Edwards symphonic tenor trombones are available in 8 or 8½” bell flares in a variety of wall thicknesses: 21 (heaviest), 22, and 23 (lightest) gauges. Jazz trombones are available in 7¾” bell flares in two wall thicknesses: 22 (heavier) and 23 (lighter) gauges.
Bells are available in yellow brass (70% copper 30% zinc), rose brass (85% copper 15% zinc), and red brass (90% copper 10% zinc). Higher copper content bells generally are very dark in the soft volumes but become more brilliant in the louder volumes. Yellow brass bells are more consistent in timbre throughout all registers and dynamics.
A soldered bell tends to have a very centered sound with a lot of core (fundamental). The articulations are slightly dampened and softer with the solder, while the sound is more direct and compact.
An unsoldered bell has a very wide sound with more overtones. Articulations are easier with an unsoldered rim. More near feel is apparent with these bells as the sound is wider, which helps give the player more feedback.
Tempering occurs when a bell is spun twice on a mandrel which work hardens the bell. This adds brilliance and colour to the sound.
Double buffing thins the bell slightly. It actually creates a thickness in between any two gauges.
Heat treating is a baking of the entire bell. This softens the metal immensely and creates a very dark sound. This works best on heavier bells as it tends to free them up. Heat treating is not recommended on thinner bells as it makes them more prone to mute dents. The CF treatment has virtually replaced heat treating.
CF treating is a partial heat treating process. This treatment allows the bell to blow more freely and adds colour to the sound.