We will pointwise outline our conclusion and discussion regarding our experimental results.

• We were not able to create closed bubbles, because we were not able to reach high enough droplet velocities.
• In the case of a single droplet creating only a crater, the impact shock generated the loudest sound of all recorded noises. However, this sound only lasted for a short instant. To our surprise, the most prominent sound frequencies were due to waves formed at the free crater surface.
• An interesting observation about the waves formed within the free crater surface is that we were dealing with traveling waves. As can be seen on camera, all traveling waves are directed towards the lowest point of the free crater surface and then disappear. We do not know exactly why, because we would expect that the waves could just travel back up and cause constructive interference (assuming the crater is spherical so there is no difference in traveled distance from the top water surface) because of superposition. Something at the bottom fully absorbs these produced waves, or the assumption of a spherical crater is wrong, allowing for a traveling wave.
• The waves formed at the free crater surface did not have a well-defined single frequency. As can be seen in our obtained frequency spectra, the frequencies of these waves were all below 2,5 kHz.
• The possible effect of different droplet sizes cannot be determined by our experiment. While performing the experiment, we noted the significant influence of the distance between the impact site and the hydrophone. When this distance is too large, the recorded signal is very weak. Since we were not able to fully control the position of the impact site, we needed to adjust the experimental setup such that the signal was strong enough. Thus, the distance between impact site and hydrophone was not constant such that we are not able to conclude that for example a different droplet size results into a louder sound. Since we obtained merely a frequency spectrum rather than a single frequency for the free crater surface waves, we also cannot conclude that the droplet size influences the frequency.
• Since raindrops fall from a bigger height outside the laboratory, we expect them to reach higher velocities. This makes it more plausible to form cavitation bubbles. Since we were not able to let our droplets reach such high velocities, our created droplets setting might not be valid to represent real rain drop settings. However, for further studies we think it is interesting to see if our ‘crater waves’ are also formed at the bubble surface.