There are many people who don’t understand the importance of the campana (cowbell) in Cuban music. Even though the bongo player usually plays the parts, if there is no bongo (very common in smaller groups), the drummer or timbalero needs to play these parts.
The campana is very important to all styles of son music from the most basic to the modern son and timba. It is also used in other styles as well.
The primary function of the campana is to keep time in the “montuno” sections. In traditional son that is when the chorus and improvisations occur. The pattern is simple, but I can’t stress the importance of the campana part. It is part of the glue that allows the other instruments the freedom to improvise and play more complex patterns.
Besides keeping time, the campana announces when the instruments enter during the montuno section. For example, in traditional or Cuban son style, the bongo player stops playing the bongo and picks up the campana. This is called a bandera, and introduces the montuno section.
Normally, the introduction of the montuno section is performed by the singer with his improvisation followed by the chorus. In the traditional son, the cowbell enters during the first half of the first phrase of the improvisation. This is a very important concept for all musicians. The singer leads, but the bongo needs to follow and announce the change to start the montuno section. It is a little behind, but still very important.
Many people hear the word bandera and think flag, it is not a literal word, but it makes sense since the campana is “flagging” the section change (see examples below).