Suggest speaker cable for long run...?

I'm going down this road myself right now. I'm looking at a run of 18 - 20ft. though. So far I've looked at building a set of WLM speaker cables as seen here:

White Lightning Moonshine

I already have the two twenty foot runs so it should be easy to see how they sound. I built an 5 ft. pair previously and they are surprisingly good. However, the extra length may cause some issues. Cheap enough to find out though.

OCOS cables are supposedly the cable to get for long runs. They'll run you quite a bit of money though.

I'll be just as interested to see what others have to say.

It depends on your speakers and your amplifier. For that long a run you obviously want a cable that has low resistance, low inductance, and low capacitance per unit length. How low is low enough will depend on speaker impedance and amplifier output impedance.

I can't offer specific cable suggestions for that long a run, but the following technical considerations should allow you to rule out a lot of unacceptable choices.

At the end of this post are links to a wire gauge table and an inductance calculator. The inductance calculator applies to a straight piece of solid core wire, but I think it can be used as a reasonable approximation for most cables which have ordinary, non-exotic construction. Of course, if inductance per unit length is provided by the manufacturer of any particular cable you are considering, use that figure instead.

Keep in mind in using this table and calculator that the length of your run is 100 feet, the length of the round-trip the signal has to make.

The gauge should be large enough to keep total resistance to a very small fraction of the speaker's impedance at the lowest point of the speaker's impedance vs. frequency curve. Total resistance should also, preferably, be low enough to not significantly add to the amplifier's output impedance (which is the amplifier's specified damping factor divided into 8 ohms).

Once you have chosen a wire gauge, determine the inductance either from the manufacturer's specifications for any cables you are considering, or, approximately, by using the inductance calculator. To use the calculator, you will have to input the wire diameter indicated in the wire gauge table, for the gauge you have selected.

Then calculate the inductive impedance at 20kHz (the worst case frequency) using the formula 2 x pi (which is 3.14) x 20000 Hz x L, where L is inductance in Henries. The result of the formula is impedance in ohms. That result should be kept small in relation to the worst-case speaker impedance, and the amplifier output impedance, similarly to how total resistance was kept small.

Then give preference to cables which meet those criteria and also have the lowest capacitance.

http://www.powerstream.com/Wire_Size.htm

http://www.consultrsr.com/resources/eis/induct5.htm

Regards,
-- Al

The OCOS cable will do the trick. By virtue of it's low capacitance, constant value impedance and effortless signal transmission, the signal remain pure, regardless of cable length. If you need a "long" cable run, this is it!

I second Al's advice and would add that you should avoid 4 ohm speakers if you desire good quality sound and furthermore (if you are serious) simply use a pro type balanced XLR preamp and run your 50 feet with XLR to your power amp close to the speakers. (XLR balanced use not only higher signal levels but are also properly shielded and much more immune to noise)

This would get you past concerns with speaker cables and low impedances dips in your speakers.

If this long run is for surround speakers in an HT system in a large room then I would not be overly concerned - just get some decent thick speaker wires. I would only be concerned if this was for a primary setup for critical listening.

Thanks for the responses.

It's for both HT and critical listening. I can't fit the amps up front (and if I could I wouldn't want to because my Pass amps glow bright blue...).

Unfortunately my speakers are 4ohms (Wilson Sophias). What I seem to notice with long runs is a degredation of upper bass (everything else seems fine).

What is OCOS cable?

See here:

http://dedicatedaudio.com/inc/sdetail/20951

I've just made a set of the WLM DIY cables and will be trying those along with some other cables I'm making out of a 30' spool of Belkin PureAV Silver Series cable that uses solid core PCOCC copper. The spool cost me $15. You can search for it on the Internet.

In addition I'll be trying out the Morrow Audio SP3 and the OCOS cables. Somewhere in this batch I should find a winner.

I took a look at the OCOS description. While I have no reason to question its being an excellent choice for longer runs (and at $1K for 7.5 meters it had better be!), I find the design rationale offered there to be, um, unpersuasive and incomplete.

There is no indication of inductance, capacitance, or resistance. The terms "characteristic impedance" and "impedance" are used interchangeably, when in fact they are very different. "Characteristic impedance" is a transmission line concept, which only comes into play when cable length is a significant fraction of a wavelength. That is not even remotely the case at bass frequencies for a 50 foot cable. Which makes the graph included in their literature meaningless.

The "impedance," on the other hand, that would result from the inductance of a 100 foot round-trip run of speaker cable certainly can be expected to be significant in relation to the nominally 4 ohm speaker impedance (which is undoubtedly even lower at some frequencies). But the OCOS' inductance is not specified.

Again, while these cables may very well be excellent choices for longer runs, aside perhaps from their cost, their technical rationale is unpersuasive, and the technical information provided is not complete enough to allow a meaningful prediction of the compromises that a 50 foot run will result in, compared to a shorter run.

Regards,
-- Al

I tried a bunch of stuff (borrowed from dealers) and ended up using Canare 4S11. Some cables beat it at shorter lengths, but nothing did at 30ft. I run it single wired instead of bi-wired. I have approx 30 ft runs that I can't do anything about until I buy my own home.

At $1.35/ft from Blue Jeans Cable, its not a huge investment if its not what you're looking for.

What is OCOS?

"'spensive"

I've gone 40 ft with the 4s11 using my receiver to drive my rear speakers without issues.... but they ain't Sophias.

Even with Sophias on the other end, I'd investigate the link Al posted and give that a try first... see if I could live with a DIY set of speaker cables.

I also run a set of SR Sig 10 x2 active bi wires that are 21 ft long with both a HT setup and my main 2 ch setup... on both 8 & 4 ohm speakers with great results.

Maybe you should also check with SR and Bruce at Voodoo cables. He's a very insightful honest, and practical person.