Notes

Musical Instrument Families



Musical Instruments are classified by the way they make sounds. Like most things in life, these classifications can be fuzzy around the edges. Is a piano a stringed instrument? It has strings. Is it a percussion instrument? It has hammers. Why is a saxophone a woodwind when it's made out of brass? Some of the fuzziness is due to history: a saxophone is a woodwind because it has a reed, and at one time most reed instruments were made of wood. Some instruments, like the piano, are just hard to classify. You'll find the various classifications listed below. Again, my major criterion for grouping the instruments is the way in which they make their sounds. Sounds are the result of vibrations, and in each type of instrument the vibrations come from a different source. You are welcome to take issue with my classifications.


Strings

Stringed instruments are characterized by having (you guessed it!) strings.

How the sounds are made

Vibrating strings provide the sound in stringed instruments. The player makes the strings vibrate in one of several ways:

Plucking, as with the harp, guitar, and mandolin

Bowing, as with the violin family

Hitting, as with the hammered dulcimer and piano

Even blowing! The aeolian harp uses the wind to set its strings in motion.

How the pitch is changed

Length, thickness, tension, and density of the string material all affect the pitch of a given string. Longer, thicker, denser, and looser strings all vibrate more slowly than shorter, thinner, less dense, and tighter strings. Slower vibration means lower pitch; faster vibration means higher pitch. The different pitches on most stringed instruments are obtained either by having many strings of different lengths, as on a harp, or by changing the vibrating length of strings by stopping them at different points, as on a violin or guitar. The washtub bass changes pitch by varying string tension.

Examples
Bowed strings violin
viola
violoncello
bass viol
bowed psaltery
Plucked strings guitar
lute
harp
sitar
balalaika
koto
mandolin
kanoon
zither
lyre
Hit stringshammered dulcimer
berimbau
Otherhurdy-gurdy (crank turns a wheel which rubs against the strings)
Aeolian harp (strings set in motion by the wind)


Woodwinds

At one time, most woodwinds were made of wood; hence the name. The easiest way to characterize them now is as wind instruments (that is, you blow into them) which aren't played by buzzing your lips together.

How the sounds are made

Most woodwind instruments are tubes. The sound comes from a vibrating column of air inside the tube. The player makes this column of air vibrate in one of several ways:

By blowing across an edge, as in the flute, recorder, whistle, and root beer bottle

By blowing between a reed and a fixed surface, as in the clarinet and saxophone

By blowing between two reeds, as in the oboe, bassoon, sarusaphone and bagpipes

How the pitch is changed

Woodwind pitch depends on the volume of air that is vibrating. A larger volume vibrates more slowly, for lower pitch; a smaller volume vibrates more quickly, for a higher pitch. For most woodwinds, the player changes pitch by opening and closing holes along the instrument's length. Without keys, there can only be as many holes as the player has fingers to cover them with. Adding keys allows the number and complexity of holes to be increased. Increasing the blowing pressure past a certain critical point (called the "break") causes the air column to resonate at a higher harmonic (see the harmonics section, below) and raises the pitch of many woodwinds by a large interval. In most cases this interval is an octave (e.g. middle C to high C), but in the clarinet it is a 12th (e.g. middle C to the G above high C). With minor variations this is the way woodwinds achieve large ranges.

Examples
Edge-blownflute
recorder
tin whistle
slide whistle
whisky jug
Single reedclarinet
saxophone
basset horn (arf!)
Double reedoboe
bassoon
English horn
bagpipes
krummhorn
shawm


Brass

Most brass instruments from the Western European tradition really are made of brass, but there are large numbers of brass-type instruments which are made of wood, horn, shell, or other materials.

How the sounds are made

As with woodwinds, the sound comes from a vibrating column of air inside the tube of the instrument. The air column vibrates in resonance with the vibrating lips of the player, who presses her or his lips together in the mouthpiece and forces air out between them, making a "raspberry" or "Bronx cheer" sound.

