Run length

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.