Subwoofer wiring

[Speedskater]

Why, technically, can’t speaker wire serve as RCA cable if the connectors were changed?

For a line level RCA unbalanced/single-ended interconnect.
Because it's not shielded.

Note that some budget systems use speaker cables with RCA connectors.

 

[highfigh]

If the sub isn't too far from the AVR/AVP, the system isn't dead- you can use a wireless transmitter/receiver to get the signal to the sub and the best part- you can't have a ground loop with it.

 

[BMXTRIX]

Why, technically, can’t speaker wire serve as RCA cable if the connectors were changed?

The most common reason is that the cable will easily pick up noise and hum in the system. This is a problem over any sort of distance in my experience. Yes, I've had to do it, and I've always regretted it. It doesn't mean it will happen every time, but it certainly has been my experience that it hasn't been the right way to go.

 

[Swerd]

Why, technically, can’t speaker wire serve as RCA cable if the connectors were changed?

The audio signal voltage coming from various sources like CD analog (line level), or from a separate pre-amp to an amp (pre-amp level) is low, in the range of 0.1 to 0.2 Volts. Amplified sub-woofers get pre-amp level signals. After amplification, the audio signal level is much higher (speaker level), in the range of 1 to 200 Volts.

The sources of hum and interference, electromagnetic interference (EMI), or radio frequency interference (RFI) are usually weak, but can cause interference in signals at pre-amp level or lower. In home audio, shielded cable is standard for line or pre-amp level connections. It is usually coaxial cable (typically RG6) but can be twisted 2-conductor wire surrounded by a shield. The shield, a braided wire tube or foil wrapping (sometimes both) is enough to block the low level interference. By convention in home audio, shielded cables are terminated with RCA plugs. Sometimes you see XLR plugs instead of RCA plugs, but shielding is still used.

At the higher voltages of speaker level, EMI and RFI are too weak to matter. Shielded speaker wire isn't needed. Again, by convention, RCA plugs are not used for speaker wire.

 

[Audiophile Heretic]

..it actually runs on “shielded RCA cable,” otherwise I’ll get a “loud hum.”

..I can just run this ”shielded RCA cable” under the carpet pad around the perimeter of the room to the cabinet.

Can I put RCA connectors on the already installed speaker wire in the wall and at least try it to see if there is a “loud hum” or is it a different kind of wire?

Where exactly do the RCA plugs plug into?

I didn't read all the other replies, so this may be a repeat.

No, you can't just put RCA connectors on speaker wire because unshielded wire may pickup noise heard as hum. You are more likely to get hum between unbalanced RCA line-level outputs and inputs than you are between balanced XLR line-level outputs and inputs with unsheilded wire. You are not required to use unbalanced RCA cables if you have balanced XLR line-level input and output connections available. If you are going to run more wire, run balanced sheilded cable with XLR connectors, not unbalanced cable with RCA connectors.

Alternatively, you could connect your main front L and R amplifier outputs to the speaker-level binding post inputs on your sub. Speaker level subwoofer inputs pad the voltage of the amplifier down to line level for the subwoofer amp. You would configure your processor as if no subwoofer was connected so it would route LFE to the main L and R channels. It's not the absolute best solution, but it will work very well if you simply can't run balanced or unbalanced line-level cable to your sub. The quality of the speaker wire to the sub is less important than wire to the main speakers because the impedance of the subwoofer speaker-level input is much greater than the impedance of speakers and the impedance is more resistive than reactive. The higher impedance of the subwoofer speaker-level input in parallel with the main speakers does not significantly load the amplifier either. Bass management subwoofer crossover frequencies and level settings would be done with the subwoofer controls rather than the AV processor.

Connect main amplifier speaker-level output terminals to the speaker-level binding post inputs on the subwoofer. Connect RCA unbalanced line-level outputs on your AV processor to the RCA unbalanced line-level inputs on the subwoofer. Connect XLR balanced line-level outputs on your AV processor to the XLR balanced line-level inputs on your subwoofer. Only use one connection. Long balanced XLR line-level cables are preferred to long unbalanced RCA cables. Long balanced line-level cables to amplifiers with short speaker wires are preferred to long speaker wires from amps to speakers, if you have a choice. Bypass the subwoofer crossover if you connect it to a XLR or RCA line-level subwoofer output on your AV processor.

The Emotiva processor doesn't have any RCA line-level outputs, so you would use XLR, or in your case connect amplifiers XLR and connect speaker level from the main amplifier output to the subwoofer speaker-level input.