Jim, thank you, apologies excepted, also have never called you stupid.
I, too checked out all the links reguarding the voice/speaking tube & went beyond that because I did find it quite interesting. Even thought when my mother (78 yrs young) needs to move & sell that the tubes may be something I want to use if & when she wants me to build her a new home. It wouuld probably work alond the lines & beside the new style flexable plumbing.

Jim as usual, I do find your input, maybe not always spot on but useful, enlightening & interesting.

Barry