Field Story

Airport PA: When Lives Depend on Intelligibility

A major airport terminal expansion measured STI of 0.38 at gate areas, well below the mandated 0.50 minimum for emergency announcements. The impulse response showed a 3.1-second RT60 caused by the soaring glass atrium. Distributed ceiling speakers on 6-meter centers with carefully delayed zones raised STI to 0.56, passing the IEC 60268-16 intelligibility requirement.

Airport Terminal

RTA Measurement per IEC 60268-16

TL;DR

The real-time analyzer is a practical tool for optimizing PA system frequency response to maximize speech intelligibility per IEC 60268-16. While STI is the definitive metric, the RTA provides immediate visual feedback during EQ adjustments that affect intelligibility. By monitoring the seven STI octave bands in real time, you can identify and correct spectral imbalances that degrade the modulation transfer function. SonaVyx RTA mode with A-weighting and octave band overlay provides the visual feedback needed for speech-focused system optimization.

RTA for Speech Optimization

IEC 60268-16 STI depends on adequate signal energy in each of the seven octave bands from 125 Hz to 8 kHz. The RTA shows these band levels in real time, guiding your equalization decisions.

Speech Spectrum Target

  • Male speech spectrum peaks around 250-500 Hz and rolls off above 1 kHz
  • Female speech spectrum is shifted higher, peaking around 500 Hz
  • The PA system should compensate for this rolloff by providing extra gain above 1 kHz
  • Monitor the speech-weighted spectrum to verify adequate energy in each band

Noise Masking Visualization

  1. Display the ambient noise spectrum on the RTA
  2. Store it as a reference trace
  3. Play the STIPA signal and compare levels band by band
  4. Identify bands where the signal barely exceeds the noise

EQ Guidance

Use the RTA to monitor the effect of EQ changes on the speech-critical bands. Boost gently in the 2-4 kHz region for consonant clarity. Reduce low-frequency energy below 200 Hz to minimize room mode excitation.

Common Mistakes

  • Tuning for flat RTA response when speech intelligibility requires a shaped spectrum
  • Not comparing signal and noise spectra on the same display
  • Making EQ changes without monitoring the effect on STI

SonaVyx Workflow

Monitor with the SonaVyx RTA during PA tuning. Validate with the STI tool. Check system response with the transfer function. Verify levels with the SPL meter. Get recommendations from AI diagnostics. See the PA tuning workflow.

Standard Reference

IEC 60268-16:

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Last updated: March 19, 2026