Digital multiplex, or DMX, is a lighting industry standard protocol that allows lighting equipment from different manufacturers to be linked and operated together. It relies upon digital signals to be networked through special DMX cable that carries control information for dimmers, strobes, and other lighting equipment. Such versatility requires being informed about cables and terminal characteristics; however, most cables that meet DMX512 cable standards can work in a system. Good-quality, individually screened or shielded twisted pairs minimize crosstalk; additionally, a characteristic impedance of 120 Ohms (Ω), three or five inputs, and a flexible, tough jacket suffice for many needs.
Many DMX signal cables can all be linked, or daisy-chained, together into a single network in order to minimize cable requirements. Channels are assigned to control equipment like strobes and fog machines, and lighting properties such as movement or color shifts. This system requires channels to be correctly mapped and networked in order to minimize interferences or reflection errors. The object is to use as little DMX cable as possible, in the shortest feasible lengths, while creating a network capacity that exceeds the needs of the venue.
Using standard DMX cable instead of microphone XLR cable ensures smooth transition of data, and can compensate for mixers with less output power. Cable should be durable enough to withstand tough conditions and still provide powerful signal transmission. A theoretical length limit is 0.6 mile (about 1 km), but this assumes zero losses or termination problems, so it's better to plan around a lower maximum. Termination resistors also aid in reducing back reflections by absorbing errant signals and keeping the data transmission clear.
All types of DMX cable possess a characteristic capacitance and inductance. A characteristic impedance between 100 and 120 Ω is usually sufficient, with 120 Ω being the common nominal rating. Use of an equivalent termination resistor between the +Data and -Data lines can also minimize signal distortion.
Desirable cable features conform to DMX512 standards that include impedances of 85-150 Ω, low capacitance, and foil and braid shielded twisted pairs. Better shielding provides cleaner signals. Use 24 American Wire Gauge (AWG) for runs of 1,000 feet (about 300 m) or less, and 22 AWG for runs up to 1,640 feet (500 m). Cable should be strong enough to provide support but flexible enough for use in different temperatures. Conditions may require cores of high-tensile fibers or heavy-duty jackets for coming into contact with hot fixtures.
While some networks rely on cables with three-pin XLR-type mic connectors, these may be prone to error, as they are designed for transmission of audio electronic signals. DMX512 standard networks limit lengths of DMX cable according to voltage drop, signal distortion, wiring and number of receivers, and their specifications. Color-coded conductors make for easier identifications. Inquire about bestselling DMX cable types with merchants; they talk to professionals, know the user-preferred brands, and which cables cause few issues in the field.
