Brass instruments make sound through a combination of elements that include flow of air, the lips of the performer, the bore -- or shape of the tube -- of the instrument and the bell, which flares out at the instrument's end. Changes to any one of these variables will have an audible effect on the sound of the instrument. In most cases, the instrument is designed to exploit these changes and give the performer flexibility in producing sound and changing notes as they play.
The most basic element of sound production with brass instruments is airflow. A performer must blow through the instrument. A good amount of breath is necessary to keep a melody going and performers breathe multiple times within a musical piece. Control of the air is important as well for a steady tone. This is maintained through good support with the stomach muscles while blowing into the brass instrument. Highly advanced players make use of a technique known as circular breathing where you inhale through the nose while still forcing air out through your mouth into the instrument.
Sound is physically described as the vibration of air. The lips of a performer are the source of the vibration for brass instruments. A brass performer must purse their lips tightly together and allow the air passing through to create a buzzing. How a performer's lips meet the instrument is called the embouchure. The location of the buzzing must be focused and contained within the mouthpiece opening. No buzzing should be noticeable externally from the instrument.
The lips start the sound by buzzing, but alterations in the pitch come with changes in lip tension. Higher tension leads to higher notes, just as lower tension leads to lower notes. There is an element of physical stamina to lip strength. Brass players can develop higher ranges, but it will require consistent practice. Brass players -- to varying personal degrees -- will have a certain reserve of lip energy that can be exhausted in the course of a day. Overuse can lead to injury.
Shape of the Instrument
A brass instrument's shape directly influences the sounds it makes. There are two types of bores of brass instruments. Cylindrical bore instruments consist of a tube with no changes in its width until the bell. Conical bore instruments have a tube that gradually widens as it gets closer to the bell at the end. The bore and bell shape affect the tone and loudness of the instrument.
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