Hear through the door

Would you ever in a situation say this? A door only constitutes part of a wall. So why would you say through the door and maybe not "though the wall"

I can't hear anything through the door. Open the door if you want to talk.

How would you say this?

The smell can go / get through under the door even if closed.

Is this sentence natural phrased and makes sense in the above?

A door only constitutes part of a wall.
Or
A door only makes up part of a wall.

If you have sliding door that separate your living room from your bedroom.
How would you ask and say this thought?
Can you hear me through those sliding doors or is it as insulating as a wall. If those doors were a wall would you hear as much as now?

Thanks