【 Weak current College 】 audio cable in the audio signal transmission in importance (2)---Power By 【 China power house network 】

Cable shielding requirements
Many kinds of interference can affect the cable in the audio signal transmission, so the cable needs to have good shielding. Common type of interference from radio signal, the English abbreviation for Radio-FrequencyInterference, RFI. Cable if you pick up the radio emission of the signal, after amplification circuit, it may be detecting mixed audio amplification and signal which cause interference. Shielding of cables as an antenna, can easily be ubiquitous radio interference. RFI is a kind of electromagnetic waves, electromagnetic interference sources belong also motor coil, fluorescent lights, neon lights, etc. Other common types of interference is called static (Electrostatic) interference from electrical discharge, electrostatic discharge, etc.
Cable's shield to protect the Center conductor from these types of interference, but screen on some types of electromagnetic waves is invalid, the balance transfer can only be used to offset their way (so that the two conductors, pick up the same interference, through transformer two interference signal in the opposite direction, the aim of achieving mutual cancellation). Shielded wire is mainly used for microphones, guitars, line cable, because these signal source levels are relatively low and needs to be expanded, and in broadening the signal at the same time, mixed into the interference signal will be magnified, with serious consequences.
Speaker cable delivery of high level signal interference signal, compared to negligible, there is no need for a shield, but the speaker cable has its own requirements. Such as conductor resistance for microphone cable not very important, but the speaker cables to pass high-current, the impedance is very prominent, in principle, the shorter the crude and better. It is important to note that the speakers are also equipped with a line end second core or Canon plug, with the microphone line, sometimes even look the same. But they are completely different, some cables do not confuse or mistyped.
Resistance, capacitance, inductance anti-
Impedance including resistance, capacitance, inductance, resistance to Ohm units. A good understanding of resistance, electrical conductivity of various materials, the same material as the diameter and length are different and have different resistance. For example, 500 feet, wire gauge copper resistance is 4 ohms, wire gauge, increase or decrease each of the 3 numbers, resistance to double or halve. 500 ft 13, wire gauge copper resistance 2 ohm, 19 wire gauge 8 Ohms of resistance, and so on. Such a small resistance change for speakers of considerable influence. Speaker impedance generally within 2 to 8-Europe, if we use a 4-impedance speaker, cable impedance is 4 euro, together they become 8-Europe, and only half of the power delivered to the speaker, the other half totally consumed in cable!
Many high-quality speaker cable with sufficient diameter (12 to 18AWG) and of medium length (less than 100 feet), and count up, even with 18 line, there is still a 1.3 Ohm resistor, lines will have some power loss. In the microphone cable, capacitance ratio resistance more problematic. In the insulation of two metal objects can form a capacitor, the audio cable of the shield and inner conductor just such a relationship, therefore the entire cable to form one large Capacitance to its capacitance blocking the flow of AC current.
According to the nature of the capacitance, frequency increase makes the capacitance decrease, however this capacitance and resistance of the cable, will form low-pass filter, cable length, the greater the cut-off frequency point down, attenuation. This is generally recommended that no important reason too long cables. Conductor of another property is inductive reactance. Audio signal wires in circulation produced with a voltage variation of magnetic field, physics is known as the "perceived". This magnetic field on the signal through the problem, it reduced the frequency and smaller, and resistance, capacitance interaction produces complex results.
In the line level circuit, due to the current weak magnetic self-induction have also not strong; however large current signal (such as the speaker signal) of the magnetic field is much more powerful. Use high-quality speaker cable can reduce the magnetic self-induction, improve sound quality.