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 ANSI S1.4
TL;DR
ANSI S1.4 defines the measurement chain from microphone to display, and correct polarity through this chain is assumed but not always verified. A polarity inversion anywhere in the chain produces magnitude-correct SPL readings but incorrect phase and impulse response data. For applications that depend on time-domain accuracy, such as impulse response measurement and delay finding, polarity verification is essential. SonaVyx polarity checker validates your complete measurement chain by sending a known positive pulse and verifying a positive response, confirming ANSI S1.4 polarity convention compliance.
ANSI S1.4 Signal Convention
The standard assumes that positive acoustic pressure produces a positive electrical signal at the microphone output, maintained through the signal chain to the measurement display.
Chain Components to Verify
- Microphone capsule: positive pressure should produce positive voltage on pin 2 (hot)
- Preamplifier: non-inverting gain stage, no polarity flip
- Cables: pin 2 to pin 2, pin 3 to pin 3 (no crossover)
- Audio interface: ADC should preserve the polarity of the analog input
When Polarity Matters
- Impulse response measurement: the first peak polarity indicates source polarity
- Delay finder: polarity affects the cross-correlation peak sign
- Phase measurement: inverted polarity adds 180 degrees to all phase readings
- SPL measurement: polarity does not affect magnitude (dB) readings
Quick Verification
Send a positive pulse (finger snap near the microphone produces a known positive initial wavefront). The captured waveform should show a positive peak first. If negative, trace the inversion through the signal chain.
Common Mistakes
- Never checking polarity because SPL readings appear correct
- Introducing polarity errors when changing audio interfaces or cables
- Not documenting the polarity verification in the measurement report
SonaVyx Approach
Use the SonaVyx polarity checker for automated verification. Check the transfer function phase for consistency. View impulse polarity with the IR tool. Verify levels with the SPL meter. Run AI diagnostics. See our learning modules for measurement chain setup.
Standard Reference
ANSI S1.4:
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Last updated: March 19, 2026