Audio Engineering

Balanced and Unbalanced Transmission Systems (1)

What are they, anyway? And why should I care?

The Music Telegraph | Text 2019/04/04 [13:22]
Audio Engineering

Balanced and Unbalanced Transmission Systems (1)

What are they, anyway? And why should I care?

The Music Telegraph| 입력 : 2019/04/04 [13:22]

▲ Unbalanced wiring

© Aviom

 

▲ Balanced wiring

© Aviom

 

 

Balanced and Unbalanced Transmission Systems (1)

 

What are they, anyway? And why should I care?

 

 

Unbalanced Transmission System

Transfer of electrical signals from one location to another can be accomplished only by means of a closed loop, meaning that for energy being sent out, an equal amount of energy with the reverse polarity should be received back. If we talk about electron flow, the amount of electrons being sent into the line should be replenished though the incoming line, thereby producing the current flow. We are talking about two wires: one, being used to send signal out, and the other which acts as a return path for the same signal. Since audio signal current changes its direction many times per second, so it can be seen that the direction of current flow in two conductors is always opposite to each other.

 

 

All audio transmission lines work on the same principle. In the case of field telephones for instance, one wire is omitted and ground is used as a return path. Therefore, basically only one wire (hot) has to be strung. Unfortunately, this single conductor also acts pretty much as an antenna, picking up random electrical fields surrounding it and mixing them with the audio signal being sent through the line. The tendency of this type of transmission line to pick up extraneous harmful fields causes electrical interference. Since one side of such a transmission line is at ground potential and the other is not, we call such lines unbalanced because it is unbalanced with respect to ground and external fields.

 

 

One way to protect an unbalanced line from picking up external interference is to isolate it from the external fields. This can be accomplished through shielding. In order to minimize the effects of external fields, insulated transmission wires are kept close together with flexible metal shield in the form of a tube surrounding them. This shield is normally grounded at either one or many points.

 

 

For this shield to be nearly 100% effective, it would have to be made of a high-quality magnetic shielding material with an ability to block all electrostatic and magnetic fields. Shields are made out of aluminum, copper, or some other non-magnetic material. (Non-ferrous materials stop almost all electrical interference caused by electrostatic and radio frequency fields, but don’t protect the wires from picking up low frequency magnetic fields from transformers, power lines, motors, solenoids, and other sources.)

 

 

 

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