[Clep]

Hi Antonio — the motivation for the project isn’t the stretching, it was just the fact that the tubes wear out (start cracking, etc) and I wanted a way to replace them without having to buy expensive melodica tubes on eBay.

The stretching issue probably isn’t a big deal, no, but the reason people care about it is that the “responsiveness” of the melodica is associated with less stretch and a more direct connection to the instrument. See for example the people that won’t use tubes (and instead use the mouthpiece) in part because of the softening of the attack of notes due to the compression of air in the tube and the stretch of the tube. See also some melodicas that use rigid metal tubes instead of plastic, etc. For me, the corrugated tubes definitely have a little bit of stretch. I don’t know if I could tell the difference in the instrument in a blind test, but I still wanted to find a tube that had minimal stretch, and the rubber surgical tube seemed like it would suffer in that department. I was happily surprised that it wasn’t an issue.

Air is definitely compressible (see e.g. air-based shock absorbers, 90psi bike inner tubes, etc.) — perhaps you were thinking of water, which, while technically compressible, is effectively not compressible.