Speaker Wire
 

Hello again, I'm back for more speaker questions. I work in the technology department of a school district, and we are currently putting SmartBoards into classrooms. Each classroom is also getting speakers mounted in the ceiling tiles, with four speakers and two channels on the output source. The contractors are using Category 5-E network cable for the passive speaker connections, using pairs at the source and splitting to individual wires to accommodate the number of speakers.

What are the properties of network cable that make it good for speaker wire? Is it a good alternative, or is it just a cheap replacement? Any ideas on how many watts it can handle? Thanks for any answers.

I just wrote out a big detailed response and it sadly disappeared when I tried to post. I don't feel like retyping, so I'll just say this:
Your contractors are idiots. If you're installing speakers (as you are), then hire an audio tech to do it, not a computer tech or a building contractor.
If you're anywhere near the NW of the United States then give me a shout ;)

I have to agree with pulpmind. While just about any wire will get the signal to the speaker, phone or data cable is not a good option.

You biggest problem is going to be voltage loss over long runs. Phones/data typically run on stepped down 14v power. Audio is typically 7v nominal. You need bigger wire to reduce loss.

I'm sure there are audio installers in your area, let them handle it (we usually charge a little less than network installers too).

Oh, and if I read you post right you're going to have an impedance problem too. If you split the channel and run it to (2) speakers on the same line, the impedance will be cut in half. Most amps don't like that and will release the magic smoke in a short period of time. Usually just after the warranty expires.

Isn't it possible to keep the impedance by wiring them correctly (from first principles, shouldn't parallel be OK, but series will be bad?)

QUOTE=Daniel_;2605218]Isn't it possible to keep the impedance by wiring them correctly (from first principles, shouldn't parallel be OK, but series will be bad?)[/QUOTE]

Yep. It can be done, but it's a series/parallel if I recall to maintain 8 Ohms in a chain. Been a while since I've done one like that. Both in parallel would add impedance values giving you 16 ohms and less volume and making the amp work harder. Series would half the impedance to 4 ohms letting the amp push more juice and increasing the volume, but shortening or ending the amp's life. I would have to dig out my notes to see how I've done it in the past, but if memory serves it's a parallel/series to keep 8 Ohms.

If you are trying something like this ALWAYS check the impedance of the circuit on the amp side with everything connected except the amp. If you are within the specified impedance of the amp, you should be good to go. In general below 4 ohms and over 16 ohms will cause failure.

You can also add a resistor block at the amp to adjust the impedance to within the amp's ratings. But you have to be VERY careful, the blocks get really, really hot. Like burn the flesh from your fingers, start a fire kind of hot. But it is an option if done correctly.

Impedance matched volume controls are usually the best option in these applications. Just run a stereo pair to the control, then wire the speakers however you like. The impedance matching in the volume control will prevent the amp from seeing anything other than 8 ohms coming from the distribution side of the control. It also gives you room by room control over the volume, from off to the max the amp is set too.

Post pics of the equipment, or at least model numbers, so we can tell you exactly what you can do to make it work.
The only time it's acceptable is when an A/V hobbyist braids a bunch of them together as a novelty item. Run proper 16ga or heavier wire if you're using powered speakers. You can pick up a 100ft roll at Radio Shack for under $10.
This will give you the proper load on the amp as far as impedance, but in practice it doesn't work so well. Best case is loss of fidelity, worst case you blow a driver. This is not an option for a guy who has to double-check that Cat5 as speaker wire is a bad idea, even if he is making the smart choice in asking since he's not sure.

I also suspect that if they're using 4 tile-mounted speakers in 2 channels, that they're using a constant voltage system, probably 70v.

Sorry it took so long to follow this, I was away all weekend after work on Friday.

If I'm getting what you mean here, then I think you misunderstood. The contractors put two wires in each positive and negative clip on the output source. Wouldn't the impedance be either the same or doubled? Of course you must understand that I have no idea what the hell I'm talking about.

They're running it because its cheap, and because Cat 5-E cable can be run through walls/ceilings without any building code issues. When you say they put two wires in each clip, do you mean a single twisted pair in each clip?

Yes, a single twisted pair to each clip, then a single wire to the speaker.

What's the wattage on the amp? It sounds like we may have found the second person in the world with that special kind of stupid that allows you to create a fire hazard with a speaker install (the first being the guy who had this job before me.)

The amp is 5 watts for each channel at 4 ohms. I just have a feeling that we will have to replace the wires, and I know it will be my job.

Hahaha, that does take some talent...

Holy shit, using cat 5 for speaker wire because it doesn't violate building codes? Well it should!

I don't think it matters what the Cat5 is being used for, n0nsensical. Speaker wire or not, it's allowed because it is Cat5.

That's the joke.. Joke's on them..