Field Story
When Stage Monitors Become the Enemy
A theatre production suffered from stage monitor bleed picked up by hanging choir microphones, causing a hollow comb-filtered sound in the house mix. The problem detector identified comb filtering with a 2.8 ms implied delay matching the monitor-to-mic path. Switching to in-ear monitors for the lead actors and reducing wedge levels by 12 dB eliminated the coloration.
TheatrePolarity Checker per IEC 60268-16
TL;DR
Polarity errors in PA systems directly degrade speech intelligibility per IEC 60268-16. When adjacent speakers or drivers are out of polarity, destructive interference creates frequency-dependent cancellations that reduce the energy in speech-critical bands. This loss of energy reduces the per-band signal-to-noise ratio and the modulation transfer function, lowering the overall STI score. SonaVyx polarity checker identifies inverted channels in the PA system before you run STI measurements, ensuring that your baseline measurement reflects the true system performance rather than a wiring error that is trivially correctable.
Polarity Impact on STI
An inverted speaker in a distributed PA system creates destructive interference in its overlap zone with adjacent speakers. This creates comb-filtered response that selectively reduces energy in certain frequency bands, degrading STI.
Detection Before STI Measurement
- Check polarity of every speaker zone independently before running STIPA
- An inverted zone can reduce STI by 0.05-0.15 in the overlap area
- Fixing polarity is a zero-cost improvement that should be caught early
- A single cable swap or processor setting change resolves the issue
Multi-Way Speaker Systems
- In systems with separate HF and LF drivers, each driver must be checked
- An inverted HF driver creates a null at the crossover frequency
- This null falls in the speech-critical 1-4 kHz range for many crossover designs
- The resulting STI impact is concentrated in the most important bands
Distributed System Checking
In large distributed systems with many speaker zones, systematic polarity checking prevents the common situation where one zone is inverted and goes unnoticed until STI fails at specific positions.
Common Mistakes
- Not checking polarity before measuring STI, then troubleshooting poor scores
- Checking only overall system polarity without verifying individual drivers
- Correcting polarity in software when the real problem is a hardware wiring error
SonaVyx Workflow
Run the SonaVyx polarity checker before STI measurement. Then measure with the STI tool. Check response with the transfer function. Verify levels with the SPL meter. Get recommendations from the AI diagnostic. Follow the PA tuning workflow.
Standard Reference
IEC 60268-16:
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Last updated: March 19, 2026