There are different types of wires that are used in swiftlet farms. In the photo, one can see four types. The left hand side are the better quality and more expensive wires whereas the ones on the right are lesser quality and cheaper wires. Novice farmers often had no idea about the wiring in their farms unless they are well verse in audio equipments or like to play around with stereo or home theater systems.
Sometimes, contractors would simply use the lower right hand type of wire to rig the sound system as this is the cheapest wire. It is the cheapest because it has very little strands of copper in it. It is white in color with a blue line indicating the positive polarity.
The good point is that this wiring is very thin and do not take up much space around the planking and it is very easy to strip away the plastic cover to expose the copper strands to make connections. Actually, it is usable but not really advisable to do so if given a choice.
The upper right hand type which is in red rubber coating is slightly better as its silicone coating provides durable protection to the copper strands which is probably slightly more than the cheap white color wire. The color is red on both lines but one side is darker than the other; so one would need to choose whether to use the darker line or the lighter color line to be the positive line. I choose the darker red line to be the positive line. However, if you use it outdoor, the color will be faded by the sun so that you will not know which is positive and negative anymore. Then you need to trace the line back to the source to check. If you like, you can use a marker pen to mark the positive line. While the silicone cover provides good insulation for the wires, it can be hard to cut the covering away to expose the copper strands to make connections especially if one use a plain scissor to do the job; if you have a stripper, it would be much easier.
The lower left hand is a good quality stereo wire with strong jacket covering and one of the line has a clear blue line indicating it be use for the positive polarity. The many strands of coppers make a thick wiring good for sound transmission. The ray of the sun also will not burn off the blue line indicating positive polarity but the silicone cover tend to become soft when exposed to the sun as when we used it around the open roof area.
The upper left hand blue color wiring with a red line running on one line (which I use to indicate negative polarity) is a very good choice for use in swiftlet farm as it is thick with strands of coppers and the blue jacket is easily cut and strip away to make connections. It is probably slightly more expensive than the stereo wire but a good choice for use in a bird farm.
If you are to build a farm today, I would suggest you use the more expensive wires as the more strands of copper should help to deliver better quality of sound; especially if you plan to operate the farm for not just a few years but decades. I think it is very much a case of false economy to save pittances on wiring unless you ignorantly allow a contractor to cut corners and to make use of the cheap white wires. Another thing to consider is to make use of different color wires for different purpose, such as the blue ones for external sounds and the stereo wires for internal sound so that you can tell them apart at a glance.