I often work in a community that was prewired for surround sound by the homebuilders. The problem is that they run 2 sets of 16/4 to the subwoofer in the back of the room. Anyway, I was wondering what you guys thought about me putting RCA ends on the speaker wire, so I can use the .1 subwoofer output to a powered sub.

The speaker wire is about 50 feet long from the front to the back of the room usually. I've never done it before just because it seems wrong to do. I guess I could easily just try it out with some loose speaker wire and listen for results. Of course there might be some noise picked up along the way, but that will vary in different rooms I imagine.

You will almost assuredly get hum. The best I've been able to do here is use the powered L&R speaker outputs, connect that to subwoofer wiring run, connect an L-pad (Sonance OP-3 or equiv.) and connect that to the sub. Don't forget to tell the receiver there is no sub in the system, and that the L&R fronts are "full size" instead of satellites.

Ditto what theaterworks said. Speaker cable is un-balanced, a sub signal coming out of a receiver is balanced. You will most definetly get a hum. You a line converter to change the high level input to low level inputs. You can find these just about anywhere. We have bought some from a car audio store. They use them for use of amplifiers with factory stereos. It gives them the lowlevel output you need to take into the amp. Same theory but you are using a subwoofer in your home.

Mike

VW, What I think you meant to say is speaker cable is un-SHIELDED not unbalanced. Cable can't be balanced or un-balanced. Signals are.

A sub signal is not balanced either. (Unless you have an balanced XLR sub output). All 2 conductor RCA terminated cables are single-ended unbalanced signals.

[Link: rane.com]

Yes, you will get hum except in the most unlikely of situations.

Are you considering doing this because you have a subwoofer with no speaker level inputs? (This is the place where mentioning that or at least telling us what brand and model would have helped.)

vwpower44 is right about the high to low converter if you MUST use a line input, though not about balanced and unbalanced.

Actually, I find a subwoofer in the back of the room to be a huge nuisance because the sound does not blend AT ALL. It will feel like you are being pulled in two directions, or if the listening position is too close to the back, you will have a tubby boomy sound all the time unless you turn the sub down to where it has little good effect.

One studio rat customer of mine (that was her description, not mine) couldn't stand the sub on the floor in front with the speakers up high. She said it just sounded like two different separated halves of the sound! So I raised the sub and all was well. She would have killed me if I had put the sub behind her!

I suggest looking for a place to integrate the sub on the front wall. That should ease your wiring burden, too.

use an in wall sub with a remote amplifier like the new def tech 10/10 in wall or the inwall reference. I don't sell Triad but I believe they make similar

Here's something corny. If you're looking for .1 with 16/4 to a subwoofer location, try this:

Low level out (.1) to a single or dual channel amp, out of the amp to the subwoofer across the room thru the 16/4. Connect the 16/4 to the speaker level input and the sub will knock it back down and amplify it.

Would I do this? I don't know. Seems you would add a little too much distortion with this method - but you would get .1. (might get me a ticket from the audio police).

You need a really nice sub to work acceptable in the rear of the room - M&K, Velodyne for ex (not a boomy cerwin vega, MTX, JBL or the between the eyes sound of Bose). The crossover needs to be sooo low that the .1 loses it's directionality. Because the crossover freq is low, it would be best to have larger L/R's to make up the difference. But, of course, sometimes we work with what the client let's us do.

16/4 is almost a certain hum used as low level. Love to know a clean cheap solution to this as well.

Use the subwoofer output to an amp and a passive subwoofer if you want to use the rear sub placement. I agree with Ernie though, that the sub belongs in front of the room.

Well the sub can not be moved to the front of the room unless the customer buys a new subwoofer and it is installed inwall. That is not going to happen.

This question isn't about acoustics, it's about electronics.

You know most subs, including the one at this house, already have the speaker level to line level built in. But I don't want to have to send bass to the small inwall main speakers...
However the customer will chose that option over running new cables throught the walls, so you can see the problem.

I just think I will try it out for my own experiment, and I'll let you guys know how it turns out. But, if anybody has actually done this then I would like to hear about it, especially if it didn't work.

We've used the line converter a number of times as well. Problem is that the HT receiver still needs to be set to "Large" to accomodate both sub and main speakers. This means the client will typically blow the cones out of the front speakers the first time Godzilla stomps or growls - or whatever the beast does (cool movie by the way).

Setting the speakers to "Small" will make for a boomy sub (especially in the back of the room). If you have In/out speaker connections on the sub you're in luck. This is your only crossover to protect the mains.

Otherwise you might try the goofy line out to amp in, amp out to speaker level in. It doesn't have to be a big external amp, just one that will send amplified signal to the speaker level ins so you don't get hum. Then you can set the mains to "small" and the Low level sub out to "On" (without the hum).

By the way, did you try low level jacks on the 16/4's? You might get lucky.

Why not try soldering on RCA ends first --- if it hums - do the line level input ,,, if not - then your set. We've solderied on RCA to speaker wire a few times when it was wired like this and had no humm probs. If the wire has a drain wire - it gets grounded at the source end, and not connected at the sub end.

Also most hi level input subs - the hi- level output is crossed-over at about 80 hz. Dunno about the one your using.

In wall sub or a sub with speaker level inputs. Make it easy on yourself.

I'd try soldering on the rca's!
I certainly don't recomend it but, it worked for me ONCE!

The contractor wired it(how hard can it be?)

Ended up with a low level cable to the center channel location and a 16-2 to the sub!

This addition was on a slab with vaulted ceilings(no attic)!

It was 'do or die', so I tried it as a last ditch effort.

I still can't beileve it worked!

I Have used 16/2 in a pinch and it worked no hum.

Side note Boston accoustics now makes a speaker level to line level adaptor.

Ohhh - I forgot --- we've done this with success a few times also. (when needed)

MIT's one wire system - the T-maxx speaker connectors. which normally convert RG-6 or 59 (preferably their MIT brand wire) to speaker connectors. ------- we have used the modules backwards ---- converting speaker wire into RG-6. and it has worked beautifully.

I haven't talked to MIT about whether this is a good use for these modules ... but I'd assume that if they did make an official module for this it would be a popular solution for faulty pre-wires or replacement situations.