A piezoelectric sounder (external drive type) is a voltage-driven type. In order to increase the sound pressure, it is necessary to raise the input voltage. However, generally it is not easy to increase the input voltage to the drive circuit. Accordingly, the sound pressure can be raised by changing the duty ratio of the input voltage without changing the input voltage. (Regarding the duty ratio, refer to Fig.1.)
Fig.1 Duty ratio
To take an example of our PKM13EPYH4002-B0 which is specified to be driven at 4 kHz, sound pressure level would be approximately 10 dB higher by changing duty ratio of input signal from 50% to 25% while being driven at 2kHz. (Refer to Fig.2 and Fig.3.)
Fig.2 Difference between the frequency characteristics of sound
pressure level for duty ratios of 25% and 50%
Fig.3 Relationship between the sound pressure and the duty
ratio for input signals of 2 kHz and 4 kHz
Because the 4 kHz sound, which is the second harmonic sound at a duty ratio of 25%, is combined with the 2 kHz sound, the sound pressure rises.
This result depends upon the frequency characteristics of sound pressure level of the piezoelectric sounder, so the value of the increase in sound pressure will differ according to the type of product. Also, if the duty ratio is changed, a frequency component that is different from the input signal will be used, so the tone will change. It is necessary to check this point while listening to the sound.