thanks and Happy New year.
David

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well, I have "visual" access to the subs and their amp , this is why I would favour the option of running 2 long balanced XLR cables from the bass processor to the amp.
Thanks for this idea of transformers but I would rule that out.
Btw, this is for my home theater ( film freak but even more a home theater freak ). The funny part is that I have never gone so much to theaters since the last 2 years. 2 or 3 movies a month generally.

For subwoofers and stage speakers, I have used 4-conductor 8AWG cable, configured the way John Allen recommends for his HPS-4000 sound systems. There was never any problems, and the sound quality, in my opinion, beat the THX system quite handsomely. I agree with Scott - keep the amplifiers in the booth.

Thanks. Mmh, 8AWG ? with speakon ? The QSC DCA use NL4FC speakon, and they only accepts 4mm2 wires ( ie, 10 AWG if I am correct ). 8 AWG would be great ( this is what I have currently with my current power amp and I CAN feel/hear the difference between 8AWG and the former 10AWG I had previously).
on the other hand, looking at what JBL recommends in its technical sheet on the 5000 screen speakers, even 12 AWG or 16 AWG would be enough for such short distances ( less than 50ft for instance ), which amazes me, knowing how much the wire can "eat" ( dB loss and damping factor loss ).

Oh, it can eat alot. But a damping factor is just a figure of merit. The closer to 200 you can get, the better off your are going to be. But if you approach 150, you probably won't hear much of a difference (if any) from 150 to 200..

There are some mighty fine sound engineers on this forum, and they know more that I do. They can give you some good advice, and some suggestions they will make won't drain your bank account.

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That is keep the amps in the booth. It isn't that the amps can't be put next to the speakers with success because they can and have. It is much more difficult to accomplish this without noise problems and no matter how you cut it, it is more difficult to troubleshoot an amp behind the screen than one in the soundrack with the rest of the equipment.

As to the loss in the wire, use a suitable wire size. Don't was your money on high-brow speaker cable either....use THHN stranded. 10awg will be fine but #8awg may make you feel better.

Oh and on damping factor, it is mostly a bogus number used by amplifier manufacturers to show some sort of superiority. The driver itself will be the big operator in that, not the cable. If you have two 4645C then run two pairs of cable.

Twisting cable is a good idea, running in grounded conduit is a VERY good idea...every once in a while a surface mounted speaker run finds out what a cabbie or walkie talkie can do.

When twisting cable (in general) DO NOT USE A DRILL!!! you are then actually twisting the strands themselves which is not the goal (you are actually breaking the cable)...the goal on twisting the cable is to create a "lay." Either get it twisted properly by the manufacturer or you will be twisting by hand. A properly twisted cable is such that if before twisting you were to put a straight line on the top side of the cable and then twist the cables the line stays straight. This will not stress the cable and not create a "spring"

Steve

I agree with Scott; it would be better to keep the amps in the booth for both troubleshooting and EQ'ing (if you have to adjust the gain pots.)

On two installations I know of where the amps were remote (to the processor) there was a slight 60cy hum in the sound. It's just too hard to keep those low-level runs quiet.

If the amp has XLR/Cannon type (3-pin balanced) plugs, use them rather than hard-wiring them to terminals. Look carefully at the documentation that shows which pin is "high" "low" and "ground." It seems that someone always reverses them somewhere.

Paul's idea of twisting them is good also. Run them in conduit if possible. If not, you will probably have to buy plenum-rated wire to adhere to building codes.

Run the thickest gauge speaker wires you can to the stage. Try to make each wire one 'unspliced' run. If you are having electricans do the work, tell them specifically there should be no splices. You might be surprised at how many times this is forgotten, and the speaker run ends up with 2-3 splices in it. Leave a lot of slack at both ends, because you may have to change around the rack equipment or the way the wires are routed at the speaker.

When you "dress" the wires in the amp rack, leave enough length to enable you to disconnect the wires from one amp and reach another; ie: the speaker wire from the bottom amp will reach the top amp, etc. Not only is this good for troubleshooting, but if (say) the center amp goes out, you can easily switch to another, less important amp (like a surround channel) until the amp is repaired. Do the same with the XLR amp inputs.

A suggestion is to color-code the wires by making the "low" or "return" wire the same color for all channels, and buying a different color for the "high." I used the resistor color code to remind me which is which during installation; ie: twist white and black for "LEFT;" white and brown for "Le," etc. You might have to order some colors in advance, because that are not commonly used. Lable them properly when you are done (nylon tie-wraps with a writing area on them.) They will probably get treated very roughly over the years, and you don't want them to come off.

Personally, (depending on the distance- up to 120 feet/ 40 meters) I think 10 or 12 gauge is fine. While it's true the bigger the gauge the better, the law of diminishing returns comes in. It's just not going to sound any better with 00 gauge wire.

The 70.7 volt transformer system is pretty much out nowadays. The transformers must be fairly large to handle the lower frequencies which means they are expensive. In addition to the benifit of "stepping up" the voltage to avoid loss in the speaker wire, it allowed you to match the impedence of several speakers to one source. Also, by using different transformers, you could tailor the sound volume at each speaker. So, a single wire-pair from an amp could go outside to a big loudspeaker array, then inside to smaller speakers in a hallway. One type of transformer would be used in the outdoor array (and be loud) and then another type would be used for the smaller speakers indoors (and be quieter.)

oops, must be blind: the DCA has screw terminals so AWG 8 might fit, right ? seems my brainstorming about wiring is coming to a good end !

happy new Year to all.
David

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I have a long length of 10 gauge solid UF (underground feeder) cable that has 3 wires with a ground. Does anyone see a problem in using this wire as the main speaker feed wires to run under the house from the booth to the screen? This run is just under 18'. The cable is flat and will be run so that there are no twists between the junction boxes that I will install at either end.

I will use the naked ground, and the white wire as the 2 negative lines, and the red and black wires for the right and left channel positives.

This wire is left over from when I ran a new 30 amp 220v line out to my garage, and had to buy a 250' roll of this wire. I also used it to supply power to my A/C system. Plus, I've already run a new pair of 20a lines out of this wire for each of my projectors. I just love working in my crawlspace!!

Anything that I need to do? Should I twist the wires at all? Is the 18' run long enough to cause any problems?

Thanks. I bear a total likeness to the guy that is sucking down the FG in the photo on the left.