Microphone line
A microphone line , also known as a microphone cable , is a special electrical line that transports the electrical output signal from a microphone to a sound system for further processing .
construction
In professional audio technology, only symmetrical microphone lines are used for reasons of signal quality and operational safety.
Symmetrical microphone cables consist of a stranded pair of insulated copper wires that are surrounded by an electrically conductive shield. The sheathing sits on top of the shield and keeps environmental influences (dirt, water, mechanical stress) away from the interior.
The copper wires are usually designed as stranded wires , typical conductor cross-sections are between 0.14 and 0.34 mm 2 . Wire helix, wire mesh, metal foil, conductive fleece or combinations thereof are used as shielding .
XLR connectors are used almost exclusively in professional technology , and three-pole screw connectors such as the Euroblock are also used in installation technology on devices . In studio environments there are space-saving special connectors, for example LEMO 3T .
Electrical function
The signal voltages emitted by microphones are very small; with normal sound events (e.g. human speech) they are in the range of a few millivolts . The task of the microphone line is to transport this weak and therefore interference-prone signal with a high signal-to-noise ratio and low distortion over usually two-digit meter distances.
Technically, the principle of symmetrical signal transmission is used in order to minimize interference. In addition, as a Faraday cage , the shielding keeps the wire pair free from external electrical fields.
Since the power transmitted is only very low, the ohmic resistance and thus the conductor cross-section of a microphone line are practically insignificant . Rather, small cross-sections can be advantageous because they have a lower operating capacity and thus lower attenuation of high frequencies. The capacitance of the signal wires to one another is typically around 60 ... 80 pF per meter of cable length.
Microphones with built-in electronic components are supplied with power via the microphone line using phantom power.
Mechanical Requirements
Microphone lines in PA systems are often free on the floor in the stage / podium area or in areas with public traffic. The necessary step resistance is achieved with a thick jacket, which can make up half of the entire cable diameter. In order not to lose their good electrical properties even with frequent assembly and dismantling, microphone cables must be constructed very flexibly; outdoor use can also expose them to extreme temperatures.
Microphone cables with a thin jacket that are not tread-resistant and only serve to connect devices that are next to each other are called patch cables .
Unbalanced microphone line
An unbalanced microphone line has only a single signal wire within a shield. The advantages are the price and the slightly smaller diameter, which is opposed to a reduced interference immunity. For this reason, this technology is only used with short cable lengths, for example in headsets or hands-free systems for cell phones.
Special cable types
Particularly high-quality microphone cables have two wire pairs in a star- quad configuration. Opposite wires of the quad are connected to a total wire at the ends. This design has a lower operating capacity compared to a simple pair of wires.
A multicore combines numerous (typically up to 48) individual symmetrical microphone lines in a common sheathing.
Web links
- Information from a cable manufacturer about important aspects of microphone cables