NC wrote:
I am trying to think of the easiest way to route cable in a house we are
looking to buy. When we move in, there will be no carpet on the floors -
and the bare chipboard under-flooring will be exposed. Can I route a
channel about 1cm wide and about .5cm deep in this to lay speaker cable

Probably a bad idea - unless you do it directly over the joists.
If it's 18mm ply, you've only got 13mm left, which is very significantly
weaker.
If you have to do this, use a snaking line going back and forward 3" or
so every 12". This will be much stronger.

"Flat" speaker cable, (I use 0.1" IDC cable*50) routed in 1mm deep wouldn't
make a significant difference.