Whistle
thingiverse
You can adjust the size to your liking, but z=15mm seems to be an optimal setting. A small opening located just beneath the ball inside the whistle works well when using a piece of string for cutting. After experimenting with various whistles, this method proved to be the most effective solution.
Download Model from thingiverse
With this file you will be able to print Whistle with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Whistle.