How does a pipe organ work? By letting different amounts of air into different length pipes to produce a sound.
A pipe organ works on the same principle as a whistle. A simple whistle is just a pipe. When you put enough air in one end, you can get a sound out of the other end. The sound is created by the column of air inside the pipe vibrating. When you blow into the whistle, you force air into the narrow space of the pipe and it builds up at the end, compressing into an area of high pressure. Air molecules have a lot of energy, and they move a lot. When you force them into a narrow pipe, they still have that original energy plus the energy you used to get them into the pipe. They cannot move as much, but all of that energy makes them vibrate. When the vibrating compressed air leaves the pipe, it creates an audible sound. Sound is caused when a vibrating object creates a pressure wave that moves through a medium, which, in the case of the whistle, is the air. We hear this vibration as a sound. If you have a short pipe, the sound will be high and if you have a long pipe, the sound will be deeper. You can see this effect in a trombone. The trombonist uses the slide to change the length of the pipe in the trombone, making the sound higher or lower. A recorder is the same. The holes in the side of the recorder shorten its length, making the note high. As you cover more holes with your fingers, you slowly lower the pitch of the note.
Because one length of pipe can only make one noise, a pipe organ has to have a different length pipe for every noise it wants to produce. For example, if the organ covers 8 octaves, it will need to have 64 pipes of varying lengths. They will be arranged in height order. All of the pipe organs we have seen have far more than 64 pipes and some of them have thousands, so why do they need these extra pipes?
The pipe will play a different pitch if you change its length, but you can make a different timbre if you change the shape or the material of the pipe. If you make the pipe wider, or square, or out of a different material, or even case the pipe in wood, you will get a different timbre of note. It will still be the same note because the length of the pipe will have changed, but it will sound different. For example, flute pipes sound a little like a flute and trumpet pipes sound a little like a trumpet.
An organ works with wind, so modern organs have a motor that produces the wind and it can be stored in a windchest to ensure that there is always a constant pressure. Before the invention of the motor, pipe organs had to be operated with a bellows, which would not have been an easy job. Once the wind has been created and stored, it has to be directed to the pipes. Each key is connected to a valve on a pipe so that when the key is pressed, the valve opens, and air goes through the pipe, creating sound. Unlike pianos, the sound will continuously sound as long as air is going through the pipe so very long notes are possible. The pipe organ also has something called stops. These shift the pipes that the air is going through. For example, if you pull out the flute stop, the air will stop going through the regular pipes and start going through the flute pipes, changing the sound of the organ. It is also possible to have the air going to multiple types of pipes to give a whole variety of sounds. When you look at a pipe organ keyboard, there are a lot of buttons. These are all of the stops. Each rack and each type of pipe will have its own stop button. The more different types of pipes, the more buttons. They can be set before a performance or changed during the performance. That is why the pipe organ can make such interesting sounds and why they sound so amazing.
The pipe organ was invented in Ancient Greece in about the 3rd century BC. It was a water organ because he used water to power the bellows to push air into the pipes. Pipe organs have gone through a lot of changes since then and the organ with the most pipes at the moment is in Atlantic City. It has 33,112 pipes. And this is what I learned today.
Photo by Julia Volk: https://www.pexels.com/photo/interior-of-majestic-lutheran-church-with-organ-5273533/
Sources
https://www.cs.toronto.edu/~gpenn/csc401/soundASR.pdf
https://sciencing.com/a-whistle-work-4601984.html
https://www.okhistory.org/learn/pipeorgan
https://www.pipedreams.org/page/how-a-pipe-organ-works
https://www.yamaha.com/en/musical_instrument_guide/pipeorgan/mechanism/
https://en.wikipedia.org/wiki/Pipe_organ
https://flypaper.soundfly.com/discover/how-a-pipe-organ-makes-sound/
https://www.classicfm.com/discover-music/instruments/organ/guide-pipes-stops-anna-lapwood/