How the pitch is changed

The pitch of a brass instrument depends on the volume of air that is vibrating, as well as the speed at which the player's lips vibrate. The volume of air depends on the length of the tube; a longer tube means a larger volume of air, hence lower pitch. By buzzing her lips faster or slower, the player can cause the air in the tube to resonate at different harmonics (see the discussion of harmonics and overtones in the physics section). With a single-length tube this yields only the notes found in bugle calls. To get all 12 notes of the chromatic scale, the player needs to change the length of the tube, as on the trombone, or play through different lengths of tubing, as on the brass instruments with valves.

Examples

trumpet
trombone
French horn
tuba
bugle
digeridu
conch shell


Percussion

Percussion instruments include just about anything you can whack with a stick.

How the sounds are made

In percussion instruments the sound source is a vibrating membrane (these instruments are called membranophones) or vibrating piece of solid material (these are ideophones). The percussionist normally causes these materials to vibrate by hitting them (hence the name percussion), but many percussion instruments are played by shaking, rubbing, or any other way of causing vibrations.

How the pitch is changed

Because of the complex ways in which the sound source vibrates, most percussion instruments do not have definite pitch. Most of the instruments that do have definite pitch are ideophones. The pitch of these instruments depends on the amount of material that is vibrating. In general this means that the instruments must have a different vibrating body for each note, such as xylophone bars, chimes, bells, or the tuned gongs of a gamelan orchestra. The pitch of membranophones (i.e. drums) depends on thickness and tension of the drumhead. The only common membranophones with definite pitch are kettledrums (timpani).

Examples
Membranophones Definite pitchkettledrums (roto-toms and some other drums have quasi-definite pitch)
 Indefinite pitch other drums of all kinds
tambourine
IdeophonesDefinite pitch xylophone
marimba
vibraphone
handbells
chimes
gamelan
 Indefinite pitch cymbals
gong
rattles of all kinds
bones
spoons
log drum
woodblock
triangle
maracas
rhythm sticks
coconuts
etc. etc.


Keyboards

Keyboard instruments produce their sounds in different ways, but they all have keyboards. In general they are somewhat more complicated machines than other instruments.

Harpsichord

Strings are the sound source. Pressing a key causes a quill to pluck the string. To change volume or sound quality, pedals or levers allow the player to link each key to one or more strings, tuned to the same note or the same note in different octaves.

Clavichord

Strings are the sound source. Pressing a key causes a hard bridge or rod (called a "tangent") to hit the string. The string vibrates only as long as the tangent is in contact with it. (This is a little bit like what happens if you press your finger down hard and fast behind a fret on the fingerboard of a guitar; the fret acts like the tangent on a clavichord.)

Piano

C'mon, you know this one! Strings are once again the sound source. Pressing a key causes a felt hammer to hit the string. The more force you use on the key, the louder the sound.

Pipe organ

Vibrating columns of air inside the pipes are the sound source. Pressing a key directs air (from a pump or compressor) across an edge into the pipe, much like the edge-blown woodwinds. The organist can link the keyboard to different arrays of pipes, called "stops." The calliope is a high-pressure, portable version of the pipe organ, originally powered by steam.

Celesta

Metal bars are the sound source. Pressing a key causes a hammer to strike the bar.

Accordion

Known to the ancients as "the most sublime of all musical instruments," the well-revered accordion uses metal reeds as the sound source, set in motion by air from a bellows. Pressing a key on the accordion opens valves allowing air from the bellows past one or more reeds.


Electronic instruments

Electronic instruments create sound through electrical signals, turned into vibrations by a speaker. The more recent electronic instruments are digital; older ones are analog. Digital instruments can talk to each other using a protocol called MIDI. MIDI is an acronym for Musical Instrument Digital Interface. If you want to know more, check out the MIDI panel in Tech Zone , near the digital piano. It's a fine, well-written, explanation.

Examples

Theremin, Hammond organ, synthesizers of all types


Copyright Pacific Science Center 1996
If you have any questions or comments please contact (Paul_Beck@pacsci.org)