Sound generator
Encyclopedia
A sound generator is a vibrating object which produces a sound. There are two main kinds of sound generators (thus, two main kinds of musical instrument
s).
A full cycle of a sound wave will be described in each example which consists of initial normal conditions (no fluctuations in atmospheric pressure), an increase of air pressure, a subsequent decrease in air pressure which brings it back to normal, a decrease in air pressure (less pressure than initial conditions), and lastly, an increase which brings atmospheric pressure back to normal again. Therefore, the final conditions are the same as the initial, at-rest conditions.
The first kind is simple and is called the vibrating or oscillating piston. Examples of this type of sound generator include the soundboard of a piano
, the surfaces of drum
s and cymbal
s, the diaphragm
of loudspeaker
s, etc. The forward movement of something through the atmosphere causes an immediate increase in air pressure (compression) or condensation in the air adjacent to the piston. A complete cycle, or one complete soundwave, consists of an increase of pressure in the air, a subsequent decrease of pressure so that the pressure is back to normal, and a following decrease in air pressure called rarefaction
. One complete cycle is produced when a drum is hit once with force.
The second kind of sound generator is the method utilized by wind instrument
s, such as trumpet
s. At the beginning of the cycle, sound pressure is normal. Then, an opening called an aperture (such as the opening on the mouthpiece of a trumpet) is partially open and a short stream of air under pressure is released. In the second step of a full cycle, the valve is completely open and pressure is at a maximum. In the third cycle, the valve is partially closed, and the pressure has decreased from the maximum value. Then, the valve is closed and the pressure is the same as normal undisturbed atmospheric pressure. Thus, a full cycle is produced. This happens very quickly in the vibration of lips (i.e., the aforementioned "valve") as they quickly open and close (or vibrate). More examples of this type of sound instrument include siren
s, organ
s, saxophone
s, and trombone
s.
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...
s).
A full cycle of a sound wave will be described in each example which consists of initial normal conditions (no fluctuations in atmospheric pressure), an increase of air pressure, a subsequent decrease in air pressure which brings it back to normal, a decrease in air pressure (less pressure than initial conditions), and lastly, an increase which brings atmospheric pressure back to normal again. Therefore, the final conditions are the same as the initial, at-rest conditions.
The first kind is simple and is called the vibrating or oscillating piston. Examples of this type of sound generator include the soundboard of a 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...
, the surfaces of drum
Drum
The drum is a member of the percussion group of musical instruments, which is technically classified as the membranophones. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a shell and struck, either directly with the player's hands, or with a...
s and cymbal
Cymbal
Cymbals are a common percussion instrument. Cymbals consist of thin, normally round plates of various alloys; see cymbal making for a discussion of their manufacture. The greater majority of cymbals are of indefinite pitch, although small disc-shaped cymbals based on ancient designs sound a...
s, the diaphragm
Diaphragm (acoustics)
In the field of acoustics, a diaphragm is a transducer intended to faithfully inter-convert mechanical motion and sound. It is commonly constructed of a thin membrane or sheet of various materials. The varying air pressure of the sound waves imparts vibrations onto the diaphragm which can then be...
of 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, etc. The forward movement of something through the atmosphere causes an immediate increase in air pressure (compression) or condensation in the air adjacent to the piston. A complete cycle, or one complete soundwave, consists of an increase of pressure in the air, a subsequent decrease of pressure so that the pressure is back to normal, and a following decrease in air pressure called rarefaction
Rarefaction
Rarefaction is the reduction of a medium's density, or the opposite of compression.A natural example of this is as a phase in a sound wave or phonon. Half of a sound wave is made up of the compression of the medium, and the other half is the decompression or rarefaction of the medium.Another...
. One complete cycle is produced when a drum is hit once with force.
The second kind of sound generator is the method utilized by wind instrument
Wind instrument
A wind instrument is a musical instrument that contains some type of resonator , in which a column of air is set into vibration by the player blowing into a mouthpiece set at the end of the resonator. The pitch of the vibration is determined by the length of the tube and by manual modifications of...
s, such as trumpet
Trumpet
The trumpet is the musical instrument with the highest register in the brass family. Trumpets are among the oldest musical instruments, dating back to at least 1500 BCE. They are played by blowing air through closed lips, producing a "buzzing" sound which starts a standing wave vibration in the air...
s. At the beginning of the cycle, sound pressure is normal. Then, an opening called an aperture (such as the opening on the mouthpiece of a trumpet) is partially open and a short stream of air under pressure is released. In the second step of a full cycle, the valve is completely open and pressure is at a maximum. In the third cycle, the valve is partially closed, and the pressure has decreased from the maximum value. Then, the valve is closed and the pressure is the same as normal undisturbed atmospheric pressure. Thus, a full cycle is produced. This happens very quickly in the vibration of lips (i.e., the aforementioned "valve") as they quickly open and close (or vibrate). More examples of this type of sound instrument include siren
Siren (noisemaker)
A siren is a loud noise making device. Most modern ones are civil defense or air raid sirens, tornado sirens, or the sirens on emergency service vehicles such as ambulances, police cars and fire trucks. There are two general types: pneumatic and electronic....
s, organ
Organ (music)
The organ , is a keyboard instrument of one or more divisions, each played with its own keyboard operated either with the hands or with the feet. The organ is a relatively old musical instrument in the Western musical tradition, dating from the time of Ctesibius of Alexandria who is credited with...
s, saxophone
Saxophone
The saxophone is a conical-bore transposing musical instrument that is a member of the woodwind family. Saxophones are usually made of brass and played with a single-reed mouthpiece similar to that of the clarinet. The saxophone was invented by the Belgian instrument maker Adolphe Sax in 1846...
s, and trombone
Trombone
The trombone is a musical instrument in the brass family. Like all brass instruments, sound is produced when the player’s vibrating lips cause the air column inside the instrument to vibrate...
s.