The DMX standard specifies cable runs up to 4,000 feet (1,200 meters, this assumes zero losses or termination problems) but in practice potential cable lengths are affected by cable quality, the characteristics of the DMX fixtures being daisy-chained together, and other factors.
For cable runs over 1,000 feet (300 meters) a repeater/booster may be needed. Placing a terminator at the end of each cable run (+Data and -Data lines) will help avoid degraded data transmission. Best practice calls for twisted-pair, shielded, low-capacitance data cable, not audio cable.
Good-quality, individually screened, 110 – 120 Ohms 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. A characteristic impedance between 100 and 120 Ω is usually sufficient, with 120 Ω being the common nominal rating. Desirable cable features conform to <span class=”notranslate”> DMX512 </span> standards that include impedances of 85-150 Ω, low capacitance, and foil and braid shielded twisted pairs.
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.
DMX 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.
Faulty fixtures or incorrect fixture settings can complicate troubleshooting DMX networks. For example, a moving head set to operate as a « master » fixture will disrupt a DMX network and should be set to « slave » mode.