Sound box
Encyclopedia
A sound box or sounding box (sometimes written soundbox) is an open chamber in the body of a musical instrument
which modifies the sound of the instrument, and helps transfer that sound to the surrounding air. Objects respond more strongly to vibrations at certain frequencies, known as resonance
s. The chamber's own resonances supply the reinforcement, and so the tone quality and resonances of the instrument are altered as a whole wherever the chamber's resonances mismatch the chamberless instrument's. The sound box typically adds resonance
s at lower frequencies, enhancing the lower-frequency response
of the instrument.
The distinctive sound of an instrument with a sound box owes a lot to the alteration made to the tone
. A sound box is found in most string instrument
s. The most notable exceptions are some electrically amplified instruments like the solid body
electric guitar
or the electric violin
, and the piano
which uses only a sound board instead. Drumhead lutes such as the banjo
or erhu
have at least one open end of the sound box covered with animal skin (or a skin-like acrylic material). Open back banjos are normally used for clawhammer
and frailing, while those used for bluegrass
have the back covered with a resonator.
In some arrangements, loudspeaker
s also are mounted on a sound box to enhance their output, particularly bass speakers. One notable example of this arrangement is called the bass reflex
enclosure. However, in these cases the box resonance is carefully tuned so as to make the sound more equal across frequencies, rather than to impart a particular character to the reinforced sound.
Musical instrument
A musical instrument is a device created or adapted for the purpose of making musical sounds. In principle, any object that produces sound can serve as a musical instrument—it is through purpose that the object becomes a musical instrument. The history of musical instruments dates back to the...
which modifies the sound of the instrument, and helps transfer that sound to the surrounding air. Objects respond more strongly to vibrations at certain frequencies, known as resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
s. The chamber's own resonances supply the reinforcement, and so the tone quality and resonances of the instrument are altered as a whole wherever the chamber's resonances mismatch the chamberless instrument's. The sound box typically adds resonance
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
s at lower frequencies, enhancing the lower-frequency response
Frequency response
Frequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
of the instrument.
The distinctive sound of an instrument with a sound box owes a lot to the alteration made to the tone
Timbre
In music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
. A sound box is found in most string instrument
String instrument
A string instrument is a musical instrument that produces sound by means of vibrating strings. In the Hornbostel-Sachs scheme of musical instrument classification, used in organology, they are called chordophones...
s. The most notable exceptions are some electrically amplified instruments like the solid body
Solid body
A solid-body instrument is a string instrument such as a guitar, bass or violin built without its normal sound box and relying on an electric pickup system to directly receive the vibrations of the strings....
electric guitar
Electric guitar
An electric guitar is a guitar that uses the principle of direct electromagnetic induction to convert vibrations of its metal strings into electric audio signals. The signal generated by an electric guitar is too weak to drive a loudspeaker, so it is amplified before sending it to a loudspeaker...
or the electric violin
Electric violin
An electric violin is a violin equipped with an electronic output of its sound. The term most properly refers to an instrument purposely made to be electrified with built-in pickups, usually with a solid body...
, and the piano
Piano
The piano is a musical instrument played by means of a keyboard. It is one of the most popular instruments in the world. Widely used in classical and jazz music for solo performances, ensemble use, chamber music and accompaniment, the piano is also very popular as an aid to composing and rehearsal...
which uses only a sound board instead. Drumhead lutes such as the banjo
Banjo
In the 1830s Sweeney became the first white man to play the banjo on stage. His version of the instrument replaced the gourd with a drum-like sound box and included four full-length strings alongside a short fifth-string. There is no proof, however, that Sweeney invented either innovation. This new...
or erhu
Erhu
The erhu is a two-stringed bowed musical instrument, more specifically a spike fiddle, which may also be called a "southern fiddle", and sometimes known in the Western world as the "Chinese violin" or a "Chinese two-stringed fiddle". It is used as a solo instrument as well as in small ensembles...
have at least one open end of the sound box covered with animal skin (or a skin-like acrylic material). Open back banjos are normally used for clawhammer
Clawhammer
Clawhammer is a highly rhythmic banjo playing style and common component of American old-time music. The principal difference between clawhammer style and other styles is the picking direction...
and frailing, while those used for bluegrass
Bluegrass music
Bluegrass music is a form of American roots music, and a sub-genre of country music. It has mixed roots in Scottish, English, Welsh and Irish traditional music...
have the back covered with a resonator.
In some arrangements, loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...
s also are mounted on a sound box to enhance their output, particularly bass speakers. One notable example of this arrangement is called the bass reflex
Bass reflex
A Bass reflex system is a type of loudspeaker enclosure that uses the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical closed box loudspeaker or an infinite baffle mounting.A reflex port is the distinctive feature of a...
enclosure. However, in these cases the box resonance is carefully tuned so as to make the sound more equal across frequencies, rather than to impart a particular character to the reinforced sound.
See also
- Acoustic guitarAcoustic guitarAn acoustic guitar is a guitar that uses only an acoustic sound board. The air in this cavity resonates with the vibrational modes of the string and at low frequencies, which depend on the size of the box, the chamber acts like a Helmholtz resonator, increasing or decreasing the volume of the sound...
- Basic physics of the violinBasic physics of the violinThe distinctive sound of a violin is the result of interactions between its many parts. Drawing a bow across the strings causes them to vibrate. This vibration is transmitted through the bridge and sound post to the body of the violin , which allows the sound to effectively radiate into the air...
- Filter (signal processing)Filter (signal processing)In signal processing, a filter is a device or process that removes from a signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal...
- Frequency responseFrequency responseFrequency response is the quantitative measure of the output spectrum of a system or device in response to a stimulus, and is used to characterize the dynamics of the system. It is a measure of magnitude and phase of the output as a function of frequency, in comparison to the input...
- Resonance chamberResonance chamberA resonance chamber uses resonance to amplify sound. The chamber has interior surfaces which reflect an acoustic wave. When a wave enters the chamber, it bounces back and forth within the chamber with low loss...