How does a pipe organ work?

“Niche” Series, issue 1.

 By Michael Studley

Welcome to the first issue of the “Niche Series.” Our first topic is the pipe organ. 

The pipe organ is a keyboard instrument which uses air to produce notes. It is found in many churches across the world, and it has an immense and voluminous sound that fills a cathedral easily. They have been around since the 3rd century, and they can contain anywhere from 61 pipes all the way to a little over 33,000 pipes.

The Pipes

Organ pipes can only produce one note, so they are usually found in groups called “ranks.” These ranks all have the same volume and tone, generally. There are two types of pipes; flue, and reed.

Flue pipes [above] are commonly made of metal, but they can also be made of wood. They look, for all intents and purposes, fairly similar to a standard metal pipe, but at the bottom of the resonator, the airflow is constricted through a sharp lip in the material which causes the air blown through it to vibrate at the pipe’s resonant frequency. They have no moving parts.

Reed pipes [above], however, are a bit more complicated. They usually look like a cone on top of a cone, but this can vary greatly. The bottom of the pipe (called the boot) contains a cavity sealed by a “block.” The resonator (the cone on the top) has a thin tube going down into the boot, which the reed is laid against. The reed is held in place by a “wedge,” and can be further altered via a tuning wire, which can be pushed in or out to adjust the pitch.

You may know this property of resonance and waves; If you have an 8-foot pipe as your base pitch (as is the case with pipe organs, in which it is called 8’), you will need a 16-foot pipe to go 1 octave down. As you can see, so lower the pitch by one octave, you must double the length of the pipe. If you need a higher octave, you half it. Therefore, the base pitch of an organ is called “8’ pitch,” 1 octave below is “16’ pitch,” an octave above is “4’ pitch,” and so on and so forth

Pipe Scaling

The scale of a pipe is the ratio of its diameter to its length. The only other thing you really need to know is that a larger diameter results in a fuller sound, and a stronger frequency at the note you’re actually playing (the fundamental).

The Manuals

So, you know how a piano will have just 1 keyboard to play the notes? An organ may have as many as five manuals, which are the keyboards of the organ. Unlike a full-sized piano keyboard, which has 88 keys, a normal organ manual will have 61 keys (or five octaves). Each manual (if you have more than one) controls a different subset of pipes.

The Console & The Stops

Let’s zoom out a bit and take a look at the entire area you play from. This area is called the console, which has not only manuals but also stops. Stops do what they’re named after; they stop airflow to a rank (or several ranks) of pipes. You have to pull out a stop in order to sound the associated group of pipes. (interesting aside, the phrase “to pull out all the stops” comes from pipe organ terminology.) 

There are many stops that an organ can have. Most fit into one of four categories: Diapasons, strings, flutes, and reeds.

Diapasons or principals are the characteristic sound of the pipe organ. They have a medium diameter and can be anywhere from 1’ pitch, all the way down to 32’ pitch. They are almost always the main feature of elegant facades you often find in churches. Strings are meant to imitate string instruments and have a narrower diameter resulting in a brighter tone. Flutes are the widest and, as a result, are the darkest. They are the closest to just the pure pitch (fundamental), and while not purposely meant to imitate a flute, they do sound quite similar. Reeds are, well, reed pipes, and are divided into two further categories. Chorus reeds are meant to complement and reinforce the larger sound of the flue pipes, while orchestral reeds are meant for solo passages, often imitating woodwind instruments.

The Pedalboard

You don’t have to play the organ with just your hands. Your feet often play an integral part too. The pedalboard is at the bottom of the organ console, and you press the keys down with your feet. It’s safe to assume that these are always used to play bass registers. They actually make special shoes [below] for playing pedalboards.

Not a fan, to be honest. They look like high heels and ballet shoes had a child who managed to inherit only the bad traits. 

(My apologies for that minor digression.)

I don’t have much else to say on this subject, so I’ll leave you with some interesting trivia.

  • The largest organ is the Boardwalk Hall Auditorium Organ, which has 449 ranks, 337 stops, and a massive 33,114 pipes.
  • The largest single organ pipe is a 64’, which has a minimum pitch of 8 Hz. That’s literally less than half of the lowest frequency a human can hear.

As a bonus, here are some pictures of some especially nice facades.