HEY PIANO 4UHow Drawbar Organs Work: Harmonics, Tonewheels and Leslie Speakers
The sound of a classic drawbar organ, the kind used in gospel, jazz, blues and rock, comes from a clever idea: build a note by adding together its parts. Understanding that idea makes the controls make sense.
A note is a stack of harmonics
A musical note is made of a main pitch, called the fundamental, plus quieter higher pitches called harmonics or overtones. The balance between them gives each instrument its tone. A flute has few strong harmonics; a trumpet has many.
What a drawbar does
A drawbar organ lets you set the mix yourself. Each drawbar is a slider that controls how loud one harmonic is, from 0 (off) to 8 (full). Pull a drawbar out and its harmonic is added to every note you play. Push it in and it disappears. Nine drawbars give you nine ingredients to blend.
Footage numbers
Drawbars are labelled with “footages” borrowed from pipe organs, where a pipe of a given length produces a given pitch. The nine standard footages are 16′, 5⅓′, 8′, 4′, 2⅔′, 2′, 1⅗′, 1⅓′ and 1′. The 8′ drawbar is the pitch you pressed. The 16′ sounds an octave lower, the 4′ an octave higher, the 2⅔′ a fifth above that, and so on up through the harmonic series.
| Drawbar | Sounds |
|---|---|
| 16′ | One octave below the key |
| 5⅓′ | A fifth above the key you pressed |
| 8′ | The key you pressed (the fundamental) |
| 4′ | One octave above |
| 2⅔′ | An octave and a fifth above |
| 2′ | Two octaves above |
| 1⅗′, 1⅓′, 1′ | Higher bright harmonics |
Tonewheels and the Hammond organ
In the Hammond organs introduced in the 1930s, the tones came from small metal discs, called tonewheels, spinning next to magnetic pickups. Each tonewheel produced one pure tone. Pressing a key combined tones from several wheels, and the drawbars decided how loud each one was. Electronic organs later copied this design with circuits and, today, with software.
The rotary speaker
Many drawbar organs are played through a rotating speaker cabinet, commonly called a Leslie. Spinning horns and drums make the sound waver in pitch and loudness, which gives the swirling effect. It usually has two speeds, slow and fast, and switching between them is part of the classic organ style.
Try it in Hey Piano 4U
Switch the dial to Organ. You will find nine drawbars and a choice of rotary speed (Off, Slow or Fast). Our organ voice builds each note from the same nine harmonics and adds a gentle key click and a tremolo for the rotary effect. It is an approximation made for practice, not a copy of any one organ. Try pulling out only the 8′ drawbar for a pure flute-like tone, then add the others one by one and listen to the sound get richer.
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