The Main Families of Musical Instruments

Grouping instruments into families is a way of bringing order to the hundreds of sound-making objects found around the world. The best-known groups, strings, winds, percussion, and keys, actually mix two kinds of criteria: how the sound is produced and how the instrument is played. Noticing that mix clears up classic puzzles, such as where the piano belongs.

The acoustic criterion: what vibrates

The most widely used scientific framework is the classification by Erich von Hornbostel and Curt Sachs, published in 1914. It looks at the body that produces the sound and divides instruments into four large groups, to which a fifth, the electrophones, was added later:

• Idiophones: the rigid body itself vibrates (triangle, xylophone, cymbals, marimba).
• Membranophones: a stretched skin or membrane vibrates (snare drum, timpani, tambourine).
• Chordophones: one or more strings vibrate (violin, guitar, harp, piano).
• Aerophones: enclosed or moving air vibrates (flute, clarinet, trumpet, pipe organ).
• Electrophones: the sound depends on electrical circuits (synthesizer, electronic organ).

This system is heavily used in museums and in ethnomusicology, because it works for instruments from any culture. The physics behind it is summarized in how musical instruments produce sound.

The practical criterion: how it is played

Musicians and orchestras use slightly different groupings, closer to gesture and function. The traditional division speaks of strings, winds, percussion, and keys. It feels intuitive because each group has its own technique, repertoire, and even its own path of study. A violinist and a flutist rarely share the same practice routine.

This practical division creates overlaps. The piano, for example, is a chordophone from an acoustic standpoint, but it is played with keys and so is usually treated as a keyboard instrument. The xylophone is an idiophone and also a percussion instrument. The pipe organ combines a keyboard with aerophones. Neither criterion is wrong; they answer different questions.

Strings

In stringed instruments, the vibration starts in taut strings stretched over a resonating body. They can be bowed, as on the violin, viola, cello, and double bass; plucked, as on the guitar, harp, and mandolin; or struck, as on the piano and the hammered dulcimer. The fundamentals of the first two techniques appear in bowed string instruments and plucked string instruments.

In a symphony orchestra, the bowed strings form the largest section, with dozens of players, and carry much of the melodic line and the harmony. The harp is usually treated as a separate instrument, with one or two harpists.

Winds

Wind instruments make sound through the vibration of a column of air inside a tube. The way that vibration is started divides them into subgroups:

1. Flutes: the air is directed against a sharp edge, as in the concert flute and the piccolo.
2. Single reed: a thin blade of cane vibrates against the mouthpiece, as in the clarinet and saxophone.
3. Double reed: two blades vibrate against each other, as in the oboe and bassoon.
4. Cup mouthpiece: the player's lips buzz in a metal mouthpiece, as in the trumpet, trombone, and tuba.

In the orchestra, winds are split into woodwinds and brass, names that come from a tradition of materials and do not exactly describe modern construction: today's concert flute is usually made of metal, and so is the saxophone, yet both are classified as woodwinds. The distinction is explained in woodwind vs. brass instruments.

Percussion

Percussion brings together instruments that sound when they are struck, shaken, or scraped. It is a large and varied family, since it includes idiophones and membranophones of definite pitch, such as the timpani and vibraphone, and of indefinite pitch, such as the snare drum, bass drum, and cymbals. Its role may be rhythmic, coloristic, or, in some cases, melodic. The internal grouping is the subject of how percussion instruments are classified.

Keys

Keyboard instruments form a peculiar family because the criterion is the interface, not the mechanism. Piano, harpsichord, organ, celesta, and piano accordion share the same arrangement of keys but produce sound by different means: hammers strike strings in the piano, small quills or plastic plectra pluck the strings in the harpsichord, and air flows through pipes in the organ. This diversity is discussed in keyboard instruments: mechanisms and differences.

How the orchestra uses this map

In an orchestral score, the instruments are arranged in groups, usually from top to bottom: woodwinds, brass, percussion, keyboards or harp when present, and strings. This order reflects the tradition of how the ensemble is organized and helps the conductor find each section. Rimsky-Korsakov's classic study of orchestration treats each group separately, precisely because each has its own qualities of tone color and agility. To see how these groups are laid out on stage, read how an orchestra is organized.

Knowing the families also helps with listening. When you can tell whether a sound is sustained or struck, and whether it comes from a string, air, or a membrane, you have already narrowed the options considerably before thinking of specific names.

Borderline cases and new families

Some instruments defy any single category. The pipe organ is both an aerophone and a keyboard instrument. The human voice, which involves the vocal folds and resonating cavities, is often studied on its own. Electronic instruments, for their part, form a group of their own that includes keyboards, synthesizers, and other gear, as you can see in the evolution of electronic musical instruments.

There are also hybrid instruments. The electric guitar is a chordophone whose sound depends on pickups and amplification; certain electric pianos, such as the Rhodes, use hammers that strike metal tines whose vibration is picked up electromagnetically. In situations like these, the most useful criterion is to ask which element starts the vibration that will be heard and which later stage merely amplifies it.

Families around the world

The Western orchestra is only one way of arranging instruments. Many musical traditions group them by other principles: by the material they are made of, by the role they play in ceremonies, or by the register they cover. The Hornbostel-Sachs system became so widely adopted precisely because it sidesteps those local habits and asks a question every instrument answers, namely what physically vibrates. That is also why a museum curator can place a West African kora, a Javanese gong, and a European lute in the same scheme without forcing any of them into an unnatural category.

For a learner, the practical takeaway is that families are tools, not laws. Use the acoustic view when you want to understand how a sound is made, and the practical view when you want to understand who plays what in a band or an orchestra.

Where to Go From Here

Choose five instruments you know and try to classify each by both criteria, the acoustic and the practical. Where the answers diverge, as with the piano, you will have found a borderline case. Then test your knowledge in the quiz and notice which families still raise questions.