The Truths and Myths of Audio Interconnects

I was struck by something today. It probably would never have come to my attention if the item that struck me were properly shelved and faced, but that is something I'll have to fire someone for later. What is notable is that the item which struck me in the head was a pair of $90 3 foot RCA cables. I decided to read what made them worth $90, and found myself laughing aloud at the "features" which made these cables "superior". Knowing full well these features were complete bullshit, I was suddenly struck with the euphoric sense of realization that placed me half way between Einstein's Theory of Relativity, and P.T. Barnum's sucker-every-minute: If you build it, they will come, and they won't even know why.

It is very true that audio interconnect technology improves on the sound quality possible in cars. Many features are essential for good sound, while others are hooey, complete and utter hooey. In this paper, I will discuss the common features of many manufacturers products, and common myths that accompany some of them.

The Skin Effect

One of my favorites, and one I fell victim to early on is the Skin Effect. Quite simply, the Skin Effect is the tendency of current to move to the outside of a conductor at high frequencies. This means that there is less total conductor area, and thus more resistance and higher signal loss. This is a real issue, mind you. However, the skin effect occurs at much higher frequencies than your typical rational audiophile will be concerned with, and it is almost nonexistent at even extended audio frequencies. The skin effect is more or less a borrowed problem from high speed digital networks, and high frequency communication equipment.

Gold is the Best Conductor

This is categorically untrue. Anyone with a physics background will tell you that the lowest conducting alloy at room temperature is Silver (Ag). However, Gold (Au) is more suited for automotive applications. Gold is a very inert metal, which means it will not readily corrode. Any tarnish that does occur is easily cleaned with a soft cotton cloth. Gold is also soft and highly malleable, so when interconnects are plated in gold, it yields more contact area than when not (albeit, on a very microscopic scale). But finally, and most importantly, gold is pretty. Gold is also expensive, and when you plate things from speaker wire to distribution blocks with gold, you can charge more.

Multi Path Interconnects

This was one of the many things that inspired laughter from those $90 rca cables. In their theory, conductors of different length are wound into a cable. It's common knowledge that given sound frequencies travel faster than others, and other sound frequencies carry farther. By using conductors of differing lengths, these given frequencies should arrive at the other end of the cable at the same time. That is complete and utter bullshit. Here's how:

  1. Sound is comprised of changes in pressure in a gas. We hear those sounds because our ears convert those changes in pressure into nerve impulses. However, audio signals carried on an interconnect consist of fluctuations in electrical flow. They do not suffer the same problems as sound travelling through a gas.
  2. Voltage changes at near the speed of light, or at least damn near it. When you change the voltage on one side of the cable, it almost instantaneously changes at the other end.
  3. Current flows extremely slowly. It may take hours for an electron at one end of an interconnect to bump it's way to the other end. A length of a few feet or centimeters will make no difference.
  4. To ensure that the frequencies travel the specified path, you would have to build a crossover into the interconnect. There was not one. Otherwise, electricity takes the path of least resistance, which would be the shortest sweetest conductor.

Capacitance

To anyone, the basic construction of an audio interconnect cable, and the construction of a capacitor are virtually the same. In a capacitor, you have two metal plates separated by a dielectric (insulator). In an interconnect cable, you have two wires, separated by insulation.

The determining factors in a capacitors capacity is the area of the two plates, and the distance between them. The more area, the more capacitance. The closer they are without actually touching, the more capacitance.

Capacitors in car audio, among other things, are used for filtering. A capacitor, depending on it's value, will resist low frequencies, while passing high ones. A very large capacitor will pass all frequencies, because all frequencies will appear to be high. A very small capacitor on the other hand, will block audio frequencies. Many cable makers tout the very low capacitance of their cables, but in truth, the capacitance in even the cheapest of RCA is on the order of picofarads, and would not have any effect on the audio signal.

Insulation

Insulation is important. The automotive environment is a very hostile one for electronics. Materials should be able to stand up to the extremes of heat and cold, as well as vibration. For the most part, any good quality pvc or plastic will work. However, there are a few situations when you will need to consider the insulation. Some cable manufacturers use special gelatins in their insulation, which reseal any punctures or breaks. However, these tend to also be easier to damage. There is also the normal PVC jacketing common to cables, which is common, durable, and cheap. However, some manufacturers are experimenting (on your pocket, no less) with silicone, oxide impregnated plastics, and good old fashioned wool. Remember....we are not dealing with high voltages here, no exceptional currents, so concentrate on insulations which offer thermal protection, and long life.

Connector Construction

In spite of it's simplicity, terminators on an interconnect have to be very precise. RCA's, which are the most common audio interconnect, have a very specific dimension that they have to conform to. While there is some room for error, a grossly mis-sized connector may not fit, or worse, could damage your equipment on insertion. Many manufacturers produce split center pins and split outer rings. This actually works two fold. If it doesn't precisely match tolerances, the springy nature of the pin/ring will accommodate the tolerance. Also, the tension will make the interconnect hang on harder.

Cable Configuration

Many design configurations are used for the actual cable itself. The most common is a coaxial design. In this design, there is the center conductor, which is insulated. Then, the outer conductor is wound around that (usually woven, which adds strength). This is again, insulated. Finally, good cable makers add a foil shielding (this is called mu metal) to reject high frequency interference, and of course, another jacketing of insulation. Coaxial cables are favored for their high bandwidth; The ablility to carry very high frequencies. However, these are often up into the radio frequency range, and do not necessarily enhance transmission of audio frequencies. This type of design does have more strength, which is a plus if you're pulling the cables under carpets.

Another common design is using twisted pair. In twisted pair, the two conductors for each signal are simply twisted. By twisting them, they are at a constant 45 degree angle from each other. This reduces the likelihood that the magnetic field around one wire will induct onto the other. It's also pretty. A lot of installers will twist wires together to keep them from turning into a rats nest. Grizz Archer hosts seminars on car audio from time to time, and one thing he likes to ask is:

"Why is it that I can pick up the phone and call half way around the world to Japan, and get a crystal clear connection, but most installers can't run a cable ten feet without getting noise? It's because phone companies use twisted pair wires for their phone lines...."

One thing to avoid is shielded wires, and special "Anti Noise" interconnects. The shielding consists of a large foil wrapping, which is connected to the shield of the RCA's. This is a borrowed technology from radio and high frequency transmission, where induced RF noise is captured by the shield and shunted out of the signal path. However, in your car, that large metal foil provides the center conductor of your RCA with more surface area, increasing the likelihood of ground loops. Anti noise interconnects, on the other hand, use an inductor at one end. This inductor will tend to squelch high frequencies, and in some designs, will actually cause a ground loop if the cable is put in backwards. Any RCA with some type of "Anti Noise" technology, is bullshit. It's just a bandaid to a bigger problem, and it doesn't matter whose name gets slapped on it.

by: Andrew Krause