on the string varies. I suspect the wall would sound different. The force on a door between vacuum and pressure is so strong that opening of the door would be impossible or the door is severly damaged.

I have seen a normal room door bending by a pressure difference between both adjacent rooms. The pressure difference was very small, only some centimeters of water or a few mbar. It was possible to open the door, but you had to use all your muscles. The force to a door 1 m wide and 2 m high from a pressure difference of 1 bar is the same as of a load of 20,000 kg to the ground below. It is better to build not a rectangular door but a circular one.


I suspect there would be a difference: a door between a pressurized area and a vacuum is under pressure from one side. Compare to a guitar string: they sound different when you vary the pressure on them.


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