Hi, it is a good experiment. Just to note that the Nano 33 BLE Sense has an incorporated microphone and can be used in the phyphox classical experiment on measuring the sound speed instead of the second smartphone.
Look my "Double acoustic stopwatch and speed of sound"
https://phyphox.org/forums/showthread.php?tid=1252
With Brest wishes
Mikhail
Look my "Double acoustic stopwatch and speed of sound"
https://phyphox.org/forums/showthread.php?tid=1252
With Brest wishes
Mikhail