This model is designed specifically for the following parameters, in order to optimize print speed and quality:

Nozzle Size: 0.4mm
Layer Height: 0.28mm
First Layer Height: 0.28mm
Wall Count: 2
Top Shell Layers: 3
Bottom Shell Layers: 3
Infill: 0%
Bridge Infill Direction: You may need to modify your Bridge Infill Direction parameter to be 90° or 180° or something like that, in order to make the bridges span the shorter distance, rather than the full length of the whistle. This should create a smoother “ceiling” inside the air chamber. (See screenshot)