Stereo Sub-woofer wiring

Factual Questions
1

I got a new tuner. I’m a smart guy and know lots of stuff, but I have a pretty specific wiring question here.

The new tuner has a single, RCA, plug for the Sub…my amplified subwoofer has one sub-rca jack and two bannana-plug compatible twist tight connectors. It’s also right next to a nice breakout box on the wall with in-wall speaker wire. (4 conductor)

So, I have:

Tuner-RCA ======= Big ol’ Airgap ======== RCA plug or Right and Left twist on connectors

Do I combine channels on the tuner and use the twist connectors, or do I wire up an RCA plug to 2 conductors on the in-wall cable, and wire an RCA plug on the other end?

(Previously, I just ran a 12 foot single pair RCA plug, but that’s kinda ugly snaking in front of the fireplace.)

I guess long story short: I have in-wall wiring that doesn’t meet up with what I want on the ends (RCA).

2

That’s what I would do.

If you do use the banana plugs, don’t combine the channels coming out of the stereo, I would think that would cause problems. You would probably only want to use one of them (left?), but I don’t remember for sure.
Go with SUB OUT on the tuner and SUB IN on the sub, everything will work better that way.

3

The RCA’s are what I want to use, but the only wire i’ve got going from the tuner to the sub is 4 conductor speaker cable…Would soldering RCA plugs to two of the conductors be a sin? Mortal or Venal? (I don’t have a million dollars to prove it sounds good or not. http://feeds.gawker.com/~r/gizmodo/full/~3/165681713/pear-cable-calls-james-randis-1-million-offer-a-hoax-307473.php )

4

Don’t solder anything to the conductors. Either find an RCA breakout cable, that breaks out to regular speaker cable, OR go down to Radio Shack and pick out two RCA conductors and make the ends yourself out of some speakerwire.

5

That’s what I was looking for, I wasn’t sure if the RCA wire was twisted, shielded, or otherwise special. I’m off to the Shack.

6

It’s coax, but I’ve used speaker wire before with no issues. Besides, it’s a subwoofer, so any distortion that it may produce, will probably go unnoticed.

7

There are some nuances here to be aware of.

First, if you use the ‘subwoofer out’ jack on your stereo, you’re getting a line-level signal that contains only low frequency information for the sub. When you’re in dolby digital 5.1 mode, your receiver will send the “LFE” channel to the subwoofer through the RCA jack. LFE stands for ‘low frequency effects’, and it’s a special channel in 5.1 for explosions, vibrations, and other low frequency goodness.

This is the prefered setup for watching movies in 5.1 surround.

If you want to use this output, you cannot feed this into the speaker wires in your wall and hook it up to the speaker terminals on the sub. You need to run a proper coax from the sub and plug it into the sub’s RCA jack.

If you want to run speaker-level stuff to the sub, then typically the proper way to do it is to run your left-right speakers to the sub, then run wires from the sub to your main speakers. The sub has a crossover in it that will filter out the high frequency signals and pass the low level stuff to the sub amp, and filter out the low frequency stuff and pass it to your speakers.

Throwing another wrinkle into the mix are the speaker settings on your receiver. On most modern receivers, there are setting for all four non-sub speakers. You can set them to be ‘small’ or ‘large’. If you set them to be small, the full frequency sounds of music and such will be send to every speaker. If you set them to ‘small’, the receiver will filter out the low frequency stuff and send it out the LFE channel to the sub, and send only the higher frequencies to the main speakers. This has several advantages. First, small speakers are lousy at recreating bass, so it’s better to let the sub do it. Second, it takes a load off the amplifier because bass frequencies eat the most amount of power. The sub has its own amp, so by setting all your speaker to ‘small’ and using the LFE output on the receiver, your system will probably sound better. But then you have to run the RCA out to the sub.

If you run your sub from the speaker outputs, you must set your speaker size to large, or your sub won’t get any bass frequencies at all. If you put the sub in parallel with your other speakers, rather than connecting your other speakers to the outputs of the sub, you’ll be sending full-range signals to all speaker, which is usually not optimal.

For most stereos, the short answer is that you should run a proper coax from the LFE output of your stereo to your sub, then connect your other speakers normally. Set your speaker sizes to ‘small’, and make sure you configure the receiver so that it knows there’s a sub on the LFE channel.

If your sub has a crossover control on it, and you feed in the LFE channel, just set the crossover up to the max. Or you can set it at 80hz, which I believe is the THX recommended setting for the subwoofer crossover - just in case your stereo isn’t doing it.

8

But can you use the in-wall non-coax wire to carry that LFE signal? That’s what I’m trying to do. It’s by no means impossible to run coax from where the stereo is to where the sub is, I have access to the area from teh basement and have the skills to run it, it’s just a hassle I’d like to avoid.

9

I’m not sure what the exact specs are on the LFE output, but I’d guess it’s a fairly high impedence (~75 ohms) low level signal in the hundreds of milliwatts range. Ideally, you want your cable to be impedence matched to the output, and with a low level signal like this you want shielded cable. Speaker wire is just wrong for the application. My guess is that if you try it you’ll hear all kinds of hum or noise from the subwoofer. But I guess it doesn’t hurt to try… Maybe you’ll get lucky and it will sound okay. But you really should use a proper shielded coax.