DMX Cables in Practice: Length, Impedance, Noise - Avoiding Flicker

1. Why DMX Is So Sensitive to Cables

DMX512 is:

• Digital

• High-speed (250 kbit/s)

• Unidirectional

• Based on RS-485 differential signaling

This means:

• It does not degrade gracefully

• Errors appear as random flicker, jumps, or fixtures freezing

• “Mostly working” is a warning sign, not success

If your cable setup is wrong, DMX doesn’t warn you—it just misbehaves.

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2. DMX Cable vs Microphone Cable (Why It Matters)

Property	DMX Cable	Mic (XLR) Cable
Characteristic impedance	120 Ω	~45–75 Ω (varies)
Twist consistency	Tight, controlled	Loose
Shielding	Designed for data	Designed for audio
Reflection resistance	High	Poor
DMX compliant	Yes	No

Using mic cable for DMX works… until it doesn’t.
Short runs may survive, but reflections and timing errors increase fast as distance grows.

Rule:

If it carries DMX, it should say DMX or 120Ω on the cable.

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3. Maximum DMX Cable Length (Reality vs Spec)

The official spec:

• 300 meters (≈1000 ft) per DMX line

The real world:

Scenario	Safe Length
High-quality DMX cable, terminated	200–300 m
Cheap cable, no termination	50–100 m
Mic cable	20–40 m (sometimes less)
Multiple daisy-chained fixtures	Reduce by 30–50%

Key insight:
Length alone isn’t the problem—reflections and noise are.

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4. Termination: The Most Ignored Fix That Actually Works

What termination does

A DMX terminator:

• Is a 120Ω resistor

• Plugs into the last fixture

• Absorbs signal reflections

Without it:

• Signals bounce back down the line

• Timing errors increase

• Flicker appears randomly, often only with movement or strobes

When you MUST use termination

• Long cable runs

• Cheap fixtures

• Flicker during fades or strobes

• Any professional setup (just do it)

If your DMX ever flickers: terminate first, debug later.

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5. Daisy-Chaining vs Splitting (and Why Y-Cables Are Evil)

Correct

Controller → Fixture → Fixture → Fixture → Terminator

Incorrect (but common)

• Y-split cables

• Passive splitters

• “DMX through” boxes without buffering

Why passive splitting breaks DMX

• Impedance mismatch

• Signal reflections

• Uneven voltage levels

Use an active DMX splitter when:

• Running multiple branches

• Covering large rigs

• Mixing fixture brands

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6. Electrical Noise: The Invisible Enemy

DMX hates:

• Power cables taped alongside data

• Dimmer packs

• Motors

• Cheap power supplies

• Long parallel runs with AC

Best practices

• Cross power and DMX at 90° angles

• Keep at least 10–20 cm separation

• Avoid coiling excess DMX cable near power

Shielding helps—but routing matters more.

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7. Common Flicker Symptoms and What They Mean

Symptom	Likely Cause
Random flashes	Missing termination
Flicker only on strobes	Reflections / timing errors
Fixtures freeze	Signal loss
Only last fixtures glitch	Too long run
Works until soundcheck	EMI from amps / dimmers

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8. Quick DMX Cable Checklist

Before blaming software check these:

• DMX-rated 120Ω cable

• Terminator on last fixture

• No Y-splits

• Power separated from data

• Active splitter if branching

• Reasonable run length

Fixing cabling solves 80% of DMX issues.

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9. The Hard Truth

DMX is simple—but unforgiving.

If you treat it like audio, it will betray you mid-show.

Related guides

• DMX Termination
• DMX Splitters & Opto-Isolation
• DMX Cables in Practice