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 Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied Periodic function, periodic force (or a Fourier analysis, Fourier component of it) is equal or close to a natural frequency of the system ...

s. The frequency and strength of the resonances of the body of a musical instrument have a significant impact on the tone quality it produces. The air inside the chamber has its own resonances, and these interact with the resonances of the body, altering the resonances of the instrument as a whole. The sound box typically adds

s at lower frequencies, enhancing the lower-

frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of s ...

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 instruments.Medieval and Tudor string instruments
/ref> The most notable exceptions are some electrically amplified instruments like the solid body

electric guitar An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...

or the

electric violin An electric violin is a violin equipped with an electronic output of its sound. The term most properly refers to an instrument intentionally made to be electrified with built-in pickups, usually with a solid body. It can also refer to a violin fi ...

, and the

piano The piano is a stringed keyboard instrument in which the strings are struck by wooden hammers that are coated with a softer material (modern hammers are covered with dense wool felt; some early pianos used leather). It is played using a keybo ...

which uses only a sound board instead. Drumhead lutes such as the banjo or ''

erhu The ''erhu'' (; ) is a Chinese two-stringed bowed musical instrument, more specifically a spike fiddle, which may also be called a ''Southern Fiddle'', and is sometimes known in the Western world as the ''Chinese violin'' or a ''Chinese two- ...

'' 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, sometimes called down-picking, overhand, or frailing, is a distinctive banjo playing style and a common component of American old-time music. The principal difference between clawhammer style and other styles is the picking direct ...

and frailing, while those used for bluegrass have the back covered with a resonator. In some arrangements,

loudspeaker A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or ...

s are also mounted on a sound box to enhance their output, particularly bass speakers. One notable example of this arrangement is called the

bass reflex A bass reflex system (also known as a ported, vented box or reflex port) is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound fro ...

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. * Acoustic guitar *

Basic physics of the violin Violin acoustics is an area of study within musical acoustics concerned with how the sound of a violin is created as the result of interactions between Violin construction and mechanics, its many parts. These acoustic qualities are similar to th ...

* Filter (signal processing) *

Frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of s ...

Resonance chamber A resonance chamber uses resonance to enhance the transfer of energy from a sound source (e.g. a vibrating string) to the air. The chamber has interior surfaces which reflect an acoustic wave. When a wave enters the chamber, it bounces back an ...

References

String instrument construction {{string-instrument-stub