1. The Wind Chest: Where an Organ Stores Air Before It Reaches the Pipes
The source of an organ’s sound is air. Air sent from a blower collects in a "wind chest" before flowing into the pipes to create sound. According to the Kyoto Concert Hall, this works on the same principle as blowing a flute. [1] The inside of the wind chest is kept at a constant air pressure. [3] When no key is pressed, the pressurized air stays in the wind chest. [3]
The method of sending this air has changed over time. Until the mid-19th century, bellows powered by human strength were used. Later, power sources like steam engines and electric blowers were also used. [3] This history shows that while the technology of moving air has evolved, the basic need for stored, pressurized air remains the same.
2. How Pressing a Key Opens a Valve in the Wind Chest
When a key is pressed, a valve inside the wind chest opens. This valve, which regulates the air, is called a "pallet" and is connected to the keyboard. [2] In an organ, a key works by opening a valve that lets air through. [2]
It helps to think of it this way: when a key is pressed, the valve opens and wind flows toward the pipe. When no key is pressed, the valve stays closed. [2] This simple action of opening and closing a gate for air is the first step in creating a note.
3. How Stops Choose Which Row of Pipes Plays
The pipes in an organ are divided into groups by tone color. A collection of pipes with the same tone color is called a "rank," and there is one pipe for each key on the keyboard. [6] Stops are the mechanism that chooses which of these ranks will sound. [2] Depending on the stop selected, air flows to specific pipes. [2]
This brings us back to the main question: why doesn’t pulling a stop make a sound on its own? It is because there is another valve, opened by the keyboard, that air must pass through before it reaches the pipes. [2] Two choices are combined: "which rank" (selected by the stop) and "which note" (selected by the key). [6] While many stops control one rank, some stops are said to have multiple pipes for a single note. [6]
4. Why a Pipe Half as Long Sounds One Octave Higher
The pitch of a pipe is determined by its length. In flue pipes, a pipe that is half the length of another will produce a sound one octave higher. [5] Stop names often include numbers like 8', 16', and 4'. These represent the pitch, originally referring to the length of an open pipe in feet. [4] An open pipe of 8 feet (about 2.4 m) is the standard for the pitch of the keyboard note. [4] A 16' stop sounds one octave lower, and a 4' stop sounds one octave higher. [4]
When the number on a stop doubles, the pitch drops by one octave. Looking at the number gives a rough idea of how high or low that row of pipes will sound. [4] However, closed pipes produce the same pitch at half the length. [4] Because actual pipe lengths vary by construction, these numbers are names based on equivalent open pipe lengths. [4]
5. Flue Pipes and Reed Pipes: Two Ways Pipes Make Sound
Pipes are broadly divided into two types: "flue pipes" and "reed pipes." Flue pipes produce sound by directing air at a mouthpiece, similar to a recorder. [3] They are said to make up about 80% of all pipes, though this number varies by instrument. [4]
Reed pipes work differently. A thin metal plate (the reed) vibrates when air flows through the pipe, and the pipe resonates with the vibration. Wikipedia describes the reed pipe as having a single reed structure, similar to a clarinet. [3] The reed is typically a piece of metal, such as brass. [3] Even with the same air supply, changing how the sound is created changes the tone color. [3]
6. Comparing the Number of Pipes in a Concert Hall Organ and a University Organ
The organ at the Kyoto Concert Hall has a total of 7,155 pipes and 90 stops. [1] Stops are knobs that select rows of pipes to play. Since some stops combine multiple ranks, the number 90 does not necessarily equal the number of pipe rows. [1]
A smaller example is the organ at Keisen Jogakuen University. It has 1,260 pipes in total, ranging in length from 1.5 cm to 2.8 m. [2] The materials are wood or an alloy of tin and lead. [2] The difference between 1.5 cm and 2.8 m is about 190 times. [2] Pipes of different lengths stand on the wind chest. [2] While larger organs exist, this article focuses on these two examples found in Japan. [1][2]
7. How to Read Stop Labels Like 16', 8', and 4' at an Organ
If you have a chance to attend a concert or a tour at a hall with an organ, try looking at the stop labels. You might see numbers like 16', 8', and 4' lined up. [1][2] Predict which stops may sound lower, then listen for the differences. [1]
It is also interesting to watch which stops the player pulls and imagine which pipes are sounding. [1] For those who wish to read the original sources, pages from the Kyoto Concert Hall and Keisen Jogakuen University are available in Japanese. [1][2]