The accordion is a musical instrument from the free-reed aerophone family. In this post I will present a general information about construction of this instrument and the process of the generating sound.

Classification

Curt Sachs and Eric M. von Hornbostel published scheme of the musical instrument classification. Based on their classification, the accordion is a musical instrument from the free-reed aerophone family. The air comes from outside the instrument. The sounds are produced by the reeds [1].

General details

In general, the accordion consists of three main parts:

There are many types of accordions – from 12 bass buttons up to 185. A typical 120 bass accordion has 3, 4 voices and weighs about 10kg. Depends on the type of accordion, the voices configurations will be different.

Below figure presents the main parts of the accordion.

Keyboard

In the accordion with a standard piano keyboard, the keyboard and registers are located on the right side of instrument. The keyboard consists of the white keys (tons) and black keys (semitones) arranged chromatically.

Using the keys, single notes and chords can be produced. The chord is a composition at least of three different sounds.

Bellows

Bellows is located at the center of the accordion, between the bass and the melody side. The bellows is used to generate the air pressure which is necessary to produce the sound. The bellows is also important for the articulation of the sounds.

Bass

The bass side is located at the left side of instrument. It consists of the bass buttons, which can produce single notes and chords.

The bass buttons are arranged in rows and columns. The root notes (such as A, C, …) are generated by buttons located in the first two rows. The chords (A-major, C-minor, …) are generated by the buttons in the particular column. Bass buttons are arranged in a circle of fifths, this means that, distance between sounds is equal fifth semitones.

Below schema presents arrangement of bass buttons in the 120 bass accordion.

Sound generation process

The accordion consists of the chromatically arranged reeds. This sequence is called the voice. When the bellows is pushed/pulled, the air flows through the specified reeds. The air flowing through the reeds causes vibration of the reed and as a result the sound at a specified frequency is produced. The reeds are mounted on the frame. Each reed’s frame has two reeds with the same pitch. When the bellows is pulled, the air flows through the first reed. In opposite situation, the air flows through the second reed. Each frame has a valve which is located on the other side of the frame. The valve is responsible for passing the flow of air in one direction in one time.

Reeds

Following figures presents reed and reed’s frame of the accordion. These figures come from [2].

Registers

The register is a special mechanism, which is used to change timbre of the produced sound. It is responsible for activating specified voices in the accordion. When the specified register has been activated, a set of active voices is changed. For example: an unison register produces the sound according to the musical sheet notation. But if a multi-voice register will be activated, one key can produce sounds in many octaves simultaneously (depends on the type of accordion).

The choice of the right register should depends on the type of performed melody. For example, the Musette register will be best for melodies like French Waltz. This full musette register has three voices (an unison, two voices tuned slighly above and below an unison).

Treble registers

The treble register switches are located above the keyboard. They are responsible for changing timbre of the sounds of the melody line. Depends on the type of accordion, their quantity and configurations will be different.

Below table presents a typical treble registers and the real sound of the musical note C5. The configuration switches comes from my accordion – Horch 120 bass.

Symbol	Real sound	Description
		Unison voice
		Voice one octave lower
		Two voices: unison, one octave lower
		Three voices: unison, tremulous (up, down)
		Two voices: unison, tremulous (down)
		Two voices: unison, tremulous (up)
		Four voices: unison, one octave lower, tremulous (up, down)

Bass registers

The bass register switches are located above the bass buttons.

Below table presents an examplary bass registers and the real sound of the root note E.

Symbol	Real sound	Description
		Unison voice
		Two voices: unison, one octave lower
		Three voices
		Four voices

References

Summary

In the first part of the article I presented the general information about the accordion. In the next part, the characteristic of the sounds will be presented.

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