WHAT IS A CONDUCTOR?
An Electrical conductor is an element (remember the periodic table in chemistry?) which conducts electricity, as opposed to an insulator, which does not, or a semiconductor which allows some electricity to pass. There are also alloys that have different electrical characteristics, and platings or other element to element contacts such as in connectors which also have electrical characteristics as well as chemical characteristics in their applications. Simply stated - it is not just a matter of connect metal to metal and you have a good connection. The best connectivity designs take into account the source connector materials, the receiving device connector materials, the audio video wire connector materials, the conductor materials and the electrical and chemical ways in which they interact with one another.
MEET THE CONDUCTORS - SILVER, COPPER, GOLD, TIN, NICKEL, STEEL
1. Silver is the best conductor, with a very slight edge over copper. Silver also has the benefit of having oxidation that conducts as well as unoxidized silver.
2. Copper is the next best conductor, with about 1.05 times the resistance of silver, and due to its lower cost is the most commonly used conductor for audio and video cables. Unfortunately copper oxidation is a semi conductor and should be avoided because of the "skin effect" which causes high frequencies to use the outside of the conductor at high frequencies. If the outside of the conductor is oxidized, the performance at very high frequencies will suffer. Note: This is does not have any significant effect in the audio frequency range. (For more on Skin effect see the Article Library at Audioholics)
3. Gold has about 1.4 times the resistance of copper and does not oxidize making it a popular plating for audio and video connectors.
4. Tin is a poor conductor, with about 8.5 times the resistance of copper, but has good resistance to oxidation and the oxide has good conductivity. Tin is quite often used to protect copper from corrosion.
5. Nickel has about 4.5 times the resistance of copper, good resistance to oxidization and good oxide conductivity. Nickel is a very common connector plating.
6. Steel has about 7 times the resistance of copper, lousy resistance to oxidization and lousy oxide conductivity. Steel is generally used only on high frequency cables plated with copper that need very high strength.
TYPES OF WIRING AND THE "BIRTH" OF THE AUDIO/VIDEO CABLE
Discreet wiring - Discreet wiring is where separate conductors, indluding speaker wires, are run in some fashion (wires or circuit board traces) to the circuit components or input/output connections to which they need to go to. In some circuits, especially non signal related connections the path or interaction of these types of wires to one another is not particularly important as long as they are separated from one another to a reasonable extent. The closer they get, the more likely they are to possibly interact. This all goes out the window when a signal or "change" (whether they are due to ac power wire, analog signals or digital signals - basically any type of current or voltage change) becomes a part of the mix.
Example: Two wires are close together while another two wires are farther apart. The closer wires act more like a capacitor (have more capacitance) than the second two wires. If the circuit is in a quiescent state - "at rest" (no changes are going on) , there is potential energy storage due to capacitance, but without change, it has no effect on any signal, since there is no change. If you then create a change, or signal wire that causes electrical current flow, the two sets of wires may then have an effect on those changes, due to capacitance, inductance, etc, and the changes created may be different depending on the frequency of the signal involved and the characteristics of the wires and the overall circuit.
Example: A wire that has current flowing through it has a magnetic field. Two wires close together with current flowing through them both have magnetic fields. The two magnetic Fields will interact with one another if close enough and this interaction will effect the currents flowing through the wires more or less, depending on the rate of the change. If the wires are "send and return" signal wires the current flow will be opposite. If the current flow is opposite, the magnetic fields are in opposite directions.
Electromagnetic noise acting on these opposite fields are canceled out (dependent on the frequency and distance between conductors) - thus is born the improvement for signal transmission called the cable.
TYPES OF SHIELDING AND PROPERTIES:
Braids, Served Shields and Foil - A braid is as it sounds a "braiding" of conductor material that in this case surrounds the inner insulator and center conductor. Served shields are a layer of individual strands of wire which are laid one next to the other with a spiraling twist around the insulator and conductor. A foil is pretty much what it sounds like - an extremely thin, solid (not stranded) foil like shield surrounding the insulation and inner conductor and often inside and/or outside of another shield.
Coverage and frequency - A served shield does quite nicely for coverage at lower frequencies, at least until flexed, which will make them more noise susceptible. A braid is great for coverage and dual braids reach up to around 95% coverage. The tighter the braid the smaller the "holes" and the higher the frequencies need to be to penetrate the shield. Obviously, dual braids would end up with smaller holes, and a foil braid can provide up to 100% coverage. So why not just use foil? Isn't 100% perfect? No, because foils just don't give a stable, and consistent impedance over the length of the cable, durability, or consistency when flexed. Many extremely cheap audio and video cables are made with a simple foil shield - they break very easily and generally perform very poorly.
Triboelectric effects, microphonic effects (handling noise) - Flexing, twisting, or transient impacts on cables with the floor, etc, while in use will cause "snaps", "crackles", "pops" and other noises in the signal due to rapid changes of capacitance between conductors. This is generally regarded an audio problem, normally effecting microphone cords and guitar cords. Served shields are ideal for reducing triboelectric effects. The geometry is good at resisting large capacitive changes while flexed or impacted. Braids are generally not nearly as good as served shields for this, again due to their design. Movement, and compression will cause noise. Foils are the worst for this - they are easily deformed causing large changes in capacitance and large "pops" coming from PA systems. Any live sound PA system engineer or studio engineer Needs to be deeply knowledgeable about these effects and how to avoid them at any cost.
*Note - Steel Coat Hangers as Cable
While the typical crazies on forums suggest that coat hangers will operate just fine as an audio cable (and poorly designed tests concur) there are definitive reasons why it is not a remotely good choice. First of all, Steel is a very poor conductor with over 7 times the resistance of copper wire. That means lots of wasted power supply wire. Second, steel oxidizes easily and the oxidization is a poor conductor. Third, steel is rather hard to make into a twisted pair, allowing for EMI and RFI resistance. Without making the steel into a twisted pair, Noise and Hum may become a larger than desired portion of the sound!