4.2 The structure of sound hole
The sound hole design will also affect the frequency and SPL (but the chamber design still must be a priority step). There are several points for designing sound hole: The larger sound hole will make the frequency higher, and the smaller one will make the frequency lower. When the sound hole is not in the middle of the buzzer, the frequency will be shifting lower. SPL will get lower if sound hole is designed to be different shapes rather than a circle type.