I have a subwoofer with a 3.5mm line-put, in the wall I have a regular speaker wite (2/12), and 40ft away I have the Sonos Amp which has a single RCA input. So what type of cables do I need to hook this up? I’ve been searching and searching but can’t find anything.
I'd get a decent quality shielded cable, like this: https://www.parts-express.com/35mm-stereo-male-to-male-super-shielded-audio-cable-50-ft--240-077
Can you cut and splice and have soldering skills? If so, remove the mini plug from the other end of the cable (you don't need it), strip the jacket, keeping the shield that covers the red and white conductors, pull and twist it into a bare, stranded wire. This is negative. The red and white are for R/L, but you need a mono signal. Check your sub's manual to see if the line out is mono; it should be. Then you can strip and twist the red and white wires together. This will reduce the wire's resistance for the long run. For the RCA end, if you have a plug like this: https://www.parts-express.com/gold-rca-super-plug-connector-black-63-mm-cable-entry--091-052 , then you can connect your cable directly to the plug, which is best. You'll have to solder the signal (red/white) to the center pin. If you have a single RCA cable with plug (which can be cut off a cable you aren't using), strip and prep for soldering. Before you twist the wires together (same as long cable), slip a small piece of heat shrink tubing over the R+W connection area to be soldered and add a larger piece, which will fit over the outer jacket of the cable, long enough to cover the splice and extend over the jacket at least an inch or so. . Be sure you have enough room to solder the signal wires without shrinking the tubing! Then, use a heat source (lighter) to shrink the tubing. If you prefer to use tape, be sure to completely cover the signal wires with a few wraps, pulling it snugly as you go. To wrap the outside, wrap the tape starting on the jacket, over the taped connection and to the other side. Be generous and pull it tight for a nice durable job.
The advice above assumes you have an extra 2 conductor speaker wire. It won't work if you only have enough conductors for the pair of speakers that you need to connect to the Sonos AMP.
A wireless subwoofer adapter will work. Some subwoofers have the receiver already built in so you just need the matching transmitter. If yours doesn't then you need both the transmitter, that will connect to the AMP sub output, and the receiver, that will connect to sub. https://www.bestbuy.com/site/rocketfish-wireless-subwoofer-transmitter-receiver-kit-black/6965266.p?skuId=6965266
Mixed reviews on the above product. americanaudiophile: No I didn't assume that. I ASSumed, based on the info provided: that there's a subwoofer with a line-level input, which means it has it's own amp. I also assumed, because he mentioned the "SINGLE RCA INPUT" and not the SUB output on his amp, that he needs to also get a MONO signal (again-single RCA) into the amp (I didn't address that) and that he also needs to get a MONO SUB signal from the amp's SUB OUT to the SUB's input. That's what I addressed.
I suggested getting decent quality SHEILDED cable and the link I provided is 3-conductor (L+R+sheild) to get a line-level MONO signal to a single RCA (which is MONO) input. Didn't he say he has a "single RCA input" on the amp" and that it's "line" level?? Going by the info we're given here, the existing 12/2 would be a bad choice for LINE LEVEL. The best way for him to get CLEAN, MONO SUB line-level signal is to do what I suggested with a shielded cable, considering some lack of info here (like the sub).
aliceinca, You know what they say...two (or more!) heads are better than one. Consider your options and do some quick research: you may want to call SONOS, call your sub mfr. I've been doing stuff like this for decades and although the tech has grown by leaps and bounds, you still need to accomplish one thing: to get the signal from point A to point B. How you do this is up to you. From a high-end audio point of view, I'd choose the option of getting the cleanest signal to the amp. 40 feet is a long run. I've seen signal degradation from various wifi and blue-tooth rigs, so I opt for the direct connection whenever possible.
I assumed that running an additional cable wasn't an option.
I agree that using Wifi and especially bluetooth doesn't work well. A dedicated RF transmitter is more reliable although not as good a a wired connection.
Sonos will suggest you get a Sonos Subwoofer which would be set up in the same zone with the AMP. It's a pretty good subwoofer but certainly a more expensive option.
Maybe it isn't an option, but if you're like me, you'll move heaven and earth to get the best sound - Git R Done! lol! At least BT and Wi-fi keep it digital, so you don't have to deal with the losses of delivering an analog signal.