How does the shape of a brass mouthpiece affect its sound?

The shape of a brass mouthpiece is a critical factor in determining an instrument's tone and technical capacity. It functions as an adapter that widens the starting diameter of the bore, allowing the player's lips to vibrate effectively.1

The internal geometry—specifically the cup, the throat, and the backbore—influences the sound as follows:

• Cup Shape and Depth: Mouthpieces with hemispheric cups and shallow walls, such as those on orchestral trumpets, produce a bright tone and favor the production of high partials. Conversely, deeper cups, such as those found on cornets and trombones, contribute to a more mellow tone.1
• Throat Design: Sharp angles where the cup meets the throat are associated with brighter sounds, while rounded-off throats help produce a mellower quality.1
• Funnel Shape: Mouthpieces that are virtually funnel-shaped, commonly used with orchestral horns, favor low partials and allow the instrument to function most efficiently in a lower range.1

Ultimately, the relationship between these elements dictates how the tremor of the player's lips is transmitted into the instrument's tubing.1