How does the sound of a clarinet get louder?

The sound of a clarinet gets louder when the player blows more air into the instrument. This increases the pressure of the air inside the clarinet, which causes the reed to vibrate more strongly. The stronger vibrations produce a louder sound.

In addition, the player can also make the sound of the clarinet louder by opening the bell of the instrument. This allows more sound to escape from the instrument, which makes it sound louder.