Polarity in Live Sound: Ensuring Proper Signal Alignment

Polarity describes the relationship between positive and negative portions of an audio signal. Correct polarity means related signals move in the same direction; reversed polarity means one signal’s positive is another’s negative. Understanding polarity prevents phase cancellation in multi-microphone setups and speaker systems.

Understanding Polarity

Audio signals represent pressure variations. Positive pressure (compression) appears as positive voltage; negative pressure (rarefaction) appears as negative voltage.

Two signals with the same polarity reinforce each other. Two signals with opposite polarity partially or fully cancel each other.

Polarity reversal swaps positive and negative—a 180-degree flip. This is different from time-based phase shift, which varies by frequency.

Polarity vs Phase

The terms “polarity” and “phase” are often confused. Polarity is a fixed inversion—positive becomes negative uniformly across all frequencies.

Phase shift varies by frequency and time delay. Different frequencies experience different amounts of phase shift.

Mixer “phase” switches actually reverse polarity. The symbol ø indicates polarity reversal despite being called “phase” on some consoles.

Standard Wiring Polarity

XLR wiring follows the convention: Pin 1 = ground, Pin 2 = positive (hot), Pin 3 = negative (cold).

Properly wired cables maintain polarity throughout the signal chain. A positive pressure at the microphone creates positive voltage at pin 2 at both ends.

Miswired cables can reverse polarity. Pin 2 and Pin 3 swapped creates consistent polarity reversal on that cable.

When Polarity Matters

Polarity matters when combining signals from the same source. Two microphones on a snare drum should have consistent polarity for coherent summing.

Polarity matters between main speakers and subwoofers at their crossover frequency. Opposite polarity causes cancellation in the crossover region.

Polarity matters less for isolated sources. A vocal microphone with reversed polarity sounds identical if it is the only vocal source.

Common Polarity Issues

Bottom snare microphone often needs polarity reversal. The top head pushes into the top mic while pulling away from the bottom mic. Without correction, the fundamental cancels.

Drum kit overheads: If one overhead is polarity-reversed relative to the other (cable wiring error), the stereo image suffers.

Multiple microphones on bass or guitar cabinets may need polarity adjustment to sum coherently.

Checking Polarity

Polarity checkers send a test pulse and indicate whether the received pulse matches the sent polarity. Galaxy Audio, Whirlwind, and others make these tools.

Listening tests work for multi-microphone setups. Solo two related sources; flip polarity on one and listen for fuller sound.

The fuller, more impactful sound indicates correct polarity alignment. Thin, hollow sound suggests polarity opposition.

Using Polarity Switches

Channel polarity switches on mixers provide quick correction. Engage the switch and listen for improvement.

If polarity reversal improves the sound of two combined sources, leave it engaged. If it makes the sound worse, disengage.

Only flip polarity on one of the two sources. Flipping both returns to the original relationship.

Speaker System Polarity

Speakers should all push outward on positive signal. Reversed polarity speakers pull inward while others push outward.

Main speaker polarity reversal relative to subwoofers causes cancellation at crossover. The bass sounds weak despite adequate subwoofer output.

Test by reversing subwoofer polarity and listening. The setting with fullest bass in the crossover region is correct.

Cable Verification

Test cables periodically for correct wiring. A cable with pins 2 and 3 reversed causes consistent polarity reversal.

Label and segregate suspect cables for repair. Do not mix them with known-good cables.

Commercial cable testers verify pin-to-pin continuity and indicate wiring errors.

Absolute Polarity

Absolute polarity refers to whether the entire system maintains the original polarity of the source. A singer’s breath pushes outward; speakers should push outward on that signal.

In practice, absolute polarity matters less than relative polarity between combined sources. Most listeners cannot perceive absolute polarity.

Some argue that kick drums and bass should move speakers outward on initial transient. This debate continues without clear resolution.

Multi-Speaker Systems

Line arrays with multiple cabinets must have consistent polarity throughout. One reversed cabinet creates destructive interference with its neighbors.

Check each cabinet’s wiring during system deployment. Polarity errors create obvious audible problems.

Subwoofer arrays benefit from consistent polarity. Cardioid arrangements intentionally use polarity reversal combined with delay, but standard arrays should be uniform.