After we managed to get our set-up ready and all the components working, we did several measurements with different drop sizes. In total we measured the sound of three different drop sizes. We measured the sound (and captured the impact with the highspeed camera) for these drop sizes:

• Large drop; Radius of 1,60 mm
• Medium drop: Radius of 1,33 mm
• Small drop: Radius of 0,95 mm

The complete videos of the impact of the raindrops can be seen on the page files (or on the home). Here we only show the part of the impact where sound is generated.

In the following video you can see the impact of the large drop (radius of 1,60 mm) and the sound measured using the hydrophone. 1 second in the video represents 1/1600 second in real time. 

As you can see in the video when the droplet hits the water surface, a sound pulse is generated. After the initial sound of the impact, a very clear oscillating sound is measured. We can also see that on the surface of the cavity there is a wave pattern visible. If you compare the frequency of the oscillating sound and the wave pattern, you can see that these frequencies seem to be the same. 

In the video below the measurement of the medium sized raindrop is shown synchronized with the sound measured using the hydrophone. The video is played at the same speed as the previous one.

In the video below the measurement of the small sized raindrop is shown synchronized with the sound measured using the  hydrophone. Again the video is played at the same speed as the previous ones. 

As you can see in the videos showing the impact of the medium and the small droplet, there is still a sound pulse when the droplet hits the water surface. You can also see a oscillating sound after the impact, although the oscillation is less clear compared to the oscillating sound from the large drop.