Bell

What it means

The bell is the flared, funnel-shaped opening at the lower end of a wind instrument, opposite the mouthpiece. There the previously narrow bore widens considerably before the air column leaves the instrument.

This widening couples the air column vibrating inside the tube to the surrounding air, instead of letting the sound simply reflect back at the end of the tube.

Musical use

On brass instruments such as the trumpet, trombone, or tuba the bell is especially pronounced and contributes substantially to volume and timbre; on the French horn it also faces backward, so the sound first reaches the audience indirectly and more muffled, and can be shaped further with the hand or a mute. Some woodwinds, such as the clarinet and oboe, also have a small bell that mainly reinforces their lowest notes.

The shape of the bell — narrow and gradually flaring, or short and wide — affects how strongly high overtones are emphasized and how directional the sound radiation is; a wide, rapidly flaring bell tends to sound brighter and project more strongly into a room.

The bell should be distinguished from the sound hole of string instruments: both radiate sound outward, but the bell shapes an air column already flowing through the tube, while the sound hole sets air enclosed in a closed body vibrating.

Performance practice

When playing, aim the bell deliberately at the audience or at a wall you want the sound to reflect from, since radiation is strongly directional. When using a mute, make sure to insert it centered and at an even distance, so the tone doesn't tip out of control.