These are made using electric wires. They are used to carry electric signals from one place to another. In the audio field there are different types of wires, generally they can be split into two main categories:
Microphone wires: they carry signals from a microphone to the piece of equipment that will handle it. The carried signal has a very low power and voltage. Being so weak is very subjected to interferences and therefore must be adequately protected against electrostatic and electromagnetic interferences. To do so, balanced connections, which will be described in the next section, are implemented.
Line wires: they carry signals which have already undergone a voltage amplification. In this case the signal still lacks of power but is less weak and therefore it is to be protected only against electrostatic interferences. This is done by implementing unbalanced connections, which also will be described in the next section.
Used to build up line wires.
These consist in two conductors: one which transports the signal, the other which acts as the mass. The mass conductor is used as a screen against electrostatic interferences. It in fact gets wrapped around the cable which transports the signal, resulting in what is called a Faraday's cage[8 ]
Used to build up microphone wires.
These consist in three conductors: the wire transporting the signal, the mass, and another wire that carries a copy of the signal which has been inverted in phase in relation to the mass. The following diagram will help us to understand this connections scheme:
For a more detailed description, read the chapter which deals with the topic of noise, in particular the section dedicated to noise-reduction techniques [Noise reduction ] .
In this section's introduction we saw how every wire introduces some distortion, which meant an attenuation in the signal passing through it. This is true for any kind of wire, be it optical or electrical.
A typical distortion of the electrical connections is called microphonic distortion. To get a better idea of it, we'll employ cable, which to simplify things shall be unbalanced, as shown in the following diagram:
In the diagram, we have the two conductors. As already mentioned, a conductor introduces a resistance, which we have represented with the resistances R1 and R2. Moreover, electrical charges pass through the two conductors thus behaving like a condenser. The derived equivalent circuit is that of a pass band filter [Filters ] and this means that the wire behaves just like a filter. As the resistance values at R1 and R2 increase, so does the action of the filter on the signal. A second problem arising from the presence of an inducted capacity, is that if the two conductors are moved one in relation to the other (for example, when the wire gets bent), the distance between the two plates (to be more precise, between the two conductors) varies thus changing the value of the capacity. This means that a current is passing through the condenser, which will be audible as a sound. For more in-depth information regarding the causes of noise in electric wires, refer to the section on noise [Noise ] .
[8 ] For a detailed description of the functions of Faraday's cage we advise you to read any physics introductory textbook which describes elementary electrical phenomenae.