The vibration frequency of piezoelectric ceramic transducer is in the ultrasonic range. To measure audible sound waves, it may be necessary to change a piezoelectric ceramic transducer with low vibration frequency (generally, a larger area is enough).

The wavelength of audible sound waves is generally longer, and the longest wavelength of ultrasonic waves in air is about 17mm, so audible sound waves are easier to measure.

However, the directivity of audible sound waves is poor, and the wavelength is too close to the scale of experimental equipment, which is easy to produce various interference and diffraction phenomena and affect experimental measurement.

So use ultrasound to do this experiment.