About a month ago, I worked on a show in a ballroom that measured about 300 feet by 200 feet. The mix position was placed at the back of the room. Our system was fairly large and included an AVID Venue digital console with a digital snake, which was a beautiful thing, considering that the length of the snake tapped out at over 400 feet.
After the massive snake (and all the lighting cable it had to run parallel with) was about halfway flown, the guest engineer showed up and wanted an analog console. Of course, it was a Saturday, so nobody was at the shop, but after a long day of creative maneuvering and rearranging, we were finally able to check the rig. As soon as we fired it up for a line check, we discovered that every channel on both the front of house and monitor consoles had a slight buzz. After going through a bunch of different troubleshooting options with no luck, we disconnected the front of house main run from the splitter and Voila! The buzz disappeared.
This is just one situation that shows an example of how cable selection and placement can have an effect on the functional quality of a system. There are three main types of cables on show site that can make for a long day if the appropriate gauge and length is not used: snake, RF (coaxial) and speaker cable. We will go over a few tips on selecting the correct types of cabling as well as why it is necessary to do so.
Snakes
The main snake in a system is one of the most essential pieces of the sound system puzzle. Two major factors can affect the integrity of a snake system: placement and length. These two factors can lead to noise in the system as well as a change in frequency response.
Most modern day snake systems are balanced. A balanced snake system in conjunction with balanced electronic devices and proper grounding can help maintain a noise-free system. While this is the dream, it is often not the reality. Placing a snake in close proximity to power cables can induce noise into a system as well.
The length of a snake can also affect the quality of a sound system. While a balanced snake can help with keeping your system's noise floor low, the shielding can increase the capacitance between signal-carrying conductors. That capacitance in conjunction with the cables' resistance can create a low-pass filter over a long distance. In other words, it can affect the overall transient response of the system. This is not typically noticeable, but with snake systems that are 400 feet and more, it can start to be noticeable.
RF
One of the most misunderstood aspects of the sound industry is RF (wireless devices). Most of us do not have the luxury of having a wireless coordinator on every show to set up our RF or to get advice when issues crop up. A very common practice is to use a long antenna cable out to the stage to get the antenna closer to the wireless device, or to simply boost the gain of an active antenna.
While getting the antenna close to the stage is important, it can be argued that it is more important to use a shorter cable, which reduces the amount of signal that is lost. A longer cable will have a higher amount of signal loss. Depending on the length and cable type used, as much as 50 percent or more of the signal could be lost.
Another factor in getting the most RF reception is using the correct type of cable: low loss cable. A few commonly-seen cable types are RG-213 and RG-8. Professional Wireless Services also makes a PWS 9046 cable, which they claim has a lower loss than all of these. I have not personally measured this, but they are a very reputable source.
Speaker Cable
Of the three types of cables discussed in this article, speaker cable is probably the one that gets the most attention. Excessive speaker cable length and too-small cable gauge can affect the damping factor as well as signal loss.
In short, the damping factor is the ability of the amplifier to control a speakers' motion. The higher the damping factor, the "tighter" the sound. The variables that can determine the damping factor include the specs of an amplifier, the load put on the amplifier, and speaker cable gauge. A pretty good standard of cable thickness is 12 gauge. This ensures that the damping factor is kept up as high as possible. A thin speaker cable can not only affect the damping factor, but can also cause the cable to actually dissipate some of the amplifier power in upwards of a couple dB. Equally as harmful is an excessive length cable run. When combined with insufficient cable thickness, it will bring the systems' SPL capability down.
Summing Up
The bottom line in the world of cables is that in the long run, it will be worth your money to spend the extra money for quality cables. It has the potential to make or break a show, which, in these rough times, can make or break a sound company.
