The SPL of a buzzer does not have a geometric
ratio relation with the voltage directly, especially close to the
According to the graph below, at 2000Hz, we have 3V with 74dB,
6V with 80dB, and 12V with 90dB results; however, at 2048Hz, we
have 3V with 84dB, 6V with 87dB, and 12V with 90dB.
Because the bandwidth of the buzzer will widen when the voltage
raises, therefore we should pay more attention to the output frequency,
even 100Hz difference might cause a big difference in 10dB!