If you have access to a simple, commercially available 3D printer, you can make tunable plugs for the resonance tubes with a little skill. To do this, two components (PLA gray and FLEX blue) are combined into one part.
When the two hard PLA plates are pressed against each other by the wing screw, the flexible blue "tubes" bulge. In this way, they seal the plug to the tube on the one hand and the screw to the plug airtight on the other.
FLEX: NINJAFLEX TPU
