Run length


Room layout dictates the sub is on the opposite wall. Not ready to run a wire across the floor. It would be 26 feet.

To skip the floor run I would have to go up and down inside the wall. That would add another 18 feet for a total of 44 feet.  Too long?  Will be using plain old 14AWG cord.
ibmjunkman
No problem. Ears just aren't that sensitive to such low bass as you're talking with a sub. For example, just that ordinary wire alone would be crap and you'd hear it as crap even at just 5ft. But with subs you can get away with cheap wire just fine. 
OP do yourself a favor, 10/2 or 12/4 Soow or Sjoow is great cable and a LOT tougher. 10AWG zip cord the smallest I’d be using even with just a meter run.. Bass loves heavy copper. In wall or under the structure, Soow or Sjoow cable.. Good ol USA materials on Ebay. .25-1.00 usd a foot.

I don’t mess around with cable size, when it’s easy to run GOOD cable at no extra cost. The same way sound moves is the same way I treat cable.

The lower the frequency the heavier the cable but the higher the strand count of copper. The higher the frequency (MIDS) the larger the strand size and a lower the count of silver clad/tungsten, to a single stinger for highs and UHF. Pure silver.

I keep spools, it’s Dirt cheap, 99.99 copper, 300/600vac, and you can bury it.. 50 year life EASY... Armor it up as it comes out of the wall (optional)..

Regards
Have you considered a wireless connection, like the below from SVS? They seem to be getting pretty common.  I have a similar situation, and have been wondering about it.


https://www.svsound.com/blogs/subwoofer-setup-and-tuning/how-to-set-up-a-wireless-subwoofer
Not too long if your source and end point are balanced.
Mr ibm, isn't your subwoofer self powered? Does it have a balanced input? Passive subs are much rarer but, if it is drop the wire to 12 or 10 gauge twisted pair or Kimber Kable 12 TC if you don't mind spending a lot of money. If the subs are active you can run a balanced line 300 feet if you want. Subwoofer drivers usually demand a lot of current so linear resistance matters. Lower gauges have lower series resistance. You want to keep induction as low as possible in a long run like that which is why you should use a twisted pair format vs Zip chord. 
Sub is a JBL B380 non-powered. Using a wireless setup would mean climbing over furniture to turn on the local amp and wireless receiver.

I need to run speaker and CAT x in an outside wall. I know what that means and I still have some paint used on the wall. I plan on using an electrician to do the work.
An electrician will probably not want to run bare wire like that. Use whatever he recommends. Wire going to main speakers handling midrange and up is incredibly important. This is not that. Use whatever.
What bare wire? CAT x is run through walls and attics all the time.  And SJOOW sure seems more encapsulated than Romex.
I have 4 JL F-113's. 2 are in the back of the room. One has about 50 feet of XLR cable running to it.  No problem.

ozzy
Sorry I did not catch that your sub is not powered. Perhaps consider going to that type of sub?

ozzy
It will not hurt anything if it is powered but if it is a passive sub you will need much heavier wire for a 44 foot run.
Is this an RCA (signal wire) or are you taking the speaker output to the sub ?

If a signal wire, make sure your wire is very well shielded.  If a speaker output, you are ok.

In any case, you can also consider wireless:

https://www.martinlogan.com/en/product/swt1
Correction, I just realized that the Martin Logan transceiver is specific only to their own Dynamo subwoofers.

But you get the idea. There are quite a few very good quality devices out there for wireless transmission with negligible latency.

Had to configure my system the same way due to room aesthetics, with equipment near one wall and speakers near the opposite wall.  Ran speaker wires internally up one wall through the attic down the other wall.  Must be around 10 meters because that is the length REL gives you for their powered sub woofer hookup.  Used 10 or 12 gage for the B&W 805's.  Ideal?  No.  Sounds great?  Yes.  Should work out.  
Dish the wire. There is nothing to turn on. The receiver is activated by the audio signal. I have used them for the last six years and never have to touch them. Mine are not SVS but I believe they all work on the same principle. You might need to move the subs around to find the best location and the wireless system will be invaluable in that respect. Good luck. 
What powers the sub? The receiver just supples a line level signal.
‘The JBL B380 is not powered.
14awg not good for long runs.
Plan changed to use 10/2 SJOOW
If your sub is 4 Ohms, the wire is more of a factor that if it's 8 ohms. You might consider 12 gauge wire. I use 14 gauge solid (twisted) for very long auditorium runs with no problems. There is flat, 50 conductor computer cable on the surplus market (65 cents/ft. in 100 ft. reels) that will be undetectable under a rug. It's ugly, but who needs to see it? Use 25 strands for plus and the rest for -.
Why run a sub at all?? Are your speakers not good with bass? Ditch the speakers and the sub and buy speakers that do bass well.