Field Story
Feedback Howl Ruins the Keynote
A hotel ballroom with reflective marble floors and glass chandeliers produced feedback at 2.2 kHz and 3.8 kHz during a corporate keynote for 800 attendees. The problem detector identified the two feedback frequencies within seconds. Applying two narrow notch filters of -9 dB and repositioning the podium mic from omnidirectional to cardioid eliminated the issue entirely.
Hotel BallroomPolarity Checker per IEC 61672-1
TL;DR
IEC 61672-1 assumes a specific polarity convention for the measurement microphone and signal chain. A polarity-inverted microphone does not affect SPL magnitude readings but will produce incorrect phase measurements and inverted impulse responses that corrupt time-domain analysis. Verifying microphone polarity is part of the complete measurement chain validation that IEC 61672-1 compliance demands. SonaVyx polarity checker can verify that your measurement microphone produces a positive-going signal for a positive pressure event, confirming the correct polarity convention for all subsequent measurements.
Microphone Polarity Convention
IEC 61672-1 follows the convention that positive acoustic pressure produces a positive electrical signal. This polarity must be maintained throughout the measurement chain.
Why Polarity Matters for Meters
- SPL magnitude (dB) is unaffected by polarity inversion
- Phase measurements are inverted by 180 degrees if polarity is wrong
- Impulse response polarity is critical for arrival time detection
- Cross-correlation based measurements depend on correct polarity
Verification Procedure
- Generate a known positive pressure pulse (e.g., hand clap or electronic pulse)
- Capture the signal and check that the first peak is positive
- If negative, the microphone or a cable is polarity-inverted
- Document the polarity check in the calibration record
Common Sources of Inversion
XLR cables with swapped pins 2 and 3, balanced-to-unbalanced adapters, and some audio interface channel configurations can invert polarity. Always verify after changing any part of the signal chain.
Common Mistakes
- Assuming that calibration at 94 dB verifies polarity (it only verifies magnitude)
- Not checking polarity after changing cables or interfaces
- Ignoring polarity because SPL readings appear correct
SonaVyx Tools
Use the SonaVyx polarity checker for microphone verification. Confirm with the transfer function phase display. Check impulse polarity with the IR tool. Verify levels with the SPL meter. Run AI diagnostics for chain validation. See our learning modules for calibration procedures.
Standard Reference
IEC 61672-1:
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Last updated: March 19, 2026