Need to lay a portion of my high-end speakers cable under the floor ...


My [unfortunate] listening room layout means I am >compelled< to lay the middle third of my high-end speaker cables [2.5m each] under the floor. Sadly, this (non-ideal) arrangement is unavoidable (not least for safety reasons). I plan to have a 1 to 2 inch diameter duct (plastic or wood) laid down under the floor to act as the cable conduit over this mid section.
Apart from the fact that this arrangement genuinely sucks, are there any tips, experiences, tricks I can do to ensure I minimize the inevitable downside from this unfortunate situation? (Yes, moving house is an option ... moving listening room is not).
Is there any "conditioning" I can do to the underfloor conduit before hand to minimize detrimental distortion? Will raising the exposed cable segments be a total waste of time? System has Nordost SPM2s, but I will be upgrading soon (Ansuz perhaps) feeding Raidho D3s. Any ideas welcome.
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..so what's the problem,?   If the cable is under or over the floor, I see no difference.  I presume the cable will not be near any a/c wiring, etc.
No problems right now as not laid them yet ... only perceived problems by myself after reading various threads and reviews on cables and set-up. I guess I'll be OK, but had to ask the experts on the forum.
I have run my speaker cables under the floor for over thirty years with no degradation in sound. This has been with two different systems; one pair of speakers driven by solid state, and my new replacement pair driven by tubes. I have never encountered any problems.
Good luck.

What's below the floor? Basement? Crawl space with exposed dirt?

If the latter I would be more concerned how will you seal the exist and entry holes through the floor for the cables.

See what the cable maker(s) say.
I can't see how a cables' position under or on the floor could possible make a difference. In my mind, having it under the floor(which is what I am doing), is preferable, to lying on the floor. As Stringreen said, is it near any AC wires?
Wow, I wish I only had 2.5 meters between the speakers and amp.
No AC or other possible issues, I think. I doubt if a plastic or wooden conduit would make any difference. Yup, 2.5m ... I guess you win some and lose some. Will post pics on the Systems when all the work is done. Glad others here have not had issues.
My  22 foot long speaker cables are under the floor and my system sounds just wonderful.  I have never had issues with any kind of noise.  Why go through the trouble of running a conduit?  Just lay em between the rafters and be done with it..  Just remember to leave some slack in the cables at both ends where it goes through the floor.
I had 40 feet of interconnect under the floor of my old house.  Since it was a 12 foot deep basement under the floor, I was able to suspend the cables from the basement ceiling with silicone coated rubber bands suspended from hooks in the beams, which did a pretty good job of isolating the cables from vibrations (more important with interconnects than speaker cable, but something you might want to keep in mind).  Did not need a conduit for them due to the depth of the basement--don't know your situation.
I say- go for it. 
Also, remember that you may need a little extra length to allow for moving equipment and speakers around. I learned that the hard way.

In my last installation I ran 35' of interconnect in the crawl space with no issues but one thing to bear in mind is making the entry/exit to the floor look nice while still keeping creepy crawlies out -- I found these products used in clean rooms to be a good thing to use
https://www.accessfloorsystems.com/index.php/raised-floor-cable-seal.html
(search for brush grommets)