Student dares - Self-built ventilation system

Uh, no... Telephone sound spreads through the lines - you just didn't consider that. The other thing normally has no impact regarding sound transmission through the ventilation system.

You notice the airflow if you stand directly in front of the door - but who does that? It's not a hurricane....

When supplying fresh air, one should also consider possible contamination/filtering

The volume flows depend on how big the house is and how quickly the air should be exchanged...

180 is already relatively low for a "normal" single-family house... you can imagine that the system is then practically running at full capacity continuously, and this unnecessarily consumes electricity. That is why systems usually have an upward reserve and operate more at half power, etc.

The ventilation ducts are, as already mentioned, smooth on the inside... they are only corrugated on the outside, as kink protection, etc.

Why not simply run the intake duct through the wall? The shorter, the better...

Okay... so rather enlarge the door gap a bit than to put such shafts into the walls? Now I know what is meant by telephone noise! Yes, that won't be a problem, I think. In front of the supply in the bedroom (ventilation outlet in the ceiling) I wanted to install a silencer.... with the remaining pipes it doesn't matter much if some noise is transmitted.

I see it differently... Certainly, plastic pipes require less maintenance... but they break after 5 years or simply become porous

Which plastic pipes?