Mains cable as speaker cable
I have moved into a house and found that the previous owner wired one of the rooms for four speakers using 2.5mm solid copper cable (twin and earth). I am tempted to use this cable as it places the speaker positions up by the ceiling well out of the way of pets, kids etc.
How much difference (I realise this is quite subjective) would it make to the human ear to switch from this to expensive cable? Is there a rule of thumb which can guide me to assess what sort of expense would need to be made on hifi overall before cable had an impact?
If it makes a lot of difference I will simply have to lift up the carpet and install new cable beneath that.
thanks in advance.
There are such a thing as solid-core speaker cables. I see no reason why it wouldn't sound similar to such cables.
I used a thick mains cable among many other things once. It works just fine 
Depending on the type of cable modern twin and earth mains cable is not solid solid but thick stranded cable
Using mains cable is very good and cost effective solution, all you have to make sure is that the cable is thick enough to carry the current, 2.5mm is fine, you could go for 4mm if you wanted a long run over say 10 meters. I doubt you will hear a difference between solid core mains cable and your £2/3/meter stranded standard speaker cable.