Air, Pipes and Keys: How a Pipe Organ Works

Air, Pipes and Keys

1Imagine a musical instrument as big as a building. Some pipe organs fill an entire wall of a concert hall, and large ones can have thousands of pipes. Yet every pipe organ, large or small, works on one simple idea: it makes music by sending air through pipes.

2Each pipe in an organ plays only one note. Many pipes work much like a whistle. Air rushes in at the bottom of the pipe and strikes a sharp edge called the lip. This makes the air inside the pipe vibrate, or shake back and forth very quickly, and the vibrating air makes a sound. Other pipes, called reed pipes, have a thin strip of metal inside that vibrates when air flows past it. Reed pipes often sound buzzy, a bit like a trumpet.

3The length of a pipe decides how high or low its note will be. A long pipe makes a low note, and a short pipe makes a high note. That is why an organ needs so many pipes. The smallest pipes may be shorter than a pencil, while the longest can be taller than a two-story house. Most pipes are made of metal or wood.

4An organist plays with both hands and feet. The hands press keys on one or more keyboards. The feet press long wooden pedals that play the lowest notes. When a key is pressed, a valve opens and lets air flow into the pipes for that note. Knobs or switches called stops let the organist choose which sets of pipes will sound. Pulling one stop might give a soft, flute-like sound, while another gives a bold, trumpet-like sound.

5The organ has a long history. More than two thousand years ago, an inventor named Ctesibius lived in Alexandria, a city in Egypt where Greek scholars studied and built machines. He is often given credit for building the first organ. It was called the hydraulis, or water organ. It used water pressing on trapped air to keep a steady flow of air moving to the pipes.

6For many centuries after that, organs got their air from bellows, which are bags that push air out when they are squeezed. Someone had to pump the bellows by hand or by foot the whole time the organ was played. If the pumper grew tired and stopped, the music faded away.

7In the late 1800s and early 1900s, electric motors began to take over this job. Today an electric fan, called a blower, pushes air into most organs, so no one has to pump. Even so, the basic idea is the same as it was long ago: air, pipes and keys working together to make music.